Corrosion, Welding & Material Defects Flashcards
7 cards from real API 510 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Corrosion, Welding & Material Defects flashcards as text
In API 510, the 'remaining life' of a pressure vessel is calculated by dividing which two values?
Answer: Actual thickness minus required thickness by the corrosion rate
Remaining life = (actual measured thickness − required minimum thickness) ÷ corrosion rate, giving the estimated years before the vessel wall reaches the retirement thickness.
Which form of corrosion attacks along grain boundaries of the metal, often caused by chromium depletion in stainless steels?
Answer: Intergranular corrosion
Intergranular corrosion in stainless steels is typically caused by sensitization — chromium carbide precipitation at grain boundaries depletes chromium in adjacent zones, making them anodic relative to the grain interior.
What is 'lamellar tearing' in the context of weld defects?
Answer: A subsurface cracking in base metal parallel to the surface caused by through-thickness stresses
Lamellar tearing occurs in rolled plate when through-thickness welding stresses exceed the low ductility of the plate in the short-transverse direction due to non-metallic inclusions aligned parallel to the plate surface.
Which API 510 inspection approach involves using risk assessment to prioritize and set inspection intervals?
Answer: Risk-based inspection (RBI)
Risk-based inspection (RBI) uses the probability and consequence of failure to establish inspection priorities and optimize intervals, allowing resources to be focused on higher-risk equipment.
Erosion-corrosion in pressure vessels is characterized by accelerated metal loss caused by:
Answer: Combined mechanical abrasion and corrosive attack from flowing fluid
Erosion-corrosion occurs when the mechanical action of a flowing fluid (especially with entrained solids or at turbulent zones) removes protective surface films, exposing fresh metal to corrosive attack in a continuous cycle.
What does the term 'sensitization' refer to in austenitic stainless steels?
Answer: Chromium carbide precipitation at grain boundaries reducing corrosion resistance
Sensitization occurs when austenitic stainless steel is heated to 800–1500°F (425–815°C), causing chromium to diffuse to grain boundaries and form chromium carbides, depleting adjacent zones of the chromium needed for corrosion resistance.
An incomplete fusion defect in a weld occurs when:
Answer: The weld metal does not bond completely to the base metal or previous weld pass
Incomplete fusion (lack of fusion) is a weld discontinuity where the weld metal fails to fuse completely with the base metal or adjacent weld beads, creating a planar unbonded interface that is highly detrimental under stress.