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6.11 MATERIALS

6.11.1 General

6.11.1.1 Materials of construction shall be selected for the operating and site environmental conditions specified (see 6.11.1.7).

Discussion: Key materials concerns are mechanical properties and corrosion resistance. The purchaser may know of requirements or stream contaminants not listed on the data sheets. There may also be differences of opinion between the purchaser and supplier on the suitability of materials for the specified process and site environments.

6.11.1.2 The material specification of all major components shall be clearly stated in the vendor's proposal. Materials shall be identified by reference to applicable international standards, including the material grade (refer to informative Annex XXX) Where international standards are not available, internationally recognized national standards may be used. When no such designation is available, the vendor's material specification, giving physical properties- chemical composition, and test requirements- shall be included in the proposal. [9.2.3, Item k]

Discussion: National Standards such as ANSI, DIN, BS are examples of internationally recognized national standards. Internationally recognized “other standards” such as API, HIS NEMA, AGMA, etc. may also be used.

6.11.1.3 If specified, copper or copper alloys shall not be used for parts of machines or auxiliaries in contact with process fluids. Nickel-copper alloy (UNS N04400), bearing babbitt, and precipitation-hardened stainless steels are excluded from this requirement.Note: Certain corrosive fluids in contact with copper alloys have been known to form explosive compounds.

Discussion: There is potential of an explosive mixture occurring under certain conditions. For example, ethylene oxide in the presence of copper can form acetylene. Nickel-copper alloys (such as Monel and its equivalents), bearing babbitts and precipitation-hardening stainless steels also contain certain amounts of copper. However, the presence of nickel in these materials acts as a barrier to the process of formation of explosive mixtures.

6.11.1.4 The vendor shall specify the optional tests and inspection procedures that may be necessary to ensure that materials are satisfactory for the service (see 6.11.1.2). Such tests and inspections shall be listed in the proposal. [9.2.3, Item j]Note The purchaser can specify additional optional tests and inspections- especially for materials used for critical components or in critical services.

[The use of the word “may” is not appropriate for use in a NOTE since it implies “permission” to perform a requirement, and requirements are not allowed in a NOTE. The use of the word “can” is used to indicate a possibility and is therefore not a requirement and is appropriately used in a NOTE. [ISO Directives Part 2 Annex G paragraph G.3].

Note to TF Chairmen: Check to be sure there is space on the data sheets to specify this option.

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Discussion: Material specifications often contain appropriate optional mechanical or chemical analysis tests and optional inspections as supplementary requirements. These requirements are considered suitable for use with each material specification aid should not surprise the supplier. For critical castings, for instance radiography of certain areas may be justified. Carbon equivalent (carbon or carbon with other elements) maximums are sometimes specified to improve weldability and to reduce hardness at welds.

6.11.1.5 External parts that are subject to rotary or sliding motions (such as control linkage joints and adjustment mechanisms) shall be of corrosion-resistant materials suitable for the site environment.

Discussion: Corrosion - resistant materials are necessary to prevent binding or seizure. Consider exposure to intermittent contaminants from wash down water, nearby process or cooling water leakage sources, and process gas leaks, for example.

6.11.1.6 Minor parts such as nuts, springs, washers, gaskets, and keys shall have corrosion resistance at least equal to that of specified parts in the same environment.

Discussion: Minor parts often perform critical functions and must be corrosion resistant to maintain their integrity. Fasteners may be higher strength than other components and therefore are more susceptible to stress corrosion cracking.

Non-ferrous materials often have lower melting points than steel, with reduced fire resistance.

6.11.1.7 The purchaser shall specify any corrosive agents (including trace quantities) present in the motive and process fluids and in the site environment, including constituents that may cause stress corrosion cracking. (SPTF are there other corrosion mechanism which should be identified)

Note Typical agents of concern are hydrogen sulfide, amines. bromides, iodides, chlorides, cyanide. fluoride, mercury, naphthenic acid and polythionic acid.

6.11.1.8 If austenitic stainless steel parts exposed to conditions that may promote intergranular corrosion are to be fabricated, hard faced, overlaid or repaired by welding, they shall be made of low-carbon or stabilized grades.

Note: Overlays or hard surfaces that contain more than 0.10% carbon can sensitize both low-carbon and stabilized grades of austenitic stainless steel unless a buffer layer that is not sensitive to intergranular corrosion is applied.

6.11.1.9 Where mating parts such as studs and nuts of austenitic stainless steel or materials with similar galling tendencies are used, they shall be lubricated with an antiseizure compound suitable for the process temperatures and compatible with the material(s) and specified process fluid(s). (ISO – David Sales)

Note The required torque values to achieve the necessary bolt preload will vary considerably depending if antiseizure compounds are used on the threads. . [6.2.8, 6.2.9.4]

Discussion: Some antiseizure compounds have been found to play a role in promoting stress corrosion cracking under certain conditions. For example, the combination of molydisulfide thread lubricants and humid air can cause SCC problems in A193 B7 materials. The

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molydisulfide decomposes at elevated temperatures to form corrosive hydrogen sulfide. Also, sulfur-based, copper-based and lead-based lubricants can contribute to cracking of materials such as l 7-4PH and cold-worked and annealed 304 SS.

6.11.1.10 When the purchaser has specified the presence of hydrogen sulfide in any fluid, materials exposed to that fluid shall be selected in accordance with the requirements of NACE Standard MRO 175. Ferrous materials not covered by NACE MR0 175 shall not have a yield strength exceeding 620 N/mm2 (90,000 psi) nor a hardness exceeding Rockwell C 22. Components that are fabricated by welding shall be postweld heat treated, if required, so that both the welds and the heat-affected zones meet the yield strength and hardness requirements.

It is the responsibility of the purchaser to determine the amount of wet H2S that may be present, considering normal operation, startup, shutdown, idle standby, upsets, or unusual operating conditions such as catalyst regeneration.

In many applications, small amounts of wet H2S are sufficient to require materials resistant to sulfide stress corrosion cracking. When there are trace quantities of wet H2S known to be present or if there is any uncertainty about the amount of wet H2S that may be present, the purchaser shall note on the data sheets that materials resistant to sulfide stress corrosion cracking are required. [ Note made part of the paragraph since it specifies requirements ]

Discussion: NACE MR0175 (2003 is the latest edition) lists ferrous and non-ferrous materials that are resistant to sulfide stress corrosion cracking. The owner can also use MR0175 to specify materials resistant to sulfide cracking for environments not specifically defined in that standard NACE is the only widely recognized standard that exists today.

Sulfide stress corrosion cracking only occurs when moisture (water) is present with the H2S. In many petrochemical applications the combination of moisture and H2S may occur during normal operation or during transient conditions (such as startups and shutdowns). The cost of complying with this requirement is often relatively low compared to the benefits realized.

Post weld heat treatment accomplishes two things: l) tempering back hardened (martensitic) transformation products produced during welding and 2) stress relief of any induced tensile stresses during welding.

6.11.1.7 The purchaser shall specify any agents (including trace quantities) present in the motive and process fluids and in the site environment, including constituents that may cause stress corrosion .

Note to Task force chairmen: Modify these form of corrosion based on your standard.

Note1: Seven common forms of corrosion are : 1) General corrosion 2) Pitting corrosion 3) High temperature corrosion 4) Intergranular corrosion (IGC) 5) Environmental corrosion 6) Selective attack 7) Erosion corrosion

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Note 2: Environment corrosion is the brittle fracture of a normally ductile material in which the corrosive effect of the environment is a causative factor.

Note 3: Environment cracking caused by environmental corrosion is a general term which includes the terms listed below. 1) Stress Corrosion Cracking (SCC) 2) Sulfide Stress Corrosion Cracking (SSC) 3) Chloride Stress Corrosion Cracking 4) Corrosion Fatigue (CF) 5) High Temperature Hydrogen Attack 6) Hydrogen Embrittlement (HE) 7) Liquid Metal Embrittlement (LME) 8) Hydrogen Blistering 9) Hydrogen Induced Cracking (HIC) 10) Stress Oriented Hydrogen Induced Cracking (SOHIC)

Note 4: Stress Corrosion Cracking (SCC) is the most dangerous of the various types of corrosion failure of metals. SCC occurs unexpectedly and is extremely localized. As a rule, SCC is accompanied by little change in the equip-ment wall thickness. During SCC, the metal or alloy is virtually unattacked over most of its surface, while fine cracks progress through it. There is no obvious correlation between the amount of corrosion and cracking due to stress corrosion cracking. SCC can cause through fracture in very short periods of time (in the most severe cases in a day or even several hours). SCC is minimized by mimimizing residual stresses, proper material selection and by lim-iting the hardness of the material.

Note 5: Typical agents of concern for environmental cracking are hydrogen sulfide, amines. Halides (bromides, iodides, chlorides, fluoride) chlorine, cyanide. fluoride, mercury, naphthenic acid, polythionic acid, hydrofluoric acid, mercury, carbon dioxide, ammonia, ammonia bisulfide, phenols, caustics (sodium, potassium and lithium hydroxide) , sea water, brine.

Note 6: The documents referenced in 6.11.1.8, 6.11.1.14, and 6.11.1.16 through 6.11.1.19 cover corrosion due to sulfide, chloride, caustic and alkaline stress corrosion cracking. Purchaser and vendor are advised to consider mitigation processes to cover the other form of corrosion outlined in Notes 1& 3 which may caused by the process fluid.

6.11.1.8 If the purchaser has specified the presence of hydrogen sulfide in any fluid, materials exposed to that fluid shall be selected and processed in accordance with the requirements of NACE Standard MRO 175103.

Discussion:Cause: Atomic Hydrogen entering the steels microstructure. Prevention: Limit strength and hardness per NACE MR0175 & MR0103 and ISO 15156.

Background: The Standard Paragraph Task Force is in the process of evaluating referencing MRO 175 and 103. MRO 715 “Metals for Sulfide Stress Crackingand Stress Corrosion Cracking Resistance in Sour Oilfield Environments” has been referenced for many years in the SOME Standards, even though its title referenced “oil field”.

ASME P-Numbers and Weld ProceduresTo reduce the number of welding and brazing procedure qualifications required, base metals have been assigned P-Numbers by Section IX of the ASME BPVC (Boiler Pressure Vessel Code) .These assignments are based essentially on comparable base metal characteristics,

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such as composition, weldability, brazeability, and mechanical properties, where this can logically be done.

Within P number categories for steel and steel alloys (i.e. P-Numbers 1-11) the base metals are further broken down into subset categories called Group Numbers. P-Number 1 has 4 sub Group numbers. P-1 and 4 groups are listed below.

P number 1: Carbon or carbon-manganese steels– Group 1: Minimum tensile strength of less than 70 ksi– Group 2: Minimum tensile strength of 70–80 ksi– Group 3: Minimum tensile strength of 80–90 ksi– Group 4: Minimum tensile strength of greater than 90 ksi

From ASME Code Section IX Table QW-422 There are 98 materials listed in P 1- Group 1There are 48 materials listed in P 1- Group 2There are 14 materials listed in P 1- Group 3There are 3 materials listed in P 1- Group 4

NO IMPACT TEST OF WELD REQUIRED: The ASME Boiler Pressure Vessel Code Section IX indicates a procedure qualification (WPS) developed for one of the materials in a P number category can be used for all the materials in that P number and all Groups associated with that P number. Thus for P 1 category, a weld procedure qualification (WPS) developed for a material in P1 Group 1 can be applied to all of the materials in P1 Groups 1,2,3 and 4. i.e one weld procedure can be applied to 98+48+14+3= 163 materials.

IMPACT ESTING REQUIRED: A separate WPS has to be developed for each Group associated with a P No. For P1 therefore, you would need 4 separate weld procedures, one for each of the Groups. The WPS developed for Group 1 could be used for all materials P1 Group 1 but not for Groups 2, 3 or 4.

If impact testing is required, and you wanted to weld a material from P1Group 1 to a material in P1 Group 2, you would need to develop a separate weld procedure. This weld procedure could then be applied to welding any material from P-1 Group 1 to any material in P-1 Group 2. (Refer to QW 403.5 Section IX of the ASME Boiler Pressure Vessel Code)

The ASME Boiler pressure vessel code approach is based on strength and structural integrity. In addition to the structural integrity, however when invoking NACE we are also concerned with the hardness of the weld ( this includes the weld metal, HAZ and base material). Structural integrity AND resistance to Sulfide Stress corrosion Cracking is required. For the materials in P 1 groups 1, 2 and 3 NACE historically ( and SP as modified) requires the weld metal, HAZ and base metal to be less than HRC 22.

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The final weld hardness, in part, depends on the Carbon Equivalent of the base metal, trace or micro-alloying elements in the base material , weld filler material and post weld heat treatment. The affect of the CE and trace metals are not covered by the ASME Boiler pressure vessel code.

CARBON EQUIVALENT: Generally the higher the amount of carbon in the base material, the harder the weld. The weld hardness is also increased by alloying elements such as Mn, Ni, Cr, Mo and V. The formula used by NACE MR0103 states:

CE=%C + (%Mn/6) + [(%Ni + %Cu)/15] + [(%Cr + %Mo + % V)/5]

There can be considerable difference in carbon equivalent between the 98 P1 Group 1 materials. Therefore a qualification procedure which was developed for a P1 Group 1 material with a CE of 0.35 may produce RC readings below HRC 22, but another P1 Group 1 material with a CE of 0.45 may result in harnesses greater than HRC 22. If the P1 Group 1material with the CE of 0.35 was used to qualify the entire P1 Group 1 category it is possible to get hardness readings exceeding HRC 22 if the material has a CE greater than the CE 0.35 used in the qualifying procedure

TRACE MICRO-ALLOYING ELEMENTS: As the result of using scrap steel in the manufacturing of “New Steel” certain trace elements are introduced. Trace elements which affect the hardness of the Heat Affected Zone are Nb(Niobium), V (Vanadium) and Cb (Columbium). Note: Nb and Cb are the same element.

The following is from the article “Vanadium and Columbium Additions in Pressure Vessel Steels by P.Xu, B.R. Somers and A.W. Pense “…The maximum harness in the HAZ increases with increasing additions of V and Cb…”“… Post weld heat treatment must be used with caution in High Strength Low alloy steels with V and/or Cb because it enhances the HAZ hardness but causes detrimental effects to the HAZ toughness.

Please note that the amount of these trace elements are not covered in the ASTM material specifications.

NACE SP 0472 ( Referenced as part of NACE MRO103)

NACE SP0427 addresses the issue of CE and Trace Micro-alloying elements in paragraphs 2.3.5.6.2.& 2.3.5.6.3 reproduced below. 2.3.5.6.2 The WPS shall state that the maximum CE of the production base metal shall not exceed the CE of the procedure qualification specimen by more than 0.03%. The base metal chemistry of the procedure qualification specimen shall be reported in the PQR. All base metal chemistry requirements shall be applied to ladle analyses, unless otherwise specified by the user.

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2.3.5.6.3 For product forms in which deliberately added microalloying elements (such as Nb [columbium {Cb}], V, titanium [Ti], and boron [B]) are used, the maximum content shall not exceed the corresponding value on the procedure qualification specimen. Deliberate additions are generally considered to be values greater than 0.01 wt% for each of Nb (Cb), V, and Ti, and greater than 0.0005 wt% of B. All base metal chemistry requirements shall be applied to ladle analyses, unless otherwise specified by the user.

It is for the above reason that NACE MR0 103 has been referenced in the SP. The CE and trace element requirements are not on NACE MR0 175.

Discussion : ISO 15156-1/ MR0175 states “ This part of ISO 15156 is not necessarily applicable to equipment used in refining or downstream processes and equipment.”

6.11.1.9 The hardness referenced for ASME Sec. IX P-No. 1 group 1 and 2 carbon steels in NACE MRO 103 – 2007 and NACE SP0472-2008 shall not exceed Rockwell hardness HRC22 in the weld, heat affected zone and base material. In accordance with ASTM E 140, HRC22 is equivalent to Brinell hardness HBW 237 and Vickers hardness 248 HV.

NOTE: Refer to NACE MRO SP0472 Appendix A, and NACE 8X194 for additional information concerning hardness testing and hardness limits.

Discussion: NACE SP0472-2008 require the referenced hardness not to exceed HRC 15 (HBW 200) . “The lower limit was applied to compensate for both the nonhomogeneity of some weld deposits and the normal variations in production hardness test results that are obtained using a comparison hardness tester.”

NACE 0472 Appendix A “A2.2.1 A number of SSC failures occurred in the late 1960s in hard weld deposits in P-No. 1 steel refinery equipment. The petroleum refining industry established a maximum hardness limit of 200 HBW for P-No. 1, Group 1 and 2 steels to ensure that weld deposits would be resistant to HSC. The 200 HBWmaximum hardness requirement is lower than the 22 HRC (237 HBW) maximum hardness requirement listed in NACE MR0175/ISO 15156 and previous editions of NACE Standard MR0175. The lower limit was applied to compensate for both the nonhomogeneity of some weld deposits and the normal variations in production hardness test results that are obtained using a comparison hardness tester.”

NACE 8X194 - Materials and Fabrication Practices for New Pressure Vessels Used in Wet H2S Refinery Service- Highlights

Hardness Acceptance Criteria“The 248 HV10 maximum value is also supported by some laboratory testing and field experience in oil and gas production environments. Most(3) ( Majority) of users have found

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that a maximum of 200 HV10 for a CS weld HAZ is overly restrictive and not practical, especially for attachments welded with low-heat-input welding processes and 248 HV10 is often used”

Some(1) users have specified a maximum hardness of 200 HBW for the weldment, including the HAZ. This value was taken from NACE Standard RP0472, which recommends a maximum hardness of 200 HBW for weld metal. By direct conversion, this is equivalent to 210 HV10; however, experience has shown that the large indenter used in the Brinell test tends to produce a hardness test result that reflects the average of harder and softer zones within the larger area of the indention, whereas the smaller indenters used in the Vickers diamond-pyramid hardness test or the Rockwell superficial hardness test tend to produce a hardness test result that better reflects the hardness within a local hard or soft zone in the HAZ. Some(2) (Minority) of users have specified a maximum hardness of 248 HV10 when utilizing these small indenter tests. The Rockwell superficial hardness equivalent to 248 HV10 is 70.5 HR15N. These values are a direct conversion from the 22 HRC maximum specified in NACEStandard MR0103 for ferritic materials to be used in petroleum refining “sour service.”

The 248 HV10 maximum value is also supported by some laboratory testing and field experience in oil and gas production environments.18,19,20 Most(3) ( Majority) of users have found that a maximum of 200 HV10 for a CS weld HAZ is overly restrictive and not practical, especially for attachments welded with low-heat-input welding processes and 248 HV10 is often used. The Rockwell superficial hardness equivalent to 200 HV10 is 90.8 HR15T.

ISO 15156-2 /NACE MR0 175Table A.1 — Maximum acceptable hardness values for carbon steel, carbon manganese steel and low alloy steel welds. This table allows a maximum hardness of HRC 22.

It’s been the experience of turbomachinery users and manufactures that HRC 22 is sufficient to prevent sulfide SCC in these steels .

6.11.1.10 Ferrous materials not covered by NACE MR0 175 103 shall not have a yield strength exceeding 620 N/mm2 (90,000 psi) nor a hardness exceeding Rockwell C 22.

6.11.1.11 Components that are fabricated by welding shall be postweld heat treated, if required, so that both the welds and the heat-affected zones meet the yield strength and hardness requirements

6.11.1.12 It is the responsibility of the purchaser to determine the amount of wet H2S that may be present, considering normal operation, startup, shutdown, idle standby, upsets, or unusual operating conditions such as catalyst regeneration.

6.11.1.13 In many applications, small amounts of wet H2S are sufficient to require materials resistant to sulfide stress corrosion cracking. When there are trace quantities of wet H2S known to be present or if there is any uncertainty about the amount of wet H2S that may be present, the

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purchaser shall note on the data sheets that materials resistant to sulfide stress corrosion cracking are required.

6.11.1.14.When the purchaser has specified the presence of environmental agents that can cause stress corrosion cracking such as hydrogen sulfide or chlorides the qualification of brazing procedure shall be in accordance with NACE TM0177 test method A The test environmental conditions for carbon and low alloy steels shall be in accordance with NACE MR0175/ISO 15156 -2 Table B1. ???

The test environmental conditions for corrosion - resistant alloys shall be in accordance with NACE MR0175/ISO 15156-3 paragraph 3.5.1.???

The lower value of the brazed joint or base material stress and time to failure test data at 720 hours (refer to Figure 6 of NACE TM0177) shall be used to determine the maximum allowable stresses for the application.

The brazing thermal cycle and the subsequent post braze heat treatment shall develop base metal hardness in accordance with NACE MR0175/ISO 15156 for the specific material.

• If specified, the manufacturer shall provide data indicating the materials tested in accordance with this procedure are adequate to prevent stress corrosion cracking in field operation.

6.11.1.15 When the purchaser has specified the presence of environmental agents that can cause stress corrosion cracking such as hydrogen sulfide or chlorides the qualification of electron beam welding procedure (welding process and PWHT) shall include hardness testing in base metal, heat affected zone and weld spike.Joint hardness shall be checked in compliance with NACE MR0175/ISO15156-2 par. 7.3.3.3 Figure 5.

The Vickers HV 10 or HV5 method in accordance with ISO 6507-1, shall be used. The hardness limit for the base metal, heat affected zone and weld spike shall be in accordance with 6.11.1.10

Homogeneous weld: weld made without the use of shim between two welded parts

6.11.1.16 When the purchaser has specified the presence of chlorides in any fluid, materials exposed to that fluid shall be selected and processed in accordance with the requirements of ISO 15156 -3 / NACE Standard MRO 175.

Note: Carbon or low alloy steels are not susceptible to cracking in chloride solutions, but some localized corrosion may occur. It is generally recognized that alloys with greater than approximately 30- 40% nickel are immune to chloride stress corrosion cracking (SCC). All austenitic (300 Series) SS are susceptible to chloride cracking. The severity of this stress corrosion cracking depends on the chloride concentration, temperature, fabrication and operational stresses.

Discussion: Cause of Chloride Stress Corrosion Cracking: Rupture of the protective film on Austinetic SS.

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Prevention: Proper selection of materials

Chloride SCC is an eloctro chemical reaction as opposed to the molecular diffusion problem with Sulfide SCC. Chloride SCC does not occur if the gas is dry, however during down periods or upsets it is not unusual for the components to be exposed to moisture. Therefore it should be assumed that the gas will always be wet. Microscopic cracks or breaks in the passive protective oxide film on SS allows the highly corrosive wet chlorides to attack the base metal. This layer is only about 1-2 nm (3.9 x 10-10 in) thick. This corrosion causes pit on the metal surface. Since this mechanism is strongly localized, chloride SCC occurs without appreciable general corrosion. There are few well developed models for crack initiation from these pits. Some observations imply that the electrochemistry in the pit is more important than the stress risers caused by the size of the pit. Chloride SCC may occur during service or down periods.

Some of the factors which contribute to chloride SCC are outlined below.

1. Chloride Concentration

The more concentrated the chloride, the more likely SCC becomes. At 10PPM in laboratory tests, the time to cracking increases so much that this concentration may be considered safe at most conditions. (6)

It should be emphasized that chloride concentration in water can increase substantially because of water vaporization. This is why API 617 7th edition paragraph 4.3.2.3 and Standard Paragraph 8.3.2.4 states “To prevent deposition of chlorides on austenitic stainless steel as a result of evaporative drying, all residual liquid shall be removed from (Hydrotested) tested parts at the conclusion of the test. Chloride contamination of Boiler feed water can result in turbine deposits which can cause chloride SCC.

2. Stresses

Residual fabricating stresses, especially at welds and normal operating stresses, even after fabrication stress relieving is sufficient to cause cracking in alloys that are susceptible to chloride SCC.

3. Temperature

Chloride SCC seldom occurs when metal temperatures are below 130 F. For example SS pump impellers in sea water service have known no cracking problems despite the presence of chloride and high oxygen content. Cracking has occurred in tropical locations where the exposure to direct sunlight could increase the metal temperature above ambient. This is particularly important in offshore locations due to the salt sea environment.

There are no simple methods of preventing SCC when austenitic SS (300 Series) are used in an environment containing chlorides.(7 ) All austenitic (300 Series) SS are susceptible to

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chloride cracking and there is not a tremendous difference between the resistance of the least resistant and the most resistant,. Chlorides are perhaps the most common cause of SCC of austenitic (300 Series) SS and nickel alloys. Refer to the figures below.

Alloys resistant to chloride SCC are Ferritic stainless steels such as 405 (12 Cr.), 430 (17 Cr.) and e-brite (26Cr - 1 Mo.) and duplex stainless steels such as 2205 and 2207. It is generally recognized that alloys with greater than approximately 30 - 40% nickel are immune to chloride SCC.

Affect of nickel on the Chloride stress corrosion cracking of austenitic SS

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Range of Nickel in 300 series SS

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Probability of Chloride SCC vs Nickel Content

Pits in 316 tubing from Chlorides

6.11.1.17 Guidelines to avoid Caustic stress corrosion cracking can be found in NACE SP0403 Note 1: Common alkalis such as caustic soda (sodium hydroxide, NaOH) and potassium hydroxide (KOH) are not particularly corrosive and can be handled in steel in most applications where contamination is not a problem. However Stress Corrosion cracking and severe uniform corrosion can occur at higher concentrations and temperatures.

Note 2: Inadvertent caustic carryover can be detrimental to aluminum labyrinths and steam turbine rotors.

Discussion: Refer to SP Annex 14 Page 60-63 for additional information on Caustic Stress Corrosion Cracking.

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6.11.1.18 Amine cracking and its prevention can be found in API RP 945.14

6.11.1.19 Further information about carbonate cracking and its prevention is currently being developed by NACE TG 347.15

6.11.1.20 If austenitic stainless steel parts exposed to conditions that may promote intergranular corrosion are to be fabricated, hard faced, overlaid or repaired by welding, they shall be made of low-carbon or stabilized grades.Note: Overlays or hard surfaces that contain more than 0.10% carbon can sensitize both low-carbon and stabilized grades of austenitic stainless steel unless a buffer layer that is not sensitive to intergranular corrosion is applied.

6.11.1.21 Where mating parts such as studs and nuts of austenitic stainless steel or materials with similar galling tendencies are used, they shall be lubricated with an antiseizure compound suitable for the process temperatures and compatible with the material(s) and specified process fluid(s). (ISO – David Sales)Note The required torque values to achieve the necessary bolt preload will vary considerably depending if antiseizure compounds are used on the threads. . [6.2.8, 6.2.9.4]

Discussion: Some antiseizure compounds have been found to play a role in promoting stress corrosion cracking under certain conditions. For example, the combination of molydisulfide thread lubricants and humid air can cause SCC problems in A193 B7 materials. The molydisulfide decomposes at elevated temperatures to form corrosive hydrogen sulfide. Also, sulfur-based, copper-based and lead-based lubricants can contribute to cracking of materials such as l 7-4PH and cold-worked and annealed 304 SS.

6.11.1.22 The vendor shall select materials to avoid conditions that may result in electrolytic corrosion. Where such conditions cannot be avoided, the purchaser and the vendor shall agree on the material selection and any other precautions necessary.Note When dissimilar materials with significantly different electrical potentials are placed in contact in the presence of an electrolytic solution, galvanic couples that can result in serious corrosion of the less noble material may can be created. The NACE Corrosion Engineer’s Reference Book is one resource for selection of suitable materials in these situations.

Discussion: An example of unacceptable galvanic couple is more noble copper alloys (brass, bronze) connected to less noble steel in an aqueous environment. Steel immediately adjacent to the copper alloy can corrode at an accelerated rate.

6.11.1.23 Materials, casting factors, and the quality of any welding shall be equal to those required by Section VIII, Division 1, of the ASME Code. The manufacturer's data report forms, as specified in the code, are not required. [6.11.4.2] SPTF Check to see if this paragraph or sections thereof have already been covered in the Casing design section of the SP. Note: For impact requirements refer to 6.11.5

Discussion: Under certain conditions and for certain applications, material traceability is needed. It is important that the manufacturer has an appropriate internal quality process for ensuring that the actual material ordered or produced conforms to specific material

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requirements for the application. Code manufacturer's data forms are not required but the quality control system should be auditable and traceable.

6.11.1.24 Low-carbon steels can be notch sensitive and susceptible to brittle fracture at ambient or lower temperatures. Therefore, only fully killed, normalized steels made to fine-grain practice are acceptable. Steel made to a coarse austenitic grain size practice (such as ASTM A 515) shall not be used. (ISO David Sales recommendation)

Discussion: Low alloy steels (such as AISI 4140) are generally made to fine-grain practice and have adequate toughness. ASTM A515 steel is made to coarse-grained practice. See Section V Division I Section UG 20F of the ASME Code for additional guidance on brittle fracture resistance of plate and forged steels.

6.11.1.25 O-ring materials shall be compatible with all specified services. Special consideration shall be given to the selection of O-rings for high pressure services to ensure that they will not be damaged upon rapid depressurization (explosive decompression). NOTE 1 Susceptibility to explosive decompression depends on the gas to which the O-ring is exposed, the compounding of the elastomer, temperature of exposure, the rate of decompression, and the number of cycles.

NOTE 2 Agents affecting elastomer selection include ketones, ethylene oxide, sodium hydroxide, methanol, benzene and solvents. (API 676)

Discussion: Explosive decompression occurs when a gas under pressure, absorbed into an elastomer over a period of time is suddenly released. Damage to the elastomer occurs during the rapid pressure release.

6.11.1.26 For cast iron casings the bolting for pressure joints shall be carbon steel in accordance with ASTM A 307 Grade B. For steel casings the bolting shall be high temperature alloy steel in accordance with ASTM A 193 Grade B7. Carbon steel ASTM A 194, Grade 2H nuts shall be used. Where space is limited, ASTM A 563, Grade A case hardened carbon steel nuts shall be used. Bolting and nuts in accordance with ASTM A 320 shall be used for temperatures below –30 °C (–20 °F). The grade of ASTM A 320 will depend on design, service conditions, mechanical properties, and low-temperature characteristics (David Sales ISO Comment & SPTF Rewording)

Discussion: Carbon steel bolting material (such as ASTM A 307 Grade B) has a yield strength in the same range as the tensile strength of the cast iron. Use of a lower strength bolt would make the bolt material the limiting factor instead of the casing. ASTM A 193 B-7 material has high enough strength to allow the steel casing material to be the limiting factor. An ASTM A320 bolt material provides protection against low temperature brittle fracture. ASTM A 320 comes in various grades and the grade i.e material properties will depend on the application.

6.11.1.27 Positive Material Identification (PMI)

6.11.1.27.1 PMI testing shall be in accordance with 6.11.16.2 through 6.11.1.16.7.

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6.11.1.27.2 If specified, the following alloy steel items shall be subject to PMI testing:a) The pressure casing of rotating equipmentb) Shaftsc) Impellersd) Blading and shroudse) Locking pins used to secure locking bucketsf) Discs of built-up rotorsg) Tie boltsh) Locking nuts on built up rotors and reciprocating piston assembliesi) Piston rodsj) Connecting rodsk) Crosshead pinsl) Cylindersm) Cylinder headsn) Valve coverso) Shaft sleevesp) Bearing oil film surfaceq) Alloy claddings and weld overlaysr) Pressure casing joint bolting (Studs and nuts) s) Inlet guide vanest) Diaphragmsu) Turbine stationary nozzles and reversing bucketsv) Pulsation Bottlesw) Balance pistonsx) Overhead seal tanky) Rundown oil tank

Note to TF Chairs: Provide boxes on the data sheets which will allow the purchaser to select which components are to be PMI Tested. This list should be modified based on the equipment being covered in the specification.

6.11.1.27.3 In addition to the components outlined in 6.11.1.16.1 other materials, welds, fabrications and piping shall be PMI tested as specified.

6.11.1. 27.4 If PMI testing has been specified for a fabrication, the components comprising the fabrication, including welds, shall be checked after the fabrication is complete except as permitted in 6.11.1.16.4. Testing may be performed prior to any heat treatment.

6.11.1. 27.5 Unique (non-stock) components such as impellers, turbine blading, and shafts may be tested after manufacturing and prior to rotor assembly.

6.11.1. 27.6 If PMI is specified, techniques providing quantitative results shall be used.

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NOTE 1 PMI test methods are intended to identify alloy materials and are not intended to establish the exact conformance of a material to an alloy specification.

NOTE 2 Additional information on PMI testing can be found in API RP 578.

NOTE 3 PMI is used to verify that the specified materials are used in the manufacturing, fabrication and assembly of components.

Discussion: Refer to the discussion paragraphs after 6.11.1.16.5 for limitations of this process. Material certifications of castings, forgings, plate, bar stock and weld rods confirm these meet the specified requirements. They do not guarantee that these were actually used to manufacturer the specified component. For example, steam turbine blading bar stock material certificates indicated the material met the drawing requirements, however the blade manufacturer inadvertently used other improper bar stock he had in inventory to manufacturer the blades. This was caught by PMI testing of the completed blading. Likewise, casings and pressure vessels may be fabricated from plate other than specified due to improper labling of the material. Improper weld rods can also be used during fabrication. PMI typically identifies alloy materials such as chromium, nickel, molybdenum, copper, columbium, and titanium.

SPTF Sampling??Ken Beckman to check

Discussion: A variety of PMI test methods are available to determine the identity of alloy materials. The primary methods include:

1) Portable X-ray fluorescence. This technique is used by Texas Nuclear 9266, Texas Nuclear 9277 X-MET 880, Texas Nuclear Metallurgist-XR instruments, Portaspec, Panalyzer 400 or CSI X-MET-840 instruments . The principal of operation is that one or more gamma ray sources are used to generate a beam of low energy gama rays to excite the material under analysis. The material under analysis then emits a characteristic spectrum of x rays which are analyzed to determine what elements are present and in what quantity.

Techniques using X-ray fluorescence do not identify elements lighter than sulfur. Therefore this technique can not be used to detect carbon. It can not differentiate therefore between 304 and 304L stainless or between plane carbon steels such as AISI 1040 or AISI 1030.

2) Portable optical emission spectroscopy. This technique is used by Spectroport TP 07 instrument. This instrument uses an electric arc to stimulate atoms in the test sample to emit a charastic spectrum of light for each element in the sample. The combine light spectra from different elements are passed through a light guide to the optical analyzer. In the analyzer the light is dispersed into its spectral components, and then measured and evaluated against stored calibaration curves.

This technique leaves a burn spot in the component. Under carefully controlled conditions some instruments using this method can determine carbon content. The burn spot should be

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removed since it is hard and could crack due to stress corrosion or high stress. If the component is finished, the test should be done on a low stressed area. For field applications, a hot work permit may be required to use this technique.

3) Laboratory chemical analysis such as:a) X-ray emisson spectrometry in accordance with ASTM E 572b) Optical spectrometry in accordance with ASTM E 227c) Wet chemical analysis in accordance with ASTM E 352 or E 353.

Chemical spot testing and resistivity testing are other quantative methods but are slower or not capable of proving consistant results with low alloy (<5% Cr) materials and are not recommended.

The above methods give quantitative results. Other techniques such as eddy-current sorters, electromagnet alloy sorters, triboelectric testing devices (e.g. ferret meters), and thermoelectric tests are qualative and as such may only be appropriate for limited sorting applications and not for specific alloy identification.

6.11.1.27.7 Mill test reports, material composition certificates, visual stamps or markings shall not be considered as substitutes for PMI testing.

6.11.1.27.8 PMI results shall be within the material specification limits, allowing for the measurement uncertainty (inaccuracy) of the PMI device as specified by the device manufacturer. (David Sales ISO)

6.11.2 Castings

6.11.2.1 Castings shall free from porosity, hot tears, shrink holes, blow holes, cracks, scale, blisters, and similar injurious defects. Surfaces of castings shall be cleaned by sandblasting, shotblasting, chemical cleaning, or other standard methods. Mold-parting fins and the remains of gates and risers shall be chipped, filed or ground flush.

6.11.2.2 The use of chaplets in pressure castings shall be held to a minimum. Where chaplets are necessary, they shall be clean and corrosion free (plating of chaplets is permitted) and of a composition compatible with the casting.

Discussion: A chaplet is a metal support that holds a casting core in place within a mold. Molten metal solidifies around a chaplet and fuses it into the finished casting. Use of chaplets of all inappropriate material is difficult to detect. In corrosive duties this can be catastrophic because the chaplet provides a clean path through the casting if it is not adequately corrosion resistant. Plating of the chaplet prevents it from corrosion. Chaplets are illustrated in the following figure.

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6.11.2.3 Pressure-containing ferrous castings shall not be repaired except as specified in a) through c). [David Sales – Hanging paragraph]

Discussion: Repair methods such as welding, peening. plugging. burning in and impregnating are mechanical and only tend to be superficial. They offer limited protection against in-service leakage.

a) Weldable grades of steel castings shall be repaired by welding, using a qualified welding procedure based on the requirements of the appropriate pressure vessel code such as Section VIII, Division 1, and Section IX of the ASME Code. or other internationally recognized standard as approved by the purchaser. After major weld repairs. and before hydrotest, the complete repaired casting shall be given a postweld heat treatment to ensure stress relief and continuity of mechanical properties of both weld and parent metal and dimensional stability during subsequent machining operations.

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Chaplets

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Discussion: Section VII Division 1 requires stress relief of carbon steel castings if the repair thickness (Not the thickness of the casing) is greater than 11/2 in. The code also allows local stress relieving. Local stress relieving may not be sufficient to develop consistent mechanical properties in both the weld and parent material and prevent subsequent distortion during machining. It is for this reason that this paragraph requires stress relieving of the entire repaired casting. Section IX covers qualification of welding procedures and welding qualifications.

SPTF: The above change was suggested by the 617 TF.

b) Cast gray iron may be repaired by plugging within the limits specified in ASTM A 278, A 395, or A 536. The holes drilled for plugs shall be carefully examined, using liquid penetrant, to ensure that all defective material has been removed.

c) All repairs that are not covered by the agreed material specification shall be subject to the purchaser’s approval.

Discussion: This paragraph is also intended to cover metallurgies other than steel and iron (such as special alloys). ASTM specifications are only one set of specifications. Worldwide, there are several other recognized material specifications.

6.11.2.4 Fully enclosed cored voids, which become fully enclosed by methods such as plugging, welding, or assembly, shall not be used. (ISO)

Discussion: Fully enclosed voids which have achieved system pressure during operation can retain pressure during shutdowns, presenting a safety hazard during any subsequent repair work (such as machining or welding). There is no satisfactory inspection method to ensure void does not become pressurized in service.

6.11.2.5 All Ductile (Nodular) iron castings shall be produced in accordance with ASTM A 395 or other internationally recognized standard as approved by the purchaser. Production of the castings shall conform to the conditions specified in 6.11.2.5.1 through 6.11.2.5.4.[API 619][617]

Discussion: Ductile (Nodular) iron is more ductile than cast iron but less ductile than steel. This ductility in all sections of the casting is highly dependent on casting technique and the material selection The following tests in paragraphs 6.11.2.5.1 through 6.11.2.5.4 are attempts to confirm the ductility at all locations. These tests help ensure the resulting casting is nodular iron. Delivery delays for nodular iron castings are more common due to probability that additional castings must be poured to achieve the required material properties.

ASTM A 395 is titled “Standard Specification for Ferritic Ductile Iron Pressure-Retaining Castings for Use at Elevated Temperatures” Although its title indicates “Pressure Containing”

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the intent of the paragraph is that it is used when Ductile (Nodular) iron castings are supplied, even if they are not Pressure containing.

6.11.2.5.1 The keel or Y block cast at the end of the pour shall have a thickness not less than the thickness of critical sections of the main casting. This test block shall be tested for tensile strength and hardness and shall be microscopically examined. Graphite nodules shall be classified under microscopic examination and shall be in accordance with ASTM A 247. There shall be no intercellular flake graphite.

Note 1: Critical sections are typically heavy sections, section changes, high-stress points such as drilled lubrication points, the cylinder bore, valve ports, and flanges. Normally, bosses and similar sections are not considered critical sections of a casting. If critical sections of a casting have different thicknesses average size keel or Y blocks can be selected in accordance with ASTM A 395. Minimum quality levels should be agreed upon between the purchaser and the vendor. Deleted by SPTF since quality levels are not listed in either ASTM A 247 or ASTM A 395 and it is not clear what Quality level needs to be agreed upon. Additionally can’t specify a requirement in a note.

Note 2: ASTM A395 requires the microstructure of Grade 60-40-18 nodular iron to be essentially ferritic, contain no massive carbides, and have a minimum of 90 % Type I and Type II Graphite nodules as in Fig. 1 or Plate I of Test Method A 247.

Note 3: ASTM A395 requires the microstructure of Grade 60-45-15 nodular iron to be 45 % pearlitic, maximum, contain no massive carbides, and have a minimum 90 % Type I and Type II Graphite nodules as in Fig.1 or Plate I of Test Method A 247

Discussion: Ensures tests are representative of casting properties. The cooling rate, determined in pad by the section thickness, can affect the casting toughness and chemical segregation. In general, Charpy V-notch impact specimens from a more rapidly cooled thinner section will be non-representative of the main casting. Thicker critical sections that are cooled more slowly are also less likely to give non-representative properties. ASTM A247 is specifically referenced because it is the only recognized standard available today. In most cases, acceptance levels depend on the service application.

The quality of the nodules depends on the innoculant such as magnesium additive. This changes the surface tension and causes the graphite to form as nodules rather than flakes. The efficiency of the innoculant decays as time and that is the reason for requiring the test blocks to be taken at the end of the pour.

Refer to SP Annex 12 for additional discussion of Nodular Iron and illustrations of the Type I & Type II graphite nodules

6.11.2.5.2 A minimum of one set (three samples) of Charpy V-notch impact specimens at one-third the thickness of the test block shall be made from the material adjacent to the tensile specimen on each keel or Y block. All three specimens shall have an impact value not less than.12 J (9 ft-lbf) and the mean of the three specimens shall not be less than 14 J (10 ft-lbf) at room temperature. (ISO - Use abbreviations not spelled out units)

Discussion: Ensures adequately uniform toughness at all locations in castings.

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6.11.2.5.3 An “as-cast” sample from each ladle shall be chemically analyzed.

6.11.2.5.4 Brinell hardness tests shall be made on the actual casting at feasible critical sections such as section changes, flanges, and other accessible locations such as the cylinder bore and valve ports. Sufficient surface material shall be removed before hardness tests are made to eliminate any skin effect. Tests shall also be made at the extremities of the casting at locations that represent the sections poured first and last. These shall be made in addition to hardness test on keel or Y blocks in accordance with 6.11.2.5.1.

Discussion: The quality and properties of ductile (nodular) iron castings is heavily dependent on procedure, pour rates, temperatures. cooling rates, section thickness, etc.

Casting material properties cannot be verified except by test of material which has undergone closely similar history.

Changes in cooling rates produced by different section thickness can affect hardness. Thinner sections generally have higher hardness.

The skin effect of a casting can contain different carbon content (either increased or decreased) and have different hardness than the cast material beneath it. Decarburization will produce lower hardness readings.

Composition differences (not only chemistry) between sections poured first and last can affect the material properties.

6.11.3 Forgings

6.11.3.1 The forging material shall be selected from those listed in Appendix XXX.Note to TF Chairmen: Forging materials cannot be referenced to an informative appendix. Tailor this paragraph to the specific components of each type of equipment.

6.11.3.2 Pressure-containing ferrous forgings shall not be repaired except as specified in a)and b).

a) Weldable grades of steel forgings shall be repaired by welding. using a qualified welding procedure based on the requirements of the appropriate pressure vessel code such as Section VIII. Division l and Section IX of the ASME Code . or other internationally recognized standard as approved by the purchaser. After major weld repairs. and before hydrotest. the complete forging shall be given a postweld heat treatment to ensure stress relief and continuity of mechanical properties of both weld and parent metal.

Discussion: ISO has indicated [API 610] that “postweld” should be “post-weld”. ASME Pressure vessel code uses the term postweld without the hyphen. Therefore we will not insert the hyphen into postweld.

b) All repairs that are not covered by ASTM specifications shall be subject to the purchaser's approval.

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6.11.4 Welding

6.11.4.1 Welding of piping, pressure-containing parts, rotating parts and other highly stressed parts, weld repairs and any dissimilar-metal welds shall be performed and inspected by operatorsand procedures qualified in accordance with Section VIII, Division l, and Section IX of the ASME Code or another purchaser approved standard such as EN 287 & EN 288 for welding procedures and welder qualification.

Note: Refeer to paragraph XXX for welding requirements when environmental corrodents are present.

Discussion: The default is the ASME code. Welding in ASME B 31.1 the piping code, refers to the ASME code for weld procedures and qualifications.

Discussion: Ensures proper qualification of both procedures and personnel.

6.11.4.2 Unless otherwise specified, other welding, such as welding on baseplates, nonpressure ducting, lagging, and control panels, shall be performed by welders qualified in accordance with AWS D1.1 or Section IX of the ASME Code or other purchaser approved welding standard. [API 614]

Discussion: Requires all non-pressure welds to be covered by a structural code unless otherwise specified. We want to provide a default and 610 defaults to this one standard. ”or other purchaser approved welding standard” allows the purchaser to approve other standards i.e. Canadian or other. Section IX is more stringent than AWS D1.1 and if a welder is qualified to Section IX he should be qualified to weld a base plate.

6.11.4.3 The vendor shall be responsible for the review of all repairs and repair welds to ensure that they are properly heat treated and nondestructively examined for soundness and compliance with the applicable qualified procedures (see 6.11.1.12). Repair welds shall be nondestructively tested by the same method used to detect the original flaw, however, the minimum level of inspection after the repair shall be by the magnetic particle method in accordance with 8.2.2.4 for magnetic material and by the liquid penetrant method in accordance with 8.2.2.5 for nonmagnetic material. Unless otherwise specified, procedures for major repairs shall be subject to review by the purchaser before any repair is made.

Discussion: Makes the vendor responsible for assuring that repairs are properly heat treated and nondestructively examined by the same method as originally used to detect the repair.

6.11.4.4 Pressure-containing casings made from wrought materials or combinations of wrought and cast materials shall conform to the conditions specified in 6.11.4.4.1 through 6.11.4.4.4.

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Discussion: Requires NDE of pressure containing casing welds to be examined to ensure their integrity.

6.11.4.4.1 Before welding, plate edges shall be examined by the magnetic particle method to confirm the absence of laminations.

Discussion: Previous paragraph required plate edges to be inspected by magnetic particle examination as required by ASME Section VIII, Division 1,UG-93(d)(3), & “internationally recognized standards”. As indicated by Davis Salles , all internaltionally recognized pressure vesssel codes do not have this requirement. Therefore the paragraph was revises to default to the Mag particle inspection and not reference any Pressure vessel code. If ASME is referenced, one may be tempted to add the “Internatinalized recognized code” phrase” which could result in a conflict witin the paragraph.

6.11.4.4.2 Accessible surfaces of welds shall be inspected by magnetic particle or liquid penetrant examination after back chipping or gouging and again after post-weld heat treatment. If specified. the quality control of welds that will be inaccessible on completion of the fabrication shall be agreed on by the purchaser and vendor prior to fabrication.

Discussion: Requires NDE after back chipping or back gouging to assure complete removal of defects before completion of welding. For welds in pressure containing components, typical NDE inspections include root passes and final welds before and after PWHT. For welds in non-pressure containing parts, the final weld before and after PWHT is typically inspected.

There is sometimes concern about the inspection of non-accessible welds, particularly if they are critical joints such as the longitudinal weld of a reciprocating compressor cylinder bore.

6.11.4.4.3 Pressure-containing welds, including welds of the case to axial- and radial-joint flanges, shall be full-penetration welds.

Discussion: This assures that the full strength of the component will be developed in the attachment weld.

6.11.4.4.4 Casings and cylinders fabricated from materials that, according to internationally recognized standards such as Section VIII, Division l, of the ASME Code or other internationally recognized standard as approved by the purchaser. require post-weld heat treatment, shall be heat treated regardless of thickness.

Discussion: This requirement applies specifically to welds used to fabricate casings and cylinders. PWHT is required for these welds regardless of the thickness of the part.

6.11.4.4.5 If specified, in addition to the requirements of 6.11.4.1, specific welds shall be subjected to 100% radiography, magnetic particle inspection, or liquid penetrant inspection.

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6.11.4.6 Connections welded to pressure casings and cylinders shall be installed as specified in a) through d). [2.4.2] Numbering changed to eliminate hanging paragraph

a) If specified, proposed connection designs shall be submitted for approval before fabrication. The drawings shall show weld designs, size, materials, and pre and post-weld heat treatments.

Discussion: Provides the option to the purchaser for approving important welding details, welding procedures. and heat treatment before the start of fabrication.

b) All welds shall be heat treated in accordance with Section VIII, Division 1, Sections UW-10 and UW- 40, of the ASME Code.

Discussion: For connections welded to pressure casings and cylinders, the requirement for PWHT depends on thickness. Deleted “internationally recognized standards” since these may not require PWHT which is required.

c) Post-weld heat treatment, when required, shall be carried out after all welds, including piping welds, have been completed.

Discussion: This requires that PWHT should be carried out when all components have been welded to the pressure casing or cylinder.

d) Auxiliary piping welded to alloy steel casings and cylinders shall be of a material with the same nominal properties as the casing or cylinder material or shall be of low carbon austenitic stainless steel. Other materials compatible with the casing or cylinder material and intended service may be used with the purchaser's approval.

Note Low carbon austenitic stainless steel is identified by the letter L after the numeritical designation such as 304L or 316 L. ( David Sales ISO)

Discussion: Other materials may include chromium-molybdenum alloys and 12-percent chrome steels, for instance. For high temperature refinery services for example a minimum alloy content of 5 Cr-1/2 Mo is generally needed in service where 12 Cr is specified. In certain situations, higher alloy pipe may be needed.

6.11.5 Low Temperature Service

6.11.5.1 The purchaser shall specify the minimum design metal temperature and concurrent pressure used to establish impact test and other material requirements.Note: Normally, this will be the lower of the minimum surrounding ambient temperature or minimum fluid pumping temperature; however, the purchaser can specify a minimum design metal temperature based on properties of the pumped fluid such as autorefrigeration at reduced pressures.

Discussion: “concurrent pressure” was added on the recommendation of API 617 TF to clarify the conditions for minimum design metal pressure.

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6.11.5.2 To avoid brittle failures, materials and construction for low temperature service shall be suitable for the minimum design metal temperature. The purchaser and the vendor shall agree upon the minimum design metal temperature and any special precautions necessary with regard to conditions that may occur during operation, maintenance, transportation, erection, commissioning and testing. Care shall be taken in the selection of fabrication methods, welding procedures, and materials for vendor furnished steel pressure retaining parts that can be subject to temperatures below the ductile-brittle transition temperature. The published design-allowable stresses for materials manufactured in accordance with internationally recognized standards such as the ASME Code and ANSI standards or other internationally recognized standard as approved by the purchaser. are based on minimum tensile properties. Some standards do not differentiate between rimmed, semikilled, fully killed, hot-rolled, and normalized material, nor do they take into account whether materials were produced under fine- or course-grain practices all of which can affect material ductility . The vendor shall exercise caution in the selection of materials intended for services between –30 °C (–20 °F) and 40 °C (100 °F).

Discussion: In general. ferritic steels (such as carbon steel and low alloy steel containing chrome and moly) and martensitic steels (such as 12% chrome) can have ductile-to-brittle transition temperatures as high as 40 °C (100 °F). The ductile-to-brittle transition temperature is affected by such items as steel manufacturing process heat treatment. and minor changes in alloy content. None of these are readily apparent to the owner.

Ductile-to-brittle transition temperatures are determined by impact testing. Common material properties such as hardness and tensile strength are not necessarily indicators of a material's toughness.

Weld heat affected zones cannot be easily measured by Charpy V-notch impact toughness tests.

Proper alloy selection, fabrication, and welding procedures are generally the best way to ensure adequate toughness.

6.11.5.3 All carbon and low alloy steel pressure containing components including nozzles, flanges, and weldments shall be impact tested in accordance with the requirements of Section VIII, Division 1, Sections UCS-65 through 68, of the ASME Code or purchasers approved equivalent standard. High-alloy steels shall be tested in accordance with Section VIII, Division l, Section UHA-51, of the ASME Code or purchasers approved equivalent standard. For materials and thicknesses not covered by Section VIII, Division l of the ASME Code or equivalent standards, the purchaser shall specify requirements. Impact testing of a material may not be required depending on the minimum design metal temperature, thermal, mechanical and cyclic loading and the governing thickness. Refer to requirements of Section VIII,Division l, Section UG-20F of the ASME Code, for example. [Note moved to paragraph since it contains requirements and “may”.

6.11.5.4 Governing thickness used to determine impact testing requirements shall be the greater of the following:

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a. The nominal thickness of the largest butt welded joint.b. The largest nominal section for pressure containment, excluding:

1. Structural support sections such as feet or lugs.2. Sections with increased thickness required for rigidity to mitigate shaft deflection.3. Structural sections required for attachment or inclusion of mechanical features such as jackets or seal chambers.

c. One fourth of the nominal flange thickness, including parting flange thickness for axially split casings (in recognition that the predominant flange stress is not a membrane stress.)

The results of the impact testing shall meet the minimum impact energy requirements of Section VIII, Division l, Section UG-84, of the ASME Code or equivalent standard.

Discussion: Selection of materials which do not require impact testing is usually' preferable to using materials which necessitate impact testing. Some codes such as ASME may not require impact tests under certain specific conditions.

6.12 NAMEPLATES AND ROTATION ARROWS

6.12.1 A nameplate shall be securely attached at a readily visible location on the equipment and on any major piece of auxiliary equipment.

Discussion: The nameplate attachment must withstand the normal wear and tear that occurs during handling, installation, and maintenance of equipment. Nameplates provide a back-up source of important equipment information. See 6.12.3.

6.12.2 Rotation arrows shall be cast-in or attached to each major item of rotating equipment at a readily visible location.

Discussion: Rotation arrow's permit easy field verification of correct equipment rotational direction.

6.12.3 Nameplates and rotation arrows (if attached) shall be of austenitic stainless steel or nickel-copper (UNS N04400) alloy. Attachment pins shall be of the same material. Welding to attach the nameplate to the casing is not permitted.

Discussion: Corrosion - resistant materials help nameplates and arrow's withstand corrosive plant environments. Welding introduces unnecessary uncertainties about the effects of intense local heating of components such as pressure casings. Nameplate data provides permanent and easily found information useful when other sources such as paper and electronic files are unavailable or of questionable accuracy.

6.12.4 The following data (where relevant) shall be clearly stamped or engraved on the nameplate:a. Vendor's nameb. Serial numberc. Size, type and model

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d. Rated capacitye. Purchaser item number or other reference

The purchaser shall specify whether SI or customary units are to be shown.Note to TF Chairmen: Data listed on the machine's nameplate should be amended for the particular class of equipment under consideration. Other nameplate data can include:a. Maximum continuous speedb. Maximum allowable casing working pressurec. Maximum and minimum allowable temperature (617) d. Critical speeds (within the operating range and die first one above)e. Hydrostatic test pressure (617)

Note: Lateral critical speeds determined from running tests shall be stamped on the nameplate followed by the word “TESTS.” Critical speeds predicted by calculation up to and including the first critical speed above trip speed and not identifiable by test shall be stamped on the nameplate followed by the abbreviation “CALC.”

6.12.5 Where the speeds require adjustment as the result of performance testing, the nameplate shall reflect this value. Rated power on the nameplate can be the calculated value provided it is within allowable tolerance. (616)

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