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ASME B31.3 Process Piping Course 3. Materials
BECHTENGINEERING COMPANY, INC. Materials - 1
ASME B31.3 Process Piping
Charles Becht IV, PhD, PE
Don Frikken, PE
Instructors
BECHTENGINEERING COMPANY, INC. Materials - 2
1. Establish applicable system standard(s)2. Establish design conditions3. Make overall piping material decisions
Pressure Class
Reliability
Materials of construction
4. Fine tune piping material decisions Materials
Determine wall thicknesses
Valves
5. Establish preliminary piping system layout & support
configuration6. Perform flexibility analysis7. Finalize layout and bill of materials8. Fabricate and install9. Examine and test
Piping Development Process
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3. Materials
Strength of Materials
Bases for Design Stresses
B31.3 Material Requirements
Listed and Unlisted Materials
Temperature Limits
Toughness Requirements
Fluid Service Requirements
Deterioration in Service
BECHTENGINEERING COMPANY, INC. Materials - 4
The Material in This Section isAddressed by B31.3 in:
Chapter II - Design
Chapter III - Materials
Appendix A - Allowable Stresses & QualityFactors Metals
Appendix F - Precautionary Considerations
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Strength of Materials
StressStrain
Stress-Strain Diagram Elastic Modulus
Yield Strength
Ultimate Strength
Creep
Fatigue
Brittle versus Ductile Behavior
BECHTENGINEERING COMPANY, INC. Materials - 6
Strength of MaterialsStress (S): force (F) divided by area (A)
over which force acts, pounds force/inch2
(psi), Pascals (Newtons/meter2)
Strain (): change in length (L) divided
by the original length (L)
F
L L
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Strength of Materials
Strain
Stress
E = Elastic Modulus = Stress/Strain
SY = Yield Strength
ST = Tensile Strength
Typical Carbon Steel
BECHTENGINEERING COMPANY, INC. Materials - 8
Strength of Materials
ST = Tensile Strength
Typical Stainless Steel Strain
Stress
SY = Yield Strength
0.2% offset
Proportional Limit
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Strength of Materials
Creep: progressive permanentdeformation of material subjected toconstant stress, AKA time dependentbehavior. Creep is of concern for
Carbon steels above ~700F (~370C)
Stainless steels above ~950F (~510C)
Aluminum alloys above ~300F (~150C)
BECHTENGINEERING COMPANY, INC. Materials - 10
Strength of Materials
Time
Strain
Primary Secondary Tertiary
Rupture
Creep Rate (strain/unit time)
Typical Creep Curve
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Strength of Materials
Minimum Stress to Rupture, 316 SS
Fig I-14.6B, ASME B&PV Code, Section III, Division 1 - NH
BECHTENGINEERING COMPANY, INC. Materials - 12
Strength of Materials
Stress
Number of Cycles
Fatigue failure: a failure which results from arepetitive load lower than that required to causefailure on a single application
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Strength of Materials
Brittle failure:
Ductile deformation:
BECHTENGINEERING COMPANY, INC. Materials - 14
Strength of MaterialsBrittle failure:
Ductile failure:
Strain
Stress
Toughness
Strain
Stress
Toughness
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Strength of Materials
Measuring Toughnessusing a Charpy impacttest H1
Charpy Impact Test
Cv = W(H1 - H2)
= Energy Absorbed
H2
H1 -H2W
Pendulum
Specimens tested at 40, 100 and 212F(4, 38 and 100C)
BECHTENGINEERING COMPANY, INC. Materials - 16
Strength of Materials
Ductile to Brittle Transition for a Carbon Steel
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Bases for Design Stresses
Most Materials
Bolting
Gray Iron
Malleable Iron
BECHTENGINEERING COMPANY, INC. Materials - 18
Bases for Design StressesMost Materials (materials other than grayiron, malleable iron and bolting) below thecreep range, the lowest of (302.3.2)
1/3 of specified minimum tensile strength (ST)
1/3 of tensile strength at temperature
2/3 of specified minimum yield strength (SY)
2/3 of yield strength at temperature; exceptfor austenitic stainless steels and nickelalloys with similar behavior, 90% of yieldstrength at temperature
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Bases for Design Stresses
Most Materials additional bases in thecreep range, the lowest of (302.3.2)
100% of the average stress for a creep rateof 0.01% per 1000 hours
67% of the average stress for rupture at theend of 100,000 hours
80% of the minimum stress for rupture at theend of 100,000 hours
BECHTENGINEERING COMPANY, INC. Materials - 20
Bases for Design StressesASTM A106 Grade B Carbon Steel (US Customary Units)
0.00
5.00
10.00
15.00
20.00
25.00
0 200 400 600 800 1000
Temperature, F
Stress,
ksi
2/3 of Yield
1/3 of Tensile
Allowable
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Bases for Design Stresses
ASTM A106 Grade B Carbon Steel (Metric Units)
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
0 100 200 300 400 500
Temperature, C
Stress,
MPa
2/3 Yield
1/3 Tensile
Allowable
BECHTENGINEERING COMPANY, INC. Materials - 22
Bases for Design StressesASTM A312 Gr TP316 Stainless Steel (US Customary Units)
0.00
5.00
10.00
15.00
20.00
25.00
30.00
0 200 400 600 800 1000
Temperature, F
Stress,
ksi 2/3 Yield
90% Yield
1/3 Tensile
Allowable
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Bases for Design Stresses
ASTM A312 Gr TP316 Stainless Steel (Metric Units)
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
200.0
0 100 200 300 400 500
Temperature, C
Stress,
MPa
2/3 Yield
90% Yield
1/3 Ultimate
Allowable
BECHTENGINEERING COMPANY, INC. Materials - 24
Bases for Design StressesAdditional Notes
For structural grade materials, design
stresses are 0.92 times the value determinedfor most materials (302.3.2)
Stress values above 2/3 SY are notrecommended for flanged joints and othercomponents in which slight deformation can
cause leakage or malfunction (302.3.2)
Design stresses for temperatures below the
minimum are the same as at the minimum
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Bases for Design Stresses
Bolting below the creep range, the lowestof (302.3.2)
1/4 of specified minimum tensile strength(ST); if properties are enhanced by heattreatment or strain hardening, 1/5 ST
1/4 of tensile strength at temperature
2/3 of specified minimum yield strength (SY);if properties are enhanced by heat treatment
or strain hardening, 1/4 SY 2/3 of yield strength at temperature
BECHTENGINEERING COMPANY, INC. Materials - 26
Bases for Design StressesBolting additional bases in the creeprange, the lowest of (302.3.2)
100% of the average stress for a creep rateof 0.01% per 1000 hours
67% of the average stress for rupture at theend of 100,000 hours
80% of the minimum stress for rupture at the
end of 100,000 hours
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Bases for Design Stresses
Gray Iron the lowest of (302.3.2)
1/10 of specified minimum tensile strength(ST)
1/10 of tensile strength at temperature
BECHTENGINEERING COMPANY, INC. Materials - 28
Bases for Design StressesMalleable Iron the lowest of (302.3.2)
1/5 of specified minimum tensile strength (ST)
1/5 of tensile strength at temperature
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B31.3 Material Requirements
Listed and Unlisted Materials
Temperature Limits
Impact Test Methods & Acceptance
Toughness Requirements
Fluid Service Requirements
BECHTENGINEERING COMPANY, INC. Materials - 30
Listed and Unlisted Materials Listed Material: a material that conforms
to a specification in Appendix A or to astandard in Table 326.1 may be used(323.1.1)
Unlisted Material: a material that is notso listed may be used under certainconditions (323.1.2)
Unknown Material: may not be used(323.1.3)
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Listed and Unlisted Materials
An unlisted material may be used if(323.1.2)
It conforms to a published specificationcovering chemistry, mechanical properties,method of manufacture, heat treatment, andquality control
Otherwise meets the requirements of theCode
Allowable stresses are determined in
accordance with Code bases, and
Qualified for serviceall temperatures (323.2.3)
BECHTENGINEERING COMPANY, INC. Materials - 32
Temperature LimitsListed materials may be used above themaximum described in the Code if (323.2.1)
There is no prohibition in the Code
The designer verifies serviceability of thematerial, considering the quality of mechanicalproperty data used to determine allowablestresses and resistance of the material to
deleterious effects in the planned fluid service(323.2.4)
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Temperature Limits
Listed materials may be used within thetemperature range described in the Code if(323.2.2)
The base metal, weld deposits and heataffected zone (HAZ) are qualified inaccordance with Column A of Table 323.2.2.
BECHTENGINEERING COMPANY, INC. Materials - 34
Table 323.2.2Requirements for Low Temperature Toughness Tests
Seepag
e21ofthesu
pplemen
t.
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Temperature Limits
Listed materials may be used below theminimum described in the Code if (323.2.2)
There is no prohibition in the Code
The base metal, weld deposits and heataffected zone (HAZ) are qualified inaccordance with Column B of Table 323.2.2.
BECHTENGINEERING COMPANY, INC. Materials - 36
Carbon Steel Lower Temperature Limits Most carbon steels have a letter
designation in the column for minimumtemperature in Appendix A
See page 26 of the supplement
Note Min. Temp. column
Read Appendix A note 7
Read Appendix A note 4 & see page 27 For those that do, the minimum
temperature is defined by Figure 323.2.2A
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Figure 323.2.2AMinimum Temperatures without Impact Testing for Carbon Steel
Seepag
e23oft
hesupp
lement.
BECHTENGINEERING COMPANY, INC. Materials - 38
Carbon Steel Lower Temperature Limits Impact testing is not required down to
-55F (-48C) if stress ratio does notexceed the value defined by Figure323.2.2B
Impact testing is not required down to-155F (-104C) if stress ratio does not
exceed 0.3
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Fig.323.2.2BReduction in Minimum Design Temperature w/o Impact Testing
See page 24 of the supplement.
BECHTENGINEERING COMPANY, INC. Materials - 40
Carbon Steel Lower Temperature LimitsFig.323.2.2B provides a further basis for useof carbon steel without impact testing. Ifused: Hydrotesting is required
Safeguarding is required for components withwall thicknesses greater than in. (13 mm)
Stress Ratiois the largest of
Nominal pressure stress / S Pressure / pressure rating
Combined longitudinal stress / S
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Carbon Steel Lower Temperature Limits
Design Pressure: 650 psig(45 bar)
Design Temperature:735F (390C).
Pipe material is ASTM A53Gr B seamless.
What options are availableto deal with expected
ambient temperaturesdown to -30F (-34C)? 0.971.000
(25.40)
30
(750)
0.860.500
(12.70)
12
(300)
0.740.237
(6.02)
4
(100)
0.710.178(4.52)
1
(25)
StressRatio
NominalWTin (mm)
NPS
(DN)
BECHTENGINEERING COMPANY, INC. Materials - 42
Impact Test Methods and Acceptance Impact testing is done in accordance with
ASTM A370
Each set of impact test specimensconsists of 3 bars
Impact test temperature:
For full size (10 mm square) Charpy V-notch
specimens, the design minimum temperature For subsize specimens smaller than 8 mm,
below the design minimum temperature[323.3]
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Impact Test Methods and Acceptance
Acceptance criteria Most steels, based on energy absorbed per
Table 323.3.5
For high strength steels, including bolting,based on minimum lateral expansion of0.015 in. (0.38 mm) opposite the notch
Retest of a second set of three specimensis permitted under certain conditions.
[323.3]
BECHTENGINEERING COMPANY, INC. Materials - 44
Fluid Service Requirements (323.4.2)
Ductile Iron
generally limited to temperature range of
-20F to 650F (-29C to 343C) and B16.42ratings
welding is not permitted
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Fluid Service Requirements (323.4.2)
Other Cast Irons may not be used under severe cyclic
conditions
may be used for other services ifsafeguarded for heat, thermal andmechanical shock, and abuse
may not be used in above ground flammableservice above 300F (149C) or above 400
psi (2760 kPa)
BECHTENGINEERING COMPANY, INC. Materials - 46
Fluid Service Requirements (323.4.2) Gray Iron
may not be used in flammable service above150 psi (1035 kPa)
may not be used in other services above 400psi (2760 kPa)
Malleable Iron may not be used outside -20F to 650F
(-29C to 343C) High Silicon Iron
may not be used in flammable service
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Fluid Service Requirements (323.4.2)
Aluminum Castings the designer is responsible for establishing
design stresses and ratings if thermal cutting isused
Lead, Tin & their Alloys
may not be used with flammable fluids
Clad Materials
cladding may be considered to be part of thethickness of components under certainconditions
BECHTENGINEERING COMPANY, INC. Materials - 48
Deterioration in Service Selection of material to resist deterioration
in service is not within the scope of theCode. (323.5)
Recommendations for material selectionare presented in Appendix F.
General considerations
Specific material considerations
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Deterioration in Service
Types of Damage Mechanisms Loss of metal
Stress Corrosion Cracking
Metallurgical and Environmental Degradation
BECHTENGINEERING COMPANY, INC. Materials - 50
Loss of MetalLoss of metal can be
General
Localized
depending on thephysical conditions andthe specific mechanism.
A Rainbow of Rust Colors
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Loss of Metal
Mechanisms include Galvanic corrosion
Atmospheric corrosion
Corrosion under insulation
Crevice
BECHTENGINEERING COMPANY, INC. Materials - 52
Galvanic CorrosionElectrochemical process
The anode is the site atwhich the metal iscorroded
The electrolyte is thecorrosive medium
The cathode forms theother electrode in the celland is not consumed inthe corrosion process
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Galvanic corrosion
GALVANIC SERIES INSEA WATER
CORRODED END (Anodic)MagnesiumZinc
AluminumCadmiumMild SteelCast IronStainless Steels 18/8 (Active)LeadTinNickel (Active)BrassCopperAluminum BronzeCupro nickelSilver SoldersNickel (Passive)Stainless Steel 18/8 (Passive)
Silver
TitaniumGraphiteGoldPlatinumPROTECTED END (Cathodic)
Carbon Steel Nipple Threaded into a
Stainless Steel Water Tank
BECHTENGINEERING COMPANY, INC. Materials - 54
Galvanic corrosionMaterials Affected
All metals, with the exception of most noble metals, are affected.
Critical Factors
For galvanic corrosion, three conditions must be met:
Presence of an electrolyte
Two different metals or alloys in contact with the electrolyte
An electrical connection between the anode and the cathode
The relative exposed surface areas between anodic material andthe cathodic material has a significant affect
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Galvanic corrosion
Prevention The best method for prevention/mitigation is through good design.
The more noble material may need to be coated. If the activematerial were coated, a large cathode to anode area can accelerate
corrosion of the anode at any breaks in the coating.
Improvements in Materials of Construction
Galvanic corrosion is the principle used in galvanized steel, wherethe zinc corrodes preferentially to protect the underlying carbonsteel.
If there is a break in the galvanized coating, a large anode to smallcathode area prevents accelerated corrosion of the steel.
This anode-to-cathode relationship reverses at water temperaturesover about 150F (65C).
BECHTENGINEERING COMPANY, INC. Materials - 56
Atmospheric CorrosionAtmospheric
corrosion is a formof galvaniccorrosion.
Different parts ofthe surface of themetal act asanodes and
cathodes.Variations in the
electrolyte alsocontribute.
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Atmospheric Corrosion
Materials Affected Carbon and low alloy steels are most affected.
Critical Factors Marine environments can be very corrosive (20 mpy) as are
industrial environments that contain acids or sulfur compounds thatcan form acids (5-10 mpy).
Inland locations exposed to a moderate amount of precipitation orhumidity are considered moderately corrosive environments (1-3mpy).
Dry rural environments usually have very low corrosion rates (
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Corrosion Under Insulation
CUI is a form ofgalvanic corrosion.
Different parts of thesurface of the metalact as anodes andcathodes.
CUI is caused bythe presence of an
electrolyte, usuallyrain water.
BECHTENGINEERING COMPANY, INC. Materials - 60
Corrosion Under InsulationMaterials Affected Carbon and low alloy steels are affected by thinning
Austenitic stainless steels are affected by SCC and biological attack
Critical Factors Poor installations that allow water to become trapped.
Corrosion rates increase with increasing metal temperature up tothe point where the water evaporates quickly.
Corrosion becomes more severe at metal temperatures betweenthe boiling point 212F (100C) and 250F (120C), where water isless likely to vaporize and insulation stays wet longer.
In areas where significant amounts of moisture are present, the
upper temperature range where CUI may occur can be extendedsignificantly above 250F (120C).
Insulating materials that hold moisture (wick) are more of aproblem.
Cyclic thermal operation can increase corrosion.
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Corrosion Under Insulation
Prevention Maintaining the insulation
sealing/vapor barriers toprevent moisture ingress
Using appropriate coatings
Selection of insulatingmaterials that will hold lesswater against the pipe wall
Using low chloride insulationwith austenitic stainless steels
Not insulating where heatconservation is not asimportant
Improvements in Materials
of Construction Generally not an economical
approach.
BECHTENGINEERING COMPANY, INC. Materials - 62
Corrosion Under Insulation
Near miss 230 psig (16 bar) propane line Remaining wall as little as 1 mm thick
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Crevice Corrosion
Localized form of corrosionStagnant solution in crevices such as
Under gaskets Under fasteners Threaded joints Socket welded joints
initiated by changes in local chemistry within thecrevice Depletion of inhibitor in the crevice Depletion of oxygen in the crevice
A shift to acid conditions in the crevice Build-up of aggressive ion species (e.g. chloride) in
the crevice
BECHTENGINEERING COMPANY, INC. Materials - 64
Crevice Corrosion
Initially, the level of
soluble oxygen and isthe same everywhere.
Oxygen consumed by
normal uniformcorrosion is very soon
depleted in thecrevice.
Corrosion products
create acidicenvironment and further
seal the creviceenvironment.
Depletion of Oxygen in the Crevice
http://www.corrosion-doctors.org/
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Crevice Corrosion
Materials Affected Carbon and low alloy steels are affected by loss of metal
Austenitic stainless steels are affected by SCC and biological attack
Critical Factors
Aggressive ions like chlorides may be present in the electrolyte.
Corrosion rates increase with increasing metal temperature.
Prevention
Avoiding crevices whenever possible; e.g. using butt weldinginstead of socket welding and threaded joints.
Improvements in Materials of Construction
Generally not an economical approach.
BECHTENGINEERING COMPANY, INC. Materials - 66
Stress Corrosion CrackingRequires Stress
o Residual from Weldingo Design
Right Material Right Environment
o Chemical, pH
o Concentrationo Temperature
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Stress Corrosion CrackingMechanisms include
Chloride stress corrosion cracking (ClSCC)
Hydrogen-induced cracking (HIC)
BECHTENGINEERING COMPANY, INC. Materials - 68
Chloride Stress Corrosion Cracking
Requires thepresence of:
Chlorides insufficientconcentration
High enough stress
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Chloride Stress Corrosion Cracking
Materials Affected All 300 Series SS are highly susceptible.
Duplex stainless steels are more resistant.
Critical Factors Increasing temperatures increase the susceptibility to cracking.
Cracking usually occurs at metal temperatures above about 140F(60C), although exceptions can be found at lower temperatures.
Increasing levels of chloride increase the likelihood of cracking. Nopractical lower limit for chlorides exists because there is always apotential for chlorides to concentrate.
SCC usually occurs at pH values above 2. At lower pH values,uniform corrosion generally predominates. SCC tendencydecreases toward the alkaline pH region.
Stress may be applied or residual. Highly stressed or cold worked
components, such as expansion bellows, are highly susceptible tocracking.
BECHTENGINEERING COMPANY, INC. Materials - 70
Chloride Stress Corrosion CrackingPrevention When hydrotesting, use low chloride content water and dry out
thoroughly and quickly.
Properly applied coatings under insulation.
Avoid designs that allow stagnant regions where chlorides canconcentrate or deposit.
Improvements in Materials of Construction Nickel content of the alloy has a major affect on resistance. The
greatest susceptibility is at a nickel content of 8% to 12%. Alloyswith nickel contents above 35% are highly resistant and alloysabove 45% are nearly immune.
Low-nickel stainless steels, such as the duplex (ferrite-austenite)stainless steels, have improved resistance over the 300 Series SSbut are not immune.
Carbon steels, low alloy steels and 400 Series SS are notsusceptible to CISCC .
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Hydrogen-Induced Cracking (HIC)
Hydrogen Blisters Hydrogen blisters are surfacebulges on the surface of a pipe.
The blister results from hydrogenatoms that diffuse into the steel,and collect at a discontinuity.
The hydrogen atoms combine toform hydrogen molecules that aretoo large to diffuse.
The gas pressure builds to thepoint where local deformationoccurs
A primary source for the H atomsis from the sulfide corrosionprocess.
BECHTENGINEERING COMPANY, INC. Materials - 72
Hydrogen-Induced Cracking (HIC) Neighboring or adjacent blisters that are at slightly
different depths (planes) can develop cracks that linkthem together.
This is hydrogen-induced cracking. Interconnecting cracks often have a stair step
appearance, and so HIC is sometimes referred to as"stepwise cracking.
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Hydrogen-Induced Cracking (HIC) When HIC is assisted by high stresses in the piping, it
is called Stress Oriented Hydrogen Induced Cracking(SOHIC).
The SOHIC cracks usually appear in the base metaladjacent to the weld heat affected zones where theyinitiate from HIC damage.
SOHlC is potentially more dangerous because it resultsin a through-thickness crack that is perpendicular to thesurface.
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Hydrogen-Induced Cracking (HIC)Critical Factors All of these damage mechanisms are related to the absorption and
permeation of hydrogen in steels.
Hydrogen permeation or diffusion rates have been found to beminimal at pH 7 and increase at both higher and lower pH's. Thepresence of hydrogen cyanide (HCN) in the water phasesignificantly increases permeation in alkaline (high pH) sour water.
Hydrogen permeation increases with increasing H2S partialpressure due to a concurrent increase in the H2S concentration inthe water phase.
Blistering, HIC, and SOHlC damage have been found to occur
between ambient and 300F (150C) or higher. HIC is often found in so-called "dirty" steels with high levels of
inclusions or other internal discontinuities from the steel-makingprocess.
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Hydrogen-Induced Cracking (HIC)
Materials Affected Carbon and low alloy steels are affected.
High alloy steels are not affected.
Critical Factors (cont.) HIC damage can occur throughout the refinery wherever there is a
wet H2S environment present.
Increasing concentration of ammonium bisulfide above 2%increases the potential for HIC.
Cyanides significantly increase the probability and severity of HICdamage.
Prevention Coatings that protect the surface of the steel from the
wet H2S environment can prevent damage.
Process changes that affect the pH of the water phaseor cyanide concentration can help to reduce damage.
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Metallurgical and Environmental DamageCauses degradation and loss of material
properties
Involve some form of mechanical and/orphysical property deterioration of thematerial due to exposure to a processenvironment
Causes of metallurgical and environmentaldegradation failures are varied
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Mechanisms include Graphitization
Decarburization
High Temperature Hydrogen Attack(HTHA)
Metallurgical and Environmental Damage
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GraphitizationGraphitization is the decomposition of
carbide phases in steels after long-termoperation in the 800F to 1100F (430C to590C) range into graphite nodules.
The decomposition causes a loss instrength, ductility, and creep resistance.
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Graphitization
Materials Affected Carbon and 0.5Mo steels are susceptible to graphitization.
Critical Factors Graphitization is not commonly observed.
What causes some steels to graphitize while others are resistant isnot well understood.
Severe heat affected zone graphitization can develop in as little as5 years at service temperatures above 1000F (540C).
Very slight graphitization would be expected to be found after 30 to40 years at 850F (450C).
Prevention Graphitization can be prevented by using chromium containing low
alloy steels for long-term operation above 800F (427C).
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DecarburizationA condition where steel looses
strength due the removal ofcarbon and carbides leaving onlyan iron matrix.
Decarburization occurs duringexposure to high temperaturessuch as
during heat treatment
from exposure to fires
from high temperature service in agas environment.
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Decarburization
Materials Affected Carbon and low alloy steels are affected.
Critical Factors The material must be exposed to a gas phase that has a low carbon
activity so that carbon in the steel will diffuse to the surface to reactwith gas phase constituents.
The extent and depth of decarburization is a function of thetemperature and exposure time.
Typically, decarburization is shallow, but loss in room temperaturetensile strength and creep strength may occur.
Prevention Decarburization can be controlled by controlling the chemistry of the
gas phase and alloy selection. Alloy steels with chromium and molybdenum form more stable
carbides and are more resistant to decarburization.
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High Temperature Hydrogen Attack High temperature hydrogen attack results from exposure
to hydrogen at elevated temperatures and pressures.
The hydrogen reacts with carbides in steel to formmethane (CH4), which cannot diffuse through the steel.
Methane pressurebuilds up, formingbubbles or cavities,micro fissures andfissures that may
combine to formcracks.
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High Temperature Hydrogen Attack
Materials Affected In order of increasing resistance: carbon steel, C-0.5Mo, Mn-0.5Mo,
1Cr-0.5Mo, 1.25Cr-0.5Mo, 2.25Cr-1Mo, 2.25Cr-1Mo-V, 3Cr-1Mo,5Cr-0.5Mo.
Critical Factors The loss of carbide causes an overall loss in strength.
Failure can occur when the cracks reduce the load carrying abilityof the pressure containing part.
For a specific material, HTHA is dependent on temperature,hydrogen partial pressure, time and stress. Service exposure timeis cumulative.
HTHA is preceded by a period of time when no noticeable changeis detectable by normal inspection techniques.
API RP 941 provides material resistance curves.
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High Temperature Hydrogen AttackAPI RP 941 provides material resistance curves.
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High Temperature Hydrogen Attack
Prevention Use alloy steels with
chromium and molybdenumto increase carbide stability
thereby minimizing methaneformation. Other carbide
stabilizing elements includetungsten and vanadium.
300 Series SS, as well as
5Cr, 9Cr and 12Cr alloys, arenot susceptible to HTHA at
conditions normally seen in
refinery units.HTHA to a Boiler Tube
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High Temperature Hydrogen Attack One employee sustained a minor injury.
NPS 8 carbon steel elbow ruptured after operating for only 3 months. The escaping hydrogen gas from the ruptured elbow quickly ignited.
HTHA to a Boiler Tube
A maintenancecontractor
accidentallyswitched a
carbon steelelbow with an
alloy steelelbow during ascheduled heat
exchangeroverhaul.
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API 571
Graphitization
Softening (Spheroidization)
Temper Embrittlement
Strain Aging
885F Embrittlement
Sigma Phase Embrittlement
Brittle Fracture
Creep / Stress Rupture
Thermal Fatigue
Short Term Overheating -Stress Rupture
Steam Blanketing
Dissimilar Metal Weld (DMW)Cracking
Thermal Shock
Erosion / Erosion-Corrosion
Cavitation
Mechanical Fatigue
Vibration-Induced Fatigue
Refractory Degradation
Reheat Cracking
Galvanic Corrosion
Atmospheric Corrosion
Much of the information presented on deterioration of metals is taken
from API 571 Damage Mechanisms Affecting Fixed Equipment in theRefining Industry API 571 addresses all of the following mechanisms:
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API 571 Corrosion Under Insulation
(CUI)
Cooling Water Corrosion
Boiler Water CondensateCorrosion
CO2 Corrosion
Flue Gas Dew Point Corrosion
Microbiologically InducedCorrosion (MIC)
Soil Corrosion
Caustic Corrosion
Dealloying
Graphitic Corrosion
Oxidation
Sulfidation
Carburization
Decarburization
Metal Dusting
Fuel Ash Corrosion
Nitriding
Chloride Stress CorrosionCracking (CI-SCC)
Corrosion Fatigue
Caustic Stress CorrosionCracking (CausticEmbrittlement)
Ammonia Stress CorrosionCracking
Liquid Metal Embrittlement(LME)
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API 571
Hydrogen Embrittlement (HE) Amine Corrosion
Ammonium Bisulfide Corrosion(Alkaline Sour Water)
Ammonium Chloride Corrosion
Hydrochloric Acid (HCI)Corrosion
High Temp H2/H2S Corrosion
Hydrofluoric (HF) AcidCorrosion
Naphthenic Acid Corrosion(NAC)
Phenol (Carbonic Acid)Corrosion
Phosphoric Acid Corrosion Sour Water Corrosion (Acidic)
Sulfuric Acid Corrosion Polythionic Acid Stress
Corrosion Cracking (PASCC)
Amine Stress CorrosionCracking
Wet H2S Damage
Hydrogen Stress Cracking HF
Carbonate Stress CorrosionCracking
High Temperature HydrogenAttack
Titanium Hydriding