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CWB WELDING INSPECTOR LEVEL 2 EXAM
QUESTIONS AND VERIFIED ANSWERS| 100%
CORRECT| GRADE A
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?
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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 edge 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
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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
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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 (Magnetic Particle Testing) *PT (Penetrant Testing)
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