The system shall be an all-welded system except where the tubing joints are readily accessible and at the individual air fill panels or stations. Where mechanical high-pressure tube fittings are used, they shall be approved for the type of materials to be joined and rated for the maximum pressure of the system.
Prior to and during the welding of sections of tubing, a continuous, regulated dry nitrogen or argon purge at 3 psi (21 kPa) shall be maintained to eliminate contamination with products of the oxidation or welding flux. The purge shall commence not less than 2 minutes prior to welding operations and continue until the welded joint is at ambient temperature. Welding procedures shall comply with the following requirements:
- Qualification of the WPS to be used, and of the performance of welders and operators, is required.
- No welding shall be done if there is impingement of rain, snow, sleet, or high wind on the weld area.
- Tack welds permitted to remain in the finished weld shall be made by a qualified welder. Tack welds made by an unqualified welder shall be removed. Tack welds that remain shall be made with an electrode and WPS, which is the same as or equivalent to the electrode and WPS to be used for the first pass. The stopping and starting ends shall be prepared by grinding or other means so that they are capable of being satisfactorily incorporated into the final weld. Tack welds that have cracked shall be removed.
- CAUTION: Arc strikes outside the area of the intended weld shall be avoided on a base metal. [ASME B31.1:127.4.1]
The system components shall not be exposed to contaminants, including but not limited to, oils, solvents, dirt, and construction materials. Where contamination of system components has occurred, the affected component shall not be installed in the system.