CWB Level 2 QUESTIONS &
ANSWERS(RATED A+)
What is the description of damage of a brittle fracture? - ANSWERSudden 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? - ANSWERCarbon
and low alloy steels. 400 series SS are also susceptible
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 has a significant influence on toughness and resistance to brittle fractures? -
ANSWERSteel cleanliness and grain size
In most cases brittle fractures occur only at what temperature? - ANSWERBelow the
charpy impact transition temperature.(or ductile-to-brittle transition temperature)
The point at which the toughness of the material drops off sharply
What is the appearance of a brittle fracture? - ANSWERTypically 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 ? - ANSWERCyclic Stress caused by variations in
temperature.
In thermal fatigue damage occurs as cracking, where may this occur? -
ANSWERCan 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? - ANSWERAll 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.
, How is thermal fatigue best prevented? - ANSWERThrough 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 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.
What are 3 methods of inspection for thermal fatigue? - ANSWER*Visual Inspection
*MT
*PT
Define Erosion? - ANSWERAccelerated 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? - ANSWERdescription 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 kind of units/equipment are affected by Erosion,
Erosion-Corrosion? - ANSWERAll 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? -
ANSWERLocalized loss in thickness in the form of pits, grooves, gullies, waves,
rounded holes or valleys. These often exhibit a directional pattern.
What are the predominant factors in determining the fatigue resistance of a
component? - ANSWERGeometry, Stress Level, Number of cycles and material
properties ( strength, hardness, micro-structure)
With mechanical fatigue where do fatigue cracks usually initiate? - ANSWERSurface
of mechanical notches, stress raisers under cyclic loading, Weld joints, tool
markings, grinding marks, corrosion areas, key holes on drive shafts
ANSWERS(RATED A+)
What is the description of damage of a brittle fracture? - ANSWERSudden 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? - ANSWERCarbon
and low alloy steels. 400 series SS are also susceptible
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 has a significant influence on toughness and resistance to brittle fractures? -
ANSWERSteel cleanliness and grain size
In most cases brittle fractures occur only at what temperature? - ANSWERBelow the
charpy impact transition temperature.(or ductile-to-brittle transition temperature)
The point at which the toughness of the material drops off sharply
What is the appearance of a brittle fracture? - ANSWERTypically 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 ? - ANSWERCyclic Stress caused by variations in
temperature.
In thermal fatigue damage occurs as cracking, where may this occur? -
ANSWERCan 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? - ANSWERAll 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.
, How is thermal fatigue best prevented? - ANSWERThrough 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 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.
What are 3 methods of inspection for thermal fatigue? - ANSWER*Visual Inspection
*MT
*PT
Define Erosion? - ANSWERAccelerated 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? - ANSWERdescription 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 kind of units/equipment are affected by Erosion,
Erosion-Corrosion? - ANSWERAll 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? -
ANSWERLocalized loss in thickness in the form of pits, grooves, gullies, waves,
rounded holes or valleys. These often exhibit a directional pattern.
What are the predominant factors in determining the fatigue resistance of a
component? - ANSWERGeometry, Stress Level, Number of cycles and material
properties ( strength, hardness, micro-structure)
With mechanical fatigue where do fatigue cracks usually initiate? - ANSWERSurface
of mechanical notches, stress raisers under cyclic loading, Weld joints, tool
markings, grinding marks, corrosion areas, key holes on drive shafts
