This WPS covers GTAW groove welds on 1/2" 316L stainless steel in the 2G (horizontal) position per AWS D1.6. The procedure specifies ER316L filler, 100% argon torch and back purge, and strict interpass temperature control. The back purge is essential — without it, the root side oxidizes (turns blue/purple) and loses corrosion resistance. IronKit generated this for a pharmaceutical equipment fabricator whose FDA-regulated clients require documented purge gas flow rates and oxygen limits. The WPS includes the purge oxygen threshold (50 ppm) that most generic WPS templates miss — a detail that has caused field rework when inspectors catch the omission.
Frequently Asked Questions
Why is back purge required for stainless groove welds?
The root side of the weld is exposed to atmosphere during welding. Without an inert gas purge, the hot stainless steel oxidizes heavily — producing a dark blue/black discoloration called "sugaring." This oxide layer has no corrosion resistance and must be removed. Back purging with argon prevents oxide formation and preserves the corrosion-resistant surface.
What is the 50 ppm oxygen limit?
Before starting the root pass, the oxygen level inside the purge zone must be verified below 50 ppm using an oxygen analyzer. Above this level, oxide formation is visible on 300-series stainless and the root will not meet inspection requirements. Some specs (pharmaceutical, semiconductor) require < 20 ppm.
Why is 316L interpass limited to 300°F vs. 350°F for 304L?
316L contains molybdenum, which shifts the sensitization range. The tighter 300°F interpass limit provides additional margin to prevent chromium carbide precipitation. Some specs for 316L go as low as 250°F interpass.
Does IronKit specify purge gas requirements?
Yes. IronKit includes torch gas, back purge gas, flow rates, and the oxygen limit in the shielding gas section. It also notes whether a trailing shield is required based on the joint type and base metal.