API 510 Pressure Relief Devices 3

Question 1

When multiple pressure relief valves are installed to protect a single pressure vessel, what is the maximum set pressure allowed for the additional (supplemental) valves per ASME Code UG-134?

Accepted Answer

105% of MAWP

Answer

Equal to the MAWP

Answer

103% of MAWP

Answer

110% of MAWP

Question 2

In pressure relief valve terminology, 'back pressure' is defined as:

Accepted Answer

The pressure existing at the outlet (discharge side) of the pressure relief device

Answer

The pressure required to reseat the valve after a relief event

Answer

The inlet pressure drop from the vessel to the valve during full flow

Answer

The hydrostatic test pressure applied to the downstream piping

Question 3

Which type of pressure relief valve is MOST sensitive to variable or high superimposed back pressure, which can raise its effective set pressure?

Accepted Answer

Conventional spring-loaded pressure relief valve

Answer

Balanced bellows pressure relief valve

Answer

Pilot-operated pressure relief valve

Answer

Modulating pilot-operated relief valve

Question 4

According to API 520, what is the maximum allowable non-recoverable inlet pressure drop to a pressure relief valve to prevent valve chatter during a relief event?

Accepted Answer

3% of set pressure

Answer

5% of set pressure

Answer

10% of set pressure

Answer

15% of set pressure

Question 5

What is 'Cold Differential Test Pressure' (CDTP) as applied to pressure relief valve bench testing?

Accepted Answer

The adjusted set pressure used during bench testing to account for operating temperature and back pressure effects

Answer

The pressure used when hydrostatic testing the valve body with cold water

Answer

The minimum burst pressure for rupture disks tested at ambient (cold) conditions

Answer

The pressure differential between the vessel MAWP and the normal operating pressure

Question 6

Why is a pilot-operated pressure relief valve (POPRV) preferred over a conventional spring-loaded PRV in applications with high or variable back pressure?

Accepted Answer

The POPRV set pressure is determined by the pilot valve sensing inlet pressure, making it independent of outlet back pressure

Answer

POPRVs are significantly less expensive to purchase and maintain

Answer

POPRVs have a much faster opening response time than spring-loaded valves

Answer

POPRVs do not require any periodic inspection or testing under API 510

Question 7

After a pressure relief valve is removed, repaired, and bench tested, what must occur before it is returned to service on a pressure vessel per API 510 requirements?

Accepted Answer

Its set pressure and operating characteristics must be verified by testing and documented

Answer

It must be hydrostatically tested at 1.5 times its set pressure before reinstallation

Answer

It must receive a new National Board 'VR' stamp from a certified repair organization

Answer

It must be approved in writing by the jurisdictional authority prior to reinstallation