TIG welded copper boilers

Hi Ken, yep otherwise they would be called 'don't know how to drive valve' instead of safety valves. Easier said than done but should be a matter of pride to try and drive without letting the safety's blow off. They should be designed to prevent damage to the boiler even with a good fire and blower on full, so in theory nothing should get damaged. I don't bother with keeping the cylinders hot in the station, on my scale I seldom get priming even after a good chat in the station.

Our rule is, in the station the loco needs to have the reverser in mid-gear to prevent mishaps if the regulator isn't shut properly.

I would say your control of your gas-fired boiler is very good practice, but it is a lot easier to maintain a suitable pressure with gas or oil firing than with coal.

It is good practice on a coal-fired engine, be it a locomotive, traction-engine or stationary plant, to try to fire at a rate that maintains the pressure just below blowing-off, and having the safety-valves lifting hard all the time shows a waste of fuel and water. The official publications for British Railways engine crews, by the British Transport Commission, go into this; and if it was good enough for the professionals crewing main-line locos on a state railway system, it's good enough for us on our miniatures!

It is not easy and requires a good deal of experience with the partlcular locomotive, but I'm afraid a few drivers of miniature engines seem never quite to grasp the principles, one or two apparently thinking the blower has to be on hard all the time, even when the train is in motion. To be fair, a lot of that is inexperience by not having locomotives of their own, and few opportunities to drive the club one.

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Good boiler management on a model locomotive is also hampered where the ashpan has no damper, as seems common; although the current writers on the subject are striving to raise design standards from prototypical aesthetic details, to hidden parts like enclosed rocking grates. ( LBSC's smaller designs don't even have ash-pans, just shields to deflect the ash from the motion.).

All miniature traction engines I have seen, do have dampers - if only because they are fairly prominent.

A brake ejector exhaust can also unfortunately act like a blower unless fitted so it does not do so, also making life more difficult. A full-size locomotive has two ejectors: the large for creating the vacuum fairly rapidly, the small for maintaining it vacuum. Most miniatures are proportionally only the large ejector, pushing a lot of steam and air up the chimney.

Scale helps too: the larger the engine the slower things respond, making it easier to control the fire especially at rest.

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On your other points: yes, it is wise to ensure both valves open at the indicated pressure at the start of operations, and also that the water-feeds work.

Warming the cylinders as you say, will work but only to a point because unless the engine itself is parked absolutely lead-for-lead on the valves (highly unlikely), steam is only being admitted to one end of each cylinder.

Long-term blowing-off won't put the safety-valves out of setting, but if habitual could erode the valve seatings by wire-drawing. A tip I was taught, by the way, is to lubricate the valve stems with a wee spot of cylinder-oil, during the initial steam-raising.

The fire can be too lively, so wasting waster and coal, but by generating too much heat, not by being too hot. (Quite different things.) The fire-bed will indeed be hotter but the boiler plates and tubes will stay at the boiling temperature of the water at that pressure.

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I am not involved with preserved Standard Gauge railways so I don't how how things are in general there, although I have heard a good many anecdotes expressing worries that the general level of steam-locomotive firing skill is diminishing, on some at least.

Many years ago my club built for its portable miniature railway a 7-1/4" g version of LBSC's 0-4-0 ST 'Juliet' - and with the ashpan the original lacked, though still no damper.. It had a steel boiler, built by a professional welder though unfortunately not one knowing locomotive boilers (thereby hangs another tale...), from ordinary mild-steel pipe-line tube and hot-rolled plate. That was decades before all the present fuss and rhubarb about certified materials - later events with this locomotive showed its the design and fabrication that really matter..

We two members who probably operated it most frequently learnt how to set this quite small engine to simmer for half an hour or more, with an apparently black fire. A few minutes with the blower soon woke it up.

This came in useful at a particular traction-engine rally we attended for several years with the railway, as with just two of us, we could have our lunch in peace - with at least one of us always by the engine.

One lunch-time there a young man driving a (full-size) roller arrived, parked it between us and the nearby refreshment-tent, and vanished inside. Soon, the roller's safety-valves were blowing off hard.. Some twenty minutes and more later and my pal and I started wondering if we ought take a discreet look at its water-gauge and if necessary suggest to the bloke in the bar his engine might like a drink too.

Then he re-appeared, put the injector on, and noticed us watching him rather critically. He wandered over, said he was driving it for the owner unable to be present that day, and added this gem:

"I'm a fireman on the ----- ----- Railway, and you should see how I have 'em blowing off there!"

My mate and I, sitting behind a little model locomotive that was simply making contented hissing little noises in her snoozing, just exchanged looks....

Exactly my view, and it's the engineer's job to deal with societally imposed limitations just as he deals with the shortcomings of materials, tools, and processes.

With all respect to the excellent Luker - I'm a big fan - there's a problem with his statement 'Bureaucracy hamstrings that process by adding unnecessary constraints restricting solutions.' It's full of words that suggest a personal attitude, which is an obstacle. 'bureaucracy, hamstring, unnecessary, constraints, and restricting' all suggest Luker personally regards the subject with disfavour. This is dangerous because personal approval or disapproval might mistakenly presuppose the thing being discussed is intrinsically good or bad.

This example illustrates the point: As an Englishman I claim 'The British are a reserved, somewhat unemotional, persevering people.' An enemy might describe us as secretive, cold and pigheaded! We are both describing the same qualities. Does either description help solve a problem?

But the real issue is the danger of failing to make progress because of an assumption. Imagining a problem can only be fixed by removing 'bureaucrats' creates an impregnable barrier. It's unhelpful because no-one is described as a Bureaucrat in their job title and because 'bureaucrats' aren't the source of the problem. The rules are set by by someone else, usually the government or commercial terms and conditions. The root cause is a hard target, not a bunch of 'jobs-worths' who will be first up against the wall when the revolution comes.

As removing bureaucracy is never going to happen, the engineer has to work with the system, either within the rules, or by getting the rules changed. Although working the system may not be cheap or easy, it's certainly possible. In this case I think it requires more than an individual, perhaps a "Welded Boiler Society" containing people who understand the technology supported by folk who know how to solve non-engineering problems like getting an Insurance Company to take on a new risk, and raising money to support the cause. Blaming bureaucrats doesn't help if the goal is getting welded boilers generally accepted on public tracks. The engineer has to understand and tackle the full problem, not just the technical bit. It's unfortunate that the 'errant behaviour of others in the past' is a factor, but there it is.

On the subject of problem solving, answers are often easier the less one knows about the problem. Given 4 or 5 facts about an issue we can all come up with a jolly good answer that's likely to be wrong. In the real world many facts usually have to be taken into account, and ignoring them causes serious problems. Wishful thinking rarely works out well because progress usually requires a good understanding and hard work. So find out why clubs aren't keen on welded boilers and come up with assurances. Don't blame Boiler Inspectors: find a way of making them able to take responsibility for assuring welded boilers, which could include paying several of them to do a course...

Dave

I have carefully read this, and anything else i can find, on TIG welded boilers, but never seen any comment on the use of mixed metals in the boiler.

A copper boiler is a single metal, copper, plus the odd gunmetal bush. But what about the use of hundreds of monel metal stays? These are metal alloys, not a pure metal. Does TIG welding work with alloys?

When welding the actual metal is melted and the two. or more parts being welded form a liquid pool which cools and freezes, so what is the end result of this pool?

With silver solder the base metal does not melt, the solder does and forms a surface coating on the base metal, and this freezes.

These are quite different. Silver solder relies on the surface tenacity between copper and solder for the joint strength. With welding the joint strength is the inside strength of the molten and then frozen pool.

The basic question is, is my professionally built TIG welded boiler ok with monel firebox stays and other parts? Why?

I am not at home to look up a book I have written by a boiler inspector in the 1870's But the repeated failure mode of steel boilers is due to grooving, where water flowing in the boiler cuts its way through the plates, bang! The worst possible place for boiler feeds is where the boiler is hot, the backhead. And where in my professional TIG welded copper boiler are the two feeds? The backhead! Whilst it is said that an injector feeds hot water, can't be that hot, don't work with a hot feed water, basic principle of operation.

An interesting question but would pick up two points.

Firstly the grooving around rivets in steel boilers was often due, paradoxically, to the structure bing too rigid, throwing all the strains into the joints rather than some being absorbed by the plates themselves. The joints were all caulked, including round rivet and stay heads, so water could not flow through them until the fault was already developing. Once it did develop the erosion could continue unchecked.

Caulking here was not as in ship-building, stuffing the joints with a sealant, but forcing the steel into intimate contact by using special chisel-shaped punches.

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Secondly, although backhead feeds are not good practice but not completely unknown in full-size practice, an injector does feed fairly hot water. Not as hot as the water in the boiler of course, but certainly hotter than their own feed water.

An injector fails if it is fed with hot water because the initial condensing and combining breaks down, but in its passage through the device the condensate imparts a lot of heat to the water it feeds to the boiler.

This is one reason why if matched properly, an injector should be a lot more efficient than a pump which canb only feed water at tank temperature. DAG Brown details this in his book on making injectors, pointing out that almost all full-size steam locomotives had injectors but no pumps, and debatably perhaps there is no reason this cannot be the case for a model. (Bearing in mind the need for at least two independent feed methods - but which can both be injectors.)

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I cannot answer the welding question but would suggest that for a model boiler it is really about the metallurgy of the materials themselves, not the structural design and nothing to do with the plumbing.

Though I agree the feed clacks should still not be on the back-head anyway, especially from a pump; and they most likely were not placed there on the model's full-size prototype.

(So why on the miniature...? The club boiler inspector will not - or should not - fail a boiler whose clacks have been moved from model-design to prototype-design, locations; but I wonder why the model's illogical "deliberate mistake" in the first place.)

Edited By Nigel Graham 2 on 04/12/2022 19:39:41

Alloys can be welded with TIG most definitely. The characteristics of the weld pool will be determined by the phase diagrams and other calculations, and this will guide what the welding procedure should look like. Common alloys are easy because the work has been done already, but the new exotic alloys, or uncommon combinations of alloys, would require the welding procedure to be drawn up and weld qualifications done for the specific joints.

Monel and copper weld joins are no problem, because the nickel-copper alloy (Monel) contains the base metal that you joining (copper) and nickel which will weld to almost anything. Joining austenitic stainless to monel with a high nickel rod is no problem. Gunmetal is a little more difficult, but can be welded with the right filler rods provided you stick to the correct amperage (heat input) to prevent the zinc from gassing in the weld pool. You’ll see clearly if this has happened. Depending on the filler rod used and adherence to the welding procedure there should be no problems with these welds. My preference would be to silver solder the alloys that contain low melting point base metals that could fume, or has a very low melting point and could end up on the grain boundarys. Incidentally I’ve TIG welded copper to gunmetal with no issues.

If your ‘professionally welded’ copper TIG boiler was done by someone that understands the fundamentals of physical metallurgy and has welded the boiler by following the welding procedures the boiler will be more than adequate.