SAFETY VALVE IN

PROCESS INDUSTRY

Safety Valve????

• Safety Valve is an automatic pressure relieving devise actuated by upstream static pressure or pressure actuated device.

Why Safety Valve?

• Safety valve prevents excessive pressure build up in the system

• Safety valve prevents of pressurizing equipments and piping above it’s design condition if designed properly.

• Safety valve is an automatic mechanical device which can work in abnormalities like power, air, utility failure.

Safety Valve in daily operation

• Pressure Cooker in kitchen

Application

Safety valve is used to prevent excessive pressure build up in

• Closed circuit Reactors, Autoclaves

• Storage equipments

• High pressure Piping

• Heat Exchangers

• Furnace, steam generator

• Long distance gas, Liquid pipelines

• Closed loop systems

• Compression systems

Safety Valve Design

• Design Code

– API 520 Part 1 & 2

– API 526

Safety Valve Design contd.

• Critical Parameters

– Type of Valve

– Pressure conditions

– Required flow rate

– Mechanical design- orifice area etc.

Definition of terms

• Pressure Relief Valve. A Pressure relief valve is a spring loaded pressure relief device which is designed to open to relieve excess pressure and to reclose and prevent the further flow of fluid after normal conditions have been restored. It is characterized by rapid opening pop action or by opening generally proportional to the increase in pressure over the opening pressure. It may be used for either compressible or incompressible fluids, depending on design, adjustment, or application.

• Safety Valve. A safety valve is a pressure relief valve actuated by inlet static pressure and characterized by rapid opening or pop action. (It is normally used for steam and air services.)

– Low Lift Safety Valve. A low lift safety valve is a safety valve in which the disc lifts automatically such that the actual discharge area is determined by the position of the disc.

– Full-Lift Safety Valve. A full-Lift safety valve is a safety valve in which the disc lifts automatically such that the actual discharge area is not determined by the position of the disc.

Definition of terms Contd.

• Relief Valve A relief valve is a pressure relief device actuated by inlet static pressure having a gradual lift generally proportional to the increase in pressure over opening pressure. It may be provided with an enclosed spring housing suitable for closed discharge system application and is primarily used for liquid service.

• Safety Relief Valve. A Safety relief valve is a pressure relief valve characterized by rapid opening or pop action, or by opening in proportion to the increase in pressure over the opening pressure, depending on the application and may be used either for liquid or compressible fluid.

– Conventional Safety Relief valve. A conventional safety relief valve is a pressure relief valve which has its spring housing vented to the discharge side of the valve. The operational characteristics (opening pressure, closing pressure, and relieving capacity) are directly affected by changes of the back pressure on the valve.

– Balanced Safety Relief Valve. A balanced safety relief valve is a pressure relief valve which incorporates means of minimizing the effect of back pressure on the operational characteristics (opening pressure, closing pressure, and relieving capacity).

Definition of terms Contd.

• Pilot-Operated Pressure Relief Valve. A pilot –operated pressure relief valve is a pressure relief valve in which the major relieving device is combined with and is controlled by a self-actuated auxiliary pressure relief valve.

• Power-Actuated Pressure Relief Valve. A power-actuated pressure relief valve is a pressure relief valve in which the major relieving device is combined with and controlled by a device requiring an external source of energy.

• Temperature-Actuated Pressure Relief Valve. A temperature-actuated pressure relief valve is a pressure relief valve which may be actuated by external or internal temperature or by pressure on the inlet side.

• Vacuum Relief Valve. A vacuum relief valve is a pressure relief device designed to admit fluid to prevent an excessive internal vacuum; it is designed to reclose and prevent further flow of fluid after normal conditions have been restored.

Safety Valve Sizing• Flow rate requirement

Safety Valve sizing• Orifice Area Calculation

Orifice DesignationRef: API 526

Designation• D• E• F• G• H• J• K• L• M• N• P• Q• R• T

Effective Orifice Area (square Inch)

• 0.110• 0.196• 0.307• 0.503• 0.785• 1.287• 1.838• 2.853• 3.60• 4.34• 6.38• 11.05• 16.0• 26.0

Conventional safety valve

Ref: API 520 part 1

Balanced Below safety valve

Ref: API 520 part 1

Pilot Operated Safety Valve

Ref: API 520 part 1

Pressure Level relationship

Terminology

• Set Pressure: is the inlet gauge pressure at which the pressure relief valve is set to open under service condition.

• Back Pressure: is the pressure that exists at the outlet of a pressure relief device as a result of the pressure in the discharge system.

• Blow down: is the difference between the set pressure and the closing pressure of a pressure relief valve, expressed as a percent of the set pressure or in pressure unit.

Terminology

• Over pressure: is the pressure increase

over the set pressure of the relieving device, expressed in pressure unit or as a percent.

• Closing Pressure: is the value of

decreasing inlet static static pressure at which valve disc reestablished contact with the seat or at which lift becomes zero.