Welding repair - need some advice

[colson04]

Well, my 10 year old outdoor wood boiler (Ridgewood brand - no longer around) developed a slight water leak. I got the front tore off and found I have cracks in all 4 corners of the door. 2 radiating straight up, 2 going straight down. Cracks propagating like this suggest a design failure (square door opening inside round firebox- different rates of expansion causing fatigue over time).


Either way, one crack made it to the weld between the firebox and water chamber causing a slow leak.

It leaks water into fire box and through the crack to the outside. The other 3 cracks haven't breached the water chamber, but if i dont address them now, they will. The outside of the firebox on the front had fiberglass insulation that was soaked, holding moisture against the steel for awhile causing surface corrosion. I'm presuming it slowly leaked for quite a while before it got bad enough for us to see the water coming out the bottom.

My instinct is to grind out the cracks, and weld them up. I don't have extensive welding repair knowledge to know if that is best option, or if that would fail the first time I light the fire. Is there a procedure that is better for this type of work? Preheat? Welding wire/rod selection? I have a Hobart 190 wire feed, and I also have a Lincoln 225 tombstone as my personal welders. I have a 100amp service in my barn so I don't lack power to run them either. The welding positions will be vertical, and overhead to repair the crack inside the boiler.

Thoughts?

 

[colson04]

A little more tear down and clean up revealed the cracks are pretty bad and all are reaching the water jacket weld. I drained down the water jacket yesterday, knowing I needed this to be dry for repair.

Outside four corners boiler:

 

[colson04]

Inside of the four corners.


I'm going to have to shave to put a respirator on before I climb inside. Boiler is 47" deep, 37" ID. Door is 24"x24" so I can squeeze inside to grind and weld the inside. Won't be comfy, but jobs like this never are.

 

[Nige]

I see your point about the corners of the hole creating the stress risers that started the cracks. Maybe it’s a daft suggestion but is there any way of modifying the boiler end plate to turn the existing square firehole door to a circular one.? If the hole was sized right maybe it could even be used with the original door.?

 

[colson04]

In an ideal world, the entire front would be water jacketed, and the door and door frame circular. I found out after posting this, that this was a chronic design issue for this wood stove, and the manufacturer went out of business as a result of excessive warranty claims. The owner later started a new business under a new name, building a very similar designed stove with an improved design. They added 6x6 plates over the corners were the old design would crack, which reinforced the area enough to prevent it from cracking.

So, I'm grinding out the cracks, welding everything with 6011, and then getting a chunk of plate and making corner reinforcements for the outside. I will then grind out the crack on the inside of the stove and weld up to make sure I get 100% penetration. I have to wire up a 50amp plug in my barn first, as I haven't got that done yet.

 

[materthegreater]

You seem to have done your research and made good preparations. Sounds like a good plan to me.

But this makes me nervous about my 17 year old Central boiler... No leaks yet but everyone says I'm lucky it's lasted this long

 

[Truck Shop]

When originally built/designed it would have been easier more economical to use a spin of 1/4 by 24"
pipe and a round door. You might want to drill the end of those cracks, use a torch on low flame it
will show the end of the crack because it's longer than it looks.

 

[Nige]

Here's an idea for the design of a reinforcement plate. You can figure out size, shape, and thickness to suit the location on your firebox. It doesn't have to be circular, it was just easier for me to draw it that way. The idea is to keep the stresses induced by the welding away from the point of the corners.
Once you've tacked them in place weld from A to B round the outer circumference, and from B to C and D to A along the straight edges. Do not weld the inner circle from C to D.

 

[colson04]

@Truck Shop , I will find and drill the ends of the cracks. I ground the cracks out last night, but I didn't think about drilling them to stop propagation.

@Nige, that's pretty much what I was thinking, but probably not a complete circle. I was going to make 6" square plates, notch out a 2" square in one corner and then put a generous radius on all corners to reduce stress risers. I have a piece of ¼" plate that is 8" x 48", so I could get all four pieces from it. I really don't know if ¼" plate is thick enough for this application though. I can go visit my neighbor. He's an old millwright that never threw away anything. He may have some thicker plate stock laying around I could use.

 

[digger doug]

I would not go too thick, you do want it to stretch and flex.
Too strong will make it crack at the end of it.
You can always run your bead off the end to a trial off.

 

[Nige]

I would not go too thick, you do want it to stretch and flex.

I would've thought that the reinforcement plate should be no thicker than the original end plate thickness.

@Nige, that's pretty much what I was thinking, but probably not a complete circle.

IMO the benefit to profiling the outside in a constant curve (doesn't have to be a perfect circle) is that the angle of the weld between the firebox end plate and the reinforcing plate is constantly changing. Stress cracks like yours generally run in (almost) straight lines, in this case from the corner of the firehole. So the more you can run the repair weld on a curve the less stress it puts into the original end plate, therefore the less likely it would be to re-crack.

 

[digger doug]

And so the weld isn't so abrupt (even though it is circular) add some holes to the re-enforcement plate, and plug weld.

 

[FarmWrench]

The square doorway is getting hotter and expanding faster than the water cooled portion and cooling more pulling in the corners.

I agree with finding the end of the cracks. Grind, preheat, weld and peen to stress relive as it cools with the expectation of more failures.

Firebrick or lightweight heat shield to temper the rates of change and the cycling. Air entrance looks to be on the door. That's cold air coming in and cooling that big square only to get the fire going and make it expand. Maybe tack on an extension to get that cold air deeper into the firebox?

There's also the wonderful world of high temp silicone. Let the crack keep moving but with some rubbery sealing. A bolted down patch that's got silicone under it to seal the water might be wise to include now.

 

[Randy88]

If it were mine, I'd repair it however it works, then do far more research on the next unit you plan to buy, and I'd be figuring it out pretty fast and place the order so hopefully this one can limp along till the new unit shows up.

I've seen so many units just like yours at several of local fix it shops, same as my old furnace, the repairs never last due to rusting from the inside out as well as the outside in. I attempted to repair my old unit, took it on to those who have fixed hundreds and they were right, its a patch and only a patch to get it till the new furnace shows up is about the jest of it. Once my new one showed up, I cut the old one apart and then tossed it into the scrap pile, nothing left of it on the inside, the heat in different area's and water circulation patterns had done it damage long before I ever attempted to fix it. Mine had a water jacketed door and whole end but with poor circulation around the door, it was all a completely rusted out shell and nothing would have saved it no matter how it was fixed.

As for the company that sold that one and then shut down to restart again under a different name, forget them, they'll do it again when the next design flaws are located in the new units. Find a company who's been in business decades and is still operating under the same name and will stand behind their products.

 

[Rob Gunn]

I totally understand that you want to fix what you have. However, I would allso do the math on your time and material to fix that old unit. Maybe time to simply purchase a new unit????
You need to make sure your fire box is mild steel and not some form of Stainless. If its stainless then you have a whole new twist to the weld fix...
I have a 22 year old Woodmaster and cant believe its still working great and no leaks. Every year I fire it up I think its going to be the last.

 

[colson04]

Cost of the cheapest, brand new stove is $7500. I already had the steel and welding consumables at my house, but we'll call that $100 or so to replace. I've got like 20 hours of my time, lazily pittling around on this, maybe a few more to go. I've been working on it as a fill in job between my other stuff. The firebox is 3/8" thick and very sound yet. Aside from the cracks in the front. The rest of the stove is sound and stable, so definitely worth trying to salvage. If the water jacket was in bad shape, I'd reconsider, but the reality is the stuff isn't too far from good, normal condition.

 

[Delmer]

It's not like you're chasing pinhole leaks or bad welds that keep popping leaks. You've got an obvious design flaw and a material that's easy to weld. Weld it up and plan to do it over in five more years. If you were afraid of work, you wouldn't be using an outdoor wood burner.

 

[colson04]

I got busy and didn't keep taking pictures.

Stove is fixed, water tight, and burning away heating the house.

 

[materthegreater]

You must have a small house if that fire heats it

 

[Rob Gunn]

Good to hear that you are all fixed and up and running. its starting to get could here in Michigan, I just lit my stove this weekend. Now we wait for spring...