Hydrostatic Pressure Loss

[jgauthier30]

Hi

 

While performing a hydrostatic pressure test with water in a pressure pipe we are experiencing loss of pressure most likely caused by leaks through pipe joints. Is there any equation that can theoretically calculate the amount of water that has leaked from the pipe based on the amount of pressure lost over a given time? Below I have some rough numbers.

 

Pipe Diameter = 30 inches

Pipe Length = 1000 feet

Pipe Volume = 4908 cubic feet = 36,710 gallons

Starting Pressure = 100 psi

Final Pressure = 95 psi or a 5 psi pressure drop

Length of Time to drop pressure = 4 hours

 

Thanks

[CaptainPanic]

It may also just be that some pockets of air that were still present in the pipe dissolved into the water. Then the pressure also drops. But it should stop dropping.

Or the temperature may have changed. Water has its highest density at 4 degrees Celsius... so if you went from 10 to 8, you can see a drop in pressure.

 

Keep monitoring the pressure, and the temperature,... if it keeps dropping, then you may have a leak. If it stops, there may be no leak at all. If it goes up again, the temperature is increasing.

 

Regarding equations, that's a little tricky.

See, in standard equations, the water is considered "incompressible". So, in a static situation, with a pipe full of water (and no gas), a tiny leak would instantly reduce the pressure in the entire pipe to atmospheric pressure. But that's the equation, not the real world.

You can also regard the water as (slightly) compressible, but I don't know the equations to solve for that.

[pioneer]

Water is only slightly compressible. You need to go to an engineering table to find the density of water at the two pressures; 95 and 100 psi. You know the volume of the pipe and assume that is fixed ffor both pressures. This volume and the two densities allows you to calculate the mass of water in the pipe at each pressure. The mass difference is the answer.