TIME OF DURATION OF HYDROSTATICS TEST PRESSURE 3

[vargaslu]

We are planning to begin a group of hydrostatics test pressure on a natural gas compression plant. One part of the pipes were designed as per ASME B31.3, and another pipes, were designed as per ASME B31.8. The pipes were divided into "packages" depending on its operating pressure to make easier the execution of the test pressure. The questions are: Which should be the time of duration of one hydrostatic test? Does the time of duration depend on the lenght of the pipe? On your experience, Which would be the criterion to applying?
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[TJHAK]

For the B31.3 piping, hydrotest durations are usually called out for by the project engineer. If you are the project engineer, B31.3 only requires a 10min leak test providing that all areas can be checked for leaks in 10min. If not, then test duration should be as long as it takes to ensure there are no leaks. (See K345)

The B31.8 piping requires an 2 hour test for prefabricated piping. Assembled piping must be tested for an 8 hour minimum.

However long the duration, the documentation requirements must be met.

 

[zdas04]

The information from TJHAK is useful, but there is another consideration. Many times regulators specify different test durations than the code (always longer). I've seen regulations that required a 24 hour test for example. Also, company policies can modify test duration. I know of one major Oil & Gas company that requires a 12 hour test unless local regulations require a longer test.

None of these regulations or company policies have to make sense, they just have to be followed. The important thing is that the test procedure be specific about the duration of the test, the start point (does the clock start at MAWP or at test pressure, I've seen both called out), and most importantly the success criteria (what is the minimum acceptable pressure at the test station at the end of the test, pressure always changes some durning the test due to temperature effects).

David

 

[HotBend]

The specified test duration (Hold Period) is normally the determined from the test system configuration taking into consideration regulatory and code requirements and your ability to detect or account for a leak (drop in pressure) during the hold period. Ultimately, regulatory and code requirements may govern the minimum duration of the hold period.

Typically the hold period for buried pipelines is 24 hours and 4 hours for above ground piping where visual checks can be made for leaks. The test durations will be significantly longer for complex systems with many potentail leak sources such as flanges. Presurisation and leak checks may take a few hours before the hold period can begin.

As mentioned previously, some companies may also have their own minimum hold periods for tests.

Hope this helps.

 

[racookpe1978]

The test procedure (or test requirements from the client) must account for temperature changes in the test fluids and piping and equipment, and the ability (or limitations on the amount of fluid) to make up test fluids to account for cooling and leakage during the test.

For example, if the system heats up from a 9:00 AM start time to the 3:00 PM stop time (or vice versa!) are you allowed to vent off fluid to maintain test pressure, or how much test fluid are you allowed to add to keep test pressure?

 

[vargaslu]

TJHAK, zdas04, HotBend, racookpe: Thanks a lot for your answers. I´m sending your coments for the construction team. Thanks again.
LV

 

[athomas236]

In my experience the usual procedure is:

1. Increase pressure to the working pressure and inspect.
2. Increase pressure to test pressure and do not approach, this is the most likely time for failre.
3. Decrease pressure to working pressure and inspect again.

Inspections should not take place at test pressure.

Regards,

athomas236

 

[Kentech394]

I just read your comments regarding pressure testing of pipes. Are these valid for CPVC pipes (Chapter VII) of ASME B31.3. If no then what should be the holding time for CPVC.

 

[IFRs]

If you hold and the sun shines, be sure to have thermal relief or some way to manage the increase in pressure when temperature increases.

 

[Kentech394]

Our client specification is suggesting us to hold for 24 hours which doesnot looks sound to me. How can i convince to my client from some ASME reference that holding time can be reduced.

 

[DSB123]

Kentech394,
24hrs hold time is not unusual for a pipeline hydrotest. The site I used to work on adopted the 24hr test period. For B31.3 piping you need to hold the test pressure (or slightly less)for as long as it would take to inspect the entire length of the pipework under test.

 

[Kentech394]

It is CPVC and not long lengths of pipes(max 10m) . Are you still suggesting for 24 hrs.

 

[DSB123]

Kentech394,
If you are talking of short spools (10m) then no I would not be going for 24hr. I assumed you were talking about pipeline length when you mentioned B31.8. However as others have said see what your Client wants - if it's 24hr then unless you can justify less and get him to waiver the duration to something more sensible then you are stuffed and will have to go with his wishes.