Understanding Relief Sizing Calculations

What is the primary purpose of a pressure relief valve (PRV) in a process system?

• To increase the flow rate of a fluid

• To protect equipment from overpressure by releasing excess pressure

• To measure the pressure of a fluid in a pipeline

• To regulate the temperature of a process stream

Which standard is most commonly referenced for the sizing of pressure relief devices in the oil and gas industry?

• ASME Section VIII

• API Standard 520

• ISO 9001

• NFPA 72

What does the term "set pressure" refer to in the context of relief valve sizing?

• The pressure at which the relief valve fully closes

• The maximum allowable working pressure of the vessel

• The pressure at which the relief valve begins to open

• The back pressure downstream of the relief valve

When sizing a relief valve for two-phase flow (vapor-liquid mixture), which of the following approaches is most appropriate according to industry best practices?

• Size the valve only for the vapor phase and ignore the liquid contribution

• Use the Omega method or homogeneous equilibrium model (HEM) to account for flashing and two-phase behavior

• Apply the standard gas sizing equation with the average density of the mixture

• Size the valve for liquid service only, as liquid is incompressible and more conservative

1. What are the steps necessary for relief sizing calculation?

A. Determining the type of flow (liquid, vapor, or two-phase)

B. Selecting the type of relief device (Spring or rupture disc)

C. Determining the rate of material release through the relief device by using an appropriate source model.

D. Determining the relief device vent area by using an appropriate equation based on fundamental hydrodynamic principles.

• A B C and D

• B A C and D

• B C A and D

• C D A and B

How the required relief vent area changes with the overpressure?

• The relief vent area is increased substantially as the overpressure increases.

• The relief vent area is reduced substantially as the overpressure increases.

• The relief vent area may increase or decrease as the overpressure increases.

Which situation may result in “chattering” ?

• Inappropriate reseat pressure

• Too large relief area

• Too low flow to maintain the valve seat in the open position.

• Too many reliefs

What different between flow through an orifice and a spring-type relief?

• An orifice has a fixed area but an area of a spring-type relief changes as the pressure changes.

• A spring-type relief has a fixed area but an area of an orifice changes as the pressure changes.

• The back pressure affects the flow throguh a spring-type relief only.

A building is made from sheet metal sides that can withstand pressure less than 0.1 bar gauge. What is the type of this building structure ?

• Low-pressure structure

• Moderate-pressure structure

• High-pressure structure