Steel pipe is now entirely welded, except for joints which need to be taken apart for service, which will be flanged. It is essential that welding is carried out by competent craftsmen and is subject to stringent inspection.
Flanges for ammonia (and preferably, also, for other refrigerants) must be of the tongued-and-grooved type which trap the gasket.
Copper tube should use brazed joints. It can be bent to shape in the smaller sizes and the use of bending springs or formers is advised, to retain the full bore.
Where fittings are required, these should be of copper or brass to give a correct capillary joint gap of not more than 0.2 mm, and joined with brazing alloy.
The brazing of copper tube in air will leave a layer of copper oxide inside, which may become detached and travel around the circuit. It is therefore necessary to pass nitrogen into the pipe before heating, and to maintain a flow until brazing is complete. The use of special grades of oxygen-free or moisture-free nitrogen is not necessary.
Posted in Refrigeration and Air Conditioning