Thermal Tensioning of Thin Steel Ship Panel Structures

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Thermal Tensioning of Thin Steel Ship Panel Structures

Project Participants: Northrop Grumman Shipbuilding

Project Start: June 2005

Several current U.S. Navy construction programs are experiencing high rates of distortion and buckling on thin steel structures. The standard shipyard practice of fabricating stiffened steel panels by arc welding causes heat-induced buckling and angular distortion. Correcting the distortion is a necessary but time-consuming operation that adds no value and ultimately tends to degrade the quality of the ship structure. Estimates of ship production costs for flame straightening, repainting, re-insulating and other rework associated with correcting distortion can exceed millions of dollar per vessel.

Northrop Grumman Ship Systems teamed with Edison Welding Institute, Battelle Memorial Institute and the University of New Orleans to develop Transient Thermal Tensioning (TTT) procedures to significantly reduce the distortions that develop during construction of the lightweight ship panels.

Thermal tensioning involves the application of a second heat source parallel to, but some distance away from, the welding torch during fabrication. This secondary heat source varies the thermal distribution around the weld joint, which alters the magnitude and distribution of the residual stress developed during welding. The positioning and amount of heating can be determined by numerical analysis of the ship panel using modeling techniques.

This two-phase, two-year project began by reviewing the results from previous experiments using transient thermal tensioning (TTT) technology and determining the best panel construction to begin testing. In the second phase, the team validated the results from Phase I and installed and tested prototype equipment on the NGSS panel line. The team also addressed more complex panel geometries. Numerical models were developed for complex panels including multiple inserts, transition thicknesses and penetrations.

Project Related Reports & Documents

Distortion Mitigation Technique for Lightweight Ship Structure Fabrication
“Originally presented at SMTC&E 2006, Ft. Lauderdale, October 2006. Reprinted with the permission of the Society of Naval Architects and Maritime Engineers (SNAME). Material originally appearing in SNAME publications cannot be reprinted without written permission from the Society, 601 Pavonia Ave., Jersey City, NJ 07306”

Numerical Prediction of Buckling in Ship Panel Structures
“Originally presented at SMTC&E 2006, Ft. Lauderdale, October 2006. Reprinted with the permission of the Society of Naval Architects and Maritime Engineers (SNAME). Material originally appearing in SNAME publications cannot be reprinted without written permission from the Society, 601 Pavonia Ave., Jersey City, NJ 07306”