CWB Level 2 Questions and Complete
Detailed Answers
What is the description of damage of a brittle fracture? - Answer: 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? - Answer: Carbon and low alloy
steels. 400 series SS are also susceptible
What has a significant influence on toughness and resistance to brittle fractures? - Answer: Steel
cleanliness and grain size
In most cases brittle fractures occur only at what temperature? - Answer: 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? - Answer: *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 is the appearance of a brittle fracture? - Answer: 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 ? - Answer: Cyclic Stress caused by variations in temperature.
In thermal fatigue damage occurs as cracking, where may this occur? - Answer: Can occur anywhere
in a metallic component where relative movement or differential expansion is constrained.
Particularly under repeated thermal cycling.
What type of material can thermal fatigue happen on? - Answer: All material of construction.
, What are a couple but not all critical factors for thermal fatigue? - Answer: *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? - Answer: *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? - Answer: *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? - Answer: 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? - Answer: *Visual Inspection
*MT
*PT
Define Erosion? - Answer: 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? - Answer: 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.
Detailed Answers
What is the description of damage of a brittle fracture? - Answer: 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? - Answer: Carbon and low alloy
steels. 400 series SS are also susceptible
What has a significant influence on toughness and resistance to brittle fractures? - Answer: Steel
cleanliness and grain size
In most cases brittle fractures occur only at what temperature? - Answer: 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? - Answer: *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 is the appearance of a brittle fracture? - Answer: 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 ? - Answer: Cyclic Stress caused by variations in temperature.
In thermal fatigue damage occurs as cracking, where may this occur? - Answer: Can occur anywhere
in a metallic component where relative movement or differential expansion is constrained.
Particularly under repeated thermal cycling.
What type of material can thermal fatigue happen on? - Answer: All material of construction.
, What are a couple but not all critical factors for thermal fatigue? - Answer: *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? - Answer: *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? - Answer: *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? - Answer: 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? - Answer: *Visual Inspection
*MT
*PT
Define Erosion? - Answer: 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? - Answer: 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.
