welding a stove flue pipe

[mattiker]

Hi,

I have yet to do a single weld - complete novice, but have bee reading a bit and wathcing youtube vids - this site is excellent too.

I have aquired an old clarke ARC welder AC 160amp (dont know the exact model) - and have just ordered a welding helmet/gloves/clamps. I bought some electrodes 2.5mm 6013 - from a local welding supplies shop - which I intend to experiment with.

There is a welding job I'd like to get done (once I've had some practice!)...

I have a wood buning stove and I'd like to weld the flue pipe to the flue collar. The collar bolts to the top of the stove and is quick thick steel (maybe 8-10mm thick - the flue pipe slides into this collar and is secured with fire-cement which has the tendancy to crack. I'd like to weld the two together to make disasembly/reassambly easier (i.e. no fire-cement) for access to sweep the chimney, and also to create good air-tight seal that wont crack like the fire-cement.

My plan was to weld from the inside of the collar so that my dodgy-weld wont be on show - but I was worried that welding thick to thin may be an issue. Along with the fact that the flue pipe may be too thin for ARC welding in the first place.

Any help, much appreciated.

Cheers.

Matt

 

[upinsmoke]

stove pipe

i use a heat prof silicone sealant now instead of fire cement on oil fired boilers even the old ones that burn at a far higher temp than the condensing ones. try a plumbing shop they should have it or be able to get it.

 

[mattiker]

High temp silicone is not an option...it's only ever rated to about 300 degrees C - and the top of my stove can get hotter than that, plus I don't want the toxic fumes of the silicone burning in my living room :-)

 

[Shox Dr]

I've just fitted a stove to my house, and had it modify a stove pipe. (Have you seen the price of that stuff)

If it's been stove enamelled, you'll have fun just grinding the enamel off. It's like diamonds, where's discs out quicker then you can change them.

After that it should be plain sailing

 

[bigtip]

theroretically, if there's nothing wrong with you stove/chimney set-up then you don't need air-tight joints in your flue. the draw of the chimney should mean that air will enter via any imperfect joints but flue gasses don't escape. entering air isn't ideal but it's not the end of the world as long as it's not major amounts which can make your flue overly cool and reduce the effective draw in the stove itself.
on my first installation, i made absolutely sure with a tube of 'silicone' which was flexible fire type stuff but i found on later installations (all at my own house, by the way) that even badly fitting flue components where there was considerable amount of movement didn't let smoke out after a few seconds, if at all, i.e. once the flue was drawing. it takes a little heat to get the flue warmed up and drawing well in most cases but unless you get a serious blockage or hole in the flue then you won't get smoke escaping and if you get a hole or blockage then your sealant won't make much difference anyway.

plus you'll have job welding 1mm to 10mm especially with an arc welder and especially trying to do it from inside i would imagine.

 

[blenkie1]

Is the flue collar not made of cast?

 

[mattiker]

Is the flue collar not made of cast?

I'm not sure, is there a way to tell? When i've had it apart before I've hit with hammer a fair bit to loosen the old fire-cement - would cast iron have broken?

 

[brightspark]

I'm not sure, is there a way to tell? When i've had it apart before I've hit with hammer a fair bit to loosen the old fire-cement - would cast iron have broken?

grind a bit/ if the sparks are a dull red its cast if there bright its steel

 

[mattiker]

The rest of the stove is steel - so I'd guess the collar is too - I will check as you say by grinding it.

If it is cast iron, I guess it's going to be even more tricky to weld right?

I think the flue pipe is probably 1-2mm thick.

Bigtip, I agree it doesn't need to be air tight - but I would like it to be all one piece. Rightly or wrongly, to properly sweep my chimney I need to disconnect the flue pipe and remove it from the register plate. So if it was all welded together I can just unbolt and slip it out.

Do you think it will be possible with cheap old 'buzz box'?

 

[keith19]

The rest of the stove is steel - so I'd guess the collar is too - I will check as you say by grinding it.

If it is cast iron, I guess it's going to be even more tricky to weld right?

I think the flue pipe is probably 1-2mm thick.

Bigtip, I agree it doesn't need to be air tight - but I would like it to be all one piece. Rightly or wrongly, to properly sweep my chimney I need to disconnect the flue pipe and remove it from the register plate. So if it was all welded together I can just unbolt and slip it out.

Do you think it will be possible with cheap old 'buzz box'?

If both collar and pipe are steel, it might be possible, with some considerable experience of using a cheap old buzzbox. With your lack of experience it is not something I would advise anyone to tackle without lots of practice.

You will be trying to pipe weld 10mm to 1-2mm with a rod which will be difficult to strike, and which when it gets going is quite likely to blow a hole in your pipe if you don't get a number of factors and techniques just right. Welding even a butt joint with a stick welder is quite difficult enough to master on 1-2mm flat plate, let alone on a pipe, for a beginner.

I would leave it alone if I was in your position, and get a pro with a big mig or tig m/c to weld it up, if you must have it welded.

 

[bigtip]

you could drill out maybe 4 holes around the collar/flue junction, apply fire sealant and fix together with self tappers.

would be easy work and also still give you the option to dismantle if you ever needed to.

but.... you want to get that new welder out don't you?

 

[julianthegypsy]

Why don't you wrap the inside of the collar with fire rope?

 

[mattiker]

you could drill out maybe 4 holes around the collar/flue junction, apply fire sealant and fix together with self tappers.

would be easy work and also still give you the option to dismantle if you ever needed to.

but.... you want to get that new welder out don't you?

LOL - I think you have rumbled me!

From what's been said I'm probably going to leave it alone, I'd rather not blow any holes in it - I may take it to local welding firm and have them do it - may be they will let me watch.

Now...what else "needs" welding, hmmm

 

[mattiker]

Why don't you wrap the inside of the collar with fire rope?

The gap is just too tight - it's made more difficult by the fact that the flue pipe doesn't enter the collar perfectly straight, it tilts a bit.

 

[KemppiFrog]

My first thought was that the bigger bit was cast. And learning to arc weld on thin stove pipe to 10mm would be a recipie for frustration, at least...and might put you off for good.

Get some scrap and try the buzz-box on 2-5mm stuff. Then think about your stove. Might have a new viewpoint.
KF