Influence of preheating on API 5L-X80 pipeline joint welding with self-shielded flux-cored wire

Abstract

The present work refers to the characterization of the mechanical properties of API 5L-X80 pipeline joints welded with self-shielded flux-cored wire. This process was evaluated under preheating conditions, with a uniform and steady heat input. All joints were welded in a flat position (IG), with the pipe turning and the torch still. Tube dimensions were 762 mm in external diameter and 16 mm in thickness. Welds were applied on single V-groove, with six weld beads, along with three levels of preheating temperatures (room temperature, 100°C and 160°C). These temperatures were maintained as the inter-pass temperature. The filler metal E71T8-K6, whose mechanical properties differ from those of the parent metal, was used in undermatched conditions. The weld characterization is presented according to the mechanical test results for tensile strength, hardness and impact testing. These tests were conducted according to API 1104, AWS and ASTM standards. API 1104 and API 5L standards were used as screening criteria. Based upon the results obtained, it was possible to note that it is appropriate to weld API 5L-X80 steel piping with self-shielded flux-cored wire, in conformance with API standards and with no need to use a preheating temperature.