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For copper natural gas systems, flared brass fittings of a single 45° flare type, forged or with a machined long nut, are used, see Figure 10.
Figure 10: Flared Brass Fittings
It is important that the tube be cleanly cut and deburred, and then a proper flare made. Connections to steel pipe are made with an NPS threaded to flared copper adapter. Compression fittings are not allowed for gas systems, unless approved by the regulatory authority.
When brazed connections are required, they are made using capillary fittings and a brazing material with a melting point of over 535°C (1000°F) that is acceptable to the regulatory authority.
All fittings for natural gas installations are rated at over 125 psig (860 kPa), but they should not be used at pressures above those permitted by local codes. When branches (tees) are installed, they are positioned on the side or the top of the line, unless the branch is a drop to an appliance and it is provided with a dirt pocket. Gas installation regulations require joints within walls or other concealed places, to be inspected and tested prior to concealment. Tube installed in existing enclosed partitions must not include any inaccessible mechanical joints. The long flexible lengths of copper tube make this requirement very easy to comply with.
Manual brass or bronze shut-off valves must be provided for all appliances, in accordance with the provisions of the local code requirements. They must be readily accessible, be identified and usually be within 50 ft (17 m) of the appliance. Systems using a distribution manifold, may have all of the manual shut-off valves installed directly at the manifold and thereby be in one place for convenience. A dirt pocket is usually installed at the base of the final vertical drop serving certain appliances, as required by local regulations. This may be made up of steel fittings with a NPS to copper adapter, the flare nut conveniently acting as a union, see Figure 11.
Figure 11: Typical Dirt Pocket Installation.
A selection of forged brass flared fittings.
A selection of flared brass fittings with machined long nuts.
Although the use of copper tube minimizes the possibility of leaks occuring, installations must be tested in accordance with the code of the regulatory authority having jurisdiction. This usually includes pressure testing with air or an inert gas (carbon dioxide, nitrogen, or a mixture of them), at the pressures and for the durations required.
After all appliances are connected and the gas is turned on, a meter dial test is carried out over a period of time, and every connection, joint, valve, and so forth, is checked with an approved liquid leak detector solution.
The installer then attaches a test tag to the system with his name, address and date as the installer, and with all other information required, including details of the test pressure and the duration of the test.
Typical copper gas system in a single-family dwelling. It has a 1/2" O.D. copper supply line, 2 psig from the meter to a regulator (conveniently installed just above the furnace) which reduces the pressure to 7" w.c. for 1/2" lines to the other appliances.
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