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Module 4 Fatigue SCC Flashcards

1
Q

Thermal Fatigue

affected material?

A

all

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2
Q

Thermal Fatigue

Magnitude of the __(2)___

A

temperature swing & frequency

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3
Q

Thermal Fatigue

There is no set limit on swings, but cracking may be suspected if the temperature swing exceeds about _____

A

200°F - 300F

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4
Q

Thermal Fatigue

where would most stress be located?

A

c. notches and sharp corners

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5
Q

Thermal Fatigue

affected equipment? (6)

A

a. Mix Points
b. Major Problem in Coke Drums
c. S/D and S/U
d. steam-generating equipment at rigid attachments
e. tubes in high temp that penetrate through the cooler waterfall tubes (tubes in the boiler where water is evaporated to steam)
f. steam actuated soot blowers in heater or boilers

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6
Q

Thermal Fatigue

Cracks usually initiate on the surface of the component __or ___

A

ID or OD.

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7
Q

Thermal Fatigue
Thermal fatigue cracks propagate ______to the stress and are usually________. However, cracking may be axial or circumferential of both

A

TRANSVERSE / dagger-shaped

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8
Q

Thermal Fatigue

NDE? most effective

A

PT/ MT / WFMT / ECT/ ACFM / EMAT/VT

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9
Q

Thermal Fatigue

best prevent through?

A

design / operations

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10
Q 
Thermal Fatigue
other prevention (3)
A

b. Incorporate sufficient flexibility
i. Drain lines should provided on soot blowers
c. a liner or sleeve installed to prevent colder liquid from contacting

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11
Q

Mechanical Fatigue

typically well below the ____ of the material

A

YS

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12
Q

Mechanical Fatigue

affected material?

A

all engineered alloys

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13
Q

Mechanical Fatigue\

___(2)___exhibit an endurance limit below which fatigue cracking will ____occur regardless of the number of cycles

A

CS and Titanium / NOT

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14
Q

Mechanical Fatigue
___(3), and most other non-ferrous alloys have a fatigue characteristic that does NOT exhibit an endurance limit (fatigue fracture can be

A

300 / 400 Series SS, aluminum

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15
Q

Mechanical Fatigue
Heat Treatment can have an effect on fatigue resistant of a metal - _______can improve fatigue resistance of CS/low alloys

A

quenching and tempering

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16
Q

Mechanical Fatigue

The ratio of endurance limit to ___is typically between 0.4 and 0.5

A

UTS

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17
Q 
Mechanical  Fatigue
affected equipment (7)
A

a. socket welds and small bore piping
b. equipment not properly supported
c. safety RV that are subject to chatter
d. high pressure drop CV and steam reducing stations (vibration problems)
e. Rotating shafts on pumps/compressors have stress concentration due to changes in radii and keyways
f. heat exchanger tubes susceptible to vortex
g. transient conditions (S/U & S/D)

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18
Q

Mechanical Fatigue

appearance?

A

clam shells /beach mark

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19
Q

Mechanical Fatigue

best defense?

A

good design

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20
Q

Mechanical Fatigue

_____to rely on the NDE methods for routine. What NDE to use for cracks???

A

impractical / PT , MT , SWUT

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21
Q

Corrosion Fatigue

factor (2)

A

corrosive environment and cyclic loading

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22
Q

Corrosion Fatigue

affected material?

A

all metals/ alloys

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23
Q

Corrosion Fatigue

endurance limit?

A

there is none

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24
Q

Corrosion Fatigue

stress concentration is important?

A

yes

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25
``` Corrosion Fatigue affected equipment (3) ```
Rotating equipment, deaerators, cycling boilers
26
Corrosion Fatigue | appearance? (4)
a. relatively straighter b. very little plastic deformation c. in cycling boilers damage appears on the water side of buckstay. d. transgranular, not branched
27
Corrosion Fatigue | prevention? for rotating equipment/deaerators/cycling boilers?
a. Rotating equipment - upgrade to corrosion resistant material, coating, use corrosion inhibitors b. Deaerators - ensure the use of proper feed water and condensate chemical control minimize residual stress c. Cycling boilers - start up slowly
28
Chloride SCC | need ____
water
29
Chloride SCC | what material is high resistant?
Nickel based /
30
Chloride SCC | which SS not susceptible?
400SS
31
Chloride SCC | what is susceptible?
All 300 series SS is highly susceptible (8-12% Ni) | duplex SS are more resistant
32
Chloride SCC | _____will increase the likelihood for cracking, but there is no identified
O2
33
Chloride SCC ClSCC usually occurs at pH values above ____ ClSCC tendency ______in the alkaline pH region.
2 ..../ decreases
34
Chloride SCC | temp when it occurs?
>140F
35
Chloride SCC | >35% ni / >45% Ni
high resistant / immune
36
Chloride SCC | % of Ni that is susceptible
8-12%
37
Chloride SCC | appearance (2)
c. spider web | d. craze cracking
38
Chloride SCC | surface breaking cracks in ____ or _____
process / externally
39
Chloride SCC even if process side has no Chloride, piping or equipment operate _____expose to alternating wet / dry conditions externally
>140F
40
Ammonia SCC | wet ammonia critical factors? what metal susceptible
i. water required ii. Oxygen required Any Temp Copper
41
Ammonia SCC | Dry ammonia critical factors? what metal susceptible
a. Dry Ammonia cracks Steel (<0.2% water) i. High temp -> increase cracks ii. Oxygen any small amount Carbon steel
42
Ammonia SCC | wet ammonia critical factors?(5) what metal susceptible
``` water required Oxygen required Any Temp stress pH > 8.5 Copper zinc content (>15%) ```
43
Ammonia SCC | Dry ammonia critical factors?(3) what metal susceptible
a. Dry Ammonia cracks Steel (<0.2% water) i. High temp -> increase cracks ii. Oxygen any small amount Carbon steel
44
Ammonia SCC | what % of zinc is susceptible?
>15%
45
Ammonia SCC for wet pH >
8.5
46
Ammonia SCC | for dry water %?
<0.2%
47
Ammonia SCC | for dry , amount of o2?
any small
48
Ammonia SCC | affected equipment?
a. copper zinc alloy tube in heat exchangers | b. where ammonia is present , BFW, CW, acid neutralizer
49
Ammonia SCC | ammonia is used as
neutralizer for acid
50
Ammonia SCC | appearance
bluish color crack
51
Ammonia SCC | prevention for copper (2) / CS (5)
``` Copper a. <15% zinc has improved resistance b. 90-10 / 70-30 Cu-Ni have low susceptibilities. CS a. Add water to >0.2% b. vapor phases could have less than 0.2% water present due to partitioning of ammonia in water phases c. low strength steels (<70 KSI) d. prevent ingress of o2 e. N2 purge ```
52
Ammonia SCC | inspection? for copper and CS
``` Copper a. pH and ammonia content draw samples b. Tubes use ECT or VT CS a. WFMT is typically used b. angle beam UT (SWUT or PAUT) can be performed from the outside surface; ```
53
Ethanol SCC | affected equipment primarily
Carbon Steel
54
Ethanol SCC | ethanol SCC has ____been reported in FGE manufacturers
NOT
55
Ethanol SCC | a. cracks both ____ to weld OR ____
parallel / transverse
56
Ethanol SCC | _____has been found in FGE meeting ASTM D4806 specs + water content
Cracking
57
Ethanol SCC | Concentration of Ethanol ppm?
as little as 20 ppm
58
Ethanol SCC water %? what may be added to __________for ____corrosion?
• Water – 0.1 to 4.5% vol% - Corrosion inhibitor may be added , but effect is not understood for Mitigation for general corrosion.
59
Ethanol SCC | most important factor?
• Aeration (oxygen) is the most important factor for determining ethanol SCC susceptibility.
60
Ethanol SCC | prevention? (2)
a. reduce by PWHT | b. apply coating
61
Ethanol SCC | ______chloride content tends to increase severity of cracking
Increasing
62
``` Ethanol SCC inspection? a. _____ to predict and detect b. routine inspection is ____ c. efforts need to be focused on prevention d. WFMT is _____Method e. ACFM for less surface prep ```
difficult not effective PREFERRED
63
Ethanol SCC | related mech
Alkanies SCC
64
Ethanol SCC | related mech
Alkanies SCC
65
Liquid Metal Embrittlement | how fast can cracking happen with molten metal
as quick as seconds
66
Liquid Metal Embrittlement | LME occurs with low melting point metals such as __(6)__
zinc, mercury, cadmium, lead , copper and tin
67
Liquid Metal Embrittlement | LME is relevant and of most concern after_______containing mercury that leaks into/onto equipment.
a fire after a failure instrument
68
Liquid Metal Embrittlement | Most RELEVANT example
is refining is 300 SS in or near contact with galvanized steel where zinc melts during a fire and crack SS
69
Liquid Metal Embrittlement | where is mercury found?
in some crude oil and can condense in the atmospheric tower overhead
70
Liquid Metal Embrittlement a. appear as b. can only be confirmed through metallography
brittle cracks in otherwise ductile material
71
Liquid Metal Embrittlement a. cracks are often _______ b. high density of mercury, ______ can be used to located deposit inside equipment c. existence through ______
a. visually apparent b. RT c. Metallography
72
Polythonic Acid SCC aka graindropping affected material? normally occur?
sensitized 300S and some 800/600 alloys | b. normally occur in s/d & s/
73
Polythonic Acid SCC aka graindropping | description
Sulfur reacts with air (oxygen) and moisture to form sulfur acids (Polythionic acid).
74
Polythonic Acid SCC aka graindropping | Material must be in a susceptible or ______condition.
“sensitized”
75
Polythonic Acid SCC aka graindropping a. Low carbon grades “L” (0.03%C) are ____susceptible b. 304/304H & 316/316H are ______susceptible to sensitizing
a. less | b. more
76
Polythonic Acid SCC aka graindropping | Sensitization definition?
is the loss of alloy integrity. It results from chromium depletion
77
Polythonic Acid SCC aka graindropping | Sensitization temperature it occurs at?
700-1500F.
78
Polythonic Acid SCC aka graindropping | __(2)___ has a significant effect on sensitization susceptibility.
carbon content and thermal history
79
Polythonic Acid SCC aka graindropping | __(2)___ has a significant effect on sensitization susceptibility.
carbon content and thermal history
80
Polythonic Acid SCC aka graindropping Sensitization is the loss of alloy integrity. It results from chromium depletion refer to the _________(3)___ dependent formation of Cr carbides .
composition/time/temperature
81
Polythonic Acid SCC aka graindropping | . typically occurs ____to welds
NEXT
82
Polythonic Acid SCC aka graindropping | corrosion or loss in thickness is usually _____
negligible
83
Polythonic Acid SCC aka graindropping | Chemically stabilized grades __(2)___ have improved resistance to PASCC.
321 & 347
84
Polythonic Acid SCC aka graindropping | Chemically stabilized grades have small amounts of __(2) ___ added.
Ti or Nb
85
Polythonic Acid SCC aka graindropping | heated the firebox heated ___ the dew point to prevent acid from forming
above
86
Polythonic Acid SCC aka graindropping | monitoring PTA SCC cracking operation is ____effective
NOT
87
Polythonic Acid SCC aka graindropping | Most effective is managed by ____rather than _____
prevention / inspection
88
Polythonic Acid SCC aka graindropping | normally occurs in
during S/D and S.U
89
Polythonic Acid SCC aka graindropping | ___(NDE)____ is MOST common to detect
PT
90
Polythonic Acid SCC aka graindropping | ______can be used to determine the degree and extent of sensitization
FMR
91
Corrosion Fatigue | inspection for Deaerators?
WFMT
92
Corrosion Fatigue | inspection for Rotating equipment?
VT as well as UT, PT, and MT
93
Corrosion Fatigue | inspection for cycling boilers
The first sign of damage is usually a pinhole leak on the cold side of a waterwall tube at a buckstay attachment. Highly stressed regions in the boiler where cracking can occur can be inspected using angle beam UT (SWUT or PAUT) or EMAT techniques.
94
Corrosion Fatigue The fatigue fracture surface will appear brittle, and the cracks will be relatively straight, _____, and unbranched. There may be multiple ______cracks
transgranular / parallel
95
LME | _____ contributes to crack propagation rates
Tensile stress
96
LME A susceptible metal in contact with a low melting metal at low temperatures may crack later when the temperature rises ____the melting temperature of the low melting alloy
above
97
PAA Cracking may propagate rapidly through the wall thickness of piping and components in a matter of ____
minutes or hours

API571 (13 decks)

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