dezinctification

[Garry Coles]

::)Hi everyone
We all know that one must use gunmetal for boiler fittings because of dezinctification of brass, but my question is why does my building manual for the 3 1/2" William say that items such as the valve chest cover and the valve rod nut can be made of brass. Surely these items are still subject to the high wet pressures of that in the boiler. So why is it OK to use brass in these parts.
Garry

[simonwass]

Good question.
On the subject, in the latest EIM there is a letter questioning the use of sifbronze in a boiler. The technical editors answer says its ok (just, as it will dezincify) inside a boiler but strangely not ok for exterior joints?
Anyone able to say why?

[baggo]

Hi Garry,

It's probably considered acceptable because failure of the brass away from the boiler environment would not cause a dangerous situation. Parts such as steam chest covers are pretty substantial items anyway and would take a long time to be seriously affected. The worst that would happen is you'd probably start to get pin holes developing and steam leakage. Possibly the oily atmosphere in the steam chest will offer some sort of protection as well.

So far as I am aware though brass is still often specified for regulator to backhead flange tubes inside the boiler although failure of such a tube would probably not be considered a risk.

Another thought - I wonder how many commercially made boiler fittings are still made from brass? I bet some are!

John

[alanstepney]

One of the risk areas with brass is where it is in contact with sulpherous material.
Such as coal or the by-products from burning it.

[havoc]

The problem is when it is in contact with water, as in boiling water. Steam itself isn't an issue. So for fittings that sit in the wet atmosphere of the boiler it matters to use bronze, for valvechests etc not.

[baggo]

Simon,

there was a bit of a debate in ME vols 197 and 198 (postbag) regarding the suitability of Sifbronze in boilers. This was instigated by Dennis Monk in reply to an article by Peter Rich in which Peter stated that he used Sifbronze in his boilers. Dennis replied that under no circumstances should Sifbronze be used as, containing zinc, it would suffer from dezincification.
A further letter by F A J Collin pointed out that Sifbronze contains phosphorous which has a great affinity to oxygen (this gives it it's self fluxing properties) but also has a great affinity for sulphur which, when used in areas exposed to same (e.g. in a firebox burning coal) causes the Sifbronze to suffer corrosion and early failure.

I suppose you could assume from that that Sifbronze is not suited to inside or outside joints!

I would imagine though that there are umpteen Sifbronzed boilers around that are still in service today! Who do you believe

John

[simonwass]

Hi John,
I'll have a look through the ME's, if I've got them. I wouldnt personally bother with sifbronze, silver solders are so good now that a few different flavours are enough for my needs without the extra heat needed for sifbronze. Now I've got oxy/acetylene/propane I could possibly do a boiler just with 1 flavour. Heating sub-assemblies for silverflo24 is hot work with just propane!

I've probably said it before but I know of a boiler with brass bushes which has done 100's of hours of hard steaming with no ill effects. I wonder if a scale layer is protecting the tiny area of the bush which is in contact with the water?

[alanstepney]

Who do you believe ?

I believe Johnson Mathey, and they have said that Sifbronze shouldnt be used for boilers.
To be accurate, I believe that, "is not recomended..." was the phrase they used.

[waggy]

Just to throw a spanner in, as they say:

"Pender", the Isle of Man loco that has been sectioned and is now on display in the Manchester Museum of Science and Technology, has brass boiler tubes!
Doug Turner, one of our club members, was in charge of this job. He gave a couple of talks on the subject and passed around a piece of tube to prove they were brass, as one or two raised an eyebrow when he told us. The tubes had waisted badly but whether this was due to internal erosion by gasses or external dezincification, I can't remember. Can't ask Doug either, he's one of St. Peters boilermen now. (No, before you ask, not the Vatican!)

Regards,

Waggy.

[circlip]

There must be thousands of "illegal" Mamod boilers about, OH b++++r I hope there's no Elfins reading this

[havoc]

A lot of these rules in model engineering are handed down from the halways of sacred time and repeated and accepted without any critical tought. This is -in my opinion- a serious defect in the hobby. When you see presciptions, materials, ways of working, plans etc handed down/reprinted without anyone pausing and thinking "why?" then it is time to drop the "engineering", just "model maker" would be better.

Real boilers -where if something went wrong some serious damage was done- used copper and brass. Copper fireboxes with copper stays using screwed in copper threads. Brass tubes, brass fittings etc. Admittedly, they were regulary inspected and the water treatment took all this into account. But still.

Anyway, where is The Viffer when you need him?

[the_viffer]

havoc said:

Anyway, where is The Viffer when you need him?

Supping ale?

Valve nuts and steam chest covers are so thick and as someone (sorry forgot who) pointed out not subjected to raw unboiled water that I'd not be too concerned. Also a valve nut is not subject to any pressure differential and so needs little strength.

Brass boiler tubes were commonly used it is true. I can think of 2 reasons. First not all brass suffers from dezincification. The reasons are complex. The problem is by looking at it you can't tell whether it is the kind likely to dezincify or not. Secondly the classic days of brass boiler tubes were the days of coke firing which abraded the tubes rapidly so they wore out before they suffered chemical degradation.

I think all my steam locos have commercial fittings like clacks and I think all apart from a Dave Noble water gauge are made of brass. Possibly they will dezincify but I think the damage from one letting go would be the same as breaking a gauge glass which is to say enough to put you off a high fibre diet for a day or two but not much more than that.

Under no circumstances will I use phosphorous containing brazing materials like Silphos which are likely to get in contact with the products of coal combustion. The ME trade don't offer them quite rightly in my view since while they are lovely to use they are just plain dangerous (IMHO) when in contact with hot (and especially wet) sulphur containing combustion products. I rather think Keith Wilson used to advocate them but back-pedalled hard following advice from Johnson-Matthey.

[circlip]

Havoc you really should think before coming out with sweeping statements about the "rules" applied to model engineering, because not only are you vilifying the works of many engineering gods, but showing an ignorance of the works carried out by them. I suggest you obtain back volumes of The Model Engineer, not LESS than 50 years old and earlier and have a serious read. You MAY change your tune.

[the_viffer]

circlip hi

I am all for debate. I was going to say for moderately expressed debate but then I recalled some of my posts.

The great gods of ME in days gone past maybe right or they maybe wrong but we do not show disrespect by reviewing those opinions IMHO. I recall both LBSC and Martin Evans for example advocating unbushed tappings into boiler shells. Time moves on and we learn more. I think it is good to challenge the views of the old men and to take what is good but discard what experience shows is not so good.

[havoc]

Havoc you really should think before coming out with sweeping statements about the "rules" applied to model engineering, because not only are you vilifying the works of many engineering gods, but showing an ignorance of the works carried out by them.

Circlip, it is indeed maybe an overly broad generalisation, but it is tought out. Just the facts that you call them "gods" is one of the issues I have with it. In calling them gods people fear to call into question their faults.

When I ask questions about ways of work or so at the club the answer is almost always "because it has always been done like that".

Well, I don't accept "it always has been like that" as an answer. IF however there can be shown that what has been done forever is good engineering practise I will agree without problem.

The Viffer summed it up well:

Time moves on and we learn more. I think it is good to challenge the views of the old men and to take what is good but discard what experience shows is not so good.

I have no problem using bronze for bushings like some seem to have. There are other reasons apart from dezincification like I prefer the movable (brass) part to wear out before I have to replace the bushing in the boiler. But I do have problems with very dogmatic choosen sizes and thickness of parts for boilers. Certainly in the face of experimental data like the australian or new-zealand destructive boiler tests. Or why are there so many plans around that need correction after correction even after several reprints? Why is there so little new?

Just like when it goes about tools. (I know this is dangerous territory) A lot of ME's prefer still the old brands making models that can be traced back for 50 years without any sizeable improvement. WHY? Because the ME gods used them so that must be the tool to use.

Oh, I do think. Maybe that's the problem.

[houstonceng]

And, all said and done, if your club boiler inspector or insurer don't like brass on your boiler you ain't goin to get a "certificate" no matter what metaleurgical evidence you submit. See, for example the Oz Boiler Code on boiler plate flange size (ie wider than necessary)

However, the ones who act intelligently and are willing to accept, for example, that the flange on a boiler bush only needs to be enough to stop it falling through during silver-soldering - thus preserving maximum metal for the studs - rather than the 1/8" shown on the original 1947 drawings, are probably willing to accept a reasoned arguement. Do you want to suss out if they're this latter type ?

I have great respect for LBSC, Martin Evans, Don Young and any other pioneer in our hobby. Without their groundbreaking work the hobby, as we know it today, probably wouldn't exist.

I don't, however, think that they were Gods, nor do I think that they were always right.

If I remember the quotation correctly "for perfection is not given to man on earth and perfect holiness belongs only to the Lord" (So there !)

[circlip]

Oh the power of the INTERNET, I wonder what the Gods would have made of it, would they have used it as a tool to promote an interchange of original experimentation and knowledge at the speed of light or opening their gobs and bumping their gums cos they could. LBSC silenced the pundits who said live steam passenger hauling was impossible in small scales, how? by actually doing it, not hypothesizing. You want to disprove the "rules?" fine, I don't dispute that technical advancement does this, but back it up with facts, not noises. We can all pick out little snippets to snipe at each other with to try to sway the argument one way or the other, but unfortunately the old adage still applies, rules are for the guidance of wise men and the obeyance of fools. As far as the boiler inspectors "whims"are concerned, in the event of a failure, whose testicles are on the chopping block?
I wonder how many of the critics would do the job, or what their reaction would be to one of their loved ones being injured by an "OK we'll just let that go" scenario? Oh dear I'm questioning on of the hallowed rules.
You're right Viff, with SOME people you can have a REASONED discussion.
"where's the viffer when you need him" can't you manage on your own Havoc?

[alanstepney]

There has been experimentation and that, added to 200-odd years of experience, and a great deal of scientific research has resulted in our having detailed formulae for boilers ( and for most aspects of steam).
However, most of us dont want to spend our time in academic studies to learn all it all, so use "rule of thumb" methods, and make generalised statements.
Nothing wrong with that, provided that such rules and statements are based upon a solid foundation.

When people question those rules or statements, as they often do, the real answer is that they should start by studying the subject to see the "why" for themselves, and /or do the basic research to "prove" or disprove the statements.

However, do any of us have the time (or in my and probably many other cases) the ability to do so?
You want to know about dezincification?
Start with studying chemisry to at least Degree level.
Meturlurgy?
The same
Engineering? (Re: length of bushes for example)
The same again.

Not going to leave much time for making models, is it?

[havoc]

"where's the viffer when you need him" can't you manage on your own Havoc?

I have no problem managing Circlip, but when it is about chemistry (like dezincification where it all started) Viffer is far more knowledgable than I am. He as already given several chemistry lessons here that were very interesting. I have no trouble in admitting that. But I have no troubles with physics and electronics.

[petercolman]

I am not a live steam man but I used to earn my living selling copper allys to all industries an I had to offer technical advice when needed. The problem with brasses is that the 'alloy' is in fact a mixture of the elements in discrete particles, this gives us the advantage of lead bearing free machining alloy as the lead particles are weak and so the chips break up.
In the 1960s we discovered that maganse bronze building fixings were failing in service, there was a fatal accident when a window cleaners cradle fell to the ground when a 1.5 inch diameter cast in bolt sheared off. It was found that the zinc had all disolved away in the sulphur bearing atmosphere (in London) and the bolt had become brittle.
This caused panic in the Non ferrous industry, there were a few tests made and several other buildings had emergency repairs.
So what I am saying is that this is a problem caused by stress in the corrosive atmosphere, lightly loaded items seem to be less prone to failure, the quality of the water is also critical with very soft supply being the worst.
Heavily built items under light load in the right atmosphere lasted well qand I think that the boiler tubes mentioed above could be in this type of siyuation, also remember that this is a relatively new discovery when copmpared to steam engine design
Finally to help you sleep well tonight we did get a case of similar fauilure in a gun metal valve in a sea water environment.
My advice is never walk too closly to those cladded buildings fom the 60s ( later they turned to stainless and I know of similar faiures with that)
Slep well
Peter