Too much silver solder?

[runner42]

I am still in the throes of trying to correct the leaks in my boiler. These occur on the firebox tubeplate between the tubeplate and the four flues. In trying to correct these I applied too much silver solder such that at the areas of concern the silver solder is 2mm thick. This was easily achieved because the firebox tubeplate formed a tray in which the silver solder could settle when the boiler is placed on end resting on the boiler barrel. This position is the most convenient for tackling the leaks at the firebox tubeplate. Recognising that to continue using propane only is counter-productive because the large propane torch heats more area than necessary, I solicited the assistance of a colleague with oxy-acetylene. Having two people, one providing preheat and background heat, whilst the other used the oxy-acetylene to hit the areas where the leaks occur. We have had two attempts at correcting these, but to no avail. There appears to be a partial lack of miniscus between the firebox tubeplate and the flue tubes, which only becomes apparent after pickling. The partial lack of miniscus is replaced by an almost descernible crack.

I can only think that the excess silver solder is partially causing the problem, so Iam thinking of ways to remove this excess. One way is to orientate the boiler in its normal position, that is firebox pointing down and apply the large propane torch from underneath and heat the tubeplate to temperature and let gravity remove the excess. This is a bit hit and miss, so if anyone has ideas for removing this excess I shall gratefully receive these.

Brian

[jo479]

Are you using a scratcher to go round the tube ends while the solder is liquid and fluxed, worth a try before trying to melt it all off, or indeed afterwards, if I'm trying toeach my granny to suck eggs, I apologise

[runner42]

Jan 26, 2022 18:05:53 GMT jo479 said:

Are you using a scratcher to go round the tube ends while the solder is liquid and fluxed, worth a try before trying to melt it all off, or indeed afterwards, if I'm trying toeach my granny to suck eggs, I apologise

A good idea and something we have already tried. Because I am not the owner or user of the oxy-acetylene I was applying the background heat to the outside of the firebox so I did not see how my colleague was using the scratcher, which was a piece of bent thin rod sharpened to a point. He is an experienced boiler maker so I am sure that what he was doing was scratching at the leaking points. 

Ther is silver solder on the flue tubes and on the firebox tubeplate. The leak manifest itself as a very fine crack between the flue tube and firebox tubeplate, so I would have thought that re-melting the silver solder would bridge the very fine crack. The silver solder isn't a gap filler, but this is so fine that it should have bridged the gap.


Brian 

[Cro]

Sorry to be a bit of a pessimist here but we are talking pressure vessels so my thinking is a little "air on the side of caution" but if we are talking about cracks on parts of a new boiler (which suggests a difference of expansion has occurred during a heating forcing something where it doesn't want to be) then I would be seriously concerned for the use and life of the boiler - especially considering the amount of solder you suggest is now in place and still not rectifying the issue.

I know you have put a significant amount of work and obviously cost into the boiler but I do fear for what people's view on it will be considering these issues if you even find a way to fix them.

Once there is that much solder in place it tends to just pool where it wants to be and as you are finding is very difficult to direct because by the time you are at the temperature you need to add any more solder or try to get it into the crack it flows into the puddle of molten solder. Trying to remove all of that solder is full of risk as to get the solder to run down the face of the tubeplate ideally it wants the whole tubeplate at solder melting temperature so it doesn't cool and clump on its way but you risk losing the fillets of solder around the other tubes and creating more leaks. I'm honestly not sure what the answer is here.

[springcrocus]

Based on my somewhat limited experience, I suspect you will be unable to effect a repair just by adding or removing solder. You may well find that the troublesome joints have become oxidised and the flux is unable to get through and do it's work. All you are doing is floating a thin skin on top of the fault which gives way again at the first opportunity. You may well have to drill out the affected tubes, clean up the tubeplate holes to nice clean metal and then set in new tubes as required. Doing it this way, your flux gets a chance to do it's job.

Regards, Steve

[uuu]

My experience, like (and shared with) Steve's is limited - but - it is very clear that the solder will only flow into a joint that is full hot. The famous "solder will flow to the hottest part" idea. To get the heat to the other side of your joints is going to be very hard. During the build of Steve's boiler, we had to come up with some cunning plans to get heat into semi-inaccessible places. So we tried squirting a cyclone burner into the dome hole (which did have an effect - we could get the tubes to glow and the heat worked its way up) and trying to get heat the full length of the tubes (which was less so).

The danger is that just heating from one side that you get a bridge, but full penetration is not achieved. If enough of the tubes are properly done to provide the necessary structural support, you'll be OK (if your inspector is OK with this). But several adjacent tubes with doubtful joints makes me nervous.

Wilf

[runner42]

Yes the problems are due to a difference in expansion, since the flues and tubes were all soundly silver soldered at the part assembly stage, eyeballed by the BI and given the OK for final assembly. The problem occurred after the smokebox tubeplate was installed and revisiting the firebox for small leaks in the stays did the problems arise. The flues were heated more than the barrel and as a consequence the force of expansion caused the cracking. 

Our approach is in recognition that oxidisation has occurred deep in the crack and is difficult to access due to too much silver solder is to change the pickle from citric acid to sulphuric acid which will be more robust in its cleaning capability. Both the BI and other boiler makers are optomistic that it can be fixed. It may be that caulking methods will eventually be required since the problem lies only in leaking and not the strength and safety of the boiler.

Brian   

[daveburrage]

100% agree. I've had this problem more than once, if you don't get the tubleplate right first time (ie as a sub assembly) its virtually impossibe to re-seal on a assembled boiler. Provided the boiler is sound structurally comsol caulking is the way to go. The other (more drastic route) is to cut away the smokebox tubeplate so that expansion/contraction no longer pulls on the firebox tubeplate.

regards

Dave Burrage

[runner42]

Feb 10, 2022 17:00:32 GMT daveburrage said:

100% agree. I've had this problem more than once, if you don't get the tubleplate right first time (ie as a sub assembly) its virtually impossibe to re-seal on a assembled boiler. Provided the boiler is sound structurally comsol caulking is the way to go. The other (more drastic route) is to cut away the smokebox tubeplate so that expansion/contraction no longer pulls on the firebox tubeplate.

regards

Dave Burrage

The caulking method is to use 965 solder which is a 5% silver soft solder lead free that can allow subsequent silver soldering on the boiler to occur without the problem of copper being affected, which occurs with lead based soft solder. In the event that part of the boiler that has been caulked with 965 is heated to silver soldering temperatures the 965 mixes with the silver solder to form an alloy of both materials. 

Brian