Hydrotesting piping systems 1

[mowlin]

I need some help or advice here. I am performing hydro testing on piping systems using dual pen recorders (one for pressure and one for temperature) and charts together with pressure gauges. What we are seeing isa that in some instances, the pressure drops by 2% of test pressures ( Three different test pressure are: test pressures are 435psi, 700psi and 1700 psi)but there are no indications of temperature drops and vice versa, pressure increases and the temperature decreases on the charts (strange.

Upon visual inpsections there are no leaks within the system. Are there any other factors which might be contibuting to this? Also, what are the final results? that of the gauges and visuals or the chart recorders readings? or a combination of all?

we are not sure of what is aceptable or not.....

Thanks...any assistance is appreciated

 

[Cockroach]

There could be an internal leakage through the system if it is not properly blocked in. Depending on your setup, the chart should be recording from the bulkhead just above the pipes.

It is not uncommon for the Haskil pump to back off and have leakage through a check valve for example. As for thermal variation, these are typically minimum noting the volume of test fluid in contact with the pressure envelope are large.

Under the spirit of the code, CSA Z245.15 or API 6D, you are only allowed one line to be crossed on the chart. This is usually about 20 psi depending on your pressure level. But the chart is 1.5 MOP for a minimum of fifteen minutes without operator interference.

Good luck with it.

Regards,
Cockroach

 

[berkshire]

Have you investigated plastic deformation in the pipe?

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[EngineerTex]

End the test and drop the pressure back to zero and then do the test again -- do you find that the 2% drop is repeatable over the course of a number of identical tests on the same piece of piping? If you've not tried to repeat the situation, that's the first thing I would do.


Engineering is not the science behind building. It is the science behind not building.

 

[mowlin]

@ berkshire interesting point...thanks guys