Hybrid Laser/Gas Metal Arc Welding of High Strength Steel Gas Transmission Pipelines

Despite significant investment, one-shot welding and power beam processes have not been very successful in achieving real benefits in pipeline construction. The most promising of the newer and more innovative welding processes is the hybrid Laser/arc welding process (HLAW), which can complete 5G welds, assure weld soundness, material properties, and an acceptable geometric profile. The combination of new lasers and pulsed gas metal arc welding (GMAW-P) power source technologies have led to important innovations in the HLAW process that have been shown to increase the travel speed for successful root pass welding. In particular, high power Yb fiber lasers with high efficiency (25% compared with 3% for a Nd:YAG laser) allow a 10kW laser to be built the size of a refrigerator. This allows for previously unheard of portability and power levels for use outside the laboratory and on the pipeline right-of-way. The objective was to develop and apply an innovative HLAW system for mechanized welding of high strength, high integrity, pipelines and develop 5G welding procedures for X80 and X100 pipe, including mechanical testing to API 1104. The main goal of a cost-matched JIP was to develop a prototype hybrid high power Yb fiber laser and GMAW head based on a commercially available bug and band system (Figure 1). Under the DOT project, the subject of this paper, innovative technologies for pipeline girth welding were developed. External hybrid root pass welding techniques were developed for variations of laser power (4–10 kW) and root face thickness (4–8 mm) as this has the greatest potential to meet existing pipeline integrity requirements and facilitate the use of new high power Yb fiber lasers for high speed HLAW of pipe root passes. Following the integration of the Yb fiber laser and GMAW head onto a commercially available bug and band system (CRC-Evans P450) the system was used to achieve full penetration welds with a 4 mm root at a travel speed of 2.3 m/min. The root welds were made in a “double down” configuration using laser powers up to 10kW and travel speeds up to 3 m/min. The final objective of the project is to demonstrate the hybrid LBW/GMAW system under field conditions.