Pressure Relief Valve Piping (PSV Piping) Stress Analysis using Caesar II

A: A is where the API 521 approach actually lands once you use relieving density and sonic velocity at the outlet — it feels high, but that's typical for DN150 at these conditions. B is tempting because engineers reach for operating cases, but momentum thrust is a relieving phenomenon; using normal density undercuts the force badly. C sounds conservative, and some clients do apply load factors, but they belong in the Caesar load case definition, not baked into the physics. D treats thrust like a pressure end cap load, which ignores velocity entirely and misses why elbows see such violent loads during relief.

A: A aligns with ASME B31.3 intent for occasional loads like PSV thrust, recognising rarity and short duration. B sounds safe, but it erases the code distinction between sustained and occasional cases and usually forces unnecessary steel. C mixes thermal expansion logic into a momentum-driven event; the governing check is not displacement-controlled. D is a trap from mechanical design thinking — piping codes never allow you to run up to yield just because the event is brief.

A: A fits the temperature and chemistry — sulfidation rates climb fast above 260 °C and thinning shows up as scale. B is a classic sour-service worry, but SSC needs liquid water and usually lower temperatures. C explains corrosion in cool, wet systems; at 350 °C you don't have stable carbonic acid. D shows up in austenitic stainless steels, not carbon steel, and needs a different temperature window.

A: A ties the symptoms together: high Mach number gas, short events, and failures concentrated on small-bore attachments. B can break things, but you'd expect large supports or elbows to show distress too. C happens over long cycles and usually produces broader cracking patterns. D is always blamed first, yet good welds still crack when excitation frequencies line up with acoustic energy.