problems. Other fluids, such as helium, also have compatibility problems
that must be considered.
a.
Compatibility with Oxygen. Oxygen is the most dangerous fluid
contained in hyperbaric chamber piping systems.
Brass or copper pipe has been appropriately used for 3,000 psig gaseous
oxygen piping at LOX vaporizing and transfer facilities and hyperbaric chamber
installations. However, with the relatively recent requirement for 5,000
psig gaseous nitrogen at these facilities, this piping material and pressure
rating is inadequate for these higher pressure and gaseous piping systems. NAVFAC
Instruction 11012.128 High Pressure Gaseous Oxygen and Nitrogen Piping at
LOX/LN2 Storage, Vaporizing, and Transfer/Generation Facilities (Reference
6) provides information for the design and fabrication and for the type of
material, pressure rating and fittings required for high pressure gaseous
oxygen and nitrogen piping systems at shore-based hyperbaric facilities.
This instruction establishes the following requirements:
(1) 3,000-5,000 psig working pressure -- piping and tubing for the
subject facilities shall be annealed austenitic stainless steel or
nickel-copper (Monel) or copper-nickel.
(2) 0-3,000 psig working pressure -- copper and brass may be used
in addition to the previously listed materials indicated for the higher
pressures.
(3) To prevent accidental use of underrated tubing on new or
rehabilitated projects, all tubing of the same nominal diameter should have
the same pressure rating. This pressure rating shall be for the highest
pressure which a given size tube will encounter on the project. The pressure
rating of these systems shall be based on a safety factor of four.
(4) Connections for pipe or tubing to all fittings, valves, and
other components of the subject plumbing systems for working pressures up to
5,000 psig must be in accordance with ANSI B 31.1, Power Piping, and must not
be in conflict with the applicable requirements of the National Fire
Protection Association Codes: NFPA 50, Bulk Oxygen Systems; NFPA 51,
Oxygen-Fuel Gas Systems; NFPA 56D, Hyperbaric Facilities; and NFPA 56F,
Nonflammable Medical Gas Systems (Reference 7).
For working pressures above 3,000 psig, all connections shall be made by
welding, by flareless tube fittings equivalent to MIL-F-182.80C, or by flared
tube fittings equivalent to MIL-F-5509C.
(5) All piping system components which come in contact with
pressurized oxygen or with nitrogen, which is used for purging oxygen
equipment, must be thoroughly cleaned to prevent explosions caused by the
highly reactive nature of oxygen. Cleaning methods and cleanness testing
techniques should be matched to the characteristics of the piping system.
Specific information on cleaning procedures and testing criteria are provided
in Chapter 12.
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