Good luck. Downhill progression is a loser's bet. Incomplete fusion is a good bet.
You mention a gap, I take that to mean a root opening on backing if it is actually 1/4 inch.
It would be interesting to hear if anyone has passed that test.
Remember, the reason austenitic stainless is so corrosion resistant is the oxide that forms thus protecting the substrate. That same oxide layer is going to resist fusion, so make sure you wire brush before making the first pass and every pass after that.
317L; sounds like an application involving sulfuric acid.
Al