Large Pipe Leaking 1

[HB2U]

Got a question for all of you fine folks....

Here's the scenario:

I've got a well station being constructed and the design used 180 feet of 48 inch DIP for the chlorine contactor. The pipe is arranged in a "U" shape, fairly level and we used TR Flex joints.

The contractor is having difficulty getting this pipe to hold pressure. The line is filled, and when the contractor pumps it up to 200 psi, the pressure drops down to 150 psi within 15 minutes. Several taps were made along the line to provide a means for letting air out of the pipe.

We had our leak detection crew out to the site to sound off the pipes, but they were able to find anything worth looking at.

The contractor has exposed joints and even removed a thrust block to inspect the back of a 90 degree fitting since their experience has been that pinholes are not a completely unheard of issue with fittings over the past few years.

I'm looking for other people's experience with such large diameter pipe installations. Is there something that we should be looking for that is a common problem with large diameter pipe? Has anyone heard of any issues with US Pipe products of that size? The contractor had US Pipe out to the site to oversee the completion of the first few joints, and things went well. An internal inspection of the pipe was also made after installation was complete. There were no visible issues.

We've run out of tricks.

Any help is greatly appreciated.

HB -PE Env.

 

[rconner]

Was just curious has the line been pumped up one time or more than one time? If more than one time, exactly what were the results? (e.g. 1st time pumped up to say exactly 200 psi and exactly 15 minutes later pressure read 150 psi. 2nd time ????? etc.) If results are in fact exactly the same multiple times, this would begin to sound like leak and not some other effect (air, slight normal movement/creep, etc.?) If the results are getting better, maybe it might make sense to "keep pumping" it up.

 

[ccor]

Seems as though you have been pretty thourough but you didn't mention what you were testing against. Many large valves, particularly butterfly valves, are only rated for 150 psi.

 

[Ashereng]

Maybe check the pressure gauge? Maybe also the needle valves, root valves, gauge valves if any?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[JStephen]

Doing some quick calculations here- assume water is incompressible, assume 0.58" wall thickness at 24x10^6 PSI modulus of elasticity.
Diameter at zero pressure- 48"
Diameter at 150 PSI- 24.006207"
Diameter at 200 PSI- 24.008275"
From this, difference in volume in 180' = 0.39 cubic feet
Or, 2.9 gallons. This should be more or less what you're losing in that pressure test.

For a big pipe, that may not be much, but seems like if you could keep it pressured up for a couple of hours, you ought to be able to find a wet area- having lost 25 gallons of water in that time.

 

[mgrez]

I'm delaing with something very similar right now. I have the same drop in pressure every 15 min. I start measuring my drop in pressure every 15 min and nothing changed,
also I looked at the amount of water I was pumping in the line every time.
Is very important to keep good records of what your doing.
Unluckily I didnt have any changes at all, so I assumed I have a leak.
My next step is to find a point in the middle of the line like a solid sleeve that the contractor will remove, a cap will be installed and then we will test the 2 section independly.
I would also would check the tapping your leak could be at the fitting coming out of your corporation.

 

[HB2U]

The line has been pressurized several times, and there doesn't seem to be any improvement, but the contractor is convinced that he's chasing a leak so he's been putting water in and letting water out etc. instead of trying to keep pressure on the line.

- I'm not so sure it's a leak. I've been trying to convince him to just keep pumping it up to see if there's any improvement. I figure that if there's a large pocket of air in there it'll take a while to get rid of it.

It's also cheaper than having an operator spot dig all over the site.

As for what we're pumping against, it's a couple of 12 inch gate valves rated for 350 psi.

Kee the info coming.

Thanks.

HB - PE Env.

 

[stanier]

I would be tempted to keep pumping the water to maintain the pressure. AT 200psi you will eventually see a fountain somewhere.

 

[mgrez]

How does the air get out when it get compressed at the valve? I have the same problem and I install an air release, but it didn't work for me. I have also a hydrant and I had been flusing for hours. After looking at the water I can see that there are not bubbles in the flow.
When the contractor filled the line with water did he do it from the top or the bottom?

 

[HB2U]

The line was filled slowly from the bottom and it's sloped along its length.

It's my understanhding that as you increase the pressure, more air can be absorbed by the water. (reverse of what happens when you open a bottle of soda and release the pressure, letting the Carbon Dioxide out of the drink).

Eventually you'lll force enough water into the pipe to absorb all or most of the air.

 

[Maury]

What does your specification require for acceptance? Typically there is a pressure requirement and an allowable leakage. It sounds like the pressure test has been met since the line was pressurized and nothing broke. The next step is the leakage test, measure the amount of water required to maintain the specified pressure.

It is quite possible that the line won't hold pressure without pumping and still pass. With water being incompressible and D.I.P. having very small expansion under pressure, even a tiny leakage will cause the pressure to drop. If the contractor is just pumping water in and letting it out without maintaining pressure, then he's wasting everybody's time.

 

[mgrez]

When you look at the manometer of your testing equipment, does the gage turns to bounce? If this happpens you have air still on the pipe and you will need more bleeding.
When you flush the pipe, can you see bubles of air trapped in the flow? if there is you need to flush more to get out the air.
You test and there is always the same drop for a same intervak of time? you have a leak.
the contractor need to go to the joints and fittings. Maybe isolate the circuit with a valve could cost him less money than digging all arround.

 

[tommyclose]

it s a bit late now but,
firstly, it would have been better to have tested the line before the final tie-in connections to whatever....there should a facility to use air vents at any high spots....

what kind of pipe is it ?

 

[marktbuckcon]

200 pounds sounds like a lot of pressure for a chlorine contact chamber. Do you realy need to test it that high.