Tuesday, October 8, 2013

What Does "Prepared for Oxygen Service" Mean for Valves?

oxygen service for valves
Image courtesy of Wikipedia
Oxygen service preparation refers to a special cleaning process that removes all traces of oils from a valve to allow use in with oxygen (O2).  Oxygen is odorless and colorless, and exists in air at approximately 21% concentration. It is non-flammable, but supports vigorous combustion to any materials that are combustible. Allowing oils or greases to contact higher concentrations of oxygen can cause ignition and even explosive outcomes. Aside from the reactive concerns, O2 preparation is also used for applications where purity is needed.

Oxygen is used extensively in medical, deep-sea, metal cutting, welding, and metal hardening. The steel industry uses oxygen to increase capacity and efficiency in furnaces. A major use is in production of gasoline, methanol and ammonia where it is used as a synthesis gas.

Oxygen, when in a gas state, is noncorrosive and may be used with a variety of metals. Stainless steel, bronze and brass are most common. Liquid oxygen presents unique challenges because of the cryogenic temperatures and valve bodies, stems, seals and packing must be carefully chosen.

RENCOR offers a variety of valves suitable for oxygen service. Valves are available with screwed, socket weld, ANSI Class 150 and ANSI Class 300, DIN PN16 and DIN PN40 flanged ends. Body materials include 316 stainless steel, monel, bronze and brass. Standard ball and stem material is 316 stainless steel or brass. PTFE or glass filled PTFE are inert in oxygen and are a common seat and seal material for oxygen service.

Common procedures for O2 service are to carefully "debur", meticulously clean to remove all traces of oil, grease and hydrocarbons before assembly. Assembly must be carried out in a clean area using special gloves to assure no grease or dust contamination. Lubricants compatible with oxygen must be used. Seating and leakage pressure tests are conducted in the clean area, using grease free nitrogen, and specially cleaned tools are used for assembly. Once assembled, the valves are tested and left in the open position. A silicone desiccant pack is inserted in the open valve port, then the valve ports are capped. A warning label about the desiccant pack's location is included, with a second tag noting "This Valve is Prepared for Oxygen Service". The valve is then sealed in its own polyethylene bag for shipment and storage.