How do you fix a leak in steam loco copper fire box?

Hi

I know some one who has a coal fired 3 1/2" gauge live steam locomotive. There appears to be a leak possibly from one of the stays inside the copper fire box. Water drips slowly when filled but can't see exactly where it's coming from. This is a very difficult area to reach. All I know is its from the top crown of the firebox. The boiler is silver soldered.

How can it be fixed?

You could try peening the stay over. Or try some high temperature soft solder with some silver and no lead in it.

Hi

Firstly let me say that I know precious little about live steam so this might not be practical.

How about draining the boiler completely and then pressurise the boiler to a few psi with compressed air. Turn the loco onto it's side with the fire grate removed and paint the inside of the firebox with water mixed with washing up fluid. With luck a stream of bubble will appear and this should identify where the leak is. It might also be possible to estimate the size of the leak by the size and how rapidly the bubbles are generated.

While I appreciate that this won't cure the leak it could help identify the scale of the leak, its position and indicate how difficult a repair may or may not be.

Martin

Hi Simon,

Most if not all older miniature locomotives will have crown girder stays between inner firebox and outer firebox. These are secured in position by a few or more rivets on the inner firebox crown before silver soldering. These rivets are silver soldered in the course of the above, but sometimes they are missed or the silver solder does not penetrate properly.

Any repair attempt is determined by whether any of the adacent firebox stays are either comsoled and nutted threaded stays, or silver soldered.

Crown stay rod stays as opposed to girder stays are quite another matter.

A very careful examination of the inner firebox crown is required.

This requires the attention of an experienced club boiler inspector and his assessment and any repairs are going to be difficult.

Depending on the design of boiler and it's detailed construction (which you do not state or the design of loco or it's age, history and usage), and any inward bulging of the inner firebox crown on discovery of the leak, I would have serious doubts about an easy repair.

Usually such a leak would condemn the boiler.

Cheers,

Julian

It may (depending on the size of the gap) help in locating the source of the leak to do the following: obtain a length of polythene or silicone tubing of 5 or so mm diameter which you will use as a makeshift stethsocope. Using, say, an airbrush compressor apply low pressure to the boiler: 15-20 PSI over gauge will do. With one end of the tube at your ear, move the other end around the area of the suspected leak. Any small jets of air getting out of the boiler will show up very clearly.

Adrian

Use flouroscein?

The answer from Martin is the most useful, this will enable location of the leak(s).Traditional methods of leak cure involve eggs( the whites I think but not sure) and oatmeal. I believe that powdered rice is also good for small leaks.

Perhaps others know of different remedies?

Brian

At 180 PSI ?.....Colin

Not that it matters but where did 180 PSI come from?

Brian

There are two issues; finding the leak and curing it. Finding it is probably straightforward given the methods suggested.

As Julian says, fixing it properly is another issue, given that it is from the firebox crown.

From a vivid imagination I would guess Brian! There are not many 3 1/2" gauge loco's around that run at that pressure but even considering a retest after 'repair' at 2xwp which could easilly be 180 the old ways still work. Key is in the units, pounds per square inch!! Consider the sort of leak described and how big the 'hole' is. Can be measured in thou so then how many pounds force on that area?

For Colin's benefit, back in the day it was not unheard of to introduce oats or even potato to a leaking traction engine boiler with great success and many compound engines did indeed have working pressures between 150 and 200 psi.

For the OP, it is important to identify EXACTLY the source of the leak. If it is a weep around a stay then peening is probably the way to go, introducing heat into the mix especially if it's an old boiler is likely to result in further leaks. Does it leak when it's hot is the question. I know of a copper boiler, silver soldered with a weep on a tube on the FB tube plate, hydraulic can be easilly achieved and in steam when it's hot there is no leak. It's been running for years like that with no problem.

Paul.

Would K seal do it ? It fixed my Shogun head gasket 7 years ago , not used any coolant since..and i flushed it and filled with antifreeze ,which always finds a leak !

What a cowboy i am...

Brian, my 180 PSI came from the hydraulic pressure often required for the 2x WP on a repaired model boiler The trouble with using one of the bodges is that it precludes a proper soldered repair due to the inability to clean it properly whereas the full size traction engines were riveted.

Colin,

All fine and dandy, but...... If say the leak is on a stay head you can only properly clean the visible and accessible surface to silver solder which will give you a fillet on the surface. Cleaning the actual interface between stay and plate to acceptable levels to get the silver solder to wick into the space is all but impossible without removing the stay entirely. Given the access to work on even a large 3 1/2" gauge loco firebox even a silver soldered repair is not going to be a permanent job. Peening or 'caulking' the stay head is perfectly acceptable. Any repair is little more than a life extension and a delay of the inevitable eventual replacement.

Paul.

chances are that it is not fixable, regardless of location and access. Over time the leaking water reacts with the copper to form oxides throughout the 'crack'. No amount of pickling will shift them. Even with the outer surface ground back to clean metal ant the right flux the solder simply wont go into the crack. It goes everywhere ekse! This applies to silver solder, but using comsol you can effectively create a dam around the crack and pour enough solder into it to seal the whole area. Unfortunately this adds next to no strength to the already weakened joint, but it works.

Can I suggest that you ignore the idea of using soft solder - however tempting it might seem. It is likely that any such repair will make a future 'proper' repair with braze or silver solder impossible. When heated for the hotter solder, the repair is going to melt first and run about, soaking into the copper and turning it into a different alloy with unknown (and perhaps disastrous) properties.

Or not, of course. I'm sure some has done it and survived, and they will be in touch shortly ...

Cheers, Tim

There may be some fancy high tech way of accessing this if the leak is conveniently within a straight line from one of the access bushings..or perhaps on a larger boiler when one could insert a flexible viewing system. I used to have rigid endoscopes down to 1.2mm diameter and flexible ones down to 2.5mm. One had to get to bigger sizes to have an operating channel down them as well though they do make tiny laser guides for breaking up bladder stones in small sizes

Would it be possible to use a hollow, conical bit to create a space around a weeping stay, then make a circular copper or bronze ring to fit and silver solder that in place? You would need an oxy torch, I expect, to get the localised heat needed inside a firebox.