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Question about Hydrotest Principle for TanksHelpful Member!(2) 

billbusy (Mechanical) (OP)
5 Jan 12 13:36
I am thinking about the hydrotest process for tanks.

Currently I am working on a tank to room a liquid which S.G. is 1.9. Per API 650, the hydrotest is required.

I have some experience for piping, normally a higher test pressure is used(i.e. 1.25 * Max Operating Pressure).

But for tanks, it seems a lower pressure is used per the smaller S.G. of the water and you also can not add presure for the water in tanks as in pipes.

I know the hydrotest is mostly for checking the leakage not the stress capability. But I am still wondering why it is acceptable even the working liquid is heavier or the working pressure is larger.



3 years industry experience;
Oil & Gas industry in Canada.

Duwe6 (Industrial)
5 Jan 12 17:54
API = American Petroleum Industry.  This spec was developed for lighter-than-water liquids.  However, it works OK for heavy liquids.  Not perfect, but OK.

billbusy (Mechanical) (OP)
5 Jan 12 18:22
Thanks. But I checked api 650. "1.1.2 This Standard is designed to provide industry with tanks of adequate safety and reasonable economy for use in the storage of
petroleum, petroleum products, and other liquid products."

It seems there is no restriction for liquid lighter than water...

3 years industry experience;
Oil & Gas industry in Canada.

billbusy (Mechanical) (OP)
5 Jan 12 18:23
Sorry, It seems there is no restriction for liquid heavier than water...  

3 years industry experience;
Oil & Gas industry in Canada.

Helpful Member!  IFRs (Petroleum)
5 Jan 12 19:31
Appendix F (internal pressure) tanks have provisions for testing at greater then atmospheric pressure, which could simulate at least a portion of your additional density.  

API answered a technical inquiry about this:
Question 1: Does API 650 require any additional testing beyond the hydrostatic (water) test specified in Section 5.3.5 for a tank designed for product with specific gravity greater than 1?
Reply 1: No. Section F.7.6 provides additional requirements for Appendix F tanks. The Purchaser may require more stringent testing as a supplemental requirement.
Helpful Member!  JStephen (Mechanical)
6 Jan 12 22:24
The hydrotest serves a couple of purposes, one of them being a leak test.  In the case of petroleum, it is usually possible to test the tank with a heavier but safe and cheap liquid (water) as a proof test.  For heavy products, there simply isn't a good way to accomplish this and it isn't done.

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