Boiler Design – issue 4765

[JasonBModerator @jasonb]

It has worked for many years and I would not be too worried about sitting astride a copper or steel boiler that a UK inspector has passed. I said they tend to be people with experience in making and running model boilers and that comes before they become an inspector. Many will also have been or still are involved in engineering as their day job. So will likely have experience before they even become a “new” inspector.

As I said the UK code does not have much in the way of technical guidance, it says suitable material but as far as I am aware does not state what is suitable. Again knowing what is generally accepted comes with experience or asking if you don’t have that experience hence my comment that the boiler inspector should be consulted early on and they will guide you through what they require. Can’t say where I picked it up from but must have taken it in some time in the last 43years which is how long ago I made my first steam engine and boiler

[lezsmithParticipant @lezsmith]

Hi Jason,
Thank you for the update, I agree the best source of knowledge at this time are the dedicated model boiler inspectors.

However, I do worry without appropriate documented codes or authoritative design documents, I’m not talking about legislation, as the Federation of model engineering societies state, “At the present time there are no nationally agreed boiler design formula for the hobby of Model Engineering.”

Changing clubs or moving to a different part of the country where different boiler inspectors work, could lead to problems. We need a nationally agreed standard that all designs must comply with.

Yes, we do have legislation in the UK, but it is so convoluted and lacking in detail it is practically worthless, I’m referring to the “PSSR 2000” Joining the EU and then leaving the EU did not help, however the PSSR is recognized as the current legislation in force by the UK.

It is commendable that the Federation of Model Engineering Societies (https://fmes.org.uk) took the initiative to define Boiler test codes and Design codes to try to fill the lack of information to help the model engineering enthusiasts. Also interesting there has been discussion about using the AMBSC codes in the UK.

During my research I have uncovered some interesting facts about the ‘6-10’ safety factor in the UTS method, that shines a light on why it is included in the UTS formula. However, this post is getting a bit long so I will post the details in a separate post.

[JasonBModerator @jasonb]

Changing clubs or moving to a different part of the country where different boiler inspectors work, could lead to problems. We need a nationally agreed standard that all designs must comply with.

 

This would be quite problematic and could well end the hobby as we know it. Many locos and traction engines are running to legacy designs and some to updated legacy designs. If all these boilers are then to be tested to a new revised code then many may not comply so you have many club members unable to run their models which will have become almost worthless.

Also why the “We” you are not in the UK so will have different rules to follow if any. Or do you want an international code that may include Duplex like the Aussie code does and stainless like Europe and SA allow at club level testing?

[lezsmithParticipant @lezsmith]

As an Engineer and probably many of the members of this forum included I do not like formulas that include hard values with no explanation as to what they represent and why the value is as stated.

First one has to consider when the formula was written and the circumstances of that time. Martin Evans and K.N.Harris were clearly two of the pioneers of the model engineering hobby, books such as Manual of model steam locomotive construction (1960) and Model boilers & boiler making by K.N.Harris (1967) are still referenced today.

The famous UTS formula P = D x F x WP / TS x T x 2
Where:
P = plate thickness in inches
D = boiler diameter in inches
F = the safety factor. (this is between 6 and 10 but usually a factor of 8 is used)
WP = the working pressure in lb/in²
TS = the tensile strength of copper (a suggested figure is 25,000 lb/in²)
T = An allowance of 0.8 for pressures between 60-100 lb/in² and 0.7 for pressures from 110 to 150 lb/in²)

Included ‘F’ a safety factor, but we have a safety factor of 2xWP so why do we need another safety factor of ‘8’?

Back to the 60’s and early 70’s when Evens and Harris were experimenting with miniature boilers and writing their books, the available material at that time was still limited, copper piping was just starting to replace lead piping and there was a shortage of copper, also the machinery did not have the accuracy we expect from modern machinery and CNC was still being developed by MIT.

So, the UTS formula had to make an allowance for inconsistent plate thickness, cylindrical tubes not being true cylinders, handmade endplates with varying gap tolerances and plate thickness, quality and availability of silver solder, etc. Therefore, some compensation factor had to be built into the formula to account for these variables.

It is unfortunate that these compensation factors were lumped together and called ‘safety factors’, I now understand why MEinThailand objected to calling the ‘F’ variable a safety factor, in reality it is a compensating factor for design issues in the materials and construction that were unavoidable at the time the formula was first published.

So where does that leave the YP method?
First, we must consider do the same limitations and factors still apply to modern model boiler construction. I personally believe some do and some do not.

Most modern workshop equipment has accuracies and repeatability significantly better than was available in the late 60’s early 70’s, with CNC retrofitting of manual equipment the accuracy and repeatability is constantly increasing. However some things like manually working copper to form an end plate has not changed much in the last 65 years.

But what about moving forward, tig welding was not considered to be something a hobby workshop would have 60 years ago, what about 3D metal printing and laser cutting, tools and technologies that were only talked about in academic circles are becoming available to the hobby workshop.

Some have mentioned FEA is the way forward, the reality is most FEA models are still very simplistic, yes there are better models and more advanced analytics, but these are generally out of the reach of the hobby engineer some costing thousands of dollars. I hope professor Beach or one of the other professors at MIT can help move that forward.

Should we cling to a formula that was designed to give a reasonable assurance that a copper boiler built with all the limitations and artifacts of the 60’s /70’s would be ok, or do we move the work practices and formulas forward as the technology advances and materials are produced with higher quality and tighter quality controls.

I will leave this question with you whilst you think about the future of our hobby.

[lezsmithParticipant @lezsmith]

Hi Jason,
Firstly, thank you for responding.

I understand your concern however I believe safety always comes first, therefore if the current boilers are as many have said in the preceding posts “built to a standard that is proven to be safe” there should be no reason to doubt they would pass any reasonable test.

I also believe any reasonable standard would allow grandfathering of existing certified boilers, with the caveat boilers just like some other potentially dangerous items should have an annual or biannual test to ensure continued safety.

Whilst it is true I now reside in Thailand, being born and raised in Yorkshire but spent most of my working life in the USA (although much of that I was traveling for extended periods of time in SE Asia and Europe) I still consider myself to be British and proud of it.

Regarding a new standard, yes it would like to see the UK be a leader to define a new international standard it would have been easier for me to work with model engineers in the USA given my federal and academic connections, I also have a large number of relatives in Australia, I chose the UK and MEW to start the ball rolling, given all the negative feedback perhaps that was a mistake.

[Nigel BennettParticipant @nigelbennett69913]

I was only looking at the KN Harris book the other day and was quite frankly horrified how out-of-date it is. It recommends phosphorus-bearing silver solders (pp80-81) and a butt-jointed barrel (p67). Using “Good quality solid drawn brass tubes” in flues (p26) is not something I’d be prepared to accept, either.

[lezsmithParticipant @lezsmith]

Just for completeness my research has taken me down many rat holes, however a few nuggets were found along the way.

One of the Best resources I found for Model builders in the UK is:
https://fmes.org.uk

Here you will find the best and possibly the most current information available on the subject of model boiler making and testing. The boiler testing FAQ volume 2 answers many of the questions regarding the current UK standards.

https://fmes.org.uk/wp-content/uploads/2021/04/BTC2018V2-FAQ-February-2019.pdf

Additionally:
https://fmes.org.uk/wp-content/uploads/2022/01/Notes-on-copper-specification-November-2021.pdf

and

https://fmes.org.uk/wp-content/uploads/2025/04/Boiler-design-calculations.pdf

Are a great place to find relevant information on material selection and boiler design.

For those of us that are relatively new to model boiler building or just want to a place to start I recommend:

A guide to boiler and other pressure vessel construction, testing, certification and operation

 

[noel shelleyParticipant @noelshelley55608]

As this thread has now moved from YP/UTS to the future of the hobby ! That the 2 methods of calculating the minimum shell thickness have been shown to for practical purposes give similar results and that there seem to be few if any recorded incidents where the 2 methods of calculation would have made any difference may be it is better to leave sleeping dog lie ?

That modern methods are used and yet buildings and bridges fail catastrophically rather than be well  designed with a large and more than adequate allowance for any variables, of course money comes into this and sometimes dishonesty.

As the owner and operator of 2 small boilers both about 50 years old, very well made all be it ” back in the dark ages ” that currently are certified. I would still operate them even IF the regulations were changed. I have little doubt that many others would do the same so I fail to see HOW any change would increase safety. As for the future of the hobby it would have a serious impact, many clubs have tracks that may become so little used that their viability and that of the club called into question.  The making of a copper boiler involves many skills that need to be carried forward for the benefit of our young ( they will not ALL become computer programmers ), not ham strung by yet more legislation that will achieve little. If one were to add plate certification and possibly a composition analysis then the costs involved may be the straw that broke the camels back, copper is already very costly, stainless not permitted ( in the UK )and steel effectively only if commercially built.

To those who say I am prepared to operate an unsafe boiler, my answer is that I have both the knowledge and equipment to carry out tests to prove them.

To the two authors of the interesting original article I would say thank you, but having had your say, please leave well alone ! Noel.

[lezsmithParticipant @lezsmith]

Hi Noel,
I was going to walk away from this forum and MEW until I saw your post.

Change is always going to happen, it is still going to happen no matter how much you close your eyes and ears or hide in your garden shed; however, you have the opportunity to influence the future by participating in honest technical debate. The reality is almost all children are now more intimate with human computer interfaces (HCI) than talking to a human directly, just walk around the mall. The future of HCI will not be screens and keyboards so designing a boiler in virtual reality will be child’s play.

Would you like to see stainless steel be part of the UK code, I would, I’m currently building a traction engine with a stainless-steel boiler.

Do you honestly believe in 200 years’ time model engineers will still be manually cranking a lathe or cross slide on a mill, even today when I talk to engineering teachers, they talk about STEM and all the cool models available for teaching engineering to 1st to 15th grade students.

The reality is our children are being taught computer-based engineering from an early age, they will change the face of model engineering in the near future.

 

[JasonBModerator @jasonb]

I just read the very informed response to the article in the latest ME&W giving an explanation of the short commings of the YS method and showing what is used in industry. Seems as the club code is based on the regs for industry that these methods should also be the basis of any methods used at club level.

 

As I have discussed with LukeR in the past the problem I see with adding Stainless to the Club inspection scheme is that there is not going to be many inspectors with the experience to test it at that level. OK if using a commercial inspector but with Model Engineers being a bit reluctant to spend money most will not want to be paying 10 times their club subs for an annual test.

 

[noel shelleyParticipant @noelshelley55608]

Being taught computer based engineering is fine, but I doubt they will ever get to make anything in metal. The lathes, mills and other metal working tools have been sold off – long since ! My shaper came from a college and one of my metal smelting furnaces came from the local high school, in a world where even a cup of coffee has a HOT warning on it such equipment is far to dangerous for a teenager to use ! May be one day we will see a plastic boiler made on a 3D printer, the entire engine printed in one piece and electric heating ? Best we don’t go down the road of the state of education in the UK, this is an area I have some knowledge of.

Your mention of HCI is interesting, How many have been hurt ( collide with tree or lamp post ) whilst glued to their screen ? Or worse, badly hurt trying to replicate some idiotic antic seen on You tube ? Their world is a virtual one devoid of any common sense or understanding of risk and hazard.

Yes I would like to see stainless boilers but understand that few would have the equipment to construct and then there would be the inspection as Jason has mentioned.

That some of the electricity that powers their computer is generated by steam is a point lost on them and the likelihood that any of them will build a boiler is VERY remote – so why do we bother about the design of a boiler ? Noel.

[Paul KempParticipant @paulkemp46892]

Well as ever this discussion has taken many diversions!  We started with a proposal that the UTS method of determining boiler shell thickness was flawed and an alternative method using YP was proposed.  Following some debate it was then claimed that boiler failures are going unreported as there is no statutory obligation to report, presumably on the basis these unreported failures would be prevented by adoption of the YPM.  Then the issue of a construction code and inspector competence was discussed.  Now we have arrived at the age old argument of new technology impacting and changing the hobby!

My take on these points (ignoring inspector competence as that is a different issue altogether and far more subjective) in the above order is as follows;

The UTS method which has been used successfully to date with its magic number of 8 is actually validated by the YPM as the results are so similar.  It shows that the choice of that particular magic number was a wise one.  Equally you could argue that as the results are so similar it may well be acceptable to use the YPM.  I have not had the benefit of seeing the response in MEW as I am not a subscriber that apparently challenges the YPM from the industrial perspective.

There is no overriding statutory obligation to report boiler failures although as a consequence they may be reportable under RIDDOR and while not a statutory obligation there is a contractural obligation under insurance to report to the insurer any incident which may give rise to a claim even if there has not been expressed intent to make a claim at the time, or of course if a claim is being made.  I put two questions with regard to boiler failures or incidents to my broker on those situations over the last 10 years.  Their response was marked confidential so I don’t think I am able to quote my actual questions or the response on a public forum but my perception of a lack of incidents was confirmed.  Personally I think the failure of a copper boiler due to inadequate shell thickness (which is the only aspect of boiler design being discussed here) would be a sudden and potentially catastrophic event that would most likely lead to some injury and an insurance claim.  Therefore the method used historically has been well proven experimentally and shown to be sound.

There is no formal construction code in the UK as there is in Australia for example.  This has been discussed in the past and the Federations have considered this and for whatever reason discounted it.  Personally I think there is sufficient guidance in the public domain to enable design and construction of a safe boiler and the constraints of a prescriptive code is not necessary.  Previously my thoughts were a UK constructional code would be a good idea but I have changed my views on that.  A prescriptive code can become restrictive, an example being the Simplex boiler design which is well proven but apparently outlawed by the Australian code.

The discussion on the future of the hobby I feel is a complete distraction on the subject being discussed.  Of course the hobby will change over time, as it has over the last 100 years where we have moved from riveted and soft solder caulked boilers to silver solder / braze and now TIG welded examples.  Builders now have the opportunity to use CAD and CNC is slowly becoming more accessible and affordable for the home workshop.  But this is a hobby, it is not industry and while developments in industry filter through it is very slow, probably the next development is the ability to purchase ex industrial CNC equipment.  However, for the individual in his shed making a model he/she is dependent on finance that can be directed to it and the available space for equipment, there is still much to commend the humble file and hacksaw in combination with a vice to shape a piece of metal – still much cheaper and accessible than the CNC alternative for those that still want to work with metal.  It’s about the challenge on what can be achieved with limited resource not how many and how fast you can make parts.  Yes change is coming and successive generations will embrace it, Jason is a good example of someone using technology to assist his aims, does that mean they will look back and laugh at a locomotive made in a shed with a file and a hacksaw in the 1900’s?  I don’t know and to be honest I don’t care!  All I am interested in is what I can achieve with what I have now.

So back to the subject!  I commend the two gentlemen that have raised this issue.  It is certainly correct that we should continually question what we do.  That is how progress is made.  My personal perception however is as previously stated, if anything this article confirms the UTS method is valid and perhaps Lez has explained how Mr Greenly arrived at his magic number!  I am quite sure that his original work was not discussed and examined as deeply as the current proposal of YPM.  If the YPM is accepted by a notified body then it provides an alternative.  I do not accept though that the many boilers designed and built using the UTS method are unsafe, the lack of reported failures evidences this.  I do not accept the lack of reported failures is not evidence of safety, as I have said before in order for there to be reports there needs to be incidents and I do not accept there is a raft of unreported catastrophic boiler failures or some conspiracy to suppress them.  The YPM debate has been a useful discussion if only to confirm the current system isn’t broken and doesn’t need fixing.

Paul.

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