Api 571

Front 1

A typical atmospheric corrosion rate in mils per year of steel in an inland location with moderate precipitation and humidity is:

Back 1

1-3 mils per year

Front 2

What is hydrogen blistering?

Back 2

H2 molecules diffuse to grain boundaries and open up the structure to cause a blister.

Front 3

What is Hydrogen induced cracking (HIC)?

Back 3

H2 blisters form into cracks with a stepped appearance.

Front 4

What is stress oriented hydrogen induced cracking (SOHIC)?

Back 4

Stacked H2 cracks driven by local stresses e.g. residual stresses in the HAZ.

Front 5

What is sulphide stress corrosion cracking (SCC)?

Back 5

SCC in areas of local high hardness. Caused by absorbtion of hydrogen atoms resulting from sulphur corrosion.

Front 6

What is temper embrittlement?

Back 6

Prolonged exposure to high temps causes the material to become more brittle over time.

Front 7

When do brittle fractures occur?

Back 7

At templs below the ductile to brittle transition temperature.

Front 8

What is generalized corrosion of carbon steels called when caused by dissolved salts of microbiological activity?

Back 8

Cooling water corrosion.

Front 9

What material is least susceptible to stress corrosion cracking?

Back 9

Nickel based alloys

Front 10

What is an effective method to prevent caustic stress corrosion cracking?

Back 10

Stress relieving at 1150 deg. F

Front 11

What is temper embrittlement?

Back 11

Temper embrittlement is a reduction in toughness due to a metallurgical change that can occur in some low alloy steels as a result of long term exposure in the temp. range of 650 to 1100 deg. F.

Front 12

What materials are prone to temper embrittlement?

Back 12

Primarily 2.25Cr-1Mo, low alloy steel, and 3Cr-1Mo.

Front 13

What is the appearance of temper embrittlement?

Back 13

Temper embrittlement is not readily apparent and can be confirmed through toughness testing. It can result in catastrophic damage.

Front 14

What is brittle fracture?

Back 14

Brittle fracture is a sudden, rapid fracture under stress where the material exhibits little or no evidence of ductility or plastic deformation.

Front 15

Which materials are affected by brittle fracture?

Back 15

Carbon steels and other low alloy steels arre of prime concern. 400 series stainless is also susceptible.

Front 16

How do most brittle fractures occur?

Back 16

At temps below the Charpy impact transition temperature.

Front 17

How do cracks from brittle fracture appear?

Back 17

Cracks will typically be straight, non branching, and largely devoid of any associated plastic deformation.

Front 18

What is the best way to prevent brittle fracture?

Back 18

It is best prevented by using materials specifically designed for low temps.

Front 19

What materials are affected by CUI?

Back 19

Carbon steel, low alloy steels, 300 series SS and duplex stainless steels.

Front 20

What is the effect of temper embrittlement, and what causes it?

Back 20

Temper embrittlement causes reduction in toughness in low alloy chromium steels due to long exposure in high temps. between 650F to 1100F

Front 21

What is brittle fracture?

Back 21

Sudden fracture under stress due to loss of ductility at low temps. Cracks are typically sharp, straight, and non branching.

Front 22

What is one way to mitigate the possibility of brittle fracture?

Back 22

PWHT

Front 23

Name two factors that contribute to fatigue?

Back 23

1. Surface notch

2. Cyclic stresses

Front 24

What do thermal fatigue cracks look like?

Back 24

They are dagger shaped and oxide filled.

Front 25

What is Erosion-Corrosion?

Back 25

Damage that occurs when the corrosion contributes to erosion by removing protective scale due to the combined action.

Front 26

What are some methods to reduce Erosion-Corrosion?

Back 26

1. Increasing pipe diameter to reduce velocity.

2. Using large radius bends.

3. Increasing surface hardness.

4. Using corrosion resistant materials.

Front 27

What causes Boiler water corrosion?

Back 27

Dissolved oxygen and carbon dioxide.

Front 28

What can be done to mitigate boiler water corrosion?

Back 28

The use of deaerators for boiler feed water and the use of oxygen scavengers like hydrazine.

Front 29

Where does Caustic stress corrosion often take place?

Back 29

Caustic stress corrosion often takes place on CS next to welds which are not stress relieved.

Higher temp and higher caustic concentration increases susceptibility.

Front 30

What is the best way to prevent Caustic stress corrosion cracking?

Back 30

PWHT of welds or the use of Ni alloys.

Front 31

What conditions lead to Sulphidation of CS?

Back 31

At temps above 500F in areas of sulphur concentration.

Front 32

What is the best way to prevent CS sulphidation?

Back 32

By using higher chromium alloys.

Front 33

At what temp. does HTHA occur?

Back 33

Temps above 400F

Front 34

What is HTHA?

Back 34

High Temp. Hydrogen Attack takes place due to migration of hydrogen atoms wich combine with carbide in CS forming methane gas which cannot diffuse out and collects at grain boundaries, causing cracking.

Front 35

What types of damages can be caused by wet H2S exposure?

Back 35

1. Hydrogen induced cracking.

2. Stress oriented hydrogen induced cracking.

3. Hydrogen blistering.

4. Sulphide stress corrosion cracking.

Front 36

What causes hydrogen blistering?

Back 36

Hydrogen blistering is caused by the migration of hydrogen atoms that combine to form hydrogen molecules which typically collect at voids.

Front 37

Describe temper embrittlement.

Back 37

Temper embrittlement is the reduction in toughness due to a metallurgical change that can occur in some low alloy steels as a result of long term exposure in the temp. range of 650F-1100F.

Front 38

What materials are affected by temper embrittlement?

Back 38

Primarily the Cr. moly steels.

Front 39

What is the appearance of temper embrittlement?

Back 39

Temper embrittlement is not easily seen and can be confirmed through impact testing.

Front 40

What materials are affected by atmospheric corrosion?

Back 40

CS, low alloy steels, and copper alloyed aluminum.

Front 41

What type if equipment is likely to be affected by atmospheric corrosion?

Back 41

Piping and equipment with operating temps. sufficiently low to allow moisture to be present.

Front 42

Describe cooling water corrosion.

Back 42

General or localized corrosion of CS and other metals caused by dissolved salts, gases, organic compounds or microbiological activity.

Front 43

What type of equipment is likely to be affected by Cooling water corrosion?

Back 43

Water cooled heat exchangers and cooling towers.

Front 44

Describe Boiler water condensate corrosion.

Back 44

General corrosion and pitting in the boiler system and condensate return piping.

Front 45

What is the appearance of boiler water condensate corrosion?

Back 45

1. Corrosion from Oxygen leads to pitting.

2. Corrosion in condensate is due to carbon dioxide and tends to be a smooth grooving in the pipe walls.

Front 46

How can boiler water condensate corrosion be mitigated?

Back 46

By using oxygen scavengers.

Front 47

Describe sulfidation

Back 47

The corrosion of CS and other alloys resulting from their reaction with sulfur compounds in high temp. environments.

Front 48

What does sulfidation look like?

Back 48

Usually in the form of uniform thinning.

Front 49

Describe Chloride Stress Corrosion Cracking.

Back 49

Surface cracks caused by environmental cracking of 300 SS, and some nickel based alloys under the combined action of tensile stress, temperature, and an aqueous chloride environment.

Front 50

What does Chloride Stress Corrosion Cracking look like?

Back 50

1. Surface breaking cracks.

2. Cracks that have many branches.

3. Branched transgranular cracks. Sometimes intergranular cracking of 300 SS.

Front 51

How can Chloride Stress Corrosion Cracking be mitigated?

Back 51

By using low chloride water during hydrotests, and drying the equipment thoroughly.

Front 52

Describe Corrosion Fatigue.

Back 52

Fatigue cracking in which cracks develop under the combined affects of cyclic loading and corrosion. Cracking often initiates at a stress concentration such as a pit in the surface.

Front 53

What does Corrosion fatigue look like?

Back 53

The fatigue fracture is brittle and the cracks are most often transgranular, but not branched.

Front 54

Describe Caustic Stress Corrosion Cracking.

Back 54

Surface initiated cracks that occur in piping and equipment exposed to caustic, primarily next to non PWHT welds.

Front 55

What does Caustic Stress Corrosion Cracking look like?

Back 55

1. Cracks propagating parallel to the weld in the adjacent base metal.

2. A spider web of small cracks.

Front 56

Describe Hydrochloric Acid (HCI) Corrosion

Back 56

1. Hydrochloric acid causes both general and localized corrosion and is very aggressive.

2. Damage in refineries most often associated with dew point corrosion in which vapors containing water and hydrogen chloride condense from the overhead stream of a distillation fractionation or stripping tower.

Front 57

What does HCI Corrosion look like?

Back 57

1. CS and low alloy steels suffer general uniform thinning.

2. 300 SS and 400 SS will often suffer pitting. 300 SS may experience chloride stress corrosion cracking.

Front 58

What is Sour Water Corrosion?

Back 58

Corrosion of steel due to acidic sour water containing H2S at a pH between 4.5-7.0

Front 59

Describe Amine Stress Corrosion cracking.

Back 59

1. Cracking of steels under teh combined actio of tensile stress and corrosion in aqueous alkanolamine systems used to remove/absorb H2S and/or CO2 from gas and liquid hydrocarbon streams.

2. Amine cracking is a form of alkaline stress corrosion cracking.

3 Most often found at or adjacent to non PWHT CS welds.

4. Amine cracking should not be confused with several other types of SCC that can occur in smine environments.

Front 60

Describe High Temp. Hydrogen Attack.

Back 60

HTHA results from exposure to hydrogen at elevated temps. and pressures. the hydrogen reacts with carbides in steel to form methane which cannot diffuse through the steel. The loss of carbide causes an overall loss in strength.

Front 61

Which type of steel is not susceptible to brittle fracture?

Back 61

300 SS Steel

Front 62

In most cases brittle fracture occurs only at temperatures below what?

Back 62

The Charpy impact transition temp.

Front 63

What year did the ASME BPVC begin to require toughness as a criteria for vessels operating at cold temp.?

Back 63

1987

Front 64

What can cause brittle fracture during hydro testing?

Back 64

High stresses and low toughness at the testing temperature.

Front 65

What materials are affected by Thermal fatigue?

Back 65

All materials of construction.

Front 66

What are two key factors affecting thermal fatigue?

Back 66

Temp. swing and frequency (number of cycles).

Front 67

What unit is most often damaged by gas borne catalyst particles?

Back 67

Fluid Catalytic Cracker.

Front 68

What type of material offers improved resustance to napthenic acid corrosion?

Back 68

Higher moly containing alloys.

Front 69

What type of inspection can detect the loss of refractory on an operating unit?

Back 69

Infrared scan

Front 70

What does fatigue failure look like?

Back 70

The failure exhibits a "clam shell" appearance that has concentric rings called "beach marks".

Front 71

What is the best defense against mechanical fatigue cracking?

Back 71

Good design.

Front 72

How many mils per year can you expect a CS liine to lose if exposed to a marine environment?

Back 72

20 mpy

Front 73

What is the atmospheric corrosion rate if CS is exposed to a dry rural environment?

Back 73

Less than 1 mpy

Front 74

In atmospheric corrosion, what can get on equipment and cause accelerated corrosion and stains?

Back 74

Bird feces.

Front 75

What temps. cause CUI to be most severe?

Back 75

Between 212F-350F

Front 76

What usually causes corrosion in boiler feedwater and condensate return systems?

Back 76

Dissolved gases, oxygen, and carbon dioxide.

Front 77

What type of corrosion is usually attributed to oxygen in boiler water condensate corrosion?

Back 77

Pitting.

Front 78

When sulfur compounds react with CS in high temp. settings, what can accelerate corrosion?

Back 78

Hydrogen

Front 79

What determines the susceptibility of an alloy to sulfidation?

Back 79

Its ability to form protective sulfide scales.

Front 80

Sulfidation of Iron based alloys usually begins at metal temps. above:

Back 80

500F

Front 81

What does sulfidation look like?

Back 81

Uniform thinning.

Front 82

Chloride stress corrosion cracking is surface initiated cracks found in:

Back 82

300 series SS and some nickel alloys.

Front 83

The presence of what other element increases the propensity for CI SCC?

Back 83

Oxygen

Front 84

What percent of chlorides is safe for exposure to 300 SS?

Back 84

0%

Front 85

SCC usually occurs at pH vallues above:

Back 85

2

Front 86

Stress corrosion cracking usually occurs at metal temps. above about:

Back 86

140F

Front 87

Nickel content of an alloy above what percent makes it highly resistant to SCC?

Back 87

35%

Front 88

What kind of steel is not susceptible to SCC?

Back 88

CS

Front 89

What is a preferred method for finding SCC?

Back 89

PT

Front 90

Caustic embrittlement is a form of:

Back 90

SCC

Front 91

Where is a likely place for caustic embrittlement?

Back 91

Next to non PWHT welds.

Front 92

What materials are affected by caustic embrittlement?

Back 92

CS and 300 SS

Front 93

In caustic embrittlement, what two conditions, if changed, can lead to more severe cracking?

Back 93

Increase in temp. and increase in the caustic concentration.

Front 94

Caustic embrittlement, or caustic stress corrosion typically propagates ____________ to the weld?

Back 94

Parallel

Front 95

If a vessel has contained caustic, why should you consider water washing it thoroughly before steaming it out?

Back 95

To prevent Caustic embrittlement cracking.

Front 96

What method of NDE is not effective for finding caustic embrittlement cracking when it is tight and scale filled?

Back 96

PT

Front 97

What are two other similar forms of alkaline stress corrosion cracking mechanisms?

Back 97

Amine and carbonate cracking.

Front 98

Name two of the four types of damage that result from wet H2S

Back 98

Hydrogen blistering

Sulfide stress corrosion cracking.

Front 99

What materials are affected by wet H2S damage?

Back 99

CS and low alloy steels.

Front 100

In Crude units, where would an inspector expect to find HCI corrosion?

Back 100

In the atmospheric tower overhead system and in the vacuum ejector system of the vacuum tower

Front 101

Temper embrittlement causes:

Back 101

A reduction in toughness.

Front 102

What materials are primarily affected by temper embrittlement?

Back 102

Primarily 2.25Cr-1Mo low alloy steels.

Front 103

What type of equipment might be affected by temper embrittlement?

Back 103

Reactors, hot feed exchangers, catalytic reformers.

Front 104

How can temper embrittlement be verified?

Back 104

Through impact testing.

Front 105

What is brittle fracture?

Back 105

Sudden rapid fracture under stress, where the material exhibits little or no evidence of ductility or plastic deformation.

Front 106

What type of material is likely to be affected by brittle fracture?

Back 106

Carbon steels and low alloy steels....also 400 SS.

Front 107

When is brittle fracture likely to occur?

Back 107

1. For processes that run at elevated temps., startup, shutdown, or hydrotesting are the main times where brittle fracture can occur.

2. During an auto refigeration event.

Front 108

What do brittle fracture cracks look like?

Back 108

Straight, non branching.

Front 109

Where are you likely to find thermal fatigue cracks?

Back 109

At the toes of welds. The change in thickness acts as a stress riser.

Front 110

What are effective NDE techniques to identify thermal fatigue?

Back 110

Cracks are on surface, so MT and PT work well.

Front 111

What is errosion-corrosion?

Back 111

When corrosion contributes to erosion by removing protective films or scales.

Front 112

What is the mark of mechanical fatigue?

Back 112

A "clam shell type" fingerprint.

Front 113

What is boiler water condensate corrosion?

Back 113

General corrosion and pitting in the boiler system and condensate return piping.

Front 114

What materials are at risk for boiler water condensate corrosion?

Back 114

Primarily CS, some low allowy steels, and some 300 seeries SS.

Front 115

What can be used to prevent boiler water condensate corrosion?

Back 115

Oxygen scavenging treatments.

Front 116

How do you monitor boiler water condensate corrosion?

Back 116

Through water analysis.

Front 117

What is sulfidation?

Back 117

Corrosion of CS and other alloys resulting from their reaction with sulfur compounds in high temp. environments. They presence of hydrogen will accelerate corrosion.

Front 118

What is chloride stress corrosion cracking?

Back 118

A cracking process that requires a corrosive environment....and applied stress.

Front 119

What materials are affected by chloride stress corrosion cracking?

Back 119

300 series SS.

Duplex and nickels are resistant.

Front 120

What does chloride stress corrosion cracking look like?

Back 120

Branched, transgranular cracks.

Front 121

What is corrosion fatigue?

Back 121

Fatigue cracking in which cracks develop under the combined affects of cyclic loading and corrosion.

Front 122

What causes hydrogen blistering?

Back 122

hydrogen molecules that are generated by corrosion.....not welding.....become trapped in and pressure builds that causes blistering.

Front 123

What is high temp. hydrogen attack?

Back 123

Results to exp. to hydrogen at elevated temps. and pressures. The hydrogen reacts with carbides in the steel to create methane, which cannot diffuse through the steel. The methane forms bubbles or cavities that can form cracks.