API 510 Pressure Relief Devices 1 — Questions and Answers
Question 1: What is the term for the pressure at which a pressure relief valve (PRV) is designed to open, as stamped on its nameplate?
- Operating pressure
- Set pressure (Correct answer)
- Accumulation pressure
- Back pressure
Correct answer: Set pressure
Set pressure is the inlet pressure at which the PRV is set to open, and it is the value stamped on the valve nameplate.
Question 2: According to ASME Code and API 510, what is the maximum allowable accumulation above MAWP for a single PRV protecting a pressure vessel during a fire exposure case?
- 3%
- 10%
- 16%
- 21% (Correct answer)
Correct answer: 21%
ASME Code allows accumulation up to 21% above MAWP for fire exposure cases when a single pressure relief valve is installed.
Question 3: In pressure relief valve terminology, what is 'blowdown'?
- The pressure increase above MAWP during relief
- The difference between set pressure and reseating pressure (Correct answer)
- The flow rate through the valve at full lift
- The pressure drop across the valve inlet piping
Correct answer: The difference between set pressure and reseating pressure
Blowdown is the difference between the set pressure and the pressure at which the valve reseats (closes) after opening.
Question 4: Which API standard specifically covers the sizing, selection, and installation of pressure-relieving devices in petroleum and petrochemical plants?
- API 510
- API 520 (Correct answer)
- API 570
- API 580
Correct answer: API 520
API 520 covers the sizing, selection, and installation of pressure-relieving systems and is a key companion document to API 510.
Question 5: When a rupture disk is installed upstream (inlet side) of a pressure relief valve, what is the primary safety concern with this arrangement?
- The disk increases the effective set pressure of the PRV
- Pressure buildup between the disk and PRV can prevent the PRV from opening correctly (Correct answer)
- This configuration is explicitly prohibited by ASME Code
- The rupture disk reduces the total flow capacity by 50%
Correct answer: Pressure buildup between the disk and PRV can prevent the PRV from opening correctly
Gas or pressure accumulation in the space between the rupture disk and PRV creates back pressure that can prevent the PRV from opening at its stamped set pressure, requiring a pressure indicator in that space.
Question 6: What is the maximum set pressure permitted for a pressure relief valve protecting a pressure vessel with an MAWP of 200 psig in normal (non-fire) service?
- 180 psig
- 190 psig
- 200 psig (Correct answer)
- 210 psig
Correct answer: 200 psig
The set pressure of a PRV must not exceed the vessel's MAWP; therefore, the maximum set pressure is 200 psig.
Question 7: According to API 510, who is responsible for establishing the inspection and testing intervals for pressure relief devices?
- The original valve manufacturer
- The local regulatory authority alone
- The inspector in conjunction with the owner/user (Correct answer)
- Only a licensed professional engineer (PE)
Correct answer: The inspector in conjunction with the owner/user
API 510 assigns responsibility for establishing PRV inspection intervals to the inspector working in conjunction with the owner/user, based on service history and risk.
API 510 Pressure Relief Devices 1
What is the term for the pressure at which a pressure relief valve (PRV) is designed to open, as stamped on its nameplate?