Post by springcrocus on Nov 26, 2022 8:58:35 GMT
They say familiarity breeds contempt. Because of increasing levels of success during our boiler build, I allowed my concentration to slip. That's when the Goddess/God of silver-solderers decided to pay the workshop a visit and give me a smack round the ear for failure to pay homage. People may recall the slight hiccup we had whilst fitting the front tube plate.
We had been bringing the top of the barrel up to temperature with two torches. Wilf was working around the top, inside and out, concentrating on getting the barrel up to temperature and I was chucking in some heat through the dome hole with the cyclone burner, heating the tubeplate from beneath. We had used this approach on the Britannia boiler to great effect because it helps draw the solder down the tubes.
As the solder around the perimeter of the tubeplate started to melt, we increased the heat a little and started carefully adding heat to the top without letting the flames touch the solder rings. I alternated by adding heat at the top, then some more through the dome hole. At the time, we weren't aware of a problem and it seemed that the melt had been very good. Once it had cooled, though, the "hiccup" appeared.
Because I was concentrating on looking at the tubeplate from above and watching the melt, I had left the cyclone burner too long in one place and burnt a hole through one of the two upper flues. S**t! That was the end of that session so we put the boiler in the pickle and discussed the options. There are only two, of course, but with variations. Blank it off or replace it. So this is how the repair went.
Later that afternoon, I sketched up a means of blanking the tube which comprised of two taper bungs and a tie-rod from 1/4" diameter copper tube. The two bungs were made from 7/16" AF hexagon phosphor bronze, drilled 5/16" deep and tapped 1/4" x 40 tpi. A shallow taper was turned on the outside with the compound set at about one and a half degrees because this produces a self-locking taper, much greater and it wont self-lock.
Once they just entered a sample of the copper tube, they were parted of about half-inch long. In the next picture, I have given the tube gentle tap and it has started to flare out and stick on the taper. Following this, they were parted of with a 3/32" wide head, just enough to get a spanner on.
The tie-rod was made from 1/4" diameter thick-walled copper tube and an offcut from a 3mm Allen key was banged in one end to create an internal hexagon to help tighten up the first bung. The length was fixed by trial and error and a good length of thread put on each end. Everything has to be done from the smokebox end and space is a bit tight in the firebox unless you have quite small hands.
However, I wasn't really comfortable with this. It's a brand-new boiler and I didn't really want to start with a bodge. A weekend of pondering and I had made my mind up, I would prefer to cut the tube out and replace it. A few months ago, I advised runner42 to replace his faulty tube, time to follow my own advice. On Monday, I made a visit to the boiler inspector, showed him the damage, explained my options, showed him the bung but told him I wanted to try a repair and he agreed.
The first job was to cut the old tube out and a router cutter was modified to core out the front part but that wasn't very successful. They are 10mm tubes so a 10mm reamer was used instead, not easy with a pistol drill but manageable. While I was cutting away material, I had a piece of thick wire poked through the dome hole and into the broken tube, just to make sure I didn't loose the freed part into the boiler.
Because we had not yet fixed the backhead, I was able to approach the other end without recourse to reverse cutters on long, thin spindles. Access was made in the fireback backplate using a cone cutter to make a hole about 12mm diameter.
I was then able to apply the reamer though the hole and core away the back end. This time, a long rod was fed into the tube from the front to catch it when it released.
These are the two pieces of the tube and the top one clearly shows the molten copper. I didn't think propane could produce enough heat to melt copper but the evidence suggests otherwise. Lesson learnt! I checked the adjacent tube very carefully but it showed no signs of damage, not even sagging a little. It's obvious that, at the moment it melted, the tube became a chimney that drew all the heat up it's core and out at the tubeplate. The other torch was playing so much flame around the top that it completely masked any effect from the damaged tube.
Up at the club, they had a life-expired boiler (wasted tubes) and I borrowed this so that Wilf and I could practice on it. I also borrowed John the Pump's oxy-propane equipment because I didn't think we would be able to effect a repair in the confines of the firebox with propane alone. This old boiler had 7/16" diameter tubes and I didn't have a reamer so I used a blunted drill to cut out one of the tubes.
At the other end, I was able to cut away the tube by drilling through the firehole but the next problem was extracting the tube. It was supported on a thin bar but we had to resort to driving it out with a shouldered rod, again applied through the firehole. It would have been smarter to open the front hole up a few thou and expand the replacement tube to fit the larger hole. A length of M5 allthread was used to create a support for the replacement tube which was set into place.
At the front end, the support plate spanned across a couple of tubes and kept the replacement one at the same level. Lots of flux was applied at both ends even though we weren't going to be heating the front end at this point.
The old boiler was stood on it's nose and heat applied, Wilf doing most of the work with the cyclone burner, heating the inside of the box and me adding background heat with the normal burner. When the flux melted, Wilf stepped back and I switched over to the oxy-propane, using the firehole to apply the solder. Once we had molten solder around the tube, we gave it a few moments to cool, then flipped the boiler over, holding it with a ceramic blanket. The front end was much simpler because of easy access. I did take a picture but it was too blurred to use. The front tubeplate was a good join but the firebox end didn't take at all. The solder just stuck to the end of the tube. More practice needed! Here, the tube has been cut free at the front and pushed back into the firebox.
A look inside the boiler with an endoscope revealed a complete absence of solder, so it obviously didn't get hot enough. I think the main problem was that it was a much bigger boiler and had a lot of limescale in it. We probably needed to put larger nozzles on our burners. It did give me a chance to experiment with the oxy-propane, though, and work out how best to control the size and intensity of the flame.
When it came to repairing Calbourne's boiler, things went a little smoother. For a start, the copper was much cleaner and also the boiler a lot lighter, requiring much less heat. Everything was set up in a similar fashion but this time it was much eaier to get heat onto the firebox tubeplate from the sides and above because of the open back. I still used oxy-propane to make the repair, applying the solder through the firehole and it was much more successful.
I had previously made a small, tapered bronze plug to fill the access hole so, while the boiler was still hot, more flux was added and the plug located with tongs. A quick blast from Wilf's cyclone burner in the box while I held the plug in place with a stainless steel rod soon saw this item soldered securely.
Once again, the boiler was flipped over, extra flux added and heat applied to the outside of the barrel, wanting to get the heat to conduct through to the tubeplate. One useful thing we discovered was to use the cyclone burner at an angle and directed at the inner surface of the barrel. This swirled the heat around the perimeter very well and gave uniform heating, making it much easier to get the tubeplate up to temperature without burning the ends of the tubes. We could have finished this with propane alone but, because the oxy-propane kit was there, it was used for the final lift of heat before applying solder. Here is the end result. The picture was actually taken while we setting up to close the backhead but it shows the tube well-soldered
It was a daunting prospect, having to cut out a tube and replace it but, as I have shown, with a bit of care and careful thought about how to approach the job, it is not as difficult as it sounds. It has certainly added to our confidence when it comes to boiler making. It may be much more difficult replacing a tube on an older boiler that is full of limescale and I expect a thorough cleaning, including de-scaling, would be required before attempting such a repair.
I deliberately held off writing this up until the boiler had passed the shell test and been certificated. Any earlier and members of the Toldyouso Society would have been sniggering in the background. As it is, the decision to replace rather than repair has been justified.
Regards, Steve
We had been bringing the top of the barrel up to temperature with two torches. Wilf was working around the top, inside and out, concentrating on getting the barrel up to temperature and I was chucking in some heat through the dome hole with the cyclone burner, heating the tubeplate from beneath. We had used this approach on the Britannia boiler to great effect because it helps draw the solder down the tubes.
As the solder around the perimeter of the tubeplate started to melt, we increased the heat a little and started carefully adding heat to the top without letting the flames touch the solder rings. I alternated by adding heat at the top, then some more through the dome hole. At the time, we weren't aware of a problem and it seemed that the melt had been very good. Once it had cooled, though, the "hiccup" appeared.
Because I was concentrating on looking at the tubeplate from above and watching the melt, I had left the cyclone burner too long in one place and burnt a hole through one of the two upper flues. S**t! That was the end of that session so we put the boiler in the pickle and discussed the options. There are only two, of course, but with variations. Blank it off or replace it. So this is how the repair went.
Later that afternoon, I sketched up a means of blanking the tube which comprised of two taper bungs and a tie-rod from 1/4" diameter copper tube. The two bungs were made from 7/16" AF hexagon phosphor bronze, drilled 5/16" deep and tapped 1/4" x 40 tpi. A shallow taper was turned on the outside with the compound set at about one and a half degrees because this produces a self-locking taper, much greater and it wont self-lock.
Once they just entered a sample of the copper tube, they were parted of about half-inch long. In the next picture, I have given the tube gentle tap and it has started to flare out and stick on the taper. Following this, they were parted of with a 3/32" wide head, just enough to get a spanner on.
The tie-rod was made from 1/4" diameter thick-walled copper tube and an offcut from a 3mm Allen key was banged in one end to create an internal hexagon to help tighten up the first bung. The length was fixed by trial and error and a good length of thread put on each end. Everything has to be done from the smokebox end and space is a bit tight in the firebox unless you have quite small hands.
However, I wasn't really comfortable with this. It's a brand-new boiler and I didn't really want to start with a bodge. A weekend of pondering and I had made my mind up, I would prefer to cut the tube out and replace it. A few months ago, I advised runner42 to replace his faulty tube, time to follow my own advice. On Monday, I made a visit to the boiler inspector, showed him the damage, explained my options, showed him the bung but told him I wanted to try a repair and he agreed.
The first job was to cut the old tube out and a router cutter was modified to core out the front part but that wasn't very successful. They are 10mm tubes so a 10mm reamer was used instead, not easy with a pistol drill but manageable. While I was cutting away material, I had a piece of thick wire poked through the dome hole and into the broken tube, just to make sure I didn't loose the freed part into the boiler.
Because we had not yet fixed the backhead, I was able to approach the other end without recourse to reverse cutters on long, thin spindles. Access was made in the fireback backplate using a cone cutter to make a hole about 12mm diameter.
I was then able to apply the reamer though the hole and core away the back end. This time, a long rod was fed into the tube from the front to catch it when it released.
These are the two pieces of the tube and the top one clearly shows the molten copper. I didn't think propane could produce enough heat to melt copper but the evidence suggests otherwise. Lesson learnt! I checked the adjacent tube very carefully but it showed no signs of damage, not even sagging a little. It's obvious that, at the moment it melted, the tube became a chimney that drew all the heat up it's core and out at the tubeplate. The other torch was playing so much flame around the top that it completely masked any effect from the damaged tube.
Up at the club, they had a life-expired boiler (wasted tubes) and I borrowed this so that Wilf and I could practice on it. I also borrowed John the Pump's oxy-propane equipment because I didn't think we would be able to effect a repair in the confines of the firebox with propane alone. This old boiler had 7/16" diameter tubes and I didn't have a reamer so I used a blunted drill to cut out one of the tubes.
At the other end, I was able to cut away the tube by drilling through the firehole but the next problem was extracting the tube. It was supported on a thin bar but we had to resort to driving it out with a shouldered rod, again applied through the firehole. It would have been smarter to open the front hole up a few thou and expand the replacement tube to fit the larger hole. A length of M5 allthread was used to create a support for the replacement tube which was set into place.
At the front end, the support plate spanned across a couple of tubes and kept the replacement one at the same level. Lots of flux was applied at both ends even though we weren't going to be heating the front end at this point.
The old boiler was stood on it's nose and heat applied, Wilf doing most of the work with the cyclone burner, heating the inside of the box and me adding background heat with the normal burner. When the flux melted, Wilf stepped back and I switched over to the oxy-propane, using the firehole to apply the solder. Once we had molten solder around the tube, we gave it a few moments to cool, then flipped the boiler over, holding it with a ceramic blanket. The front end was much simpler because of easy access. I did take a picture but it was too blurred to use. The front tubeplate was a good join but the firebox end didn't take at all. The solder just stuck to the end of the tube. More practice needed! Here, the tube has been cut free at the front and pushed back into the firebox.
A look inside the boiler with an endoscope revealed a complete absence of solder, so it obviously didn't get hot enough. I think the main problem was that it was a much bigger boiler and had a lot of limescale in it. We probably needed to put larger nozzles on our burners. It did give me a chance to experiment with the oxy-propane, though, and work out how best to control the size and intensity of the flame.
When it came to repairing Calbourne's boiler, things went a little smoother. For a start, the copper was much cleaner and also the boiler a lot lighter, requiring much less heat. Everything was set up in a similar fashion but this time it was much eaier to get heat onto the firebox tubeplate from the sides and above because of the open back. I still used oxy-propane to make the repair, applying the solder through the firehole and it was much more successful.
I had previously made a small, tapered bronze plug to fill the access hole so, while the boiler was still hot, more flux was added and the plug located with tongs. A quick blast from Wilf's cyclone burner in the box while I held the plug in place with a stainless steel rod soon saw this item soldered securely.
Once again, the boiler was flipped over, extra flux added and heat applied to the outside of the barrel, wanting to get the heat to conduct through to the tubeplate. One useful thing we discovered was to use the cyclone burner at an angle and directed at the inner surface of the barrel. This swirled the heat around the perimeter very well and gave uniform heating, making it much easier to get the tubeplate up to temperature without burning the ends of the tubes. We could have finished this with propane alone but, because the oxy-propane kit was there, it was used for the final lift of heat before applying solder. Here is the end result. The picture was actually taken while we setting up to close the backhead but it shows the tube well-soldered
It was a daunting prospect, having to cut out a tube and replace it but, as I have shown, with a bit of care and careful thought about how to approach the job, it is not as difficult as it sounds. It has certainly added to our confidence when it comes to boiler making. It may be much more difficult replacing a tube on an older boiler that is full of limescale and I expect a thorough cleaning, including de-scaling, would be required before attempting such a repair.
I deliberately held off writing this up until the boiler had passed the shell test and been certificated. Any earlier and members of the Toldyouso Society would have been sniggering in the background. As it is, the decision to replace rather than repair has been justified.
Regards, Steve
