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Pressure Testing Plastic Lined Pipe
These recommendations are derived from ASME standard B31.3. The only
limitations that are placed on this testing relate to the pressure
ratings of our diaphragm valves. The maximum test pressures for our
diaphragm valves are the following:
- 1-4" diaphragm valves 225 psi
- 6" diaphragm valves 200 psi
- 8" diaphragm valves 150 psi
Other than this limitation, our pipe and fittings can be tested at the
pressures recommended by B31.3.
Hydrostatic Test
The fluid used for the hydrostatic test is typically water. Another
suitable non-toxic liquid can be substituted if there is the risk of
damage due to the adverse effects of having water in the system. The
system should be tested at a pressure not less than 1.5 times the
design pressure. If the design temperature is above the test
temperature then the required test pressure is calculated by the
following equation:
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| where |
Pt = minimum hydrostatic test gauge pressure
P = internal design gauge pressure
St = stress value at test temperature
S = stress value at design temperature
Typically, for the pressures and temperatures in which plastic-lined pipe
is used, the above calculation reduces to:
Pt = 1.5 P
We recommend that the system be retorqued after the first thermocycle. If
the hydrostatic test is performed at the expected operating temperature
(a "hot hydrotest") then the hydrotest can constitute the first thermocycle
and the recommended retorquing can occur after the pressure test.
Pneumatic Leak Test
This pressure test is performed in some situations where the presence of
any water in the system is forbidden. The test is very dangerous due to
the stored energy of the compressed gas. ASME B31.3 refers to the dangers
of performing this test and provides safety considerations in the standard.
For a pneumatic pressure test, a pressure relief device must be in the
system. This relief device should be set at the test pressure plus either
50 psi or 10% of the test pressure, whichever is lower. The gas used for
the pneumatic test, if not air, can be any nonflammable and non-toxic
gas. The test pressure required for this test is 110% of the design
pressure.
To perform the pneumatic leak test, begin by increasing the pressure until
a gauge pressure of 25 psi is attained. At this point, a preliminary check
for leaks must be made. After the initial check, the pressure should be
incrementally increased, holding the pressure at each increment long
enough to equalize the piping strains. Once the test pressure is reached,
the pressure is then reduced to the design pressure before examining for
leakage.
Alternative Leak Test
If a hydrostatic pressure test is undesirable due to the possible chemical
reactions with water and a pneumatic test in undesirable due to the
potential hazards, then an alternative leak test can be used. This test
is not applicable to plastic lined pipe because it relates to welded
systems.
Initial Service Leak Test
This test is applicable only to systems which meet the following requirements:
- the fluid handled is nonflammable, non-toxic, and not damaging to human
tissues.
- the design gauge pressure does not exceed 150 psi.
- the design temperature is between -20°F and 366°F.
In this test, the test fluid is the service fluid. It is rare that this
test is used with plastic-lined pipe. ASME B31.3 should be considered if
more information concerning this test is required.
Other Tests
Another option, which is not included in ASME B31.3, is the "halogen test
with Freon". This test will find leaks in the piping system, but it does
not meet the code.
The above is a description of some pressure test methods. In general, most
systems are hydrostatically tested as described in the ASME standard. If
the hydrostatic test is impractical, then the pneumatic test can be
substituted, however, extreme caution must be observed during this
potentially hazardous test.
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