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NBBI Inservice Inspector (IS) study materials
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NBBI Inservice Inspector (IS): NBIC Part 4 - Pressure Relief Devices

NBBI Inservice Inspector (IS) · Work through your exam, one topic at a time.

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NBIC Part 4 - Pressure Relief Devices

Scope and stamps

Part 4 covers pressure relief valves, pilot-operated valves, and rupture disk devices: installation, inspection, testing, setting, and repair. Manufacturers hold ASME V (boilers) or UV (vessels) stamps; repair organizations hold a National Board VR Certificate of Authorization. Rupture disks are never repaired - they are replaced.

Requirements

  • Rated capacity must equal or exceed the maximum pressure source, and set pressure must not exceed the MAWP of the protected item.
  • Set pressure tolerance: ±2 psi at or below 70 psi set pressure; ±3% above 70 psi.
  • Bench test with a medium matching the service - steam for steam, air or gas for gas, water for liquid relief. Record as-found set pressure first, then as-left after adjustment.
  • Blowdown must fall within the code of construction's limit (Section VIII adjustable valves close within 7% of set pressure).
  • After setting, seal the valve and record set pressure, date, and tester. At inspection verify the seal is intact, the gag is removed, no isolation valve is closed, and discharge piping is supported and drained.
  • Repairs produce Form R-4, and the repaired valve is re-set and re-tested before return to service.

Worked example

An air receiver with 150 psi MAWP carries a relief valve set at 150 psi. The as-found bench test pops at 143 psi - 4.7% low, outside the ±3% band of 145.5 to 154.5 psi. The valve is repaired by a VR shop, re-tested, and as-left found at 149 psi, which is acceptable; the valve is sealed and Form R-4 is issued.

Traps

Mixing the ±2 psi and ±3% rules. Testing a steam-service valve on air. Ignoring backpressure on a conventional valve's discharge. Accepting a valve with a broken or missing seal.