You need to review the requirements of the contract to see what fabrication standard, i.e., NAVSEA TP278, etc. is specified. If this was for the Navy, NAVSEA TP278 would direct you to 1688 for the recommended filler metal. Pay close attention to NAVSEA TP 248 if this is for the Navy.
In short, more information is required before any recommendations can be offered.
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