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

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.

A: A goes straight at boundary conditions — if restraints don't behave as modelled, every stress result is suspect. B matters for overpressure protection, but it doesn't change thrust paths. C affects operability and corrosion, not thrust resolution. D is a finishing activity and tells you nothing about load paths during a lift.

A: A is the straight calculation and lands in the range that causes real support problems if ignored. B sneaks in the wrong material property — stainless expands more, not less, and the number doesn't line up anyway. C double counts temperature effect and ignores realistic coefficients. D reflects a common myth; short duration doesn't make expansion disappear when metal heats quickly.

A: A is the functional reason — spring forces balance incorrectly when backpressure rises, and the valve can't behave predictably. B mixes thermal concerns into a pressure control issue. C is a piping consequence, not why API sets the rule. D can happen, but it's not what drives PSV stability criteria.

A: A is a classic trap — over-constraining the valve forces thrust to dump into the first spool, leading to plastic strain there. B affects sag and sustained stress, not a one-off thrust event. C shifts the problem downstream but doesn't explain flange-level distortion. D changes pass/fail reporting, not physical load paths.

A: A closes the loop between analysis and steel — wrong cold settings shift loads and kill the expansion case. B is a relief sizing issue, not a piping response check. C proves pressure integrity but tells you nothing about movement. D sits at the far end of the system and doesn't influence local stress.

A: A matches code intent and relief philosophy — occasional loads follow credible events, not mathematical worst cases. B feels safe but creates non-physical stresses that no real scenario produces. C ignores the dominant driver for relief piping failures. D misclassifies a short-duration momentum event and distorts allowables.