Safety valves are automatic pressure relief devices that prevent excessive pressure buildup in systems like reactors, pipelines, and compressors. They open rapidly when pressure exceeds the set point to safely release pressure and reclose once normal pressure is restored. Proper safety valve design and sizing according to codes like API 520 and 526 is critical to ensure the valve can relieve the required flow rate without overpressurizing equipment. Key parameters include pressure conditions, required flow rate, orifice area, and type of valve.

1. SAFETY VALVE IN
PROCESS INDUSTRY

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

3. 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.

4. Safety Valve in daily operation
• Pressure Cooker in kitchen

5. 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

6. Safety Valve Design
• Design Code
– API 520 Part 1 & 2
– API 526

7. Safety Valve Design contd.
• Critical Parameters
– Type of Valve
– Pressure conditions
– Required flow rate
– Mechanical design- orifice area etc.

8. 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.

9. 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).

10. 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.

11. Safety Valve Sizing• Flow rate requirement

12. Safety Valve sizing
• Orifice Area Calculation

13. Orifice Designation
Ref: 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

14. Conventional safety valve
Ref: API 520 part 1

15. Balanced Below safety valve
Ref: API 520 part 1

16. Pilot Operated Safety Valve
Ref: API 520 part 1

17. Pressure Level relationship

18. 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.

19. 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.