Hydraulic pressure test

These are not normally required. Where wet gas is supplied, it will be necessary to fit a vessel at low points in the installation to collect any condensate or fluid. This vessel shall be in a readily accessible position and a valve, suitably plugged or capped, shall be fitted to its drain connection. In the exceptional case where hydraulic pressure testing is to be carried out, similar provisions must be made. 

The weight of liquid to fill the vessel. The vessel will be filled with water for the hydraulic pressure test and may fill with process liquid due to misoperation. 

Deflagration Arrester Testing For end-of-line, tank vent, and in-line deflagration flame arresters, approval agencies may require manufacturers to provide users with data for flow capacity at operating ressures, proof of success during an endurance burn or continuous ame test, evidence of flashback test results (for end-of-line arresters) or explosion test results (for in-line or tank vent arrester applications), hydraulic pressure test results, and results of a corrosion test. 

Pressure tests by compressed air or hydraulic pressure tests by water (boiler, steam coils in evaporators, air receivers, and pressure vessels to be used for process),... 

Non-destmctive testing (NDT) such as dye penetration and hydraulic pressure tests are a must for at least 1.5 times the maximum operating pressure. 

Hydraulic pressure test (only chloride-free demineralised water shall be used),... 

The weld repairs as well as hydraulic pressure testing had induced more stresses on the vessel wall and were not followed by stress relief. 

Final drying should be done by hot dry air/nitrogen purging after hydraulic pressure test is over since any leftover moisture in vessel can cause corrosion or problerrrs... 

In process plant, it had become normal practice to subject new, large pressure vessels to hydraulic proof pressure tests. The distinction between hydraulic and pneumatic pressure tests is an important one. Water is essentially incompressible - its volume barely changes when it is pressurized. Gas (or steam) is, however, highly compressible. Hence, in a hydraulic pressure test, the pressure vessel is filled with water, and if any failure should occur, as soon as the enclosed volume begins to increase because of the developing failure, the pressure immediately collapses. This means there is no explosion - just a bang as the metal fails, followed by a flood of water. By contrast, if a pressure vessel fails when pressurized with gas or steam, as in the boiler explosions described above, the energy of the compressed gas/steam drives the failure to create a violent explosion, and pieces of the failed pressure vessel become missiles. 

The Cockenzie steam drum failure of May 6 1966 [5] happened during the final, seventh cycle of hydraulic pressure testing before the steam drum would have been declared ready for service. It failed adjacent to one of the economizer nozzles, the transition pieces to the high-pressure pipes in operational service, would have led water from the underside of the drum to the boiler tubes (See Fig. 7.6.)... 

If the Cockenzie drum had survived this hydraulic pressure test (the seventh and last) it would have entered service. Sometime later, when pressurized with steam, it would have failed, and the explosion would have caused massive damage, and probably injuries and deaths. The question is this How can we be really sure that there are no significant cracks in thick-walled pressure vessels ... 

In the case of the reactor coolant circuit of the Prototype, the cold hydraulic pressure test at 16OO Ib/ln g properly tested only the stainless steel components of the circuit. The zirconivim alloy pressure tubes were subjected to a stress that did not approach the stress to which they are subjected in normal operation when temperature effects are taken into account. 

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