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Up until now i've been welding non-sanitary/critical parts that won't come into contact with beer/wort etc. But still always in SS - mostly 316.
Now I want to be able to confidently weld sanitary parts (always in 316) for beer/wort transfer and other food grade applications. The problem I'm having is with the backpurge.
My pipe/tube and RJT fittings are 1.6mm wall, with 1" pipe. 1.6mm 2% lanthanated tungsten is ground to a point with just under 1/4" stick out with number 8 cup, gas flow to torch is 15L/m, and running from 30-45 amps depending on the ease of weld - travel speed. Most welds seem to be fine with good penetration.
When backpurging though, I still tend to get huge discolouration on the backside of the weld - inside the pipe/tube - and with limited penetration. I've played around with pulsing at 1 pulse a second, 25-45% down, but again with no success, so have left that well alone. The backpurge i've tried at 4 right up to 20 L/m, but nowhere seems to work. At the higher end of the scale the gas pressure seems to blow holes in the weld and shoot the arc off all over the place (usually when nearing the end of the weld) and still discolours the inside of the pipe/fitting, at the lower end of the scale I still get discolouration. Nothing I seem to do works. Even parts of the weld that does penetrate, finishes with colours typical of an external weld - blues and golds - Most frustrating.
Needless to say, the argon flow from my gas is sealed to one side of the tube/pipe with no holes, and the other end is also sealed with tape, but with half a dozen tungsten holes in for the gas to escape.
I'm not using filler wire for these welds, although I do have plenty of 316 filler available in various sizes of diameter.
I''ve attached 2 shameful pictures of one of the messed up parts I welded today. Granted, I could get in and grind away aforementioned discolouration, but most of the other parts I'll weld will be obscured for this - Hence the reason I started with this weld first. I want to be confident that the welds are successful.
As with the nature of the welds, I'm guessing penetration here is vital, so what can I do to improve this and avoid further discolouration?
I'd be grateful for any help/suggestions on this. I have plenty of 'scrap' 1" pipe to practice with left over from the old brewery.
Apologies for the quality of photos, lighting along with a royally buggered phone hinders my photography skills.
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