Hydrotesting Instrument Tubing
Hydrotesting Instrument Tubing
(OP)
Is anyone aware of a Code requirement to hydrotest stainless steel instrument tubing in gas plants (the compression jointed type)
I am familiar with the normal procedure for hydrotesting pipework prior to commissioning, however the stainless steel instrument tubing appears to not normally be tested. I've reviewed a couple of the piping standards and they appear to neither specifically exclude the tubing or include it. Any help or experiences on this topic would be most appreciated.
Cheers
I am familiar with the normal procedure for hydrotesting pipework prior to commissioning, however the stainless steel instrument tubing appears to not normally be tested. I've reviewed a couple of the piping standards and they appear to neither specifically exclude the tubing or include it. Any help or experiences on this topic would be most appreciated.
Cheers





RE: Hydrotesting Instrument Tubing
The choice of hydrostatic or pneumatic testing of the tubing will depend on whether or not a meaningful hydrotest can be accomplished (i.e. if the system can be completely filled with water such that the test is sensitive enough to leakage), and whether or not the instruments in question can survive the test pressure without damage. Pneumatic testing of tubing systems is not without its hazards and must be done under conditions which guarantee the safety of the tester.
Inevitably, you end up with a few joints that cannot be part of the hydrotest, i.e. the connection between the relief device and a vessel etc.). These are tested generally in a pre-start leakage test at the design pressure before operation.
RE: Hydrotesting Instrument Tubing
We spend a lot of money on equipment to filter and dry the air for the instrument air system so there will not be any rust or corrosion in the valve diaphram or cylinder operators which might then cause a malfunction of a critical system.
And now you say you want to hydrotest this system? This sound like a very dumb thing to do.
RE: Hydrotesting Instrument Tubing
Instrument tubing and air lines are rarely hydro'd unless there is a specific need for it. Air receivers are shop hydro'd usually.
RE: Hydrotesting Instrument Tubing
RE: Hydrotesting Instrument Tubing
dcasto: read my original post: what I said is that ALL tubing containing hazardous process fluids (i.e. "general fluid service" under B31.3), including instrument impulse legs, must be tested prior to being put in service if you are to be in compliance with B31.3. The test is for leakage to the external environment, which is indicative of badly-made joints or other flaws in the fabrication. You are correct that it is not truly a proof test- but it's a hell of a lot better than NO test, or a test with live hazardous fluid like liquid propane!
The choice of which test method (hydro or pneumatic) is used for tubing systems is a matter for the engineer to decide based on the risks and benefits of using either method. Hydrotesting of small tubing lines is seldom warranted. A properly designed pneumatic test carried out correctly is safe, gives a more dependable result and results in much less risk of problems to the process equipment later. But if you've ever seen a tubing line let go under significant pressure, you'll gain the respect needed to spend the time to design a proper test that doesn't put the tester in harm's way.
RE: Hydrotesting Instrument Tubing
RE: Hydrotesting Instrument Tubing
Cheers