Gas piping shall be gas-tight and built along lines that are unlikely to cause physical injury to inhabitants, or weakness in the building structure. All pipe shall be either new, or shall previously been used for no other purposes than conveying gas, and shall be in good condition, free from internal obstruction and burred ends reamed to the full bore of the pipe.
In NO case is it recommended to repair defects in pipe or fittings by caulking, peeling, or the use of clamps or cement. The defective pipe, fitting, or threaded joint, having been located, shall be removed and replaced with new material. (NFPA 54 5.6.5)