Safety standards for oxygen and other positive-pressure medical gases require the use of Type K or L copper tube (see ASTM B 819). Special cleanliness requirements are called for because oxygen under pressure may cause the spontaneous combustion of some organic oils (the residual of lubricating oil used during manufacture) and for the safety of patients receiving medical gases.
Copper tube for medical gas lines is furnished by the manufacturers suitably cleaned and capped or plugged. Care must be taken to prevent contamination of the system when the caps or plugs are removed and tube is installed. The installer must satisfy himself and the inspection department that the cleanliness requirements of the code have been met.
The following requirements are based on those found in NFPA Standard No. 99, Health Care Facilities, Chapter 4, Gas and Vacuum Systems.
Installation and Testing of Medical Gas Piping Systems
- All piping, valves, fittings and other components for use in all non-flammable medical gas systems must be thoroughly cleaned by the manufacturer to remove oil, grease and other readily oxidizable materials as if they were being prepared for oxygen service. Use particular care in storage and handling. Such material must be capped or plugged to prevent recontamination before final assembly. Just prior to final assembly, the material must be examined internally for contamination.
- Cleaning must be done in accordance with the provisions of CGA Pamphlet G-4.1, Cleaning Equipment for Oxygen Service.
- All brazed joints in the piping shall be made up using brazing filler metals that bond with the base metals being brazed and that comply with Specification for Brazing Filler Metal, ANSI/AWS A5.8.
- Copper-to-copper joints shall be made using a copper-phosphorus brazing filler metal (BCuP series) without flux.
- Dissimilar metals such as copper and brass shall be joined using an appropriate flux with either a copper-phosphorus (BCuP series) or a silver (BAg series) brazing filler metal. Apply flux sparingly to the clean tube only and in a manner to avoid leaving any excess inside of completed joints.
(NOTE: Ensure proper ventilation. Some BAg series filler metals contain cadmium, which, when heated during brazing, can produce toxic fumes.)
- During brazing, the system shall be continuously purged with oil-free dry nitrogen to prevent the formation of scale within the tubing. The purge shall be maintained until the joint is cool to the touch.
- The outside of all tubes, joints and fittings shall be cleaned by washing with hot water after assembly to remove any excess flux and provide for clear visual inspection of brazed connections.
- A visual inspection of each brazed joint shall be made to assure that the alloy has flowed completely around the joint at the tube-fitting interface. Where flux has been used, assure that solidified flux residue has not formed a temporary seal that could hold test pressure.
- Threaded joints in piping systems shall be tinned or made up with polytetrafluoroethylene (such as Teflon®) tape or other thread sealants suitable for oxygen services. Sealants shall be applied to the male threads only.