TIG stainless tubing to heavy gauge

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Hello, I am a new guy to this forum and have a couple questions for anyone that wished to comment.  I am mostly concerned with welding stainless exhaust tubing (light gauge, maybe 16ga) to a heavier 3/8" flange. I am having a hard time getting enough heat in the heavier flange without over-heating the tubing. When I reduce the heat setting and/or back off the foot pedal, it seems like I am not getting any penetration on the flange where the weld just lays on top. I guess I could have picked an easier project to start with...Should I be using a particular type of motion or pattern?  Should I be trying to focus the heat on the flange and then draw it to the tubing?  Any comments would be appreciated.  Thanks.
Reply:i've been thinking about this for about a week now. I don't have an answer for you but my gut feeling is what you said, focus heat on the flange and draw the heat into the tube then dip your filler. kind of this motion:flange/tubeEEEELike I said though, I honestly don't know, it's just a guess. I'm interested in what others have to say
Reply:Set your heat for about the thickness of the flange. Once you get a puddle going keep the heat on the flange and kinda roll it up to the tubing. Kinda hard to explain. Also you said you are doing stainless tubing, are you back purging it also?ShaneYa gotta spend money to make money!
Reply:Thanks for the replies.  I am not purging the tubing with Argon and don't really have the set up for it.  I know that is the correct procedure, but I have simply set that aside as not an option for this project.  It is work I am doing for my own car on used parts I acquired fairly cheap.  The flanges are new but the headers were from another type of engine that will fit my chassis.  I had removed the old flanges and were welding the new ones on.  I have already welded the pipes to the flanges on the back side (cylinder head side) where I pulled them through but I would like to do the outside now and have them look nice.  The inside job was not pretty at all but I was basically welding inside a hole that is only 1.875 in diameter.
Reply:i lot of guys like solar flux when purging isn't an option. i've never used either though. i've never welded stainless!
Reply:I am not sure that it matters, but I also took them to my machinist to have a look as well and he said he thinks the tubing is Inconel and "good luck" was what he added.  He is the best guy I know and I would like to have him do the welding, but he is also extremely busy!  They are very lightweight and don't have the same appearance as other stainless pipes I have come across, so I don't know.  Maybe they are an even lighter gauge than I thought... But I will say the tubing is very stiff and "hard".Last edited by melsie68; 11-24-2010 at 11:26 AM.
Reply:where did you get the header? I feel like you would know if it was inconel or not. inconel headers don't grow on trees like stainless headers.
Reply:I had been dealing with some guys over the past 6-7 years that buy used Nascar parts in bulk from teams when they recycle.  Typically what you get is some really top notch gear that has approximatley 85% of its life left in it.  I cannot claim for sure these pipes are inconel, but I know some of the teams were using it in recent years.  It has a lower coefficient of thermal conductivity than 304 or 321 stainless therefore it has the potential to produce more power.  What that means is, if the heat is not going through the wall of the pipes as quickly; it is going to find the nearest way out which is out the exhaust exit.  The faster the exhaust gases are removed or scavenged, the more power you can produce.  When I purchased the headers, they were not specified as inconel so I didn't give it any thought until my machinist mentioned it.  He is a very sharp guy and is truly up to speed on the latest materials being used out there so I have to consider what he says.  What I have welded so far didn't appear to be very strange, but I wouldn't know the difference anyway!
Reply:wash it from the flange to the pipe keep filler wire close  to cood puddleidealarc 250/250 ac-dc tigidealarc 250/250 ac-dc tig #2 used for sticklincoln sp100hh125dual arbor grinder polisher30 yrs of hand tools52 pitch blocks 6p-26prake gauge -pitch gaugeG&D prop repair 918-207-6938Hulbert,okla 74441
Reply:I thought I read in the Lincoln catalog that they had a rod for inconel to steel ?I also remember that Brownells sells a high nickel rod for welding gun parts.( appairently it re-blues nicely and doesn't show the transition)Maybe you could try to preheat the flange up to about 300 f with propane and then when you weld try to put the torch electrode about 75 degrees - so as to be all most pertindicular to the thick flange- then when you get a puddle started make a periodic excursion uphill onto the thin sidewall but spend more time on the flange and less on the thin tube.  That would be my approach if I were stick welding it ........it should work for Tig too I would think.    But..... I have never welded Inconel either !!!!!!!!T
Reply:[QUOTE=mels.  It has a lower coefficient of thermal conductivity than 304 or 321 stainless therefore it has the potential to produce more power.  What that means is, if the heat is not going through the wall of the pipes as quickly; it is going to find the nearest way out which is out the exhaust exit.  The faster the exhaust gases are removed or scavenged, the more power you can produce.  i think the thermal conductivity issue has to do with keeping the exhaust hot while in the pipes which in turn keeps the density  of the gas low and improves flow and therefore hp as well..as the gas cools it gets denser and impedes flow..there are insulating wraps made for exhausts to accomplish this..
Reply:Does it seem like the flange is the same material as the tubing, or are they dissimilar?Point your electrode into the thicker piece to direct more arc heat to the thicker piece.  Also, you can hold the electrode "offset" over closer to the thicker piece than the thin one to also direct more heat onto the thicker piece.  With these torch manipulation techniques, you should be able to control the heat so you get a puddle of about equal sizes on both sides at the same time.FYI, I believe the main benefit of Inconel such as is found on on formula 1 exhausts, gas turbine engines, etc is to have higher strength at elevated temperatures than stainless steels would provide.  http://www.burnsstainless.com/Inconel.aspxAlso, could it be possible that the tubing is titanium, or perhaps just some other "high grade" form of stainless that your machinist hasn't encountered much?  I can tell you that 316 stainless is a *lot* harder to cut/machine than 304 is, and both of those are significantly harder to cut/machine than 409 is.You might consider "helibrazing" the tubing to flanges on the outside using a filler rod such as silicon bronze.  The braize will give a yellowish appearance, and won't distort the flange anywhere near as much as welding on it would.
Reply:I got to it and it wasn't as troublesome as I thought it would be.  The tubing did have a different appearance than the flange itself which is why my machinist mentioned it may be inconel.  They are welded all the way around with no problems.  There was about a half inch on a couple tubes which I could not get to with my torch.  I brought them over to my machinist who has a nice assortment of small cups and short length caps that make the torch much smaller.  We were able to get in there with some of his gear.  All and all, they were the cheapest headers I have ever bought for the car and of the highest quality by far.  Thank you everyone for your suggestions and advice.
Reply:Originally Posted by jakeruDoes it seem like the flange is the same material as the tubing, or are they dissimilar?Also, could it be possible that the tubing is titanium, or perhaps just some other "high grade" form of stainless that your machinist hasn't encountered much?  I can tell you that 316 stainless is a *lot* harder to cut/machine than 304 is, and both of those are significantly harder to cut/machine than 409 is.You might consider "helibrazing" the tubing to flanges on the outside using a filler rod such as silicon bronze.  The braize will give a yellowish appearance, and won't distort the flange anywhere near as much as welding on it would.