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ISO 4126-4-2013 pdf free download
ISO 4126-4-2013 pdf free download.Safety devices for protection against excessive pressure Part 4:Pilot operated safety valves
Dispositifs de sécurité pour protection contre les pressions excessives — Partie 4: Soupapes de sâreté pilotées.
6.3.4 Safety requirements
Water of suitable purity shall normally be used as the test medium. Where other testing media are used, additional precautions may be necessary. Valve bodies shall be properly vented to remove entrapped air.
If materials which are liable to failure by brittle fracture are Incorporated in that part of the pilot operated safety valve which is to be hydrostatically tested, then both the pilot operated safety valve, or part thereof, and the testing medium shall be at a sufficient temperature to prevent the possibility of such failure.
No valve or part thereof undergoing pressure testing shall he subjected to any form of shock loading, for example hammer testing.
6.4 Pneumatic testing
6.4.1 Application and duration of test
Pressure testing with air or other suitable gas should be avoided but may be carried out in place of the standard body hydrostatic test with the agreement of all parties involved in the following cases:
a) valves of such design and construction that it is not practicable for them to be filled with liquid; and/or
b) valves that are to be used in service where even small traces of water cannot be tolerated. The portions of the valve to be tested, test pressure, duration of application and acceptance criteria shall be as specified in 6.3.
6.4.2 Safety requirements
The hazards involved in pneumatic pressure testing shall be considered and adequate precautions taken. Particular attention is drawn to some relevant factors as follows.
a) I ía major rupture of the valve should occur at some stage during application of pressure, considerable energy will be released; hence no personnel should be in the immediate vicinity during pressure raising (for example a given volume of air contains 200 times the amount of energy that a similar volume of water contains when both are at the same pressure).
b) The risk of brittle failure under test conditions shall have been critically assessed at the design stage and the choice of materials for valves which are to be pneumatically tested shall be such as to avoid the risk of brittle failure during test. This necessitates provision of an adequate margin between the transition temperature of all parts and the metal temperature during testing.
c) Attention Is drawn to the fact that if there isa reduction In gas pressure between the high-pressure storage and the valve tinder test, the temperature will decrease.ISO 4126-4-2013 pdf free download.
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