API576 Flashcards
The use of an O-ring or resilient seat in a pressure-relief valve may stop
lakage past the seating surface and eliminate corrosion in the valve’s working parts.
Bellows seal can be used to protect the spring and the bonnet cavity of the valve from the
corrosive loading fluid.
O-ring elastomers may have a limited life under stress
due to degradation caused by temperature, corrosive species, aging, or swelling.
springs may weaken and fail due to the use of improper materials in high-temperature 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.
Hydrogen sulfide (H2S) frequently causes
SCC of springs
Valve testing - Special attention is needed if the relief
valve is placed in
superheated steam service to compensate for temperature.
To ensure that the valve is opening, some overpressure should be carefully applied because an
audible leak could otherwise be misinterpreted as the result of reaching the set pressure.
Incorrect calibration of pressure gauges is a frequent cause of
improper valve setting.
gauges should be calibrated frequently on a calibrated
dead weight tester.
Snubbers on pressure gauges are not generally recommended since they tend to
clog and produce pressure lag.
Many direct-acting spring-loaded pressure-relief valves have one or more internal rings that can be adjusted. The pressure-relief valve adjusting ring or rings will control the
- valve blowdown—the difference between the
set pressure and the reseating pressure—and valve simmer, depending on the design of the valve being tested.
To functionally test the pressure-relief valve and measure the blowdown
, similar media properties of the service fluid and adequate flow capacities to fully cycle the valve are needed.
All valve parts, particularly guiding surfaces and bellows, should be checked thoroughly
for any type of fouling.
galling
A condition whereby excessive friction between high spots results in localized welding with subsequent splitting and a further roughening of rubbing surfaces of one or both of two mating parts
galling happens (3)
- corrosion or foreign particles,
- valve chatter or flutter caused by improper piping at the valve inlet or outlet or by severe oversizing of the valve.
- system operates too close to the set pressure resulting in frequent relieving.
Improper handling can occur during
shipment, maintenance, or installation.
Lifting lever wiring is only used for
transport and needs to be removed before installation
in making this determination,
four types of inspections can be used.
They are “shop as-received pop test,”
“shop inspection/overhauls,”
“field internal inlet and outlet piping inspections,” and “visual on-stream inspections.
Only an _________ should isolate a relief device by closing any adjacent block valves upstream or downstream
authorized person
Block valves used with relief devices should be verified to have sufficient flow area (e.g. full port) to prevent
low restriction and excessive pressure drop.
Some precautions to follow when inspecting valves exposed to hazardous materials include the following. (2)
- a) Evaluate the potential for the valve to contain pyrophoric [e.g. iron sulfide (FeS)] or reactive materials, and determine the appropriate precautions for the material involve
2.Valves in acid or caustic service should be handled very carefully adhering to rigorous handling procedures prior to pre-pop testing of the “as-removed” pressure-relief valve. After pre-popping,
pressure-relief valves should be immediately neutralized.
where block valves are closed to enable removal of relief devices from equipment during operation, it is usually impossible to directly inspect this piping. In potential fouling services, __________ should be considered for piping upstream or downstream of pressure-relief valves looking for locations where potential fouling deposits may collect that could restrict flow or cause corrosion under deposits.
profile radiography
Pressure-relief valves that do not pop at inlet pressures of 150 % of CDTP should be considered as
stuck shut,
If the valve initially opens at the cold differential test pressure (CDTP),
no further testing to determine the “as-received” pop pressure is needed.
If the initial pop is at a pressure higher than the CDTP, the valve should be
tested a second time.
If the initial pop is at a pressure lower than the CDTP, the spring may have become weakened, the valve may (3)
- have been set improperly at its last testing,
- the seat may have been damaged
- or the setting changed during operation.
It is the first test that is recorded as the “as-received” pop pressure. This “as-received” pop pressure is used in determining
the inspection interval.
The ___________ should define the criteria that constitute an “as-received” pop test failure
owner-user
as-received pop testing should be conducted ____ to cleaning in order to yield accurate
as-received pop testing results
prior
the results of the “as-received” test show that the valve tests properly, then disassembly of the
valve for further inspection ___(is or is not required)_____ unless restoration of the valve to the “as new” condition is
required
may not be required,
After the valve has been adjusted/cleaned, it should be actuated at least once to prove the accuracy of the setting. Some manufacturers recommend a valve be actuated (popped) ______
at least three times,
ASME BPVC Section VIII valves, the deviation of the as-found set pressure from the nameplate set
pressure should not exceed ___for pressures less than or equal to 70 psi (500 kPa) or _____for
pressures greater than 70 psi (500 kPa)
±2 psi (±15 kPa) / ±3 %
ASME BPVC Section VIII, Division 1, deviation shall not be less than ____ or greater than______
0 % / +10 %.
Once the valve is set to pop at its CDTP, it should be checked for
leakage.
it can be tested for seat tightness by increasing the pressure on the valve up to the manufacturer’s specified simmer pressure
(oftentimes this is 90 % of the CDTP) and observing the discharge side of the valve for evidence of leakage.
a relief valve that does not pop at _____ of the set
pressure is considered a failure to open.
130 %
accumulation
The pressure increase over the maximum allowable working pressure (MAWP) of the vessel or piping system,
backpressure
The pressure that exists at the outlet of a pressure-relief device as a result of the pressure in the discharge system. Backpressure is the sum of the superimposed and built-up backpressures.
blowdown
The difference between the set pressure and the closing pressure of a pressure-relief valve,
cold differential test pressure
CDTP
The pressure at which a pressure-relief valve is adjusted to open on the test stand. The cold differential test pressure includes corrections for the service conditions of superimposed backpressure or temperature or both.
simmer
The audible or visible escape of compressible fluid between the seat and disc,
as-received pop testing results that will help establish the appropriate .
inspection and servicing interval
if fouling is noticed when RV is removed , what should be done?
reduce inspection cycle
oversizing the valve can?
open/close valve repeatedly
To prevent leakage of the loading fluid, an optical precision on the order of ____________
specifications should be maintained in the flatness of seating surfaces on metal-seated pressure-relief valves
three light beads
