Module 5 Hydrogen cracking Flashcards
1
Q
Hydrogen Embrittlement
description loss of?
A
loss of ductility , strength, and/or fracture toughness
2
Q
Hydrogen Embrittlement
what happens to the H+?
A
H+ get between grain boundaries
3
Q
Hydrogen Embrittlement
affect material?
AND _____ STEELS
A
- Carbon steel
- Low alloy steels,
- HIGH STRENGTH steels,
- 400 Series SS,
- Precipitation hardenable stainless steel,
- Duplex stainless steel
- Some high-strength nickel-based alloys
4
Q
Hydrogen Embrittlement
which material is not affected?
A
300 SS
5
Q
Hydrogen Embrittlement
critical factor? (4)
A
- concentration
- Stress
- Temp
- Material
6
Q
Hydrogen Embrittlement
effects of temperature?
A
effects decrease with INCREASING temps
7
Q
Hydrogen Embrittlement
temperature range?
A
AMBIENT temp is most pronounced …. decrease rapidly at 150F and disappears >300F
8
Q
Hydrogen Embrittlement
strength and hardness
A
must be high
9
Q
Hydrogen Embrittlement
hydrogen must be at critical ____
A
concentration
10
Q
Hydrogen Embrittlement
where does hydrogen come from? (6)
A
- electrodes
- corrosion reactions
- high temp >400F in h2 gas
- cleaning and pickling
- high strength bolts plated with cadmium
- cathodic protection
11
Q
Hydrogen Embrittlement
is HE reversible and when?
A
Yes/ when no cracking has occured
12
Q
Hydrogen Embrittlement
when temp to bake out Hydrogen
A
600F
13
Q
Hydrogen Embrittlement
affected equipment?
1. service that contain ____ OR _____
2. corrosive service containing _______and/or
contaminated with recombination poisons
3. hydrogen service above _________ after cool down
4. weld HAZ with HB____________
5. storage sphere b/c ______________
6. ____and _____made of high strength are more prone
A
- wet H2s or sour water
- sulfur
- e above 400F
- > 225
- > 70KSi
- bolts and spring
14
Q
Hydrogen Embrittlement
what are the corrosion reaction ? (2)
A
sulfur and arsenic - they act as atomic H2 recombination plosions and form h2 gas
15
Q
Hydrogen Embrittlement
appearance?
cracking is typically _____. In high strength steels it is often _______
A
branched / intergranular
16
Q
Hydrogen Embrittlement
a. HE____ visible only appear when cracking
b. can initiate ____but most is ____
c. HE at ____stress
d. little evidence of ____
A
a. is not
b. subsurface / surface
c. high
d. deformation
17
Q
Hydrogen Embrittlement
• Maximum hardness is often held to _____HB.
• High strength bolts, such as ASTM A 193 Grade
B7, should _____ used.
A
200
not be
18
Q
Hydrogen Embrittlement
HE is ____cumulative
A
not
19
Q
Hydrogen Embrittlement
A. heavy wall equipment in hot hydrogen service require _____S/D & S/u to control the pressurization sequence as a function of temp.
A
CONTROL /
20
Q
Hydrogen Embrittlement
If the source of hydrogen is a low-temperature aqueous environment, hydrogen flux can be monitored using ______
.
A
specialized instruments.
21
Q
Hydrogen Embrittlement
NDE to use?
A
B. PT MT WFMT, Angle Beam,
22
Q
Hydrogen Embrittlement
NDE to not use
A
c. RT/UT not to be used
23
Q
Wet H2S
4 damage?
A
- Hydrogen blistering
- HIC
- SOHIC
- SSC
24
Q
Wet H2S -
description?
Form of HE but occurs in high ____
steels or at local high ____areas (such as HAZ)
A
hardness / hardness
25
Wet H2S -
| critical factors? (4)
1. Environmental conditions (pH, H2S level, contaminants, & temperature),
2. material properties
3. stress
4. Water
26
Wet H2S -
| Must have ____presense
WATER
27
Wet H2S -
| related to _____and ____of h2
absorption / permeation
28
Wet H2S -
Hydrogen permeation increases with increasing _____partial pressure Partial Pressure = (H2S Concentration X Operating Pressure)
H2S
29
Wet H2S -
| min PPM of H2S?
50 ppm of H2S as min concentration
30
Wet H2S -
| min pH? and increase at both high and lower pH
7
31
Wet H2S -
| effects of contaminants?
- salt or other than decrease pH (increasing CR will increase hydrogen permeation).
32
Wet H2S -
| effect of HCN (Cyanide)?
increase CR (weakens protective films)
33
Wet H2S -
| temperate range?
- ambient to 300°F (though sometimes higher) - Blistering, HIC and SOHIC
34
Wet H2S -
| Hardness – Primarily an issue with SSC when weld hardness >____ HB
237
35
Wet H2S -
• Blistering and HIC are strongly affected by the presence of ____and _____which provide sites for diffusing hydrogen to accumulate.
inclusions / laminations
36
Wet H2S -
prevention?
• Use ____, ____ steel
a. clean / resistant (killed)
37
Wet H2S -
prevention?
b) PWHT
c) Control weld hardness to less than ____HB. (NACE RP0427)
d) Use ASTM _____ bolts. They are softer and lower strength than B7 bolts.
e) Use carbon steels with Carbon Equivalents (CE) less than ____
200
A B7M
0.43.
38
Wet H2S - Hydrogen Blistering
| appearance?
Bulges and/or cracking (both can be internal or external) - primarily on ID surface
39
Wet H2S affected material? for blistering / HIC/ SOHIC
• Carbon steel, and in the case of SSC, low-alloy steels, and martensitic stainless steels
40
Wet H2S - Hydrogen Blistering
| description?
hydrogen diffuses into the steel
41
Wet H2S - Hydrogen Blistering
| where is it rare to see it?
seamless pipes
42
Wet H2S - Hydrogen Blistering
| common to see it where?
vessels and larger diameter seam- welded pipe (which are usually made from plate
43
Wet H2S - Hydrogen Blistering
| temperature for Blistering, HIC and SOHIC
ambient to 300°F (though sometimes higher) -
44
Wet H2S - Hydrogen Blistering / HIC are affected by? (2)
inclusion and laminations
45
Wet H2S
| blistering, HIC, SOHIC damage are NOT related to _______
hardness.
46
Wet H2S - blistering / HIC, and SOHIC.
| critical factors?
a. ammonium bisulfide concentration >2% increase the potential for blistering/HIC and SOHIC
47
Wet H2S - blistering / HIC, and SOHIC.
| _____increase the probability and severity of blistering, HIC, and SOHIC
Cyanides
48
Wet H2S - blistering
appearance
a. Blisters: show on the ID (typically)
b. Internal separations ________to the surface of the steel (for HIC as well - not SOHIC)
parallel
49
```
Wet H2S - blistering / HIC and SOHIC prevention?
Effective ___(3)____ can prevent blistering HIC, and SOHIC.
```
barriers, including alloy cladding and coating,
50
Wet H2S - blistering / HIC
| Blistering and HIC can develop _________ stress.
with or without
51
Wet H2S - HIC
| appearance
"step wise cracking"
52
Wet H2S for blistering and HIC
| Key Factors: (2)
(1) Steel Cleanliness and
| (2) Reduction of Discontinuities
53
Wet H2S
| - late stage HIC or SOHIC will create surface breaking ____
cracks.
54
Wet H2S
| SOHIC or surface breaking HIC may be seen visually through ___(3 NDE) ___ in early stage
WFMT, ECT, ACFM
55
Wet H2S SOHIC-
| description is -
HIC under stress
56
Wet H2S SOHIC-
| appearance?
array of HIC stacked on top of each other
57
Wet H2S SOHIC-
| is more damaging form of cracking than HIC because of it relatively high rate of developing a ______
thru-wall crack
58
Wet H2S SOHIC-
| High stress, most commonly in base metal _____to HAZ.
adjacent
59
Wet H2S SOHIC-
| Interconnecting crack is usually _______to surface but may follow high stress.
perpendicular
60
Wet H2S SOHIC-SSC
| -SOHIC and SSC damage MOST OFTEN associate with _______
weldments
61
Wet H2S SOHIC
| ____can help minimize susceptibility to SOHIC.
PWHT
62
Wet H2S SOHIC
| SOHIC occurs in the _____metal alongside the weld. If found in the weld, they are likely fabrication weld flaws.
base
63
Wet H2S - SSC definition
Sulfide Stress Cracking
64
Wet H2S - SSC
| Cracking under the combined action of ______ and corrosion in the presence of ____and _____.
tensile stress
water / H2S
65
Wet H2S - SSC
| SSC is a form of _____Embrittlement.
Hydrogen
66
Wet H2S - SSC
| Factors (3)
Factors:
(1) Hard Weld Cracking
(2) Weld Chemistry
(3) Weld Procedure Related
67
Wet H2S - SSC
| SCC greatest at ____F and generally a concern _<__F-
70 / <200F.
68
Wet H2S - SSC
_____is primarily an issue with SCC
-stress is needed to cause SSC
hardness
-
69
Wet H2S - SSC
| how to minimize?
PWHT (and also SOHIC)
70
Hydrogen Stress Cracking in Hydrofluoric Acid
| a. due to _____of atomic hydrogen
penetration
71
Hydrogen Stress Cracking in Hydrofluoric Acid
| Cracking under the combined action of ____ and corrosion in the presence of ____and HF.
tensile stress / water
72
```
Hydrogen Stress Cracking in Hydrofluoric Acid
affected materials (2)
```
Carbon Steel and low-alloy steels.
73
Hydrogen Stress Cracking in Hydrofluoric Acid
| Susceptibility increases with increasing _____. Steels with levels above (HB ____) are highly susceptible
hardness / 237
74
Hydrogen Stress Cracking in Hydrofluoric Acid
a. Primarily_______in carbon steel but may be intergranular in high strength steels.
b. Typically associated with _____.
c. can only be confirmed by _____ examination
d. surface breaking flaws
a. trans granular
b. weldments
c. metallographic
75
Hydrogen Stress Cracking in Hydrofluoric Acid
1. Weld procedure qualification, chemistry controls, and PWHT are the methods used to avoid high-hardness HAZs.
a) PWHT
b) Control weld hardness to less than _____HB & localized zones above 237 HB.
(NACE RP0427)
c) Use ASTM A B7M bolts. They are softer and lower strength than B7 bolts.
d) Control of Residual Elements (RE). Controls are same as for HF Acid Corrosion
e) Use carbon steels with Carbon Equivalents (CE) less than 0.43
b. 200
76
Hydrogen Stress Cracking in Hydrofluoric Acid
| _____is not susceptible to this form but may be susceptible to SCC
alloy 400
77
Hydrogen Stress Cracking in Hydrofluoric Acid
| Serious corrosion can occur around ______ where dry chloride containing streams mix
mix points
78
Hydrogen Stress Cracking in Hydrofluoric Acid
| Corrosion can occur where a cool stream forces _____ of the HCl.
dew point
79
Hydrogen Stress Cracking in Hydrofluoric Acid
| Relate mech?
• Blistering, HIC and SOHIC damage in HF acid is similar to that found in wet H2S
80
Hydrogen Stress Cracking in Hydrofluoric Acid
| _______ damage in HF acid is similar to that found in wet H2S
• Blistering, HIC and SOHIC
81
High-Temperature Hydrogen Attack (HTHA)
| At high temperatures atomic H+ diffuses in steel, reacts with carbon to form ________and results in cracking.
methane (CH4)
82
High-Temperature Hydrogen Attack (HTHA)
| Methane cannot migrate through steel. As methane content increases, internal pressure . _________
increases
83
High-Temperature Hydrogen Attack (HTHA)
| increasing resistance ->
as welded CS/ non welded CS / CS with PWHT / C-0.5Mo , 2.25 CR (with increasing Cr)
84
High-Temperature Hydrogen Attack (HTHA) -
| _________and higher are typically not susceptible in refinery conditions
5Cr-.5
85
High-Temperature Hydrogen Attack (HTHA)
Higher ______ → higher resistance to HTHA
(stabilizes carbide stability → minimizes methane formation)
Cr/Mo
86
High-Temperature Hydrogen Attack (HTHA)
| • See API ____Nelson curves
941
87
High-Temperature Hydrogen Attack (HTHA)
| HTHA damage is ____and ______. Exposure time is cumulative
permanent / irreversible
88
High-Temperature Hydrogen Attack (HTHA)
| Not detectable during _______ which may vary from hours to years.
“incubation period”,
89
High-Temperature Hydrogen Attack (HTHA)
| Use______and ____safety factor when using curves.
25-50 F
25 psia to 50 psia hydrogen partial pressure
90
```
High-Temperature Hydrogen Attack (HTHA)
crtical factor (3)
```
- Hydrogen partial pressure
- temperature
- metallurgy (more chrome the better)
91
High-Temperature Hydrogen Attack (HTHA)
| affected units
hydro processing units
92
High-Temperature Hydrogen Attack (HTHA)
| found in weld HAZ as well as ____metal away from welds.
base
93
High-Temperature Hydrogen Attack (HTHA)
| ______commonly found in weld metal.
LESS
94
High-Temperature Hydrogen Attack (HTHA)
| internal _______can lead to internal fissuring and cracking.
decarburization
95
High-Temperature Hydrogen Attack (HTHA)
| non stress relieved carbon steel is more _____that stress relieved and non welded components
susceptible
96
High-Temperature Hydrogen Attack (HTHA)
| While _____can detect, most equipment has decarburized surface , micro void and fissures may be absent.
FMR
97
High-Temperature Hydrogen Attack (HTHA)
C-1/2 Mo curve removed in 1990
added a new lower curve with CS with no PWHT (RP941)
a
98
High-Temperature Hydrogen Attack (HTHA)
| non stress relieve carbon steel is more susceptible that stress relieved and non welded components
b
99
High-Temperature Hydrogen Attack (HTHA)
| Properly metallurgically bonded SS overlay and cladding can prevent HTHA
c
100
High-Temperature Hydrogen Attack (HTHA)
| New equipment should be designed so the base material is inherently resistant to HTHA
d
101
High-Temperature Hydrogen Attack (HTHA)
| Experience shown that removal of metal up to ___" may be needed for finding HTHA.
0.1"
102
Wet H2s - Blistering
Blistering only results from hydrogen generated by ________, not from hydrogen gas in the process stream.
corrosion
103
High-Temperature Hydrogen Attack (HTHA)
____ and ______ have been found to be unreliable techniques for HTHA detection and should not be used as primary inspection methods.
Ultrasonic attenuation and velocity ratio
104
Wet H2s - SSC
SSC can initiate on the ____of steels in highly localized zones of high hardness in the weld metal
and heat affected zones.
surface
105
Wet H2s
Conditions which are known to promote blistering, HIC, SOHIC and SSC are those containing
free water (in liquid phase) and:
• >50 wppm dissolved H2S in the free water, or
• free water with pH <4 and some dissolved H2S present, or
• free water with pH >7.6 and 20 wppm dissolved hydrogen cyanide (HCN) in the water
and some dissolved H2S present, or
• >0.0003 MPa (0.05 psia) partial pressure of H2S in the gas phase
a
106
Wet H2s
An arbitrary value of ____wppm H2S in the water phase is often used as the defining concentration
where wet H2S damage becomes a problem.
50
107
Wet H2s -SOHIC
| PWHT can also help to ____susceptibility to SOHIC.
minimize
108
Wet H2s -SSC
| PWHT is highly ____in preventing or eliminating SSC by reduction of both hardness and residual stress.
effective
109
Wet H2S
| Inspection for wet H2S damage generally focuses on _____
weld seams and nozzles.
110
Wet H2S
Although cracks may be seen visually, crack detection is best performed with ______
techniques.
WFMT, EC, RT or ACFM
111
High Temperature Hydrogen Attack (HTHA)
The loss of _______causes an overall loss in strength
carbide
112
High Temperature Hydrogen Attack (HTHA)
Cracking and fissuring are ____and occur adjacent to pearlite (layers of ferrite and iron carbide) areas in carbon steels.
intergranular
113
High Temperature Hydrogen Attack (HTHA)
| affect units? (3)
hydrotreaters (desulfurizers) and hydrocrackers, catalytic reformers
114
High Temperature Hydrogen Attack (HTHA)
| what has been removed on the nelson curve?
c-1/2mo
115
High Temperature Hydrogen Attack (HTHA)
| Damage may occur ___in the base metal, weld HAZs, and occasionally in welds.
randomly
116
High Temperature Hydrogen Attack (HTHA)
| _________ is not a proven method for the detection of damage.
AET
