Temperatures for Pipe Hydrotesting

Test Temperature = Ambient (natural site temperature or 70 degrees "F" +/-)

Test Duration = Minimum 4 hours/recommended 24 hours

The preferred hydrostatic test temp of most material is around 70 degrees F. For ASME repairs they list a range of not less than 60 degrees F and not over 120 degrees F. These temperatures are referenced in the National Board Inspection Code, paragraph 4.4.1 (a), (3) Page 79, Part 3, section 4 for examination and testing. There are exceptions to this rule if the owner has documentation showing that the particular material can be tested at a lower or higher temperature and the AI accepts it.

On most piping systems temperature is not critical but testing at to high of temp can cause a small leak to seal off from the thermal expansion of the pipe material. One of the best places to see thermal expansion at work during a hydro test is when testing boiler generating banks that have the tubing rolled instead of welded into the steam and mud drum to make a seal. Many times I have seen engineers and project managers get into long heated discussions about what constitutes a true leak in a system. They will even start categorizing the leaks as "weepers", "drippers", "pissers," etc. and then waste allot of time auguring that the "weepers" are not worth repairing. The more times a company unsuccessfully hydro-tests a system the more chance they will try and say the weepers are not really leaks and that they will seal off once the system gets hot. While it is true that very small leaks in a boiler generating bank will seal off once it gets hot most piping systems will not get hot enough for small leaks to seal off .There is no getting around the fact that no matter how small a leak is it is still a leak and if you want a truly "dry" hydrostatic pressure test all leaks must be repaired.

I had one company try (behind my back) to test using boiler feedwater which can be in the 500 degree F temperature range instead of just accepting a leak is damn leak and repair it. The bottom line is that if a leak is not repaired when it is found the next guy that performs a hydro will have to repair it and it may have grown larger.

I am not sure where some people get the 24 or even 4 hour hold time because the NBIC requires to hold pressure for only 10 minutes on ASME boilers, pressure vessels and some piping systems.

In a 24 hour time frame many things can happen that would make appear that you have a leak but in reality the system pressure just bled down during the hold time. A loose packing nut, bad thread or gasket etc could make one think the pipe is leaking.

I do a complete visual inspection of all of the components in a system while it is under pressure no matter what type of system it is. Some people just watch the test gauge to determine if they have a leak. Although this a good way to determine if you have a leak it is possible to miss small leaks if the pressure on the gauge does not drop significantly. A drop in the pressure gauge could be caused by not properly bleeding off the air in the system or a leaking-by valve that isolates the system from being tested from another piping system. It is impossible to find a leak without inspecting each and every component on a system or at least I have never found a way to do it.

Dear pipewelder,

Good answer with my GA.

Thank you very much for all in giving solution.

Regards,

k.Uthayasankar.