stainless tig questions

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I managed to scrounge up some stainless pipe and plate but the type is an unknown. I cleaned the pipe inside and out as well as the plate with new flap wheels.I welded the plate in the pipe so as to cap one end but the weld doesn't look right. Its black and looks kinda like a ER70S weld does. For filler I used 309 rod cause thats all I had.I know 309 is for mating mild steel to stainless and I know I should have just fused the 2 pieces together but I vee'd the pipe and plate for 100% penetration and fusing it wouldn't have filled the vee in.I know its not the machine settings because I did a fusion weld as a root and then capped it with the 309. The root was nice and shiny and had the cool colors like a nice stainless weld should but the 309 cap is black.Question1Is there a way to tell what type of stainless it is without it being marked on it so I can buy the proper rod?Question2Is there a general rod to use when you have unknown stainless or a combination of unknown stainless?Question3 what type of stainless holds up best to extreme heat (2200 degrees) and corrosive environments (salt)?
Reply:Originally Posted by teknitionI managed to scrounge up some stainless pipe and plate but the type is an unknown. I cleaned the pipe inside and out as well as the plate with new flap wheels.I welded the plate in the pipe so as to cap one end but the weld doesn't look right. Its black and looks kinda like a ER70S weld does. For filler I used 309 rod cause thats all I had.I know 309 is for mating mild steel to stainless and I know I should have just fused the 2 pieces together but I vee'd the pipe and plate for 100% penetration and fusing it wouldn't have filled the vee in.I know its not the machine settings because I did a fusion weld as a root and then capped it with the 309. The root was nice and shiny and had the cool colors like a nice stainless weld should but the 309 cap is black.Question1Is there a way to tell what type of stainless it is without it being marked on it so I can buy the proper rod?Question2Is there a general rod to use when you have unknown stainless or a combination of unknown stainless?Question3 what type of stainless holds up best to extreme heat (2200 degrees) and corrosive environments (salt)?
Reply:Thanks for the post Paul, every bit of info I can get is helpful  So, if 309 is the proper choice, is it normal for a stainless to stainless 309 weld to not look bright and shiny like a stainless fusion weld?
Reply:When I get the argon flow just right, and my speed is right, I get these beautiful rainbow colored welds, or welds that look almost golden. Most of my stainless welds come out a little blackish, due to carbuerizing.Either too slow a weld, too hot, not perfect gas coverage, etc. The good news, in destructive testing, the welds were very strong, and performed well. And, as a bonus, when you buff it out, they look good. So, I am happy enough.
Reply:Hi, I can't help with questions 1 or 2, but can give an opinion for 3. Austenetic stainless steels are the most suitable for high temps. Being in New Zealand my reference books list temps in Celcius not Farenheit, so you'll have to convert. Maximum service temperature for 310 is 1100 degrees C. Max service temp for 302, 303, 304, 304L, 316, 316L, 317, 317L and 321 is 800 degrees C. 310 is suitable for furnace parts, heat exchangers, etc, but I don't know how or if it will handle salt. 316 will handle the salt but not as much heat.As for black welds, I'd be looking at too much heat, not enough sheilding gas, or maybe you are pulling your fillerwire out of the gas envelope and oxidising the end of it and then adding this to the weld pool. Hope some of this helps.
Reply:Thank you Kelzweld and Paul for the posts.I haven't had time to persue this any further because we are extremely busy at work. When things slow down a bit I will be looking for some more stainless pipe to make my project out of. Im a bit concerned with the welds and type of stainless I have now and the ldea of 2000 degree salt all over the garage floor if this fails doesn't impress me.I will most likely end up buying new pipe so I know what type of stainless I have and will get the proper filler for it.
Reply:Originally Posted by teknitionThank you Kelzweld and Paul for the posts. Im a bit concerned with the welds and type of stainless I have now and the ldea of 2000 degree salt all over the garage floor if this fails doesn't impress me.
Reply:Originally Posted by CaptainfabIf I may ask...what the heck are you building?
Reply:Thanks for the reply Teknition. That's some interesting stuff
Reply:Yuk the dreaded black stuff this is normally caused by dirt gas travel speed and inherent temp try putting a good root in first and let it cool down before the rest of the welding this way you wont have to change any settings as this is normally caused by carbon burning off on the hot weld material as there is no shield gas as you have allready left this area with your torch before it has coold enuough to stop oxygen burning off on the hot metal