CWB LEVEL 2 QUESTIONS AND ANSWERS
What is the description of damage of a brittle fracture? - Answers-Sudden rapid fracture
under stress (residual or applied) where material exhibits little or no evidence of ductility
or plastic deformation
What type of Steel are of primary concern with brittle fractures? - Answers-Carbon and
low alloy steels. 400 series SS are also susceptible
What has a significant influence on toughness and resistance to brittle fractures? -
Answers-Steel cleanliness and grain size
In most cases brittle fractures occur only at what temperature? - Answers-Below the
charpy impact transition temperature.(or ductile-to-brittle transition temperature)
The point at which the toughness of the material drops off sharply
What kind of equipment or units can be affected for brittle fractures? - Answers-*Can
occur during ambient temperature hydro testing due to high stresses and low toughness
at the testing temperature
*Most processes run at elevated temperature so the main concern is during startup,
shutdown, or hydro/tightening testing.
What type of material can thermal fatigue happen on? - Answers-All material of
construction.
What are a couple but not all critical factors for thermal fatigue? - Answers-*Key factors
affecting thermal fatigue are the magnitude of the temperature swing and the frequency
(number of cycles)
*Damage is also prompted by rapid changes in surface temperature that results in
thermal gradient through the thickness or along the length of a component.
What are some affected units or equipment of thermal fatigue? - Answers-*Major
problem in coke drum shells
*another example is the mix point of hot/cold streams such as hydrogen mix points in
hydroprocessing units.
*locations where condensate comes in contact with steam systems such as de-
superheating or attemporating equipment
What is the appearance of a thermal fatigue crack? - Answers-*Usually initiates on the
surface. Generally wide and often filled with oxides due to elevated temperature
exposure. *May occur as single or multiple cracks
*usually propagate transverse to the stress and are usually dagger shaped,
transgranular, and oxide filled.
, *Can also sometimes be axial, or circumferential or both at the same location.
How is thermal fatigue best prevented? - Answers-Through design and operation to
minimize thermal stresses and thermal cycling. Methods of prevention include but not
all:
Control rate of heating and cooling during startup and shut down
Design that incorporates reduction of stress concentrators, blend grinding of weld
profiles & smooth transitions should be used.
What are 3 methods of inspection for thermal fatigue? - Answers-*Visual Inspection
*MT
*PT
Define Erosion? - Answers-Accelerated mechanical removal of surface material as a
result of relative movement between, or impact from solids, liquids, vapors or any
combination thereof.
Define Erosion-Corrosion? - Answers-description of the damage that occurs when
corrosion contributes to erosion by removing protective films or scales, or by exposing
the metal surface to further corrosion under the combined action of erosion and
corrosion.
What is the appearance of a brittle fracture? - Answers-Typically appear straight, non
branching, and largely devoid of any associated plastic deformation. (Although fine
shear lips may be found along free adge of the fracture or localized necking around
neck of crack.
What is thermal fatigue a result of ? - Answers-Cyclic Stress caused by variations in
temperature.
In thermal fatigue damage occurs as cracking, where may this occur? - Answers-Can
occur anywhere in a metallic component where relative movement or differential
expansion is constrained. Particularly under repeated thermal cycling.
What kind of units/equipment are affected by Erosion,
Erosion-Corrosion? - Answers-All types of equipment tat are exposed to moving fluid
and/or catalyst are subject to erosion, erosion-corrosion.
What is the appearance of damage for Erosion, Erosion-Corrosion? - Answers-
Localized loss in thickness in the form of pits, grooves, gullies, waves, rounded holes or
valleys. These often exhibit a directional pattern.
What are some ways of prevention/Mitigation for Erosion, Corrosion-Erosion? -
Answers--Improvement in design. Involving *shape, geometry, material selection
What is the description of damage of a brittle fracture? - Answers-Sudden rapid fracture
under stress (residual or applied) where material exhibits little or no evidence of ductility
or plastic deformation
What type of Steel are of primary concern with brittle fractures? - Answers-Carbon and
low alloy steels. 400 series SS are also susceptible
What has a significant influence on toughness and resistance to brittle fractures? -
Answers-Steel cleanliness and grain size
In most cases brittle fractures occur only at what temperature? - Answers-Below the
charpy impact transition temperature.(or ductile-to-brittle transition temperature)
The point at which the toughness of the material drops off sharply
What kind of equipment or units can be affected for brittle fractures? - Answers-*Can
occur during ambient temperature hydro testing due to high stresses and low toughness
at the testing temperature
*Most processes run at elevated temperature so the main concern is during startup,
shutdown, or hydro/tightening testing.
What type of material can thermal fatigue happen on? - Answers-All material of
construction.
What are a couple but not all critical factors for thermal fatigue? - Answers-*Key factors
affecting thermal fatigue are the magnitude of the temperature swing and the frequency
(number of cycles)
*Damage is also prompted by rapid changes in surface temperature that results in
thermal gradient through the thickness or along the length of a component.
What are some affected units or equipment of thermal fatigue? - Answers-*Major
problem in coke drum shells
*another example is the mix point of hot/cold streams such as hydrogen mix points in
hydroprocessing units.
*locations where condensate comes in contact with steam systems such as de-
superheating or attemporating equipment
What is the appearance of a thermal fatigue crack? - Answers-*Usually initiates on the
surface. Generally wide and often filled with oxides due to elevated temperature
exposure. *May occur as single or multiple cracks
*usually propagate transverse to the stress and are usually dagger shaped,
transgranular, and oxide filled.
, *Can also sometimes be axial, or circumferential or both at the same location.
How is thermal fatigue best prevented? - Answers-Through design and operation to
minimize thermal stresses and thermal cycling. Methods of prevention include but not
all:
Control rate of heating and cooling during startup and shut down
Design that incorporates reduction of stress concentrators, blend grinding of weld
profiles & smooth transitions should be used.
What are 3 methods of inspection for thermal fatigue? - Answers-*Visual Inspection
*MT
*PT
Define Erosion? - Answers-Accelerated mechanical removal of surface material as a
result of relative movement between, or impact from solids, liquids, vapors or any
combination thereof.
Define Erosion-Corrosion? - Answers-description of the damage that occurs when
corrosion contributes to erosion by removing protective films or scales, or by exposing
the metal surface to further corrosion under the combined action of erosion and
corrosion.
What is the appearance of a brittle fracture? - Answers-Typically appear straight, non
branching, and largely devoid of any associated plastic deformation. (Although fine
shear lips may be found along free adge of the fracture or localized necking around
neck of crack.
What is thermal fatigue a result of ? - Answers-Cyclic Stress caused by variations in
temperature.
In thermal fatigue damage occurs as cracking, where may this occur? - Answers-Can
occur anywhere in a metallic component where relative movement or differential
expansion is constrained. Particularly under repeated thermal cycling.
What kind of units/equipment are affected by Erosion,
Erosion-Corrosion? - Answers-All types of equipment tat are exposed to moving fluid
and/or catalyst are subject to erosion, erosion-corrosion.
What is the appearance of damage for Erosion, Erosion-Corrosion? - Answers-
Localized loss in thickness in the form of pits, grooves, gullies, waves, rounded holes or
valleys. These often exhibit a directional pattern.
What are some ways of prevention/Mitigation for Erosion, Corrosion-Erosion? -
Answers--Improvement in design. Involving *shape, geometry, material selection
