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.

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