Sulfur Concentrations of 316L for Orbital Welding. For more critical applications using small diameter thin-wall tubing, sulfur concentrations of to wt.% sulfur are routinely and successfuly orbitally welded but may require more complex welding procedures and allowances made for higher weld bead W/D ratios. Cost considerations of achieving an excellent surface finish and optimal corrosion resistance for orbitally welded piping systems must include the cost of more complex welding procedures, including training of welding personnel, that may be needed to weld these materials. For less critical applications where weldability is of foremost consideration, a sulfur range of to wt.% may be appropriate.
On installations where there may be heats of 316 with a large range of sulfur concentrations it is essential that installers carefully track the heats of tubing, fittings, and other system components being welded and attempt to keep the sulfur contents of materials being joined as similar as is practical.
In so far as possible, it is necessary to aim for consistency of orbital welding procedures and to avoid unnecessary changes in procedures. An understanding of the effects of sulfur concentrations in stainless steel is essential for making the best choice of materials for a particular application, but be aware that sulfur is not the only element controlling the weldability of 304 and 316 materials and that the effects of other trace elements and combinations of elements may also have a significant effect. Limiting the sulfur range of 316L in order to optimize orbital fusion butt welding would eliminate some, but not all of the weldability problems associated with sulfur. Inaccuracies of the MTRs, lack of reporting of some trace elements such as aluminum, selenium, manganese, iodine, and others that may affect weldability, and the unpredictability of interactions between the various trace elements make it impossible to predict from the MTRs whether or not a particular heat of stainless steel will be weldable using conventional orbital welding techniques.
Although the incidence of problem heats is very low, at least one major end user of 316L semiconductor grade stainless steel tubing has their materials prescreened for weldability prior to purchase to assure that orbital welds on every heat they purchase will meet their stringent weld quality requirements.
Presented by Barbara K. Henon, ., Arc Machines, Inc. at the SEMI Workshop on Stainless Steel, Semicon Southwest Austin, Texas October 16, 2000.