Introduction: Shipyards have traditionally used submerged arc welding (SAW), flux cored arc welding (FCAW) and gas metal arc welding (GMAW) to fabricate butt joints on thick steel plate. When joining plates of ½” or greater, a bevel, along with multiple weld passes are routinely required. Two-sided welding with back gouging and grinding prior to welding the second side is also frequently implemented. Thick-section, single-pass welding is possible using a hybrid laser arc welding (HLAW) process, but this technology requires expensive equipment and stringent fit-up quality that can be difficult or costly to achieve in a shipyard environment. Buried arc GMAW (GMAW-B) is a GMAW process variant that provides the ability to weld thick plate (1/2”) in one pass using copper or ceramic backing.
Work has been completed in a previous NSRP project to develop GMAW-B procedures and benchmark the process against existing welding operations currently used in naval shipyards. The work discussed in this presentation pertains to the development of mechanized procedures and the implementation of GMAW-B technology.
Experimental Approach: GMAW-B is being evaluated for improved productivity and quality with a focus on implementable solutions for a shipyard environment. To achieve a significant increase in productivity, the system must be both portable and mechanized. The GMAW-B equipment was set up on a designated tractor-based system and steady state and start/stop procedures are being developed. With satisfactory procedures developed, nondestructive evaluation (NDE) along with mechanical testing will be performed to qualify the developed procedures.
With steady-state and start/stop parameters developed and procedures qualified, the project work will be completed with a demonstration and implementation in the shipyard.
Results and Discussion: Previous project work has found that GMAW-B provides significant productivity and process improvements over legacy SAW procedures currently in being used. On 3/8” mild steel plate, GMAW-B procedures resulted in an 11% reduction in arc-on-time and a 14% reduction in total heat input. When welding on ½” steel plate, the resulting benefits of the process improved with a 31% decrease in arc-on-time and a 49% decrease in total heat input. The reduction in arc-on time results in a significant improvement in productivity while the decrease in total heat input assists in reducing distortion and degradation in base material properties.
The current project using GMAW-B will integrate the process with a portable tractor-based system to further improve on the productivity and quality increases that have already been established.
Conclusions: Previous project work has established the ability for GMAW-B to improve efficiency and reduce total heat input without sacrificing weldment quality. Work on the current project is ongoing and conclusions based on this work will be included in the final presentation.
Acknowledgements: This work was funded by the NSRP and completed in cooperation with Vigor Shipbuilding, NNS, NSWCCD, VT Halter and OTC.