Gas Tungsten Arc Welding (GTAW) process is at present the most preferred process for CRA pipeline welding, particularly to perform the root pass. The reason is mainly due to the high quality of the welds made with this process, particularly when is associated to a mechanised system. Welds made with GTAW process has resulted so far, on the basis of field experience, of high integrity and more specifically with mechanical and corrosion properties in line with the requirements of the major welding/corrosion Standards i.e.: B.S., D.N.V., NACE..

On the other hand, GTAW process, due to its nature, is rather slow and a significant improvement in the welding speed is needed to make it more attractive for future pipeline application.

To improve root pass welding speed in CRA girth welding, a dedicated research project, funded by the European Community (Thermie OG 329-93) was performed and successfully completed. Aim of this research project was to demonstrate the applicability of GMAW process for full welding, including root, of Corrosion Resistant Alloy materials (Duplex and Clad). The welds were made by the PASSO (GMAW) mechanised system which proved its applicability and the potentiality to increase the pipelaying rate of at least 20% with respect to that of the standard GTAW process. The PASSO system was subsequently used in production to lay 38 Kms of the 10' offshore 'Clyde Project' in Clad material. Results of the research program and laying operation are reported.