Hydrostatic/pneumatic tests

The system should be pressure tested (details are provided in the next section). There should be no loss of pressure or leakage from equipment, piping, and joints during hydrostatic/pneumatic testing. 

If hydrostatic testing is not considered practicable by the owner, a pneumatic test in accordance with the following procedure may be substituted, using air or another nonflammable gas. 

All pressure vessels must pass appropriate hydrostatic testing before approval for service. For safety reasons, hydrostatic pressure testing is almost always recommended over a pneumatic test. The recommended... 

Depending on the services, the pipeline will usually be hydrostatically or pneumatically tested. Normally a section is specified for testing from flange point to flange point. Once tested the blank flanges at the ends of the section are removed and the tested portions are permanently connected... 

Preliminary Pneumatic Test. A preliminary test using air at no more than 170 kPa (25 psi) gage pressure may be made prior to hydrostatic testing to locate major leaks. 

If a combination hydrostatic-pneumatic leak test is used, the requirements of para. IP-10.8 shall be met, and the pressure in the liquid-filled part of the piping shall not exceed the limits stated in para. IP-10.7. 

The pneumatic test may be used in lieu of the hydrostatic test for hydrogen systems designed or supported so they cannot safely be filled with liquid, or if the vessel or system cannot be readily dried or is to be used in services in which traces of the testing liquid cannot be tolerated. The substitution requires that the parts of the system, when possible, are previously tested by hydrostatic pressure. The pneumatic test pressure should be 1.25 times the MAWP. 

Inspection and testing requirements are covered in detail. Most vessels are required to be hydrostatic-tested (generally with water) at 1.3 times the maximum allowable working pressure. Some enameled (glass-lined) vessels are permitted to be hydrostatic-tested at lower pressures. Pneumatic tests are permitted and are carried to at least IV4 times the maximum allowable working pressure, and there is provision for proof testing when the strength of the vessel or any of its parts cannot be computed with satisfactory assurance of accuracy. Pneumatic or proof tests are rarely conducted. 

The hydrostatic test pressure is 1.25 times the design pressure corrected for temperature, rather than the usual 1.5. Division 2 establishes upper limits for the test pressure relative to the yield strength at test temperature. The pneumatic test pressure is 1.15 times the design pressure corrected for temperature rather than 1.25 required by Division 1. Division 2 has no provision for proof tests to establish the maximum allowable working pressure. But Appendix 6, Experimental Stress Analysis, provides for the determination of the critical or governing stresses for unusual geometries for which theoretical stress analysis is inadequate. 

Hydrostatic testing is carried out at pressures above system design pressures pneumatic testing often is restricted to lower values. Under certain circumstances, however, hydrostatic testing may be unacceptable for technical reasons. These include ... 

A low-pressure pneumatic test often precedes hydrostatic testing as a quick and simple way to identify bad connections. The system then chosen for testing should be as large as is convenient and practicable. Some gas-processing lines and equipment may require additional support during hydrostatic testing. It is important to have the system liquid-full, and so the addition of water should be from a low point Filling should be... 

Hydrostatic, Pneumatic, and Proof Testing of Pressure Vessels... 

Pneumatic testing may be used in lieu of hydrostatic testing provided ... 

In the second test, at least two vessels are built by identical means. One vessel is pressured to either failure, leakage or bursting. This failure pressure is then used to develop an MAWP for the other vessel. The surviving vessel is then given a standard hydrostatic or pneumatic test based on the MAWP established. 

In the ASME Code, VIII-2, and Section III, Division 1, optional Part NC-3200 of Subsection NC, a factor of k is applied to various loading combinations somewhat related to whether or not the loading is sustained or transient. The factors are = 1.0 for sustained loads including dead loads and pressure A 1.2 for sustained load plus wind or earthquake loads k = 1.25 for hydrostatic tests and A = 1.15 for pneumatic tests. 

The two types of pressure testing are hydrostatic and pneumatic. Hydrostatic pressure testing with clean water is the preferred method. The test section should be completely filled with the test medium, taking care to bleed off any trapped air. Venting at high points may be required to purge air pockets while the test section is filling. 

Welds, including those used in the manufacture of welded pipe and fittings, which have not been subjected to hydrostatic or pneumatic leak tests in accordance with this Code, shall be examined as follows ... 

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