How to create some space when making tube using migwelding

[oldwelderman]

Hi,

I have a steel tube (40 mm. outer diameter).
I need a piece of steel tube that slides over this tube (a sleeve)
As I could not find steel tubing that can do this, I tried to solve it in the following way:
I took a piece of sheet steel, around 1,6mm. thick.
After cutting it to size, I shaped it around the existing tube (by hand-bending and some hammering).
The created piece was snugly fitting, and the ends did overlap 5mm. or so.
After that I mig-welded at the edge of the overlap to 'close' the sleeve.
It looked quite good, but sadly, due to shrinking, I can not remove my creation from the tube I formed it on.

So I will have to do this again, now shaping the sleeve using some sort of spacer (to create room between
the original tube and my sleeve).
Now my question
what material can I use for this?
It should be a sheet of something, around 1 mm. thick, that does not burn when I am welding the sleeve.
Thin cardboard could do, but will burn in the welding process and contaminate the weld (imho).
I want to weld the sleeve as it is over the tube -to preserve its shape.

Anybody with a suggestion?

Thank you

[danielplace]

Seems that whatever you put between will also capture the inner tube when squeezed by the outer. Same outcome as the first one. Can't get the core out. Gonna have to maybe just tack the outer and get the core out before you weld the seam out completely.

[Oldendum]

If you have a torch, you could heat the outer sleeve and tap it all over as though you are planishing it. Not hard blows, but enough to stretch the outer tube a bit. If the inside tube is thin this may not work.

[albrightree]

why not take another piece of the 40mm tube, and cut a seam in it. The take another piece of 40mm tube, and cut a small section of tubing to insert in that seam to enlarge the tube. I do it alot on 4",6", 8" stainless duct work. Its much easier than forming a whole new tube. It helps to have extra tube. You will still have a little fitting to do to make it work.




Any smaller aluminum tube ro round, probably at least 30mm will act as a backer to keep from burning through.



This is a 22ga. stainless 8" tube that I shrank by removing a section, and welding back together



HTH

[tapwelder]

What is the usage, is it a coupler? How wide? At that diameter you could wrap strap metal (1inch x1/8 or 1/16 inch) in a spiral around the 40mm turn. Then you could cut rings or weld up the spiral to form a tube.

[oldwelderman]

Thanks to those who wanted to respond.

@tapwelder: yes, it is intended as a coupling between two pipes of 40 mm. outer diameter. Actually exhaust pipes of my car (pipes in this diameter are no longer available over here, so I was forced to help myself.

@albrightree: I used your method of inserting a strip to widen a pipe in another way, read below.
The 'backing' with Cu or Al pipe I didn't do, because your tip entered after my action.

@Oldendum: I got the pipe off, without heating.

@danielplace: will do the tacking as a follow-up.

To my situation: I now have 2 selfmade pipe sleeves:
one not described before: around a 40 mm. outside diameter 'placeholder pipe' I fomed a tube out of 2 mm. steel flat plate. With force and a persuader (hammer) this is possible. I first cut the plate to a width and a length. The length I thought to correctly get by the circumference rule: 2*pi*r, or pi*diameter or 22/7*diameter.
My calculation gave 125,71 mm. for the length.
I took a bit more, believe 128 mm.
After wrapping the steel around the placeholder, a gap of about 8 mm. resulted....
(when you are finished laughing, will somebody explain me where my fault was, as up to now I don't know);
Desparate I cut a strip of 8 mm. and welded this into the opening.
Finished this today and after grinding and making nice, the pipe seems quite usable, but on one side it slides fine onto the placeholder, the other end is not exactly round.
Tried to correct this by clamping/pressing with my vice helped a bit but not to the desired extend.

The other pipe I wrote about in my first message (the one too tight on the placeholder pipe): I grinded away the weld blobs and cutted a groove with a cutting disk on my grinder through the top sheet of the overlap (the sheet metal 1,6 mm. overlapped on the closing edge of the pipe.
Careful grinding resulted in just the top sheet cut, the lower one is untochted. As a result dhe pipe opened itself 1 or 2 mm. and I could easily take the sleeve off.
Nice: there were no blobs of weld on the inside, the clamping actions seems to have come from my tight wrapping of the steel around the placeholder in the first place,
with an adding of some shrinkage by the welding process.
I could weld the opened seam in a new position now, maybe using tacks and tackwelding in a row (the stepping method).

The sleeve described above has tiny blobs on the inside, which don't contribute to easy mounting on the placeholder.
Is there an easy way to smoothen the inside of such a workpiece?
On modellers-miniature-electric drills you often see extensions with a sawcut in it, you can mount sandpaper in that, and with that rotating clean the inner side of a pipe.
For my normal drill I don't know these are available (and useful to remove metal drops).

Maybe some can give me a hint.

Thank you.

[jmm03]

would something the right size like this be of help? https://www.grainger.com/product/1MU...P7A1P:20501231 (a tube expander) Jim

[farmersammm]

I know this sounds like a smartazz reply, but believe me, it isn't. Exhaust is dangerous (believe me, I know), so it should be done right.

Quit messing around, and take a piece of the pipe to an exhaust shop, and have them put it on their mandrel pipe expander. About a 2 minute job.