What is the set pressure for a gas carrier cargo tank pressure relief valve and how do you test its lifting?

flowchart TD
    A[Identify valve and current setting] --> B[Prepare: isolate tank, inert, permit-to-work]
    B --> C[Apply pressure with nitrogen/inert gas]
    C --> D[Monitor at valve: lift at set pressure ± tolerance]
    D --> E[Check reseat pressure and tightness]
    E --> F[Seal and record in log and certificate]

• Set pressure limit: not higher than vapour pressure used in tank design (IGC Code Ch 8 §8.2.5; MSC.1/Circ.1687 §6.7.2.3)
• Typical setting: 1,400–1,800 mmWG (MEPC.1/Circ.680 §2.4.4)
• Sequential lifting allowance: up to 5% above MARVS for ≤50% of total capacity (MSC.1/Circ.1687 §6.7.2.3)
• Test tolerance: ±10% (0–1.5 kp/cm²), ±6% (1.5–3.0), ±3% (≥3.0) (GC Code Ch 8 §8.2.5)
• Test action: open, examine, adjust, function test, seal; replace non-metallic membranes; record set pressure (UR Z16 §2.2.10; GC Code Ch 8 §8.2.5)
• Record: set pressure values retained aboard (GC Code Ch 8 §8.2.5)
• Survey: examined at Special Survey (2011 ESP Code Part B para 3.3.2; UR Z16 §2.2.10)