New pipe for oxygen service

[imatasb]

Dear colleagues,

I am designing a new 3" pipe for oxygen service. The pressure at the inlet will be 7 barg (101 psig). At the end of the line will be a pressure control valve, followed by an orifice plate and a flow control valve.

The material for the line will be seamless steel ASTM A-312 Tp. 304.

I have never designed a line for oxygen service but I know that there are restrictions in the materials that can be used.

I am specially concerned about which materials to use for the gaskets and internals of the valves.

Is there any problem in using graphite?

Cheers

 

[gr2vessels]

imatasb,
The materials suitability in oxygen service depends also by the maximum operating temperature, the lowest temperature due to depressurization, dry or moist oxygen, liquid oxygen, etc...The austenitic stainless steel is better than the carbon steel in most cases, graphite and any similar combustible material is not compatible with oxygen service. The valving internals could generate sometimes high level of energy due to flow friction, hence a real risk of ignition in an oxygen saturated atmosphere, if combustible materials are used. However, your valving / piping / gasket supplier should be notified to supply and guarantee the equipment suitable for oxygen service.
cheers,
gr2vessels

 

[imatasb]

Thanks you for your answer, I forgot to mention the temperature of the oxygen flow which will be 25 C. The flow will be pure oxygen.

I have already specified that the equipment will be used for oxygen service but I will be insterested in knowing some details about the kind of materials they should be using.

 

[iainuts]

Hi imatasb,
I'd suggest obtaining the CGA pamphlet for "Oxygen Pipeline Systems" CGA G-4.4-2003. You can obtain a copy here:

http://www.cganet.com/Publication.asp?mode=g

In there, you'll find a information about impingment velocity for example. They have a graph that provides maximum velocity in the pipe versus pressure. Note that stainless steel, although somewhat better than carbon steel, is still flammable in pure oxygen.

A better solution would be to use copper pipe and fittings which doesn't have the impingment concerns.

The spec also covers a wide variety of coniderations such as underground pipe, cathodic protection, valves and other equipment, cleaning considerations, construction considerations, design, operation, monitoring, maintenance, emergency responce, safety management etc... It's a wealth of knowledge crammed into 70 pages.

 

[imatasb]

iainuts,

Thank you for your answer. I have already a got adossier with the velocity impingment curves but there are no recommendations for the materials for internals, gaskets,etc..