hydrotest

As I understand your post, you're doing hydrostatic testing and seeing a large pressure difference due to temperature. Is this correct? Can you provide some specific details of that?

whats the pressure you are testing

also mention the temp. difference and the volume of tank.

Your tests should be completed at a temperature of 65*f plus or minus 5*f. Testing with hotter water will give a false leak tests because cold water can leak under conditions that hot water may not. The Navy and bureau of shipping will not allow hot hyrdotests. Don't try to out smart your vessel hyrdotest at 65*f.

Mike

How is it that cold water will leak where warmer water does not?

I agree. There must be something wrong in the system, not in the temperature of the medium. Remember that the physical property of water is almost constant in its liquid state, and its virtually incompressible property is the reason why it is used for hydrotesting.

All these other excuses/theories/explanation are pure B.S.

In this case the word ALMOST takes on a new meaning. Water does not compress but it does expand...

CTE

I would venture to guess that the ideal operating temperature of the water line is expected to not leak under normal operating conditions.

Temperatures above normal operating temperatures would cause fittings and other associated materials to expand and seal up any potential leaks during testing.

Temperatures below normal operating temperatures would cause fittings and other associated materials to contract and cause leaking when a leak wouldn't ordinarily be present.

Then there is the issue of testing under conditions that are warmer then normal operating conditions and after cooling and the seals not resuming shape after being compressed by the expanded fittings causing leaks until the seals resume their normal shape.

Its a fact. If you fill a large vessel up with 60*f water and "squeeze it" you made find "weeper". If you do the test with 70-75* f water the weepers will be less noticable. Done it dozens of times 30% you will see moisture. There must be something to this because the authorities will not allow hot water hyrdo test.Obviously if you are in an area that is very hot and ground water is also hot you have no choice. I have never been in that position though.

Include me in the thread.

I would like to see the comments from all of our astute members.

The variation will be governed by pv/t.As your volume is constant v.Maintain P/T do not worry of 65f, many places ambient is 105f.

I recommend using of a recorder for pressure along 24 hours only if there is no a limitation by the process or there is no limitation for the long period to corrosion to occur, and taking into account to avoid freezing of the hydrostatic fluid inside the piping system. In addition a close observation is required to any higher variation of pressure during recording. You can install a relief valve into your piping system to avoid any excessive raising of pressure. At end of 24 hour, you can analyze the variations, and if you found that the reading of pressure at the same time of day are equals, here be sure that your system is approved.