Dear All,

How to decide on Hydrotest Pressure for Tank within Design Limits of APRI 650 Appendix F

Regards

Rajesh

Hello Rajesh

Usually the tank is hydrotested with a complete water fill. The tank water fill should stop as the top of the shell, and must not go into the roof space. It is not normal to put and gas pressure in the tank for the hydrotest, however if gas pressure is introduced, it cannot exceed 2-1/2 psi (18 kPa) as that is the maximum gas pressure permitted by API 650.

The necessity of tank's "internal pressure" is a consequence of Process evaluation; of course this internal pressure cannot exceed the mechanical capabilities of tank and tank foundation capabilities (you may note that the internal pressure affects the foundation load) .

If the internal pressure and the associated "maximum design pressure" are less than 18 kPa (2.5 PSIG), Appendix F contains provisions for design and the overall design remains under Api 650. For pressure exceeding 2.5 psig, API 620 may be used- also here are limits for pressure.

Strictly speaking, Appendix F contains a procedure to determine the maximum design pressure for a tank that has been constructed or that has had its design details established- see F4.1, F4.2, F4.3, F6, F7, table 5-21 etc.
In practice, of course you can use the same formulas to design the tank and to prove in the end that everything comply with App F requirements.

So, after this analysis an "internal design pressure" (compatible with Process, Mechanical and Civil requirements) is established.

The test procedure may be as F.4.4 requires:

When the entire tank is completed, it shall be filled with water to the top angle or the design liquid level, and the design internal air pressure shall be applied to the enclosed space above the water level and held for 15 minutes. The air pressure shall then be reduced to one-half the design pressure, and all welded joints above the liquid level shall be checked for leaks by means of a soap film, linseed oil, or another suitable material. Tank vents shall be tested during or after this test.

(I have a remark here- in fact the water test level must be that one which was considered in calculation- 5.6.3.2 formula, where has been evaluated the necessary tt = hydrostatic test shell thickness)


Or, for Anchored Tanks, paragraph F.7.6 must be followed:

F.7.6 After the tank is filled with water, the shell and the anchorage shall be visually inspected for tightness. Air pressure of 1.25 times the design pressure shall be applied to the tank filled with water to the design liquid height. The air pressure shall be reduced to the design pressure, and the tank shall be checked for tightness. In addition, all seams above the water level shall be tested using a soap film or another material suitable for the detection of leaks. After the test water has been emptied from the tank and the tank is at atmospheric pressure), the anchorage shall be checked for tightness. The design air pressure shall then be applied to the tank for a final check of the anchorage.

My regards.

Useful Information Thanks a lot