API RP 576
Third Edition, November 2009
Inspection of Pressure-relieving Devices
4.3 Safety Valve
General
A safety valve is a direct spring-loaded pressure-relief valve that is actuated by the static
pressure upstream of the valve and characterized by rapid opening or pop action.
A typical safety valve has a lifting lever for manual opening to ensure the freedom of
the working parts.
4.3.2 Applications
A safety valve is normally used with compressible fluids.
Safety valves are used on steam boiler drums and superheaters.
They are also used for general air and steam services in refinery and petrochemical
plants.
1. Which of the following application of safety valve?
A) steam
B) liquid service
C) incompressible fluids
D) none of the above
2. A typical safety valve has _______for manual opening to ensure the freedom of the
working parts.
A) a lifting lever
B) a Test gag
C) a self-actuated auxiliary pressure-relief valve (pilot).
D) Spindle /stem
4.4 Relief Valve
relief valve is a direct spring-loaded pressure-relief valve actuated by the static pressure
upstream of the valve. The valve opens normally in proportion to the pressure increase
over the opening pressure.
4.4.2 Applications
 Relief valves are normally used for incompressible fluids (in liquid service,)
3. API 576 Recommended the use relief Valve________.
A) in liquid service
B) in steam, services
C) in air, gas, or other vapor services
D) none of the above
4.5 Safety-relief Valve
A safety-relief valve is a direct spring-loaded pressure-relief valve that may be used as
either a safety or relief valve depending on the application.
A safety-relief valve is normally fully open at 10 % overpressure when in gas or vapor
service.
When installed in liquid service, full lift will be achieved at approximately 10 % or 25 %
overpressure, depending on trim type
3. API 576 Recommended the use Safety-relief Valve________.
A) on vapor with constant pressure
B) on vapor or liquid with constant pressure
C) on vapor or liquid with variable pressure
D) on vapor or liquid with constant and variable pressure
4.8 Pilot-operated Pressure-relief Valve
4.8.1 General
A pilot-operated safety-relief valve is a pressure-relief valve in which the major
relieving device or main valve is combined with and controlled by a self-actuated
auxiliary pressure-relief valve (pilot).
Pilot-operated safety-relief valves are not generally used in service where fluid is
dirty, or where there is a potential for fouling or solidification (e.g. hydrates, wax, or
ice).
4. In a PRV in which the major relieving device or main valve is combined with and
controlled by a self-activated auxiliary pressure relief valve is:
a. Pilot operated valve
b. Bellow type balancing valve
c. Relief valve
d. Safety valve
5. a pilot-operated safety relief valve limitation should not be used in ____
A) low viscosity liquid service
B) low corrosive environments
C) dirty fluid service and fouling medium without a filtering system
D) all of the above
4.10.2 Types of Rupture Disk Devices
4.10.2.2 Scored Tension-loaded Rupture Disk
The scored tension loaded rupture disk is manufactured from thicker material than is used
for unscored disks for the same burst pressure.
4.10.4 Limitations
For prebulged metal rupture disks installed so that pressure acts against the concave side
and for flat metal rupture disks, the operating pressure of the protected system is usually
limited to 65 % to 85 % of the disk's marked bursting pressure.
6. The scored tension loaded rupture disk is manufactured from______
A) thicker material than is used for unscored disks for the same burst pressure
B) thinner material than is used for unscored disks for the same burst pressure
C) A composite rupture disk is a flat or domed metallic or nonmetallic multipiece construction
disk
D) all of the above
7. For prebulged metal rupture disks installed so that pressure acts against the concave
side and for flat metal rupture disks, the operating pressure of the protected system is
usually limited to
A) 65 % to 85 % of the disk's marked bursting pressure.
B) 65 % to 95 % of the disk's marked bursting pressure.
C) 85 % of the disk's marked bursting pressure.
D) 65 % of the disk's marked bursting pressure
5.3 Failed Springs
5.3.1 Spring failures occur in two forms. The first is a weakening of the spring, which causes a
reduction in set pressure and the possibility of premature opening. The second is a mechanical
failure (complete break) of the spring, which causes uncontrolled valve opening.
5.3.2 Although springs may weaken and fail due to the use of improper materials in hightemperature service, failed springs are almost always caused by corrosion. Surface corrosion
and stress corrosion cracking are the most prevalent of this type of failure in refineries.
8. Of the following, what is the most common cause of spring failure in pressure relief
valves?
A) Surface Corrosion
B) Creep
C) Erosion
D) Tensile overload
9. Spring Failure lead to__________
A) uncontrolled valve opening.
B) improper valve setting.
C) valve chatter or flutter.
D) None of the above.
5.5 Plugging and Sticking
10. When four pressure relief valves on the fractionator of a fluid catalytic cracking unit
are removed for testing while the unit is in service, the inspector notices that the inlets are
heavily coked. There are two pressure relief valves with manual bypasses on an NPS 10
pipe header with block valves on their inlets and outlets. Which of the following should be
performed?
A) Hammer test the inlet and outlet piping of the pressure relief valves to see if any thinning
can be detected
B) Take radiographs of the header and related piping of the pressure relief valves and inspect
the system at the next shutdown of the tower
C) Require that the tower be shut down immediately and all of the pressure relief valves
and the related piping be removed for cleaning
D) The header and the inlet and outlet piping of the pressure relief valves should be
thoroughly tested for thickness using ultrasonic examination
5.10 Improper Discharge Piping Test Procedures
When hydrostatic tests of discharge piping are performed, blinds shall be installed.
11. A hydrostatic test is to be performed on the piping on the discharge side of a pressure
relief device. Which of the following is correct regarding blinding/blanking?
a) Blinds need not be installed
b) Blinds should be installed between the vessel nozzle and the pressure relief device
c) Blinds should be installed between the pressure relieving device discharge flange and
the pipe flange
d) Blinds should be installed wherever it is most accessible or convenient
6.2.3 Valve Identification
To minimize errors in the testing and handling of pressure-relief valves, each should
carry an identifying tag, stencil, plate, or other means to show its company equipment
number.
the date of its last test (see Figure 37for an example of an identifying tag).
12. Where can YOU find these data, unit designation, company Name, set pressure
equipment, designation, test dates?
A) Identification Tag for Pressure-relieving Device alteration.
D) MSDS.
C) MTC
D) None of the above
6.2.15 Setting of Valve Set Pressure
6.2.15.2 After the valve has been adjusted,
it should be popped at least once to prove the accuracy of the setting.
Some manufacturers recommend a valve be popped at least three times, as the first pop
helps align all of the components after the overhaul while the successive pops verify the set
pressure.
Normally, the deviation of the pop pressure from the set pressure should not exceed
 ±2 PSI (±13.8 kPa) for pressures less than or equal to 70 PSI (483.0 kPa) or
 ±3 % for pressures greater than 70 PSI 2 (483.0 kPa).
13. A pressure relief valve has a set pressure of 400 psi. The valve is tested for accuracy of
set pressure before it is installed. What is the maximum acceptable test pressure?
A) 400 psi
B) 402 psi
C) 412 psi
D) 420 PSI
14. A pressure vessel is designed for 300 psig at 500˚F Which of the following is the
permissible opening pressure range for a single safety relief valve?
A) 291-309 psig
B) 281-309 psig
C) 298-302 psig
D) 343-357 psig
15. A pressure vessel is designed for 350 psig at 500˚F Which of the following is the
permissible opening pressure range for a single safety relief valve?
A) 339.5-350 psig
B) 339.5-360.5 psig
C) 343-350 psig
D) 343-357 psig
16. what relieve valve set pressure tolerances, for pressure operate at 125 psi?
A) ±3 %
B) ±2 PSI (±13.8 kPa)
C) 5%
D) none of the above.
6.2.19 Inspection, Testing, Maintenance, and Setting of ASME BPVC Section I Boiler
Safety Valves
Caution—This method of checking the set pressure and functioning of a safety valve identifies
the opening pressure but does not satisfy the need to periodically remove the valve for
physical inspection and verification that all of its components are in satisfactory and safe
working condition.
15. on-stream testing of steam safety valves to identifies the opening pressure but does not
satisfy the need to __________
A) periodically remove the valve for physical inspection.
B) to check for inlet/outlet line fouling.
C) to remove a valve for physical inspection
D) None of the above