Tack stainless without purge

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I dd some tacks on my stainless exhaust without running a back purge. There is some sugaring. I wonder if this will be fine as long as I purge my full pass? I am not sure and it would be a huge pain to have to rip it all apart.
Reply:You need to back purge your tacks and root pass on stainless pipe/tube. Your tacks are part of the root pass. The sugaring presents defects/porosity in your weld.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Originally Posted by vortspI dd some tacks on my stainless exhaust without running a back purge. There is some sugaring. I wonder if this will be fine as long as I purge my full pass? I am not sure and it would be a huge pain to have to rip it all apart.
Reply:are you trying to run the tacks into the root or are you trying to bridge tack it? Pretty common to put bridge tacks on alloy pipe, but you have to make sure you're not melting the ID edges, tack to the outer edges of the bevels . Plus you have to grind them all the way out when you come up to them. you can melt that sugar when you put the root in, but you have to grind it thin and hang on it for a while, depending how bad it is.Not sure how much difference a little sugar really makes on an exhaust manifold, though.
Reply:The "sugar" shows that you burned it without a shield and got oxidation, which changed the structure of the metal itself. It will rust in short order when you start to use it and is not nearly as strong as a shielded weld would have been...Like dave p. said, it depends on what you're planning to do with the part...
Reply:I spent the day pulling things apart, and where the tacks were small checking with a mirror. As it turns out there were no "sugared" pieces of metal as the tacks were not fully penetrating. There is a minor amount of heat affect inside the pipe but no sugared pieces. I did not re-tack any of the pieces that looked OK. I pulled apart all suspect pieces, but then found they looked OK. I then remade some pieces and purge tacked. I must have used at least half my gas bottle today with the back purge. I put in another 10 hours today, after the 10 I spent yesterday on the headers.Putting a set of headers together should be fun, but this has taken away some of the welding joy! I have spent a couple of months on this exhaust system. It is finally tacked together, but I am not sure when I will do the root pass. I am a bit concerned I will bugger it up. It is intended to go on car I am restoring which will be a regular street driven "show car". I am considering purchasing a weld positioner for the root pass. I have a rotary table but cannot turn it quick enough whilst holding wire and welding! I did however make a decent jig for it.Anymore more thoughts? I am hoping my root pass will blow away any hidden sugar in between the weld seams.. I have a bore-scope on the way so I will be able to check.
Reply:If the inside of your pipe/tube does not need to be sanitary clean, I'd use SolarB weld flux to achieve a back purge without having to use a bunch of argon,JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Originally Posted by vortsp I must have used at least half my gas bottle today with the back purge. I put in another 10 hours today, after the 10 I spent yesterday on the headers.Putting a set of headers together should be fun, but this has taken away some of the welding joy! I have spent a couple of months on this exhaust system. It is finally tacked together, but I am not sure when I will do the root pass. I am a bit concerned I will bugger it up. It is intended to go on car I am restoring which will be a regular street driven "show car". I am considering purchasing a weld positioner for the root pass. I have a rotary table but cannot turn it quick enough whilst holding wire and welding! I did however make a decent jig for it.
Reply:Originally Posted by DSWI've seen guys do very basic tacks to line everything up, then mark all the joints and label them, then pull it all apart and weld up each section 100% lining up each piece as they go with the marks they made.
Reply:If you look inside a set of stainless headers You will most likely see a nightmare of bleed Through and "sugaring"  probably wrong But the sugaring issue is really a problem With dairy or food product stainless welding Not do much because it I'd a bad weld but Because it creates pockets for food to get caught in and make decay and unsanitary Areas....... An exhaust system....... I wouldn't lose sleep on that one......  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:Are you talking about welding exhaust manifolds made of schedule pipe, or exhaust systems made of thin wall tube?  I'm assuming manifolds made of schedule pipe, based on your discussion of root passes...   If schedule, are you using 10 or 40?
Reply:Thanks B_C. I am just a bit worried about corrosion. That said, I am probably concerned over nothing significant. I certainly won't be eating out of the pipes Mr. Moose: I am not up on the terms for pipe. The system is just standard Columbia River 304 stainless mandrel bends in 16 gauge. I have tacked the bends in place and I will do a final weld. People have called this the root pass. Again I am not up on the terminology.
Reply:You might find this read helpful, given what you're doing:http://weldingweb.com/vbb/showthread.php?t=116181A root pass is typically the term used to describe the first pass of two or more in a beveled schedule pipe weld.  The material in that process is substantially thicker than you are using, which is why more than one pass is used.  For your application, a butt joint with no bevel (as discussed at length in the thread I linked) is what you'd be more likely to be doing, and the process is discussed at length there...
Reply:I have a friend that makes Stainless Porsche exhaust systems (High dollar)  and he purges everything........But like I mentioned unless the weld fails what more do you what the headers to do?     Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:I thought one was not to remove the filler rod from the shielding gas coverage to prevent oxidation?
Reply:Mr Moose: I have read that thread 100x. It is a brilliant thread. I erred in judgement on my surface tacks and it was clearly a mistake. Now I will spend the week building a tool to sand the ID of the pipe. For the record, I always snip my stainless rod after it exits the gas. B_C: I want them to last. Things rust far too quickly here.
Reply:Hmmmmmmmm that's pretty fast if you need to make them out material that's twice the price........  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:ideally you should have no sugaring at all before a turbo, like say inside a turbo header... a few spots from tacks after a turbo really isn't so much to worry about, just purge it to weld it out and it'll be fine, the welds will almost consume the sugared tacks and the few spots won't compromise the integrity of the exhaust at all reallymiller 330a bp TIGmiller dynasty 200DX TIGmillermatic 185 MIGthermal dynamics cutmaster 101 plasma cuttersnap-on YA5550 plasma cutterhypertherm powermax 30 plasma cutterbaileigh CS225 cold sawetc....
Reply:Originally Posted by vortspMr Moose: I have read that thread 100x. It is a brilliant thread. I erred in judgement on my surface tacks and it was clearly a mistake. Now I will spend the week building a tool to sand the ID of the pipe.  .
Reply:If you have a sufficient back purge and make sure you get good penetration over your tacks you should be fine. Also are you using rod? I weld food grade stainless pipe and on .065 it's all a fusion weld. But it just being exhaust a little contamination in the final weld won't hurt anything. Post some pics when you finish!