ASME B31.3 Hydrostatic-Pneumatic Leak Tests

[pauljj]

Just a quick one.
What is a hydrostatic-pneumatic leak test in accordance with ASME B31.3 Section 345.6?

I've seen references to it being a lower pressure pneumatic test followed by a higher pressure hydrostatic test.
I don't think that's right though.

I've also seen references to it being a combined test with both liquid and gas in the system being tested.
But the reference to 345.5 would appear to limit the test to a maximum of 1.33 x design whereas the reference to 345.4.2 would appear to limit it to a minimum of 1.5 x design.
Unless that's the static head effect.

I seem to remember seeing a nitrogen 'squeeze' providing the pressure for a hydrostatic leak test before, but can't remember the details.
Is that what it is?

So:
What is a hydrostatic-pneumatic leak test?
When would it usually be used?
What are the main problems to consider?

Thanks.

 

[weldstan]

The test media is a combination of a liquid and a gas. It is used when the available quantity of water is too low, the weight of the water dictates additional reinforcement (added costs) during the test and for other economic/engineering reasons.

 

[pauljj]

Thanks weldstan.
Most of the 'hands-on' people that I know had differing opinions, with none actually carrying one out.

Does the pneumatic part of the test determine the test pressure?
Is the 'pressure' usually provided pneumatically or hydraulically?

 

[Duwe6]

B31.3 doesn't define the Test Pressure for hydro-pneumatics -- one problem. Another problem is how to detect small leaks in the pneumatic portion of the test; determining the actual pneumo areas will be tough, so you end up applying soapbubbles to a LOT of welds.

A properly designed piping system allows hydro testing - it has high-point vents and low-point drains. A properly specified system includes the requirement "contractor to add all vents and drains required for hydrostatic testing, even if no vents/drains are shown on the pipe dwgs".

 

[DekDee]

Duwe6,
Is this not the code determination of pressure requirements ?

345.6 Hydrostatic-Pneumatic Leak Test
If a combination hydrostatic-pneumatic leak test is
used, the requirements of para. 345.5 shall be met, and
the pressure in the liquid filled part of the piping shall
not exceed the limits stated in para. 345.4.2.

Would that not be 1.1 times design pressure minimum (with a max of 1.33) for the pneumatic filled part of the piping and 1.5 times design minimum for the liquid filled part of the piping ?

I have never done a hydrostatic/pneumatic test - would you have one gauge on the high point vent and one on the low point drain ?
Cheers,
DD

 

[Duwe6]

DekDee, you found the citation - thank you. And top & bottom* gauges are a great idea. Although the hydro pressure will probably never get to 1.5 x Design.

*"Official" hydro pressure would be at the water/air interface; hydro pressure-of-record is measured at the high point. Giving yet another reason that a Hydro/Pneumatic has so many intricacies that nobody I know of has ever done one.