Design of Pressure Vessel using PV Elite – Fabrication & Heat Treatment Requirement for Design Engineer

A: Governing principle: PWHT primarily manages residual stress and fracture toughness, not steady-state strength. Applied here: Using a later UCS-56 exemption without contractual cover leaves high residual stress locked in, and offshore hydrotests or cold start-ups push the vessel into the brittle regime where cracks can run. Distractor trap: Option C catches engineers who equate PWHT with allowable stress tables, but Div 1 allowable stress isn’t automatically reduced just because PWHT is skipped.

A: Governing principle: UCS-56 soak time is based on controlling thickness, typically 1 hour per 25 mm with a stated minimum. Applied here: 60 mm gives about 2.4 hours, so a practical answer is roughly 2–3 hours, not a full shift. Distractor trap: Option C mixes up exemption thresholds with soak duration and ignores that exemption isn’t automatic once you choose to PWHT.

A: Governing principle: PWHT doesn’t heal hydrogen cracks; it can actually make pre-existing defects easier to propagate under load. Applied here: Linear toe cracks post-PWHT and during hydrotest point back to hydrogen picked up during welding, not a service-related mechanism. Distractor trap: Option B sounds metallurgically credible but lamellar tearing shows step-like internal cracking, not toe-linear surface indications.

A: Governing principle: UCS-56 controls heating and cooling rates to limit thermal gradients and stress reintroduction. Applied here: Letting the vessel cool too fast reintroduces residual stress, so you stabilize and recover soak before proceeding. Distractor trap: Option D misapplies temper embrittlement concerns and ignores that uncontrolled gradients are the immediate risk.