Hydro test

In order to design piping system, piping designer must be familiar with hydro test equipment and procedure. Not only placing vents and drains is important, but also piping system as whole must be design in the way that hydro test can be carried out.
Typical hydro test equipment is shown on the figure above. Note that in the case of long pipe run, some companies will require placing additional pressure gauge at the very far end of the pipe. All in-line instruments shall be either removed or blocked prior testing. Control valve must be replaced with pipe spool or internals must be removed during hydro test. Same is applied for check valve; flap must be removed. A spectacle blinds are not required to be tested if they built as per 14.48. Equipment shall be either disconnected from the system or isolated by spectacle blinds or other means during the test. A pipe plug can be used for blocking part of piping system as well as isolating valve. If isolating valve is used, ensure that maximum test pressure for the valve conforming B16.34. Spring hangers shall be locked during the testing and expansion joints shall be removed and replaced by pipe spool. Lines those are open to atmosphere such as last shut off valve, need not to be tested. Minimum design metal temperature is temperature for which material is normally suitable without impact testing. In cold climate condition antifreeze agent can be used to prevent water freezing during testing. If agents are used, provision for disposition of test fluid must be made. Testing pressure is 1.5 times the design pressure multiplied by ratio St/S, where St is allowable stress at test temperature and S is allowable stress at design temperature. If test pressure as defined above produce a stress in excess of yield strength at test pressure, the test pressure must be reduced to a level that will not exceed the yield strength at test temperature. Hydro test is mandatory as per B31.3 and it addresses pipe integrity and leak test. However, if owner consider hydrostatic test impracticable, pneumatic or combined hydrostatic-pneumatic test may substituted. If pneumatic test is used, hazard of energy stored must be recognized. When the owner consider both hydrostatic and pneumatic test impracticable the alternative of examination of welds may be used if both of following condition is apply:
1.Hydrostatic test would: damage linings, contaminate process or required significant support modification.
2.Pneumatic test would present the danger of brittle fracture or an
undue hazard of possible release of energy stored.
As a rule, above conditions are very rarely met in petrochemical and mining industry, therefore hydrostatic or pneumatic test must be carried on. We had a case when contractor wanted to do 100% weld examination in substitution of hydro test. Using weld examination as substitution of hydro test is not allowed by piping code B31.3, and hydro test must be carried on.