ASME B31.3 Process Piping Course
3. Materials
ASME B31.3 Process Piping
Charles Becht IV, PhD, PE
Don Frikken, PE
Instructors
BECHT ENGINEERING COMPANY, INC.
Materials -
1
Piping Development Process
1. Establish applicable system standard(s)
2. Establish design conditions
3. 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
configuration
6. Perform flexibility analysis
7. Finalize layout and bill of materials
8. Fabricate and install
9. Examine and test
BECHT ENGINEERING COMPANY, INC.
Materials -
2
ASME B31.3 Process Piping Course
3. Materials
3. Materials
ÜStrength of Materials
ÜBases for Design Stresses
ÜB31.3 Material Requirements
̇
̇
̇
̇
Listed and Unlisted Materials
Temperature Limits
Toughness Requirements
Fluid Service Requirements
ÜDeterioration in Service
BECHT ENGINEERING COMPANY, INC.
Materials -
3
The Material in This Section is
Addressed by B31.3 in:
Chapter II - Design
Chapter III - Materials
Appendix A - Allowable Stresses & Quality
Factors – Metals
Appendix F - Precautionary Considerations
BECHT ENGINEERING COMPANY, INC.
Materials -
4
ASME B31.3 Process Piping Course
3. Materials
Strength of Materials
ÜStress
ÜStrain
ÜStress-Strain Diagram
̇ Elastic Modulus
̇ Yield Strength
̇ Ultimate Strength
ÜCreep
ÜFatigue
ÜBrittle versus Ductile Behavior
BECHT ENGINEERING COMPANY, INC.
Materials -
5
Strength of Materials
Stress (S): force (F) divided by area (A)
over which force acts, pounds force/inch2
(psi), Pascals (Newtons/meter2)
Strain (ε): change in length (ΔL) divided
by the original length (L)
F
L
BECHT ENGINEERING COMPANY, INC.
ΔL
Materials -
6
ASME B31.3 Process Piping Course
3. Materials
Stress
Strength of Materials
ST = Tensile Strength
SY = Yield Strength
E = Elastic Modulus = Stress/Strain
Typical Carbon Steel
Strain
BECHT ENGINEERING COMPANY, INC.
Materials -
7
Stress
Strength of Materials
ST = Tensile Strength
SY = Yield Strength
Proportional Limit
0.2% offset
Typical Stainless Steel
BECHT ENGINEERING COMPANY, INC.
Strain
Materials -
8
ASME B31.3 Process Piping Course
3. Materials
Strength of Materials
Creep: progressive permanent
deformation of material subjected to
constant stress, AKA time dependent
behavior. Creep is of concern for
̇ Carbon steels above ~700ºF (~370ºC)
̇ Stainless steels above ~950ºF (~510ºC)
̇ Aluminum alloys above ~300ºF (~150ºC)
BECHT ENGINEERING COMPANY, INC.
Materials -
9
Strain
Strength of Materials
Primary
Secondary
Tertiary
Rupture
Creep Rate (strain/unit time)
Typical Creep Curve
Time
BECHT ENGINEERING COMPANY, INC.
Materials -
10
ASME B31.3 Process Piping Course
3. Materials
Strength of Materials
Minimum Stress to Rupture, 316 SS
Fig I-14.6B, ASME B&PV Code, Section III, Division 1 - NH
BECHT ENGINEERING COMPANY, INC.
Materials -
11
Strength of Materials
Stress
Fatigue failure: a failure which results from a
repetitive load lower than that required to cause
failure on a single application
Number of Cycles
BECHT ENGINEERING COMPANY, INC.
Materials -
12
ASME B31.3 Process Piping Course
3. Materials
Strength of Materials
Brittle failure:
Ductile deformation:
BECHT ENGINEERING COMPANY, INC.
Materials -
13
Materials -
14
Brittle failure:
Stress
Strength of Materials
Toughness
Ductile failure:
Stress
Strain
Toughness
BECHT ENGINEERING COMPANY, INC.
Strain
ASME B31.3 Process Piping Course
3. Materials
Strength of Materials
Measuring Toughness
using a Charpy impact
test
W
H1 -H2
Pendulum
H1
H2
Charpy Impact Test
Cv = W(H1 - H2)
Specimens tested at 40, 100 and 212ºF
(4, 38 and 100ºC)
= Energy Absorbed
BECHT ENGINEERING COMPANY, INC.
Materials -
15
Strength of Materials
Ductile to Brittle Transition for a Carbon Steel
BECHT ENGINEERING COMPANY, INC.
Materials - 16
ASME B31.3 Process Piping Course
Ü
Ü
Ü
Ü
3. Materials
Bases for Design Stresses
Most Materials
Bolting
Gray Iron
Malleable Iron
BECHT ENGINEERING COMPANY, INC.
Materials -
17
Bases for Design Stresses
Most Materials – (materials other than gray
iron, malleable iron and bolting) below the
creep 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; except
for austenitic stainless steels and nickel
alloys with similar behavior, 90% of yield
strength at temperature
BECHT ENGINEERING COMPANY, INC.
Materials -
18
ASME B31.3 Process Piping Course
3. Materials
Bases for Design Stresses
Most Materials – additional bases in the
creep range, the lowest of (302.3.2)
̇ 100% of the average stress for a creep rate
of 0.01% per 1000 hours
̇ 67% of the average stress for rupture at the
end of 100,000 hours
̇ 80% of the minimum stress for rupture at the
end of 100,000 hours
BECHT ENGINEERING COMPANY, INC.
Materials -
19
Bases for Design Stresses
ASTM A106 Grade B Carbon Steel (US Customary Units)
25.00
Stress, ksi
20.00
15.00
2/3 of Yield
1/3 of Tensile
10.00
Allowable
5.00
0.00
0
200
400
600
800
1000
Temperature, F
BECHT ENGINEERING COMPANY, INC.
Materials -
20
ASME B31.3 Process Piping Course
3. Materials
Bases for Design Stresses
ASTM A106 Grade B Carbon Steel (Metric Units)
180.0
160.0
Stress, MPa
140.0
120.0
2/3 Yield
100.0
1/3 Tensile
80.0
Allowable
60.0
40.0
20.0
0.0
0
100
200
300
400
500
Temperature, C
BECHT ENGINEERING COMPANY, INC.
Materials -
21
Bases for Design Stresses
ASTM A312 Gr TP316 Stainless Steel (US Customary Units)
30.00
Stress, ksi
25.00
20.00
2/3 Yield
90% Yield
1/3 Tensile
Allowable
15.00
10.00
5.00
0.00
0
200
400
600
800
1000
Temperature, F
BECHT ENGINEERING COMPANY, INC.
Materials -
22
ASME B31.3 Process Piping Course
3. Materials
Bases for Design Stresses
ASTM A312 Gr TP316 Stainless Steel (Metric Units)
200.0
180.0
Stress, MPa
160.0
140.0
120.0
2/3 Yield
100.0
90% Yield
80.0
1/3 Ultimate
60.0
Allowable
40.0
20.0
0.0
0
100
200
300
400
500
Temperature, C
BECHT ENGINEERING COMPANY, INC.
Materials -
23
Bases for Design Stresses
Additional Notes
̇ For structural grade materials, design
stresses are 0.92 times the value determined
for most materials (302.3.2)
̇ Stress values above 2/3 SY are not
recommended for flanged joints and other
components 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
BECHT ENGINEERING COMPANY, INC.
Materials -
24
ASME B31.3 Process Piping Course
3. Materials
Bases for Design Stresses
Bolting – below the creep range, the lowest
of (302.3.2)
̇ 1/4 of specified minimum tensile strength
(ST); if properties are enhanced by heat
treatment 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
BECHT ENGINEERING COMPANY, INC.
Materials -
25
Bases for Design Stresses
Bolting – additional bases in the creep
range, the lowest of (302.3.2)
̇ 100% of the average stress for a creep rate
of 0.01% per 1000 hours
̇ 67% of the average stress for rupture at the
end of 100,000 hours
̇ 80% of the minimum stress for rupture at the
end of 100,000 hours
BECHT ENGINEERING COMPANY, INC.
Materials -
26
ASME B31.3 Process Piping Course
3. Materials
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
BECHT ENGINEERING COMPANY, INC.
Materials -
27
Bases for Design Stresses
Malleable Iron – the lowest of (302.3.2)
̇ 1/5 of specified minimum tensile strength (ST)
̇ 1/5 of tensile strength at temperature
BECHT ENGINEERING COMPANY, INC.
Materials -
28
ASME B31.3 Process Piping Course
3. Materials
B31.3 Material Requirements
ÜListed and Unlisted Materials
ÜTemperature Limits
ÜImpact Test Methods & Acceptance
ÜToughness Requirements
ÜFluid Service Requirements
BECHT ENGINEERING COMPANY, INC.
Materials -
29
Listed and Unlisted Materials
Ü Listed Material: a material that conforms
to a specification in Appendix A or to a
standard in Table 326.1 – may be used
(323.1.1)
Ü Unlisted Material: a material that is not
so listed – may be used under certain
conditions (323.1.2)
Ü Unknown Material: may not be used
(323.1.3)
BECHT ENGINEERING COMPANY, INC.
Materials -
30
ASME B31.3 Process Piping Course
3. Materials
Listed and Unlisted Materials
An unlisted material may be used if (323.1.2)
Ü It conforms to a published specification
covering chemistry, mechanical properties,
method of manufacture, heat treatment, and
quality control
Ü Otherwise meets the requirements of the
Code
Ü Allowable stresses are determined in
accordance with Code bases, and
Ü Qualified for service…all temperatures (323.2.3)
BECHT ENGINEERING COMPANY, INC.
Materials -
31
Temperature Limits
Listed materials may be used above the
maximum described in the Code if (323.2.1)
̇ There is no prohibition in the Code
̇ The designer verifies serviceability of the
material, considering the quality of mechanical
property data used to determine allowable
stresses and resistance of the material to
deleterious effects in the planned fluid service
(323.2.4)
BECHT ENGINEERING COMPANY, INC.
Materials -
32
ASME B31.3 Process Piping Course
3. Materials
Temperature Limits
Listed materials may be used within the
temperature range described in the Code if
(323.2.2)
̇ The base metal, weld deposits and heat
affected zone (HAZ) are qualified in
accordance with Column A of Table 323.2.2.
BECHT ENGINEERING COMPANY, INC.
Materials -
33
Table 323.2.2
Requirements for Low Temperature Toughness Tests
e2
g
a
p
See
1
nt.
e
m
pple
u
s
e
of th
BECHT ENGINEERING COMPANY, INC.
Materials -
34
ASME B31.3 Process Piping Course
3. Materials
Temperature Limits
Listed materials may be used below the
minimum described in the Code if (323.2.2)
̇ There is no prohibition in the Code
̇ The base metal, weld deposits and heat
affected zone (HAZ) are qualified in
accordance with Column B of Table 323.2.2.
BECHT ENGINEERING COMPANY, INC.
Materials -
35
Carbon Steel Lower Temperature Limits
Ü Most carbon steels have a letter
designation in the column for minimum
temperature in Appendix A
Ü See page 26 of the supplement
̇ Note “Min. Temp.” column
̇ Read Appendix A note 7
̇ Read Appendix A note 4 & see page 27
Ü For those that do, the minimum
temperature is defined by Figure 323.2.2A
BECHT ENGINEERING COMPANY, INC.
Materials -
36
ASME B31.3 Process Piping Course
3. Materials
Figure 323.2.2A
Minimum Temperatures without Impact Testing for Carbon Steel
nt.
e
m
pple
u
s
the
f
o
e 23
g
a
p
See
BECHT ENGINEERING COMPANY, INC.
Materials -
37
Carbon Steel Lower Temperature Limits
Ü Impact testing is not required down to
-55ºF (-48ºC) if stress ratio does not
exceed the value defined by Figure
323.2.2B
Ü Impact testing is not required down to
-155ºF (-104ºC) if stress ratio does not
exceed 0.3
BECHT ENGINEERING COMPANY, INC.
Materials -
38
ASME B31.3 Process Piping Course
3. Materials
Fig.323.2.2B
Reduction in Minimum Design Temperature w/o Impact Testing
See page 24 of the supplement.
BECHT ENGINEERING COMPANY, INC.
Materials -
39
Carbon Steel Lower Temperature Limits
Fig.323.2.2B provides a further basis for use
of carbon steel without impact testing. If
used:
̇ Hydrotesting is required
̇ Safeguarding is required for components with
wall thicknesses greater than ½ in. (13 mm)
Stress Ratio is the largest of
̇ Nominal pressure stress / S
̇ Pressure / pressure rating
̇ Combined longitudinal stress / S
BECHT ENGINEERING COMPANY, INC.
Materials -
40
ASME B31.3 Process Piping Course
3. Materials
Carbon Steel Lower Temperature Limits
Design Pressure: 650 psig NPS
(45 bar)
(DN)
Design Temperature:
1
735°F (390°C).
Pipe material is ASTM A53 (25)
Gr B seamless.
4
(100)
What options are available
12
to deal with expected
(300)
ambient temperatures
down to -30°F (-34°C)?
30
(750)
BECHT ENGINEERING COMPANY, INC.
Nominal Stress
WT
Ratio
in (mm)
0.178
(4.52)
0.71
0.237
(6.02)
0.500
(12.70)
1.000
(25.40)
0.74
0.86
0.97
Materials -
41
Impact Test Methods and Acceptance
Ü Impact testing is done in accordance with
ASTM A370
Ü Each set of impact test specimens
consists of 3 bars
Ü 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]
BECHT ENGINEERING COMPANY, INC.
Materials -
42
ASME B31.3 Process Piping Course
3. Materials
Impact Test Methods and Acceptance
Ü Acceptance criteria
̇ Most steels, based on energy absorbed per
Table 323.3.5
̇ For high strength steels, including bolting,
based on minimum lateral expansion of
0.015 in. (0.38 mm) opposite the notch
Ü Retest of a second set of three specimens
is permitted under certain conditions.
[323.3]
BECHT ENGINEERING COMPANY, INC.
Materials -
43
Fluid Service Requirements (323.4.2)
Ü Ductile Iron
̇ generally limited to temperature range of
-20ºF to 650ºF (-29ºC to 343ºC) and B16.42
ratings
̇ welding is not permitted
BECHT ENGINEERING COMPANY, INC.
Materials -
44
ASME B31.3 Process Piping Course
3. Materials
Fluid Service Requirements (323.4.2)
Ü Other Cast Irons
̇ may not be used under severe cyclic
conditions
̇ may be used for other services if
safeguarded for heat, thermal and
mechanical shock, and abuse
̇ may not be used in above ground flammable
service above 300ºF (149ºC) or above 400
psi (2760 kPa)
BECHT ENGINEERING COMPANY, INC.
Materials -
45
Fluid Service Requirements (323.4.2)
Ü Gray Iron
̇ may not be used in flammable service above
150 psi (1035 kPa)
̇ may not be used in other services above 400
psi (2760 kPa)
Ü Malleable Iron
̇ may not be used outside -20ºF to 650ºF
(-29ºC to 343ºC)
Ü High Silicon Iron
̇ may not be used in flammable service
BECHT ENGINEERING COMPANY, INC.
Materials -
46
ASME B31.3 Process Piping Course
3. Materials
Fluid Service Requirements (323.4.2)
Ü Aluminum Castings
̇ the designer is responsible for establishing
design stresses and ratings if thermal cutting is
used
Ü Lead, Tin & their Alloys
̇ may not be used with flammable fluids
Ü Clad Materials
̇ cladding may be considered to be part of the
thickness of components under certain
conditions
BECHT ENGINEERING COMPANY, INC.
Materials -
47
Deterioration in Service
Ü Selection of material to resist deterioration
in service is not within the scope of the
Code. (323.5)
Ü Recommendations for material selection
are presented in Appendix F.
̇ General considerations
̇ Specific material considerations
BECHT ENGINEERING COMPANY, INC.
Materials -
48
ASME B31.3 Process Piping Course
3. Materials
Deterioration in Service
Types of Damage Mechanisms
̇ Loss of metal
̇ Stress Corrosion Cracking
̇ Metallurgical and Environmental Degradation
BECHT ENGINEERING COMPANY, INC.
Materials -
49
Materials -
50
Loss of Metal
Loss of metal can be
̇ General
̇ Localized
depending on the
physical conditions and
the specific mechanism.
A Rainbow of Rust Colors
BECHT ENGINEERING COMPANY, INC.
ASME B31.3 Process Piping Course
3. Materials
Loss of Metal
Mechanisms include
̇
̇
̇
̇
Galvanic corrosion
Atmospheric corrosion
Corrosion under insulation
Crevice
BECHT ENGINEERING COMPANY, INC.
Materials -
51
Galvanic Corrosion
Electrochemical process
• The anode is the site at
which the metal is
corroded
• The electrolyte is the
corrosive medium
• The cathode forms the
other electrode in the cell
and is not consumed in
the corrosion process
BECHT ENGINEERING COMPANY, INC.
Materials -
52
ASME B31.3 Process Piping Course
Galvanic corrosion
GALVANIC SERIES IN
SEA WATER
Carbon Steel Nipple Threaded into a
Stainless Steel Water Tank
3. Materials
CORRODED END (Anodic)
Magnesium
Zinc
Aluminum
Cadmium
Mild Steel
Cast Iron
Stainless Steels 18/8 (Active)
Lead
Tin
Nickel (Active)
Brass
Copper
Aluminum Bronze
Cupro nickel
Silver Solders
Nickel (Passive)
Stainless Steel 18/8 (Passive)
Silver
Titanium
Graphite
Gold
Platinum
PROTECTED END (Cathodic)
BECHT ENGINEERING COMPANY, INC.
Materials -
53
Galvanic corrosion
Materials 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 and
the cathodic material has a significant affect
BECHT ENGINEERING COMPANY, INC.
Materials -
54
ASME B31.3 Process Piping Course
3. Materials
Galvanic corrosion
Prevention
̇ The best method for prevention/mitigation is through good design.
̇ The more noble material may need to be coated. If the active
material 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, where
the zinc corrodes preferentially to protect the underlying carbon
steel.
̇ If there is a break in the galvanized coating, a large anode to small
cathode area prevents accelerated corrosion of the steel.
̇ This anode-to-cathode relationship reverses at water temperatures
over about 150°F (65°C).
BECHT ENGINEERING COMPANY, INC.
Materials -
55
Atmospheric Corrosion
Ü Atmospheric
corrosion is a form
of galvanic
corrosion.
Ü Different parts of
the surface of the
metal act as
anodes and
cathodes.
Ü Variations in the
electrolyte also
contribute.
BECHT ENGINEERING COMPANY, INC.
Materials -
56
ASME B31.3 Process Piping Course
3. Materials
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 that
can form acids (5-10 mpy).
̇ Inland locations exposed to a moderate amount of precipitation or
humidity are considered moderately corrosive environments (1-3
mpy).
̇ Dry rural environments usually have very low corrosion rates (<1
mpy).
̇ Corrosion rates increase with temperature up to about 250°F
(120°C). At higher temperatures, surfaces are usually too dry for
corrosion to occur except under insulation
̇ Chlorides, H2S, fly ash and other airborne contaminates from
cooling tower drift, furnace stacks and other equipment accelerate
corrosion.
BECHT ENGINEERING COMPANY, INC.
Materials -
57
Atmospheric Corrosion
Prevention
̇ Avoid Designs that trap water or moisture.
̇ Surface preparation and proper coating application
are critical for long-term protection.
Improvements in Materials of
Construction
̇ Use zinc coated materials
̇ Use stainless steels or other materials resistant to
atmospheric corrosion
BECHT ENGINEERING COMPANY, INC.
Materials -
58
ASME B31.3 Process Piping Course
3. Materials
Corrosion Under Insulation
Ü CUI is a form of
galvanic corrosion.
Ü Different parts of the
surface of the metal
act as anodes and
cathodes.
Ü CUI is caused by
the presence of an
electrolyte, usually
rain water.
BECHT ENGINEERING COMPANY, INC.
Materials -
59
Corrosion Under Insulation
Materials 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 to
the point where the water evaporates quickly.
̇ Corrosion becomes more severe at metal temperatures between
the boiling point 212°F (100°C) and 250°F (120°C), where water is
less 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 extended
significantly above 250°F (120°C).
̇ Insulating materials that hold moisture (wick) are more of a
problem.
̇ Cyclic thermal operation can increase corrosion.
BECHT ENGINEERING COMPANY, INC.
Materials -
60
ASME B31.3 Process Piping Course
3. Materials
Corrosion Under Insulation
Prevention
̇ Maintaining the insulation
sealing/vapor barriers to
prevent moisture ingress
̇ Using appropriate coatings
̇ Selection of insulating
materials that will hold less
water against the pipe wall
̇ Using low chloride insulation
with austenitic stainless steels
̇ Not insulating where heat
conservation is not as
important
Improvements in Materials
of Construction
̇ Generally not an economical
approach.
BECHT ENGINEERING COMPANY, INC.
Materials -
61
Corrosion Under Insulation
•
•
•
Near miss
230 psig (16 bar) propane line
Remaining wall as little as 1 mm thick
BECHT ENGINEERING COMPANY, INC.
Materials -
62
ASME B31.3 Process Piping Course
3. Materials
Crevice Corrosion
Ü Localized form of corrosion
Ü Stagnant solution in crevices such as
̇
̇
̇
̇
Under gaskets
Under fasteners
Threaded joints
Socket welded joints
Ü initiated by changes in local chemistry within the
crevice
̇
̇
̇
̇
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
BECHT ENGINEERING COMPANY, INC.
Materials -
63
Crevice Corrosion
Depletion of Oxygen in the Crevice
Initially, the level of
Oxygen consumed by
soluble oxygen and is normal uniform
the same everywhere. corrosion is very soon
depleted in the
crevice.
Corrosion products
create acidic
environment and further
seal the crevice
environment.
http://www.corrosion-doctors.org/
BECHT ENGINEERING COMPANY, INC.
Materials -
64
ASME B31.3 Process Piping Course
3. Materials
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 welding
instead of socket welding and threaded joints.
Improvements in Materials of Construction
̇ Generally not an economical approach.
BECHT ENGINEERING COMPANY, INC.
Materials -
65
Stress Corrosion Cracking
Requires
• Stress
o
o
Residual from Welding
Design
• Right Material
• Right Environment
o
o
o
BECHT ENGINEERING COMPANY, INC.
Chemical, pH
Concentration
Temperature
Materials -
66
ASME B31.3 Process Piping Course
3. Materials
Stress Corrosion Cracking
Mechanisms include
̇ Chloride stress corrosion cracking (ClSCC)
̇ Hydrogen-induced cracking (HIC)
BECHT ENGINEERING COMPANY, INC.
Materials -
67
Chloride Stress Corrosion Cracking
Requires the
presence of:
̇ Chlorides in
sufficient
concentration
̇ High enough stress
BECHT ENGINEERING COMPANY, INC.
Materials -
68
ASME B31.3 Process Piping Course
3. Materials
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 140°F
(60°C), although exceptions can be found at lower temperatures.
̇ Increasing levels of chloride increase the likelihood of cracking. No
practical lower limit for chlorides exists because there is always a
potential for chlorides to concentrate.
̇ SCC usually occurs at pH values above 2. At lower pH values,
uniform corrosion generally predominates. SCC tendency
decreases toward the alkaline pH region.
̇ Stress may be applied or residual. Highly stressed or cold worked
components, such as expansion bellows, are highly susceptible to
cracking.
BECHT ENGINEERING COMPANY, INC.
Materials -
69
Chloride Stress Corrosion Cracking
Prevention
̇ 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 can
concentrate 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%. Alloys
with nickel contents above 35% are highly resistant and alloys
above 45% are nearly immune.
̇ Low-nickel stainless steels, such as the duplex (ferrite-austenite)
stainless steels, have improved resistance over the 300 Series SS
but are not immune.
̇ Carbon steels, low alloy steels and 400 Series SS are not
susceptible to CISCC .
BECHT ENGINEERING COMPANY, INC.
Materials -
70
ASME B31.3 Process Piping Course
3. Materials
Hydrogen-Induced Cracking (HIC)
Hydrogen Blisters
̇ Hydrogen blisters are surface
bulges on the surface of a pipe.
̇ The blister results from hydrogen
atoms that diffuse into the steel,
and collect at a discontinuity.
̇ The hydrogen atoms combine to
form hydrogen molecules that are
too large to diffuse.
̇ The gas pressure builds to the
point where local deformation
occurs
̇ A primary source for the H atoms
is from the sulfide corrosion
process.
BECHT ENGINEERING COMPANY, INC.
Materials -
71
Hydrogen-Induced Cracking (HIC)
Ü Neighboring or adjacent blisters that are at slightly
different depths (planes) can develop cracks that link
them together.
Ü This is hydrogen-induced cracking.
Ü Interconnecting cracks often have a stair step
appearance, and so HIC is sometimes referred to as
"stepwise cracking”.
BECHT ENGINEERING COMPANY, INC.
Materials -
72
ASME B31.3 Process Piping Course
3. Materials
Hydrogen-Induced Cracking (HIC)
Ü When HIC is assisted by high stresses in the piping, it
is called Stress Oriented Hydrogen Induced Cracking
(SOHIC).
Ü The SOHIC cracks usually appear in the base metal
adjacent to the weld heat affected zones where they
initiate from HIC damage.
Ü SOHlC is potentially more dangerous because it results
in a through-thickness crack that is perpendicular to the
surface.
BECHT ENGINEERING COMPANY, INC.
Materials -
73
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 be
minimal at pH 7 and increase at both higher and lower pH's. The
presence of hydrogen cyanide (HCN) in the water phase
significantly increases permeation in alkaline (high pH) sour water.
̇ Hydrogen permeation increases with increasing H2S partial
pressure due to a concurrent increase in the H2S concentration in
the water phase.
̇ Blistering, HIC, and SOHlC damage have been found to occur
between ambient and 300°F (150°C) or higher.
̇ HIC is often found in so-called "dirty" steels with high levels of
inclusions or other internal discontinuities from the steel-making
process.
BECHT ENGINEERING COMPANY, INC.
Materials -
74
ASME B31.3 Process Piping Course
3. Materials
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 HIC
damage.
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 phase
or cyanide concentration can help to reduce damage.
BECHT ENGINEERING COMPANY, INC.
Materials -
75
Metallurgical and Environmental Damage
ÜCauses degradation and loss of material
properties
ÜInvolve some form of mechanical and/or
physical property deterioration of the
material due to exposure to a process
environment
ÜCauses of metallurgical and environmental
degradation failures are varied
BECHT ENGINEERING COMPANY, INC.
Materials -
76
ASME B31.3 Process Piping Course
3. Materials
Metallurgical and Environmental Damage
Mechanisms include
̇ Graphitization
̇ Decarburization
̇ High Temperature Hydrogen Attack
(HTHA)
BECHT ENGINEERING COMPANY, INC.
Materials -
77
Graphitization
ÜGraphitization is the decomposition of
carbide phases in steels after long-term
operation in the 800°F to 1100°F (430°C to
590°C) range into graphite nodules.
ÜThe decomposition causes a loss in
strength, ductility, and creep resistance.
BECHT ENGINEERING COMPANY, INC.
Materials -
78
ASME B31.3 Process Piping Course
3. Materials
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 is
not well understood.
̇ Severe heat affected zone graphitization can develop in as little as
5 years at service temperatures above 1000°F (540°C).
̇ Very slight graphitization would be expected to be found after 30 to
40 years at 850°F (450°C).
Prevention
̇ Graphitization can be prevented by using chromium containing low
alloy steels for long-term operation above 800°F (427°C).
BECHT ENGINEERING COMPANY, INC.
Materials -
79
Materials -
80
Decarburization
Ü A condition where steel looses
strength due the removal of
carbon and carbides leaving only
an iron matrix.
Ü Decarburization occurs during
exposure to high temperatures
such as
̇ during heat treatment
̇ from exposure to fires
̇ from high temperature service in a
gas environment.
BECHT ENGINEERING COMPANY, INC.
ASME B31.3 Process Piping Course
3. Materials
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 react
with gas phase constituents.
̇ The extent and depth of decarburization is a function of the
temperature and exposure time.
̇ Typically, decarburization is shallow, but loss in room temperature
tensile 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.
BECHT ENGINEERING COMPANY, INC.
Materials -
81
High Temperature Hydrogen Attack
Ü High temperature hydrogen attack results from exposure
to hydrogen at elevated temperatures and pressures.
Ü The hydrogen reacts with carbides in steel to form
methane (CH4), which cannot diffuse through the steel.
Ü Methane pressure
builds up, forming
bubbles or cavities,
micro fissures and
fissures that may
combine to form
cracks.
BECHT ENGINEERING COMPANY, INC.
Materials -
82
ASME B31.3 Process Piping Course
3. Materials
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 ability
of the pressure containing part.
• For a specific material, HTHA is dependent on temperature,
hydrogen partial pressure, time and stress. Service exposure time
is cumulative.
̇ HTHA is preceded by a period of time when no noticeable change
is detectable by normal inspection techniques.
̇ API RP 941 provides material resistance curves.
BECHT ENGINEERING COMPANY, INC.
Materials -
83
High Temperature Hydrogen Attack
API RP 941 provides material resistance curves.
BECHT ENGINEERING COMPANY, INC.
Materials -
84
ASME B31.3 Process Piping Course
3. Materials
High Temperature Hydrogen Attack
Prevention
̇ Use alloy steels with
chromium and molybdenum
to increase carbide stability
thereby minimizing methane
formation. Other carbide
stabilizing elements include
tungsten and vanadium.
̇ 300 Series SS, as well as
5Cr, 9Cr and 12Cr alloys, are
not susceptible to HTHA at
conditions normally seen in
refinery units.
HTHA to a Boiler Tube
BECHT ENGINEERING COMPANY, INC.
Ü
Ü
Ü
Ü
Materials -
85
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.
A maintenance
contractor
accidentally
switched a
carbon steel
elbow with an
alloy steel
elbow during a
scheduled heat
exchanger
overhaul.
HTHA to a Boiler Tube
BECHT ENGINEERING COMPANY, INC.
Materials -
86
ASME B31.3 Process Piping Course
3. Materials
API 571
Much of the information presented on deterioration of metals is taken
from API 571 – Damage Mechanisms Affecting Fixed Equipment in the
Refining Industry API 571 addresses all of the following mechanisms:
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Graphitization
Softening (Spheroidization)
Temper Embrittlement
Strain Aging
885°F Embrittlement
Sigma Phase Embrittlement
Brittle Fracture
Creep / Stress Rupture
Thermal Fatigue
Short Term Overheating Stress Rupture
Ü Steam Blanketing
Ü Dissimilar Metal Weld (DMW)
Cracking
Ü Thermal Shock
Ü Erosion / Erosion-Corrosion
Ü Cavitation
Ü Mechanical Fatigue
Ü Vibration-Induced Fatigue
Ü Refractory Degradation
Ü Reheat Cracking
Ü Galvanic Corrosion
Ü Atmospheric Corrosion
BECHT ENGINEERING COMPANY, INC.
Materials -
87
API 571
Ü Corrosion Under Insulation
(CUI)
Ü Cooling Water Corrosion
Ü Boiler Water Condensate
Corrosion
Ü CO2 Corrosion
Ü Flue Gas Dew Point Corrosion
Ü Microbiologically Induced
Corrosion (MIC)
Ü Soil Corrosion
Ü Caustic Corrosion
Ü Dealloying
Ü Graphitic Corrosion
Ü Oxidation
Ü Sulfidation
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
BECHT ENGINEERING COMPANY, INC.
Carburization
Decarburization
Metal Dusting
Fuel Ash Corrosion
Nitriding
Chloride Stress Corrosion
Cracking (CI-SCC)
Corrosion Fatigue
Caustic Stress Corrosion
Cracking (Caustic
Embrittlement)
Ammonia Stress Corrosion
Cracking
Liquid Metal Embrittlement
(LME)
Materials -
88
ASME B31.3 Process Piping Course
3. Materials
API 571
Ü Hydrogen Embrittlement (HE)
Ü Amine Corrosion
Ü Ammonium Bisulfide Corrosion
(Alkaline Sour Water)
Ü Ammonium Chloride Corrosion
Ü Hydrochloric Acid (HCI)
Corrosion
Ü High Temp H2/H2S Corrosion
Ü Hydrofluoric (HF) Acid
Corrosion
Ü Naphthenic Acid Corrosion
(NAC)
Ü Phenol (Carbonic Acid)
Corrosion
Ü Phosphoric Acid Corrosion
Ü Sour Water Corrosion (Acidic)
Ü Sulfuric Acid Corrosion
Ü Polythionic Acid Stress
Corrosion Cracking (PASCC)
Ü Amine Stress Corrosion
Cracking
Ü Wet H2S Damage
Ü Hydrogen Stress Cracking –
HF
Ü Carbonate Stress Corrosion
Cracking
Ü High Temperature Hydrogen
Attack
Ü Titanium Hydriding
BECHT ENGINEERING COMPANY, INC.
Materials -
89