B31.3 Process Piping Course - 03 Materials-libre

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ASME B31.3 Process Piping

Charles Becht IV, PhD, PE

Don Frikken, PE

Instructors

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

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3. Materials

Ü

Strength of Materials

Ü

Bases for Design Stresses

Ü

B31.3 Material Requirements

̇

Listed and Unlisted Materials

̇

Temperature Limits

̇

Toughness Requirements

̇

Fluid Service Requirements

Ü

Deterioration in Service

The Material in This Section is

Addressed by B31.3 in:

Chapter II

- Design

Chapter III - Materials

Appendix A - Allowable Stresses & Quality

Factors – Metals

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Strength of Materials

Ü

Stress

Ü

Strain

Ü

Stress-Strain Diagram

̇

Elastic Modulus

̇

Yield Strength

̇

Ultimate Strength

Ü

Creep

Ü

Fatigue

Ü

Brittle versus Ductile Behavior

Strength of Materials

Stress (S):

force (F) divided by area (A)

over which force acts, pounds force/inch

(psi), Pascals (Newtons/meter

₎

Strain (

ε):

change in length (

ΔL)

divided

by the original length (L)

F

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Strength of Materials

Strain

Stress

E = Elastic Modulus = Stress/Strain

S

= Yield Strength

S

= Tensile Strength

Typical Carbon Steel

Strength of Materials

S

= Tensile Strength

Typical Stainless Steel

Strain

Stress

S

= Yield Strength

0.2% offset

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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)

Strength of Materials

Time

Strain

Primary Secondary Tertiary

Rupture

Creep Rate (strain/unit time)

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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

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

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Strength of Materials

Brittle failure:

Ductile deformation:

Strength of Materials

Brittle failure:

Ductile failure:

Strain

Stress

Toughness

Stress

Toughness

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Strength of Materials

Measuring Toughness

using a Charpy impact

test

H1

Charpy Impact Test

C

= W(H1 - H2)

= Energy Absorbed

H2

H1 -H2

W

Specimens tested at 40, 100 and 212ºF (4, 38 and 100ºC)

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Bases for Design Stresses

Ü

Most Materials

Ü

Bolting

Ü

Gray Iron

Ü

Malleable Iron

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 (S

)

̇

1/3 of tensile strength at temperature

̇

2/3 of specified minimum yield strength (S

)

̇

2/3 of yield strength at temperature; except

for austenitic stainless steels and nickel

alloys with similar behavior, 90% of yield

strength at temperature

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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

Bases for Design Stresses

ASTM 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 S tr ess , ks i 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 Te mpe rature , C S tr ess, M P a 2/3 Yield 1/3 Tensile Allowable

Bases for Design Stresses

ASTM 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 S tr ess, 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 S tr ess, M P a 2/3 Yield 90% Yield 1/3 Ultimate Allowable

Bases for Design Stresses

Additional Notes

̇

For structural grade materials, design

stresses are 0.92 times the value determined

for most materials

̇

Stress values above 2/3 S

are not

recommended for flanged joints and other

components in which slight deformation can

cause leakage or malfunction

̇

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 lowest

of

(302.3.2)

̇

1/4 of specified minimum tensile strength

(S

); if properties are enhanced by heat

treatment or strain hardening, 1/5 S

̇

1/4 of tensile strength at temperature

̇

2/3 of specified minimum yield strength (S

);

if properties are enhanced by heat treatment

or strain hardening, 1/4 S

̇

2/3 of yield strength at temperature

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

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Bases for Design Stresses

Gray Iron – the lowest of

(302.3.2)

̇

1/10 of specified minimum tensile strength

(S

)

̇

1/10 of tensile strength at temperature

Bases for Design Stresses

Malleable Iron – the lowest of

(302.3.2)

̇

1/5 of specified minimum tensile strength (S

)

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B31.3 Material Requirements

Ü

Listed and Unlisted Materials

Ü

Temperature Limits

Ü

Impact Test Methods & Acceptance

Ü

Toughness Requirements

Ü

Fluid Service Requirements

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

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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)

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)

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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.

Table 323.2.2

Requirements for Low Temperature Toughness Tests

See

pag

e 21

of t

he s

upp

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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.

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

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Figure 323.2.2A

Minimum Temperatures without Impact Testing for Carbon Steel

See

pa

ge

23

of t

he

sup

ple

me

nt.

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

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Fig.323.2.2B

Reduction in Minimum Design Temperature w/o Impact Testing

See page 24 of the supplement.

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

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Carbon Steel Lower Temperature Limits

Design Pressure: 650 psig

(45 bar)

Design Temperature:

735°F (390°C).

Pipe material is ASTM A53

Gr B seamless.

What options are available

to deal with expected

ambient temperatures

down to -30°F (-34°C)?

_1.000

_0.97

(

25.40

)

30

(750)

0.86

0.500

(

12.70

)

12

(300)

0.74

0.237

(

6.02

)

4

(100)

0.71

0.178

(

4.52

)

1

(25)

Stress

Ratio

Nominal

WT

NPS

(DN)

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

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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]

Fluid Service Requirements

Ü

Ductile Iron

̇

generally limited to temperature range of

-20ºF to 650ºF (-29ºC to 343ºC) and B16.42

ratings

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Fluid Service Requirements

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)

Fluid Service Requirements

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

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Fluid Service Requirements

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

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

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Deterioration in Service

Types of Damage Mechanisms

̇

Loss of metal

̇

Stress Corrosion Cracking

̇

Metallurgical and Environmental Degradation

Loss of Metal

Loss of metal can be

̇

General

̇

Localized

depending on the

physical conditions and

the specific mechanism.

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Loss of Metal

Mechanisms include

̇

Galvanic corrosion

̇

Atmospheric corrosion

̇

Corrosion under insulation

̇

Crevice

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

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Galvanic corrosion

GALVANIC SERIES IN

SEA WATER

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) Carbon Steel Nipple Threaded into a

Stainless Steel Water Tank

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

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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 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).

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.

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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 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.

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

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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.

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.

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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.

Corrosion Under Insulation

•

Near miss

•

230 psig (16 bar) propane line

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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

Crevice Corrosion

Initially, the level of soluble oxygen and is the same everywhere.

Oxygen consumed by normal uniform corrosion is very soon depleted in the crevice.

Corrosion products create acidic

environment and further seal the crevice

environment.

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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 welding instead of socket welding and threaded joints.

Improvements in Materials of Construction

̇ Generally not an economical approach.

Stress Corrosion Cracking

Requires

• Stress

o

Residual from Welding

Design

• Right Material

• Right Environment

Chemical, pH

Concentration

Temperature

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Stress Corrosion Cracking

Mechanisms include

̇

Chloride stress corrosion cracking (ClSCC)

̇

Hydrogen-induced cracking (HIC)

Chloride Stress Corrosion Cracking

Requires the

presence of:

̇

Chlorides in

sufficient

concentration

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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 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.

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 .

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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.

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”.

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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.

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.

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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 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.

Metallurgical and Environmental Damage

Ü

Causes degradation and loss of material

properties

Ü

Involve some form of mechanical and/or

physical property deterioration of the

material due to exposure to a process

environment

Ü

Causes of metallurgical and environmental

degradation failures are varied

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Mechanisms include

̇

Graphitization

̇

Decarburization

̇

High Temperature Hydrogen Attack

(HTHA)

Metallurgical and Environmental Damage

Graphitization

Ü

Graphitization 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.

Ü

The decomposition causes a loss in

strength, 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 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).

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

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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 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.

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.

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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 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.

High Temperature Hydrogen Attack

BECHT

85

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

High Temperature Hydrogen Attack

Ü One employee sustained a minor injury.

Ü NPS 8 carbon steel elbow ruptured after operating for only 3 months.

Ü The escaping hydrogen gas from the ruptured elbow quickly ignited.

HTHA to a Boiler Tube

Ü A maintenance contractor accidentally switched a carbon steel elbow with an alloy steel elbow during a scheduled heat exchanger overhaul.

BECHT

87

API 571

Ü Sigma Phase Embrittlement

Ü Brittle Fracture

Ü Creep / Stress Rupture

Ü Thermal Fatigue

Ü 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 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:

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 Ü Carburization Ü Decarburization Ü Metal Dusting

Ü Fuel Ash Corrosion

Ü Nitriding

Ü Chloride Stress Corrosion Cracking (CI-SCC)

Ü Corrosion Fatigue

Ü Caustic Stress Corrosion Cracking (Caustic Embrittlement)

Ü Ammonia Stress Corrosion Cracking

Ü Liquid Metal Embrittlement (LME)

BECHT

89

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