Pressure drop in fire fighting pipes

[anoopjohn]

The hydrostatic testing is conducted on the fire fighting pipes, which is of the material Black Steel Schedule 40. The pipe system for the floor is isolated from the main riser and the hydrostatic test is conducted. Thus, static pressure is acting inside the pipes.
The pipe is pressurized from the further-most point, to a pressure of 16 Bar (232 PSI), and is observed after 2 hours if there is any pressure drop. No pressure drop is observed over the period of 2 hours. But when the pipe is left pressurized and untouched for 24 hours, a pressure drop of 2 bar (29 PSI) is observed. If there was a leakage in the pipe system, the pressure would gradually drop to 0 Bar over time. But since a pressure drop of 2 Bar is observed, the reason is unknown.
Therefore, can I get an explanation on why the static pressure drop is observed? Is it because of the temperature at which the pipe is located? (The pipes are located in the area conditioned between 25-30°C.) Or is it because of the ingredient of the water used for pressurizing the pipes? As in, if there are particles in the water used, how does it affect to drop the static pressure?

Thank you!

 

[BigInch]

Most likely cause is temperature change or a leak. If no leaked fluid is observed, probable cause by temperature change becomes more likely. Measure temperature continuously during the test. If temperature is the cause, you should easily be able to establish a good correlation between pressure and temperature. If temperatures return to previous levels, the same pressures should be observed at each previous temperature. Otherwise look for leakage.

 

[bimr]

Various reason can be proposed. Leakage through block valves, entrapped air, etc.

 

[LittleInch]

2 bar loss is only about half a degree centigrade change. Water filled pipes are very sensitive to temperature change when filled with 100% liquid.

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