Hydrostatic Pressure Testing - Potable Water Piping

[John_187]

There is a project where the contractor is asking if he can pressure test the potable water piping system with dry nitrogen instead of water. The reason this was asked is because "it would will be very difficult to get the air out of the pipe if water test is done". The pressure test is to be 125 psig for 1 hour. Is this acceptable and/or common practice? Thanks

 

[LittleInch]

Well if he can't the air out of the pipe for the test, how is he going to do it when the system is commissioned?

Sounds like a poor excuse to me, but then we can't see the size and complexity of this system, what it's made of, where it is ( house, factory, office block etc which might make you a little more accommodating.

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

 

[PEDARRIN2]

In the International Plumbing Code, section 312.5 allows for 50 psig air to be used if the pipe is not plastic.

The rationale I have heard is if there is a leak, they have to drain (all/some) of the water which has to go somewhere. This can be problematic especially if the sanitary is not operational yet. Then the plumber has to figure out something else to dispose of it. Air can be discharge to atmosphere.

Also, water is typically metered so it costs, whereas air is free (except for the energy for the compressor). Nitrogen might be pricey, though.

 

[bimr]

Pressure testing should normally be carried out using potable water. Only in rare circumstances should a pneumatic pressure test be done using compressed gas, and then only under carefully controlled conditions. The reason for this is because water is virtually incompressible and only a small quantity of energy needs to be introduced to increase the pressure significantly. Gas, is compressible and, as a result, much more energy has to be put into the gas to raise its pressure.

At the pressure ranges normally used for testing water-piping systems, approximately 200 times more energy is stored in a compressed gas compared to water at the same pressure and volume. So, should a joint, pipe, or any other component fail under test pressure when using compressed gas, the energy can be released with deadly force. When water leakage may cause unacceptable damage to property, a very low pressure pneumatic leak test (at ~0.5 psig) may be used initially and then followed by a hydraulic leak test.

 

[John_187]

Thank you all for the help