Beyond specifying that recognized welding procedures be followed, you might consider "over alloying" to ensure that the weld metal and heat affected zones have/maintain the same/similar corrosion resistance as the 316L base metal. When 316L stainless steel is welded, there is a tendency for molybdenum (Mo) to be lost during welding. Since molybdenum content is the main difference between 304L (no molybdenum, less corrosion resistant) and 316L (2-3% molybdenum, more corrosion resistant), any loss of molybdenum will lead to a corrosion characteristic in the weld zone that tends toward 304L. So "over alloying" with a weld wire like 317/317L, that contains 3-4% molybdenum, will ensure that the final weldment has molybdenum content equal to or greater than 316/316L and give the corrosion resistance at least as good as the 316L base metal.
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