A: Governing principle: MAWP is the maximum allowable pressure at a given temperature based on code calculations. Applied here, design pressure cannot exceed MAWP at the same temperature, regardless of relief protection. Option C catches engineers importing PSV logic into mechanical design limits.

A: Governing principle: Code thickness is tied to design conditions, not day-to-day operation. Applied here, lowering operating pressure has no mechanical credit unless the vessel is re-rated under the code. Option A attracts engineers thinking in control terms rather than certification terms.

A: Governing principle: Brittle fracture risk is managed through MDMT and material toughness, not pressure limits alone. Applied here, operating below MDMT falls outside the safe envelope even if the vessel was code-built. Option A catches those who overgeneralize impact testing requirements.

A: Governing principle: Hydrotest pressure scales with MAWP and allowable stress ratio at test temperature. Applied here, 1.3 × 20 barg × 1.2 gives 31.2 barg. Option A traps engineers who drop the stress ratio adjustment.

A: Governing principle: Nameplate requirements are explicitly listed in the code. Applied here, corrosion allowance informs design thickness but is not a mandatory stamping item. Option C appeals to inspectors thinking operationally rather than by code text.

A: Governing principle: MAWP is the maximum pressure the vessel can safely withstand by design. Applied here, relief devices cannot be used to justify exceeding that limit. Option A catches engineers used to focusing only on overpressure scenarios.

A: Governing principle: Codes address general membrane stresses, not all local damage mechanisms. Applied here, nozzle areas often see flow-induced corrosion outside code thickness assumptions. Option A traps engineers blaming the code rather than service conditions.

A: Governing principle: Corrosion allowance is sacrificial and excluded from required thickness. Applied here, loss within the allowance does not breach code limits if structural thickness remains. Option A appeals to those treating allowance as a hard limit.

A: Governing principle: Code compliance is based on assumed load cases at design time. Applied here, unanticipated cyclic duty can introduce fatigue outside original assumptions. Option A traps engineers who know fatigue is limited in Section VIII but overstate the gap.