Welding Flanges onto Pipe and Bolting - Warping Issues?

[sudnak]

Hi All,

I am an artist/fabricator out of California. I am making a 9 meter tall rideable chaotic pendulum, and have some questions about flanges. Essentially, the pendulum will be held up by a tripod of 16 cm steel pipe. These legs will be around 9 meters in length, but will break apart into 4.5 meter sections. What I plan to do is weld a 0.6 meter circular flange onto the cut end of the pipe, and brace the flange with (8) 90 degree pieces of plate. This circular flange will line up with another flange attached to the next pipe, and bolt together with 8 structural bolts. Here is an image to help visualize: http://imgur.com/D7plgPD (I know its not perfect perspective, please forgive).

I plan on pre-drilling the flanges and bolting them together before welding, so I can get them lined up. The pipe, flange, and plate are 0.635 cm steel, and I am using a Miller MIG machine to put it all together. What I worry about is that when I weld it all on, the plate will warp. The bolts will then get pinched in and not come out, or if they do come out, will not be able to get back in. Has anyone had any experience welding around bolted materials?

Thanks!
Nathan
PS, for anyone interested here are some images of what the finished piece will look like: http://www.nathankandus.com/Chaotic_Affair2.html

 

[Welderpaul]

I would be using much thicker flanges than 1/4".
Can you not just buy standard pipe flanges which come ready-drilled - save a lot of messing about.

 

[sudnak]

I wish I could, but I can't find anything. Know anywhere to look? You would go thicker with the flange, even with the 8 supports?

 

[mike 109444]

I would go for the pre-made. It seams that any tv show from the states that involves a chase through a basement in a large building seams to go past miles of that sort of pipe. Used for steam. Take care that the pipe with flanges has not been carrying nasty chemicals. Doing it that way will save you heaps of work and would have professional welds (no reflection on your welding intended).

 

[Rrunnach]

When welding flange to pipe, 4 hole square then tack & weld all round, easier than bolting, then welding one to other............

 

[sudnak]

I wish I could just weld it together, but it needs to be able to come apart again. I don't think premade is an option, I cannot find anything out there. Does anyone have any intuition on whether the metal would warp too much, and how to minimize that warping? I imagine doing many small welds alternating sides would help...

 

[scotty41]

If your pipe is cut square you half way there, do what Rrunnach said, i would drill the 2 flanges that meet in one hit, keep them bolted together when welding. lay you 9m length out and get it perfectly level with packers so when you cut it you can lay the 2 halfs down and they are perfectly straight, you can judge when tacking by eye when it pulls, 160mm pipe with a 600mm flange, i think that 600 may a bit much, drawn a quick pic. you could go out to 320 pcd but i dont think any more is worth it.

http://www.mig-welding.co.uk/forum/album.php?albumid=1499&pictureid=8516

 

[RubberDuck]

My method though i'm using a semi auto mig welding manipulator,
is bolt everything up and weld it (after tack welding the whole flange).
Just finished fabricating 17 Pipes of 2000X900X8 mm with 5mm flange on both sides. Not a single warp or problem.
Just for perspective.

 

[jinjahbiscuit]

Look out for "Lap Joint Flanges", they come with a bevelled inside diameter for welding. If your pipe is a standard size, then the flange should just slip on ready to weld.
Google lap joint flange and being in the US, you should have no problems finding a supply. Standard stuff for oil, gas and water.
Good luck