fang
Seasoned Member
Posts: 100
|
Post by fang on Jul 25, 2014 17:45:15 GMT
Yes I realise it is for flue tubes, but my point is that surely 1.5mm is far too thin to be used in the construction of a steel boiler, I was always told 6mm was the minimum thickness which also takes into account a corrosion allowance. But if you refer to the strength as I have previously mentioned copper is 1/3rd of steel, therefore a 3mm thick steel boiler will take far more pressure than a 3mm copper would.
This is my point about the lack of information, I can do all the calcs for a steel boiler, and the material thicknesses will be far too thin to be sensible to be used when corrosion is allowed for, so as far as I can tell it is between me and the boiler inspector to agree on wall thickness. And one boiler inspectors opinion will probably be different to another. In the Martin Evans book there is a percentage corrosion allowance, but as has been mentioned in the Model Engineering press "you cannot scale nature" so therefore surely a defined thickness (e.g. 2mm, 3mm, etc) for corrosion would be better for corrosion. Again most industrial pressure vessels I have seen have a corrosion allowance given for them
|
|
jackrae
Elder Statesman
Posts: 1,333
|
Post by jackrae on Jul 25, 2014 19:14:01 GMT
There is a basic difference in failure mode between a collapsing tube, which tends to go flat (and remain pressure tight), and a pressure vessel which tends to rupture catastrophically.
The problem that club inspectors have to consider is the "code of practice" that have been formally agreed between the various associations, the insurance companies' representative company and the HSE.
You may design your own boiler to your own set of calculations but you will probably have to have the appropriate 'fired pressure vessel' examination and test certification undertaken by an insurance company that handles such business. With that certificate to hand you may then find your local club happy to accept your locomotive (or whatever) for steam test and operation.
|
|
jma1009
Elder Statesman
Posts: 5,901
|
Post by jma1009 on Jul 25, 2014 20:27:01 GMT
there is a very simple way of getting a what you want. decide what the boiler is you want to build (so far lacking from your posts) and then quite a few of us will be able to point you in the right direction, from our own experience of such matters. simply asking 'why'? without stating what you plan to do is frankly pointless! i hope this isnt too dismissive but ive been in this game far too long to deal with generalised assaults on accepted practices! cheers, julian
|
|
bhk
Part of the e-furniture
Posts: 458
|
Post by bhk on Jul 25, 2014 20:55:37 GMT
buy a copy of the OZ code, design your boiler to that, then once you got it take it to your boiler inspector along with OZ code and you can then say that it is designed to that standard.
I agree completely fang (and others) that the green book is completely lacking, but it's not going to change overnight so work with what you got.
|
|
jma1009
Elder Statesman
Posts: 5,901
|
Post by jma1009 on Jul 25, 2014 21:16:58 GMT
i dont agree with bhk. i know what my club boiler inspector would say if i quoted the australian code! on the other hand if i said i'd designed a 5"g MABEL boiler to the 1968 martin evans drawings with the firebox 1/4" longer and the stays considerably increased as per don young, and all silver soldered boiler bushes and bushes for the wet header and regulator, he would say 'ok, julian, thats fine with me'. 'I know you can do the calculations but i dont need them as i know you know what's what'. this is where things get tricky. if i copied the original SIMPLEX boiler with crownstays not fixed to the outer wrapper and gunmetal stays of large pitch and a slight deviation from the drawings he would say 'i'm not happy with that - the stays are far too far apart and i dont approve of gunmetal stays and crownstays not attached to the outer wrapper'. and i wouldnt disagree with him because the original SIMPLEX boiler design is IMHO very suspect. though many have been built that are quite ok! cheers, julian
|
|
pault
Elder Statesman
Posts: 1,497
|
Post by pault on Jul 25, 2014 21:58:32 GMT
Personally I would sack a boiler inspector who declined to physically review the calculations and design of a modified design based on the character of the person carrying out the redesign. After all we can all make mistakes. If you use that logic a boiler inspector would only look at boilers built or used by the incompetent or untrustworthy.
|
|
bhk
Part of the e-furniture
Posts: 458
|
Post by bhk on Jul 25, 2014 22:05:13 GMT
i dont agree with bhk. i know what my club boiler inspector would say if i quoted the australian code! on the other hand if i said i'd designed a 5"g MABEL boiler to the 1968 martin evans drawings with the firebox 1/4" longer and the stays considerably increased as per don young, and all silver soldered boiler bushes and bushes for the wet header and regulator, he would say 'ok, julian, thats fine with me'. 'I know you can do the calculations but i dont need them as i know you know what's what'. this is where things get tricky. if i copied the original SIMPLEX boiler with crownstays not fixed to the outer wrapper and gunmetal stays of large pitch and a slight deviation from the drawings he would say 'i'm not happy with that - the stays are far too far apart and i dont approve of gunmetal stays and crownstays not attached to the outer wrapper'. and i wouldnt disagree with him because the original SIMPLEX boiler design is IMHO very suspect. though many have been built that are quite ok! cheers, julian Julian that's great for you and your inspector, you obviously have a good relationship, which Is not a healthy one, as the reason we have boiler inspectors is to regulate work done by us, not hand out free cards to mates (that's kept for the government) The fact of the matter is, boilers built to the OZ code are far superior in design and strength. It would be a very "old boys network" type inspector to discount it.
|
|
Geoff
Hi-poster
Posts: 170
|
Post by Geoff on Jul 26, 2014 5:04:26 GMT
I detect in some of the opinions in this thread, a hesitance to accept the Australian code in the UK for whatever reason .... Perhaps it is thought to be too conservative, or perhaps just because it's not British. The point is, however, that no matter where it comes from, the engineering principles on which it is based are the same everywhere, and it does provide a comprehensive guide as to how to calculate things, and how to do things.
i have issue 2 of this code which is 12 pages long and cost $1 in 1976. The 2012 version is 66 pages long. Either this fraternity is also affected by the worlds ever strengthening bureaucracy, or the code now provides better information than it did before.
One thing with boiler inspectors .... I'm sure they are all experienced and have done it all before, and they do sometimes tend to place their tried and tested methods ahead of the code requirements. But if you believe the inspector to be overly conservative, and you still fall within the guidelines of the code, are you ill advised to contradict the inspector? Personally, I am here to build a boiler .... not to have an argument.
|
|
jma1009
Elder Statesman
Posts: 5,901
|
Post by jma1009 on Jul 26, 2014 6:22:45 GMT
i apologise for not making my point clear in my last posting.
the UK system for club boiler inspectors is primarily based on existing 'tried and tested' designs. i am not criticising the Australian code at all, and i agree with Ed that we ought to have the same system here. my point was that in codifying things you will (i presume, as i dont have a copy of the australian code) condemn a number of boiler designs particularly by martin evans which are 'tried and tested' such as his SIMPLEX boiler, and his use of large stay pitches and gunmetal stays.
i know for a fact that don young and martin evans had strongly differing views on miniature locomotive boiler design.
those who know the 5"g MABEL boiler will know it is a completely different type of boiler design from the SIMPLEX boiler design. the 5"g MABEL design is what i would call an LBSC/don young type of boiler. the SIMPLEX boiler on the otherhand is not and was not of traditional design either at the time (both are 1968) or now.
i would be interested to know how the australian code deals with the original SIMPLEX boiler design!
cheers, julian
|
|
bhk
Part of the e-furniture
Posts: 458
|
Post by bhk on Jul 26, 2014 6:31:13 GMT
i apologise for not making my point clear in my last posting. the UK system for club boiler inspectors is primarily based on existing 'tried and tested' designs. i am not criticising the Australian code at all, and i agree with Ed that we ought to have the same system here. my point was that in codifying things you will (i presume, as i dont have a copy of the australian code) condemn a number of boiler designs particularly by martin evans which are 'tried and tested' such as his SIMPLEX boiler, and his use of large stay pitches and gunmetal stays. i know for a fact that don young and martin evans had strongly differing views on miniature locomotive boiler design. those who know the 5"g MABEL boiler will know it is a completely different type of boiler design from the SIMPLEX boiler design. the 5"g MABEL design is what i would call an LBSC/don young type of boiler. the SIMPLEX boiler on the otherhand is not and was not of traditional design either at the time (both are 1968) or now. i would be interested to know how the australian code deals with the original SIMPLEX boiler design! cheers, julian Quite simply a lot of them are not allowed, there are M/E supplies here that supply drawings for boiler reworked to comply with the code, failing that the code gives the builder all the information he and the inspector needs to modify the design to comply Cheers Sean
|
|
jma1009
Elder Statesman
Posts: 5,901
|
Post by jma1009 on Jul 26, 2014 6:41:12 GMT
thank you Sean, that is very useful and illuminating information, and might perhaps explain why the UK regs are years behind the Australian code even though it is 11 years since martin evans' death. cheers, julian
|
|
|
Post by alanstepney on Jul 26, 2014 7:20:10 GMT
The Australian code is good, but there is no GUARANTEE that a UK Insurance company will accept it, and that alone is a good reason for our inspectors not to automatically accept it.
What IS accepted is always down to the Insurance companies, although for our models, where the risk is minimal, they delegate their responsibility to club inspectors, who must (should ) adhere to the guidelines and follow the <colour> book.
Like all systems, it isnt perfect but it is what we have to live with, so may as well accept it.
|
|
|
Post by Roger on Jul 27, 2014 8:12:46 GMT
I get the impression that the UK situation doesn't change because it suits the social network that exists and those who administer it. I doubt if change will come about voluntarily until there's an accident and the insurers are alerted to better defined standards. If it comes from anywhere, it's most likely to be from the GL5 group who take the trouble to lay down specifications.
|
|
jackrae
Elder Statesman
Posts: 1,333
|
Post by jackrae on Jul 27, 2014 9:37:31 GMT
To my mind, section 5 of the green book gives boiler designer/builders more than sufficient leeway to produce a design and build to whatever code they wish (including the excellent Australian one) provided they can demonstrate by historical precedent or calculation that what they intend to build is sound and meets any legal requirements as laid down by the HSE. The most important requirement is that the designer/builder discusses with his/her intended inspection authority what they intend to do BEFORE they actually commence design/construction. As others have indicated, the physics of pressure vessels is global and no country has the right to claim that Johny Foreigner couldn't possibly be better than us.
|
|
|
Post by Roger on Jul 27, 2014 10:46:04 GMT
To my mind, section 5 of the green book gives boiler designer/builders more than sufficient leeway to produce a design and build to whatever code they wish (including the excellent Australian one) provided they can demonstrate by historical precedent or calculation that what they intend to build is sound and meets any legal requirements as laid down by the HSE. The most important requirement is that the designer/builder discusses with his/her intended inspection authority what they intend to do BEFORE they actually commence design/construction. As others have indicated, the physics of pressure vessels is global and no country has the right to claim that Johny Foreigner couldn't possibly be better than us. Especially when that 'Johnny Foreigner' might be us after the referendum.
|
|
Tony K
Elder Statesman
Posts: 1,573
|
Post by Tony K on Jul 28, 2014 7:59:23 GMT
I get the impression that the UK situation doesn't change because it suits the social network that exists and those who administer it. I doubt if change will come about voluntarily until there's an accident and the insurers are alerted to better defined standards. If it comes from anywhere, it's most likely to be from the GL5 group who take the trouble to lay down specifications. It will only change if people who want it to change actually get off their rump and wade in there to make it happen. I think we know those who are unhappy with it only want to moan - in the forlorn hope someone else will change it, don't we.
|
|
|
Post by Deleted on Jul 28, 2014 8:33:11 GMT
"I think we know those who are unhappy with it only want to moan - in the forlorn hope someone else will change it, don't we."
Ah, those would be British then ?? LoL !!!
|
|
|
Post by ejparrott on Jul 28, 2014 10:30:49 GMT
I and several others tried during the consultation period leading up to the publication of the current scheme. We were ignored.
|
|
|
Post by GeorgeRay on Jul 28, 2014 16:52:27 GMT
Has anyone else read the minutes of the MELG from 7 March this year. They can be found on the NAME site under news. It appears that consideration is being given to providing design advice as I read it. It's para 69.
|
|
|
Post by ejparrott on Jul 28, 2014 20:00:25 GMT
nope. Didn't know they were available.
|
|