To the basement, or to the scrapyard? My attempt to resurrect a Tarm Excel 2200

[peakbagger]

My two cents would be to fix the leaks individually. When I worked in industry, plating a tank with one big plate to deal with leaks created a future corrosion cell between the patch and the original wall that eventually would cause future leaks. The new leaks would be at the edges of the patch plates and nowhere near the original leak so the only choice was to put another patch on patch. I used to have to do repairs to large tanks that had been patched multiple times in the past and generally we would end up cutting all the old patches out, sometimes two or three plates thick and replacing it with new wall plates with no voids to cause future corrosion cells. Some of these tanks were 70 years old.

Looking at the failure points, they are all at stays intended to keep the wall from flexing in and out when under pressure. My approach, if I could get to it would rather be reweld and reinforce each leak point at each stay. Of course, getting to the root cause should be done. Given its prior use/abuse was there a properly sized expansion tank and makeup system on the boiler feedwater to keep it at constant pressure?. It that was messed up, the tank walls could have been flexing far more than originally designed for and in that situation failure at the stays combined with heat stress may be the root cause of the leaks. Was there a theromovar three way valve system on the piping? as that also contributes to fire side corrosion/cracking.

 

[aczlan]

Is that cracked where the soapy water is running down on the left side?

One leak inside each circle, all right at the end of the stamped "ribs" in the back wall.
One at the bottom of each of the middle ribs and one at the top of the left rib in the bottom row:

I would get the biggest piece of steel you can fit through the door and try to cover as much as possible with one piece,

Debating cutting/grinding the "ribs" all off and putting a plate over the whole back or cutting the whole back out and putting in a new (thicker?) sheet.
It would be a good excuse to buy the 220V mig welder that I have been eyeing on CL as I am not sure I could get it to hold pressure with my stick welder.

maybe lay it on it's back somehow so don't have to hold the steel in place. Looks like a fun project. I have a Tarm that was made in 1979 and it didn't have any leaks at all when I took it out the beginning of last winter, never had any storage and definitely was a creosote maker, has me wondering how much water quality has to do with it.

If I were to go that route I would set something in there to push from front to back and hold it in place, either a pair of clamps, or some pieces of 2x2 cut to be just a little too long.

Aaron Z

 

[pettibone]

That's a good point, probably would be better cutting out a piece and welding in a new one and by doing that you'd see how thick it is and what kind of condition the inside is where the water is. Whole thing could be bad. Replying to Peakbagger. Those struts go from inside to outside and look like they all failed on the weld not the steel.

 

[peakbagger]

That is going to be point of high stress. I had the luxury in the past of having a ultrasonic tester so I could take spot thicknesses. Cutting the entire panel out and replacing it is the right fix if the metal is thin but those wall stays need to be reinstalled.

 

[aczlan]

My two cents would be to fix the leaks individually. When I worked in industry, plating a tank with one big plate to deal with leaks created a future corrosion cell between the patch and the original wall that eventually would cause future leaks. The new leaks would be at the edges of the patch plates and nowhere near the original leak so the only choice was to put another patch on patch. I used to have to do repairs to large tanks that had been patched multiple times in the past and generally we would end up cutting all the old patches out, sometimes two or three plates thick and replacing it with new wall plates with no voids to cause future corrosion cells. Some of these tanks were 7o years old.

Good to know. I was curious if the corrosion on these was from the inside or from the firebox side.

Looking at the failure points, they are all at stays intended to keep the wall from flexing in and out when under pressure. My approach, if I could get to it would rather be reweld and reinforce each leak point at each stay. Of course, getting to the root cause should be done. Given its prior use/abuse was there a properly sized expansion tank and makeup system on the boiler feedwater to keep it at constant pressure?. It that was messed up, the tank walls could have been flexing far more than originally designed for and in that situation failure at the stays combined with heat stress may be the root cause of the leaks. Was there a theromovar three way valve system on the piping? as that also contributes to fire side corrosion/cracking.

There was an expansion tank, I would guess it was similar to an Extrol 60 (7.6 Gal) as it about was the same diameter as the Extrol 30 that I have, but taller.
No thermovar, no storage and it ran with a DHW coil for most of its life.

That is going to be point of high stress. I had the luxury in the past of having a ultrasonic tester so I could take spot thicknesses. Cutting the entire panel out and replacing it is the right fix if the metal is thin but those wall stays need to be reinstalled.

I guess the next step will be to pull the DHW coil and see if I can use that to drop my "camera on a wire" in that area to see how it is put together.
The right hand one (with the sharpie circle around it as well as a red loop) is the biggest leak.

Aaron Z

 

[aczlan]

Curiosity got the better of me, so I went out and drilled out the worst of the leak points with a 3/16" drill bit.

It looks like I was incorrect in my assumption, I was thinking that these were dimples stamped into flat plate, in actuality it was a flat plate that had slots cut into it and these are reinforcing slats or stays that are welded from one wall to the other to keep the walls from spreading apart. Thanks @peakbagger for pointing that out.

If my HF micrometer is accurate, the metal has not eroded, it is still 1/4" thick.

The leak is a crack at the point where the stay is welded into the wall plate.

A couple of pictures:




Also found a couple more leaking stays on the sides, one on each side:




So I guess the question is, do I weld these up with the stick (and if so which rod), or with a MIG...

Aaron Z

 

[pettibone]

I would think either way would work, just get everything super clean. That would be sweet if that's all you needed to do. On my solo plus those stays stick out on the outside but not the inside so maybe they changed their methods over the years although mine was built in 05 so not a whole lot newer.

 

[peakbagger]

Either welding process will work. Its 1/4" plate so a good welder can get enough penetration as long as they can get the weld clean in advance. I am just a hobby welder who uses straight MIG on clean metal. Conventional welding rods are coated with flux so that the welds do not have to be as clean as the flux carries the contaminants out of the weld. The trade off is a much larger heat affected zone. MIG has the problem that if someone does not know what they are doing, they can lay a nice looking bead on top of the weld without getting enough penetration. It is also darn near impossible to do a nice looking weld with dirty metal with MIG and that can be a problem when you only have access to one side of the weld as crap on the back side can be pulled in. The pretty much standard process for repairing boiler tubes is stick welding by someone who knows what they are doing so my guess the pro would stick it due to only being able to clean up one side.

My guess is without a thermovar (return water temp protection), and no storage, along with the leaks being in the same location, its a mix of welds with poor penetration from the factory and stress corrosion of the weak spots by running the boiler with out return water temp protection. Running a boiler with a cold jacket is a known corrosion issue and that is why Tarm and most other boiler manufacturers require return water temperature protection (and installation by a professional). I think the good news is that the metal is not thin so get a good weld in there and it should work.

With respect to the welds, the trick is to create a molten puddle of metal and drag or push it along to fuse the two metals together. If the puddle cools down, contaminants "freeze" at the edge forming a weak inclusion that can leak and can be attacked later on preferentially. My guess is the pins sticking out through the plate are in a hard spot to get to at the factory and the pins are sealed by running a bead around the pin. The welder starts a puddle and runs it around the pin but if they do not overlap the beginning of the weld (which is now cooled by the time they get to it) they could form a weak spot. It may hold pressure at the factory, but years of operation in a slightly corrosive atmosphere due to no feedwater protection will attack the weak spots.

 

[aczlan]

Either welding process will work. Its 1/4" plate so a good welder can get enough penetration as long as they can get the weld clean in advance. I am just a hobby welder who uses straight MIG on clean metal. Conventional welding rods are coated with flux so that the welds do not have to be as clean as the flux carries the contaminants out of the weld. The trade off is a much larger heat affected zone. MIG has the problem that if someone does not know what they are doing, they can lay a nice looking bead on top of the weld without getting enough penetration. It is also darn near impossible to do a nice looking weld with dirty metal with MIG and that can be problem when you only have access to one side of the weld as crap on the back side can be pulled in.

Stack of dimes on the surface that just pops off?

The pretty much standard process for repairing boiler tubes is stick welding by someone who knows what they are doing so my guess the pro would stick it do to only being able to clean up one side

All of our pressure piping at work is stick welded, IIRC a root of 6010 followed by a cap of 7018.

My guess is without a thermovar (return water temp protection), and no storage, along with the leaks being in the same location, its a mix of welds with poor penetration from the factory and stress corrosion of the weak spots by running the boiler with out return water temp protection. Running a boiler with cold jacket is a known corrosion issue and that is why Tarm and most other boiler manufacturers require return water temperature protection (and installation by a professional).

Makes sense, IIRC the manual that came with it says that the thermovar is only required if you use storage (which it says is recommended, but not required), so it may have been installed to the manufacturers specifications (at the time of installation) by a professional.

I think the good news is that the metal is not thin so get a good weld in there and it should work.

That was great news for me.

With respect to the welds, the trick is to create a molten puddle of metal and drag or push it along to fuse the two metals together. If the puddle cools down, contaminants "freeze" at the edge forming a weak inclusion that can leak and can be attacked later on preferentially. My guess is the pins sticking out through the plate are in a hard spot to get to at the factory and the pins are sealed by running a bead around the pin. The welder starts a puddle and runs it around the pin but if they do not overlap the beginning of the weld (which is now cooled by the time they get to it) they could form a weak spot. It may hold pressure at the factory, but years of operation in a slightly corrosive atmosphere due to no feedwater protection will attack the weak spots.

Makes sense, I can generally make metal stick together (making/fixing implements for our small farm), but don't have much practice with making watertight welds.
Will see if one of the guys at work who welds a lot more than I do will take a stab at it.

Aaron Z

 

[brenndatomu]

Will see if one of the guys at work who welds a lot more than I do will take a stab at it.

Good idea...if you have access to someone who repairs boiler tubes for a living, that is your best chance for a permanent repair.
I had a cracked steel stove repaired by a retired certified boiler welder, it was one n done...this was on a unit that was warranty replaced due to that particular models known (and experienced) cracking issues.

 

[peakbagger]

Definitely, find a pro worth the money (or the beer)

 

[hedge wood]

All the leak repair welding done on my Garn was done with stick. I wouldn't use a Mig on your leaks. Mig welding has its place this is not one of them.

 

[aczlan]

Is that cracked where the soapy water is running down on the left side? I would get the biggest piece of steel you can fit through the door and try to cover as much as possible with one piece, maybe lay it on it's back somehow so don't have to hold the steel in place. Looks like a fun project. I have a Tarm that was made in 1979 and it didn't have any leaks at all when I took it out the beginning of last winter, never had any storage and definitely was a creosote maker, has me wondering how much water quality has to do with it.

I was wondering about the condition of the inside of the "boiler tank", so I pulled the DHW coil out so I could look into it.
All the cracks are at the welds, the steel plate of the walls is still 1/4" thick from what I can see, so there is no need to add a plate to them.


Aaron Z

 

[aczlan]

Pulled out the DHW (Domestic Hot Water) coil to look at the inside of the vessel last night, this is looking across above the top of the firebox, the two cylinders on the far side are thermowells:

Looking down the sidewall of the firebox from the DHW opening:

Looking over and toward the back/chimney from the DHW opening

The DHW coil:

All in all, it looks pretty clean inside, I think the leaks are just from the welds cracking.


Aaron Z

 

[peakbagger]

Great shots. Looking at the close up of the spacer, it looks like the welds from the other side of wall did not have great penetration. There was potential for stress raisers in those pockets. The water side looks remarkably clean. I think you should be in good shape once you deal with the pinhole leaks by getting someone to weld them up.

 

[cumminstinkerer]

looks to me like someone welded those stays in on friday afternoon or monday morning, pretty crappy penetration for sure, get them cleaned and ground out good on the easy side to access, also at the ends of each crack drill a small (3/16") hole, then get it welded good, and you'll be in business.

 

[aczlan]

Looking at this picture and discussing the boiler with the "old timers" at work:

We are thinking that the root cause of the cracks is stress risers coming off of the corners of the square holes punched in the walls that the stays go through.

My plan is to clean up all the points where the risers are welded in, drill all 4 corners with a 3/16" drill bit and weld around each one.

If it works, great. If not, it will either get migrated to the scrapyard, or make a trip to MI (if the guy up there still wants it at that point)

Related to heat cycling, these are all in the bottom half of the firebox where it would change temperature more when the boiler cycles on and off as the "flame" goes down to get to the exhaust.


Aaron Z

 

[peakbagger]

It is not a flaw as much as a cost benefit decision on Tarm's part. They used that detail up into newer models and as far as I know this is not a common failure. In my experience this is no stress riser if properly welded. When a weld is laid down it creates a molten puddle that would convert that sharp corner into a corner with a radius. The problem is that that only works if the person welding up the assembly had gotten a full depth weld so the puddle makes it down to the backside. I do not know what welding process they used at the factory but in general a gas shield wire fed MIG is lot easier and healthier for the employees. As mentioned, the trade off with MIG (or TIG) is less penetration than from a conventional welding rod based weld. It looks to me that they used some sort of punch press to punch out the slots. Thats quick and repeatable in a factory. The problem is the holes produced are going to be straight with no taper. The normal approach to get around poor penetration with MIG is to taper the hole out at 45 degrees down to only thin section that is straight. That would require a different process, in low production, an air grinder and burr. This would add a lot of time to the assembly, so the temptation is to just try to depend on the welders skill to get as much penetration as possible. Alternatively they do the extra weld prep and raise the price to the point where no one buys them. Tarm has a 20 year guarantee and they could make reasonable assumptions about how many times the boiler is cycled from hot to cold and make an economic decision that not prepping the joint is a worthwhile risk. As it is, Tarm's seem to last a long time past the guarantee so the trade off was worth it at the time. I have heard of earlier coal/oil Tarms having a large gasket leak on flanged connection. They tended to start with minor leak that was barely noticeable to most homeowners and by the time it got bad enough then mating surfaces were rusted and pitted and could not be sealed without building it up with weld and grinding it down to establish a smooth surface. That as the end of many. In most cases these were old units well past the guarantee. Ultimately any piece of equipment is compromise between commercial interests and design and ultimately if no one can afford it, it does not get built. NASA, in theory goes way to far on the design end while Space X goes with iterative "good enough". That works and cost's less until someone is strapped on top of one of those rockets.

Standard arc welding generally has far deeper penetration, the trade off is it requires more skill to keep from burning through the metal. Unlike MIG, anyone with a stinger can run a bead outdoors while a shield gas application requires a stinger and gas supply and if there is any wind or air flow past the weld the shield gas can get blown out of the arc. Since I do not currently own an arc welder, I use my MIG and when I need to weld big thick stuff for structural purposes, I do a lot of grinding to taper back the joints. The first weld can be hairy to keep the metal from burning back but after that I just do multipasses to build the weld back up to the original thickness. If everything is clean, I get very little slag or inclusions.

BTW I had to keep an eye on a project once to install a higher alloy tee into a main boiler steam line running at 850PSI at 875F (superheated steam), in that case the joints were preground and then they welded TIGed the root pass then spent the next 20 hours building it up with stick. There was a post weld X ray required and when they did it they found an inclusion half way down in the weld, the welders then needed to grind down the weld to the inclusion which took another 12 hours and then had to weld it all back up and Xray it again. Odds are if that inclusion was missed it would have been years before that inclusion propagated through the weld and caused a failure but when it did if anyone was nearby they would be parboiled in an instant if they were not hit by shrapnel. You will hear quite often about large construction projects that have issues with quality control, the temptation is to skip or fake Xrays as fixing one bad weld can ruin a schedule and cost tens of thousands of dollars. Odds are the people involved will be long gone before its an issue. In my case that expensive T was never used and that piping got torn out and scrapped less than 5 years later.

I guess it comes down to if you really want to go overkill on the repair, feel free to do so but IMHO, clean it up as well as you can and then get a good welder with fresh out of the package rod to run a bead over the cracks. Anymore than that is overkill. Note a lot of folks are cheap and keep rods around or take rods left over from jobs home. The problem is the coatings on the rod are somewhat hydroscopic and absorb moisture, if used in that condition, the moisture in the coating can lead to premature failure due to hydrogen embrittlement (crappy welds) that also can be prone to leaking. Ideally welding rods need to be stored dry in special ovens or hermetically sealed in packages.

 

[aczlan]

It is not a flaw as much as a cost benefit decision on Tarm's part. They used that detail up into newer models and as far as I know this is not a common failure. In my experience this is no stress riser if properly welded. When a weld is laid down it creates a molten puddle that would convert that sharp corner into a corner with a radius. The problem is that that only works if the person welding up the assembly had gotten a full depth weld so the puddle makes it down to the backside. I do not know what welding process they used at the factory but in general a gas shield wire fed MIG is lot easier and healthier for the employees. As mentioned, the trade off with MIG (or TIG) is less penetration than from a conventional welding rod based weld. It looks to me that they used some sort of punch press to punch out the slots. Thats quick and repeatable in a factory.

I have (between the threads on this project on 4 forums) heard from several people who have had a similar failure with Tarm boilers and I wonder how many of the "firebox back wall sprung a leak" issues that people have experienced could be attributed to this.

Switching to a punch/die in the press with rounded ends would have reduced the probability of stress risers at the corners without increasing the amount of work needed to fit up and weld the boiler together at the expense of a slightly more expensive punch/die.

Aaron Z

 

[hedge wood]

After the first failed weld that cased a leak on my Garn a close inspection was done on the welds. It was very clear that three different welders had welded on the Garn during the building process and the one didn't do very good work. I was recovering from two shoulder surgery's at the time so I didn't get into or do any of the work. But the pictures the guy I hired for the clean up work and the ones the welder that did the repair took you could see the different welding style that went on. The welder I hired cleaned up and rewelded a lot welds the one person had done. Hopefully I can get some more years out of it. There are places inside of it that could leak that you can't get to reweld. We'll cross that bridge when we get there. Its not if it leaks again but when .

 

[peakbagger]

I have (between the threads on this project on 4 forums) heard from several people who have had a similar failure with Tarm boilers and I wonder how many of the "firebox back wall sprung a leak" issues that people have experienced could be attributed to this.

Switching to a punch/die in the press with rounded ends would have reduced the probability of stress risers at the corners without increasing the amount of work needed to fit up and weld the boiler together at the expense of a slightly more expensive punch/die.

Aaron Z

I wonder how this project came out?

 

[pettibone]

Talked to a guy in southern vermont a while ago that had a solo plus listed on CL for parts. He said his, a 2008 I think, started leaking on the back wall and when he pushed his finger on it went right through. So guess the stays had nothing to do with that. I also wonder how this came out.