Feasibility study on the application of laser butt welding of tubes to a pipe coil production line

Abstract

Summary This paper describes a feasibility study on the integration of a laser source as an automatic unit for circumferential butt welding of tubes on pipe coil production lines, immediately prior to the cold-bending station. Using a 6 kW CO2 source, carbon low-alloy Cr-Mo and austenitic stainless steel tube, in thicknesses ranging from 3.4–11.2 mm, were successfully welded. Cr-Mo steels require on-line preheating treatment which can be achieved by laser defocused passes immediately prior to welding. The results of the preliminary qualification tests performed on laser-welded joints on the types of joint configurations involved (materials, diameters and thicknesses) are described, together with the technological tests required for final approval of the process. Laser circumferential butt welding of tube has proven to be effective, giving satisfactory, repeatable results and good joint performance. An exhaustive comparison with current welding techniques (TIG and MIG) is then made, together with a detailed analysis of the potential advantages and benefits which may be expected from using the laser-welding technique, as well as a preliminary estimate of investments and running costs. An accurate analysis of other possible applications and a possible layout of a laser working cell integrated into factory production lines is presented. Thus maximum production is obtained while benefitting fully from the potential of laser technology.