Flame Bending 1/4" Plate

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I'm building a BBQ pit and just cut out the doors.  Pit is made from 24" OD 1/4" wall pipe.  I cut it slow, left the corners uncut to let the steel cool, but still got some warping.  Then welded on the perimeter flange (1" x 1/8 strip), jumping around and trying to keep the heat in the weld area as low as possible and the warping got worse still  .  How can I fix the warp in the door?  As it is now the thing isnt goint to seal worth a darn.  I have been reading about flame bending and have tried using the torch on the inside (oppostie from welds) of the door with no change...I'm at a loss...And getting a bit frustrated...
Reply:Some pictures of the problem would help. People can understand whats going on better if they have a visual reference. What process are you using to weld the fire pit?
Reply:Paging Farmersamm...Paging Farmersamm...Farmersamm Please report ASAP. Your expertise in flame straightening is needed in General Welding Qusetions stat. It's not just heating, but heating then cooling to shrink the metal back. I don't know how exactly to suggest doing it on thin steel, but I know it's used fixing sheetmetal autobody stuff some times. I've only done it with thicker sections myself. Samm's done a bunch, maybe he can make suggestions. Picts would help, so people can suggest where exactly to heat and cool...No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Heat shrinking will work if you apply force, heat it, and allow it to cool.  Force is applied in the opposite direction of the warp, and the heat is applied where the metal stretched.Sometimes this is unwieldy, and your only alternative is to weld on the opposite side of the welds that caused the problem in the first place.  Backbeading.The backbead will shrink, hopefully as much as the original weld, and pull it back straight.Pics might help, and try to use some sort of straightedge to help illustrate the problem, or show how the part now fits as opposed as to how it's supposed to fit."Any day above ground is a good day"http://www.farmersamm.com/
Reply:My that was a fast response! .No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:...."Any day above ground is a good day"http://www.farmersamm.com/
Reply:If you warped it where I think you warped it.........the door.Weld a bunch of beads on the inside of the door opposite the welds on the sealing flange.  These welds will pull it back true.  They can be ground off later, they don't need to stay.  Their only purpose is to shrink the backside of the plate.You may have to make quite a few welds, grind, and repeat, to pull it back.  Welcome to the wonderful world of heat distortionThe pic shows probably what happened with the original welds, it probably bowed it up in the direction of the arrows.  Heat on the opposite side, accompanied by shrinkage will pull it back.  Applying water to the hot backbeads can increase the shrinkage.  It can be a slow go, but don't get encouraged.  You'll see the progress almost immediately, but it may take a few passes to get thereAnd if you have some laying around..........use 6013 for the backbeads, easier to grind off Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Here are some pics of the offending door.  If I do try to flame straighten, how much heat and how fast should i move along the heat trianlges?
Reply:Should those backbeads run from top of door to bottom (verticle) behind the flange welds or run from one side of the door to the other (horizontal) making a series of passes from the bottom of the door to the top?
Reply:If you used a rosebud, you'd have to do small spots.  And just keep working the spots until you got to where you wanted to be.  The problem is applying the force to bend it back. Awkward on the doorI feel your first error was the continuous bead on the flange.  You should have done some stitch welds.  One inch welds around 3-8" apart.  The continuous weld warped it due to the huge amount of force when it was cooling.At this point, I 'd try an identical bead on the inside of the door.  Any force you can apply from the outside of the circumfrence towards the inside (opposite the bow) would help.  Would be like pressing the door closed.A chain binder with chain wrapped around the door, and a set of blocks on the inside of the circle would do the trick.  It would try to fold it back to where it was.I'm afraid you'll have to remove the door to do this, but the alternative is a door that doesn't fit.I think flame shrinking is out at this point, it's too cumbersome, and the area too large.  You'd have to heat small spots, and hope you can keep the radius as each spot shrunkAfter you pull the door, if you choose to pull it, start the backbead at the point where the mismatch has occured.  You don't have to backbead towards the top of the grill if it fits ok.You could try a bead with the door still on, and see if it works, but I'm afraid it won't shrink enough without some force being applied.  But it might be an alternative to grinding the hinges off.  And it wouldn't hurt anything, just have to grind it off if it doesn't work. Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by TXTimberMulcherShould those backbeads run from top of door to bottom (verticle) behind the flange welds or run from one side of the door to the other (horizontal) making a series of passes from the bottom of the door to the top?
Reply:Hey, I just noticed, you didn't finish weld the hinges, they're just clamped to check fitYou're golden!!!!"Any day above ground is a good day"http://www.farmersamm.com/
Reply:mark the spot where the misfit starts, and start your bead there and continue it along the part that's sticking out, the other part of the door looks ok higher up"Any day above ground is a good day"http://www.farmersamm.com/
Reply:I'd start with the bottom side first because it's the longest stretch, and may have really been the cause of the greatest part of the problem.  Then do the radius on the sides.Starting with the radius on the sides might be ok too, if it doesn't pull it back, then you know the bottom has to be shrunk also.You actually have two areas of distortion.........sides, and bottom"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Yeah, I already cut the door off in anticipation of the pain that this fix was going to be.  The flange was stitched on, like small sections of connecting spot welds.  I liken it to spotting in a patch in sheet metal with MIG.  I used to just stich like you said, but some customers want a continuous bead.  What can I do to prevent this from happening when weld the flanges on the firebox door (the other door on the pit)?  The only thing I can think of is to remove the door and pre-load it with the blocks and chain like you suggested to fix the problem I have now.  It just seems that there are a lot of guys that make pits, weld the flanges all the way around and I am sure they dont go to all this trouble...Thanks a ton for all of the help.  I will take some pictures of the circus that is about to insue in the garage and let you know how this repair works out.
Reply:I would imagine a preload would be your only alternative if they want a continuous bead.At least you have some idea now just how far to preload it by seeing how much it pulled without the preload.  It's tricky  when you start preloading.  Trying to figure out just how much springback you'll have is a PITAGood luck, I hope you can maybe use something from what I've suggested."Any day above ground is a good day"http://www.farmersamm.com/
Reply:also, if you don't have a ratcheting binder, or the angle is wrongwrap a chain around both ends, put a long piece of heavy wall square tubing under the chain, and use a jack to pull the chain tight and bend the plate to put some stress on it.  you'll need a jack at either end"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Put enough stress on it to load it, but don't try to bend it back to it's original shape, because when you backbead it it could bend further back the other way Just enough to feel some pull, then weld.Believe, I've been there done that  Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:bring over to Sam- he'll talk it back to shapeEd Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:Originally Posted by Broccoli1bring over to Sam- he'll talk it back to shape
Reply:Loading and backbeading worked great.  I returned it about 80% of the way or so.  I didn't want to over do it.  I too have been down that road and it sure makes for a long night with lots of stomping and cussing.   Had to run three passes on the bad side and just one on the other.  I did notice that putting water on the bead to rapidly cool off helped move more per pass.  I did one side at a time...just had one come-a-long.  I am sure doing both at the same time would be better but all my big ratchet binders are on a jobsite...figures.  Thanks again...you saved me tons of time.  I am going to keep researching to see what some of the other pit builders do to fight this and will add info to this post as i come across it.
Reply:..... Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:No after pics?Maybe on the next one you could try cutting the door smaller than the opening  and  welding the flange to it on the inside.  Then weld the flange on the outside.  Maybe you'd get lucky and it would even out.  No extra grinding.My name's not Jim....
Reply:When you think about it that pipe, most all pipes, started life as a sheet and were rolled into the shape they are now. The entire interior is under some serious compression. I've cut short sections and had them -bink- pop open as much as 1/8th for a lil two inch pipe. Cut windows in rolled tanks and had the opening bell out a tiny bit in the middle area of the opening. Some real stresses built in there. With that in mind it seems as tho just about anything you do to to it once it's cut or do with any section cut out of it it is going to want to open up. Especially if it involves heat. These sections cut out of a pipe aren't going act or react the same as some straight section that has been bent either by force or heat.The back beading you did was probably only one of the two ways to really straighten it. Heating to the soft stage and using force would be the other. The flame bending/straightening that we normally use at other times I don't think would get the results we are used to seeing. I do recall some saying they built a bonfire and threw their pipe in the fire to  get most of the stresses out of the way before starting all the cutting and welding. Sounds logical. Don't know if it works or not."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:I'll get some pics in here as soon as I get the flanges fit nicely.  They are a bit beat up from me trying to compensate prior to backbeading.Sandy, those are really good points.  I did notice that on this particular piece of pipe, as soon as the corners were cut they popped out at least 3/16".  That had never happened before and the scenerio that you described is exactly what I was thinking.  The plate was rolled, the seam welded under stress, and that tension is still present in the pipe. The idea of building a fire in or around the pipe prior to doing any cutting is a good idea that I think would help.  It's just a little tough to do unless you have the place to do it.  I was wondering if I could achieve the same effect with the rosebud, just moving quickly.  Seems like it would use a ton of fuel and I would worry about hot spots that I might create and possibly making a bad situation even worse.I guess I could build so that the doors get cut later, after the firebox and all caps are welded on, then build a fire in the pit like you normally would, get it super hot, let cool fully and then cut doors...maybe i'll try that...Last edited by TXTimberMulcher; 02-25-2010 at 01:02 PM.May I get to Heaven fifteen minutes before the Devil hears I'm dead!Originally Posted by TXTimberMulcher..................................................  ..............................The idea of building a fire in or around the pipe prior to doing any cutting is a good idea that I think would help.  It's just a little tough to do unless you have the place to do it.  I was wondering if I could achieve the same effect with the rosebud, just moving quickly.  Seems like it would use a ton of fuel and I would worry about hot spots that I might create and possibly making a bad situation even worse.I guess I could build so that the doors get cut later, after the firebox and all caps are welded on, then build a fire in the pit like you normally would, get it super hot, let cool fully and then cut doors...maybe i'll try that...
Reply:Sandy, I'm not sure what the temp is, and the time required for stress relief.I do know that stress relieving small parts requires an oven which is capable of holding a very high temp for extended soak times.  And I believe there's a graduated cool down period depending on the material.Where I shy away from trying stress relief just with a torch is the question of annealing.  Am I actually anealing the material, and making it softer.  Or does it matter with a-36.The heat issues are fascintating, and many of them are beyond my expertise.From what I understand, heating reorients the granular structure of the metal, along with the way it's cooled.  I think work hardening during machining is an example of this, not sure.It's complicated stuff, and I try not to go beyond my boundaries, there's a lot I don't know"Any day above ground is a good day"http://www.farmersamm.com/