Dual tandem narrow groove pipe welding

The development of a new high productivity pipeline welding system - CAPS (Cranfield Automated Pipeline System) - is described. The system uses two tandem torches on a single welding carriage and is capable of welding in all positions (5G girth welds). Productivity is substantially enhanced and welding speeds can be twice that of single wire conventional gas metal arc welding (GMAW), resulting in major savings in labour and equipment costs. The weld profile is similar to that produced by conventional GMAW and therefore conventional radiography and ultrasonic testing can be used for weld inspection. Welds of good quality were obtained. Initial trials using the same consumable in both wires produced a weld metal yield strength outside than the target range of 810 to 860 MPa. However, the target was achieved with the combination of a low alloy (1 % Ni 0.3% Mo) and a higher alloy (1.8% Ni 0.5% Mo 0.25% Cr) wire, by feeding two wires into the same weld pool. This mixed wire technique was implemented and welding procedures were developed. The all weld metal tensile strength 840 MPa met the overmatching criterion and the cross-weld tensile, nick break and side bends tests were all acceptable. Weld metal toughness results were very good giving values above 100 J at -60 C. This paper reviews the development of the system together with results relating welding parameters and mechanical properties.