Overlap edges 6” (152.4 mm) in preparation for thermal seaming. This overlap area must be cleaned of all dust, dirt, water and foreign debris no more than 30 minutes prior to the heat-seaming operation. Acceptable field-welding methods are thermal fusion and extrusion. The thermal energy for fusion welding can be provided by a single or dual hot wedge welder, hot air or a combination. Extrusion welding rod should be made from the same resin class as the bonding surface of the gas barrier being extruded to. Trial welds, at least 4’ (1.2 m) long, shall be made on scraps of the same material being installed.
Three non-destructive test methods are available to verify field welds, including: center air channel pressure testing for double-track fusion seams, vacuum box testing for single-track fusion seams and extrusion seams or patches, and air lance testing for single-track fusion seams.