Chasing pinhole leaks

[Deleted]

Hi All.

Progress in the little boiler I am building has been slowed in various ways, such as domestic circumstances, but I am especially frustrated by pinhole leaks. At the appropriate stage, the formative boiler was given the all clear by my society inspector and thus I went away to progress it further, with my intention being that I would not visit him again until I satisfied myself that it passed its first hydraulic test. Having completed the fabrication of the boiler, I carried out a hydraulic test and at 80psi found a few pinhole leaks. Having drained down, these were re-soldered and the test carried out again. A recurring cycle started of test – pinhole found – drain down – solder. Eventually I stopped even trying a hydraulic test and just tested on air, with detergent as a means of spotting the leaks. Clearly, the re-soldering is weakening other joints, maybe even to the extent of re-mobilising and losing some of the solder alloy. This is frustrating and I would be grateful for your thoughts please.

With thanks,

Dave

[Deleted]

Further info:- heating apparatus is mostly Sievert 2941 general burner but a Sievert 3524 cyclone burner has also been used inside the firebox; flux is Easy-flo and silver solder is SilverFlo55, although at the doorplate/firehole ring joint, Silverflo24 and Tenacity5 flux was used. At the time of writing, the pinholes are at several of the side stays and possibly at one of the tube/tubeplate joints in the firebox. Construction is as specified on the drawings, although, with boiler inspector’s approval, the screwed/blind nipple side stays originally specified have been replaced with 1/8” copper rivets, which protrude from the wrapper by ~1/8”.  Use of these older stays might well have prevented some of the pinhole leaks now being experienced!
Thanks

[robmort]

I had this problem with an earlier boiler. As you say, repeated re-brazing does not work. The simplest solution is to use a radiator sealant of which there are many on the market, or simply a bit of porridge! This is a permanent solution believe it or not. This is also assuming the joints are structurally sound.

[daveburrage]

My experience is that where expansion effects come in then that is where re-brazing is difficult. I've not had much problen re-brazing stays for exanple (although I have got the luxury of oxy-propane). Firebox tube plates on the other hand seem to suffer badly from expansion effects (presumably the difficulty of keeping outer shell and tubes at similar temps). Repeated re-heating sees the tubes actually start to move out of the plates. My thoughts are - if its a pin hole in the firebox tubeplate - use HT soft solder.

regards

Dave Burrage

[jackrae]

Oct 23, 2016 9:24:39 GMT robmort said:

I had this problem with an earlier boiler. As you say, repeated re-brazing does not work. The simplest solution is to use a radiator sealant of which there are many on the market, or simply a bit of porridge! This is a permanent solution believe it or not. This is also assuming the joints are structurally sound.

Working to scale I presume a canary egg would be about the right size to replace use of a hen's egg in leaking car radiators (just showing my age

[nonort]

I would suggest a couple of things. After preparing all the joints up heat the entire boiler to near melting point of the flux. repair the pin holes as required and then spend a long period with the torch still lit letting the heat off gently. I suspect that some of the pin holes are being caused by the cooling contracting effects. For very small pin holes I have used 'water glass' which sets permanently and unlike some products will not cause priming. The first priority must be to make sure that the pin holes that you are trying to seal is fully sound in all other aspects, fully penetrated and good fillets.

[philh1aa]

Gents,

Are you guys suggesting that if I have a couple of pin hole leaks in the silver soldered firebox - it is ok to repair with HT soft solder?

Background:

I part built a Rob Roy boiler about 30 years ago. I built the majority of it to the old book published in 1972. It shows threaded longitudinal stays in threaded unions that are screwed into the backhead and smokebox tubeplate and the regulator (smokebox end) is also screwed directly into the tube plate. It also shows the top water gauge fitted with screws and sealed with high temperature soft solder. I followed this design but used 1/8" rivets silver soldered into the firebox sides in accordance with more modern practice. I have already received some advice which suggests that my boiler should be fine and the horizontal stays can be sealed with high temperature soft solder etc. My main concern is the work that has already been completed. If I pressure test at say 25lbs/ sq inch and discover that one or two pin holes in the side stays - is it ok to repair using HT soft solder?

Phil H

[uuu]

As with all things boiler related, the advice of your boiler inspector is paramount. No point arguing that so-and-so on pro boards said it would be fine if he disagrees.

As noted by nonort, if you have a leak, there's a big difference between one which indicates a structural weakness, and one where the boiler is sound, just with a "pinhole" as you describe it.

We've faced the challenge of chasing pinholes several times in the Pumphouse. Heating to silver-soldering temperature has frequently opened leaks elsewhere. Better results have been achieved with soft solder, or with gentle peening.

Good luck.

Wilf

[philh1aa]

Thanks Wilf,

I was a member of a club and will be going back shortly. However, I feel that it is better to go back to the inspector with a reasonable view rather than no view at all. Looking at my boiler, I would say that it is structurally sound but untested at this point. If there are any tiny holes, I would not wish to waste time if it is not necessary. However, if the inspectors opinion suggests, even slightly, that there is a lack of integrity then I will definitely be reaching for the silver solder.

Thanks,

Phil H

[jma1009]

Hi Phil,

If you can only get your Rob Roy boiler up to 25 psi, then my usual pessimistic approach on these things is that something is amiss and you need a club boiler inspector to have a close look and a pressure test, and obviously you must first rejoin your local club.

What might be a pinhole weap at 25 psi might be a gushing tidal wave at 160 psi. If you cant keep pumping at a boiler test rig to get the pressure above 25 psi then something is seriously amiss I suggest!

Cheers,
Julian

[philh1aa]

Hi Julian,

Its the same Phil H from the other site/e-mail.

I am guilty of following the book again. The book (years out of date) suggests doing the main silver soldering followed by a 25 psi test. The next step was to fix the stays with HT soft solder and pressure test fully. The book suggests any weeps/ pinhole leaks identified during the first stage are repaired with tight fitting 10BA screws!

I will be going back to my local club, hopefully next week and Ill get back to you to let you know what happened with my 30 year old saga when I have had the discussion.

Thanks,

Phil H