Published Boiler Design

[Roger Mason]

Hi All,

I see that the Model Engineer is publishing the drawings for Martin Evans's Metro loco.

The most recent sheet of drawings contain details of the boiler. As this is reproducing a design which has been previously published, it is presumably accepted as a design which meets the general strength requirements for model boilers. Do folk on this forum think that it would be useful to publish the calculations which would have been necessary to determine the thickness/size/spacing of the components of this boiler?

I don't recall seeing a set of calculations for a published boiler design, can anyone point me to a recently published set of calculations?

Cheers,

Roger Mason, in St. Agnes.

[steam4ian]

G'day Roger

This business of "published designs" amazes me because as I have been told quite a few pulished designs do not meet the requirements of the AMBSC Code.

Do these "published designs" comply with current UK standards?

I have a published book by a respected author in workshop practice and other things which details a boiler comprising a coffee can. There is no way this boiler complies with any code or standard.

Regards
Ian

[alanstepney]

The situation regarding designs and testing thereof is clearly stated in the Boiler Test regulations.
From the 2008 book:
Section 4.1 states: The constructor of a boiler to other than a recognised design
available through the model engineering trade and/or press shall
produce design drawings...etc

4.3. If a boiler is being made to a published/established design but is
intended to be used at a higher pressure...

Thus it is clear that published designs are acceptable, and all others, or variations to published designs, require the usual design calculations.

I dont see the problem.

[simonwass]

Apr 11, 2009 19:49:49 GMT @paul1979 said:

A boiler drawing from the 1950's with nutted and caulked stays won't be accepted as a new boiler construction at a majority of clubs, so how can that boiler drawing be acceptable?
cheers
Paul

Which clubs specifically exclude boilers with nutted & caulked stays? A boiler tester in our club has a very nice boiler which has nutted & loctited stays. Nothing wrong with nuts & solder although I do prefer fully silver soldered stays.

[alanstepney]

Guys, I would be careful what you ask for.

Are you, for example saying that all published designs should be scrapped until they can be proven to be safe?
Or just some, and in that case, which ones and why?
And if some are unsafe, why are others safe?

Now, before you know where you are, we will have a total ban on non-commercial boilers.
And, I can assure you that is a distinct possibility.

Right now we have a simple system, and the enviable safety record indicates that most boilers are safe.

The AMBSC code differs from some of the UK design rules, but that is not to say that either is right or wrong.

[baggo]

Some time ago I downloaded a set of very useful spreadsheets, one of which can be used to calculate the safety factor of a particular boiler design:

calslivesteam.org/calculations/Calculations.htm

I've used this a couple of times to check stay size and spacing for a particular boiler. Putting the figures in for Metro gives a safety factor of at least 6. However, the original design calls for Monel or gunmetal stays. Most builders would now use plain copper rivets and the diameter would need to be increased to say 5/32" or 3/16" to give the equivalent strength.

As a matter of interest, what is the accepted safety factor for a boiler design now? The above spreadsheet suggests a minimum of 5.

With regard to some clubs not allowing caulked stays-is there anything in the boiler regs which states these are no longer allowed or is it the boiler inspectors who have taken it upon themselves to make that decision? Personally, I would sooner trust properly nutted and caulked stays than poorly silver soldered plain rivets!

John

[havoc]

Get your drift, and that is what should be done. Our rules say that "old" designs should be presented to the boiler inspector who will decide if changes are needed (and what needs to be changed in case). But they don't expect muche trouble to bring these up to date.

[steam4ian]

G'day all

I frequently laud the AMBSC Codes. Are their similar UK and European codes which give design direction?

What I observe from this forum is that things are rather adhoc. All is OK provided you don't sell it, but then you can sell it if it is part of a complete model. Witness also the comments about SS boilers in Europe.

I accept Alan's comments that as a small subset of pressure vessel builders and operators we have and need certain concessions; and what you have is hard won. I would have thought that to have a decent altenative codes and certification arrangements would have been satisfactory.

Again some of the reports seem to indicate that there is a lack of training and consistency in the boiler inspectorate. Southern Fed, Northern Fed, Fed Up!

Seems to me that the home of the majority* (Alan's statistics) of model loco and other steam engines needs to get its act together.

Yours from the armchair (for Dr J ;D )
Ian

[Deleted]

Apr 12, 2009 22:43:13 GMT steam4ian said:

Yours from the armchair (for Dr J ;D )
Ian

Ian, does this mean you are of the seat of learning?

JB

[baggo]

Apr 12, 2009 22:43:13 GMT steam4ian said:

I accept Alan's comments that as a small subset of pressure vessel builders and operators we have and need certain concessions; and what you have is hard won. I would have thought that to have a decent altenative codes and certification arrangements would have been satisfactory.

Again some of the reports seem to indicate that there is a lack of training and consistency in the boiler inspectorate. Southern Fed, Northern Fed, Fed Up!

So far as I am aware, we do have a set of boiler codes over here which are satisfactory. What bothers me is that there seems to be certain 'inspectors' and/or clubs who are making rules of their own.

I quite agree with Paul that old deigns should be checked and altered if necessary to bring them up to 'modern' regulations ( I always check a design to my own satisfaction anyway) but when inspectors/clubs start banning perfectly acceptable methods of construction, then I worry

John

[Tony K]

Apr 12, 2009 22:43:13 GMT steam4ian said:

Southern Fed, Northern Fed, Fed Up! Ian

Not only that - Midland Fed. Surprisingly Ian, they appear to be pulling in the same direction with the latest Blue Book. However, the devil is in the implementation. One federation would be best for us though.
I agree with Paul, but I can see Baggo's point. I have heard of some boiler inspectors at some clubs saying it is not to the published design, therefore no joy e.g. the metric thickness is not the same as the imperial drawing. Others would look at it and possibly say actually it is better and improves the design - using judgement/common sense, a skill often lost on some people and discouraged by many safety wallers.
Definitely, the former type of boiler inspector should be taken out and shot.

[chameleonrob]

Apr 12, 2009 23:41:06 GMT John Baguley said:

So far as I am aware, we do have a set of boiler codes over here which are satisfactory. What bothers me is that there seems to be certain 'inspectors' and/or clubs who are making rules of their own.

I quite agree with Paul that old deigns should be checked and altered if necessary to bring them up to 'modern' regulations ( I always check a design to my own satisfaction anyway) but when inspectors/clubs start banning perfectly acceptable methods of construction, then I worry

John

some times it is necessary to to change the design even on recently published designs, I recently saw a design published in model engineer with the dome pipe soldered directly into the boiler barrel with no dome bush. this to me is a big no no as all the metal removed must be replaced to keep the strength the same, every boiler book I have read says the same. If someone came to me with their own design of boiler with no dome bush I would consider the design unfit for purpose yet should I let this published design though?

rob

[alanstepney]

It is my understanding that all published designs are checked out by a qualified engineer when published.
Certainly that used to be so back in the days when Percival Marshal was in charge, and for a few years therefter, although I dont know if it continued up to todays designs.

Deciding whether or not any specific design is safe is relatively easy (the formulae have been around for many years and it aint rocket science) and any suitably qualified engineer could do the qualifications.
Indeed, the vast majority of us could do them, or use, for example, the link provided by John (Baggo), to check any design. That, plus some common sense and a little experience is sufficient.
But, for that assesment to be accepted would require someone with the right qualifications to give it the OK.

Even so, the fact that a qualifed engineer has pronounced any design as safe, doesnt guarantee it wont ever fail, and there are many examples of supposedly correctly designed structures failing in service.

What isnt acceptable (and here I mean from an official viewpoint) is for the average guy to modify a design willy-nilly, without producing the calculations that prove that the modified design is also safe, or safer, than the original.

Who decides?
Ultimately, the insurers, or to be accurate, the insurers engineers.
As we have the concession that clubs are allowed to test boilers , which they do on behalf of the insurance companies, that responsibility os therefore delegated to the club boiler inspectors.

Like any collection of people, some will adopt a different approach to others regarding changes in design, some will take a hard like, and others be more lenient.

Ultimately, anyone could go dirent to the insurance company and have their engineers check out a design, and that is what happens with full size boilers.

There may well be a "better" way of assesing designs and altering them when it is felt they should be altered, but I am sure that any such change would be more expensive than what we have now.
Would it improve safety?
Given the existing track record it is hard to see how it could be improved.

[Shawki Shlemon]

I am completely confused after reading all the threads
A code generally specify a minimum or a maximum limitation on whatever thickness verses pressure , number of stays per x area and so on , gives a formula to calculate the size of bush required for a hole like the dome, material specifications just to mention some . The design published or not , if it meets all the min/max requirements of the code then one can build the boiler and the inspector have nothing to complain about unless he shouldn't be one. We approve boiler drawings for club members as long as the plan meets all the code requirements .( no such thing as published )The code is published .

[havoc]

Are their similar UK and European codes which give design direction?

Our does. It list for each material (copper, steel and SS) the materials to be used, the relations between size, pressure and thickness, things like bend radius, how far to stay away from bends, obligatory appendages etc etc. Also the tests to be done and the what has to be inspected when. There is even a small chapter about storage and water.

[alanstepney]

Shawki, it is only because (and here I can only comment upon the UK situation), published designs were approved by a qualified engineer, that they are automatically accepted.

Any other design can be accepted provided all the requisite calculations are given and approved.
"Approved", by whom?

A suitably qualfied engineer.
That might be a Chartered Engineer, or someone who holds recognised professional qualifications in a field that covers such work.

[steam4ian]

G'day Allan

This why the AMBSC Codes are particularly helpful. They give both direction and guidance for design and inspection by boiler inspectors. They even set down the "qualifications" for a boler inspector which include that the prospective inspector has a track record in building boilers. I doubt that Shawki is a Charterd Engineer but by virtue of the boilers he has built and the wisdom he shows on these pages he is well qualified to approve boiler designs to the Code.

The Codes set out shell thicknesses, plate thicknesses, stay spacings and types etc. I have no doubt that following the code any person with sufficient nous to build a loco could design a boiler that would be passed by an inspector, constructed and proven by testing. I must admit it is easier for me, I am a Chartered Engineer, but not in the field, and used to reading and applying codes, most of which are much less helpful than those set out by the AMBSC.

There are areas where the AMBSC Codes have been demonstrated to be overly conservative but in the interest of universality it is better that they er on the side of caution.

Summary. Good codes should obviate the need for a Chartered Engineer to review an unpublished design. Who reviewed the coffee can boiler and signed their professional name to it?

Regards,
Ian

[wayne]

Allan you are quite correct in stating only qualified engineers may alter the specifications of a pressure vessel under Pssr

For example

Engineering Technician* can inspect and test certain minor pressure systems and in the case of a pressure vessel, only to the vessels original parameters or parameters set by a higher qualified engineer, the eng techs findings must be endorsed by one of the following.

Incorporated engineer, can alter specifications for minor systems i.e. de-rate a pressure vessel in line with the corrosion he finds of the shell

Charted Engineer, large systems and has the final say over the previous qualifications

The above qualifications must be in an engineering and not electrical, the examiner must display he has undergone Non Destructive Testing. The qualification for all three classes is renewed each year.

*In the case of Engineering Technician the HSE also recognise a person with 10 years experience in the given field and suitably qualified may also inspect certain minor pressure systems but same criteria for ratification applies.

Under industrial pssr the inspection body is the competent person ( a widely misunderstood point) and the person ratifying any inspection must be registered with ecuk, so when even when an insurance company employs or contracts inspectors it is still the insurance company that is the competent person..

Also most insurance companies in the past, and some still do, exempt things relating to pressure systems on the ground that it will not give rise to danger, however its the responsibility person/company who order any inspections to ensure that the persons conducting the inspection is suitably competent to do so ( I personally find this unbelievable).

In a nut shell each insurance company has it own criteria; some inspectors stick to the book and do a superb job, hoverer some cut corners

For example.

I have been requested to test the safety valve and gauge after reassembling a vessel; the insurance inspector had left the premises having completed the paperwork.

I have seen ABS compressed air pipe work exempt from inspection despite it been run directly under the UV lighting in a food factory, ( UV lighting causes ABS pipe work to become brttial and fracture)

Steam Pipe work exempt inspection, despite been badly corroded and fitted with malleable iron elbows and tees

So my to my point, I am not surprised there can be confusion in the model world, at times it not that clear in Industry, but after all who dares argue with an industrial insurance inspector, (and the bad ones know this)

[baggo]

Apr 13, 2009 21:47:15 GMT steam4ian said:

This why the AMBSC Codes are particularly helpful. They give both direction and guidance for design and inspection by boiler inspectors. They even set down the "qualifications" for a boler inspector which include that the prospective inspector has a track record in building boilers.

The Codes set out shell thicknesses, plate thicknesses, stay spacings and types etc. I have no doubt that following the code any person with sufficient nous to build a loco could design a boiler that would be passed by an inspector, constructed and proven by testing.

This, to me, is the information that should be available but, do we in the UK have a similar code? We have 'the Blue Book' which defines how a boiler should be tested but do we have a modern set of rules for actually designing a boiler in the first place? Mention is often made of the books by K N Harris and Martin Evans on boiler design and construction but these are both donkey's years old and possibly now out of date.

This is of interest to me as I tend to alter designs to try out ideas hopefully leading to improved boiler efficiency.

John

[Shawki Shlemon]

Alan
If the professional engineer/s has checked and approved the code and its requirements and the club/inspectors/builders adhere to the rules ( we do here ) then there is no need for published design . Also as the code is updated regularly to meet new situations such as the availability of materials, new materials and practices , the new boilers build are up to date . The entire operation is flexible and safe and within our means .