" Why Oh Why"...
I hear you Buddy!
I could sit for the next hour and list very good reasons why not to allow SS to sugar, all based not only on previous experience but technical research as well.
I'm writing a specification to require back purging, even on miscellaneous, non crucial sheet metal welds where purging is going to be impractical and even problematic, because that's the right way to do it.
I'm just trying to cover my bases before hand because inevitably, some hard headed person with well meaning cost reduction ideas in mind will challenge me on this.
That's OK, I'm used to it, but the fact is that I've never actually tried to pickle off sugar before and I don't have the materials in hand yet to run a test, so I'm checking to see if someone on here has.
I've also never coated SS before, so I'm wondering if that will make a difference.
( The primer coat is "E" coat in a dip tank that does a very good job of getting in all the nooks and crannies that are hard to access otherwise.)
Have you ever seen a weld that was done all wrong, but lo and behold, it works anyway?
I understand that an unpurged root will be rough, irregular and full of stress risers, even under the oxide.
In a case where this doesn't matter because the weld will not be stressed or fatigued, and the surface will be sealed from the elements by an instrusive and resilient paint coat, and if any brittle oxide that may cause a coating failure has been removed before coating, is it still worth the money to back purge?
Tim