Pressure test for oxygen piping 3

[nicorvp]

I'm compiling a piping specification for oxygen gas and liquid and I need to have some information about the type of pressure test usually used: pneumatic (with dry air) or hydraulic? And which precaution I need?
I will use 316 piping with 100% Rx
Thanks in advance
Nicorvp

 

[PlantEng]

The test requirements depend on the Piping Code that you are designing the system to. B31.3 Process Piping Code gives guidance on Hydraulic or Pneumatic testing pressures based on the pressure of the pipe, material strength and temperature. My philosopy is to use hydrotest unless the water will mess up the process. Then use pneumatic unless the risk of energy release is to great (large volume systems). In that case you can take an exception to pressure testing because you have 100% xray testing. We do this often in Dowtherm systems because water and dowtherm do not mix well, and our systems are in large populated areas so we would rather not pneumatically test. We just fully x-ray or ut and then service test. When in doubt, follow the code.

 

[Montemayor]

nicorvp:

Please heed some words of hard-earned advice - never, never, employ the terms "hydraulic" and "Oxygen" in the same application!

I must emphasize the importance that the term hydraulic infers: the use or tolerance of oil (or hydrocarbon liquids). This is simply not tolerable in any Oxygen application. I realize that most engineers know this; however, using the term(s) loosely can be fatally mis-interpreted. For example: note that while I highly recommmend a hydrostatic test on the stainless pipe instead of a pneumatic one, I would highly caution you to insist and ensure that the water is totally oil and grease-free. Additionally, I would run an oil and grease solvent through the piping to ensure that it is, in fact, free of any hydrocarbon substance prior to being filled with Oxygen. (of course, you have to purge and evaporate the residual solvent - more expense and labor, typical of Oxygen installations). The big concern in an Oxygen application is not the high pressures used or the gas itself; it is the potential, dangerous mixture of pure Oxygen with a readily oxidizable substance, such as a hydrocarbon. This is never to be allowed or credibly achievable. Mechanical engineers will recognize the product of such a mixture as an explosion.

Bear in mind that the B31.3 Process Piping Code is a mechanical code; this has nothing to do with the ultimate hazard and danger when dealing specifically with Oxygen: it will oxidize efficiently and instantly if given the right opportunity - in other words, it will detonate any hydrocarbon it comes in contact with under the right conditions. Your application is very process sensitive and you should consider the process needs and precautions rather than just applying strictly mechanical codes in his instance. There are existing standards for Oxygen service within some organizations - especially producers like Air Products, Praxair, Liquid Air, etc. These people can give you all the correct and safe guidelines to put your Oxygen system into service under the best and most experienced guidelines and standards - besides those of B31.3. You may, in fact, be purchasing your Oxygen from such suppliers and it would be a smart move to get their expert advice on how to test, clean, and ensure a safe Oxygen piping system.

Art Montemayor
Spring, TX

 

[aberta]

For testing oxygen piping which has been radiographed, nitrogen 9or inert gas) is the best medium. The nitrogen must be DRY and OIL FREE. the pressure test should be carried out in several small increments. We would normally snoop for leakage at all welds and gasket joints. When the final test pressure has been reached, the pressure is then lowered to operating pressure, and piping re-snooped. After a successful test,the piping is then blown clean by opening valves. We would normally pce a clean cloth to catch the blast and notice level on any contaminants blown out. This process is then repated if necessary. the piping is then padded to a pressure lower than operating pressure.
Note that this procedure does not clean pipe but merely removes any contaminants caught in the piping after cleaning process. If we re-open the piping, black light is used to check against contamination.
Hope this helps. regards.

 

[scooter911]

If your going to work with Oxygen, you need to know what your doing. Montemayor has some good advise and I would suggest you also look at some of the Compressed Gas Association's (CGA) literature. Fluid velocity, adiabadic heating, internal protrusions(mig wire stubs), sharp corners, and material compatability are just a few thing to worry about. I've seen the seat on a regulator burn out and start leaking in a high pressure system; then again, I've seen what was left of a few that went boom.

Just a note: Never blow yourself off with a cutting torch, it's pure Oxygen. Just an accident waiting to happen.

Hope it Helps