How dangerous is air testing pipework

fowlerboi · Feb 24, 2024

I've air tested pipework for years, typically 4 bar for 30 minutes. I've never had an issue with any pipework that has passed that test, occasionally you get a small leak from the air test typically old cap ends/scratched pipe which shows up easily on the test without having to inspect anything, but once re-tested it is then water tight.

It wasn't until this week when someone joked about it being a pipe bomb that I suddenly thought, actually this could be really really dangerous. I can't find any calculations online to actually get a feel for how much energy is stored in a given system.

The system this week was large, by my calculations 45L of air in pipework plus 5x 6 column radiators and 3x 4 column estimating volume to be 210L, totalling 255L of air at 4 bar

As I see it the only dangerous part would be if something let go. Cap ends would be the most dangerous as they could point in a direction of someone. The other part would be a fitting rapidly failing but I see the damage as limited as long as pipes are clipped thoroughly as nothing could then become shrapnel

Is there anything I'm overlooking? Is this a bit of a non-issue or do I need to do this a little more safely?

Chuck · Feb 25, 2024

The stored energy (assuming isentropic expansion) in your system (0.255 m^3, Pabs=505 kPa, Patm=101 kPa) is about 119 kJ that the equivalent of 26 g of TNT. Stored energies of more than 100 kJ are considered 'highly hazardous'. See for example:

https://ncnr.nist.gov/equipment/pressure/NCNR%20Pressure%20Vessel%20Stored%20Energy%20Limit%20Calculation.pdf

The correct way to pressure test pipework is to employ a fluid, normally water. There are kits sold specifically for this purpose.

Stigster · Feb 25, 2024

When I was an apprentice at college, they were air testing a 100mm cement lined steel water main type pipe that was bolted together with compressed o-rings holding everything together. I did not like this at all and despite my protests they went ahead and did it anyway. People standing around this big T-shaped assembly and filling it with compressed air. They were going for 6 bar as the pipe was rated way higher than that. They laughed at me for hiding around the corner.

Then there was an almighty bang and it threw a 100mm stop end that was made of steel, easily weighing several kilos, the full length of the workshop corridor, across the trowel trades workshop and smashed into the wall about 20 metres away. It made a decent sized mark on the concrete block it hit. I am sure it could easily have killed someone.

From memory, air testing above 0.5 BAR requires a lot of safety precautions, including not being in the area when testing, sand-bagging joints and the like. There's hardly ever a good reason to test with air in domestic situations at least.

fowlerboi · Feb 25, 2024

Testing with water has its issues, time being the biggest. Filling a system with 250L of water would take a long period of time to stabilise and then would continue to fluctuate large amounts between night and day making the process to get an accurate test a long one, you also have the issue of dealing with 250L of water if you have an issue. Then you have labour on top of that, filling a large system needs a spotter and a filler in case there are any issues.

Some of that is not achievable if you're testing blind when parts of the build are in a finished state.

I think going forward a little more precaution needed, not testing with humungous radiators would bring it down to a slightly more acceptable level and then cap ends are probably the biggest risk which can be mitigated quite easily for the duration of a test.

I can't find any regulations or procedures on air testing pipework which seems mad to me as it is a common practice with disastrous consequences

ShaunCorbs · Feb 25, 2024

Yep it’s because air compresses so volume is your issue if you test over 0.5 bar you have to sand bag the entire run and wear a hurtlock suit (eod)

ShaunCorbs · Feb 25, 2024

fowlerboi said:
Testing with water has its issues, time being the biggest. Filling a system with 250L of water would take a long period of time to stabilise and then would continue to fluctuate large amounts between night and day making the process to get an accurate test a long one, you also have the issue of dealing with 250L of water if you have an issue. Then you have labour on top of that, filling a large system needs a spotter and a filler in case there are any issues.

Some of that is not achievable if you're testing blind when parts of the build are in a finished state.

I think going forward a little more precaution needed, not testing with humungous radiators would bring it down to a slightly more acceptable level and then cap ends are probably the biggest risk which can be mitigated quite easily for the duration of a test.

I can't find any regulations or procedures on air testing pipework which seems mad to me as it is a common practice with disastrous consequences

Single impella shower pump and a wheely bin I use if mains isn’t available

Stigster · Feb 25, 2024

fowlerboi said:
I can't find any regulations or procedures on air testing pipework which seems mad to me as it is a common practice with disastrous consequences

Here is a good overview of the subject with some links to regulations about halfway through, both for UK and US. Worth noting they are saying 0.5 bar max pressure with air here too.

LOW PRESSURE PNEUMATIC TEST | Prior To Hydraulic Testing - Constructandcommission.com

Pneumatic Pressure Testing, in this instance, is a non-destructive test used to prove the integrity of a pipework system or vessel before conducting a

constructandcommission.com

fowlerboi · Feb 25, 2024

Exactly what I was after. Thank you

Stigster · Feb 25, 2024

fowlerboi said:
Exactly what I was after. Thank you

My pleasure. It's particularly worth noting that testing with air at just 0.5 bar will show pretty much any problem you are looking for. e.g. an open end, a compression fitting not properly tightened, a badly soldered joint, or a badly sealed threaded fitting so no real need to go any higher pressure in a test of domestic plumbing. Keep doing your air tests, I can fully appreciate the benefits but just keep it to 0.5 bar. When you are happy with that test, fill with water and do a pressure test with the water you will be using in the system, or the water you are using to do a flush.

How dangerous is air testing pipework

fowlerboi

Chuck

Stigster

fowlerboi

ShaunCorbs

Super Moderator

ShaunCorbs

Super Moderator

Stigster

LOW PRESSURE PNEUMATIC TEST | Prior To Hydraulic Testing - Constructandcommission.com

fowlerboi

Stigster

Similar plumbing topics

Newest Plumbing Threads