Stainless Steel Flu Pipe.

[Jen-in-Wellies]

On 29/09/2023 at 11:56, rusty69 said:

So, as I know you guys are really interested about my flue pipe, and welfare over the cooler months, here is an update.

I finally got around to fitting the new flue. I went for the cheap stainless pipe in the end, which cost a little over 40 quid. Ordered on Wednesday, arrived Thursday, and fitted in under an hour today. Chopped the ends off to match the angle with, would you believe it, an angle grinder. Stuffed with fire rope and ordinary silicone. Ok, so, it's not the high temperature envirograf stuff, but interested to see if it will work. Worst case scenario is we die of carbon monoxide poisoning, best case scenario is I save 10 quid on silicone, so its win win really, except for the death bit I suppose.

The end.

 

17 minutes ago, rusty69 said:

Update 2. The new stainless flue is working out well so far. Requires less sweeping than the old steel one for some reason that I don't understand. The ordinary silicone sealant is standing up well too. I was expecting it to burn and melt away, but seems ok.

Can you confirm it was the 304 grade, 1.5mm wall thickness you went for? Looking back through the thread, it seems so. Good to know that you are not dead yet. At some point, the current steel flu on my stove is going to rust through and living in the area it was invented, stainless steel seems a good idea for the replacement.

[rusty69]

4 minutes ago, Jen-in-Wellies said:

24 minutes ago, rusty69 said:

 

Can you confirm it was the 304 grade, 1.5mm wall thickness you went for?

Yes, and yes. 

 

From here, though there are lots of suppliers:

 

https://www.ebay.co.uk/itm/265328014769

 

There is a link to the thicker (more expensive stuff)further up thread. My intention was to replace the current one with the thicker stuff after winter should it be required, but it looks to me that this one may last a number of years.

[Alan de Enfield]

15 minutes ago, Jen-in-Wellies said:

Can you confirm it was the 304 grade, 1.5mm wall thickness you went for?

 

 

Us as well (70mm which is an odd size)

 

 

 

 

 

[MtB]

43 minutes ago, rusty69 said:

Yes, and yes. 

 

From here, though there are lots of suppliers:

 

https://www.ebay.co.uk/itm/265328014769

 

There is a link to the thicker (more expensive stuff)further up thread. My intention was to replace the current one with the thicker stuff after winter should it be required, but it looks to me that this one may last a number of years.

 

Blimey that stuff is cheaper than the 3mm wall thickness plain mild steel flue pipe that Midland Chandeliers sell! 

 

 

 

[rusty69]

Just now, MtB said:

 

Blimey that stuff is cheaper than the 3mm wall thickness plain mild steel flue pipe that Midland Chandeliers sell! 

 

 

 

Hey, I'm nothing if not cheap. I think it's gone up 10% since I bought it too. 

[MtB]

1 minute ago, rusty69 said:

Hey, I'm nothing if not cheap. I think it's gone up 10% since I bought it too. 

 

And I always imagined you were really expensive. 

 

 

[magnetman]

Calling welded steel tube a 'flue pipe' in chandleries is a bit of a con.  You are just paying for the convenience. 

 

Its nothing special just a standard product from a steel stockholder. 

[MtB]

3 minutes ago, magnetman said:

Calling welded steel tube a 'flue pipe' in chandleries is a bit of a con.  You are just paying for the convenience. 

 

Its nothing special just a standard product from a steel stockholder. 

 

True.

 

I also suspect the same 3mm 'flue pipe' gets used for rudder tubes quite often.

[magnetman]

Going back to the stainless steel. 

 

304 is inferior to 316 in a flue application. It can corrode and eventually start getting pinholes. For this reason I think removal of the flue and careful inspection every spring would probably be wise. 

[rusty69]

1 minute ago, magnetman said:

Going back to the stainless steel. 

 

304 is inferior to 316 in a flue application. It can corrode and eventually start getting pinholes. For this reason I think removal of the flue and careful inspection every spring would probably be wise. 

Would you recommed such action with a steel flue pipe too?

[magnetman]

Yes it would be sensible. 

 

Interesting to note that a potential failure area is the weld. The 304 exhaust pipe tubes are welded tube not seamless.

 

Investigation into failure of 304 stainless tubes in a gas boiler.

 

https://www.mdpi.com/2075-4701/9/9/969

 

 

 

"The failure is in the form of circumferential cracks in the vicinity of the weld."

One wonders if a similar thing happens in the longitudinal welds found on these pipes under discussion. 

[rusty69]

Perhaps i need to buy an endoscope.

Edited December 29, 2023 by rusty69

[magnetman]

Also these people make an interesting point. 

 

 

 

After electric welding of stainless steel welded pipes, post-weld treatment processes such as pickling, passivation and milling must be carried out to remove air oxide layers (colored plates) and repair the corrosion resistance again.

https://www.kaysuns.com/blog/why-stainless-steel-welded-pipe-will-rust-after-welding/

 

 

I bet the car modification lads and ladies will have discovered if there are issues with these pipes. 

[rusty69]

Wht couldn't you have told me all this stuff before I installed it huh? I'm gonna be worried until spring now.

[magnetman]

Mine has been alright for two and a half winters burning wood. 

I don't think they are suddenly going to fail just worth being aware of potential issues over time. 

[rusty69]

I'm not burning wood.

[waterworks]

2 hours ago, rusty69 said:

Update 2. The new stainless flue is working out well so far. Requires less sweeping than the old steel one for some reason that I don't understand. The ordinary silicone sealant is standing up well too. I was expecting it to burn and melt away, but seems ok.

If its thin say 1 mm ( like mine ) then it will expand and contract and get much hotter than thick mild steel so it sheds all the soot by itself. I never need to sweep mine .

[blackrose]

I've never had a problem with mild steel flue pipes. 4mm wall thickness will never rot through unless you're doing something very odd with your stove. I might be covering old ground in this thread, but doesn't a decent wall thickness mild steel flue act like part of the (thick walled) stove and put more heat into the boat than a thin stainless pipe? Or perhaps it makes no difference.

[magnetman]

Not sure but as waterworks says if the flue is very hot it helps reduce the soot. I find my 70mm stainless flue stays clear and that is even when like now I am burning freshly felled green sycamore. Its just not a problem because the flue is so hot. 

 

Suspect a lot of flue problems are from fires being run too cool.

 

I do very occasionally need to clean the flue. This requirement is advertised by the fire smoking into the cabin with the door open. Most of the time it is no problem but a lot of wood burned slowly can cause issues. 

 

[rusty69]

I think what MM says about running the stove cool, and the introduction of condensation that eventually caused the pipe to rot is what has happened to our pipe. That coupled with some dodgy mix of smokless that hasn't been very kind led to premature failure, I suspect. 

 

It may be that running the stove on low overnight helps with condensation higher up, and that liquid is not burnt off, but runs down the pipe, eventually leading to rust holes, but short of letting the stove go out overnight or running it hard, I can see no way around this.

 

I have certainly not experienced degredation of the pipe quite so quickly as I have experienced over the previous 25 years of useage, but in the earlier yrars did let the stove go out overnight, so perhaps that helped with the situation.

 

Time will tell whether the stainless holds up better than the steel. I have not noticed any performance degredation regarding heat output since changing the pipe.

[magnetman]

I let my fire go out overnight. 

It heats up fast so this is not a problem. I have a duvet. 

[MtB]

5 hours ago, magnetman said:

I have a duvet. 

 

Cheers. I'm a fan of Belgian beer too!! 

 

 

[blackrose]

On 29/12/2023 at 20:48, magnetman said:

I find my 70mm stainless flue stays clear 

 

70mm diameter? That is tiny. Must be a very small stove?

 

Mine is about 140mm OD. A larger flue doesn't tend to suffer from soot build up so much simply because as a proportion of the overall cross section area the area of soot is less significant. 

 

My stove is run cool every night when it dies down but I only sweep it out once midwinter and once at the end of winter.

Edited December 31, 2023 by blackrose

[rusty69]

6 hours ago, blackrose said:

Must be a very small stove?

deleted. Wrong stove

Edited December 31, 2023 by rusty69

[magnetman]

6 hours ago, blackrose said:

 

70mm diameter? That is tiny. Must be a very small stove?

 

 

Its a custom made fire. Not specially small its tall and narrow. I estimate about 3.5 or 4kw. Chucks out a lot of heat.

 

The 70mm flue was an experiment based on the fact my other fire has an 80mm flue. 

 

Works nicely and the door can be left open.

 

Advantage of narrower flue is it all heats up better so doesn't get blocked up. Suboptimal flue temperature is what causes the problems.

 

 

 

 

 

Edited December 31, 2023 by magnetman