Boiler Examinations: 7-yearly External Query

[Nigel Graham 2Participant @nigelgraham2]

This emerged in a recent discussion within my society, involving its boiler-testers (including me) and three owners of traction-engines of 3″ scale upwards.

We know the exterior of any steel boiler must now be examined, with the cladding off, at seven-yearly intervals starting from 2018.

So among our own club that’s already several engines due such admiring this year.

 

Removing all the cladding from a locomotive’s boiler is a chore and risks damage to paintwork, even to small fittings; but not overly difficult. Anyway, steel boilers are mainly confined to 7-1/4″ g. , especially narrow-gauge outline, engines. Including our own society’s club work-horse!

 

A traction-engine is a different beast. The boiler is the vehicle’s chassis and the firebox sides are concealed by the hornplates, plus a lot of machinery and other steelwork.

So does “removing the cladding” on such engines refer only to the insulation and sheet metal covering “just” the barrel from throat-plate to smokebox, or….?

… dismantling the whole vehicle aft of the cross-head? Surely not! That was the fear expressed.

 

Has anyone else encountered this thorny question, and know how we are supposed to interpret the code in this respect?

 

Please Note: I am asking ONLY about the MELG Boiler Test Requirements; as applicable to our NAME-affiliated club .

I am NOT asking about the commercial schemes, nor in comparing the MELG with any other scheme.  A member may wish to use a professional or other boiler tester external to the club, but that is his decision and not the subject of my question.

[Harry WilkesParticipant @harrywilkes58467]

Nigel have you asked the question to the Fmes ?

H

[Chris GunnParticipant @chrisgunn36534]

In our club we have been taking the cladding off our road vehicles every 7 years, and removing blow downs and mud holes, and inspecting the inside of the boiler with a camera, and the outside visually. we also have a thickness tester and test the thickness of the platework if we think it is needed. We have found that if some types of insulating material have been used it holds water, and this can rust the outside of the boiler barrel. This can be addressed once the cladding is off.

Chris Gunn

[Nigel Graham 2Participant @nigelgraham2]

Harry –

I will be, well, NAME actually as my club is affiliated to that. It should return basically the same answer!

I am casting my enquiry fairly wide.

.

Chris –

The tests your society includes are extra to the MELG scheme, as that does not expect methods that need a lot of specialist experience to be of any value. I am sure your own boiler-examiners have that, but not all clubs will, hence the formal scheme not requiring them.

However, the point of my enquiry was external, visual examinations, and the feasibility of them on boiler sides buried in a mass of other structures.

I am not sure when the seven-year requirement was actually introduced but we discovered it is back-dated to 2018; hence it suddenly hitting our society.

 

Yes, you are of course right about wet lagging. We understand the point of such an examination; but we are trying to establish how far the denuding a boiler is reasonably expected to go.

At least traction-engines’ total-loss lubrication systems are liable to coat the boiler below the lagging with oil, and one or two of our members had observed that on their own engines.

I think the railway locomotives are the more likely to have wet lagging, because it seems common to use the safety-valves as also filling-plugs. With the best will in the world, it can be hard to prevent some water spilling and penetrating the lagging around the safety-valve bushes.

Though slower, I would suggest using a hose on the blow-down valve spout would be the better cold-filling inlet, and also avoids wearing the safety-valve mounting threads.

 

[Paul KempParticipant @paulkemp46892]

Nigel,

9.2 gives the “tester” the discretion to extend the 7 yr requirement to 10yrs (in line with commercial requirements although you did say you didn’t want a comparison!).  If extending to 10 years then a reason needs to be given.

The 7yr requirement of the code is not well thought out in my opinion.  The first 1.5 hydraulic on a new steel boiler can be given for 4 years and thereafter every 2 years (12.5b) so effectively multiples of 2 years, so at year 6 from the last cladding removal to comply with the code you can only issue a 1yr hydraulic cert.  What is special about 7 years?  If the scheme wishes to be conservative then why not go for 6 yrs or impose an annual hydraulic (not a clever idea!)

Our club also has an endoscope and ultrasonic thickness measuring equipment.  At the 2 yearly hydraulic test we do a thorough inspection of major threaded fittings including fusible plug, blow down’s, wash out plugs etc.  Most steel boilers tested have been in the club for many years and there is documented history of previous inspections.  Our inspectors take a pragmatic and practical view and take into account the age of the boiler it’s construction and original material thicknesses, treatment regime and the lagging material (if any) and generally extend the trousers down inspection to 10 yrs as long as under hydraulic there is no evidence of leakage under the cladding or behind the horns.  Given that the outer firebox is generally thicker than the inner, the wastage on the inner firebox is a reasonable guide to general condition when combined with an internal inspection with the scope.  There have been a couple of larger scale (4”) traction engines come into the club with uncertain prior history and poor documentation, these have been required to remove all lagging but I don’t think there has been sufficient concern to require the removal of the horn plates.

Whilst the club scheme has to have a simple yard stick and time has been chosen, there are other factors that undermine the validity of time.  Some boilers only get used a few times every year and are properly dry stored in between, others may be running 20 or 30 times a year.  My own 6” engine which I only got running last year and only attended 2 events was steamed 7 times between July and Sept.  This year I am hoping to do 10 events which are all 2 or 3 day affairs so should be steamed at least 25 times for 6-8 hrs a session.  So 7 years might be reasonable for me but probably not for someone using their boiler only occasionally (if they are looking after it properly).

One of the worst things for a boiler (copper or steel) is raising steam too quickly leading to unequal expansion, I cringe seeing some of the supercharged electric “blowers” you often see people using!

Paul.

[Nigel Graham 2Participant @nigelgraham2]

Thankyou Paul.

I have had correspondence with the NAME registrar to the effect that removing the hornplates from a traction-engine is not necessary if a fair assessment can be made from the visible areas. It is very much at the boiler examiner’s discretion.

The procedure is not sufficiently clear on this point as everyone in the session that triggered my query, had read it as prescriptive.

He also pointed out a thickness-tester will only work on properly-prepared areas. The MELG scheme, and the message from boiler-testing seminars I have attended, does not call for such devices because they require specialist experience to be of any real value; and by no means all clubs will have that.

For example, how is an ultrasonic tester affected by closely-pitched stays? How does it show the difference between thick but clean steel, and the same thickness by a corroded plate covered in scale? What quality of surface preparation and the use of a matching-layer are needed? (I have never used one but would expect from basic acoustics-laboratory knowledge, these showing some of the operating skill needed.)

My view is that an endoscope would be a lot more useful, and would reveal how badly the water-legs are scaled if the engine habitually uses hard water. (From experience, this can hasten the boiler’s “death”.)

 

I agree about the forcing of boilers. Many owners of larger-scale traction-engines do use long natural-draught extension-chimeys. I have even helped raise steam in a two-foot gauge locomotive in just that way – with a ten-foot length of large-diameter plastic drain-pipe stood in the already-tall chimney!  (By the time the chimney and flue gases were too hot for the plastic, the loco’s own blower could be used.)

One alternative to the “supercharger” is a low-volume fan driving air into a discreetly-fitted exhaust or blower connection; though such discretion is not easy on a traction-engine’s exposed plumbing.  Just use a much less powerful fan if an extension-tube is insufficient!

Blowing-down fully from high pressure can be just as bad. The instructions that came with my wagon boiler advise this be done from no more than 30psi, to remove sediment and loose scale. I think too, unless there are pressing reasons otherwise, it better to let the fire die out naturally and leave cleaning the boiler until it has cooled to no more than hand-warmth.

 

[Paul KempParticipant @paulkemp46892]

Nigel,

I must confess I don’t really understand the reservations of the Fed’s around ultrasonic thickness measurement.  I fully agree ultrasonic flaw detection is a skilled operation needing interpretation of the trace having lugged a 70 degree angle probe and oscilloscope around the world on a couple of occasions looking for cracks in connecting rods.  Modern thickness gauges though are pretty foolproof to set up being pre programmed for material and having test blocks with a digital direct readout.  As long as it is used as one tool in the inspection armoury it provides a useful double check of what you see through an endoscope and may detect through other means.  Thickness testing is a sampling process and only checks the point being measured, there could be a pit a few mm away that is 50% through the plate so it should not be relied on as the full story!  It does at least provide general verification the boiler was built from the thickness plate specified on the drawing.

Regarding blow down I adopt full size practice and blow down at full pressure with the fire in!  Process is to fill to the top of the glass, open the blow down until you have a quarter glass and then close it.  If you try it you will observe no appreciable drop in pressure during the process so no undue stress on the boiler at all and effective at shifting any sediment.  I also open the blow down with the boiler cold with no pressure before lighting up, if you put a white container under the valve you will see initially settled sediment, followed by ‘clear water’ at which point I close it.  This year I will be testing ph when the boiler is cold also to better manage the treatment.  My steel boilers stay full all year.  I also wash out mid season.  I don’t count the steaming days religiously but it would be between 14 and 21.  ‘Blowing down’ from 30 psi with the fire out in my view is little more than draining the boiler hot, that will not remove scale. If you really want to look after your boiler (even a copper one) then pay attention to the water going into it and if you have to use hard water then treat it.

Paul.

[Nigel Graham 2Participant @nigelgraham2]

Your first sentence or so show why the MELG scheme does not suggest using ultrasonic test equipment. You clearly have considerable professional knowledge and experience in industrial conditions, and most model-engineering societies are very unlikely to have anything like that among their members.

By my own professional background I know some of the basics of acoustics, but that does not qualify me to buy an ultrasonic thickness-tester and claim to use it at all sensibly on a miniature boiler that has seen a rally-field or two. And you do point out its value is very limited anyway by the likelihood of missing serious pitting.

If all you want to verify is the plate thickness against the drawing, it’s likely there are visible places you can wave a six-inch rule over. However, if the boiler was professionally built and certified as are most steel ones we now see, I think we can take the manufacturer’s word for it. Even if we had the drawings.

Perhaps the procedure was written to avoid “little-learning” situations. Results that are unwittingly wrong because the user convinced himself and his pals he knew all about it (from YouTube and some practice on oddments of plate?) are worse than useless. So the simpler the method the better for amateur use, provided it still satisfies the H&S and insurance engineers who reviewed it.

 

On Saturday we did have two boilers to test without their lagging.

One had just been re-tubed so had, and passed, a new shell-test (X2 w.p.).

The owner of the other wants the unlagged inspection every six years, not that rather peculiar seven in the rules. This would keep it matching every third two-yearly hydraulic test; and since the interval is shorter than the requirement there is no reason not to. We thought whoever was responsible for The Procedure might like to think again and change the 7 to either 6 or 8 years.

 

There was a fair amount of discussion on how to lay up a boiler safely – full of water, or drained and left open. I recall seeing a booklet issued by Cochran, who made stationary plant boilers, which suggested either according to which suited the owner better. For the latter, during long lay-ups, it suggested a small wood fire at intervals to dry the internals.

For a miniature, a small electric heater would be better. One former club-member kept the emptied steel boiler on his 7-1/4″ g. narrow-gauge loco dry in the shed by placing an inspection-lamp with a 40W filament bulb, in the firebox; and an old blanket over the entire locomotive.  Much to the delight of a wood-mouse who made his nest on the footplate!

.

Blowing-down: doing so from a fairly low pressure is specified in the manufacturer’s literature for my steam-wagon boiler. In any case, blowing-down at high pressure will not remove scale already deposited. As you say, really the only way to avoid the problem in the first place is to use soft, or treated, water.

 

[Paul KempParticipant @paulkemp46892]

Nigel,

Well we will have to agree to disagree on the UT point.  Personally I think any one with the competence to examine a boiler ought to have little trouble in grasping the use and limitations of an ultrasound thickness instrument as an additional aid to the examination.

We are agreed on the 7 year point, as I said I think it was poorly considered.

You have neatly summarised the two factors that will affect the life of a properly manufactured boiler, how it is operated and how it is laid up.

There is one point you mention though that to my mind is a grey area, re-tubing and a repeat shell test.

The code states at 12.5 a “The Initial Hydraulic Shell test is valid for the life of the boiler unless the boiler is subject to repair or modification which would affect the structural integrity of the boiler.”

Changing the tubes (on a steel boiler) it can be argued is not a structural repair, it involves no welding, they do not act as stays per se and to an extent are a consumable item.  So under the code is a new shell test required?  The text suggests 1.5 would be adequate.  The tubes definitely affect the pressure integrity of the boiler but structural integrity?  That could be open to debate.

I believe for full size, re tubing does not trigger a 2xWP test (I am meeting a professional boiler inspector in a couple of months and will ask him).

To be clear I am not advocating one way or the other, just posing the question and interested in your rationale.

Paul.

[duncan webster 1Participant @duncanwebster1]

I think at least some of the stays in a full size boiler are treated as stay tubes.

There is a very good book on full size boiler design by a chap called Alan Haigh

[Nigel Graham 2Participant @nigelgraham2]

Yes, but we are not testing full-size boilers!

My original enquiry was about miniature steel boilers tested under the MELG scheme, and most likely but not necessarily built by a professional fabricator.

 

The tubes have some staying power by default, but in a small boiler where they are not designed as stays as well (e.g by nuts on threaded ends), I do agree replacing them presents a grey area for testing.

At the weekend I helped a cold hydraulic test on a boiler that had just been retubed, and all, including the owner, agreed that needed a shell test as a result. It passed, but since then I did start to wonder if that was necessary.  Its shiny new tubes, of steel, are expanded in: not welded, brazed or threaded.

 

Really these are matters that need sorting out. The basic requirements have not changed much over the years apart from the hydraulic tests being less severe than in the past; but odd additions, ambiguities and a test-certificate among the most confusing forms concocted, are making the whole procedure needlessly difficult.

Enquiries like mine, extra tests clumsily out of step with the regular ones, and tales of other clubs going beyond the “Orange Book” or failing boilers on points not in the test code, suggest to me the hobby is tying itself in knots trying to complicate rules written for industry.

[Harry WilkesParticipant @harrywilkes58467]

Gents the discussion on the 7 year boiler inspection came up at my club on Thursday, I have a copper boiler but was still interested in the discussion there was much take about endoscopes and ultrasonic thickness testers and the question of what to buy so I would be interested to know what’s being used for test equipment in your club ?

H

[Nigel Graham 2Participant @nigelgraham2]

In my club we use only the equipment specified in the handbook.

There may be members who would be competent with ultrasonic thickness testers on large structures but trying to use the instruments sensibly on a small boiler with all its corners, close-set stays and so on would be a gamble.

It would certainly be very hard to use on the side-walls of a traction-engine’s outer firebox!

An endoscope could be useful for investigating scale deposits, which I have known practically fill the water-legs of a small 7-1/4″g. loco boiler.

The upshot with my enquiries was that the club’s boiler examiners do have some flexibility to use their judgement – that seven-year rule for example is not so set in stone that it can’t be made 6-yearly to cope with the normal hydraulic tests. The Mystic Number is in the Regulations, but those were written for industrial or full-size practice.

 

Really the “Orange & White Book” needs revising to clarify points like these, and make it easier to use. As for the forms…. if ever a simple task could be made complicated…!

Over the years I have heard of or read accounts of club boiler examiners gold-plating the regulations, in one case even banning a locomotive’s use because it had a prototypical rocking-grate and hopper ashpan not made for “instant” dropping.

[noel shelleyParticipant @noelshelley55608]

The issue of boilers and their testing and certification has always  been a bit of a mine field due to poor writing of the ” rules ” though more a case of leaving room for interpretation. This is illustrated by the comments above.

I had started to build a 6″ vertical to a well known design only for the club inspector to state that in his opinion the design was flawed in 3 areas  and if I built it he would NOT certify it. I started to redesign to address the shortcomings but this then was no longer an accepted design. I tired of the nonsense and left the club ! 30 years later I presented a boiler to the original design to the same club and it passed without issue – a different inspector and the £300 of materials I first bought are still in the back bedroom !

7 years seems an odd number to use in view of the other periods, what problem has arisen that requires this ? Or is it another example of the risk averse world we live in.

The use of an ultrasonic tester I think would be of limited use, though might be handy as a back up test or to confirm the thickness as per design. A scope would be useful if only to show the degree of scaling, the more so in the legs. Since these pieces of equipment are now quite affordable they would be within the reach of a club.

What is the considered opinion on the use of rain water as feed water ?  Noel.

[Brian Baker 2Participant @brianbaker2]

Greeting Noel, I think rain water is so much better than high Total dissolved Solids (TDS) tap water such as we get in Norfolk.  Great Yarmouth has, I think tap water with the highest TDS in the UK.

Canvey Club, the late Parklands railway are two of many tracks that use it.

The great value of a scope is indicating corrosion in steels boilers, apart from scale build up as you mentioned.

Regards

Brian B

[duncan webster 1Participant @duncanwebster1]

It will continue to be a minefield until we have a design code for model copper boilers. The Australians have one which is very good, why don’t we just adopt it? I’ve compared it with my interpretation of British standards and it is very close. There has been a lot of nonsense talked about it, my only reservation is that it has a downer on girder stays on top if the firebox not attached to the outer shell, in my view they are fine for shortish fireboxes, but need some thought for long ones

[Nigel Graham 2Participant @nigelgraham2]

Noel –

The seven-year interval recommendation comes from rules written for industry, not the model-engineering hobby trying to adopt them to be legal but in a sensible way. ]

The original EU-Directive based rules only talk of pressure-vessles made from aluminum-alloy and stainless-steel, of unspecified grades, and helpfully contain the clause, “… and in fact are safe.” As if something of an afterthought.

 

Duncan –

Where is the evidence for needing a “design code” beyond what we already have, intended to allow us to design and build miniature boilers that “are, in fact, safe”? And indeed, to use long-published designs or to recommission ancient family heirlooms, as long as they pass the tests given in the MELG handbook; though I would decline to test, or refuse to certify, a boiler I felt was unsafe by condition.

There are flaws in some of the old designs, perhaps the most common being fastenings tapped directly into copper plates, but they are all now recognised and easily avoided without yet more bureaucracy. Though I would say the publishers ought have these drawings modified.

 

My original question has nothing to do with how to design and build boilers.

I sought clarifying how they are examined; but should have expected the thread to wander off in more directions than Clapham Junction.

 

The minefield is not due to the construction and test requirements.

There is nothing wrong with those. Instead, the mines are poorly-written instructions for meeting the requirements, compunded by incredibly tangled “certificates”. These create ambiguities and uncertainties in the examinations (the point of my OP); and as Noel indicates, encourage club boiler-inspectors not operating the system properly.

 

You can dictate the construction all you like, risking barring many well-proven designs as “not approved” (by whom on what grounds?), but that won’t stop nervous boiler-examiners refusing perfectly good boilers on spurious grounds. A boiler examiner may decline to test a boiler that looks well-made but is of a design personally too unfamiliar, but should have the courage to say so and help find more experienced opinion; not condemn the boiler out of hand.

Know examples of examiners’ excuses have been plates slightly thicker than the published design (due to material-stock metrication?), feed-clacks installed in more faithful locations than on the backhead as published, and a locomotive refused for having a prototypical rocking-grate that could not be dropped.

 

A boiler examiner may decline to test a boiler of a design personally too unfamiliar, but should have the courage to say so and help find more experienced opinion; not condemn the boiler out of hand.

[duncan webster 1Participant @duncanwebster1]

Nigel  have a read at the FMES test code. Clause 5 requires that for a boiler not to a published design the constructor shall demonstrate by calculation or well proven example that boiler has adequate strength. How is he meant to do this without some agreement as to how to do it, and what is meant by adequate. A design code lays out how to do the calcs, and what strength is adequate. Without it we would have different inspectors insisting on different plate thickness or stay spacing depending on whim. I would point out that some historical designs have plates which are thicker than they need be, leading to boilers being more expensive than they need be. Once something is strong enough,  making it stronger doesn’t make it better, just more expensive.

[Nigel Graham 2]

On Nigel Graham 2 Said:

…Where is the evidence for needing a “design code” beyond what we already have, intended to allow us to design and build miniature boilers that “are, in fact, safe”? ….

 

…

There’s plenty of evidence in this thread suggesting something is wrong.  Inspecting boilers shouldn’t be a “minefield”!

As I understand it, the present UK system depends more on experience than compliance. May have made sense in the past, when many model engineers had direct experience of full-size steam, but times have changed.  High pressure boilers used to be everywhere, but steam was on the way out in the 1930s, and by 1970 had become a bygone.   So the number of Model Engineers joining the 21st century hobby with a professional background in boilers must be falling.

Thus ME Boiler Inspectors as a class tend to rely ever more on proven designs and methods than current industry best practice.  That has consequences:

• As boiler inspection is a responsible job, anyone without formal qualifications is likely to become conservative.
• Experience is inconsistent, so, at the same time, an ignorant inspector might accidentally pass a dud boiler.
• Not clear what owners, builders or inspectors need to do.

I think a well-written Design Code would help.  Rather than relying on what individuals know, or think they know, everyone works to a Code.  Important to keep the Code up-to-date with an effective process for fixing mistakes, ambiguities, and supporting new ideas.

The present system allows ambiguities and has no way of removing them. Commercially made boilers are the main exception; the difference being professional design, build and test.  Tin hat on, dare I suggest Model Engineers could be more professional!

It’s running a boiler in public that drives the need for sensible inspections.   The “Health and Safety gone mad” brigade seem not to understand how expensive a serious accident is!  Just before I retired an ordinary fatality cost between two and three million pounds, which is why clubs insure.  The cost in time and stress is very high too.   Jack-the-Lad may think accidents don’t matter much, but he’s wrong!

A bad accident at a UK club, god forbid, could affect the whole hobby. A formal external enquiry will address responsibility, accountability and the changes needed to prevent the accident happening again.  It will ask searching questions like:

• What rules, guidelines, and training ensure that boiler inspectors are competent?
• Are Boiler Inspectors ‘competent persons’ as defined by H&S legislation? (Requires more than technical competences)
• How does the club confirm that its boiler inspectors remain competent between recruitment and retirement?
• Does the club have processes that inspectors have to follow?
• Who in the club is responsible for overseeing inspectors?
• Did the inspector follow processes?
• What does the Risk Assessment say?

Bad things happen to individuals if it turns out the club and/or their inspector don’t have good answers.  A court will probably decide they are legally incompetent. A fatality could result in a manslaughter charge and prison sentence.

A bad persons-injured accident could be very bad for the hobby as a whole.  If insurers discover a club wasn’t managing risks competently, they might look at the whole system.  If they find a ‘minefield’ that doesn’t manage their risk, they will demand improvements, increase premiums, or refuse to insure.   A hobby that can’t get insurance is in big trouble. because the financial risk of an accident is too high for a club to bear alone.

Clubs, I suggest, should manage the risk.  Can’t be assumed that all is well just because there hasn’t been a serious accident for decades!  Very common for accident investigations to find root cause was an organisation or individual grown complacent over time.

A further benefit is that a well-written Code could accommodate modern designs and materials.  At present, these are inhibited because relatively few boiler inspectors know how to deal with them.  As Duncan suggests, a Code can explain what “adequate” means in terms of calculation, FEA, or otherwise.   No need for an inspector to guess; can the builder show it’s to code or not!

Will UK hobbyists still be building and operating model steam locos in 2075? I hope so, but change is required.  The present system isn’t horribly wrong, but it’s crumbling.   Where will the next generation of boiler inspectors come from, and how can we ensure they are competent?   I think a Code is the easiest answer.

Dave

 

[Harry WilkesParticipant @harrywilkes58467]

My club is suffering from shrinking membership but fortunately we have two boiler inspectors who don’t or who will need zimmer frames for some years.

H

[Colin BishopModerator @colinbishop34627]

This has been discussed on the Model Boats Forum. We have an experienced contributor who has posted relevant articles.

 

Boiler Room – Richard Simpson’s series on model steam plants

https://www.modelboats.co.uk/members/richardsimpson88330/mediapress/steam-related-documents/

Colin

[Nigel Graham 2Participant @nigelgraham2]

Colin –

Oops!

Sorry, but your merely opened a great long advertisement for umpteen editions of the magazine.

That aside, those two books in the photograph you quote are seven years out-of-date!

The current edition is dated May 2018, with a white cover and orange lettering.

I assume of course that Richard Simpson now works from the 2018 scriptures; but I would suggest the image ought  only be of the one edition current at the time of writing, even if having to change the image at Part-Umpteen. Showing consecutive previous editions as in the illustration, is only valid for an article comparing editions, and otherwise risks more confusion..

I think the primary changes for 2018 involve testing gas tanks. Among other things I recall the previous book contained a rather irrelevant table intended for LPG industry use.

 

Dave –

Two questions in your list are, do clubs have procedures, and were they followed?

The answer to the first is “YES”; the MELG book is written to satisfy the insurers and bodies like the HSE; but I do think it is not very clear and the forms it requires are some of the worst-designed I have seen, because they are very confusing.

The answer to the second, is they should be. What seems happening is boiler inspectors being too conservative rather than too lax, refusing to certify boilers for reasons outside the guidelines and sometimes (as with the rocking-grate example) not even part of what is being tested. Although erring on the side of safety, it is not good practice and risks bringing the scheme into disrepute.

”””’

The whole scheme is a compromise, I would agree, between trying to help the hobby act safely, and enforcing such regulations on it that it would become “safe” simply by destruction.

We saw off that threat a long time ago when the HSE originally wanted miniature-railways operated under commercial fairground rules covering designing, building, operating and maintaining rides. I attended a symposium hosted by the Southampton ME Society, at which the HSE’s Principal Inspector of Fairgrounds was the main speaker. He accepted the original requirement was impossible, and the upshot was the Guidance that gave a lot of advice without prescriptive “codes” or “qualifications”; though as I recall, requires operational procedures such as risk-assessments, physically inspecting the railway before operating, and recording maintainance and repairs.

The MELG scheme for miniature boilers is in similar spirit. It does not try to tell us how to design boilers (nor do the original PER). It tells us to ensure they are safe, and how to test them for safety.

 

The Boiler Examination seminars give you a bundle of documents including one telling you how to calculate the strength or plate thickness for a cylindrical shell subject to internal pressure. It does not tell you how to design for external pressure on cylinders, odd shapes like Belpaire and LNER-pattern fireboxes, and flat plates. The nearest you will find is guidance on stay pitches for flat water-walls. Read, or more likely look in, a professional engineers’ text book on stress and strain and you realise those would be extraordinarily complex mathematical problems indeed and may cause more trouble than we are trying to avoid. Though I remember Luker describing software he found that will do such sums – for his boilers he welds from stainless-steel…

Yet how many miniature boilers built to, or based fairly closely on, established designs that are almost certainly deigned without such “aid”, have failed by being too weak?  More likely failed by poor fabrication or maintenance; or in one case I was told of by a near-witness to it, over-straining the boiler by testing at excessive pressure. The present regime is designed to prevent that last practice, too.

The first can be answered to some extent by the club boiler-inspector examining the intended design prior to cutting any metal (if the builder is also the designer); and by the quality of the workmanship at suitable construction stages. I may not be the only one here who recalls having seen, at one of the major exhibitions, a sectioned, large copper boiler no-one could possibly have accepted by the obvious results of the unfortunate builder finding its assembly beyond his skill and equipment.

 

My own locomotive, re-boilered well before I bought it, originally had a steel boiler built long before all the PER and so forth, professionally welded but using whatever steel was evidently to hand;, but it was corrosion and scale that killed it eventually, not a lack of paperwork. In post-mortem I did find the lower gauge-glass fitting was too low, so the crown likely ran dry at times, but the history showed the fatal problem had little or nothing to do with the boiler’s design. It was a servicing problem.

Unlike one boiler my club had to fail because a very serious but oh-so-basic design-flaw led to the inner firebox collapsing under a preliminary hydraulic test to working-pressure. Curiously, we had no idea who had designed it or published the boiler drawing. It was anonymous, and for some unfathomable reason the upset builder would not reveal its source…. So, yes, rogue designs can slip through; but so they could whatever additional rules or “code” we might invent.

”””

The boiler examination system we have does work: it was created in conjuction with, and approved by, the HSE’s and Insurers’ engineers.

It is up to us to use the system properly – but the system’s instructions are rather vague and confusing. Even if you use the correct colour book.

That is what I was asking about in the first place… and notably, no-one really answered what I asked!

 

[noel shelleyParticipant @noelshelley55608]

This has all been very interesting, many have put much time into the comments, particularly,Duncan, Nigel and Dave, thank you. The important thing is we are not here following an accident ! This could be said to be due to circumstantial evidence showing that such systems as we have are working ?

The range of different boiler types, materials and construction methods mean that any code or system would have to reasonably open to allow for this – too loose and trouble would ensue too tight and nobody would be pleased. I have never seen at a boiler test or in ME any mention of the calculations that have arrived at the strength of the boiler shell prior to a hydraulic test, something even my secondary school maths finds easy to do. The issue of safety factors is interesting in said calculations, 6, 8, 10, where does one draw the line ? On the matter of calculations my vertical boiler design working pressure is 80 psi, yet doing the calculations show that even with a good safety factor it could be 120psi, or a thinner (cheaper ) shell used. If one is to have the flexibility to allow the inspector to use his judgement then how does one avoid the problems I suffered (he didn’t like the design ). A new boiler can be inspected during construction, though if construction takes years or is completed by a second person then how does one check the crown staying for example on completion  ? Then there is the matter of old boilers, one I have was steamed for the first time when nearly 40 years old, I don’t have the drawings though it appears to be identical to a well known design and commercially built, the other, second hand, is over 40 with pre existing paperwork and drawings that show it was NOT built to the drawings, the deviations on the pressure vessel are minor and sensible. Under a working pressure test a steel boiler showed no sign of bowing or collapse even though the fire box sides had NO stays !

It is plain that there are many very knowledgeable and experienced people here asking intelligent questions BUT –

The system such as it is may not be ideal but it does seem to work for most and I don’t recall any notable failures. On the basis of better the devil you know I think we would best to let sleeping dogs lie ? The world we live in with it’s preoccupation on theory and qualification rather than experience and competency could spoil it for all of us.  Noel

[Paul KempParticipant @paulkemp46892]

Every time boiler safety is discussed on a forum there is fact, myth and hysteria raised.  The boundaries of each being blurred.  It is a fact that there has not been a miniature boiler “explode” resulting in a fatality or life changing injuries in the UK.  Miniature boilers have however failed but generally in far less spectacular events than than the “it’s a bomb waiting to go off” brigade would have us believe!  The reasons for this are that generally they are massively over engineered and whatever the perceived faults of the existing inspection regime, as noted by Noel it is fulfilling its purpose.

Nigel, I have no idea why the MELG decided on the period of 7 years but I have never seen in PSSR or PER that period specified.  In my experience of the marine field all pressure testing revolves around periods of 5 or 10 years.  Likewise with my involvement in the heritage rail sector and full size road steam the hydraulic cycle and invasive exam is based on a 10 year cycle.  Can you direct us to a document in the commercial world that specifies 7 years?  I suspect it was driven by inspections being carried out by “amateurs” with appropriate theoretical knowledge and practical experience in the same vein as the hydraulic intervals of 4 / 2 years – giving greater confidence.

Duncan, I fully agree there should be a construction code or set of common standards on design parameters.  As you correctly state the test code requires club inspectors to be able to approve non published designs.  However those standards should be flexible on design points as the Australian construction code disallows some designs of boilers that are commonly built and operated in the UK successfully and safely.

Perhaps the most salient point is Noel’s.  The UK test code is not perfect but it is broadly fit for purpose and is achieving the desired result – which is to maintain a level of public safety while allowing blokes in sheds to build and operate boilers without government oversight or undue interference or incurring great cost.  It should be considered that it has the backing of the insurers who clearly feel the degree of risk is not sufficient to adversely affect their profits!  If it ain’t broke then it doesn’t need fixing!

The one point that is almost always overlooked is that PSSR requires the owner / operator of a pressure system to appoint a competent person to examine the system.  What that means in law is the owner of the boiler has a responsibility to engage an inspector that they know / believe is competent.  If your boiler goes bang because the inspector missed an issue it is possible you could be asked on what basis did you trust the inspector?  Also remember that a boiler inspection is like an MOT, correct on the day of issue!  There are plenty of things the irresponsible owner or operator can do to a boiler during the period a boiler certificate is valid that will compromise its condition / safety.  A poorly boiler will generally give some clues before it fails that the owner / operator should be noticing!  If it is scaling up for example its steam generating properties will be compromised.  The quality of inspection is one thing, the quality of operation and maintenance is equally important – some countries require a boiler operator to be licensed……….

Paul.

[duncan webster 1Participant @duncanwebster1]

The only significant thing used in UK and banned by Aus code is girder crown stays not attached to outer shell. These are often used in UK and are successful. However with a long firebox it gets increasingly difficult to get enough depth, and you have to think about the loading on the firebox tube plate. I’ve often wondered whether girder stays side to side might work. They would need cutouts to allow circulation.

Aus code also doesn’t like end to end stays silver soldered both ends. The reason seems to be that when soldering, the stay tends to get hotter than the shell, and so when it cools down the stay goes slack. Been there, done that. However, if you know what you’re doing, this can be avoided by putting heat into the shell.

With these provisos, the Aus code could be adopted, it doesn’t need sums,everything is lookup tables

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