02. Inquiries and Interpretations June 2010

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Inquiries and interpretations for NACE MR0175/ISO 15156(Updated June 22, 2010)

Foreword

NACE MR0175/ISO 15156, “Petroleum and natural gas industries—Materials foruse in H2S-containing environments in oil and gas production,” was firstcompleted and published in December 2003.

In 2003 the ISO 15156 Maintenance Panel was set up to maintain this widelyused standard during and after publication.

Since that time this panel together with NACE TG 299 and ISO TC67 WG7 haveprocessed and accepted more than 20 proposals for amendment.Amendments made to NACE MR0175/ISO 15156 are published as TechnicalCorrigenda or Technical Circulars the references to which are provided at the

end of this document. Copies of the documents can be found via:-

www.iso.org/iso15156maintenance or www.nace.org

These Technical Corrigenda and Technical Circulars were incorporated intothe main three parts of ISO 15156, approved by the member countries ofISO/TC 67, and the 2009 version of ISO 15156 was published in October 2009.

During the same period the Maintenance Panel has dealt with more than 120inquiries for help with interpretation. The majority of these inquiries and theresponses provided are reproduced below.

The inquiries and responses are listed in the order of the sections of NACEMR0175/ISO 15156-1, -2, and -3 to which they refer.

These responses represent a consensus of the members of the ISO 15156Maintenance Panel and should not be construed to reflect the opinions ofNACE International, its officers, directors, or members.

Notes:

When an inquiry has been resolved by corrigendum or circular, the inquiry and the reference to the appropriate corrigendum or circular is provided.

To allow cross reference, the references to NACE MR0175-2003 in the original questions and answers have been retained.

This compendium is usually updated at least once per year and new additions to the compendium since the last edition are shown in a green font.

http://www.iso.org/iso15156maintenance


http://www.nace.org/







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General

Scope of NACE MR0175/ISO 15156

QUESTION:

Some of the materials we produce are in thicknesses or diameters that fall outsidethe scope of MR0175. We request clarification or guidance as to how hardnesstesting requirements that fall outside the scope of MR0175 should be addressed.

(MP INQUIRY #2003-05)ANSWER:The Maintenance Panel cannot provide interpretations that are outside the scope ofMR0175.

QUESTION:MR0175 is obviously written for guidance in meeting the H2S corrosion problem.Where does NACE address chloride corrosion cracking, particularly in pipe and tubematerials? We are seeing more and more customer specs calling for specialmaterials. What is the NACE opinion on best pipe/tube materials for defeatingchloride corrosion cracking?

(MP INQUIRY #2003-24 Q2)ANSWER:Please refer to Section 1 of NACE Standard MR0175-2003 and also to ISO 15156Part 1 for the scope of the documents for which cracking mechanisms areconsidered in H2S service.

QUESTION:The "Changes to NACE Standard MR0175-2003" document states the following:"MR0175 is not expected to be technically changed before it is combined with ISO15156. ISO 15156 is in a different format, with most information provided in tables,so it will not look the same, but it will be technically equivalent." Although thisstatement says that the two standards will be technically equivalent, their respectivesections on applicability show the following deviations:

a) NACE MR0175 has a generic rule (1.4.1.1) of a H2S partial pressure above0.0003 MPa abs, whereas NACE MR0175/ISO 15156 has no such rule.

b) NACE MR0175 has a generic exception rule (1.4.2.1) of a total pressure lessthan 0.45 MPa abs, whereas, within NACE MR0175/ISO 15156, this is onlyapplicable to "Flow-lines, gathering lines, field facilities and field processing plants"and "Water-handling equipment." (I assume that you are aware that MR0175/ISO15156 Part 1 (2001) mentions 4.3 bar whereas Parts 2 and 3 (2003) mention 0.45MPa abs).

c) NACE MR0175 has a generic exception rule (1.4.2.2) for multiphase systemsunder certain conditions, whereas NACE MR0175/ISO 15156 has no such rule. Canyou please clarify?

(MP INQUIRY #2005-05)

ANSWER:



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Response to Questions 1, 2a, and 3. Your interpretations of the NACE MR0175/ISO15156 are correct. In all cases the decisions to accept differences between NACEMR0175-2003 and NACE MR0175/ISO 15156 were only taken after discussions inthe ISO/TC 67/WG 7 committee charged with the preparation of the three parts ofthe standard.

Response to Question 2b. The difference between 0.45 MPa and 4.3 bar wasrecognized and has been corrected in a Technical Corrigendum for ISO 15156-1,Reference 2.

QUESTION:Crude oil storage and handling facilities operating at a total absolute pressure below0.45 MPa. My understanding of the above paragraph is that, it includes only deadoils with no gas in equilibrium. If any gas is in equilibrium with a crude (operating lessthan 0.45 MPa) which contains H2S more than 0.3kPa (in the gas phase), the whole

system is considered as sour. I need your advice for my understanding, if correct ornot?

(MP INQUIRY #2009-14)ANSWER:Crude oil storage and handling facilities means that it is dead oil and H2S/CO2 havebeen removed. The very low residual amount is considered negligible. This is thereason why these facilities are permitted exclusions from the standard. However, it isup to the user to check that these statements are true for the considered facilities.

QUESTION:

Water handling facilities (less than 0.45 MPa) I really don’t know what does it mean?

It means that the possibility of corrosion is low enough to be excluded from thestandard requirements? Or the consequence of the problem is minimum? Can weconclude from the above paragraph that, low pressure water handling facilities, hasno gas to be released which may produce SSC or any hydrogen problems?

(MP INQUIRY #2009-15)ANSWER:Water handling facilities have typically low service pressure, a near neutral pH andthey usually contain trace amounts of H2S. Consequently their sour service severityis quite low. However, it is the responsibility of the user to check whether these

assumptions are correct for the particular equipment considered.

Certification and Compliance to NACE MR0175/ISO 15156

QUESTION:Is it the intent of NACE MR0175/ISO 15156-2 that material manufacturers state onthe Material Test Certificates that material conforms to the NACE standard eventhough no operating criteria are known?

(MP INQUIRY 2006-13)ANSWER:

Certification requirements are outside the scope of the standard and there are nostipulations concerning certification in NACE MR0175/ISO 15156.



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The compliance with the NACE/ISO standard of a material for use in H2S-containingenvironments in oil and gas can only be assessed for the material in its final productform and this may differ metallurgically from that of the material supplied by thematerials manufacturer. In addition, compliance with the standard also depends on

the cracking mechanisms that have to be considered.

NACE MR0175/ISO 15156-2, Clause 9, Annex E (Informative) and NACEMR0175/ISO 15156-3, 7.2, Annex C (Informative) make some suggestions on howmaterials manufacturers and other suppliers might mark their materials to indicatethe evaluation (testing) that they have carried out.

Address for requests for interpretations of any part of NACE MR0175/ISO15156

QUESTION:

Is a NACE office available in Italy or in other European countries?(MP INQUIRY #2003-26 Q5)

ANSWER:All inquiries should be transmitted to the ISO Maintenance Panel through LindaGoldberg at NACE Headquarters in Houston, Texas. The Maintenance Panel hasinternational membership. A membership roster is attached.

NACE MR0175/ISO 15156-1

General

QUESTION:With reference to Paragraph 1.10.2: Equipment manufactured with UNS N04400and operating before the issuing of the last MR0175 edition may be replaced todaywith equipment manufactured with the same material, if the equipment design andenvironmental conditions have not been changed? If a conformity declaration toMR0175 is required for the new equipment, which edition must be declared (2003 orprevious)?

(MP INQUIRY #2003-26 Q2)QUESTION:

For new wells and/or petroleum plants designed according to MR0175 before its lastedition, but manufactured after the last edition was issued, may materials consideredby the design but not listed in the new standard edition be used?

If a conformity declaration to MR0175 is required for the equipment of the newwell/plant, which edition must be declared (2003 or previous)?

(MP INQUIRY #2003-26 Q3)QUESTION:May materials not listed in the last edition of MR0175, which have successfullypassed test requirements of TM0177 and/or have demonstrated adequacy forservice performances, have your declaration of conformity and be certified by themanufacturer "in conformity with NACE MR0175-2003"?

(MP INQUIRY #2003-26 Q4)



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ANSWERS 2, 3, 4:NACE and ISO support the latest editions of their documents. We cannot commenton conformity declarations. Please see ISO 15156 for requirements to documentmaterials performance outside the current limits. This documentation may bethrough laboratory data or from field experience.

Clause 1, Table 1

The revised version of this Table is given in Reference 1.

Clause 3

QUESTION:I need your help with the definition of CRAs in Part 3 of MR0175/ISO 15156.

The "corrosion-resistant alloys" is very general and does not specify whether or not

the definition includes the Fe-based alloys or not. More than that, the term CRA isused together with "other alloys" making it even more confusing.

(MP INQUIRY #2004-12)ANSWER:NACE MR0175/ISO 15156-1, Paragraph 3.6 contains a definition of "corrosion-resistant alloy" (CRA). It reads: "alloy intended to be resistant to general andlocalized corrosion of oilfield environments that are corrosive to carbon steel." Thisis taken from EFC 17.

"Other Alloys" are those not covered by the definitions of carbon steel or CRA. For

example, copper is not considered resistant to general corrosion but is considered inNACE MR0175/ISO 15156-3.

QUESTION:Could you please confirm that NACE MR0175/ISO 15156:1: 2001, Paragraph 3.3contains errors in some copies of the document and should read:

3.3carbon steelalloy of carbon and iron containing up to 2% carbon and up to 1.65% manganeseand residual quantities of other elements, except those intentionally added in specific

quantities for de-oxidation (usually silicon and/or aluminum)

NOTE: Carbon steels used in the petroleum industry usually contain less than 0.8%carbon.

(MP INQUIRY #2005-11)ANSWER:Yes.

Clause 5 and Clause 8

QUESTION:

Paragraph 1.8.3.3.1 of the 2003 edition allows "interpolation" between datapresented in the tables. If these data are plotted on semi-logarithmic graph paper



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such that the ordinate is temperature and abscissa H2S partial pressure, much of thedata plots as curves rather than straight lines making "interpolation" problematiclacking the polynomial expression for the curves obtained by a curve-fitting,mathematical routine. Since graphical data are easier to use than the discrete,Cartesian coordinates, I suggest that NACE give the data in the various tables in

graphical form, along with the respective polynomial expressions for the resultingcurves that enable the user to calculate pH2S for any given temperature.

(MP INQUIRY #2003-13 Q6)ANSWER:Since the data are limited it is not appropriate to attempt interpolation in all cases.Interpolation can only be valid for cases in which all environmental and metallurgicallimits, other than those for which a particular interpolation is being carried out, areidentical. The solution for this problem chosen in NACE MR0175/ISO 15156-1,Clause 5, is as follows: "Qualification, with respect to a particular mode of failure, foruse in defined service conditions, also qualifies a material for use under otherservice conditions that are equal to or less severe in all respects than the conditions

for which qualification was carried out.

QUESTION:In Paragraph 1.8.3.3.1 it is mentioned that interpolation between H2S levels andtemperature is acceptable. When applying this to Table 3 (as an example) what willbe the maximum partial H2S pressure at 140°C, where an interpolation is requiredbetween 2.8 MPa and unlimited? Does this mean that below 149°C there is no limitto the maximum partial H2S pressure?

(MP INQUIRY #2003-19 Q1b)ANSWER:

ISO 15156, Clause 5, states: "Qualification, with respect to a particular mode offailure, for use in defined service conditions, also qualifies a material for use underother service conditions that are equal to or less severe in all respects than theconditions for which qualification was carried out." In this case, for the precipitation-hardenable nickel-based alloys addressed in Table 3, this automatically qualifies thematerial for use at temperatures below 149°C and below 2.8 MPa H2S partialpressure. Qualification of a material for application under specific conditions that aremore severe than those listed in ISO 15156/NACE MR0175 is allowed. Qualificationon the basis of laboratory testing or field experience is required to comply with the(ISO) standard. The equipment user is responsible for ensuring a material is properlyqualified.

Clause 6

QUESTION:My customer has some swab tanks that were manufactured in 1953; they are madeof rolled 1/2-inch plate A283C; the tank is 84 in. in diameter and is rated for 100-psiservice. The question is given the following conditions does this tank meet NACEMR0175? According to Section A2.1.6 the requirement that all rolled or deformedmaterial must be stress relieved and have a hardness of 22 HRC max. The problemis we cannot or have no documentation as it relates to the heat treat of the plate postwelding. yet when tested the material meets the A283C requirements and the

hardness are in the 120-127 HB. Ultrasonic testing as part of a corrosion survey onthe tank was performed and all was in order. Engineering approval was granted on



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the status of the vessel as a pressure vessel under the ABSA (Alberta Boilers SafetyAssociation). This tank is 52 years old, is in excellent condition, and the customerwants to have more current documents on the tank as it relates to its status as anABSA pressure vessel and it's NACE MR0175.

With all this information can a determination be made that this material in its currentstate is suitable as a material that qualifies as a NACE MR0175/ISO 15156-compliant material? Using the long life, performance, and the mechanical datagathered can this determination be made? If so, can these criteria be used toestablish a basis for performing future work on this exact style of tank?

(MP INQUIRY #2005-31)ANSWERThe ISO 15156 Maintenance Panel cannot advise on the suitability of this tank foruse in sour service.

It is the responsibility of the equipment user to assess the suitability of the material

and to ensure compliance with NACE MR0175 / ISO 15156.

Consideration of the following could contribute to any evaluation of suitability youundertake:-

For some equipment NACE MR0175/ISO 15156-2, Table 1 allows the equipmentuser to categorize equipment as a "Permitted exclusion" where the operatingpressure does not exceed 0.45 MPa (65 psi).

NACE MR0175/ISO 15156-1, Clause 6 and in particular 6.2 d) offer some guidance

on the fitness for purpose evaluation of materials in existing equipment.

Clause 7

QUESTION:Base Material

In accordance to NACE MR0175/ISO 15156, Part 1, Item 7, 3rd paragraph, "noadditional laboratory testing of pre-qualified materials selected in these ways isrequired."

In accordance to NACE MR0175/ISO 15156, Part 2, Item B1, letter "a," "Somecarbon and low alloy steels described or listed in A.2 might not pass some oflaboratory . . ."

In our understanding, NACE Standards TM0177 and TM0284 are used to qualifynew materials that are not previously included in NACE MR0175. If we are usingmaterials previously included in NACE MR0175, it is not necessary to test themaccording to NACE TM0177 and TM0284.

We would like you to confirm if our interpretation below is correct and if not give usthe correct interpretation.

(MP INQUIRY #2005-08 Q1)ANSWER:



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See response posted under ISO 15156-2, B.1 below.

Clause 8

8.2

QUESTION:

Paragraph 1.10.2 states, ―The user may replace materials in kind for existingwells or for new wells within a given field if the design basis for the equipment hasnot changed.‖ Does this statement include valves or valve components that are used within wells?

(MP INQUIRY #2003-12 Q1)ANSWER:Yes, this paragraph does apply to valves and valve components used within thewells.

QUESTION:When materials in an existing field are replaced, what criteria should be used?Paragraph 8.2 of ISO 15156-1 provides some criteria for qualification, but it is notclear what approach should be used for materials that have been in use with noproblems, but documentation does not exist.

(MP INQUIRY #2003-41)ANSWER:NACE MR0175/ISO 15156-1 Paragraphs 6.2, 8.1, 8.2, and 9.0 provide a completedescription of the documentation required for two years’ successful field service.These paragraphs replace Paragraphs 1.10.1 and 1.10.2 in the 2003 edition of

NACE MR0175. There has been no change in intent. These paragraphs in the 2003edition required that ―The user shall verify that the environmental conditions of thefield have not changed.‖ Documentation has always been required.

QUESTION:I need some clarifications on the clause 8.2 of the MR0175/ISO 15156-1(Qualification based upon field experience).

―A material may be qualified by documented field experience‖--‖the duration of thedocumented field experience shall be at least two years. . . ―

What kind of documentation is expected? We need to know exactly what to ask fromthe end user. Is a letter describing the conditions for which the material qualified forthe past two years enough?

(MP INQUIRY #2004-05 Q1)ANSWER:NACE MR0175/ISO 15156-1 2003, Paragraphs 6.2, 8.1, 8.2, and 9.0 provide acomplete description of the documentation required for two years’ successful fieldservice. These paragraphs replace Paragraphs 1.10.1 and 1.10.2 in the 2003edition of NACE MR0175. There has been no change in intent. These paragraphsin the 2003 edition required that ―The user shall verify that the environmentalconditions of the field have not changed.‖ Documentation has always been required.

QUESTION:



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What do we (the equipment manufacturer) do with this documentation? Does it haveto be filed with NACE? If yes, is this our responsibility?


a) The equipment user is responsible for the preparation of the requireddocumentation (see NACE MR0175/ISO 15156-1, Clause 9, Paragraph 1 to supportthe use of a material in a plant on the basis of field experience. It would also be inthe equipment user’s interest to keep copies of this documentation in their records incase they are challenged to prove they are responsible operators. The equipmentmanufacturer can choose to retain a copy for future reference.

b) The equipment user may feel that they would wish to make the decision to file theinformation with NACE given that this would involve their actual field conditionsrather than laboratory test conditions.

c) It is not the responsibility of the equipment manufacturer to file information withNACE, unless they choose to. This may be the case because the equipmentmanufacturer has made the effort to compile a non-proprietary database that theybelieve supports the use of alloys for their equipment under the conditionsdocumented by the process in Question One.

QUESTION:If filing with NACE is not required, do we have to verify the claims or can we justprovide the materials as requested by the end user?

(MP INQUIRY #2004-05 Q3) ANSWER:The manufacturer can provide this information to a user, but it is the user’sresponsibility to determine the operating conditions and select the appropriatematerials. It is the manufacturer’s responsibility to meet the metallurgicalrequirements of the appropriate alloys in NACE MR0175/ISO 15156-2003.

QUESTION:In the pre-December 2003 MR0175, Paragraph 1.10 (The Effect of ChangingRequirements in MR0175 on Existing Equipment) spelled out how to handlematerials that MR0175 made changes to. Where is such a statement or treatment inthe December 2003 MR0175/ISO 15156?

If it was left out, is there a way of handling those changes?(MP INQUIRY #2005-10)

ANSWER:There is no such statement in NACE MR0175/ISO 15156. By convention, a newversion of an ISO standard is not applied retrospectively to equipment built to theprevious version of the standard (in this case NACE MR0175:2003 or earlier) valid atthe time of equipment construction.

New requirements in the latest version may be applied retrospectively by anequipment user or mandated for retrospective application by a regulatory authority.



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ISO 15156-1, 8.2 and the responses to inquiries on Clause 8 in Document 02.Inquiries and Answers at the Web site . . .

www.iso.org/iso15156maintenance

. . . offer further guidance on how such changes might be handled.

NACE MR0175/ISO 15156-2

Clause 1, Table 1

The revised version of this Table is given in Reference 2.

Clause 3

3.1, 3.16 and 3.2.3

For the use of ASTM E 10, ASTM E 18, and ASTM E 92 as alternatives to ISO 6506-1, ISO 6508-1 and ISO 6507-1 respectively see Reference 2

3.14

QUESTION:Definition of pressure-containing parts on page 7. ―Those parts whose failure tofunction as intended would result in a release of retained fluid to the atmosphere.

Examples are valve bodies, bonnets, and stems.‖

Are stems always defined as pressure-containing parts , regardless of features thatby design keep the stem intact?Example #1: Internal entry stems for ball valves that have a shoulder that restsagainst the body around the stem bore.Example #2: Shafts for butterfly valves that have a retaining ring holding the shaftinside the valve.

(MP INQUIRY #2003-12 Q2)ANSWER:NACE Standard MR0175 cannot interpret design issues. The Maintenance Panelmay only refer you to the definition of pressure-containing parts in Section 2 and theuse of this definition with restrictions in Section 9.

Clause 7

7.1.2, A.2.2.3.3, Table A.2, and Table A.3

QUESTION:Sub-clause 7.1.2 says SSC Resistant Steels for partial pressures equal to or above0.3 kPa (0.05 psi) can be selected using A.2.



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a) If criteria, like temperature, hardness are met, do we assume that for all partialpressures above 0.05 psi the suggested SSC-resistant materials could be used?E.g., SSC-resistant materials mentioned in Table A.2 and Table A.3.

b) What are the acceptable pH and Cl- limits?

c) Does A.2.2.3.3 cover L80 type 1?

d) For low-alloy steels described in Section A.2 of this standard, what are the caseswhere injection of corrosion inhibitors are required, both for downhole casings/tubingand surface pipelines?


ANSWER:a) This is correct.

b) No limits of pH and Cl- have been formally defined for carbon and low-alloysteels. Any combinations of chloride concentration and in situ pH occurring inproduction environments are considered acceptable. Metal loss corrosion, whichcan be influenced by both pH and chlorides, is not the subject of the standard.

c) No, this grade is covered in Paragraphs A.2.2.3.1 and A.2.2.3.4.

d) NACE MR0175/ISO 15156 does not cover the use of corrosion inhibitors. Theuse of any kind of corrosion inhibitor is not considered to allow any relaxation of therequirements for cracking resistance of materials in sour service.

QUESTION:I was wondering if you could assist me in interpreting the partial pressure limitationfor Carbon Steels referenced in part 2 section 7.1.2 and A.2.

Is there a partial pressure max limit for carbon steels? If so, where is the referencein MR0175?

(MP INQUIRY #2010-09)ANSWER:The partial pressure mentioned in Section 7.1.2 is the partial pressure of H2S in the

gas phase in equilibrium with the water in the production fluid. Annex C givesinformation on how to calculate H2S partial pressure.

Regions 1, 2, and 3 cover usual conditions above 0.3 kPa. Note 1 mentions theunknown performance of steels above 1 MPa. The maximum partial pressure limitfor carbon steels depends on many variables as noted in 15156-2 Clause 6.Currently a NACE TM0177 test with 100 kPa H2S, ~2.7 pH, room temperature, 50g/L NaCl is considered to cover all normal production conditions for carbon steels.

7.2.1.2, Fig.1

QUESTION:



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There is the sentence in the note 1 of Figure 1 in ISO 15156-2: "The discontinuitiesin the figure below 0.3 kPa (0.05 psi) and above 1 MPa (150 psi) partial pressureH2S reflect uncertainty with respect to the measurement of H2S partial pressure (lowH2S) and steels performance outside these limits (both lower and higher H2S)." Iunderstand the above sentence, and if I will use the carbon steel and low-alloy steel

in the sour service above 1 MPa (150 psi) of partial pressure of H2S, what can I do?Should I require a special laboratory test imitating the H2S partial pressure and pH inthe service for SSC of the carbon steel and low-alloy steel? Which solution can I usein the special laboratory test?

NACE TM0177 A solution or the imitating solution in the service?(MP INQUIRY #2005-17)

ANSWER:The following response must be seen in the context of NACE MR0175/ISO 15156-2,Clause 7.

1. NACE MR0175/ISO 15156-2, Fig. 1 is a schematic definition of Regions ofenvironmental severity with respect to SSC of carbon and low alloy steels. Asmentioned in Paragraph 7.2.1.4, qualification for the use of a material not listed inAnnex A for use in one or more of the Regions of Fig. 1 is always dependent onreported field experience or laboratory testing.

There is little documented evidence that describes the SSC resistance of carbon andlow alloy steels in H2S-containing environments outside the H2S limits of Fig. 1. TheNote quoted reflects this.

2. The equipment user must decide whether the listing of a steel in Annex A servesas an adequate guide for its behavior in H2S-containing field environments that mightbe more severe with respect to SSC than those represented by the SSC testingmethods normally used; see Annex B.1a).

For qualification for a specific application all the test conditions must be at least assevere, with respect to the potential mode of failure, as those expected to occur infield service.

7.3.2

QUESTION:Does the MR0175/ISO 15156-2, 7.3.2 also apply to low-alloy martensitic steels suchas CA6NM which is in fact considered a CRA (MR0175/ISO 15156-3)?

(MP INQUIRY #2004-18 Q2)ANSWER:No, it does not. Please see ISO 15156-3, 6.2.1 and ISO 15156-3, A.6.2, Table A18.

7.3.3

QUESTION:Seal welding of vent holes on saddle plates welded to pipe. We have provided vent

holes on saddle plates in accordance with ASME B31.3. We have used thesesaddle plates at support locations as a protective shield to pipe. Now we would like



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to close the vent hole by seal welding after completion of saddle welding with pipeand carrying out PWHT. Permanent closing of vent hole is required to avoidcorrosion in offshore conditions. Service is crude oil with H2S, i.e., NACE MR0175 isapplicable.

Kindly advise us about the acceptance of seal welding for these service conditions.(MP INQUIRY #2005-21)

ANSWER:The ISO 15156 Maintenance Panel cannot provide guidance on the acceptability ofseal welding in this application.

It is the responsibility of the equipment user to decide whether NACE MR0175/ISO15156-2 (the latest edition of this NACE standard) is applicable to these seal welds.The applicability of this standard is described in Clause 1, Scope.

If this standard is considered applicable then the seal welds must comply with the

requirements of NACE MR0175/ISO 15156-2, 7.3.3 or NACE MR0175/ISO 15156-3,6.2.2.

Figure 2, Table A.1

QUESTION:Ref Part 2 Figure 2 Butt Weld Survey method for Vickers Hardness Measurement.Location points 17, 18 & 19. What is the acceptance criteria? Table A.1 onlyprovides acceptance for the Weld Cap and Root. As the area is not exposed shouldthe acceptance level be 275 HV 10?

(MP INQUIRY #2009-04)ANSWER:Since it is not at the cap the acceptance level should be 250 HV 10 unless it isproven that it can be relaxed. For now there is no demonstrated evidence to showthat 250 Hv can be relaxed at location points 17, 18, and 19 of Part 2 Figure 2.

7.3.3.2

QUESTION:Is it acceptable to use HV 500g (microhardness) testing for NACE applications forWPS qualification? I understand that Paragraph 7.3.3.2 of NACE MR0175/ISO

15156 Part 2 says that hardness testing shall normally be carried out using HV 10kgor HV 5kg, which is our usual practice.

FYI, the hardness testing was done with HV 500g on CSA Z245.1 Grade 359 pipematerial.

(MP INQUIRY #2006-08) ANSWER:Yes, subject to the agreement of the equipment user. Please see NACEMR0175/ISO 15156-2, Para. 7.3.3.2.

7.3.3.2 and 7.3.3.3

The revised texts for these sub-clauses are included in Reference 2.



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7.3.3.3

QUESTION:Per 7.3.3.3 as modified in NACE / ISO 15156-2:2003/Cor.1:2005(E), "Using the

Vickers or Rockwell 15N measurement methods, hardness impressions 2, 6, and 10should be entirely within the heat-affected zone and located as close as possible to,but no more than 1mm from, the fusion boundary between the weld overlay andHAZ."

Is a correct interpretation that when welding dissimilar metals such as corrosionresistant overlays on low alloy steels, the phrase, "as close as possible to, but nomore than 1mm from, the fusion boundary" means that the indentation should be noless than 3x the mean diagonal length of the indentation from the fusion boundary asis required for adjacent indentations in ISO 6507-1:1998?

Note: ISO 6507-1:1998 is referenced by NACE/ISO 15156-2:2003 in the firstparagraph of Section 7.3.3.2 (Hardness testing methods for welding procedurequalification).

(MP INQUIRY #2006-01Q2)ANSWER:The ISO 15156 Maintenance Panel cannot provide an interpretation of the ISO 6507-1:1998 in relation to the minimum distance of hardness indentations from theboundary between the base metal and the overlay weld.

As stated in ISO 15156-2, 7.3.3.2 and ISO 15156-3, 6.2.2.2.2 hardness

measurements can also be carried out using a smaller indentation load, for exampleHV5 rather than HV10, and in many cases this will allow compliance with therequirements of ISO 15156-2, Fig. 6.

It is important to recognize that there will be a gradient in HAZ hardness in any case,and thus measurements too far from the fusion boundary could be un-conservative.

In all cases it is the task of the equipment user (and hence the supplier) to ensurethat the hardness values measured are the most representative possible of thecracking resistance of the welded material in any sour service it is expected toexperience.

7.3.3.4

QUESTION:About welds, in accordance with NACE MR0175/ISO 15156, Part 2, Item 7.3.3.4,"hardness acceptance criteria for welds," "weld hardness acceptance criteria forsteels selected using option 1 (see 7.1) shall be as specified in A.2.1.4. Alternativeweld hardness acceptance criteria may be established from successful SSC testingof welded samples. SSC testing shall be in accordance with Annex B."

So, in our understanding, if our welding procedure qualifications (WPSs) are

qualified in accordance with NACE MR0175/ISO 15156, Part 2, Item A.2.1.4, it is notnecessary to test them according to TM0177.



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We would like you to confirm whether our interpretation below is correct and if notgive us the correct interpretation.

(MP INQUIRY #2005-08Q2)

ANSWER:Your interpretation is correct.

QUESTION:NACE MR0175 and NACE TM0177--WELDSOn the other hand, if we make the test in accordance with NACE TM0177 in ourWPSs that are previously qualified to conform to NACE MR0175, what kind of resultswill we have? Will we have a necessary or redundant results?

(MP INQUIRY #2005-08Q3)ANSWER:A manufacturer may choose to qualify a welding procedure specification in

accordance with ANNEX B. Testing welds acceptable in accordance with A.2.1.4 isan optional activity chosen by the manufacturer to confirm resistance to cracking.This is not necessarily a redundant result depending on the anticipated serviceconditions and the selected test environment, the results could be used

-to confirm that the hardness control specified in A.2.1.4 is adequate to preventsulfide stress cracking

-or to define alternative weld hardness control requirements that will not lead tosulfide stress cracking when the requirements of A.2.1.4 are not met.

Clause 8

QUESTION:We are trying to interpret the NACE requirements for pressure vessel plate material.The NACE standard leaves the option of HIC testing with the client, as it appears. Inaccordance with the standard, the condition in which the HIC testing becomesmandatory should be based on some criteria other than H2S partial pressure. Wewould appreciate it if you can guide in giving the other conditions if sulfur andphosphorous content are controlled in accordance with NACE. Does HICbecome mandatory due to non-uniformity of sulfur and phosphorous in the material

due to steelmaking process even if the limit of these elements are maintained? Arethere other reasons such as chloride environment?


ANSWER:The statements in ISO 15156-2, 8 "Evaluation of carbon and low-alloy steels for theirresistance to HIC/SWC" are based on the extensive experience of the experts whodrew up the requirements of the standard.

They serve as a warning to the equipment user that damage to products from someflat-rolled carbon steel types due to HIC has been common and the risk of attack

must be considered when selecting such materials for sour service. (See ISO15156-1, 3.19 for definition of sour service in this context.) They also provide some



16

indications of the types of flat-rolled carbon steel likely to give satisfactory resistanceto HIC.

The overall aim of ISO 15156-2, Clause 8, is to ensure that materials that givesatisfactory HIC performance in sour service can be selected. It is not the intention

of this Clause to provide detailed information that can lead to the qualification,without testing, of HIC-resistant steels.

If, in accordance with NACE MR0175/ISO 15156:2, Clause A.2.2.2, Paragraph 3, theHIC resistance of flat-rolled plate is uncertain then the equipment user can elect tocarry out HIC testing, possibly for use in an application-specific environment.Testing in accordance with Annex B.5 is proposed as a means of qualifying thematerial to ISO 15156-2.

Testing is not necessary if the equipment user can document that he has evaluatedthe risk of HIC failure of his equipment and considers the risk acceptable.

QUESTION:According to NACE MR0175/ISO 15156, Part 2, Paragraph 8, HIC test is notmandatory for carbon steel SMLS pipe. But what about maximum sulfur content?Do we have to apply maximum sulfur content requirement to carbon steel regardlessof HIC test?


ANSWER:There are no requirements for the control of the chemistry of any elements to

prevent HIC in NACE MR0175/ISO 15156. Some guidance concerning acceptablesulfur levels is given in Section 8 of NACE MR0175/ISO 15156 Part 2. For seamlessproducts, testing can also be performed according to Table B.3 if deemednecessary.

QUESTIONS:It appears that ISO 15156-2 is ambiguous in defining the acceptance criteria for HICtesting. Section B.5 and Table B.3 refer to NACE TM0284. This TM prescribesCLR, CTR, and CSR results to be reported for each of the three sections taken froma specimen and also as the average per specimen.

Q1. Could you please confirm that the intention of Section B.5 and Table B.3 is thatthe requirements of NACE TM0284 for the evaluation of test specimens should befollowed and that CLR, CTR, and CSR should be calculated and reported for eachsection and the average for each test specimen.

Table B.3 does not specify if the criteria apply to the single section numbers or to theaverages per specimen or to the averages over a series of specimens. The last ofthese was suggested recently to us, for qualification purposes, by a materialsmanufacturer.

ISO 3183-3 (the successor to API 5L) uses the same CLR, CTR, and CSR values as

criteria as ISO 15156 but in addition it mentions that averages per specimen should



17

be measured against the acceptance criteria (not single section numbers). I think itis common practice to apply this approach.

If one decides that the acceptance criteria are to be applied to single sections, I donot believe that using, in addition, the same criteria for the average per specimen

yields any useful additional information (because it is less restrictive), but it does noharm either.

If, however, one decides that the acceptance criteria are to be applied only to theaverage per specimen, I am of the opinion that an additional condition should beimposed for single section results or for single crack lengths, for instance, no singlecrack length should exceed 5 mm, as part of the overall acceptance requirements.

Q2. Are the acceptance criteria intended to apply to the test results of both singlesection and the average per specimen?

Q3. Is the intention that, in coming to a qualification the CLR, CTR, and CSR valuesbe calculated by averaging the results for a series of specimens?

Q4. If they are intended to apply to only the average per specimen, what additionalrequirements should be placed on the results of single section results?

(MP INQUIRY #2006-11)ANSWERS:A1. Yes.

A2. The referenced standard, NACE TM0284, Paragraph 8.4, requires the

(calculation and) reporting of test results for each of three sections and the averagefor each test specimen. The application of the acceptance criteria to single sectionand/or the average for a specimen is subject to agreement between equipment userand the manufacturer.

A3. See Answer A.2 above, the referenced standard NACE TM0284 makes nomention of calculating results by averaging the results for a series of test specimens.

A4. The Maintenance Panel is unable to comment on issues that would involve anextension of the requirements of the standard. Any materials purchaser is free toadd requirements beyond those required or made optional by the standard.

Any amendment proposal to extend the requirements for single section test resultsmust be submitted in accordance with the requirements outlined in:-

01. Introduction to ISO 15156 maintenance activities (Annex C) of the web sitewww.iso.org/iso15156maintenance.

Annex A

A.2.1.1

QUESTION:



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ISO 15156 / NACE MR0175 does not mention clearly about sulfur restrictions forcarbon steel forgings and castings to ASTM-A105 and ASTM-A216 respectively.

These two specs are work-horse of any oil/gas processing industry. Almost 75% to90% of materials of construction would fall into these specifications. For example:

flanges and fittings and valves and rotating machinery casings.

The paragraph A.2.1.3 states:

A.2.1.3 Carbon steels acceptable with revised or additional restrictions

In addition to the restrictions of A.2.1.2, some carbon steels are acceptable subjectto the revised or additional restrictions as follows.

a) Forgings produced in accordance with ASTM A 105 are acceptable if thehardness does not exceed 187 HBW.

Please note: In the original standards ASTM-A105 allows sulfur up to 0.040% andASTM A 216 allows sulfur up to 0.045%.

However, NACE MR0175/ISO 15156, Section 8 says: Conventional forgings withsulfur levels less than 0.025 %, and castings, are not normally considered sensitiveto HIC or SOHIC.

The above statement means ASTM A 105 forgings are acceptable, if sulfur is limitedto 0.025% and hardness to 187 HBW

Castings have no additional sulfur limit other than specified in the base spec. (forexample: 0.045% for ASTM-A216).

The document has reference to many casting and forging grades, but, these twogrades are not adequately covered. ASTM A 216 is not covered at all.

It would be appreciated if NACE clearly makes mention of these two importantmaterials with limitations if any clearly stated. Would such changes be possible?

(MP INQUIRY #2007-05)ANSWER:

It is outside the scope of the standard to provide information concerning the"limitations" of ASTM A 105 and ASTM A 216 in the specific form you request.

Many steels, including ASTM A 216, are not individually listed in NACE MR0175/ISO15156-2. As stated in A.2.1.1 General, Para. 3:"The majority of steels that comply with the general requirements of A.2 are notindividually listed; however, for convenience, some examples of such steels arelisted in Table A.2, Table A.3 and Table A.4." A.2.1.1 deals only with sulfide stresscorrosion resistance.

Where any possible additional restrictions are mentioned (as is the case in Section 8

in relation to HIC/SWC resistance), they refer to any carbon or low alloy steel towhich the text might apply.



19

Table A.2

QUESTION:Question No. 1

Could you please define the word "Qualification."

In our understanding, qualification is required for new materials that are not listed inTable A.2 of NACE MR0175/ISO 15156-2. We would like you to confirm that ourinterpretation is correct and if not what is your position?

(MP INQUIRY #2009-01)ANSWER:Table A.2 of ISO 15156-2 gives examples of materials that can be qualified providedthey comply with Paragraph A.2.1. If not listed in Table A.2, materials must beassessed in the terms of the requirements given in Annex A as explained inParagraph 7 of Part 1. Again it is up to the user to decide if materials need further

qualification through testing or field experience as explained in Paragraph 8.

A.2.1.2 and A.2.1.3

QUESTION:Paragraph A.2.1.2 on page 17 still shows hot-rolled yet Paragraph A.2.1.3 states thatASTM A 234 grade WPB is an acceptable material. My question is as follows:

--Does NACE MR0175/ISO 15156-2 allow the use of material ASTM A 234 gradeWPB with a heat treatment as shown in ASTM A 234/A 234M-02 Section 7 Heat

treatment, subsection 7.2.1, although this type of forming and cooling in still air is notlisted in Paragraph A.2.1.2 of the NACE standard?

--Does the term ―hot rolled‖ referred to in Paragraph A.2.1.2 only apply to sheet or plate material and as such cannot be applied to the forming of butt weld fittings?

(MP INQUIRY #2004-06)ANSWER:Answer 1: The first paragraph of ISO 15156-2, A.2.1.3 is not intended to imply thatthe requirements of A.2.1.2 also apply to A.2.1.3.

ASTM A 234 Grades WPB and WPC are acceptable subject to a hardness limit of

197 HBW.

The Maintenance Panel will consider an amendment to A.2.1.3 to make this clearer.

Answer 2: Yes, ―hot rolled,‖ in the view of the Maintenance Panel, does not apply tothe forming of butt weld fittings.

QUESTION:Often my company is asked by customers to certify our forgings to NACE MR0175.It is my understanding from them that our competition (including imports), certifies toMR0175 without normalizing and consequently we are pressured to do the same.



20

We have three presses, two are fed by gas-fired furnaces, and one is with inductionheaters. The gas heat forgings are typically heated to 2,300 to 2,350°F and forgedon a 900T or 3500T open die press in a tooling pot, then still air cooled to ambient.The forgings heated by induction are heated to similar temperatures but only aportion of a bar and the flange end is forged close to shape, then air cooled in still

air.

Customers can order these forgings in the "as forged" or "normalized" condition perSA105. My question is do we have to normalize the forgings coming from eitherforging process in order to certify to NACE MR0175? The problem is interpretationof NACE MR0175/ISO 15156-2:2003(E), page 17, Annex A, Paragraph A.2.1.2. Theheat-treated condition "hot-rolled" is not clearly understood and competitors withsimilar processes interpret that if the entire raw material piece prior to forge, let's callit a mult, is taken to 2,300 to 2,350°F prior to forge that this satisfies the "hot-rolled"definition.

We have contended that our products need to be subsequently followed with anormalizing cycle after being fully cooled to ambient in order to be certified to NACEand that neither of the forging processes listed above satisfies the definition of "hot-rolled" process.

(MP INQUIRY #2005-25)ANSWER:Hot-forged material does not meet the intent of NACE MR0175/ISO 15156-2,A.2.1.2a).

An exception to this statement is given in A.2.1.3a).

Other hot-forged materials would have to be treated according to one of the fiveother heat-treatment conditions described in Paragraph A.2.1.2 to comply with thisstandard.

Please note: We acknowledge that paragraph 1 of A.2.1.3 is poorly worded. Theintent of this paragraph is to allow forgings according to ASTM A 105 to be used,subject to A.2.1.3a) free of the restrictions stated in A.2.1.2.

As a consequence, ASTM A 105 material is acceptable in the "as-forged" conditionnot because it is equivalent to a "hot rolled" condition in A.2.1.2, but because it is a

permitted exception in A.2.1.3.a.

A.2.1.3, and Table A.3

QUESTION:We require a determination on the acceptability of products manufactured out ofmaterials meeting ASTM A 234 Gr WPB, ASTM A 420 Gr WPL6, ASTM A 350 GrLF2, and API 5CT J55, K55, N80, and L80 materials.

Alberta Oil Tool manufactures Swage Nipples and Bull Plugs primarily for use in theoil and gas industry. Swage Nipples and Bull Plugs are manufactured from line pipe,

tubing, and casing. Line pipe swage nipples and bull plugs are manufactured withmaterials that meet the requirements of the following specifications:



21

ASTM A 234/ASME SA 234 Gr. WPBASTM A 350/ASME SA 350 Gr. LF2ASTM A 420/ASME SA 420 Gr. WPL6

Tubing and casing swage nipples and bull plugs available in materials meeting API5CT Grades J55, K55, N80, and L80.

Our initial determination is that these products fall into the scope of Section 11.Paragraph 11.5, Pipe Fittings, states that fittings meeting the requirements of ASTMA 234 Grade WPB and ASTM A 105 are acceptable. However, we can find nocriteria for pipe fittings that are to be used in low-temperature service applications.In comparison to ASTM A 350 Gr. LF 2 (a low-temperature specification), ASTM A105 is congruent and therefore we determined that fittings manufactured to ASTM A350 Gr. LF2 are acceptable under NACE MR0275-2003.

Table D2, Acceptable API and ASTM Specifications for Tubular Goods, lists API 5CTGrades J55, K55, and L80 as acceptable materials for tubing and casing, as well asASTM A 106 Gr. B and ASTM A 333 Gr. 6 materials for pipe. This table lists manyof the materials in question. ASTM A 106, GR. B material is used to manufacturefittings that comply with ASTM A 234 Gr. B material is used to manufacture fittingsthat comply with ASTM A 234 Gr. WPB, while ASTM A 333 Gr. 6 material is used tomanufacture ASTM A 420 Gr. WPB, while ASTM A 333 Gr. 6 material is used tomanufacture ASTM A 420 Gr. WPL6 fittings.

As NACE Standard MR0175-2003 does not clearly identify all the acceptable

materials in one location, our interpretation of the entire standard is that all of theswage nipples and bull plugs that we manufacture are acceptable, and meet therequirements of NACE MR0275-2003.

Is this interpretation correct? Please have our findings confirmed by answering thefollowing questions. Please provide reasons for any products that do not complywith NACE MR0175-2003.

1. Are fittings meeting ASTM A 234/ASME SA 234 Grade WPB acceptable for useunder the scope of NACE MR0175-2003?2. Are fittings meeting ASTM A 420/ASME SA 420 Grade WPL6 acceptable for use

under the scope of NACE MR0175-2003?3. Are fittings meeting ASTM A 350/ASME SA 350 Grade LF2 acceptable for useunder the scope of NACE MR0175-2003?4. Are fittings manufactured from API 5CT Grade J55 material acceptable for use uunder the scope of NACE MR0175-2003?5. Are fittings manufactured from API 5CT Grade K55 material acceptable for useunder the scope of NACE MR0175-2003?6. Are fittings manufactured from API 5CT Grade N80 material acceptable for useunder the scope of NACE MR0175-2003?7. Are fittings manufactured from API 5CT Grade L80 material acceptable for useunder the scope of NACE MR0175-2003?




22

API grades in Table A.3 of NACE MR0175/ISO 15156-2 are acceptable as downholetubular goods under the environmental temperatures if they meet the respective APIrequirements in NACE MR0175/ISO 15156-2. Only if Swage nipples and bull plugsare downhole tubular goods are API 5CT Grades J55, K55, N80, and L80acceptable.

Also see notes below.#1. This must meet the requirements of A.2 and of hardness control as specified inA.2.1.3.#2. This must meet the requirements of A.2.#3. This must meet the requirements of A.2.#4. The material manufactured to API J55 applies only to downhhole tubular goods.#5. The material manufactured to API K55 applies only to downhole tubular goods.#6. The material manufactured to API N80 applies only to downhole tubular goods.#7. The material manufactured to API L80 applies only to downhole tubular goods.

A.2.1.4

QUESTION:Per A.2.1.4 as modified in NACE / ISO 15156-2:2003/Cor.1:2005(E), "Tubularproducts with an SMYS not exceeding 360 MPa (52ksi) and listed in Table A.2 areacceptable in the as-welded condition. For these products, hardness testing ofwelding procedures may be waived if agreed by the equipment user".

Is a correct interpretation that all hardness testing is being waived for tubularproducts with an SMYS not exceeding 52ksi in the as-welded condition if as agreed

by the equipment user? (MP INQUIRY #2006-01Q1)ANSWER:No, tubular products listed in Table A.2 with an SMYS not exceeding 360 MPa (52ksi) are acceptable in the as welded condition. For these products hardness testingOF WELDING PROCEDURES may be waived if agreed by the equipment user.

A.2.1.4 and Table A.1

The revised versions of A.2.1.4 and Table A.1 are included in Reference 2.

A.2.1.4 and A.2.1.5

QUESTION:We have weld overlays (Inconel 625 filler metal with SAW process) applied to low-alloy ferritic steel valves (ASME/ASTM A 352 Gr LCC). The steel valve is used onwet gas wellhead production platform with operating temperatures at 93°C, operatingpressure of 145 bar with vapor fraction of H2S (177 kg-mol/h) and CO2 (877 kg-mol/h). Hardness tests were performed on the as-welded condition. The resultsachieved were well below the 250 HV criteria of Table A.1 of NACE MR0175/ISO15156-2 first edition. Since the hardness results complied with the requirements ofTable A.1 of NACE MR0175/ISO 15156-2, we believe and understand that the valve

does not require postweld heat treatment after the weld overlay. Having met the



23

hardness criteria after overlay we believe that we met the requirements of thefollowing paragraphs of NACE MR0175/ISO 15156-2 first edition:-Paragraph A.2.1.5-Paragraph A.2.1.4

Question: Is our interpretation of Paragraphs A.2.1.5 and A.2.1.4 of NACEMR0175/ISO 15156-2 correct based on the above-stated specific application andconditions and that the valves overlayed with Inconel 625 consumables do notrequire postweld heat treatment?

(MP INQUIRY #2004-11)ANSWER:Paragraph A.2.1.4 states (in the third sentence):―As welded carbon steels, carbon manganese steels, and low-alloy steels thatcomply with the hardness requirements of Table A.1 do not require postweld heattreatment.‖ Paragraph A.2.1.5 states: ―Overlays applied by thermal processes suchas welding . . . are acceptable if they comply with one of the following: (a) The heat-

treated condition of the substrate is unchanged, i.e., it does not exceed the lowercritical temperature during application of the overlay. (b) The maximum hardnessand final heat-treated condition of the base metal substrate comply with A.2.1.2 and,in the case of welded overlays, A.2.1.4.

Therefore, your interpretation is correct. Provided your weld procedure qualificationcomplies with the hardness requirements in A.2.1.4 and A.2.1.5, no postweld heattreatment is required.

A.2.1.5 b)

The revised text for this sub-clause is included in Reference 2.

A.2.2.1, A.2.2.2 and A.2.2.3

QUESTION:We need a clarification on MR0175/ISO 15156 Part 2:2003, Annex A. We are amanufacturer of temporary pipe work, flowlines, etc., for sour gas service in welltesting and process use in a surface application.

As such we believe Paragraphs A.2.1 through A.2.4 and Table A.1 with a hardness

limit of 22 HRC are applicable in these circumstances.

However, pipe suppliers in this region tell us that 26 HRC is acceptable in suchapplications. I believe the 26 HRC limit is only applicable to material used in adownhole application as in Paragraph A.2.2.3, etc. (i.e., not a surface application)and that this is in error in terms of our usage.

(MP INQUIRY #2005-23)ANSWER:ISO 15156-2, A.2.2.1 indicates that carbon and low alloy steels for use in anyproduct form must comply with the requirements of A.2.1 which include the hardnessrequirement of maximum 22 HRC for the parent material. Exceptions to this rule are

named specifically in other paragraphs of Annex A.



24

Welds in such materials shall comply with the requirements of A.2.1.4 that alsorefers to Table A.1 that sets hardness requirements for welds.

Please note that ISO 15156-2 Technical Corrigendum 1 includes revised versions ofA.2.1.4 and Table A.1.

Sub-clause A.2.2.2 provides examples of materials that can comply with A.2.1,including some examples of tubular products in Table A.2.

Sub-clause A.2.2.3 addresses downhole components only.

The standard allows materials, such as AISI 4130, to be qualified at higher hardnessthan 22 HRC for possible use as pipe in sour service by laboratory testing inaccordance with Annex B and Table B.1 or on the basis of field experience asdescribed in ISO 15156-1, 8.2. Welds must be shown to comply with therequirements of Paragraph 7.3.3.4.

A.2.2.2 and A.2.2.3

QUESTION:In reference to Table D2, Acceptable Specifications for Tubular Goods, in the leftcolumn titled ―For All Temperatures,‖ why is Pipe a separate category from Tubing and Casing ? In the API 5CT specification (see Paragraph 1.1), as well as the NACEMR0175-2003 standard, ―casing‖ is identical to ―pipe‖ (see Sections 10 and 2,Tubular Components).


ANSWER :Casing and tubing are generally but not always intended for the completion of oil andgas wells. These materials are referred to and specified in API Spec. 5CT.

Pipe may have many intended uses and is referred to and specified in API Spec. 5Land other industry standards.

A.2.2.4

QUESTION:Are the bolting materials and nuts specified in Paragraphs 6.2.1.2 and 6.2.1.3,

respectively, the only acceptable materials in compliance with MR0175-2003 forExposed Bolting?

(MP INQUIRY #2003-22 Q1)ANSWER:Bolting materials may be chosen in accordance with Sections 3 and 4 as describedin MR0175-2003, Paragraph 6.2.1.1.

QUESTION:Does Paragraph 6.2.1.1 allow other nuts and bolting materials besides the oneslisted in Paragraphs 6.2.1.2 and 6.2.1.3?


ANSWER:Yes, in accordance with NACE Standard MR0175-2003 Sections 3 and 4.



25

QUESTION:Are the following ASTM bolting materials and nuts acceptable for exposed bolting inaccordance with Paragraph 6.2 of MR0175-2003? (ASTM A 193, carbide solutiontreated, GR B8R, B8RA, B8, B8M; A 194, carbide solution treated, Gr 8R, 8RA; A

320, carbide solution treated, Gr B8, B8M)(MP INQUIRY #2003-22 Q3)

ANSWER:The manufacturer is responsible for the effects of carbide solution treatment on thematerial properties.

QUESTION:SUBJECT: Paragraph 6.2.1.1 of NACE MR0175-2003 StandardQUESTION: It is not clear whether or not the word "restrictions" as used inParagraph 6.2.1.1 of NACE MR0175-2003 includes any environmental restrictionsfor bolting and nuts exposed to sour gas environments. Are bolting and nuts, which

are manufactured from wrought austenitic stainless steel materials in accordancewith the applicable paragraph in Section 4 of NACE MR0175-2003, acceptable foruse in exposed sour environments with no environmental limits with respect tochloride content, partial pressure of H2S, temperature, and free elemental sulfur?QUESTION: Is the answer to the above question in agreement with ISO 15156?

(MP INQUIRY #2003-39)ANSWER:Paragraph 6.2.1.1 requires materials to meet the requirements of Sections 3 and 4as applicable to the base material. This paragraph does not specify just"metallurgical requirements." If the bolting is non-exposed in accordance with

Paragraph 6.3.1, then the environmental requirements are not necessary.

QUESTION:Does NACE MR0175/ISO 15156-2, Paragraph A.2.2.4 apply to Gr. 660 flangebolting materials or only to carbon and low alloy steel bolting materials in Part 2?


ANSWER:Paragraph A.2.2.4 only applies to materials in Part 2. See also response to MP Inquiry #2005-09Q2 posted under ISO 15156-3, Table A.26.

QUESTION:This query is about specifications of external bolting material in NACE MR0175/ISO15156.

In MR0175-2003, Section 6, Paragraph 6.2.1, all external bolting on sour systemsthat is denied direct atmospheric exposure, due to insulation or flange protectors, isconsidered to be in sour service because of the chance of exposure to H2S leaks.

This seems to be in contradiction with Paragraph 1.4/Appendix A, where a minimumtotal pressure of 0.45 MPa (4.5 bara) is given as a minimum pressure level forsulfide stress cracking in gas.



26

External bolting is normally at a lower pressure than that. On the other hand,external bolting may be considered potentially wet, which would lower the limit to apartial pressure of 0.0003 MPa H2S.

In NACE MR0175/ISO 15156 Part 2, this specification is maintained for C-steel

bolting but it is not extended to CRA bolting in Part 3. I have two questions aboutthis guideline:

How should I interpret the ambiguity/exception that exists in regard to minimumpressure level around external bolting?

What is the current position of CRA external bolting on sour systems?

Is Class 2 bolting accepted or shall it be Class 1?(MP INQUIRY #2006-09)

ANSWER:The ambiguity you describe does not exist in NACE MR0175/ISO 15156. As shownin Table 1 of all parts of the standard, no gas systems, whatever their total pressure,are included in the "Permitted exclusions" listed in Column 2.

The equipment user is responsible for the selection of materials suitable for theintended service.

The requirements of NACE MR0175/ISO 15156-2, A.2.2.4 apply only to carbon andlow-alloy steels.

NACE MR0175/ISO 15156-3 does not address the selection of materials external tothe production environment.

A.2.3.2.2

QUESTION:The title of Paragraph A.2.3.2.2 in NACE MR0175/ISO 15156-2 is ―Shear rams.‖This section allows the use of rams made from quenched and tempered, Cr-Mo, low-alloy steels up to a maximum hardness of 26 HRC provided the composition andheat treatment are carefully controlled and supporting SSC testing is performed.

The text of this section does not limit these provisions to just shear rams; however,the section title would imply that only shear rams are covered by its provisions. Thisapparent shear ram restriction was not in previous revisions to NACE MR0175 (see12.4.3 in NACE MR0175-2003 for example). It is important to ram manufacturers aswell as end users that all Cr-Mo, low-alloy steel rams, not just shear rams, beallowed up to 26 HRC to ensure maximum hang-off capacity and for anti-extrusionpurposes. Do the provisions of A.2.3.2.2 apply only to shear rams or can they beapplied to other types of rams as well?


ANSWER:



27

The requirements for Cr-Mo, low-alloy steel rams in A.2.3.2.2 in NACE MR0175/ISO15156-2 are not intended to be restricted to shear rams only, but may be applied toother types of rams as well. This is consistent with all previous revisions of MR0175.

A.2.4.1 and Table A.5

QUESTION:In NACE MR0175/ISO 15156 Part 2, Paragraph A.2.4, ductile iron ASTM A 536 islisted in Table A.5 as acceptable materials for drillable packer components for sourservice. However, it is not mentioned in Paragraph A.2.4.1. Can we use thismaterial for pressure-containing parts, i.e., valve stems?


ANSWER:No, ductile iron ASTM A 536 is not listed in A.2.4.1 and may not be used forpressure-containing parts.

A.2.4.3

QUESTION:I have a query regarding material suitability on a recent enquiry to supply a nodulariron screw compressor.

NACE Standard MR0175 accepts ferritic ductile iron to ASTM A 395. My question isif our existing in-house standard of ASTM A 536 Grade 60/40/18 will comply as adirect alternative. On the face of it tensile strength, elongation are similar at

415N/mm2 and 18%! (MP INQUIRY #2005-27)ANSWER:The ISO Maintenance Panel cannot advise on materials selection issues. The roleof the Maintenance Panel is solely to ensure that NACE MR0175/ISO 15156 (thecurrent edition of NACE MR0175) is clear in its stated requirements and is kept up-to-date.

Should you wish, the procedure to propose an amendment to the standard to includeASTM A 536 Grade 60/40/18 is described in

"01. Introduction to ISO 15156 Maintenance Activities" on the Web site

www.iso.org/iso15156maintenance.

Annex B

B.1

QUESTION:Base Material



28

In accordance to NACE MR0175/ISO 15156, Part 1, Item 7, 3rd paragraph, "noadditional laboratory testing of pre-qualified materials selected in these ways isrequired."

In accordance to NACE MR0175/ISO 15156, Part 2, Item B1, letter "a," "Some

carbon and low alloy steels described or listed in A.2 might not pass some oflaboratory . . ."

In our understanding, NACE Standards TM0177 and TM0284 are used to qualifynew materials that are not previously included in NACE MR0175. If we are usingmaterials previously included in NACE MR0175, it is not necessary to test themaccording to NACE TM0177 and TM0284.

We would like you to confirm if our interpretation below is correct and if not give usthe correct interpretation.


ANSWER:NACE MR0175-2003 and its earlier editions only aimed to specify materials inrelation to their resistance to SSC, SCC, and GHSC. They did not specify materialsin relation to their resistance to SOHIC, SZC, HIC, or SWC.

For carbon and low alloy steels, their resistance to SSC is referred to in ISO 15156-1, Clause 7, Para. 1 and in ISO 15156-2, Annex A.2 and Annex B.1 a).

Many materials included in NACE MR0175-2003 and its earlier editions wereallowed by these documents on the basis of the general rules of acceptance now

given in ISO 15156-2, Annex B.1 a).

ISO 15156-2, Annex A.2, Para. 2 explains that carbon and low alloy steels complyingwith Annex A.2.1 " . . . might not resist SOHIC, SZC, HIC, or SWC without thespecification of additional requirements."

Hence, you may apply ISO 15156-1, 7 in relation to SSC of carbon and low alloysteels, but more testing may be required to evaluate carbon and low alloy steels fortheir resistance to HIC/SWC and other forms of H2S cracking. These requirementsare addressed in ISO 15156-2, 7.2.2, 8, and in Annexes B.4 and B.5. No additionaltesting is required, but testing and weld qualification is recommended for cases in

which HIC and SOHIC are considered a risk.

Table B.1

QUESTION:We have some questions about some particular points concerning the SSC (NACEStandard TM0177) and HIC (NACE Standard TM0284) tests and the requirements ofNACE MR0175/ISO 15156-2003.

Our understandings are:

SSC tests shall be performed in accordance with NACE Standard TM0177. Thesolution shall be Solution A given in TM0177 in accordance with requirements given



29

in Table B.1 of NACE MR0175/ISO 15156-Part 2. The duration of the test shall be720 h in accordance with Paragraph 8.6.7 of TM0177.

Test method used shall be in accordance with guideline given in Table B.1 of NACEMNR0175/ISO 15156-Part 2, for severe sour service, i.e., Region 3. UT (Method A)

appears to be more adapted to test raw plate and FPB (Method B) to revealsusceptibility to SOHIC and/or SZC that occur at welds, then this latest test appearsto be more adapted to test welds.

Our questions are:1) What would you recommend for SSC test methods (refer to TM0177: Method A,B, C, or D) for:

-Raw plates-Weld (to qualify a welding procedure)?

In addition, we would like to know which method--A or B--is more contraingnant.(MP INQUIRY #2005-26Q1)

ANSWER:The ISO 15156 Maintenance Panel cannot make recommendations with respect tothe test method to be used in particular circumstances; however, ISO 15156-2 TableB.1, Footnote (b) provides some guidance. The test method must be acceptable tothe equipment user.

Table B.3

QUESTION:For HIC test, NACE MR0175/ISO 15156-2:2003 Table B.3 is not clear regarding theacceptance criteria to be taken into account. We usually understood that "CLR,CTR, CSR" to be taken into account is the average of the values measured from onetest specimen as defined in NACE Standard TM0284, Paragraph 4.2.1. What is yourposition?

(MP INQUIRY #2005-26Q2)ANSWER:ISO 15156-2, B.5, Paragraph 3 makes clear that where no requirement is givenNACE TM0284 shall be followed.

Annex C

QUESTION:NACE MR0175/ISO 15156, Part 2, Annex C, Section C.1 states that "The partialpressure of H2S may be calculated by multiplying the system total pressure by themole fraction of H2S in the gas." Does the word "may" permit other methods, suchas incorporating the effects of non-ideal gas behavior, to calculate partial pressurefor determining material selection?

(MP INQUIRY #2004-08)ANSWER:Yes. Please note: Annex C as a whole is "informative" rather than "normative" and

is therefore not mandatory.



30

Annex D

Figure D.2

QUESTION:

I have a request for a clarification for a possible error in Annex D of NACEMR0175/ISO 15156-2 dealing with pH estimation. I've posted it at the ISOMaintenance users' forum, but I had no reply.

Annex D (informative) of ISO 15156 Part 2 reports a procedure for in situ pHestimation based on pCO2 + pH2S, T and HCO3-.

The maps reported were previously published on EFC 16 (not 17 as quoted) andbased, if I'm not wrong, on papers by J.L. Crolet and M. Bonis.

However, Figure D.2 is different from the maps published by EFC 16: the pH axis

seems shifted some 3/4 of pH unit upward, producing a more neutral pH.

I assume the former EFC map is correct and not the ISO. Can somebody confirmmy assumption is correct?

(MP INQUIRY #2006-16)ANSWER:The author has confirmed that you are correct and that there is an error in Figure D.2of this Annex.

He has agreed to recalculate the Figure and to provide us with a corrected version.

The Maintenance Panel will publish this correction as soon as possible.



31

NACE MR0175/ISO 15156-3

General

QUESTION:I need your help with the definition of CRAs in Part 3 of MR0175/ISO 15156.

The "corrosion-resistant alloys" is very general and does not specify whether or notthe definition includes the Fe-based alloys or not. More than that, the term CRA isused together with "other alloys" making it even more confusing.

(MP INQUIRY #2004-12)ANSWER:NACE MR0175/ISO 15156-1, Paragraph 3.6 contains a definition of "corrosion-resistant alloy" (CRA). It reads: "alloy intended to be resistant to general andlocalized corrosion of oilfield environments that are corrosive to carbon steel." This

is taken from EFC 17.

"Other Alloys" are those not covered by the definitions of carbon steel or CRA. Forexample, copper is not considered resistant to general corrosion but is considered inNACE MR0175/ISO 15156-3.

QUESTION:Please see the answer included in this compendium under NACE MR0175/ISO15156-2, A.2.2.4.

(MP INQUIRY #2006-09)Contents

The revision of the contents list to highlight "Table A.1 Guide to the use of thematerials selection tables of Annex A" is included in Reference 3

Clause 1, Table 1

The revised version of this Table is given in Reference 3

Clause 3

QUESTION:

Paragraph 9.2.4.1 Pressure Containing Components--What is the definition ofbonnets? What about drain plugs?

(MP INQUIRY #2003-27 Q1)ANSWER:Unfortunately, as you have noted, there are no NACE definitions for the terms youhave listed. Therefore, they are open to your interpretation.

Clause 6

6.2.1

QUESTION:



32

Our company has understood that NACE Standard MR0175 required the maximumspecified hardness for austenitic stainless steels be satisfied at any location on barstock (e.g., at locations considered significant by the user). Since cold-finished barsfrequently have surface hardness values above the maximum specified in MR0175,we have declined to certify these products as compliant to the specification. We

appear to be in the minority, or perhaps the only stainless bar producer thatinterprets the standard in this way. We routinely find competitors' cold-finishedstainless bar in the marketplace certified to MR0175 based on a mid-radius hardnesseven though the surface hardness is above the maximum permitted in the standard.

We realize this is a long-standing issue, but would like to clarify the hardnessrequirements of the MR0175 standard. We understand the logic in requiring thematerial meet a hardness maximum at any location (e.g., surface) in order to providea predictable level of stress corrosion cracking resistance. Yet the standard doesnot clearly state, for example, that meeting surface hardness is a requirement.Please clarify the hardness requirements of MR0175 to allow all stainless bar

producers to provide a uniform product to this standard.(MP INQUIRY #2003-06)

ANSWER:NACE cannot provide assistance in specifying where to take hardness impressionsand readings for this alloy or for any other alloy. This is because NACE StandardMR0175-2003 is not a quality assurance document. It is the responsibility of the alloysupplier to meet the hardness requirements and metallurgical requirements of theaustenitic stainless steels in Paragraph 4.2.

6.2.2

QUESTION:We have some 316 stainless steel housings with a large through bore machined.Inadvertently this bore was machined oversize. We would like to flame spray buildup the surface with 316 or 316L stainless material and remachine to size. As weunderstand the standard, 316 and 316L stainless are both included in a lengthy listof materials accepted for direct exposure to sour gas. As we intend to applystainless to stainless for the purpose of remachining to dimension and not as acorrosion-inhibiting coating, would this process be acceptable and compliant with theNACE Standard MR0175/ISO 15156?


ANSWER:See response posted under ISO 15156-3, A.1.5.1 below.

QUESTION:For the cast austenitic and duplex stainless steels there is no specific mention of arequirement for post weld heat treatment in Part 3 that discusses welding of thesealloys. However, there is a statement in the application of these alloys that they areonly acceptable in the solution annealed and quench condition. In my opinion, theas welded condition does not meet the intent of being solution annealed andquenched. So can these alloys be used in the as welded condition?


ANSWER:



33

These alloys can be used in the as welded condition provided they meet therequirements of Paragraph 6.2 of ISO 15156-3 and the corresponding Tables inAnnex A. In particular Paragraph 6.2.2 indicates that welding PQRs shall includedocumented evidence of satisfactory cracking resistance.

QUESTION:Seal welding of vent holes on saddle plates welded to pipe. We have provided ventholes on saddle plates in accordance with ASME B31.3. We have used thesesaddle plates at support locations as a protective shield to pipe. Now we would liketo close the vent hole by seal welding after completion of saddle welding with pipeand carrying out PWHT. Permanent closing of vent hole is required to avoidcorrosion in offshore conditions. Service is crude oil with H2S, i.e., NACE MR0175 isapplicable.

Kindly advise us about the acceptance of seal welding for these service conditions.(MP INQUIRY #2005-21)

ANSWER:See answer given to this inquiry under ISO 15156-2, 7.3.3.

6.2.2.2.2

QUESTION:Per A.6.3 as modified in NACE/ISO 15156-3:2003/Cor.2:2005(E), "The hardness ofthe HAZ after welding shall not exceed the maximum hardness allowed for the basemetal, and the hardness of the weld metal shall not exceed the maximum hardness

limit of the respective alloy used for the welding consumable."

Per Table A.23 note (b) as modified in NACE/ISO 15156-3:2003/Cor.2:2005(E),"Low-carbon, Martensitic stainless steels either cast J91540 (CA6NM) or wroughtS42400 or S41500 (F6NM) shall have 23 HRC maximum hardness..."

Per 6.2.2.2.2 as modified in NACE/ISO 15156-3:2003/Cor.2:2005(E), "Hardnesstesting for welding procedure qualification shall be carried out using Vickers HV 10 orHV 5 methods in accordance with ISO 6507-1 or the Rockwell 15N method inaccordance with ISO 6508-1. The use of other methods shall require explicit userapproval."

However, neither a Vickers nor Rockwell 15N acceptance criteria is specified forMartensitic Stainless Steels. Furthermore, ASTM E140 does not provide a hardnessconversion for Martensitic Stainless Steels. Thus, there is neither a Vickers norRockwell 15N acceptance criteria.

Is a correct interpretation that the acceptable hardness test method for qualificationof Martensitic Stainless Steels is the Rockwell C Method, regardless of the appliedstress, and without the need for explicit user approval?


ANSWER:



34

No, ISO 15156-3, 6.2.1, Para. 2 states "The conversion of hardness readings to andfrom other scales is material dependent; the user may establish the requiredconversion tables".

6.2.2.2.2 and 6.2.2.2.3

The revised texts for these sub-clauses are included in Reference 3.

Annex A

A.1.3

QUESTION:If I want to ballot a new alloy to be used in the acceptable environments described inTable A.32 of NACE MR0175/ISO 15156, which environmental test conditionsshould be used to qualify for ―Any combination of hydrogen sulfide, chloride

concentration, and pH‖ at 135°C (275°F) with elemental sulfur? The same questionapplies to Table A.34.

(MP INQUIRY #2004-09, Q1)QUESTION:In general, for the tables listed in Annex A of NACE MR0175/ISO 15156, whatshould the environmental test conditions be to qualify a new alloy where the―Remarks‖ in the respective tables state ―Any combinations of temperature, partialpressure H2S, chloride concentration, and pH‖?

(MP INQUIRY #2004-09, Q2)ANSWER:

NACE MR0175/ISO 15156 reflects the content of the 2003 edition of NACEStandard MR0175.

The wording ―Any combination of temperature, pH . . . Is acceptable‖ in varioustables of NACE MR0175/ISO 15156-3 indicates that previous (early) editions ofNACE documents had no environmental limits set for the alloys mentioned. Thealloys were not tested to procedures laid out in later editions of NACE StandardMR0175 but instead ―grandfathered‖ into the standard (i.e., they were added to thevarious early editions by common consent and common experience of goodperformance). No formal environmental limits were established and listed.

The process for the addition of an alloy to later editions of MR0175 includedlaboratory testing under defined environmental conditions, which resulted in theenvironmental limitations for the alloy as listed in NACE MR0175/ISO 15156. Thisprocess will continue to be used for future additions of alloys to NACE MR0175/ISO15156.

Any proposal for additions/changes to NACE MR0175/ISO 15156 will be subject to aballot/approval process.

See also ISO 15156-1, 6 and ISO 15156-3, 6

A.1.5.1



35

QUESTION:We have some 316 stainless steel housings with a large through bore machined.Inadvertently this bore was machined oversize. We would like to flame spray buildup the surface with 316 or 316L stainless material and remachine to size. As weunderstand the standard, 316 and 316L stainless are both included in a lengthy list

of materials accepted for direct exposure to sour gas. As we intend to applystainless to stainless for the purpose of remachining to dimension and not as acorrosion-inhibiting coating, would this process be acceptable and compliant with theNACE Standard MR0175/ISO 15156?


ANSWER1.0 Flame spraying as a coating for corrosion resistance over a base material thatis resistant to sulfide stress cracking is acceptable within the requirements of NACEMR0175/ISO15156 Part 2 Paragraph A.2.1.5 when applied over carbon steels and ofPart 3 Paragraph A.1.5.1. In the case of your inquiry, the 316 or 316L base

materials are acceptable coating substrates if they conform tothe metallurgical requirements of Part 3 Table A.2 and are used within theenvironmental restrictions of this table for any equipment.

2.0 If this application of flame spray is for the replacement of material that will beload bearing of tensile stresses, then the inquiry is not currently addressed by NACEMR0175/ISO15156. NACE/ISO have not been balloted with data to demonstratethat the 316 SS or 316L SS deposited flame spray coating has the same crackingresistance as the materials referenced in Part 3 Table A.2, which are assumed to bein the cast or wrought conditions.

A.1.6

GENERAL REMARKS: The following remarks are prompted by questions related to Table A.2 (See alsoReference 3), Table A.18, and Table A.23.

Note: The revised version of Table A.2 is included in Reference 3.

As indicated in ISO 15156-3, A.1.6, the Tables of Annex A fall into two groups:those for the selection of materials for "Any equipment or component" and a second

group for specific named equipment or components when other, less restrictiveenvironmental and metallurgical limits may be applied as an alternative.

The scopes and contents of the Tables of ISO 15156-3, Annex A are notinterdependent.


A.1.6, Table A.1

The revised version of Table A.1 is included in Reference 3

QUESTION:



36

Do Paragraphs 9.2 and 9.5 both apply to choke valves? Additionally, choke valvesare also used in applications where they are not directly mounted on the Christmastree (i.e., manifolds, heaters, separators, etc.); can we still consider the choke valveto fall under Paragraph 9.2 for these applications?

(MP INQUIRY #2003-02 Q1) ANSWER:Please see attached ISO 15156-3 Table A.1, which will provide the interpretation ofNACE MR0175 Paragraphs 9.2, 9.3, and 9.5. NACE will be adopting ISO 15156 in2003 as a technically equivalent document.

QUESTION:Paragraph 9.2—Wellheads and Christmas trees. Does this paragraph include thevalve bodies that are on the Christmas trees as well as other valve bodies exposedto H2S? In other words, which paragraph in Section 9 refers to the valve body?


See attached ISO 15156-3 Table A.1, which will provide the interpretation of NACEMR0175 Paragraph 9.3. NACE will be adopting ISO 15156 in 2003 as a technicallyequivalent document. Please see ISO 15156 Part 1 for guidance as to how to usefield experience or laboratory data to qualify a material for H2S service.

QUESTION:Paragraph 11.4 of the standard, which is titled "Compressors and Pumps," appearsto not address many significant applications for pumps. None of the material classesaddressed in Paragraphs 11.4.2, 11.4.3, 11.4.4, 11.4.5, 11.4.6, or 11.4.7 speak toapplications in pumps in sour service. Is this intentional? It would appear that the

limitations applied to compressors would be also applicable to pumps.(MP INQUIRY #2003-20 Q2)ANSWER:It is intentional that the paragraphs you have cited apply only to compressors. TheParagraphs 11.4.2 and 11.4.3 come from the previous 2002 edition. The otherparagraphs were added as a result of the balloting process for the 2003 edition.

A.1.6 Table A.1 (Row “Any equipment or component”)

QUESTION:

Are the bolting materials and nuts specified in Paragraphs 6.2.1.2 and 6.2.1.3,respectively, the only acceptable materials in compliance with MR0175-2003 forExposed Bolting?

(MP INQUIRY #2003-22 Q1)ANSWER:Bolting materials may be chosen in accordance with Sections 3 and 4 as describedin MR0175-2003, Paragraph 6.2.1.1.

QUESTION:Does Paragraph 6.2.1.1 allow other nuts and bolting materials besides the oneslisted in Paragraphs 6.2.1.2 and 6.2.1.3?




37

Yes, in accordance with NACE Standard MR0175-2003 Sections 3 and 4. ISO15156-3, Table A.1 (Row ―Any equipment or component‖) lists the tables which maybe used to select bolting materials.

A.2.1 and A.2.2, Table A.2

QUESTION:With the former MR0175-2000 the material 316L (bar and pipe material) and CF8M(casting material) was allowed for use for NACE applications. With the new revision(MR0175-2003) the 316L does not fulfill the new allowed limits of the chemicalcomponents any more and the allowed temperature range to use CF8M is drasticallyreduced (so that it has nearly no meaning anymore for the NACE applications).According to our experiences these two materials have been very common forapplications that require the "NACE conformity."

Now we are very interested in the reasons why these two materials are (nearly) not

possible with the new specification any more.

--Do you know what have been the reasons to change the limits of the allowed alloysand the allowed maximum temperature in this way?

--Have there been serious problems with these materials in NACE applications in thepast?

(MP INQUIRY #2003-30)ANSWER:1. We are not aware of having restricted the general composition of 316 SS beyond

that of an industry consensus that was reviewed during the balloting process for the2003 edition. It is important to emphasize that the chemical compositions for anyalloy category in the 2003 edition are those of the alloys as delivered and not fromthe specifications. 316L SS is within the range as specified in Paragraph 4.2.1 ofMR0175-2003 and is acceptable.

2. The austenitic stainless steels were restricted because of industry and lab failures.Please see the attached documentation. Upon the final ballot, there was a singlenegative that was not withdrawn. This negative suggested making the restrictions on316 SS even more restrictive. You may choose for a future addendum to proposenew limits based on the documentation described in NACE MR0175/ISO 15156.

This documentation may be either laboratory data or successful field experience.

A.2.2, Table A.2

The version of Table A.2 included in Reference 3 provides new guidance on theenvironmental limits of temperature, H2S, chlorides, pH and sulfur for austeniticstainless steels in sour service.

QUESTION:Paragraph 4.2—Austenitic Steels (say 316 SS). One of the acceptance limits forthese materials is a maximum H2S partial pressure of 15 psia at a maximum of

140°F when no chlorides are present. Can I assume that I can still use a material



38

from this category at a higher temperature than 140°F if the partial pressure of H2S islower than 15 psia?

(MP INQUIRY #2003-04 Q1)REVISED ANSWER 2005-09-01:See Reference 3

QUESTION:In the past we have used 300 series SS pipes and valves in sour service. We arenot sure of the implications and use of SS in sour service according to NACEStandard MR0175-2003. Could you please advise whether 300 series SS (304/316,etc.) can be used at lower H2S partial pressures for temperatures above 60°C(140°F)?

(MP INQUIRY #2003-08)REVISED ANSWER 2005-09-01:See revised version of Table A.2 included in Reference 3

Please see ISO 15156 Part 1 for guidance as to how to use field experience orlaboratory data to qualify a material for H2S service.

QUESTION:Paragraph 4.2.2 is new. Would you let us know which interpretation applies?

1. Paragraph 4.2.2 is intended to place a limit on acceptable H2S content under theconditions stated, i.e., when temperature does not exceed 60°C, when no elementalsulfur is present, but without restriction on chlorides.

2. Paragraph 4.2.2 places a maximum temperature limit of 60°C on the use ofaustenitic stainless steel under any conditions in which MR0175 applies, forexample, at 0.1 psia H2S partial pressure with no chlorides present.

(MP INQUIRY #2003-23 Q1)REVISED ANSWER 2005-09-01:See revised version of Table A.2 included in Reference 3

QUESTION:In addition, please clarify the reason for the 60°C limit in Paragraph 4.2.2:

We have noted that a limit of 60°C is commonly cited with respect to chloride stress

corrosion for austenitic SST in other publications, and that chloride is mentioned inParagraph 4.2.2. Are we correct in assuming, therefore, that the 60°C limit inParagraph 4.2.2 is based on chloride stress corrosion concerns above 60°C whenchloride concentrations above 50 mg/L are present rather than H2S corrosionconcerns? That is, the first sentence of Paragraph 4.2.2 does not have a limit onchlorides but does have a temperature limit, whereas the second sentence limitschlorides but does not have a temperature limit.


See Paragraph 1.1 in NACE Standard MR0175-2003 for the scope of MR0175. Theenvironmental restrictions in Paragraph 4.2.2 were established to provide resistance



39

to sulfide stress cracking (SSC) and/or stress corrosion cracking (SCC) in austeniticstainless steels.

QUESTION:AISI 316: Technical justification of the temperature limitation to 60°C.


The austenitic stainless steels were restricted because of industry and lab failures.Please see the attached documentation. Upon the final ballot, there was a singlenegative that was not withdrawn. This negative suggested making the restrictions on316 SS even more restrictive.

QUESTION:SUBJECT: Paragraph 6.2.1.1 of NACE MR0175-2003 Standard

QUESTION: It is not clear whether or not the word "restrictions" as used inParagraph 6.2.1.1 of NACE MR0175-2003 includes any environmental restrictionsfor bolting and nuts exposed to sour gas environments. Are bolting and nuts, whichare manufactured from wrought austenitic stainless steel materials in accordancewith the applicable paragraph in Section 4 of NACE MR0175-2003, acceptable foruse in exposed sour environments with no environmental limits with respect tochloride content, partial pressure of H2S, temperature, and free elemental sulfur?

QUESTION: Is the answer to the above question in agreement with ISO 15156?(MP INQUIRY #2003-39)

ANSWER:Paragraph 6.2.1.1 requires materials to meet the requirements of Sections 3 and 4as applicable to the base material. This paragraph does not specify just"metallurgical requirements." If the bolting is non-exposed in accordance withParagraph 6.3.1, then the environmental requirements are not necessary.

QUESTION:NACE MR0175/ISO 15156-Part 3: From Table A.2 it seems that AISI 316/316L SScan no longer be used whenever the process temperature is above 60°C even ifchlorides are totally absent from the environment. As this could have an enormousimpact on the material selection for oil and gas processing plants, I would like to

have a confirmation of the above. (MP INQUIRY #2004-17)REVISED ANSWER 2005-09-01:See revised version of Table A.2 included in Reference 3

QUESTION:We are now in the detailed engineering design phase of a sour gas refinery, and wehave implemented NACE MR0175/ISO 15156 for design purposes. NaCl (sodiumchloride) will come to the refinery through three-phase flow pipeline from offshore,after liquid separation in slug catcher; then the sour gas will go to gas treatment unitsfor further processing. Table A.2 refers to chloride content in aqueous solution as

mg/L; my question is in sour gas treatment units in which we use austenitic stainlesssteel, what are the criteria for the limitation of application of austenitic stainless



40

steel? My idea is we have to comply with the first row of Table A.2. There is nomeans to identify the chloride content in the gas stream.

(MP INQUIRY #2004-21)REVISED ANSWER 2005-09-01:It is assumed in Table A.2 that this is a mixed-phase environment with both a gas

phase and a liquid phase. This is always true throughout the document.

The operator is responsible for determining the service conditions, including chloridecontent (see ISO 15156-1, 6.1) and the ISO Maintenance Panel cannot provideadvice.

As mentioned in ISO 15156-3, A.1.3, Paragraph 2: ―The tables show the applicationlimits with respect to temperature, pH2S, Cl, pH, S. These limits apply collectively.‖

See also revised version of Table A.2 included in Reference 3

However, if, as an equipment user, you feel that ISO 15156-3, Table A.2 does notaddress your expected field conditions you have the freedom to test materials underalternative environmental limits and to use the outcome of successful tests to justifythe use of a material outside the limits set in the standard. (See ISO 15156-3, 6.1,Para. 5.)

QUESTION:Would you let me know whether our interpretation is correct? NACE MR0175/ISO15156-3:2003 Para. A.2.2 states environment limits for austenitic stainless steel.According to Para. A.2.2, austenitic stainless steel (304/316 SS) is applicable with

max. H2S partial pressure of 15 psi at a max. temperature of 140°F and UNSS20910 for valve stem is applicable without environmental limit.

Austenitic stainless steel (304/316 SS) is applicable to valve stem material at a max.H2S partial pressure of 15 psi and a max. temperature of 140°F. Over a temperatureof 140°F, UNS S20910 is applicable material to valve stem.


"Any equipment or component" includes valve stems, pins, and shafts. Table A.3

allows the use of UNS S20910 without environmental restrictions for "valve stems,pins, and shafts" but not for other equipment.

See also "General Remarks" under ISO 15156-3, A.1.6 of this "Inquiries andinterpretations" document.

QUESTION:I have a technical query related to the latest edition of MR0175/ISO 15156 and theuse of 316 stainless steel for sour service application. This latest edition of thestandard imposes new restrictions on the use of 316 SS in environments operatingabove 60°C.



41

My question is can 316 SS be used above 60°C for non-stressed vessel internals orfor items such as thermowells located into sour lines or vessels? I ask this because Inote that the standard need not be applied to parts loaded in compression (Part 2,Table 1). The implication may be that parts have to be stressed for SCC to be anissue.

As a similar situation to vessel internals and thermowells, please could you adviseon the use of 316 stainless steel for valve internals in a sour application, operatingabove 60°C. Of particular interest is the use of solid 316 SS balls for ball valves.

(MP INQUIRY #2005-03)ANSWER:1.0 The scope of NACE MR0175/ISO 15156 Part 3, Paragraph 1, Sentence 1defines the applicability of the standard. The standard need not be applied forequipment not covered by this sentence. In addition, in Table 1, parts loaded incompression are included among those considered to be "permitted exclusions."SCC requires a tensile stress (applied and/or residual) to occur. There is no

provision for any of the alloys in the standard for a threshold tensile stress belowwhich failure cannot occur.

2.0 The Maintenance Panel cannot analyze the design of equipment. It is up to themanufacturer and equipment user to agree whether or not the scope or any of thelisted exclusions in Table 1 apply for a given design.

A.2.2 including Table A.2

QUESTION:

Paragraphs 4.2 and 4.2.1 refer to all CRAs being used in contact with well fluids butdo not necessarily include instrument or control tubing (Bourdon tubes) being used inpressure indicators as listed in Paragraph 8.4.4.1. Currently this means that 316stainless steel alloys (L, Ti, etc.) containing those elements are not ruled out fromtheir being used in gauges where the well fluid wetted parts are not exposed to fluidsthat do not exceed:4.2.2 The maximum acceptable H2S partial pressure shall be 100 kPa abs (15 psia)at a maximum temperature of 60°C (140°F), with no restrictions on chlorides, and noelemental sulfur.

If the chloride content is less than 50 mg/L, the H2S partial pressure shall be less

than 150 kPa abs (50 psia).

Each application is subject to the specific environmental conditions to the equipmentsupplier, particularly if the equipment will be used in sour service.

Under the above stated conditions, do gauges that are made with 316 SS alloysteels comply with NACE Standard MR0175-2003?

(MP INQUIRY #2003-18)REVISED ANSWER 2005-09-01:You have correctly cited Paragraph 4.2 of MR0175 for the general use of austeniticstainless steels. It is the manufacturer's responsibility to determine whether the 316

SS meets the metallurgical requirements of this paragraph, including the requirementthat the alloy will be "free of cold work . . . "



42

--There is no exclusion for Type 316 stainless steel from the metallurgical or theenvironmental requirements of Paragraph 4.2 in Paragraph 8.4.2 of MR0175-2003.

--NACE will adopt in 2003 the ISO 15156 document as being technically equivalent

to MR0175. At this time there will be only a joint standard, NACE MR0175/ISO15156. The NACE MR0175 2003 edition will cease to exist.

See revised version of Table A.2 included in Reference 3.

QUESTION:For round bar stock 304/316 SS material, does the NACE MR0175 Rockwell C 22max hardness requirement refer to the hardness anywhere on the raw material ordoes it refer to the hardness measured at mid-radius, which is the location whereASTM standards require the hardness measurement to be made?

For 304/316 austenitic stainless steel MR0175 indicates that the hardness must beRockwell C 22 max as long as the material was not hardened to enhancemechanical properties. The hardness on 304/316 SS round bar typically varies withradial position. The material typically has the highest hardness readings at the outersurface and lowest in the center. ASTM standards define hardness measurementsfor bar stock to be taken at mid-radius. In purchasing raw material, the hardnessreadings reported are at mid-radius.

(MP INQUIRY #2006-05)ANSWER:The Maintenance Panel cannot comment on the hardness test locations specified in

ASTM standards.

These materials, when used for sour service, must comply with all the requirementsof NACE MR0175/ISO 15156-3, Table A.2. The definition of the hardness testinglocation is outside the scope of the standard, but hardness requirements must bemet regardless of the chosen test location.

Table A.2 Revised version (see Reference 3)

QUESTION:I would like to have advice regarding the addenda with particular focus on Reference

3.

Q1. According to Table A.2 of NACE MR0175/ISO 15156-3-2003/Cor. 2-2005 (E),an environmental limit for austenitic stainless steel was added under the title of "Anyequipment or components in oil and gas processing and injection facilities afterseparation."

Fluid from the oil wells is processed in the gathering center, which usually consists offlow lines, separators, desalter, storage tanks and gas processing facilities.

1. What does the "separation" facility mean? Is "separation" the facility downstream

from the separator in the gathering center?



43

2. In case that environmental condition of a stream after separation is maximumchloride content above 50 mg/L and max H2S partial pressure below 15 psia, is theaustenitic stainless steel acceptable for use?

3. If not, is there any technical reason for different environmental limits defined for

the facilities before and after separation?(MP INQUIRY #2005-30Q1)

ANSWERQ1.1)The subsection you refer to was introduced to correspond to a category ofequipment that was familiar to users of NACE MR0175:2003 and had been omittedin NACE MR0175/ISO 15156-3. The environmental limits upstream anddownstream of separation are identical.

Q1.2)Yes, if the temperature is less than 60°C.

Q1.3)No, see answer Q1.1)

Q2. According to NACE MR0175/ISO 15156-3-2003/Cor. 2-2005 (E), environmentallimits for some materials. Please advise when NACE MR0175/ISO 15156 would beaccordingly revised.

(MP INQUIRY #2005-30Q2)ANSWERQ2

This is addressed under the topic "FAQs" on the ISO 15156 Maintenance Web siteat www.iso.org/iso15156maintenance.

A.2.2, Table A.3

QUESTION:Paragraph 4.3.1 for UNS S20910 allows this material to be used in sulfur-freeenvironments when the maximum H2S partial pressure is 15 psia to 150°F in theannealed or hot-rolled (hot/cold-worked) condition at 35 HRC maximum hardness.

Paragraph 9.4.1 for UNS S20910 allows this material to be used for valve shafts,stems, and pins at a maximum hardness level of 35 HRC in the cold-workedcondition, provided this cold working is preceded by a solution-anneal heattreatment.

Does this mean that I can use UNS S20910 for valve stems in the cold-worked condition (preceded by a solution-anneal heat treatment) at 35 HRC max with no environmental restrictions?

(MP INQUIRY #2003-12 Q3)ANSWER:There are no environmental restrictions for UNS S20910 permitted at the higher

hardness of 35 HRC in Paragraph 9.4.1 for the applications defined in Paragraph9.4. Please see the attached Table A.3 from ISO 15156, which provides the correct





44

interpretation of this paragraph. NACE will be adopting ISO 15156 in 2003 as atechnically equivalent document.

QUESTIONWe have a client that wishes us to use UNS S17400 double age-hardened stainless

steel for the valve stem on some 4.1/16-in. 5k gate valves (basically because wehave some in redundant stock and can deliver far quicker than the nickel alloyversion of stem we currently use).

He does, however, want the valves to comply with API 6A material class DD and thelatest version of NACE MR0175. Where there is slight ambiguity is with the use ofUNS S17400 for valves and choke components (excluding bodies and bonnets) withan allowable partial pressure of 0.5 psi (ref. Table A.27).

Is it correct to assume that this additionally excludes valve stems because these arespecifically dealt with in Table A.3, or can valve stems be used manufactured from

UNS S17400 (in the required treated condition), as they are a valve component, withan allowable partial pressure of 0.5 psi in accordance with Table A.27?


Answer:No, Table A.3 does not preclude the selection of other materials for valve stems.

Please see Table A.1.In general, materials for equipment or components may be chosen from Tables for"Any equipment or component" or from Tables for specific named equipment or

components when other, less restrictive environmental and metallurgical limits maybe applied as an alternative.

For the specific example of UNS S17400 valve stems, they may be selected usingTable A.27 subject to the environmental and metallurgical limits of this Table.

A.2.2, Table A.2, Table A.3, and Table A.6


QUESTION:

SUBJECT: Paragraph 9.4 of NACE MR0175-2003 StandardQUESTION: Are shafts, stems, and pins used in valves, unloaders, and otherdevices, when manufactured from austenitic stainless steel materials in accordancewith Section 4 of NACE MR0175-2003, acceptable for use in sour environments withno environmental limits with respect to chloride content, partial pressure of H2S,temperature and free elemental sulfur?QUESTION: If the answer to the former question is no, what are the specificenvironmental limits?

(MP INQUIRY #2003-36)ANSWER:1) For stainless steels, the environmental limits of Paragraph 4.2 apply (as opposed

to compressors where in Paragraph 11.4.7 there are no restrictions).



45

(2) For individual alloy UNS S20910 there are no environmental restrictions if coldwork and hardness are set within the restrictions of Paragraph 9.4.1 in Table A.3 ofNACE MR0175/ISO 15156-3. Since in Paragraph 9.4.1 of MR0175-2003 there areno environmental restrictions, then the environmental restrictions of Paragraph 4.3.1do not apply for shafts, stems, and pins.

QUESTION:SUBJECT: Paragraph 9.4 of NACE MR0175-2003 StandardQUESTION: Are shafts, stems, and pins manufactured from austenitic stainlesssteels in accordance with and meet the hardness and heat-treat requirements ofSection 4 of MR0175-2003 acceptable for use in sour environments with noenvironmental limits with respect to chloride content, partial pressure of H 2S,temperature and free elemental sulfur?QUESTION: Is the answer to the above question in agreement with ISO 15156?


(1) For stainless steels, the environmental limits of Paragraph 4.2 apply (as opposedto compressors where in Paragraph 11.4.7 there are no restrictions).(2) For individual alloy UNS S20910 there are no environmental restrictions if coldwork and hardness are set within the restrictions of Paragraph 9.4.1 in Table A.3 ofISO 15156-3. Since in Paragraph 9.4.1 of MR0175-2003 there are no environmentalrestrictions, then the environmental restrictions of Paragraph 4.3.1 do not apply forshafts, stems, and pins.

A.2.2, Table A.2 and Table A.6


QUESTION: SUBJECT: Paragraph 9.3 of NACE MR0175-2003 StandardThe packaging content of large skid-mounted gas compressors applied in the oil andgas, gas processing, and process industries generally include several valves variedin type, such as relief valves, ball valves, globe valves, plug valves, gate valves,butterfly valves, and check valves installed on scrubbers, in process gas piping, andin off-skid mounted header systems and sometimes contain chokes in higherpressure scrubber drain systems. Are the body and bonnet components of valves,when manufactured from austenitic stainless steel materials in accordance with

Section 4 of NACE MR0175-2003, acceptable for use in sour environments with noenvironmental limits with respect to chloride content, partial pressure of H2S,temperature, and free elemental sulfur.


ANSWER:The latest editions of API Standard 618 for Reciprocating compressors and APIStandard 617 for Axial and Centrifugal compressors define the scope of equipmentassociated with the compressor environment including accessories, instrumentationand piping systems. It is the user’s responsibility to determine whether theequipment mentioned in your inquiry is directly associated with the compressor and

experiences the same service environment as inferred for compressors in NACEMR0175/ISO 15156-2003 Table A.6.



46

QUESTION: If the answer to the former question is no, what are the specificenvironmental limits?

(MP INQUIRY #2003-35 Q2)REVISED ANSWER 2005-09-01:

a) The austenitic stainless steels when used outside the compressorenvironment are subject to the environmental restrictions in NACE MR0175/ISO15156-2003 Table A.2.

See revised version of Table A.2 included in Reference 3

b) The austenitic stainless steels were restricted because of industry and labfailures.

QUESTION: Are the non-pressure-containing components of valves, whenmanufactured from austenitic stainless steel materials in accordance with Section 4

of NACE MR0175-2003, acceptable for use in sour environments with noenvironmental limits with respect to chloride content, partial pressure of H 2S,temperature, and free elemental sulfur?

(MP INQUIRY #2003-35 Q3)ANSWER:a.) The user must determine if individual components or parts of equipment mustmeet the requirements of NACE MR0175/ISO 15156-2003.b) NACE MR0175-2003 provided guidance for this applicability of the standard inParagraph 1.3. This paragraph stated that ―This standard applies to all componentswhere failure by SSC or SCC would (1) prevent the equipment from being restored

to an operating condition while continuing to contain pressure, (2) compromise theintegrity of the system, and/or (3) prevent the basic function of the equipment fromoccurring.‖ These guidelines can be applied within NACE MR0175/ ISO 15156-2003.

QUESTION: If the answer to the former question is no, what are the specificenvironmental limits?

(MP INQUIRY #2003-35 Q4)ANSWER:The austenitic stainless steels when used outside of the compressor environmentare subject to the environmental restrictions in NACE MR0175/ISO 15156-2003

Table A.2.Note: The revised version of Table A.2 is included in Reference 3.

QUESTION: Are the answers to all of the above questions in agreement with ISO15156?

(MP INQUIRY #2003-35 Q5)ANSWER:Yes.

QUESTIONS:

I have an application where I am supplying a pipeline from a gas compressor to aturbine generator. The pipe is 10 in. in diameter and contains natural gas with H2S.



47

The H2S concentration is 250 ppm by volume. The gas is pressurized to 475 psi@152°F. I would like to know what table from Annex A this pipe would fall under.The material I would like to use is 304L SS, which satisfies the requirements in A.2.I would appreciate any guidance you can provide with this subject.


ANSWERS:1a) NACE MR0175/ISO 15156-3:2003 Table A.6 provides environmental andmaterials limits for austenitic stainless steels used in compressors. NACEMR0175/ISO 15156-3:2003 Table A.2 applies to austenitic stainless steels used forany equipment or components.Note: The revised version of Table A.2 is included in Reference 3.

b) The limits on austenitic stainless steels in NACE MR0175/ISO 15156-3:2003Table A.6 (when compared to those of NACE MR0175/ISO 15156-3:2003 Table A.2)are based upon industry experience with these alloys in compressors.

c) The latest editions of API Standard 618 for Reciprocating compressors and APIStandard 617 for Axial and Centrifugal compressors define the scope of equipmentassociated with the compressor environment including accessories, instrumentation,and piping systems.

d) It is the user’s responsibility to determine if the pipe mentioned in your inquiry isdirectly associated with the compressor and experiences the same serviceenvironment as inferred for compressors in NACE MR0175/ISO 15156-3:2003 TableA.6.

e) The Maintenance Panel cannot review individually designed equipment andpressure stations to make this interpretation.

2a) The manufacturer and user may consider documenting previous experience withpipelines in accordance with NACE MR0175/ISO 15156-1:2001 Paragraphs 8.2 and9.0.

b) NACE MR0175/ISO 15156-1:2001 provides minimal requirements for theseissues and the user is ultimately responsible for ensuring the alloy in final fabricatedform has adequate resistance to the types of cracking listed in the Scope 1.0 of

NACE MR0175/ISO 15156-1:2001.

3. The ISO Maintenance Panel cannot comment on the suitability of using the 304LSS materials compared to alternative alloys.

QUESTION:Recently I have down loaded a NACE MR0175-ISO 15156-3 Technical Circular 1from your web.According to the revised Table A.2, we can use austenitic stainless steel 316 up to93 degree C.I have one simple question whether the following condition is allowed for 316SS

according to the NACE MR-0175/ISO 1515 Code.



48

When the temperature is more than 95 degree C and the chloride content is lessthan 4,500 ppm, can we use 316SS for facilities?


ANSWER:

Table A.2 of Tech Circular states that 316 SS can be used if all requirements aresimultaneously fulfilled: 93°C max, 5000 ppm chlorides max, calculated in situ pHequal at least to 5 and a partial pressure of H2S max of 10 kPa (1 bar). So just thechlorides and the temperature are not sufficient. In addition the material must complywith the requirements given at the bottom of Table A.2 and in Paragraph A.2.1.

QUESTION:I am requesting a clarification of intent for comments included in Tables A.2 and A.6in Annex A of the 2003 edition.

In both of these tables there is a statement "these materials shall also -- -- be in the

solution-annealed and quenched . . . . condition."

It is my interpretation that this was a requirement for the base material and was notintended for a fabricated part, e.g., a welded compressor housing.

We have to complete some fabrications and believe the required heat treatment willcause cracking and distortion of the part--however, a part must meet therequirements of MR0175/ISO 15156.


You are correct. NACE MR0175/ISO 15156-3, Tables A.2 and A.6 apply to basematerials only.

The requirements for welding are given in NACE MR0175/ISO 15156-3, A.2.3,"Welding of austentitic stainless steels of this materials group."

QUESTION:Part 3 of the standard for austenitic stainless steels requires a solution anneal andquench or thermal stabilization along with no cold-work intended to enhancemechanical properties. I have a 316 st/st (UNS S31600) part that we spec 1/4 hardtemper, but still falls under the max hardness requirement of HRC 22. My

mechanical engineer tells me 1/4 hard in essence means cold-working the materialto increase its properties.

My question is: Can we do 1/4 hard if we still meet the hardness requirement? I amlooking to comply with Annex A.2 and Tables A.2 & A.6 for this part.

(MP INQUIRY #2006-14)ANSWER:No, ¼ hard temper UNS S31600 does not comply with the conditions set out in thenotes to Tables A.2 and A.6 as it is used to purposely enhance the mechanicalproperties of the alloy by cold working.

A.2.2, Table A4QUESTION:



49

In the latest NACE MR0175 there are two component categories "Instrument tubingand associated compression fittings,..." and "Diaphragms, pressure measuringdevices and pressure seals." To which category does the Bourdon tube belong?


Bourdon tubes are not specifically addressed in NACE MR0175/ISO 15156.

The Maintenance Panel cannot meet your request to categorize Bourdon tubesbetween "Instrument tubing and associated compression fittings,..." and"Diaphragms, pressure measuring devices and pressure seals."

In all cases the material selected must be acceptable to the equipment user for theirservice conditions.

A.2.2, Table A.6

The revised version of Table A.6 is included in Reference 3

QUESTION:SUBJECT: Paragraph 11.4.7 of NACE MR0175-2003 StandardQUESTION: It is not clear whether or not the word "restrictions" as used inparagraph 11.4.7 of NACE MR0175-2003 includes any environmental restrictions.Does Paragraph 11.4.7 provide an exemption to all of the environmental restrictionsor limits detailed in Paragraph 4.2.2 in cases in which an austenitic stainless steelmaterial has been selected for use in compressors in sour environments?QUESTION: If the answer to the former question is no, are all of the environmental

restrictions detailed in Paragraph 4.2.2 of NACE MR0175-2003 included in the word"restrictions" as used in Paragraph 11.4.7?(MP INQUIRY #2003-33)

ANSWER:NACE MR0175/ISO 15156 provides a clear interpretation in Table A.6 that only themetallurgical limits in Paragraphs 4.2 and 4.2.1 apply. Environmental restrictions donot apply. No data have been submitted to verify resistance to cracking in thepresence of elemental sulfur.

QUESTION:As a manufacturer of reciprocating compressors, we supply machines for

compressing sour gas sometimes with a H2S partial pressure up to 10 bar. BeforeNACE Standard MR0175-2003 came into force, compressor components like valves,valve cages as well as packing cups were manufactured out of austenitic stainlesssteel to prevent corrosion.

The 2003 edition of MR0175 now contains many restrictions regarding the use ofaustenitic SS, limiting the H2S partial pressure and temperature to very low values(see page 9, item 4.2.2). Under these circumstances (max. temperature 60°C) thesematerials are not any more applicable for the compression part.

On the contrary, the use of austenitic SS (UNS S31635/1.4571) acc. EN ISO 15156-

3:2003 is allowed--presumed the required heat treatment has been carried out (seepage 19, Table A.6). In order to avoid surface corrosion we furthermore intend to



50

use austenitic SS. But by doing so we are contradicting the NACE standardrequirements--the standard that is mostly quoted by our customers. We ask forclarification on your part.


For your informationISO 15156-1, ISO 15156-2, and ISO 15156-3 (and their EN versions) all have NACEversions with identical technical content; they are:

NACE MR0175/ISO 15156-1,NACE MR0175/ISO 15156-2, andNACE MR0175/ISO 15156-3

These NACE/ISO documents replace all earlier versions of NACE MR0175 includingNACE MR0175-2003.

In addition, there have been a number of inquiries on NACE MR0175/ISO 15156-3,Table A.6 since this standard was published; the answers provided by the ISO15156 Maintenance Panel are included in the document titled "02. Inquiries andAnswers" available on the ISO 15156 Maintenance Web site at

www.iso.org/iso15156maintenance

These answers provide clarification of the intent of Table A.6.

A.2.2, Table A.2 and A.2.3


QUESTION:The way I read Paragraph 4.2, austenitic stainless steels meeting Paragraph 4.2.1must be solution-annealed and quenched or annealed and thermally stabilized with amaximum hardness of 22 HRC. (1) Am I correct in assuming these materials mustbe annealed regardless of hardness? (2) If a construction started with materials inthis condition, would it be necessary to anneal again following a welding operation?


You are correct that materials must meet the requirements of MR0175-2003,Paragraph 4.2 regardless of their hardness. Please see Paragraph 5.3.3 forrequirements for welding the austenitic stainless steels. Paragraph 5.3.3 does notspecifically require an anneal after welding to meet the requirements of 5.3.3.

The requirements for austenitic stainless steels are now presented in Table A.2,NACE MR0175/ISO 15156; you are correct that the materials must meet thetreatment conditions regardless of their hardness (maximum 22 HRC). Please seeNACE MR0175/ISO 15156 A.2.3 for requirements for welding austenitic stainlesssteels.

Tables A.2 and A.4



51

QUESTION:In Part 3, Table A.4 it shows S31600 stainless, but not S31603 stainless (316Lss).Also, our equipment is a flowmeter which is not specifically referred to anywhere inthe standard, so do I treat it as a fitting? As for the bolt material, ASTM A354/ UNSK04100, I don’t see this material anywhere in any of the 3 parts, but I believe it goes

into the Part 3 category. This is where I also need help.(MP INQUIRY #2009-17)

ANSWER:Table A.2 applies for austenitic stainless steels whose composition are defined in §A.2. It includes low C 316L SS. Note that the 2009 version of the Standard has anerror: the first column should read S31600, S31603. In this case it can be eitherTable A.2 that applies to any equipment or components or another Table that appliesto the specific equipment or component. It is up to the user to determine which Tableto use. Your last point cannot be answered as the MP does not do consulting work.

A.2.3

QUESTION: My stainless steel sheet material qualifies to Section A.2. I am forming this sheetinto tubes and (longitudinally) welding the formed tube without filler metals using anautomatic arc welding process (ASTM 249/ASTM 269). After welding the tube isfully annealed per ASTM. My hardness values are all below 22 HRC as required.A. Is my welded and annealed tubing bound to the welding requirements of A.2.3and 6.2.2?B. After annealing, if I now butt weld two ends of the tubing above using the orbitalweld (no filler metal) process (no additional anneal), am I now bound to A.2.3 and

6.2.2? (MP INQUIRY #2004-19 Q2)ANSWER:A. Yes, this is still a weld even if it was made without filler materials.B. Yes.

QUESTION:Inconel 600 (UNS N06600) was an included material in the 2002 revision ofMR0175, per section 4.1.4.1. In both the 2003 revision of MR0175 and MR0175/ISO15156-3:2003, I have not been able to find any references to N06600 or any materialcategory/type that would cover this material. Am I overlooking a reference to this

material, or was this material removed from the specification? If it was removed,were their specific reasons that lead to its removal?

(MP INQUIRY #2009-07)ANSWER:Indeed alloy UNS N06600 was part of the 2002 version with a limit at 25 HRC and itis not included in ISO 15156-3. You may read the answer to a previous inquiry #2004-19 Q1 at the following link and then go to "02 Inquiries and InterpretationSeptember 2007." [now June 2010][http://isotc.iso.org/livelink/livelink?func=ll&objId=3340364&objAction=browse&sort=name

QUESTION:In Section of Part 3: Table A.2 (austenitic stainless steel) states:

http://isotc.iso.org/livelink/livelink?func=ll&objId=3340364&objAction=browse&sort=name






52

"These materials shall also-be in the solution-annealed and quenched, or annealed and thermally stabilizedheat-treatment condition,-be free of cold work intended to enhance their mechanical properties, and-have a maximum hardness of 22 HRC."

Whereas for welding in Section A.2.3 it is stated that:"The hardness of the HAZ after welding shall not exceed the maximum hardnessallowed for the base metal, and the hardness of the weld metal shall not exceed themaximum hardness limit of the respective alloy used for the welding consumable."

I addition Section 6.2.2.2.2 states that "Hardness testing for welding procedurequalification shall be carried out using Vickers HV 10 or HV 5 methods in accordancewith ISO 6507-1 or the Rockwell 15N method in accordance with ISO 6508-1.

The use of other methods shall require explicit user approval."

Q1. Please clarify how the requirement for 22 HRC is interpreted in light of this, i.e.,what Vickers (HV 10 or HV 5) or Rockwell (15N) value should be used as amaximum for weld HAZ and weld metal?

On an associated point, for solid-solution nickel-based alloys (Section A.4) andduplex stainless steels (Section A.7) there are no hardness requirements formaterials in the solution-annealed condition (with the exception of one HIP duplexstainless steel alloy). The relevant sections (A.4.3 and A.7.3) on welding state:

"The hardness of the HAZ after welding shall not exceed the maximum hardnessallowed for the base metal, and the hardness of the weld metal shall not exceed themaximum hardness limit of the respective alloy used for the welding consumable".

Q2. Please confirm that the interpretation that NACE MR0175/ISO 15156 thereforeplaces no hardness restrictions for welds in these materials is correct.

(MP INQUIRY #2005-13)ANSWER:(1) NACE MR0175/ISO 15156 provides no guidance for hardness conversion fromthe Vickers to the Rockwell scales for the austenitic stainless steels, which is thenleft to an agreement between the manufacturer and the equipment user possibly

based on conversion tables made using empirical data; see ISO 15156-3, 6.2.1,Paragraph 2.

(2) There are no hardness limits for the HAZ of welds of corrosion-resistant alloyswhen there are no hardness limits in the tables or the text of the document for thebase materials.

For the weld metal, any hardness limit depends on any hardness limit set for thealloy used as consumable. For matching consumables for solid-solution nickel-based alloys (Section A.4) and duplex stainless steels (Section A.7) there are nohardness limits for weld metal.

A.3 and A.4



53

QUESTION:In several paragraphs of both NACE MR0175 and ISO 15156 it is stated thatmaterials (e.g., austenitic SS) are acceptable if they are free of cold work intended toenhance their mechanical properties or is stated "in the annealed or solution-

annealed condition only" (e.g., Ni-based only).

Question: Is there a limit to what is considered cold work, e.g., 5%, or is any coldwork whatsoever included?

(MP INQUIRY #2003-28 Q1)ANSWER:NACE MR0175/ISO 15156-3 does not prohibit all cold work of the austeniticstainless steels; it prohibits cold work intended to enhance mechanical properties. Alimit for the percentage of cold work is not provided.

QUESTION:

In order to decrease the danger of low stress creep we slightly overstresssuperaustenitic SS and Ni-based alloy valve bodies during hydrotesting. Thisoverstressing causes a "cold deformation" of 0.2-0.5%. We do not use the colddeformation in order to enhance the mechanical properties!

Is this practice allowed under the rules of NACE MR0175/ISO 15156 ?(MP INQUIRY #2003-28 Q2)

ANSWER:Hydrotesting the austenitic stainless steels to the appropriate industry or design codeis acceptable.

A.3.2, Table A.8

The revised version of Table A.8 is included in Reference 3.

QUESTION:We have requirement of 6Mo valves for one of our ongoing projects wherein weneed to use A 351 CK3MCuN (J 93254) body material.

With reference to Table A -8 of NACE MR0175/ISO-15156 - 2003 Environmental andmaterials limits for highly alloyed austenitic steels used for any equipment or

components ) we have following clarification:

Table A - 8 lists the above material J 93254 (ASTM A 351 CK3MCuN) can beused for any combinations of temperature, pH2S, chloride concentration and in situpH occurring in production environments are acceptable.

We understand that forging grade equivalent of above J 93254 which is UNS 31254will also be qualified under these conditions.

Please confirm /clarify the whether forging grade equivalent of J 93254 which is UNS31254 will also be qualified?




54

Answer:-Table A.8 is the subject of an amendment proposal that has been accepted by theISO 15156 Maintenance Panel, by NACE TG 299 (ISO 15156 Oversight Committee)and by ISO TC67 WG7 and will now go forward for publication.

The revision involves limits being placed upon the application of UNS J93254.Publication of this document can be expected within the coming year.


QUESTION:We have a question regarding the meaning of a sentence in Paragraph 4.4 inMR0175-2003. This same sentence is repeated in Paragraph 10.2.1.

The paragraph states:Highly alloyed austenitic stainless steels in this category are those with Ni% + 2

Mo% >30 and 2% Mo minimum.

A1. Does the statement mean that there are essentially two groups in this category?Such that . . .

One qualifying group consists of materials that contain N% + 2 Mo% >30

Another qualifying group consists of any austenitic stainless steel with 2% Mominimum (such as 316, 317).

A2. Or does the statement mean that there must be a minimum of 2% Mo in the Ni%+ 2 Mo% >30 requirement?

Since the environmental restrictions in Paragraph 4.4 are the same as in 4.2 (wheremost austenitics are acceptable), I assume #A1 is the correct interpretation since thiswould allow for inclusion of 316 and 317.

(MP INQUIRY #2003-15)ANSWER:Your answer A2 is correct. The chemistry requirements are additive.

QUESTION:

NACE Standard MR0175-2003 has two different highly alloyed austenitic SSfamilies, one (Paragraph 4.4) with Ni% + 2 Mo% >30 (and Mo>=2%) and one(Paragraph 4.5) with PREN >40. Both have two different ranges for temperature,partial H2S partial pressure, and maximum chloride content. Which environmentallimits have to be used for materials applicable for both categories like UNS S31254?

(MP INQUIRY #2003-19 Q1a)ANSWER:If UNS S31254 has a PREN >40, then the less restrictive environmental limits inParagraph 4.5 apply.

QUESTION:

Paragraph 4.4 in MR0175 identifies "Highly Alloyed Austenitic Stainless Steels withNi% + Mo>30 and 2% Mo minimum" as a category. Is it intended by the standard



55

writers that the two conditions be both present? In other words, is it Ni% + Mo>30with 2% Mo minimum? Or is the 2% Mo minimum another defined material group inthe category? I believe it to be the former as I am not aware of highly alloyedaustenitic stainless steels only defined by the term "2% Mo minimum."


ANSWER:Paragraph 4.4 in NACE Standard MR0175 is a single alloy category defined by theadditive requirements of Ni% + Mo% >30 and 2% Mo. Both requirements forchemistry must be met.

A.4

QUESTION:Alloys 400 (N04400), 600 (N06600), and 800 (N08800) were previously listed inMR0175-94 as acceptable to 35 HRC. The newest revision does not list either 600or 800 and now appears to place equipment restrictions on alloy 400 (Table A.16).

None of these alloys appear to qualify by chemistry under A.4 Solid Solution NickelBased Alloys (Table A.12, p. 21).A. Does 600 qualify anywhere in NACE MR0175/ISO 15156?B. Does 800 qualify anywhere in NACE MR0175/ISO 15156? Can 800 be qualifiedunder A.2.1 Austenitic Stainless Steels? Some publications refer to 800 as astainless steel and others as a nickel alloy. ASTM lists it as an Ni-Fe-Cr alloy as didMR0175-94.C. I assume 400 is restricted to only the equipment and conditions listed in TableA.16?


REVISED ANSWER 2005-09-01:A. Alloys UNS N06600 and N08800 were inadvertently left out of the document.Unfortunately after 6-plus years of balloting, no one noticed this. The MaintenancePanel will be grateful if you would submit a ballot item for their inclusion in the set ofaddenda now being prepared for 2005. This ballot should take the form illustrated in―01. Introduction to ISO 15156 Maintenance Activities‖ Annex C. This document isavailable at www.iso.org/iso15156maintenance. B. See answer A.C. No, it is included in the revised version of Table A.13, that is included inReference 3, that allows less restricted use.

QUESTION:Are "contained" electrical tubular heating elements manufactured from solution-annealed or annealed UNS N08800 tube (sheath material) acceptable forapplications under Paragraph A.4.1 (MR0175/ISO 15156-3)? By "contained" wemean that the heating elements are in a bundle totally enclosed inside a pipe body,shell, or tank.


ANSWER:1.0 The solution-annealed or annealed material UNS N08800 does not match any ofthe materials groups mentioned in NACE MR0175/ISO 15156:3, A.4.1 and Table

A.12. Please see also the previous interpretation (2004-19Q1) provided in responseto a similar question to the ISO Maintenance Panel and listed under "Inquiries and





56

Answers" for NACE MR0175/ISO 15156-3, A.4 athttp://www.iso.org/iso15156maintenance.

2.0 Please note the ISO 15156 Maintenance Panel is unable to comment onquestions related to design. In addition, any decision concerning the applicability of

the standard is the responsibility of the equipment user. Please refer to the Scope ofNACE MR0175/ISO 15156-3 on page 1 for the applicability of the standard.

A.4.1, Table A.12

QUESTION:Paragraph 10.5.1.1 (NACE MR0175/ISO 15156-3, Sub-clause A.4, Table A.12))requires a minimum Ni content of 29.5%, but solution-annealed and cold-workedalloy UNS N08535 (Alloy 2535, classified as a "nonferrous alloy" in MR0175-2002)only contains 29.0% Ni (minimum).

Does this mean that Alloy 2535 must be restricted to environments described byParagraph 10.2.1.1 of MR0175-2003 (NACE MR0175/ISO 15156-3, Sub-clause A.2,Table A.9) that are the same as for austenitic stainless steels like 316?

(MP INQUIRY #2003-13 Q1)ANSWER:You are correct; without further restrictions on their chemical compositions, materialsto the specification UNS N08535 can only be guaranteed to match the Categoryrequirements of "Austenitic stainless steel" (Covered in NACE MR0175-2003 asParagraph 4.2 (NACE MR0175/ISO 15156-3, Sub-clause A.2)) or of "Highly alloyedstainless steel" (Covered in NACE MR0175-2003 as Paragraph 4.4 (NACE

MR0175/ISO 15156-3, Sub-clause A.3)). Use in accordance with either of these twosub-clauses does require adherence to the relevant environmental limits.

Use in accordance with Paragraph 10.2.1.1 (NACE MR0175/ISO 15156-3, Sub-clause A.2, Table A.9), while applying the same environmental limits, does acceptcold-worked material with a maximum hardness of 35 HRC.

However, if the chemical composition of heats of UNS N08535 is specified to aminimum nickel concentration of 29.5%, i.e., higher than the minimum stated Nicontent of 29%, the alloy qualifies as a material of Type 4c as defined in NACEMR0175/ISO 15156-3, Table A.12 and is acceptable for use in accordance with the

requirements of NACE MR0175/ISO 15156-3, Table A.14, Rows 2-6. These rowsinclude the provisions of NACE MR0175-2003, Table 5.

QUESTION:Alloy G-3 (UNS N06985, classified as a "Nonferrous alloy" in MR0175-2002), a 6%Mo, solution-annealed and cold-worked alloy, may contain as little as 35.9% Ni.Does this mean that its environmental limits are given in Table 5 of MR0175-2003instead of Table 6 (NACE MR0175/ISO 15156-3, Sub-clause A.2, Table A.12)?

(MP INQUIRY #2003-13 Q2a)ANSWER:Yes, you are correct. However, for NACE MR0175/ISO 15156, if the chemical

composition is specified to a minimum nickel + cobalt concentration of 45% the alloyqualifies as a material of Type 4d and can be used in accordance with the



57

requirements of NACE MR0175/ISO 15156-3, Sub-clause A.4, Table A.14, Rows 2-8. These rows include the provisions of NACE MR0175-2003, Table 6.

QUESTION:Question: Is annealed UNS N06625, Grade 1, per ASTM B443, B444, or B446 (also

commonly referenced as stabilized or stabilize annealed) acceptable as a materialunder Paragraph 4.11.1 of MR0175-2003?

Discussion: It clearly was acceptable in the previous version of MR0175; however,Grade 1 material is NOT solution annealed, as appears to be required by Paragraph4.11.1. Solution-annealed material requires annealing at a temperature above2,000°F and is identified as Grade 2. This condition is typically reserved for servicetemperatures in excess of 1,100°F.

(MP INQUIRY #2003-40)ANSWER:Please see the definition of solution anneal in NACE MR0175 Section 2. This

Maintenance Panel cannot interpret ASTM specifications. However, please note thatUNS N06625 is considered in NACE MR0175/ISO 15156 Table A.12 as an alloy thatmay be used in the solution-annealed or annealed metallurgical condition.

A.4.1, Table A.12 and sub-clause A.4.2, Table A.13

QUESTION:Paragraph 4.11 of NACE Standard MR0175-2003 does not stipulate a minimumcobalt content. Do solid-solution nickel-based alloy wrought materials complyingwith either of the two chemical composition alternatives detailed in Paragraph 4.11.1,

but with zero percent cobalt, qualify for no environmental limits with respect to partialpressures of H2S in accordance with Paragraph 4.11.2?(MP INQUIRY #2003-25)

ANSWER:There are no environmental limits with respect to partial pressures of H2S orelemental sulfur as stated in NACE Standard MR0175-2003 Paragraph 4.11.2 forsolid-solution nickel-based alloys defined as a category in Paragraph 4.11. There isno individual requirement for the minimum content of Co alone in Paragraph 4.11.Chemistry requirements for Co are expressed only for the sum of nickel and cobalt.

QUESTION:

We manufacture a fluid-handling product machined from UNS N06600 in the cold-worked condition with a hardness less than 35 HRC. We have certified that thisproduct meets MR0175 based on Paragraph 4.1.4.1 of MR0175-2002.a) It appears this material is not included in MR0275-2003. Is it acceptable to certifythat this material meets MR0175-2003 based on the listing in previous versions?b) If not, is it acceptable to continue to certify meeting MR0175-2002?

(MP INQUIRY #2003-10 Q2)ANSWER:The MP cannot provide interpretations involving the certification of equipment. Wecan only interpret the current edition of MR0175.The MP will investigate the history of this alloy in NACE MR0175 and may make an

amendment proposal to re-include it.



58

QUESTION:Old (2002) Paragraph 4.1.5.1 UNS N06625 HRC >35New (2003) Paragraph 4.11 and A13: N06625 solution-annealed only: Technical justification?


ANSWER:The consensus during the balloting process for the 2003 edition was that nohardness limit was required for solution-annealed material. Alloy manufacturers didnot object to the change.

QUESTION:I have a query regarding UNS N08825 pipe material in hot finished annealed deliverycondition as availability of ASTM B 423 (UNS N08825) material in cold finishedannealed condition is scarce but it is generally available in hot finished deliverycondition above 8" size.

Therefore my query goes as follows:

"NACE MR0175/ISO 15156-3:2003(E) does not list UNS No. N08825 in hot finishedannealed condition in Table A.12, A.13 and A.14. Table A.12 breaks down solidsolution nickel-based alloys into Type-4a, 4b, 4c and 4d depending on Cr, Ni+Co, Moand Mo+W mass fraction and metallurgical condition. Now my question is whetherASTM B 423 (UNS N08825) pipe in hot finished annealed delivery condition for 8"and 10" pipe shall be acceptable for piping because for type 4a and 4b metallurgicalcondition does states the requirement of cold-worked or hot worked."


ANSWER:The alloy UNS N08825 in the annealed condition falls under the materials Type 4a inTables A.12 and A.13. The term "annealed" refers to the final stage of the heattreatment of the material or component that determines its metallurgical condition inthe service environment.

A.4.1 and A.4.2, Table A.13 and Table A.16

QUESTION:We believe that Alloy 400, UNS N04400, should be included in both the latestversion of MR0175 and the imminent ISO 15156 standard. As outlined in the

foreword of MR0175-2003, ―Many of the guidelines and specific requirements in this standard are based on field experience with the materials listed . . . ―

We propose that Alloy 400, UNS N04400, be added to Section 8, Special Components , Paragraph 8.4.2, Diaphragms, Pressure-Measuring Devices, and Pressure Seals .

(MP INQUIRY #2003-07)REVISED ANSWER 2005-09-01:The revised version of Table A.13 is included in Reference 3.

QUESTION:



59

In what paragraph are the requirements for wrought bar in nickel-copper alloy (i.e.,UNS N04400 and N04405)? In the 2002 version, these materials were covered inParagraph 4.1.1.

(MP INQUIRY #2003-09 Q1)REVISED ANSWER 2005-09-01:

The omission of UNS N04400 and N04405 has now been rectified. See Reference3.

QUESTION:We manufacture a fluid-handling product machined from UNS N04400 and N04405in the cold-worked condition with a hardness less than 35 HRC. We have certifiedthat this product meets MR0175 based on Paragraph 4.1.1.1 of MR0175-2002.a) May we continue to certify that this product meets MR0175-2003, since thismaterial is mentioned in Paragraph 10.6.2.2?b) Is it acceptable to continue to certify meeting MR0175-2002?


REVISED ANSWER:The MP cannot provide interpretations involving the certification of equipment. Wecan only interpret the current edition of MR0175. More information on the use limitsfor UNS N04400 and N04405 are provided in the revised version of Table A.13 inReference 3.

QUESTION:What are the reasons for the exclusion of nickel-copper alloys, e.g., UNS N04400,from the materials listed in Section 4?


REVISED ANSWER 2005-09-01:The omission of UNS N04400 and N04405 has now been rectified. See the revisedversion of Table A.13 in Reference 3.

QUESTION:NACE Standard MR0175-96, Section 4, includes Paragraph 4.1.1 titled Nickel-Copper Alloys specifically listing UNS N04400 (K-Monel), UNS N04405, andN05500. These CRA metals have been omitted from MR0175-2003 except for briefmention under Section 10 for specific equipment not related to our business. We area manufacturer of process gauges, some of which are for use in sour gasenvironments. These metals (especially N04400) have always been used in our

(and other manufacturers') gauges for pressure-containing parts having directexposure to sour gas. Have these materials been omitted for a reason or are theystill acceptable?

(MP INQUIRY #2003-29)REVISED ANSWER 2005-09-01:The omission of UNS N04400 and N04405 has now been rectified. See the revisedversion of Table A.13 in Reference 3.

QUESTION:We manufacture instrumentation and in particular, BOURDON TUBE-type pressuregauges. Due to the manufacturing process, 316 SS tube exceeds the hardness limit

in NACE MR0175. The alternative has always been to supp ly ―MONEL‖ UNSN04400 to comply with NACE MR0175. Paragraph 8.4 would previously have



60

referenced N04400 in Section 4, thus meeting the requirements. We note N04400 isreferenced in Section 10 only, specific to downhole equipment. We are holders ofyour standard NACE MR0175-2003. We have a particular query regarding UNSN04400. The 2003 edition of the standard does not contain in Section 4 (CRAs) asection for nickel-copper alloys (NACE MR0175—ALL PREVIOUS ISSUES), and as

UNS N04400 does not fall within the stated parameters within Section 4, can youplease clarify: Is UNS N04400 no longer within the scope of MR0175-2003 section4, or will an amendment be issued to re-include it in Section 4?

(MP INQUIRY #2003-31)REVISED ANSWER 2005-09-01:The omission of UNS N04400 has now been rectified. See the revised version ofTable A.13 in Reference 3.

A.4.2

QUESTION:

According to NACE Standard MR0175-2003, 625 material, as a solid-solution nickel-based alloy, is acceptable only in the solution-annealed condition. This constitutes amajor change with respect to previous editions, in which 625 material was acceptedup to 35 HRC regardless of the delivery condition. The annealed condition isconsidered the most suitable condition by most of our customers and we are notaware of problems or failures with material 625 used in this condition for NACEapplications. Unless a real problem exists in using annealed 625, we would like tounderstand whether:

The definition of solution annealing given in NACE Standard MR0175-2003 has

to be interpreted to exclude 625 material in the annealed condition; or

For 625 material, annealing performed in a given temperature range (to besuitably defined, even more narrow than the range from 1,600 to 1,900°F) can beconsidered a solution-annealing heat treatment as defined in Section 2.

(MP INQUIRY #2003-11)ANSWER:Tables A.12, A.13, and A.14 in ISO 15156 provide answers to your requests forinterpretations.

NACE will be adopting ISO 15156 in 2003 as a technically equivalent document.

The nickel-based alloys may be used in the annealed or solution-annealed conditionwithin the requirements of these ISO tables.

Please also refer to the definition of ―solution-annealed‖ in Section 2 of NACEStandard MR0175. This definition does not prescribe the temperature for thesolution-annealing heat treatment.

A.4.2, Table A.12

QUESTION:

Question on Alloy 31 (UNS N08031)



61

The typical chemical composition of this alloy is: Fe bal, Ni 31, Cr 27, Mo 6.5, Cu1.2, N 0.20. Based on the individual heat chemistry, the alloy could be either anickel-based alloy (nickel being the highest element) or high-performance stainlesssteel in which iron is the highest element.

NACE MR0175-2002:*Alloy 31 appears in Section 4: Nonferrous Metals.*4.1.3 Nickel-Iron-Molybdenum Alloys Paragraph 4.1.3.14 (provides allowed use andthe table of balloted data).NACE MR0175-2003: The nonferrous section is no longer present in this version.*Section 4 is now entitled ―Corrosion-Resistant Alloys (CRAs)--All Other Alloys NotDefined As Carbon and Low-Alloy Steels and Cast Irons in Section 3‖ *Section 4.11 Solid-Solution Nickel-Based Alloys (Category) appears to be thesection in which Alloy 31 fits the category of 4.11.1: 19.0% Cr min., 29.5% Ni + Comin., and 2.5% Mo min. No specific mention of alloy 31 is made in this section.*The balloted table of data for alloy 31 appears in Appendix C: Ballot Submittal

Data, Table C7.It appears that name of this alloy UNS N08031 (alloy 31) began to disappear in thisversion.

I fully understand that this document NACE MR0175-2003 is no longer valid and nowhas been replaced by NACE MR0175/ISO 15156 First Edition, Part 3.

NACE MR0175/ISO 15156 First Edition, 2003-12-15, Part 3 (Comments andQuestions)

It appears that alloy 31 (UNS N08031) should appear in Section A.4 Solid-solutionnickel-based alloys.

It would further appear that alloy 31 (UNS N08031) fits the materials type 4cdescribed in Table A.12 as: 19.5% Cr min., 29.5% Ni + Co min., and 2.5% Mo min.Is this the material type/grouping that alloy 31 (UNS N08031) should be groupedwith?

Table D.4 lists various alloys included in the Section A.4 Solid-solution nickel-basedalloys. Alloy 28 (Alloy 28 in reality is not a nickel-based alloy) and 32 are listed inthis table. No mention is made of alloy 31 in this table or within the document.

Could 32 be a typo error and should be 31??

It appears that alloy 31 (UNS N08031) has completely disappeared from this version.

I would appreciate clarification on this point. Alloy 31 (UNS N08031) should be listedin this NACE MR0175/ISO 15156-3 First Edition, 2003-12-15, Part 3 document. Ifthis is an error, how do we get it corrected and if this is not an error how do we getalloy 31 in this document?

(MP INQUIRY #2004-15)ANSWER:Alloy 31 as you describe it fits in Type 4c as defined in NACE MR0175/ISO 15156-3,

Table A.12.



62

Alloys that comply with the requirements of Table A.12 for solid-solution nickel-basedalloys are not individually listed in NACE MR0175/ISO 15156-3, Annex A. Thedocument makes use of alloy types in order to avoid the listing of all possibleexamples of such alloys.

Similarly, NACE MR0175/ISO 15156-3, Table D.3, as noted in its title, does notattempt to provide an exhaustive list of alloys that can meet the requirements ofthese types of alloys.

Please note it is not a requirement of NACE MR0175/ISO 15156 that an alloy beindividually listed to meet the requirements of the document.

If a solid-solution nickel-based alloy, as defined in NACE MR0175/ISO 15156-3,Table A.12, is used within the environmental and metallurgical limits defined in TableA.13 or Table A.14 it meets the requirements of the standard.

QUESTION:I have a query regarding UNS N08825 pipe material in hot finished annealed deliverycondition as availability of ASTM B 423 (UNS N08825) material in cold finishedannealed condition is scarce but it is generally available in hot finished deliverycondition above 8" size. Therefore my query goes as follows:

"NACE MR0175/ISO 15156-3:2003(E) does not list UNS No. N08825 in hot finishedannealed condition in Table A.12, A.13 and A.14. Table A.12 breaks down Solidsolution nickel-based alloys into Type-4a, 4b, 4c and 4d depending on Cr, Ni+Co, Moand Mo+W mass fraction and metallurgical condition. Now my question is whether

ASTM B 423 (UNS N08825) pipe in hot finished annealed delivery condition for 8"and 10" pipe shall be acceptable for piping because for type 4a and 4b metallurgicalcondition does states the requirement of cold-worked or hot worked".

(MP INQUIRY #2006-15)ANSWER:The alloy UNS N08825 in the annealed condition falls under the materials Type 4a inTables A.12, A.13. The term "annealed" refers to the final stage of the heattreatment of the material or component that determines its metallurgical condition inthe service environment.

A.4.2, Table A.13


A.4.2, Table A.14


QUESTION:Table 4 (for precipitation-hardenable, 6Mo alloys) (NACE MR0175/ISO 15156-3,Sub-clause A.9.2, Table A.33) permits elemental sulfur in the environment at 450°F,but not at 425°F, yet again at 400°F. Where does the user discover whether sulfur is

or is not acceptable for applications between these temperatures? This is oddenough, but Table 6 (for 6 Mo, precipitation-hardenable 6 Mo alloys) (NACE



63

MR0175/ISO 15156-3, Sub-clause A.4.2, Table A.14) does allow sulfur at 425°F.Are the precipitation-hardenable versions of these alloys more resistant to crackingthan their solution-annealed and cold-worked analogs?


In response to your questions 3 and 4a): The data used in NACE MR0175-2003 andNACE MR0175/ISO 15156-3 represent the limits of successful laboratory testsreported to NACE so far. In some cases the available data cannot be used toanswer the questions you pose.

QUESTION:(a) Table 6 (NACE MR0175/ISO 15156-3, Sub-clause A.4.2, Table A.14) permitssulfur at 300°F in any H2S partial pressure, but not at 425°F. Where, if anywhere,between 425°F and 300°F are alloys in this category sulfur-resistant? If an oil-company client has a well with bottom-hole temperature of 350°F with producedbrine that contains sulfur, will an alloy like 2550 (UNS N06975) be sufficiently

resistant, or (b) must C-276 (UNS N10276) be deployed?(MP INQUIRY #2003-13 Q4)

ANSWER(a) In some cases the comparisons you make are not strictly valid because the datasets for the materials considered vary in the H2S limits, in the temperature limits, andin the metallurgical limits that are imposed. It is thought that the limits given areconservative and further testing could demonstrate that the true limits are lessrestrictive than those shown; see also the answer to MP Inquiry #2003-13 Q6 underISO 15156-1 Clause 5.

ANSWER:(b) UNS N10276 would be acceptable.

QUESTION:Could you please confirm that the kPa units of the H2S column of ISO 15156-3,Table A.14 are incorrect and that the units should be MPa not kPa?

(MP INQUIRY #2004-07)REVISED ANSWER 2005-09-01:The revised version of Table A.14 is included in Reference 3.

QUESTION:NACE MR0175/ISO 15156-3: We make bellows for use in Safety Relief Valves. Weuse all nickel alloy materials but we are particularly concerned with Inconel625/Inconel 625LCF. In previous editions of the NACE standard, the materialhardness value for UNS N06625 is clearly stated as being acceptable to 35 HRCmaximum, but in the above-referenced latest edition we are finding it difficult to tracethis requirement and keep our records and practices updated. Would you pleaseconfirm the hardness requirements stated in the above-referenced latest edition andalso reference relevant paragraphs and tables.

We buy the strip material in the solution-annealed condition, but there is a certainamount of work hardening that takes place during the bellows forming process.



64

(MP INQUIRY #2004-10)REVISED ANSWER 2005-09-01:The individual hardness limit of 35 HRC max. for cold-worked alloy UNS N06625 hasbeen dropped in NACE MR0175/ISO 15156-2003. Please see Table A.14 forhardness and yield strength limits achieved by cold work for nickel-based alloys.


A.4.2, Table A.16

QUESTION:Does Monel in the annealed condition in accordance with ASTM B 127 and Monel inthe as-cast condition in accordance with ASTM A 494 M-35-2 and M-30C meetNACE Standard MR0175-2003?


(Response from Transition Team)As a sub-paragraph to 4.11, Paragraph 4.11.1 is a constraint. Therefore, Monels donot apply since they are not alloyed with chromium or molybdenum. UNS N04400appears in MR0175 in Paragraphs 10.6.2.2 and 10.7.3; the use must fit anapplication described in one of these two paragraphs in order to be directlyacceptable. Otherwise, please note Paragraph 1.8.4, which directs the reader to theoptions of balloting the material and/or application for inclusion into MR0175 or usingthe material for application-specific cases without balloting.

A.4.3

See A.2.3, MP inquiry #2005-13

QUESTION:This question relates to NACE MR0175/ISO 15156 Part 3, Appendix A, ParagraphA.4.3. Is the hardness testing survey required as part of the welding procedurequalification for solution heat-treated nickel-based alloys welded with solid-solutionnickel-based weld metal? In accordance with A.4.3 there are no hardnessrequirements.

A.4.3 Welding solid-solution nickel-based alloys of this materials group. The

requirements for the cracking-resistance properties of welds shall apply (see 6.2.2).

The hardness of the HAZ after welding shall not exceed the maximum hardnessallowed for the base metal, and the hardness of the weld metal shall not exceed themaximum hardness limit of the respective alloy used for the welding consumable.

There are no hardness requirements for welding solid-solution nickel-based alloyswith solid-solution nickel-based weld metal.

Is the hardness testing survey required as part of the welding procedure qualificationfor solid solution nickel-based alloys (as addressed in NACE MR0175/ISO 15156-3,

A.4) welded with solid-solution nickel-based weld metal?(MP INQUIRY #2006-06)



65

ANSWERNo.

A.6.2, Table A.18

QUESTION:We need clarification of Paragraph 4.8.2—Low-Carbon Martensitic Stainless Steels.In the 2002 edition this was Paragraph 3.7.2.1. The 2002 edition allowed wroughtmaterial meeting the chemistry requirements of ASTM A 487 CA6NM. The 2003edition appears not to allow these F6NM wrought materials (UNS S41500), justS42400, which is not the same thing. Please advise whether this material isacceptable.

(MP INQUIRY #2003-17)REVISED ANSWER 2005-09-01: The revised version of Table A.18 is included in Reference 3.

QUESTION:My inquiry concerns CA6NM: In the old MR0175-2002 this material is discussed inParagraph 3.7.2.1. In this paragraph there is a note (12) stating that the hardnesscorrelation in ASTM E 140 doesn’t apply to CA6NM and that for this material themaximum permissible value (in Brinell) is 255 BHN.

In the new MR0175/ISO 15156, this statement is no longer used. There is, however,a paragraph in Paragraph 7.3.2 of MR01756/ISO 15156-2 which stipulates that userscan establish hardness correlations for individual materials. Please see below:

For ferritic steels EFC Publication 16 shows graphs for the conversion of hardnessreadings, from Vickers (HV) to Rockwell (HRC) and from Vickers (HV) to Brinell(HBW), derived from the tables of ASTM E 140 and BS 860. Other conversiontables also exist. Users may establish correlations for individual materials.

Finally the questions:Is CA6NM acceptable per MR0175/ISO 15156 at a hardness of max 255 BHN whichhas been (empirically) determined to be the equivalent of 23 HRC (but which on theASTM E 140 scale corresponds to about 25 HRC)?


ANSWER:The prescribed hardness limit of 23 HRC for CA6NM in Table A.18 in NACEMR0175/ISO 15156-3 utilizes the Rockwell C scale as the basis for acceptance.Conversions to other hardness scales are no longer included in the standard. Otherhardness scales may still be used provided a correlation can be shown between thescale used and the prescribed Rockwell C scale for the particular material beingtested. As stated in Paragraph 6.2.1 of NACE MR0175/ISO 15156-3, conversionbetween hardness scales is material-dependent. The ISO Maintenance Panelcannot make this conversion for you. The user may establish the requiredconversion tables.

QUESTION:



66

My question is about SS 431 (wnr 1.4057/S43100) which is a martensitic stainlesssteel.

In Part 3 of the documentation, according to A.6 Martensitic (stainless) steels(identified as individual alloys) and Table A.18. Environmental and materials limits for

martensitic stainless steels used for any equipment or components.

As the alloy SS 431 (wnr 1.4057/S43100) is not mentioned, does that mean that itcannot be used according to NACE or can we use it as long as the hardness of thematerial is max. 22 HRC?

Do we need to apply any special attention to the heat treatments, as shown in TableA.18?

(MP INQUIRY #2005-29)ANSWER:Alloy UNS S43100 is not at present qualified to the requirements of NACE

MR0175/ISO 15156 for inclusion in Table A.18.

A proposal to amend Table A.18 may be submitted and must contain supportingevidence from field experience or laboratory testing.

With the agreement of the equipment user, the alloy may be qualified for specificapplications and may then be used without listing in the standard.

Requirements/procedures for qualification are given in NACE MR0175/ISO 15156-1,Clause 8, NACE MR0175/ISO 15156-3, Annex B and in "01. Introduction to ISO

15156 maintenance activities" at www.iso.org/iso15156maintenance.

QUESTION:I have a question regarding NACE MR0175/ISO 15156-3:2003. On Table A.18, theheat treatment requirements for CA6NM and F6NM are listed. Is this the onlyapproved heat treatment? If we follow this heat treatment initially, are other heattreatments allowed as long as they do not exceed the original? We're trying to findout if a supplemental stress relieve is acceptable to try and lower the materialhardness.


Only the heat treatments listed are currently acceptable. Other heat treatments maybe qualified in accordance with the requirements of NACE MR0175/ISO 15156-3Annex B.


QUESTION:Inconsistency between Table A.18 and A.23 of Para. A.6.2 in NACE MR0175/ISO15156-3:2003. Table A.18 allows martensitic stainless steels for any equipment orcomponent, but Table A.23 excludes casing and tubing hanger and valve stems.What is the meaning of any equipment or component ? Does any equipment or

component from Table A.18 exclude casing and tubing hangers and valve stems?(MP INQUIRY 2004-23 Q2)






67

ANSWER:No, ISO 15156-3, Tables A.18 and A.23 set different H2S limits for the sameselection of martensitic stainless steels. The other environmental limits are thesame.

Table A.18 addresses the use of the materials under the environmental limits of thistable. "Any equipment or component" included wellhead and tree components andvalve and choke components, and casing and tubing hangers and valve stems.Table A.23 allows the use of the same selection of materials for wellhead and treecomponents and valve and choke components under a less restrictive set ofenvironmental conditions but excludes casing and tubing hangers and valve stemsunder these less restrictive conditions.

Please see Table 1 of NACE MR0175/ISO15156-3 for the list of equipment coveredby this standard and also "General Remarks" under ISO 15156-3, A.1.6 of this"Inquiries and interpretations" document.

A.6.2, Table A.19


QUESTION:Is the maximum hardness limit for ISO 11960 L-80 Type 13 Cr tubing used as adownhole tubular component, packer, and other subsurface equipment inaccordance with NACE MR0175/ISO 15156 the maximum hardness as specified inthe latest edition of ISO 11960?

Note: ISO 11960 is also designated as API 5CT.

Note: ISO 11960 currently specifies 23 HRC as the maximum hardness forL-80 Type 13 Cr tubing.

Discussion: NACE MR0175/ISO 15156-3, Table A.19 lists ISO 11960 L-80Type 13 Cr and two other materials as begin acceptable for "downhole tubularcomponents, packers, and other subsurface equipment."

There are notes in this table that specify the maximum hardness limits of the other

two materials, individually. However, there is no note to specify the maximumhardness limit of ISO 11960 L-80 Type 13 Cr tubing.

This seems to indicate that ISO 11960 becomes the controlling document for L-80Type 13 Cr, and therefore the maximum hardness for ISO 11960 L-80 13 Cr tubingis currently 23 HRC as specified in Table C.6 and Table E.6 of ISO 11960.

(MP INQUIRY 2006-03) ANSWER:Your interpretation is correct.

As a general rule during the preparation of ISO 15156, the unnecessary repetition of

information provided in cited sources was avoided.



68

A.6.2, Table A.19, A.20 and A.21

QUESTION:I need to clarify a confusion about NACE MR0175/ISO 15156-3:2003 (E).

Why are tubing and subsurface equipment in Tables A.19 and A.20, respectively,treated as two separate categories? Tubing itself is subsurface equipment so why isit treated separately? Moreover, K90941 as mentioned in Table A.20 isrecommended for subsurface equipment under any H2S partial pressure but not fortubing, exposed to the same condition; why? L-80 type 13 Cr is more cracking-resistant material than K90941; still it is not recommended for subsurface equipmentapart from tubing; why?

We are in a process of developing a sour gas field and purchased a copy of thisstandard to be a guideline for material selection. We need answers to thesequestions so we can select the most appropriate material for downhole

casing/tubing.(MP INQUIRY #2005-22)

ANSWER:NACE MR0175/ISO 15156-3 reflects the contents of NACE MR0175-2003 andearlier editions of this NACE standard. These contents in turn reflect the experienceof the oil industry and its experts in the use of materials in sour service over manyyears.

The separation of materials into Tables A.19, A.20, and A.21 allowed convenientgrouping of the data available and is the same as the grouping in the previous NACE

standard.

In some cases the differences you identify reflect the availability of different productforms manufactured from the different materials.

As indicated in the title of Table A.19, ISO 11960 L80 type 13Cr is acceptable forother subsurface equipment (other than tubing) providing the material fully meets theapplicable material requirements of ISO 11960 L80 type 13Cr. Additionally asindicated in the title and notes of Table A.21, 420 (modified) having the chemicalcomposition of ISO 11960 L80 type 13Cr is acceptable for packers and subsurfaceequipment.

In all cases the data presented reflect successful laboratory testing of an alloy orsuccessful field experience with the alloy used in the product form listed.

For martensitic alloys not listed in Tables A.19, A.20, and A.21 qualification of thealloy for use in accordance with ISO 15156-3 can be carried out in accordanceAnnex B.

Please note: A revised version of ISO 15156-3, Table A.19 is included in ISO15156-3 Technical Corrigendum 2 that was published September 1, 2005.

A.6.2, Table A.22



69


A.6.2, Table A.23


A.6.3

The revised version of the text of A.6.3 is included in Reference 3.

A.7.2, Table A.24


QUESTION:In the 2002 version of MR0175, the maximum hardness requirement for duplex UNS

S32550 was covered in Paragraph 3.9.1. This same material is now covered inParagraph 4.9 of the 2003 version of this standard, but the hardness requirementseems to be missing. Has the hardness requirement been dropped for this material,or is the hardness assumed to be acceptable as long as the material has beensolution annealed and liquid quenched?

(MP INQUIRY #2003-09 Q2)ANSWER:This is correct. There is no hardness requirement for the duplex stainless steelscovered in Paragraph 4.9.1.

QUESTION:What is the foundation for limiting forged and cast UNS S31803 (Paragraph 4.9.3) toa maximum partial H2S pressure and temperature while the hot isostatic pressure-produced equivalent (Paragraph 4.9.4) is only limited to maximum hardness?

(MP INQUIRY #2003-19 Q2)ANSWER:Paragraph 4.9.4 should have been 4.9.3.1, having the same environmental limits asParagraph 4.9.3, and this error has been corrected in an interpretation and in TableA.24 of ISO 15156. Paragraph 4.9.4 was intended to provide metallurgicalrequirements only for the HIP alloy.

QUESTION:Zeron 100: Old (2002): Paragraph 3.9.6/3.9.7: pH2S <0.2 bar (20 kPa) and 120pH2S <1 bar (100 kPa) and 15 g/L Cl- and pH >5.6

New (2003) Paragraphs 4.10 and A24: pH2S <0.2 bar (20 kPa) only: What is thetechnical justification for this change?

(MP INQUIRY #2003-27 Q3)ANSWER:The restrictions for duplex stainless steels was a consensus of the original draftingteam based on their review of the literature. There was no negative on the finalballot for the 2003 edition.

A.7.3



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See A.2.3, MP inquiry #2005-13.

QUESTION:The question is in regard to Appendix A.7 of NACE MR0175/ISO 15156-3:2003(E).

In A.7.3 third paragraph, it requires that "the microstructure ... shall have grainboundaries with no continuous precipitates". Is there any guidance as to whatcontinuous means? For example, does it mean continuous throughout themicrostructure?

Our laboratory has reported suspected continuous precipitates "at some locations".(MP INQUIRY #2005-18)

ANSWER:There is no definition of "continuous precipitates" in the standard. An acceptancecriterion or other quantitative limit shall be agreed between the manufacturer/supplierand the equipment user.

As noted in the WARNING above ISO 15156-3, Scope, it is the equipment user'sresponsibility to select the CRAs and other alloys suitable for the intended service.This responsibility includes the selection of specific quality requirements when noneare given by the standard.

QUESTION:ISO 15156-3, A.7.3--Regarding metallographic examination of the microstructure:

a) Do closely spaced spheroidal precipitates such as grain boundary carbides

constitute continuous precipitates?b) At what spacing would closely spaced spheroidal precipitates be consideredcontinuous?c) Are the quantification of precipitates (intermetallic phases, nitrides, carbides) to beevaluated as a volume fraction relative to the bulk sample?d) In cases where only grain boundary precipitates are observed, is the quantificationto be made as a volume fraction relative to the bulk sample or as a lineal fractionrelative to grain boundary length?e) In the absence of intermetallic phases and nitrides, does 1 vol.% represent themaximum allowable carbide precipitate content?f) What is a suitable recommended practice or standard by which to perform this

quantification? (MP INQUIRY #2005-28)ANSWER:a), b), e)For NACE MR0175/ISO 15156-3, A.7.3 it is the responsibility of the equipment userand the manufacturer to set the quantitative standard they wish to follow when thisgoes beyond the guidance given.c), d), f)It is the responsibility of the equipment user and the manufacturer to agree on themethod and acceptance criteria for the measurement of precipitates.

QUESTION:



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Can you please answer the following queries or pass to committee. These queriesrelate to welding of 22% Cr duplex/25% Cr duplex Annex A7, of MR0175/ISO 15156-3, A.7.3 (2nd para) " The hardness of the HAZ after welding shall not exceed themaximum hardness allowed for the base metal," When applied to ASTM A790 UNS32760 (see attachment) only a Brinel hardness is given 270 BHN (28 HRC equiv.).

This is a reduction of 6 HRC from the 34 HRC allowance in NACE MR0175:2000.

If no HRC limit is given in the material specification do we assume no maximumHRC hardness limit or use the Brinel hardness specified (28 HRC equiv.).

Alternatively do we revert to the referenced NACE MR0175 [14] and assume34 HRC.


ANSWERThe ISO 15156 Maintenance Panel can only provide a response to the inquiry in the

context of NACE MR0175/ISO 15156-3 and cannot give interpretations based uponearlier editions of NACE MR0175.

The texts that form the lower parts of Table A.24 " Environmental and materials limitsfor duplex stainless steels used for any equipment or component" and Table A.25 "Environmental and materials limits for duplex stainless steels used as downholetubular components and as packers and other subsurface equipment " provideinformation on the metallurgical requirements, such as heat treatment and hardnessetc., which must be met by duplex stainless steels in sour service. In most casesTable A.24 does not define a maximum acceptable base material hardness.

As indicated in the first paragraph, last sentence of Clause 1 "Scope", alloys mustalso meet the requirements of the appropriate design codes, standards orregulations such as, for the example quoted, ASTM A790 UNS S32760. For thisalloy, the use of Brinell 270, as maximum base metal hardness in the interpretationof A.7.3, is correct. (The equivalent Vickers/Rockwell 15N hardness for use inwelding procedure qualification can be determined in accordance with ISO 15156-3,6.2.1, Para. 2.)

Where the material manufacturing specification does not define a hardness limit butthe alloy base metal does comply with the requirements of one of the Tables, it is theresponsibility of the equipment user and the manufacturer to agree on any hardness

limit used for welding procedure qualification.

Please note, for Table A.25 the maximum hardness of 36 HRC refers to themaximum hardness of any solution annealed, liquid-quenched and cold-worked alloybase metal that qualifies for use in sour service.

A.8, Table A.26

QUESTION:What grade of stainless steel meeting NACE requirements can be used for a tubinghanger when the pH is <3.5?



72

My interpretation based on understanding Paragraph 9.2 of NACE MR0175 andSection A.8 of ISO 15156 is that only UNS S66286 is acceptable. Could you pleaseconfirm my statement or correct it?


UNS S66286 is the only precipitation-hardenable stainless steel that is acceptablefor tubing hangers in environments with pH <3.5. The martensitic stainless steelsare also not acceptable for environments with pH <3.5.

QUESTION:Table A.26 limits the precipitation-hardened austenitic steel UNS S66286 to 150°Fand 15 psi H2S when chlorides are present.

a)Can this material be used at higher temperature if no chlorides are present?

(MP INQUIRY #2005-02 Qa)

ANSWER:No, it may not. The table states that the temperature restriction is for "Anycombinations of chlorides . . . " Neither ISO 15156-3 nor its predecessor NACEMR0175-2003 defines the expected performance of UNS S66286 in environmentscontaining no chlorides.

b)Is this material included in the current ballot for austenitic steels which (apparently)would allow their use at a higher temperature if no chlorides are present?

(MP INQUIRY #2005-02 Qb)

ANSWER:No, it is not. The current ballot is for materials currently covered in Table A.2, whichrepresent materials free of cold work to enhance their properties and withhardnesses of 22 HRC maximum.

c)Would the MP consider adding an unrestricted clause for the use of this material forvalve stems, pins, and shafts (similar to Table A.3 for UNS S20910)? This materialwould perform much better as a valve stem in H2S environment than the cold-workedNitronic 50.

(MP INQUIRY #2005-02 Qc)

ANSWER:The IMP would accept a ballot item with the proper documented laboratory dataand/or field experience to expand the acceptable environmental limitations for thealloy. The procedure for the submission of a ballot item is described in the document"01. Introduction to ISO 15156 Maintenance Activities," which can be found athttp://www.iso.org/ISO15156Maintenance.

QUESTION:Does NACE MR0175/ISO 15156-3 Table A.26 apply to Gr. 660 material used in

subsea bolting applications external to the production wellbore environment whenindirectly heated above 150°F?



73


ANSWER:Table A.26 does not apply to Grade 660 material used in subsea bolting applicationsexternal to the production wellbore environment.

A.8.2, Tables A.27

QUESTION:Reference: NACE MR0175/ISO 15156-3 Table A.27--Environmental and materialslimits for martensitic precipitation-hardened stainless steels used for wellhead andchristmas tree components (excluding bodies and bonnets), valves and chokes(excluding bodies and bonnets) and packers and other subsurface equipment

API 6A makes a distinction between hangers and body components. NACEMR0175/ISO 15156 doesn't define either. This has led to some confusion regarding

whether or not UNS S17400 material may be used as hangers in a sourenvironment.

Q1. Does the exclusion of wellhead "bodies and bonnets" in Table A.27 also meanthat hangers are excluded?

Q2. Are hangers considered "subsurface equipment" in the context of Table A.27?

Q3. Does Table A.27 prohibit the use of UNS S17400 material for hangers in sourservice?


ANSWERS:A1. No, it does not.

A2. In the context of Table A.27, hangers are more commonly considered to becovered by the term "wellhead and christmas tree components."

A3. No, it does not provided the environmental limits and metallurgical requirementsof Table A.27 are followed.

See also response to MP Inquiry #2006-07 posted under ISO 15156-3, Table A.3.

A.8.2, Tables A.27 and A.28

QUESTION:If both Paragraphs 9.2 and 9.5 are applicable, as we believe they are, can we selectwhich paragraph we follow when they cover the same component or materials?Does Paragraph 9.4 apply to choke valves?

(MP INQUIRY #2003-02 Q2) ANSWER:Choke non-pressure-containing parts made of alloy UNS S17400 have no

environmental restrictions in accordance with Paragraph 9.5.2, while there is a limitof 0.5 psi H2S for pressure-containing parts in Paragraph 9.2.4.1.



74

QUESTION:Paragraphs 9.2.4.1 and 9.5.2. Why is it that UNS S17400 can be used for pressure- containing wellhead and Christmas tree components (Paragraph 9.2.4.1) but not for pressure-containing valve components (Paragraph 9.5.2)?

(MP INQUIRY #2003-12 Q4)ANSWER:Paragraph 9.5.2 allows UNS S17400 to be used with no environmental restrictions.Therefore, the alloy is not allowed for pressure-containing components in valves. Incomparison, Paragraph 9.2.4 has environmental restrictions and will therefore allowthe use of S17400 for parts other than bodies and bonnets.

A.8.2, Tables A.27, A.28 and A.30

QUESTION:17-4 pH: Old (2002): Paragraph 3.8.1. Only requirement: HRC 33

New (2003): Paragraph 9.2.4.1 and A27: pH2S <0.034 bar: Technical justification?(MP INQUIRY #2003-27 Q4)

ANSWER:The 17-4 pH SS alloy was restricted because of industry failures. Please see theattached documentation. There was no negative on the final ballot.

A.8.2, Table A.28

QUESTION:

Can you provide clarification on Paragraph 9.5.7: ―UNS S17400 …. has been used in

service tool applications at the surface when stressed at less than 60% of itsminimum specified yield strength under working conditions.‖ Paragraph 9.5 isconcerned with Internal Components for Valves, Pressure Regulators, and LevelControllers. What exactly do service tool applications encompass?

(MP INQUIRY #2003-32)ANSWER:This paragraph is intended to apply to components that are temporarily installed atthe surface as part of routine well servicing. For example, components of wirelinevalves used during a wireline job are considered as service tools.

A.8.2, Table A.30

QUESTION:SUBJECT: Paragraph 11.4.5 of NACE MR0175-2003 StandardQUESTION: Are wrought UNS S17400 and S15500 martensitic precipitation-hardenable stainless steels that meet the hardness and heat-treat requirements ofParagraph 11.4.5 of NACE MR0175-2003 acceptable for use in compressors in sourenvironments with no environmental limits with respect to chloride content, partialpressure of H2S, temperature, and free elemental sulfur?QUESTION: If the answer to the former question is no, what are the specificenvironmental limits?




75

Yes, they are acceptable with no environmental limits in accordance with NACEMR0175/ISO 15156 Table A.30. No data have been submitted to verify resistance tocracking in the presence of elemental sulfur.

QUESTION:

SUBJECT: Paragraphs 11.4.4 and 11.4.6 of NACE MR0175-2003QUESTION: Are the martensitic stainless steels that are listed in Paragraphs 11.4.4and 11.4.6 of NACE MR1075-2003 and meet the hardness and heat-treatrequirements specified in their respective paragraphs acceptable for use incompressors in sour environments with no environmental limits with respect tochloride content, partial pressure of H2S, temperature, and free elemental sulfur?QUESTION: If the answer to the former question is no, what are the specificenvironmental limits?QUESTION: Are the answers to the above questions in agreement with ISO 15156?


Yes, they are acceptable with no environmental limits in accordance with ISO 15156Table A.30. No data have been submitted to verify resistance to cracking in thepresence of elemental sulfur.

A.9.2, Table A.31


QUESTION:The precipitation-hardenable version of G-3 has no environmental limits per

Paragraph 4.15.6 of the 2003 edition. "Conventional wisdom" has it that a solution-annealed and cold-worked nickel-based alloy is more resistant to environmentalcracking than its precipitation-hardenable clone.

(MP INQUIRY #2003-13 Q2b)ANSWER:Materials used in accordance with Paragraph 4.15.6 are subject to the environmentallimits stated in Paragraph 4.15, i.e., the limits of Table 2. These limits are restated inNACE MR0175/ISO 15156-3, Table A.31, Rows 2-5 for material UNS N07048.

A.9.2, Table A.32

QUESTION:I think that the (Cartesian) coordinates in Table 3 (NACE MR0175/ISO 15156-3,Sub-clause A.9.2, Table A.32) {T 390°F, pH2S 360 psi} may have come from datasupplied by me to NACE from my office files for recommendations made to oilcompanies for Alloy 925 (UNS N09935). If so, I have no confirmation that the oilcompanies ever deployed equipment made from Alloy 925 in these environments. Irecommend that NACE remove these data from Table 3, replacing them with testdata from Battelle showing cracking resistance at 450°F, pH2S 400 psi in 15% Cl andalso a second set of coordinates at 425°F, pH2S 300 psi in the presence ofelemental sulfur (Hibner).




76

A technical change such as that suggested can only be made following a ballotprocess involving the ISO 15156 Maintenance Panel and the Oversight Committee(NACE TG 299) on behalf of ISO/TC 67/WG 7. Ballot proposal forms can beobtained from [email protected].

QUESTION:Our question relates to ISO 15156-3, Table A.32:How should the table be interpreted in terms of the maximum allowable temperaturefor applications with less than 30 psi partial pressure of H2S?

For example, in its current layout the table prohibits the use of UNS N07718 attemperatures higher than 450°F at any H2S pressure below 30 psi.

(MP INQUIRY #2005-20)ANSWER:ISO 15156-3, Table A.32 does not qualify UNS N07718 for use at highertemperatures than 450°F.

The limits on temperature, H2S, Cl-, pH, and sulfur defined in some of the tables ofISO 15156-3, Annex A apply collectively and reflect the knowledge available, usuallyfrom laboratory tests, at the time the standard was published. There were no dataavailable related to the use of UNS N07718 at any temperature higher than 450°F.

ISO 15156 allows the qualification and use of materials, to an equipment user'srequirements, outside the limits stated in the tables. (See ISO 15156-3, Figure B.1,Column 2.)

A qualification to define an alternative temperature limit for UNS N07718 for a partialpressure of H2S less than 30 psi must be carried out in accordance with ISO 15156-3, Annex B.

A.9.2, Table A.33


QUESTION:Table 4 (for precipitation-hardenable, 6Mo alloys) (NACE MR0175/ISO 15156-3,Sub-clause A.9.2, Table A.33) permits elemental sulfur in the environment at 450°F,

but not at 425°F, yet again at 400°F. Where does the user discover whether sulfur isor is not acceptable for applications between these temperatures? This is oddenough, but Table 6 (NACE MR0175/ISO 15156-3, Sub-clause A.4.2, Table A.14)(for 6 Mo, precipitation-hardenable 6 Mo alloys) does allow sulfur at 425°F. Are theprecipitation-hardenable versions of these alloys more resistant to cracking than theirsolution-annealed and cold-worked analogs?

(MP INQUIRY #2003-13 Q3)ANSWER:In response to your questions 3 and 4a): The data used in NACE MR0175-2003 andNACE MR0175/ISO 15156-3 represent the limits of successful laboratory testsreported to NACE so far. In some cases the available data cannot be used to

answer the questions you pose. (MP INQUIRY #2003-13 Q4a is addressed underheading NACE MR0175/ISO 15156-3, Table A.14)

mailto:[email protected]

mailto:[email protected]



77

QUESTION:In MR0175/ISO 15156-3, Corrigendum 2 there is a new version of Table A.33. In thelast row of this table, under the heading "Temperature," is a blank. I don't seeanywhere else in all of MR0175 where a field in a table is left blank. This is

suspicious to me. Prior versions of Table A.33 placed a temperature of 175 C in thisfield. Can you tell me if this field is intended to be empty, or if there should be somedata here?

(MP INQUIRY #2009-09)ANSWER:You are right; this box should read "175°C (350°F). This has been corrected in the2009 Version of ISO 15156 Part 3.

Table A.39

QUESTION:

1) Does NACE MR0175 / ISO 15156 apply to the spring application as depicted infigure 1, when areas of the spring are plastically deformed (not more than 1 or 2%strain)? 2) Why does NACE MR0175 / ISO 15156, Part 3 specifically demand age-hardening although age-hardening typically increases the hardness of UNS R30003?Is this because problems were reported when the material was not age-hardened,because data is only available for age-hardened material, or another reason?

(MP INQUIRY #2009-05)ANSWER:1) NACE MR0175/ISO 15156 does not apply to design made with plasticdeformation criteria, as written in Paragraph 5 of Part 1. Qualification through testing

or field experience may be used to qualify this type of design but this will be outsidethe limits of the standard.

2) In Table A.39 the cold worked + age hardened condition of UNS R30003 was theonly condition originally balloted and accepted.

A.10.2, Table A.40See question and response posted under A.2.2, Table A.4.

A.12

QUESTION:Because UNS C72900 and C96900 are copper alloys, are they, by definition,covered by Section 4 of NACE Standard MR0175, which basically states copperalloys are suitable for use without restriction other than as noted in the footnote,which informs the user that such materials may exhibit accelerated general weight-loss corrosion in some sour environments?

(MP INQUIRY #2003-21)ANSWER:The UNS C72900 and UNS C96900 copper alloys are included in NACE StandardMR0175 Paragraph 4.20.

A.13.1



78

QUESTION:Paragraph 1.5.1 of NACE Standard MR0175-2003 states that ―SCC may becontrolled by any or all of three measures: (1) using the materials and processesdescribed in this standard; (2) controlling the environment; or (3) isolating the

components from the sour environment.‖

My client has an application in which Inconel 625 weld metal is overlay welded ontoa martensitic steel component. The martensitic steel component base material andheat-affected zones are isolated from the fluids by the Inconel 625; all wettedsurfaces are Inconel 625.

My client’s customer believes the base material must be stress relieved inaccordance with Paragraph 5.2.1, which states: ―Overlays applied to carbon andlow-alloy steel or to martensitic stainless steels by thermal processes such aswelding, silver brazing, or spray metallizing systems are acceptable for use in sour

environments, provided the substrate does not exceed the lower critical temperatureduring application. In those cases in which the lower critical temperature isexceeded, the component must be heat treated or thermally stress relieved inaccordance with procedures that have been shown to return the base metal to thebase metal hardness as specified in this standard.‖

We believe that Paragraph 5.2.1 does not apply since the base metal is isolated fromthe sour environment with Inconel 625, which is acceptable to 35 HRC.

(MP INQUIRY #2003-16)REVISED ANSWER 2005-09-01:

The requirements of NACE MR0175-2003 are provided in Paras 5.2 and 5.3. Therequirements of NACE MR0175/ISO 15156 are provided in ISO 15156-3, Sub-clauseA.13.1. The revised version of the text of A.13.1 is included in Reference 3.

A.13.2

The revised versions of A.13.2.1 and A.13.2.2 are included in Reference 3.

A.13.2.2

QUESTIONS:

(1) Subject: Equivalency of the technical content of both MR0175-2003 andMR0175/ISO 15156 in relation to the use of Stellite 6 cladding.

Question: In NACE MR0175-2003 cobalt-based alloys (e.g., Stellite 6) areacceptable for hardfacing applications (Section 5, Paragraph 5.2.5).

In NACE MR0175/ISO 15156, Paragraph A.13.2.2 states "the cracking resistance ofalloys specifically designed to provide hard-facing is not specified in this part ofNACE MR0175/ISO 15156." Is there perhaps another part of this specification thatwe may have overseen?

(2) Subject: Solid Stellite 6 Castings.



79

Question: Are solid Stellite 6 castings are permitted for wear-resistant parts invalves under the MR0175/ISO 15156 regime?

(MP INQUIRY #2004-01)REVISED ANSWER 2005-09-01:There has been no change of technical intent between previous editions of NACE

MR0175 and NACE MR0175/ISO 15156.

For ISO documents, that something is not listed as approved is not a sign that it maynot be used; it becomes the equipment user's responsibility to use it or not. Thiscontrasts to the approach in earlier editions of NACE MR0175 when not being listedwas a bar to use.

Nevertheless, the Maintenance Panel accepts that the intent of A.13.2.1 andA.13.2.2 should be made clearer and is processing a ballot to achieve this.

The revised versions of the texts that clarify the intents of A.13.1 and A.13.2 are

included in Reference 3.

Annex D

General

QUESTION:We believe that the inclusion of some alloy trade names in the second columns ofISO 15156-3, Annex D Tables D.1-D.12 is in conflict with the NACE policy on theuse of trade names in standards. Could the Maintenance Panel please propose

steps to resolve this policy problem? (MP INQUIRY #2004-22)REVISED ANSWER 2005-02-15:

This issue is resolved by the publication of ISO 15156-3:2003/Cor.1:2005(E) 2005-02-15, see Reference 4.

QUESTION:

It is our understanding of NACE MR0175/ISO 15156 that provided ASTM A 995Grade 4A (UNS J92205) 22 Cr duplex stainless steel complies with the materiallimits

of Table A24 of Annex A, it can be selected for use in H2S-containing environmentsprovided the environmental limits given in Table A24 are not exceeded.

(MP INQUIRY #2006-04Q1)ANSWER:Your understanding is correct.

Q2 It does not ALSO have to be listed in Annex D Table D7, which webelieve is for information only and lists only SOME duplex stainless steels.

(MP INQUIRY #2006-04Q2)ANSWER:You are correct.

Table D.2



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QUESTION:Could you please confirm that the information given for alloy UNS N08367 in NACEMR0175/ISO 15156-3, Table D2 is incorrect and should be that shown below for theelements affected?

S maximum should be 0,03N range should be 0,18 to 0,25Cu range should be 0,00 to 0,75FPREN should be 42 to 49Ni + 2 Mo should be 35,5 to39,5

(MP INQUIRY #2005-24)ANSWER:Yes.

QUESTION:

In Table D2, the alloy N08367 was assigned a PREN of 20 - 23. Calculations basedon Cr +3.3 Mo yields much higher PREN (40 - 45). If this was a mistake, pleasecorrect.

(MP INQUIRY #2007-04)ANSWER:Thank you for raising this issue. The ISO 15156 Maintenance Panel will ensure thatany errors found in the Tables of NACE MR0175/ISO 15156-3,Annex D will be corrected the next time the document is fully updated.

Table D.6

QUESTION:In NACE MR0175/ISO 15156-3 Table D.6, F6NM is associated with UNS S42400.In ASTM A182, F6NM is associated with UNS S41500. But composition listed inTable D.6 for F6NM does not match either one of these UNS numbers. Is there areason for that or is it a mistake? The composition is similar to both but does notmatch up.

(MP INQUIRY #2007-06)ANSWER:Thank you for raising this issue. The ISO 15156 Maintenance Panel will ensure thatany errors found in the Tables of NACE MR0175/ISO 15156-3, Annex D will be

corrected the next time the document is fully updated.

Please note: Annex D is described as "Informative" and no requirement to meet thechemical analysis for an alloy given in Table D.6 is implied by the data included inthis Table.



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References:

1.Petroleum and natural gas industries — Materials for use inH2S-containing environments in oil and gas production —

Part 1:General principles for selection of cracking –resistant materialsTECHNICAL CORRIGENDUM 1 (2005-09-01)

2.Petroleum and natural gas industries — Materials for use inH2S-containing environments in oil and gas production — Part 2:Cracking-resistant carbon and low alloy steels, and the use of cast ironsTECHNICAL CORRIGENDUM 1 (2005-09-01)

3.Petroleum and natural gas industries — Materials for use inH2S-containing environments in oil and gas production — Part 3:Cracking-resistant CRAs (corrosion-resistant alloys) and otheralloys:TECHNICAL CORRIGENDUM 2 (2005-09-01)

4.Petroleum and natural gas industries — Materials for use in

H2S-containing environments in oil and gas production—

Part 3:Cracking-resistant CRAs (corrosion-resistant alloys) and otheralloys:TECHNICAL CORRIGENDUM 1 (2005-02-15)

All are available via www.iso.org/iso15156maintenance



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