Hydrostatic Pressure Test

Currently I’m working under a 600mm pipe laying project in Middle East. We had finished the pipe laying work and now come to the final stage of the work.

Previously we have done and passed the 1st pressure test along the pipe laying sections. As per requested by the authority, we need to complete another pressure test (9 Bars) by testing the whole pipe length before we can divert the water supply to the new laid pipe.

We have tuned the pressure to 9 bars and maintained for 24 hours. However the pressure was dropped to 7 bars and extra 400 liters of water was pump into the water pipe. The pressure test was failed but we could not locate any leakage along the pipeline.

Information for my pipeline:

Pipe Diameter : 600mm Ductile Iron Pipe
Pipe Length : 1500m
Pressure : 9 Bars
Allowable water tolerance : 180 liter/km/24hrs
Highest Elevation : 41.225m
Lowest Elevation : 34.384m
Pressure Gauge : 37.781m (End of pipeline)
Valve Chamber : 2 nos. Air Valve, 2 nos. Washout Valve, 2 nos. Butterfly Valve

My subcontractor had fixed the pressure gauge at the end point of the pipe instead of the lowest point. Thus I’m seeking help here since this is the first pipe laying project for me. Kindly provide me any advice or guidelines before I redo or conduct the pressure test.

For the second pressure test, the specification is almost the same except,

Pipe Length : 19000m (approx.)
Highest Elevation : 49.368m
Lowest Elevation : 30.749m
Valve Chamber : Total 42 nos. 15 nos Air Valve, 16 nos Wash Out Valve, 11 nos Butterfly Valve.

Thanks for your time and help.

You lost 7 bars of pressure and 400 litres of water? You have a leak.

Big project. 24 inch pipe almost a mile long 4920’ Volume lost about a 105 gallons and a pressure drop of 29 psi. Not exactly a home project with a one inch supply line.

Sounds like a trap or a bubble around one of the valves. Poor purge of the line before the test. Did anyone do a volume calculation and a metering of the water placed into the line?


Ah my mistake 2 bar loss, but with that amount of water added I still vote leak. Check the valves again, packing and any test plates. Is the line under test attached to an existing line at any point?

Wow, that a volume of about 115,500 gallons of water. Loss of product was about 1/10 of 1 %. One single leak at that rate would create a loss around 0.072 gpm. or 9 ozs a minute. What also is not in the equation is water temperature, what temp was the water at at the start and what was the final temp, expansion and contraction. We’re just assuming standard temp and pressure through out the test. Middle east location hot days cold nights.

No leak, someone messing around :mrgreen: At the top of the thread

I agree with the temperature change. This would allow for a pressure difference in that massive amount of area.
Need data before and after.

And the percentage of pressure loss is? :mrgreen:

About the same as the amount of gas expelled from a belch after chugging a 6 pack of beer :twisted:

The thermal coefficient of expansion of water is 0.00021 per 1° Celsius at 20° Celsius.

There is no record for temperature. However the ambient temperature is between 39-41° Celsius. Most of the pipeline is backfilled and covered except the valve chamber areas. No leakage of the water in the previous tests (tested between chamber). Thus, we had inspected the connection between the valve chamber and water pipe. However there is no sign of water leakage.

In order to find out the possible leakage point, we had re-adjusted the pressure back to the 9 Bars. Two readings were taken at both ends of the water pipeline. One of butterfly at the middle of the pipeline was closed. From this, we hope that we can narrow down the search for the leakage.