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

ASME Code UG-134 allows supplemental PRVs (additional valves beyond the first) to be set at up to 105% of the vessel 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

Back pressure is the pressure at the outlet of a pressure relief device resulting from conditions in the discharge system such as header pressure or elevation.

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

In a conventional spring-loaded PRV, back pressure acts directly against the spring force on the disk, effectively increasing the set pressure by the amount of back pressure.

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

API 520 recommends that the non-recoverable inlet pressure drop not exceed 3% of the set pressure to prevent chatter, which causes rapid cyclic opening and closing that can damage the valve.

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

CDTP is the adjusted set pressure applied during bench testing at ambient conditions to compensate for the effect of operating temperature on spring characteristics and for superimposed back pressure.

(API 510) Certified Pressure Vessel Inspector Practice Test

(API 510) Certified Pressure Vessel Inspector Practice Test

API 510 Pressure Relief Devices 3