7.6.1 The following prototype tests should be
performed on each type of expansion bellows intended for use in gas
piping, primarily on those used outside the gas tank:
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.1 An overpressure test. A type element of the
bellows, not pre-compressed, should be pressure tested to a pressure
not less than 5 times the design pressure without bursting. The duration
of the test should not be less than 5 min.
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.2 A pressure test on a type expansion joint complete
with all the accessories (flanges, stays, articulations, etc.) at
twice the design pressure at the extreme displacement conditions recommended
by the manufacturer. No permanent deformations should be allowed.
Depending on materials the test may be required to be performed at
the minimum design temperature.
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.3 A cyclic test (thermal movements). The test
should be performed on a complete expansion joint, which is to successfully
withstand at least as many cycles, under the conditions of pressure,
temperature, axial movement, rotational movement and transverse movement,
as it will encounter in actual service. Testing at room temperature,
when conservative, is permitted.
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.4 A cyclic fatigue test (ship deformation). The
test should be performed on a complete expansion joint, without internal
pressure, by simulating the bellow movement corresponding to a compensated
pipe length for at least 2 x 106 cycles at a frequency
not higher than 5 Hz. This test is only required when, due to the
piping arrangement, ship deformation loads are actually experienced.
7.6.2 The Administration may waive performance
of the tests specified in 7.6.1, provided that complete documentation
is supplied to establish the suitability of the expansion joints to
withstand the expected working conditions. When the maximum internal
pressure exceeds 1 bar, this documentation should include sufficient
tests data to justify the design method used, with particular reference
to correlation between calculation and test results.