API 510 Pressure Relief Devices 2 — Questions and Answers
Question 1: What is the maximum PRV inspection interval permitted by API 510 for a pressure relief valve in clean, non-corrosive, non-fouling service with documented good performance history?
- 1 year
- 3 years
- 5 years
- 10 years (Correct answer)
Correct answer: 10 years
API 510 allows inspection intervals up to 10 years for PRVs in proven non-corrosive, non-fouling services where performance history justifies the extension.
Question 2: During bench testing of a pressure relief valve, the valve opens at 108% of its stamped set pressure. What is the most likely cause?
- The valve spring is too weak
- Seat fouling, corrosion, or deposits are preventing normal opening (Correct answer)
- The test bench pressure gauge is out of calibration
- The valve inlet diameter is too small for the test flow
Correct answer: Seat fouling, corrosion, or deposits are preventing normal opening
Opening above set pressure typically indicates seat fouling, corrosion, or scale buildup that is mechanically preventing the valve disk from lifting at the correct pressure.
Question 3: Which type of pressure relief device provides zero leakage before activation and is non-reclosing after operation?
- Conventional spring-loaded safety relief valve
- Pilot-operated pressure relief valve
- Rupture disk (Correct answer)
- Balanced bellows relief valve
Correct answer: Rupture disk
A rupture disk is a solid membrane that provides zero leakage before burst and is non-reclosing, meaning it must be replaced after every activation.
Question 4: A pressure indicator or 'tell-tale' gauge is required between a rupture disk and a downstream PRV. What is its primary function?
- To indicate when the PRV has fully opened during a relief event
- To detect premature rupture disk failure or leakage and alert operators (Correct answer)
- To measure the normal operating pressure of the protected vessel
- To verify the set pressure of the PRV after installation
Correct answer: To detect premature rupture disk failure or leakage and alert operators
The tell-tale detects premature disk failure or leakage so operators can replace the disk before vessel pressure reaches the PRV set pressure, maintaining the dual-protection integrity.
Question 5: A pressure vessel with an MAWP of 150 psig is protected by a single PRV set at 150 psig. During a fire exposure scenario, what is the maximum allowable vessel pressure?
- 150 psig
- 165 psig
- 172.5 psig
- 181.5 psig (Correct answer)
Correct answer: 181.5 psig
For fire exposure with a single PRV, ASME Code allows 21% accumulation above MAWP: 150 × 1.21 = 181.5 psig maximum allowable pressure.
Question 6: Which of the following is NOT an acceptable method for testing and inspecting a pressure relief valve according to API 576?
- Bench testing with air or nitrogen at a certified test facility
- In-situ pop testing on the vessel using a lift assist device
- Calculation-only verification without any physical actuation of the valve (Correct answer)
- Visual inspection combined with bench testing after removal from service
Correct answer: Calculation-only verification without any physical actuation of the valve
Calculation-only verification without physical testing is never acceptable; PRVs must be physically actuated and tested by an approved method to confirm set pressure and operability.
Question 7: What distinguishes a 'relief valve' from a 'safety valve' in pressure relief device terminology?
- A relief valve is used only for gas service; a safety valve is used only for liquid service
- A relief valve opens gradually in proportion to overpressure; a safety valve opens with a rapid full-lift pop action (Correct answer)
- A relief valve has a higher flow capacity than a safety valve of the same size
- A relief valve requires an external power source; a safety valve is self-actuating
Correct answer: A relief valve opens gradually in proportion to overpressure; a safety valve opens with a rapid full-lift pop action
A relief valve opens gradually proportional to pressure increase above set and is typically used for liquid service, while a safety valve opens rapidly (pops) to full lift and is used for compressible fluids.
API 510 Pressure Relief Devices 2
What is the maximum PRV inspection interval permitted by API 510 for a pressure relief valve in clean, non-corrosive, non-fouling service with documented good performance history?