Material Evaluation and Selection 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 Material Evaluation and Selection flashcards as text
When inspecting a weld overlay (cladding) applied for corrosion protection in a pressure vessel, the most critical metallurgical concern is:
Answer: Excessive dilution of the overlay by the base metal, which reduces corrosion resistance
High dilution of the overlay by the base metal reduces the alloy content (particularly chromium in stainless overlays), which can eliminate the corrosion protection the overlay was intended to provide.
Post-weld heat treatment (PWHT) of carbon steel pressure vessel welds is performed primarily to:
Answer: Reduce residual welding stresses and lower HAZ hardness to improve toughness and SCC resistance
PWHT relieves thermally induced residual stresses and tempers hard martensite in the HAZ, reducing susceptibility to brittle fracture and environmentally assisted cracking.
The risk of High-Temperature Hydrogen Attack (HTHA) in pressure vessels operating at elevated temperatures and hydrogen partial pressures is evaluated using:
Answer: API RP 941 (Nelson Curves)
API RP 941 provides the Nelson Curves that define temperature and hydrogen partial pressure limits for carbon and alloy steels to avoid HTHA in refinery hydrogen service.
Austenitic stainless steel pressure vessels in service above approximately 140°F (60°C) in the presence of chlorides are most likely to fail by:
Answer: Chloride stress corrosion cracking (SCC)
Chloride SCC is the dominant failure mode for austenitic stainless steels in chloride environments above roughly 140°F, requiring only tensile stress, chloride ions, and elevated temperature.
Chrome-moly alloy steels such as 2.25Cr-1Mo (P22) are selected over carbon steel for service above approximately 850°F (454°C) primarily because they offer:
Answer: Higher creep strength and greater oxidation resistance at elevated temperatures
Chromium and molybdenum additions significantly raise the creep strength and oxidation resistance, allowing these steels to sustain design stresses where carbon steel would fail by creep deformation.
When selecting a replacement material for a high-temperature pressure vessel shell, the allowable stress at the design temperature must be obtained from:
Answer: ASME Section II Part D stress tables for the selected material
ASME Section II Part D contains the allowable stress tables for all code-approved pressure vessel materials across the full design temperature range.
If the original ASME design specification required supplemental impact testing (e.g., S-2 supplementary requirements), replacement material used in a repair must:
Answer: Meet at minimum the same supplemental impact test requirements as the original specification
Replacement material must maintain the original design intent, including any supplemental testing requirements established by the original code of construction.