Boiler construction.

[waggy]

Good afternoon all,

One of our members has an old boiler from a “Rob Roy” that requires repair to the fire hole hinge attachment which were held by tapping straight into the copper using bronze screws. The threads have worn creating a leak. The member has asked if there is any written guideline covering modern repairs to such a boiler ie, should blind bushes be fitted?

Does such a guide exist?

Regards,

Waggy.

[uuu]

As with all things boiler related, your local club boiler inspector should be consulted. There's no point undertaking a course of action that they frown upon.

A relevant paragraph from the boiler test code is this:

12.5 The validity period of test certificates are as follows:
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.

and:

f. Any structural alteration or repair of the boiler shall invalidate
all current certificates. This will necessitate a new initial shell
test followed by a 1.5xPW system hydraulic test and a steam
test.

So an obvious question is: Does this repair affect the structural integrity and/or is a "structural alteration or repair"?

Clearly if you wanted to solder in some blind bushes, you might loosen some other joints with the heat. However, just re-tapping for fatter screws, or even larger for screw-in bushes, might be considered not to be a structural thing. Only if your inspector shares this view of course.

Or you might not be frightened of a full two-times shell retest.

Wilf

[waggy]

Thanks for your reply, Wilf.

But again I’ll ask, Does such a guide exist?

Waggy.

[uuu]

Not as far as I know. Which is the source of many people's problems when dealing with older boilers. With so much left to the discretion of the inspector, you can get an easy ride or a hard one. Some inspectors err heavily on the side of caution, and insist on applying modern design requirements to repairs, which can be the devil's own job to implement. Or they expect features that are not even mandatory on new boilers, just recommended in the code. The code requirement in sub-paragraph "f" above for a "new initial shell test" can be interpreted as a need for the retested boiler to comply with all the new boiler standards.


Hopefully your inspector is more sympathetic, accepting the design standards of the original model. And hence my hope that your repair can be classed as non-structural.

Wilf

[waggy]

Hello Wilf,

Thanks again . I’m sure you’re right, nobody I’ve spoken to locally has heard of one.

Waggy.

[oldnorton]

I agree with Wilf. You are into a level of detail that has to be interpreted from the test documents.

This is the key phrase.. "...repair or modification which would affect the structural integrity of the boiler."

My understanding is that if you follow the established boiler design as drawn then a repair involving a slightly over-thick screw (of the same nominal thread) is not a modification. If however you re-tapped for larger and different screw threads then that 'might' be considered a modification, but it would be undetectable. If someone silver soldered new blind bushes then that would be a clear modification that requires a re-test, and it would be highly inadvisable because of disturbing old joints.

Safer to get a mechanically secure thread and use Rocol Steamseal.

Just my opinion..
Norm

[runner42]

Sept 1, 2023 14:58:09 GMT uuu said:

Not as far as I know. Which is the source of many people's problems when dealing with older boilers. With so much left to the discretion of the inspector, you can get an easy ride or a hard one. Some inspectors err heavily on the side of caution, and insist on applying modern design requirements to repairs, which can be the devil's own job to implement. Or they expect features that are not even mandatory on new boilers, just recommended in the code. The code requirement in sub-paragraph "f" above for a "new initial shell test" can be interpreted as a need for the retested boiler to comply with all the new boiler standards.


Hopefully your inspector is more sympathetic, accepting the design standards of the original model. And hence my hope that your repair can be classed as non-structural.

Wilf

Isn't there a procedure where the BI'S judgement can be challenged and referred to a higher authority if it appears to be OTT?

Brian

[waggy]

Hello Brian,

The UK test code states that the inspectors decision is final, no mention of appeal.

I once read the Australian code but can’t remember any right of appeal therein.

Regards,

Waggy.

[uuu]

I don't think there's a way of challenging a BI's judgement on an area where the UK code gives them discretion. Here's an obvious dispute area:

c. Inspectors may, at their discretion, issue a certificate of
hydraulic test with a shorter validity period where the Inspector
considers that the above periods are inappropriate to the age
and/or condition of the boiler.

and

"...to allow the Inspector to be satisfied..."

and

"...which is at an unacceptable level..."

and

"...check adequacy of screw threads..."

There are so many areas where judgement is required.



Here's the Federation website giving details of their services: fmes.org.uk/pressure-vessels-and-testing/

This does offer a "contact us" section with a suggestion there's someone to contact with questions:

"Safety Officer for questions relating to the proper conduct of tests, what must be tested and with regard to other pressure vessels such as for LPG"

I suspect, without having used this service, that it might enable a clarification of the proper interpretation of the code. And the point I made above, where an inspector might argue that a shell re-test for a repair could require a more modern approach to the boiler's construction than the original design, might be just such a clarification.

Wilf

[runner42]

Sept 6, 2023 6:37:04 GMT waggy said:

Hello Brian,

The UK test code states that the inspectors decision is final, no mention of appeal.

I once read the Australian code but can’t remember any right of appeal therein.

Regards,

Waggy.

Waggy,

Para 7.4.3 In the event of rejection of a boiler or air receiver by the boiler inspector, the owner and or builder shall have the right of appeal to the AMBSC in writing.

I am sure that this rarely used, but it at least ensures some standardization of the boiler code in it's application.

Brian

[Boadicea]

Waggy, with apologies for not being quite on subject, but you've probably got as good as you are going to get as an answer. Therefore my slightly related comments.

Firstly, why are people so worried about doing a 2x shell test. If the extra from 1.5 to 2 times pressure is going to significantly change things, it's dodgy anyway and needs attention or replacing.

Obviously tapping into copper is not the best but I have found it best to change from bolts to threaded rod and nuts and proceeding much as Old Norton suggests. At least you can remove whatever as many times as you like without as much risk.
I cannot see that would be weakening the sructure in any way.

There are BIs who would never pass tapped copper boilers - others are more accommodating. They are volunteers - that's their prerogative.

[millman]

My gripe about Boiler Inspectors is that they don’t stick to what’s in the book and make it up as they go. All the old designs had expansion brackets and firedoor fittings drilled and tapped into the boiler shell. The main thing is does it hold pressure, and if it does, what’s the problem. Regarding 2x shell test, why not? I would complain if it was done every time as there is no need but if a 80psi working pressure boiler withstands 120psi what’s the problem with 160psi if it means it shuts up some jobsworth and gets you a certificate. I would demand though that he writes on the certificate all his reasons for testing to the higher pressure. Thinking about inspectors in general, I have worked in industry all my life and have had dealings with loads of inspectors and they all find it impossible to check something to a drawing, a component can be absolutely perfect dimensionally, bang on mid limit everywhere but that’s not good enough, they will say that the turning is a bit rough, does the drawing call for a particular finish, well no but I would like it better, you can guess my reply, starts with F and ends in off. They just cannot adhere to the rules and sadly some of our boiler inspectors have the same problem.

[SteveW]

Sept 1, 2023 12:50:03 GMT uuu said:

f. ... <snipped> followed by a 1.5xPW system hydraulic test and a steam
test.

Wilf

Excuse my confusion but what is a "PW" and how big is it?

[millman]

I think he means WP, working pressure.

[uuu]

A PW is a Percy William. He starts off quite thin (say 150 lbs), then gets fatter as he ages (perhaps up to 220 lbs).

Wilf

[kelvin]

I was reading Alec Farmer's book this afternoon. Towards the end he discusses options for boiler making if oxy acetylene is not available and goes into considerable detail on the procedures for the more traditional threaded stays, nuts and soft solder caulking as used by LBSC. I wonder if anyone making their own boilers still uses this method?

[mbrown]

I certainly don't.

There was a piece in ME c.1970 by Norman Spink which he wrote following a visit to Alec Farmer, after which he concluded that Alec's techniques could be adapted for using propane, with everything silver soldered and rivets used as stays. The article showed a Pansy boiler under construction by this method. I have now made four boilers following this approach exactly and apart from the awkward leak which I described in my thread on 99 3462, which I dealt with using oxy-acetylene, they have all been completely successful using propane and nothing else.

Malcolm

[jo479]

Oct 1, 2023 18:54:38 GMT kelvin said:

I was reading Alec Farmer's book this afternoon. Towards the end he discusses options for boiler making if oxy acetylene is not available and goes into considerable detail on the procedures for the more traditional threaded stays, nuts and soft solder caulking as used by LBSC. I wonder if anyone making their own boilers still uses this method?

I used that method a couple of years ago, I drilled clear holes in the wrapper and tapped the holes in the firebox, screwed the stays in, silver soldered the outside stays, then nutted and soft soldered the inside stays, no problems, BI was quite happy, it stands the pressure x 2, that's all that matters.

[kelvin]

Oct 1, 2023 19:02:13 GMT mbrown said:

I certainly don't.

There was a piece in ME c.1970 by Norman Spink which he wrote following a visit to Alec Farmer, after which he concluded that Alec's techniques could be adapted for using propane, with everything silver soldered and rivets used as stays. The article showed a Pansy boiler under construction by this method. I have now made four boilers following this approach exactly and apart from the awkward leak which I described in my thread on 99 3462, which I dealt with using oxy-acetylene, they have all been completely successful using propane and nothing else.

Malcolm

Spot on thanks.   Sept 1970. Luckily my club has a good archive.