Minimum Pipe Length For Hydrostatic Test (Internal Water Reticulation) 2

[mahara7a]

Hi!

I'm an engineer working for construction industry and currently having difficulties to determine the suitable test pressure for our internal water reticulation system. The pipe that we've used is Stainless Steel Schedule 40S TP304. For usual section test (done it by divided sections of building), we would normally use 12bar or 1.5 times working pressure for 24 hour as stated in contract requirement. Normally this would work just fine. But, there is a scenario of where 3m length of pipe (Size 100mm) left untested and when tested with the aforementioned requirement resulting to leaks at the fittings. This 3m section is due to its location which is before entering the building and after the water main supplied by other discipline (mine is mechanical) and need to be tested before connecting it to main line and to the building. Is there any formula or rule of thumb in doing this or is it just not feasible to the test? The problem now is it has caused some management paperwork issue. Based on my engineering judgement, this pipe will work just fine.

Thanks in advance.

 

[pennpiper]

mahara7a,
You already have the answer.
"we would normally use 12bar or 1.5 times working pressure for 24 hour as stated in contract requirement."
This works for a short pipe and for a long pipe. What are you expecting that would cause a different answer?

Sometimes its possible to do all the right things and still get bad results

 

[LittleInch]

I'mk not really understanding the issue here.

You normally have a demarcation point / connection point where one party is responsible for one side and another (you) responsible for the other side. This looks like it is the meter connection.

Why is it so hard to test this 3m of 4" pipe?.

As you point out, the pipe is probably OK and could be tested before installation, but it's the joints which leak.

If the fittings can't handle the test pressure then they need to be isolated during the test.

The rule of thumb is that all pressure containing parts should be pressure tested. Length doesn't come into it.

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

 

[mahara7a]

Thanks pennpiper and LittleInch for your reply.

I'm assuming that when the pipe length is shorter,volume inside the pipe become smaller. Thus making its harder to pump a certain amount of water inside until it reach 12 bar. Even after we pumped it to 12 bar, it wont hold the pressure for 24 hours as the pressure will try to escape through the thread of the end cap at end of the pipe. We did tried to fix the end cap and ensuring the thread is properly sealed twice but still, the pressure dropped to 10 and 9.7 bar and usually after this it wont drop any below. I'm a bit new to this and just found out about the allowable leakage. Is this considered allowable leakage?

 

[LittleInch]

I was a little surprised about the 24 hour test period.

Normally you get a strength test of 1.5 for a shorter period ( say 1 hour or 4 hours max) then a leak test at 1.1 for say 8 hours or 24 max.

The 1.5 is really to make sure nothing breaks, not so much leakage, but I don't know what your specification or contract states.

Yes sealing for small distances is a pain but you will need to find a way or a better sealing system.

Usually you need to add water to keep it at 12 bar plus minus 5%. If you can measure the water out and then measure water in then you can show that you're just replacing the lost water, but it's much better to seal the end cap. I appreciate for such a small length and size this is probably very small amounts, but then you really need to talk to the client or his inspector and see whether they are practical about this or not.

for a 100mm water pipe this seems rather onerous....

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

 

[mahara7a]

LittleInch,

Thanks for your input. I have talked to my client regarding the requirement and explaining the situation to them. They also realized that the requirement is troublesome and not practical for this particular case. They then allowed us to test it using 8 bar for 24 hours and passed the inspection.
Thanks again!