Hydro test Pressure Increment per Minute

[aida2011]

Dear all

I need your advice because I have so many versions of answers.

What is the rate of increment in pressure per minute for the hydrostatic test? People are saying that the increment must be gradual to prevent shock, some say 5 bar per minute, others said 10 bar per minute (wow pretty quick).

If pause, how long you need to pause and at what pressure?

Thanks very much.

Aida

 

[mk3223]

I could be wrong, I thought you may watch out the percentage of the pressure increment during the hydro instead of the increment rate. The duration of each step should be long enough, so the system pressure can be stabilized and the inspection be completed.

 

[Dhurjati Sen]

aida2011
Shell DEP 31.40.40.38-Gen. HYDROSTATIC PRESSURE TESTING OF NEW PIPELINES Section 7.3 clearly specifies 1 bar / minute until a pressure of 35 bar or 50 % of the test pressure, whichever is lower, has been attained.

 

[LittleInch]

aida 2011

You need to have a look at whatever design code you are using to see if it says anything. Chances are it doesn't say anything as design codes try not to define how to do something only what needs to be done.

Hence things like pressurisation time, so long as it doesn't create a "shock" loading ( say 0-100% in 1 second) are down to individuals. Normally pressurisation pumps are quite small and you want to control the loading so you don't exceed the test pressure and allow the pipe or vessel to react to the pressure and stress change.

Pauses or hold periods are again, if not specified in the code, simply good practice. it's good to go to something like 30% and then pause to see if there is some sort of catastrophic failure or weeping flange or weld but all depends on the ability to inspect the item you're pressure testing. You haven't told us what you're testing.

The test pressure also makes a difference. Testing to 10 bar in a big volume, 1 bar/minute is probably Ok, but 350 bar of a small volume 1bar/ minute would take hours so 50 bar/minute might be Ok.

Things like Shell DEPs are not codes although some like to think so and can be seen as useful guides, unless you're working on a shell project...

This post had similar issues

http://www.eng-tips.com/viewthread.cfm?qid=432588

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Hurmanetar]

I don't think there is any requirement in ASME VIII for pressure up rate or pauses. I've seen a lot of customer specs and only recall seeing one that specified pause intervals on the hydro. I think they required a pause at half the design pressure, again at design pressure, and then go on up to 1.3x. Most of the time vessels will be pressured up as fast as the pump will go. For very high pressure or for large assemblies, it might be wise to pause a couple of times to visually inspect.

 

Look up the applicable Code or ask your authorized Inspector.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[r6155]

Also consider "The test pressure shall not be applied until the vessel and its contents are at about the same temperature".
See UG-99

Regards
r6155

 

[Dhurjati Sen]

Do you know of any code that mentions increment of pressure in a hydrostatic test? Recommended Practices like Shell DEPs take over where codes are silent.

 

[r6155]

Not only the filling rate must be specified on the Data Sheet, also emptying rate (venting device must be specified).
See API 650 7.3.7.5 The minimum fill and discharge rate, if any, shall be specified by the Purchaser on the Data Sheet, Line 23. When settlement measurements are specified by the Purchaser, the maximum filling rates shall be as follows, unless otherwise restricted by the requirements in 5.8.5

Large vertical pressure vessel should be checked for filling and discharge rate to inspect the settlement.

Regards
r6155