TIG welded copper boilers

[Nick Clarke 3Participant @nickclarke3]

Posted by noel shelley on 21/10/2022 11:26:58:

Having started to build a copper boiler to a well known design only to have my club boiler inspector refuse to test the boiler as he did not consider the design to be safe, not withstanding that it's designer was well respected AND that it complied with the oft mentioned Australian rules left me feeling very strongly on this matter ! Noel..

I feel that it is important boiler examiners have the freedom to refuse to test any boiler presented to them, but they need to be able to justify this decision, and if necessary be taken to task. However in practical terms as a boiler inspector is often a senior and respected member of a club and differences like this can split a club in two, this is often hard to do.

What is interesting is that looking back in time expertise as defined today is not always there. The boiler designed for the Willoughby GWR Dock tank was solder caulked and rivetted. LBSC did not visit clubs and his boilers don't seem to have been tested apart from when first built. Also he used brazing spelter a lot at first and later Sifbronze which would be frowned upon today. Both J.Austen Walton and Keith Wilson recommended self fluxing on copper alloys and neither Martin Evans nor Don Young built enough boilers to be experts. L,C.Mason and W.J.Hughes in the traction engine world produced designs for their engines that have turned out to be excellent – but again their designs were few in number.

So even a well known design really should come under the supervision of a boiler inspector for their wider experience.

Edited By Nick Clarke 3 on 21/10/2022 16:06:22

[JellyParticipant @jelly]

Posted by Luker on 21/10/2022 13:19:18:

Posted by Jelly on 21/10/2022 12:30:01:

Posted by Luker on 21/10/2022 07:10:10:

Posted by Jelly on 20/10/2022 23:04:54:

…

In fairness, I wasn't explicitly thinking of copper when I wrote that but of low-carbon steel and stainless steel, which are the de-facto materials for any welded pressure vessel design in my professional life.

I'm more than willing to accept that copper has it's own specific faults and modes of failure.

The OP was for a TIG welded copper boiler, and this is to save the cost of silver soldering the joints. I’ve only built (TIG welded copper) one such boiler and it still steams just fine (10 years later).

I don't doubt that it does, my whole point was that compared to silver soldering, there's a lot of additional nuance to what makes a good or bad weld, so it's not unreasonable that the code (which is agreed with the insurers) insists on an increased level of scrutiny of the process.

 

Posted by Luker on 21/10/2022 13:19:18:

I agree with you questioning the use of copper instead of stainless. To digress a little, stainless steel TIG welded boilers work incredibly well. I’ve designed and built 4. Life cycle fatigue (and surface potential calculations for corrosion cracking) is normally catered for in the design phase and cannot be determined by NDT, but that is outside the scope of this thread. Boiler plate is technically more difficult to TIG weld than stainless (and normally not recommended), so we need to be specific with materials and welding procedures.

I am entirely unsurprised that the stainless boilers you have built worked out so well, and I'd be interested to learn more about the design options it offered you over "traditional" methods.

Out of curiosity, do you mind me asking why stainless over carbon/alloy steel, was it just the corrosion / water treatment aspects or was there more to it?

 

Posted by Luker on 21/10/2022 13:19:18:

Life cycle fatigue (and surface potential calculations for corrosion cracking) is normally catered for in the design phase and cannot be determined by NDT, but that is outside the scope of this thread. Boiler plate is technically more difficult to TIG weld than stainless (and normally not recommended), so we need to be specific with materials and welding procedures.

My point around lifecycle fatigue and corrosion cracking is that (and it's probably more common or at least has happened more often with carbon steels than any other material) is that weld defects (or even just poorly executed welding processes) can introduce unintended failure modes, by deviating from the design intent.

The Alexander L Kielland disaster is a particularly good example: a badly executed non-load-bearing 6mm plate to pipe fillet weld, caused a stress concentration in the structural member to which the weld, this in turn created fatigue cracking in the structural member, which in time snapped the oil rig in half, capsizing it and killing 123 people; whilst the investigation found the lack of structural redundancy was a major factor in the disaster, it was also made clear that had the weld been executed properly, the rig would have functioned as designed and not snapped in half…Despite the fact that as a non-load-bearing joint to hold a bolt that secured a sonar transciever no one at the yard which built her thought the weld mattered.

Your comment about it not being preferred to use TIG for boiler plate, whilst that's generally held to be "the best" process for stainless only serves to further illustrate the relative complexity that welding introduces relative compared to soldered construction.

That complexity is not a bad thing, it is just something which needs to be managed.

 

Posted by Luker on 21/10/2022 13:19:18:

Of course if you weld with clothe hangers, and rusty wire you’ll get rubbish… I’m not sure why anybody would TIG weld copper with Phosphor bearing rods, this doesn’t make sense.

I was specifically referring to the fact that if you use rods intended for welding Oxygen Free Copper to weld Phosphorous Deoxidised Copper, the lack of a deoxidant additive in the rods will result in embrittlement or even porosity.

And if you bring hard-pitch copper base metal into the equation (which is still used in full-size heritage steam, and other niche applications) instead of de-oxidised or oxygen free copper, then you find yourself having to Oxy-Fuel weld with a very specific flame condition (I think MMA/Arc is also technically feasible but I've never known it to be done.)

Edited By Jelly on 21/10/2022 16:10:05

[JellyParticipant @jelly]

Split post because too long

Posted by Luker on 21/10/2022 13:19:18:

Engineers solve real world problems from first principles. Bureaucracy hamstrings that process by adding unnecessary constraints restricting solutions. I.e. How does a professionally checked sample add any more value than having a technically competent club boiler inspector check the sample, and then help and guide the model ‘boiler maker’?

Society, People, Money, Law are all part of the real world, and they inevitably pose problems which are much more complicated and intractable than mere physical phenomena.

"In general, people are averse to risk", and "Society as a whole is bad at discussing the concept of acceptable/tolerable risk" both hold true about as strongly as the Laws of Thermodynamics at the present moment, and I can't see any sign of that changing in my life time.

So the fact that we have societally imposed limitations, (usually as a reaction to the errant behaviour of others in the past) is in my mind just part of the design landscape…

Edited By Jelly on 21/10/2022 16:10:39

[LukerParticipant @luker]

Posted by Jelly on 21/10/2022 16:08:03:

Posted by Luker on 21/10/2022 13:19:18:

Posted by Jelly on 21/10/2022 12:30:01:

Posted by Luker on 21/10/2022 07:10:10:

Posted by Jelly on 20/10/2022 23:04:54:

Out of curiosity, do you mind me asking why stainless over carbon/alloy steel, was it just the corrosion / water treatment aspects or was there more to it?

And if you bring hard-pitch copper base metal into the equation (which is still used in full-size heritage steam, and other niche applications) instead of de-oxidised or oxygen free copper, then you find yourself having to Oxy-Fuel weld with a very specific flame condition (I think MMA/Arc is also technically feasible but I've never known it to be done.)

Edited By Jelly on 21/10/2022 16:10:05

The choice of stainless was actually based on thermal simulations of one of my boilers. Counter to popular belief, the lower thermal conductivity has benefits for the heat transfer and nucleate boiling on the tubes. Practically, if I compare two of my boilers with similar volume/heated surface area the stainless steel does outperform copper. It also stays much cleaner inside the boiler. I checked one of my stainless boilers that has been steaming for a little under 6 years and when I put the scope down the wet-leg there was no build-up. The copper boilers have scaled far more than my stainless boilers. Bear in mind that my boilers are relatively small, and if I were to ever make a large loco I would go for steel.

Pitch copper or oxidised copper is another animal entirely, but not that common nowadays. You'll pick it up quickly when you try to TIG weld it (will just make a porous weld).

[D.A.GodleyParticipant @d-a-godley]

Jelly , Clearly you know your welding , and are out to have the last word over Luker .

It is my view that your replies have been most educational, but in some ways off the mark from the original question revolving around tig welding of copper boilers .

It must be in the interests , long term , to settle on a simple set of regs which enable a confident , experienced model engineer to construct a Copper Boiler using the most up to date technology available and which performs as well , or better , than the methods currently used .

If this requires higher test pressure test for tig boilers , assuming the design will theoretically cope , then so be it , but I come back to the basic issue , if silver soldered boilers are seen as acceptable when made in the home workshop , then tig should be seen in a similar light since both operate under the same conditions .

Test samples are a wast of time , unless done in the presence of the Club Boiler Tester , but that still would need to be finely examined with almost laboratory standards , which is not done for silver soldered boilers , however , I see no problem with the intended builder producing the materials and some proof of their source / quality for examination by the Tester prior to commencement, and perhaps some form of staged checks .

FMES should be pushing this forward on behalf of the Model Engineering Fraternity.

Did I hear a rumour that some people are using a machine , controlled by a computer , to make parts ? What will the world come too ? .

[duncan webster 1Participant @duncanwebster1]

What many are ignoring is that we have to comply with UK legislation, it's not down to SFED. We have an exemption for silver soldered copper. Let's not rock the boat or we could lose that. Commercial builders can comply, and it shouldn't cost much in the scale of a couple of £k, as commercial guys can spread the certification cost across a number of boilers.

[Ken Chicken 1Participant @kenchicken1]

D.A. Godley asks: "At the point of hydraulic testing, does a tig welded boiler fail with a bigger bang than that of a silver soldered boiler?" – My observation: At an Hydraulic test, neither makes a big bang, as the stored energy is in the "spring" of the metal, and usually a tiny amount of compressed was trapped when the boiler was filled. – But the real difference is when the boiler fails at a TIG welded joint or silver soldered joint. – I understand under steam pressure, where the firebox is exposed and the top tubes become overheated, a silver soldered joint on a tube will fail due to the loss of strength of the silver soldered joint due to temperature. This will cause steam in the firebox, and loss of performance before becoming catastrophic. Otherwise, the Safety valve will prevent overpressure failures. However, a TIG welded joint failure is most likely at a hidden flaw in the weld which could become a catastrophic explosion from the stored energy of steam in the boiler as the joint fails at a point and rapidly over-stresses the adjacent copper or weld which fails "instantly" – and explosively as the escaping steam releases all the stored energy at once. – But that is all in my imagination as an engineer, not a TV/Film producer, so can be ignored.

"If not, where is the greater risk, it either satisfies the test requirements, as does a silver soldered boiler, or it does not, and there cannot be any greater risk involved since they both fail or pass that particular test before moving on to the next examination under steam." – agree, there should be no difference in "risk" – just consequence. When hydraulically tested, the boiler is NOT taken to extreme design stresses, just to a "proof limit" – which has been common practice for well over 100 years (Including many boilers that have failed in service).

Incidentally, ASME used in USA and many other countries uses a test limit based on Engineering calculation of stresses in materials at elevated temperature, so, in their wisdom they test at HIGHER pressures than we do in the UK. It is really all about interpretation of the science and maths to the real world, and what the Money Makers will tolerate. (Insurance companies, lawyers, etc.).

I trust my opinion expressed here does not raise too much blood pressure, I just thought the question deserved my answer.

Ken

[Ken Chicken 1Participant @kenchicken1]

Re: Nick Clarke:

"I feel that it is important boiler examiners have the freedom to refuse to test any boiler presented to them, but they need to be able to justify this decision, and if necessary be taken to task. However, in practical terms, as a boiler inspector is often a senior and respected member of a club and differences like this can split a club in two, this is often hard to do."

Fair comment Nick: Perhaps this is based on a bad experience? But the corollary is the aircraft industry, where many pilots (ex. RAF and extremely capable and experienced) became commercial pilots: When the people who do such things studied some crashes in the 1960s, they concluded that the "domineering" (Armed forces trained) decision-making by "the Captain" rarely, but catastrophically caused the aircraft to not perform as planned, and the remaining crew were "equally at fault" for not correcting "the Captain". Hence a new school of thought came in and trained ALL crew to work as a team – accepting expertise while questioning decisions where necessary, without fear of come-backs. – Surely this is the society and attitude we should be living in today? Perhaps this forum is such a "society"? – We all express opinions, and debate them, to find the best solution.

But equally, the inspector may have had good cause to refuse the test, as we don't know the full story. – And FMES codes, etc. permit that decision. e.g. I would "fly to the moon" with Neil Armstrong at the helm, but not Frank Sinatra! – Even if NASA had demonstrated how safe it was (like Apollo 13). And if Neil A refused to fly me I would stay on Earth. Sometimes there are other good reasons than "engineering" for choosing not to do something.

Ken

[Ken Chicken 1Participant @kenchicken1]

Interesting to read the comment "ME shell design safety factors are orders of magnitude larger than large scale." – My reading of ASME information suggests that in the USA and many countries, the rules are the same – based on the calculated stress in the materials.

On the suggestion that "Steel boilers are stronger than copper" – I propose that Steel can manage a higher stress than copper, but if you have enough copper it will be stronger than the "minimum" of steel. – The statement is too simple for proper decision making.

Also, the Regulations require an excess of material thickness in the steel as a corrosion allowance, but this thickness is "not permitted " in the calculation of stress in the material, although in the real world it carries some stress, reducing stress in the adjacent metal. You may only need 1 mm of steel, or 3mm of copper, but the codes state "1/4in minimum for steel" – so the boiler is stronger, but heavier, and allows for >1/8in of corrosion of the steel!

Putting it simply, it's just a case of horses for courses. The Engineer will calculate both, considering all the factors of cost, manufacturing capability, testing costs, corrosion protection, regulations, application and a host of other factors before deciding which design and materials are best for the job in hand. I.E. There is NEVER a simple answer to an engineering problem, in my professional experience. (Just "Simple Management" decisions based on fewer factors than the engineer will consider!).

Been there, dunnit, had Management make the wrong decision – then been asked to correct "the mess" and use the right decision originally proposed. – I have the chip-carrying shoulders to prove it.

Ken

[Ken Chicken 1Participant @kenchicken1]

Hi Luker:

I have picked-up on your comment: "At our club we emphasis good driving and boiler management practices; nearly all failures I’ve come across can be attributed to abuse while on steam. If the boiler passes the shell test and the safety valves are adequately designed and maintained, then any problems are driver related." – Commendable.

But I am not (and with a crocked back I never expect to be…) an engine driver. Though I once had a 3/4-hour session driving – under instruction of an experienced driver sitting behind me – a Pacific loco belonging to my club. An interesting experience, but it led to a week of suffering a bad back, so "never again".

But I have seen (at more than 1 club) locos that are sitting – maybe in "station areas", or sidings – and the safety valves are blowing-off quite excessively. Surely this is a "bad practice" – as in my experience in industry (Compressed air equipment), the only times you would expect "a safety device" to function would be as a consequence of "poor management or maintenance" of the system. I have seen a commercially run railway where the driver had the safety valves blowing well for a full lap or more of the track. I do not know what effect this may have on the safety valves – e.g. a deterioration in their accuracy, requiring resetting? – or something? But I would guess that the fire is simply too big and too hot, so risking excessive heating of the firebox and/or superheater tubes? Can you advise the "good practice" required? – and what is considered permissible for the safety valve continuously blowing off? (Perhaps at initial firing, to be sure it operates at the correct pressure on the gauge?). – My guess is that a driver could set the gear in mid-point (neutral), open the cylinder drains, open the regulator a touch, to keep the cylinders warm while venting some excessive pressure, while he tends the fire and water level and stabilises the system?

My practice (Gas fired stationary boilers running static steam engines) is to bring the boiler to pressure to check the safety valves(s) at the start of every firing, but then drop the fire down (easy with a gas valve) to maintain the NWP (which is just below where the safety will operate) for running whatever engine. If the engine is happy at lower pressures, then I drop the boiler pressure to the appropriate value for the engine. But apart from the initial test on first firing-up, my safety valves never operate. – Seems common sense to me? – But am I using "bad practice"? – What is "normal" practice in industry/your club?

Ken

[Ken Chicken 1Participant @kenchicken1]

D.A.Godley, Duncan Webster, I wish to comment on your recent posts:

"to settle on a simple set of regs which enable a confident, experienced model engineer to construct a Copper Boiler using the most up to date technology available and which performs as well, or better, than the methods currently used." – Perhaps I am wrong, but reading all the stuff I have been able to obtain from FMES and others seems to give us exactly what you request? – And in the USA and other countries, ASME et al do basically the same?

"If this requires higher test pressure test for TIG welded boilers" – I disagree, I think "all boilers should be equal", as it is the basic material strength and shape that determines the stress in the materials, and joint design should always be well in excess of these limitations.

"If silver soldered boilers are seen as acceptable when made in the home workshop, then TIG welded boilers should be seen in a similar light since both operate under the same conditions." – here's where I and some others disagree, because the processes are different, joint designs and process control are different, and the skill in making and recognising a "good" joint are different. – Most model boilermakers use silver soldered assembly as the (proven) designs readily available are all of silver soldered copper boilers. To make a model to a design that exists, but using a TIG welded copper boiler, would need a whole lot of examination, testing and proving of the "new" design, as the national regulations existing have different criteria for joint designs, etc. for the different processes.

"Test samples are a waste of time, unless done in the presence of the Club Boiler Tester" – I almost agree, but Regulations require sample welds (to prove the welders' competence) to be done in the presence of an Accredited Welding Examiner, and usually tested to destruction or sectioned, etc., for examination, not by the "Club boiler inspector" unless he happens to be that accredited welding examiner. Then when the WELDER is certified, he can do the welding on pressure vessels. The Quality is thus assured by having a certified Design, Process, Materials and Man. Not by the final test witnessed by the Club's boiler inspector. The responsibility of the inspector is to thus certify the hydraulic test, a visual examination, and completeness of the documentation of the new boiler. – e.g. if the design is for silver soldered joints, then welded joints will be rejected – and vice-versa!

And the comment "We have to comply with UK legislation, it's not down to SFED. We have an exemption for silver soldered copper" is most appropriate.

Incidentally, without wanting to rock the boat, it is relatively easy to take any old design – that is proven by "historical use" – and demonstrate that it would be rejected as a new design according to ASME or other Regulations, but the "Historical precedent" allows insurance companies, etc. to accept these exceptions to current regulations. But NEW designs (such as TIG welded copper boilers) must comply to the latest regulations. As we expect all commercially made boilers to do so.

Hope this is OK?

Ken

[LukerParticipant @luker]

Posted by Ken Chicken 1 on 22/10/2022 09:01:49:

Hi Luker:

…Surely this is a "bad practice" – as in my experience in industry (Compressed air equipment), the only times you would expect "a safety device" to function would be as a consequence of "poor management or maintenance" of the system. …

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.

[Nigel Graham 2Participant @nigelgraham2]

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.

'

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.

'

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.

'

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….

[SillyOldDufferModerator @sillyoldduffer]

Posted by Jelly on 21/10/2022 16:08:55:

Split post because too long

Posted by Luker on 21/10/2022 13:19:18:

Engineers solve real world problems from first principles. Bureaucracy hamstrings that process by adding unnecessary constraints restricting solutions. I.e. How does a professionally checked sample add any more value than having a technically competent club boiler inspector check the sample, and then help and guide the model ‘boiler maker’?

Society, People, Money, Law are all part of the real world, and they inevitably pose problems which are much more complicated and intractable than mere physical phenomena.

"In general, people are averse to risk", and "Society as a whole is bad at discussing the concept of acceptable/tolerable risk" both hold true about as strongly as the Laws of Thermodynamics at the present moment, and I can't see any sign of that changing in my life time.

So the fact that we have societally imposed limitations, (usually as a reaction to the errant behaviour of others in the past) is in my mind just part of the design landscape…

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

[Ken Chicken 1Participant @kenchicken1]

Thanks Dave. A good response. I concur. Having been "the Engineer" in various different offices and factories, dealing with design and manufacturing compliance with Regulations for various (and interesting) regulated products, I have experienced the "bureaucrats" – and in part have been one. The Committees are usually made up of a variety of "trades" and "experts". One product (High Voltage circuit breakers for the UK National electric power grid) had the committee made up mostly of ENGINEERS from the Electricity Board, Manufacturers, and users, and the support of lawyer(s) and other where other expertise was required. Another (Cars for Public roads) was made of ENGINEERS from the SMMT, vehicle Manufacturers, etc… I.E. The "best" ENGINEERS for the job of writing the rule book for the rest of us to follow. And after 45 years or so found them to be a good bunch of guys who looked in detail at the whole picture, not to supress anything good, just the occasional "bad" practice or omission. I certainly welcome regulation as it makes the design job easier. – Managers argue against the Engineers' decisions much less when told – "If you don't adhere to these Regulations you (the top management) will go to jail." Many have in my experience: Top Directors from Japanese, European, American and British companies have all spent time in prison as a result of breach of regulations in the car industry, within my experience. But they rarely get into the news. Just retire afterwards as NOBODY will employ such people afterwards.

But I am not a certified welder.

That is just my experience and opinions.

Ken

[Bob WorsleyParticipant @bobworsley31976]

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.

[Nigel Graham 2Participant @nigelgraham2]

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.

'

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

[LukerParticipant @luker]

Posted by Bob Worsley on 04/12/2022 18:33:03:

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?

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.

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