TIG welded copper boilers

Back in the sixties there were no cheap small welders, so to weld a boiler you would have to take it to someone who could weld properly or let you use their gear and probably keep an eye while you did it yourself to a reasonable standard. Today anyone can go out and buy a small cheap, MIG, TIG, MMA, be it a transformer type or inverter and start to weld. Understanding NOTHING of the process or practice ! With so many coming into model engineering from outside the field of engineering being able to buy equipment that requires years of experience and training to be able to use properly the issue of welded steel boilers has become more of a problem. How many boiler inspectors know enough about welding to be able to satisfactorily even test the samples, or even want to test the welded boiler ? In this day and age I'm surprised we are allowed to build any sort of pressure vessel, even a copper one !

Like Luker I would be happy to make a steel welded boiler, Though I agree with the need for a strict code for design and construction. That I don't think I have heard of a catastrophic boiler failure would seem to indicate that the current system works.

For anyone who thinks that slackening of standards is needed PLEASE read the book by Alan Mc Ewen, Historic Steam Boiler Explosions, The awsome power contained in a boiler that is realeased in a catastrophic shell failure is beyoud belief ! Stay Safe, Noel

Further to Noel's comment about the destructive capacity of a pressure vessel failure:

A colleague at work lost two fingers when a compressed air tank exploded.

In a book on US trains, there is a picture of the after effects of a 1953 explosion on a 1942 manufactured 400 ton articulated steam locomotive. It killed three enginemen, tore the boiler from the frames and severly damaged the track.

A steam boiler can be a very dangerous item. Not only does it contain a lot of pressure energy, but the steam contained under pressure is at high temperature, and so contains a LOT of heat energy.

At atmospheric pressure water boils at 100'C and it takes 536 calories to turn one gramme of water into steam.

So there is a lot of heat energy released when the steam condenses. Think of a domestic kettle!

At 70 psi the steam will be about 170'C so again, there is a lot of heat energy available.

In short DON'T take any chances with any pressure vessel, even a small one. Ensure that it is well made, and the materials used are traceable..

Model Engineering Clubs test boilers every year to maintain their insurance.

Howard

Hi Ian, I think I may have caused some confusion and I apologise. The point I was trying to make was that; as a Mickey Mouse welder with a Mickey Mouse setup I was able to TIG weld a copper boiler that has been running for many years. Whereas a well-known UK based professional boiler manufacturer failed dismally to understand some rudimentary basics in physical metallurgy, and joint design.

I've always thought the idea of model engineering was to develop as many artisan type skills as possible, and the best way to do that is to give everything a bash. Welding, like machining, is one of those skills that can be developed and honed by reading a few books and practice.

I would encourage anyone to give boiler manufacture a bash (this includes TIG welding copper). If the club has members that guide and help the builder, and a boiler inspector that keeps up with modern manufacturing techniques I can see no reason for a ‘poor boiler’ outcome. If on the other hand the boiler inspectors are not knowledgeable enough and are unwilling to up skill; that is an entirely different matter…

Hi, your original question: "How do TIG welded copper boilers compare with traditional silver soldered boilers? What are the advantages and disadvantages?"

My opinion:

Welded boilers - properly made and certified - will perform and last as long as silver soldered boilers.

Because of the controlled manufacture and certification required, they both meet the "same" standards - in the result that means you have a boiler powering your loco. I should not expect you to experience any difference when using your loco, even in 50 year's time. Abuse will destroy anything quickly, but treated with appropriate care (no difference between a welded or silver soldered copper boiler) they should both outlast many of us.

However, a steel welded boiler is a different animal. It NEEDS water treatment and more cars due to the normal corrosion of the steel.

Boiler testing and certification is basically the same, whatever you have on your loco. But the inspector may be trained to certify silver soldered copper boilers, but not other types, so won't do those. Check your local club, to be sure.

K

There should not be a problem with a club boiler inspector faced with a professionally-made copper-boiler, at all; and does not need some sort of extra training for them.

Without ploughing through it, I am pretty sure the matter is covered in the MELG book (the current edition, orange print on white covers). He might be nervous of a home-welded copper boiler, as that does need a particular grade of copper, unlike the "ordinary" metal suitable for silver soldered and indeed rivetted-and-caulked boilers.

Otherwise the test regime and methods are the same and are those laid down in the book, not invented or 'gold-plated' locally! (That tendency has caused problems, such as the bloke who refused a locomotive with a rocking-grate - the code does not even mention grates.)

The boiler inspector though, should have attended at least one reasonably recent, of the Boiler Testing seminars run from time to time around the country, usually once a year.

This exists in the form of the conformity assessment procedures of the Pressure Equipment Directive 2014/68/EU as implemented by the Pressure Equipment (Safety) Regulations 2016 SI 2016/1105.

Which in turn will likely require the design and execution to be conducted with reference to (for a fire-tube boiler) either BS EN 12953 or another relevant standard like the ASME BPVC with some additional sprinkles of validation done in the technical file for UKCA marking.

In some respects, this can seem to be quite onerous at first, however...

• boilers under 2lt are exempted from conformity assessment and must only meet "sound engineering practice", whilst the requirements get increasingly onerous as you increase the desired volume, and pressure...
• boilers where the gauge pressure (in Bar) multiplied by the volume (in litres), referred to as "PS​•V" is less than 50 are subject only to Module A "Internal Production Control", which is a self-certification process.
• where the PS​•V <200, then only modules A2, D1, & E1 apply, in which a final examination of the product by a authorised body. is an acceptable route to compliance.

From a model engineering perspective, many if not most boilers will fall into the first two categories, and those which move through to the lower category are likely part of a very large and complex model with the attendant expectations around cost.

​

The rub to the above statements about how much of the assessment criteria apply for "in-scope" boilers is that the person welding them up would need to take a weld qualification test to either ASME Code Part IX or BS EN ISO 9606 (or hold a valid cert already), to meet the criteria. This means that the person must:

• be genuinely very skilled at the type of welding they intend to use,
• be familiar with following a Weld Procedure Specification in a test environment,
• have the time to take at least a full day to go to a certification body and do a weld-test,
• have the money to do the same (it's not expensive, but it's not nothing, and would add up quickly if your design used several different welded joints with different WPS's)

However, the requirement to go and have quality assurance of your standard of welding done, does take the onus away from boiler inspectors to also be welding inspectors (which is it's own speciality entirely).

Edited By Jelly on 19/10/2022 15:34:06

In addition and I refer to professional Tig welded boilers which is the route I took, whilst the copper cost remin the sme the cost saving in silver solder is appreciable. Also the technique usually goes for a fusion welded shell with silver soldered bushes fo if at some stage there is a problem with a bush it can be heated to melt the solder and replaced. Not something you could do with a fully silver soldered boiler without fear of causing issues in other joints.

regards Martin

Noted: But the Midland Federation book (2018), and others, instruct: "The individual should know his own limitations and should not act outside his level of qualification or knowledge." - I.E. if you don't know "welding", don't inspect a welded boiler. - I can weld, but only after a bit of practice do my welds look OK. - 10 rods a decade does NOT make me a welder! - Nor an inspector of welded boilers! - Though my job has involved me with certifying welders after taking tests and destroying and examining their samples, communicating with the Welding Institute on various welding matters, Aluminium, steel and copper welding (Including MIG copper to aluminium), Hydraulic testing of air receivers, design of pressure vessels, Dye penetrant testing, micrographic examination, etc. - BUT I still do not consider that I have the "Sound practical and theoretical knowledge and actual experience of the type of system which is to be examined as will enable defects or weaknesses to be detected which is the purpose of the examination to discover". - The challenge I face is how to obtain such "knowledge and expertise," etc. and be certified "OK"...

Don't knock people who say "No, I am not adequately experienced" - or whatever, as they are being responsible within the Federation codes and national regulations.

Stay safe.

Ken

I wonder if anyone else is interested to know if the "well known UK based professional boiler manufacturer" mentioned by Luker is still in business?

I only know of two firms that advertise this type of construction, maybe there are others.

Andy

Unfortunately the UK FMES code is quite specific in saying:-

6.2 If welding is undertaken by a person who is not a coded welder the Inspector shall require that weld samples be made available for inspection and testing prior to the commencement of the welding of the boiler, or that the welder shall have proof of test pieces being satisfactorily tested within the 12 months prior to the jointing being undertaken. Weld samples shall be tested by appropriate testing laboratories.

The material being welded is not specified so both steel and TIG Copper are equally covered by this requirement if they are to be tested and certified.

While an amateur could I suppose meet these requirements, I suspect the expense of professional materials testing might be prohibitive.

£150-175 per mode (welding process and material type) for a ASME IX or BS EN ISO 9606 weld test which would meet the requirement of:

"the welder shall have proof of test pieces being satisfactorily tested within the 12 months prior to the jointing being undertaken"

Via national providers like The Engineering College, The Welding Academy and TWIcert (the certification body of The Welding Institute), most local colleges doing welding could probably arrange something similar via their external certification body.

That includes the coupons being tested internally (twice, examiner and verifier) and then externally including both NDT and destructive (sectioned and etched) testing.

That would almost certainly work out cheaper than commissioning bespoke materials testing on weld coupons by a lab.

Whilst that sort of money is not nothing, it's not really prohibitive either when considering the cost of building a boiler in the first place and the potential savings of using a welded construction.

Edited By Jelly on 20/10/2022 15:20:19

A look online confirms that a test is £175 from several places but that is for the test to become BS EN ISO 9606 coded and half of that is deducted from the £500 cost of the day - so it will still cost you £600 just for the test with no training beforehand - and if you don't pass it will be another £600 or no boiler.

This suggests that there is an opportunity to engage with a company like TWI who charges for the Assessor's time by the day (or a local college who are open minded) rather than per candidate.

That could allow a group of interested model engineers go take their weld-test together (like colleagues would in a manufacturing environment) to keep costs manageable.

Certainly Northampton College, where I did my C&G II arc and TIG courses, did 'coding days' with multiple paople as well as individual coding tests.

Fizzy has posted before that getting your welds non destructive tested is a cheaper route if they are not done by a coded welder. Whole boiler for less than £200 (steel)

Edited By JasonB on 20/10/2022 16:54:32

I think my Club's attempt to get the Welding Institute to visit and advise on TIG Welding of copper boilers, although welcomed and planned, fell through due to costs of certification and equipment. - Beyond the Club's financial resources. Then Covid, cancer, ageing personnel and a few other troubles hit the club, so that will not happen in the foreseeable future now.

C'est la Vie!

A gentle reminder not to forget two aspects:

Under the UK codes -

- A boiler built commercially, whether silver-soldered or welded, copper or welded steel, since (2012? I forget the actual year) will have complied with the Regulations and come with the appropriate paperwork.

- If home-built by welding, the materials, welder and welding have to meet certain regulatory minima.

'

- For the first case, the club boiler-inspector does not need know welding, weld-analysis, etc. The donkey-work has been done for him by the manufacturer, and he needs only follow only what the MELG book tells him - and only what it tells him.

- For the second, both the builder and the boiler inspector will need knowledge and equipment few model-engineering clubs are likely to have; and the inspector can decline to admire it on the basis of that lack.

'

In both cases - no gold-plating. No refusing feed clacks moved from the design's back-head bushes to a prototypical and preferable top-feed, a slightly longer shell or 4mm firebox plates instead of the drawing's 10swg! (Worry if bigger diameter or thinner plate.)

'

Please note that remark about test equipment.

Commercial boiler-testers and weld-inspectors have access to sophisticated NDT methods and tools - and the skill to use them - the majority of us lack. Consequently the MELG system does not call for them.

At the seminar I attended hosted by the Wimborne society, someone asked about ultrasound. We were advised not even to think about it.

They are not part of the test regime designed for amateur model-engineers, so using only simple, practical external examinations, hydraulic and steam-accumulation tests.

Please explain, because I am failing to understand the aversion to tig welded boilers .

At the point of hydraulic testing , does a tig welded boiler fail with a bigger bang than that of a silver soldered boiler ?

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 can not be any greater risk involved since they both fail or pass that particular test before moving on to the next examination under steam .

It's quite easy to make a weld which visually looks good but conceals a defect which makes it susceptible to rapid fatigue once in service.

Without NDT, the only person who can detect that is the welder who makes the weld (if they're knowledgeable/skilled enough to understand).

Consequently either detailed testing of the workpiece or validation of the skill of the welder is required.

As compared to the level of scrutiny that welded pressure vessels in industry come under, the model engineering approach to welding seems entirely proportionate.

I’m sorry Jelly but I don’t agree. ‘Rapid fatigue’ (low-cycle fatigue) failure is uncommon in welded copper (or copper in general for that matter) due to the ductility of the material and the heating/annealing during the welding process. When welds fail due to ‘cracking’ in copper it’s normally due to hot tears because of low melting point (elements) contaminants that never went into solution; or just poorly designed welds.

TIG welding isn’t very forgiving when it comes to visual inspection. Unlike some of the other welding processes it is very easy to pick up poor quality welds. In industry, 100% NDT is normally limited to dye pen and MPI, both of which won’t pick up root defects, and won’t pick up much more than a good set of eyes and some good light. UT and X-ray picks up root defects and sidewall fusion defects but this is practically limited to a percentage of the welds. Personally I have very little faith in these reports, they only good for the bureaucrats and lawyers. I’ve stopped a few components from going to site where all the NTD passed inspection scrutiny but visual inspection made me look a little deeper and low and behold there were welding defects that were very dangerous.

To Godley’s point (and I agree with him): In industry, as with hobby boilers, my go-to has always been the pressure test and the visual inspection of the welds. It’s not easy to gippo these two tests.

The sad fact is; with all the legislation/ bureaucracy and club boiler inspectors that are unwilling to up-skill you effectively limiting innovation and restricting the hobby to people with deep pockets. Where, in the past, the rest of the world was looking to the UK for innovative designs and manufacturing techniques with our models, now it seems like other countries are leading, especially with boilers. Maybe its time to take your hobby back from these bureaucrats!