For copper natural gas systems joined with flared tube connections, flared brass fittings of a single 45 o flare type are used, Figure 15. Connections to steel pipe are made with an NPS threaded-to-flared copper adapter. Compression fittings in a gas piping system are not permitted unless allowed by the authority having jurisdiction.
All tube fittings for natural gas installations are rated at more than 125 psig, but should not be used at pressures beyond those allowed by local codes. When branches (tees) are installed, these should be positioned with the branch on the side or the top of the line, unless the branch is a drop to an appliance and is provided with a dirt pocket (drip leg).
In addition to mechanical joints, or in many cases instead of mechanical joints, brazed joints utilizing ASME/ANSI B16.22 wrought copper fittings may be used in copper gas distribution systems. When brazed connections are required, they should be made using a brazing alloy with a melting point above 1,000 F. The brazing alloy must contain less than 0.05% phosphorus.
Gas installation regulations aim to avoid joints within walls or other inaccessible places where undetected leakage might cause an accumulation of gas. However, joints in these locations may sometimes be unavoidable. Since mechanical joints are prohibited in inaccessible locations, brazed joints should be used, provided they are approved by the authority having jurisdiction. These joints should be inspected and tested prior to enclosure to ensure a leak-free system. Minimization of joints, especially in inaccessible areas, can be easily accomplished using long, flexible lengths of copper tube.
Approved appliance stops (manual shut-off valves) are required for each appliance and must be readily accessible. Where it is acceptable to the authority having jurisdiction, systems using a distribution manifold may have all the stops at the manifold. In some jurisdictions, dirt pockets are required at the inlet to an appliance regulator or at the base of a vertical drop to an appliance. This dirt pocket may be made up of steel fittings with an NPS to-copper adapter with the flare nut acting as a union, Figure 16.