I recently provided some 11 gauge type 304 Stainless steel containment pans for an equipment manufacturer to set metal lathe and drilling equipment into. These pans have 3 1/2" sidewalls and were break formed from sheets. Corners and seams where the pans were joined were field welded with GMAW application. All welds were visually checked then pans filled with water tightness.

Now months later the manufacturer of the equipment wants a letter stating the pans are leak proof? What criteria should I include in the letter.