Seattle-based Elliott Bay Design Group has completed a weld engineering and inspection project for USNS SBX-1, a floating, self-propelled early-warning radar station designed to operate in high winds and heavy seas.
SBX-1 was developed as part of the Defense Department’s Basic Missile Defense System.
As the SBX-1 is a semi-submersible platform vessel, it was necessary to cut large access hatches in the hull columns to extract equipment being refurbished and replaced. The work required replacement and re-welding of the access cutouts in steel plating up to over 1.5 inches thick.
EBDG officials said they developed an optimized weld procedure for an uncommon grade of steel for TOTE Services LLC, meeting the challenge of a regulatory-approved weld procedure appropriate to the exotic grade of steel used for the hull of the SBX-1.
The metal is an American Bureau of Shipping (ABS) grade FH-36 low-temperature steel, suitable for arctic conditions as it retains higher impact toughness in very cold ambient temperatures when compared to more common ABS grade-A steel.
For the ABS steel on the project, the critical material property to manage was toughness, a measure of the ductility of the steel at the lower required temperatures. When steel is welded, it changes from solid to liquid and back again. The rate at which the steel transitions between phases impact resulting microstructure of the steel.
EBDG partnered with Industrial Resources Inc. (IRI) at its Sedro Woolley, Washington facility for fabrication and welding of the test assembles for the range of weld procedure configurations. EBDG then determined the widest range possible on the critical weld parameters, it said, to get the most possible flexibility in weld machine setup, which helps accommodate a range of welding techniques between different operators.
At IRI’s fabrication shop, test assemblies were welded using a matrix of preheat values and heat inputs to allowed EBDG to understand how different inputs affected the critical material property of low temperature toughness. EBDG then worked with IRI to fine tune the joint dimensions, root gap, and weld parameters to encourage high quality welds, and inspected and recorded every weld pass on each test assembly.
As final proof of the success of the procedure development, it was implemented by the shipyard with the final weld joints passing quality assurance and performance requirements, EBDG officials said.