The initial goal of this project was to identify and implement new welding technique(s) to address the rejection of large diameter, thin-walled alloy 625 pipe welds on VCS. NMC and the Integrated Project Team (IPT) discovered, however, that improving the fit up rather than the welding techniques would reduce the weld rejection rate. Specifically, the IPT identified that fabrication of these welds to the existing specifications was not conducive to obtaining acceptable welds. The project provided evidence that currently used practices and techniques, when followed meticulously, and the implementation of “better than specification” fit-up tolerances will result in acceptable welded joints.
The improved fit-up specifications identified in this project were successfully applied to SSN 778 at General Dynamics Electric Boat (GDEB). Any future cost savings achieved through application of this improved process will be monitored. These benefits will apply to other submarine classes using large diameter, thin-wall alloy 625 pipe.
GDEB used the results of this project to refine some of the methods and techniques for pipe fit-up. GDEB implemented these improved processes in July and August 2007 on re-welding of shipboard welds for SSN 778 and will also use them for initial welding applications by GDEB at both Groton and Quonset Point. The project team included shipyards GDEB and Northrop Grumman Shipbuilding-Newport News, VCS Program Office (PMS 450), NAVSEA, NMC, Navy Joining Center and Naval Surface Warfare Center Carderock Division.