Stainless steel boilers

[PH]

The article in French on stainless boilers is probably:

www.letraintrain.com/magazine/chaudiere%20inox.html

It's a summary of the way we do things here, where, as far as I know, boiler explosions are not regular occurences, contrary to what some of the posters would appear to assume must be the case.

[havoc]

Tel, I do understand that if you are equiped and have experience with certain procedures then as long as they are allowed/usable that you stick with it. I would probably do the same.

I'm not taking it personally either but I do have a problem with the attitude of saying "no" without tought or reasoning or with faulty reasoning.

I read a long article on building and using ss boilers on a French website, I'll see if I can find it again.

This one? www.letraintrain.com/magazine/chaudiere%20inox.html

[alanstepney]

Right now, I wouldnt even consider building a boiler in stainless steel.
As I am in the UK, there is no point in my spending time and money on something that I wouldnt be allowed to use.
Hence I will dismiss them out of hand.

I know that some countries do allow it, and were I in one of them, might give it a closer look.
But, would I build one?
That is a different question.
I have read extensively on the subject, and all I have seen seems to indicate that, in some cases, there can be serious problems with SS for boilers.

As the number of (model) boilers in the UK vastly exceeds those in the rest of the world combined, and the majority are of copper, it is safe to say that we have a long track record, and tried and tested procedures that result in an enviable safety record.

Would SS be better, safer, more efficient, or...?
It certainly wont be more efficient.
Safer?
Who knows. Ask me in 20 or 30 years time.
Better?
Please define.

About the only argument I have seen here that makes sense is the economic one, with, at present SS being cheaper than copper.
Even so, to me that is a minor point.
Given the time that one spends building a locomotive, not to mention the cost of other parts, I wouldnt begrudge the cost of either, if it leads to a longer safer working life.

[steam4ian]

G'day Alan

I started this "argument" and I can't say I am sorry. ;D

Whilst copper would be the material of choice for the home builder some form of high alloy steel may well offer advantages for the commercial manufacturer of boilers. It appears many purchase their boilers, even the esteemed Dr John.

If I had to say what I am actually against it is the refering to the material as "stainless steel" because that leads to dangerous misconception in the minds of the ill informed.

If the alloy is strong, light, resistant to the various corrosive elements found in steam boiler service, there is an well established means of manufacture, maintenance and inspection then I am all for it. The fact that the alloy contains Chromium and Nickel with other elements is then of no concern.

A cursory inspection of the article referred to by Havoc appears even to a non French reader to be covering the right areas. But my "polly voo fronzie" is no help. Havoc please help with a translation!!! Please!!

Regards,
Ian

[mutley]

try this. if it doesn't work copy and paste the link into Bable Fish.
babelfish.yahoo.com/translate_url?doit=done&tt=url&intl=1&fr=bf-home&trurl=http%3A%2F%2Fwww.letraintrain.com%2Fmagazine%2Fchaudiere%2520inox.html&lp=fr_en&btnTrUrl=Translate

Andy

Update.
I have now had the chance to read this article and it doesn't really seem to add much to the arguments for or against. It has a brief description of the main groups of stainless but the rest of it refers to techniques which are already well known in this country and others from the construction of steel boilers.
it has certain info about construction detail specific to working with stainless or I have missed something here?


Andy

[havoc]

Havoc please help with a translation!!! Please!!

Here it comes (in several parts). I used the Bablefish translation as a start. That translation is very good to be honest. I didn't expect something understandable of such a rather technical article. The translation is rather rough, I'm neither french speaking nor english speaking so somethings could have been better had more time been put into it.

part 1:

How to build a stainless boiler?




Of the three metals most usually used for the construction of the boilers stainless steel is the most recent and is often discussed the most, this controversy being often fed by model makers sensitive to the generally accepted ideas conveyed by “specialists”.
Since the origin of steam the boilers were built out of copper, because this very old and well-known metal lent itself well to this use. Reliable, stable, not very oxydable by water and the flame, its assembly by riveting gave satisfaction. Then with help from the progress of metallurgy, the ironmongers used mild steel always riveted, then welded in certain assemblies.
Combinations coppers/steel were carried out to improve the performances, but especially to limit the corrosion of certain parts of the boilers. Thousands of boilers were built out of steel all over the world. All were confronted sooner or later with their archenemy rust which comes to end any mild steel subjected to water and the flame.
Our century saw also important progress in the making of these steel alloys known as stainless which one at the present time finds in all the fields of our civilization. All the branches of modern industry use these steels. Transport, food, household, nuclear power, chemistry, medical, aeronautics, space, electronics, and I forget some, make huge use of these stainless steels of which there exists a multitude of grades.

part 2:

CLASSIFICATION OF STAINLESS:
Reassure I will not be made a metallurgy course, I do not have competences for it. It should be known that stainless are grouped in three families what must make good about fifty nuances!! (transl: why are there then 4 in this article?)
Stainless martensitic:. Strongly charged with carbon they are used in “heavy” mechanics for their good mechanical resistance. For example the Z20C13 also called AlSi420 is martensitic stainless with 13% chromium used in turbine shafts or oil industry.
Stainless ferritic like Z8C17: . They are stainless which “takes” the magnet. For reasons of mechanical resistance after welding it is not advised using them. It is preferable to use stainless austenitic which represents the third family of stainless. In AlSi classification they are indexed in the 300 series (304, 309,316 etc).
Stainless austenitic: They contain between 16 and 25% of chromium (C) between 9 and 20% of nickel (NR) and can contain 2 to 3% of molybdenum (D) and titanium (T). Their carbon content varies from 0,02% to 0,15%. The letter L which follows names 304L or 316L indicates that we are in the presence of a steel with low carbon rate (Low carbon), which is interesting for our live steam applications. Indeed these grades resist better than the others inter granular corrosion.
Refractory stainless: Which gives our gridirons a quasi unlimited lifespan.
These are quite simply about the grades 309S and 310S which resist temperatures ranging between 750°C and 1100°C depending on the atmosphere to which they are subjected, (750°C for a sulfurous reducing atmosphere and 1100°C for an oxidizing atmosphere). This range of temperature is reached without difficulties in our fireboxes and the random quality of our coals leads to combustions of which the atmosphere is badly defined.

part 3:

PROVISIONING:
Obviously the metal traders are capable to provide you the most current grades. Unfortunately the quantities are seldom compatible with the desired quantities and dimensions. Dimensions of stainless tubes being standardized, it is an illusion search for a non-existent diameter of tube. In this case it is wiser to make roll a sheet with an often poor result, or more simply to adopt the closest diameter of (tr: standard) tube.
The abundant use of stainless in industry makes that many scrap merchands have pieces very interesting for our uses. Of course the identification of the grade is more difficult. It should be known that very often on the tubes the grade is clearly indicated in full (Z3CN19/11 for example) and that the presence of a small magnet will inform you very quickly.
Stainless 304L (Z3CN19/09) or 316L (Z3CND17/11 02) is very widespread and emminently usable for our boilers.
Refractory stainless is of an almost black colour and slightly magnetic.
The systematic search of seamless tubes is exaggerated when one sees the pressures which the welded tubes resist….

MACHINING:
Pet peeve of the turners/milling machine operators, stainless with the reputation to be a nasty trick to work due to its diversity of behavior under the tool. It is at the same time soft and resistant. The tools must be perfectly sharpened with cut and "skin" (tr I think this should be "relief")as for brass. The use of carbide tools is useless if it is not for an increased longevity. Still it is necessary that they are sharpened like a ARS or HSS tool. (beware for breakage when stopping the cut!).
The cutting speeds are not very high and lubrication reveils here all its importance.
By applying these principles one can obtain a polished surface finish.
The forming of stainless thicker than 2mm is a delicate operation and it is better avoided as much as possible. That is: hot or cold stainless folds badly unless you have a good quality and powerful press/folding machine. Shearing is only carried out correctly with the guillotine. Stainless behaves a little like blue (tr: steel-) sheet.
A good angle grinder and a good hacksaw are still on our level the best tools to work stainless.
We will further see that the difficulty of forming will lead us to modify the manufacturing process of a boiler in a very interesting way.

[steam4ian]

G'day havoc and Andy

I just penned a reply but lost it and have now run out of time. Must rush to catch my train.

Regards,
Ian

[havoc]

part 4:

WELDING: .
In this field also a generally accepted idea circulates which wants that stainless should be welded only under gas atmosphere. The six or seven stainless boilers which I welded with traditional coated rods prove ten or twelve years later that this method is perfectly valid. It is especially usable by the average live steamer having only avarage tools.
It is not essential to have a very sophisticated and powerful welding set. One can perfectly make good work with an ordinary setup delivering at least a hundred amps with rods of 2,5mm for sheet ranging between 2,5mm and 3mm. The manufacturers of rods put on the market of the products whose user friendliness is disconcerting. Facilitated starting and stability of the arc, excellent fusion of metal, cord of beautiful quality, perfect sealing if work is correct, easy detachment of the slag (attention to projections during cooling!) everything adds to a good performance even for an average welder. Only disadvantage (one needs one of them!) the rods are a little more expensive than rods for use on steel. Many brands of similar quality are available, the prefered grades and most usually suggested remains 304L or 316L.
For a good performance and ease of execution it is prefered to work flat and by carrying out the cord (tr: bead?) from left to right (or vice versa for the left-handeds person). It is necessary to manage to weld in the same way that one writes, comfortably installed, with natural and soft gestures. Just as of long hours of writing to the hand end up deteriorating the quality of it, long sessionss of welding will see a deterioration of the quality of your welds. We are not welding professionals and the quite remote from the concept of output for our activities. In what relates to me, the welding of a boiler is spread out over two or three days while having at my disposition an electronically controlled welding set with D.C. current which can melt 4mm rods continously! The small welding sets available to the general public provided with thermal trips will very judiciously calm your possible drive!!
Working flat has the advantage of needing only one average intensity setting which you will have had the care to set before on some scraps. Before any welding your new rod will have to be scraped on the mass (tr: earth connection?). Starting must be frank without joining, the arc must be maintained without difficulty and does not have to splash (tr: spatter?) at the sides. The starting voltage of stainless rods are sometimes low than for steel rods. The adjustment of the intensity is paramount for a good flat work. It is necessary to take time to do it.
The stoping of the arc must be instantaneous as not to create a crater source of micro leakages. The resumption of the weld must be carried out with a good overlap of the preceding end. The hammer to prick the slag is useless because the stainless slag jumps all alone, sometimes violently to the eyes, (protective) glasses imperative in addition to the -not too dark- mask for having a good view of your work, not too clear either for a good protection.
The speed in advance of your weld should not be too fast (frequent error!)It is necessary to leave the metal the time to melt and its correct deposit on the parts. A millimetre per second constitutes a median value in advance.
The rod must be well positioned on the middle of the angle formed by the parts with a slope of 30° approximately in the direction of the advance. It is not useful to describe arabesques with the rod as some do. A rectilinear and regular advance is to be preferred.
Before carrying out a final weld it is essential to put in a few points on your parts or your whole of parts to prohibit any relative displacement. Two parts perfectly square will not be square once your weld is carried out if they are not joined at a few points before you start. The welding makes metal“work”, it is necessary to take this into account. Putting in a few points with the stainless rods is facilitated by the quality (tr: ease) of starting with these rods. And if your points are not good, do not break it as for a rod steel. Firstly it will break with difficulty, secondly you will twist the edges of your part. It is by far preferable it to saw or it grind it and to point again next to it.

part 5:

SEALING OF THE WELDINGS:
It is one of the paramount questions for a boiler. If your welds are regular with a continous metal deposit and distributed on the two parts, if your starts and stops of welds are frank and without craters with correct retakes of welds, you have all the chances not to have any leaks. Contrary to the welding under argon which can present the risk to make porosities, execution with the rod puts you practically safe from this.
To be sure of the quality of your weldings it should be checked with simple and effective means. The acquisition of aerosols for revelation of cracks is a small investment for many work pieces. The first consists of a coloured wetting agent will be pulverized on the back of the weld. After washing of the surplus and drying, the white indicator will be pulverized on the other side of the weld. At the end of a few moments small (or gross!) color stains will be spread out around even the smallest leak. A small blow of strawberry files at the end of a flexible device, a pretty point of arc above and the turn is played (tr: ?? what he means is a bit of filing and a spot weld I think). A new checking on the spot is not useless because it happens that under the effect of the arc the leak moves without being stopped.
This method of checking is reliable and must be used throughout manufacture. It should not be forgotten that certain weldings will become inaccessible later on. You cannot make any error here. Any weld must be checked in this way. That can appear tiresome, but in my opinion quality and safety are at this price. And considering the difficulties which the European regulation prepares us, the live steamers must be serious.

GRINDING OF THE WELDINGS:
This operation is as far as possible to avoid, because if your welds are regular they must remain in that state. However so for aesthetic reasons you are brought to grind surpluses of welding, be careful in the handling of the grinder or the flexible device (tr: an abrasive flap disc?). And systematically carry out a checking afterwards. One never knows!

If there is interest I'll do the rest. It is less about techniques used. More about the parts of a boiler and the sequence of putting it together.

[steam4ian]

Thank you again Havoc.

I have waded through the rest of the article, the translation is only approximate and yours is most helpful.

A few points (don't take as a criticism) I note are:
There is no reference to certification for use in public areas; I don't know what the French requirements might be.
There is no reference to a certificated welder with proven competence. The writer seems to be recommending MMA, but with careful choice of rods, using a common or garden welding transformer.
No post welding heat treatment is mentioned.
Both 304 and 316 are considered acceptable.
The firebox crown sheet design is interesting with no stays.
No reference is made to stays

Regarding use I particularly note the reference to calcarious water. As I have written elsewhere the Ca buffers the water and increases the pH reducing the likelihood of corrosion. Quite possibly a layer of high pH lime scale helps. Don't like the idea of an HCl wash though.

Not mentioned is how the boiler is laid up between uses. If it is blown down hot and dried out after each use it may well be fine because any weakness in the oxide coating will have the chance to heal.

It would be great to be able to get a much fuller picture of what those with SS boilers are doing.

Regards,
Ian

[drjohn]

Mar 19, 2009 8:00:09 GMT steam4ian said:

It would be great to be able to get a much fuller picture of what those with SS boilers are doing.

They're waiting patiently for the heat transfer through the stainless to the water to make a cup of tea, Ian ;D ;D

To be fair, coffee disguised the interesting metallic flavour of blow-down water better than tea.

So where is it all going? Lead-free solder, cadmium-free silver solder, now copper-free boilers - it'll be iron-free wheels next - plastic toys eat your heart out!

DJ

[havoc]

1: There is no reference to certification for use in public areas; I don't know what the French requirements might be.
2: There is no reference to a certificated welder with proven competence. The writer seems to be recommending MMA, but with careful choice of rods, using a common or garden welding transformer.
3: No post welding heat treatment is mentioned.
4: Both 304 and 316 are considered acceptable.
5: The firebox crown sheet design is interesting with no stays.
6: No reference is made to stays

Ian, I numbered your items to make a reply easier.

1: you can find a short reference to the french boiler rules here: www.cav-escarbille.com/chaudiere/index.htm
It comes down to defining 4 cases op boilers. Two of those can be self certified, the other 2 need to be certified by an official instance. Additional they make a distinction between making for own use and making for putting on the market.
2: no idea either.
3: no, no post welding treatment apart from inspection for leaks
4: 304 and 316 are NOT acceptable, 304L and 316L are acceptable.
5: he seems to use plate stays. I don't fancy leaving away stays just because the crown is round. The idea of puting in tubes from the sides to the crown looks interesting however.
6: no, he doesn't mention stays. But if you look at his photo of the boiler on the locomotive you see that there are stays in the side of the firebox just like you would expect.

it'll be iron-free wheels next

Well, the fibers and resins mentioned earlier might be used instead of casting for spoked wheels. Just put a steel thread over them and a steel bush for the axle. Probably far easier than finding a foundry willing to do the job.

[Laurie_B]

Traditional copper boilers for model engineering applications usually specify flanged plates for the firebox construction and at the smokebox end.With frequent annealing it is possible to form these plates without too much difficulty (unless I'm making them of course!).
Has anyone given any thought as to how these plates might be formed in stainless steel?Hardly within the capabilities of the average home workshop I would guess.
Or does the AMBSC code call for flat plates and simple 'end attachment welds'?In which case,the question should be asked who,as a 'Competent Person' has fully assessed the designs for stainless boilers?

[drjohn]

Our engineering forefathers learnt from countless years of experience and experimentation and they came up with copper as the best heat conductor able to withstand the boiler pressures -- now you Euro citizens are trying to tell us different - ok - you go ahead and build your non heat conducting potential stainless bombs, but give me copper every time.

Incidentally, would any of you, in your wildest dreams, from first principles, ever imagined you could pump water back into a boiler using the output steam from said boiler - I doubt it - that injector concept had to be from an Irish brain! ;D ;D

As I keep on saying to the pontificators, "get out of your chairs, and go do it, to prove me wrong"

DJ

Ascerbism starting to creep in again so maybe I should go away.

[havoc]

Has anyone given any thought as to how these plates might be formed in stainless steel?Hardly within the capabilities of the average home workshop I would guess.
Or does the AMBSC code call for flat plates and simple 'end attachment welds'?In which case,the question should be asked who,as a 'Competent Person' has fully assessed the designs for stainless boilers?

This isn't any different from steel boilers as they have been made in full scale or model since long years. The flanging is needed for silver soldering, this is welding.

Funny how suddenly we are driving around "bombs" while copper boilers seem to be inherently safe. Bit of dual standards there.

As I keep on saying to the pontificators, "get out of your chairs, and go do it, to prove me wrong"

Apparantly lots of people have been doing this for at least 25 years. Can't help that you have your eyes shut, your fingers in your ears and shouting "la la la".

Becoming just as ascerbic...

[engineernut]

Mar 19, 2009 12:00:32 GMT drjohn said:

Our engineering forefathers learnt from countless years of experience and experimentation and they came up with copper as the best heat conductor able to withstand the boiler pressures -- now you Euro citizens are trying to tell us different - ok - you go ahead and build your non heat conducting potential stainless bombs, but give me copper every time.

Incidentally, would any of you, in your wildest dreams, from first principles, ever imagined you could pump water back into a boiler using the output steam from said boiler - I doubt it - that injector concept had to be from an Irish brain! ;D ;D

As I keep on saying to the pontificators, "get out of your chairs, and go do it, to prove me wrong"

DJ

Ascerbism starting to creep in again so maybe I should go away.

There is a very simple answer, and hopefully one day in the not to distant future we will tell these euro bureaucrats to get lost, to put it politely. ;D

[steam4ian]

G'day all

As Havoc says, copper boilers are flanged to allow silver soldered joints. Even this is traditional dating back to rivetted and soft solder caulked joints. The AMBSC Code has even brazed joints flanged but with shallower flanges. This last aspect is almost laughable because brazing does not penetrate like silver solder and the braze beed is much stronger.

A paper was published by some Ozzies who experimented with edge silver soldered ends in tubes. Even with no flanging and partial penetration the tube failed before the edge joint. Unfortunately the AMBSC didn't seem (Careful here) to take their testing into account when issuing the code for Sub-miniature boilers. Tests have also been done with stays simply silver soldered into holes; under extreme tension the stays have pulled out a disc of the sheet withe the joint staying intact.

One of the problems is that copper is just too expensive to do lots of tests. I well feel that flanging of copper connections could be done away with if brazed edge connections were developed.

Back on topic.
I can see the possibility of SS boilers BUT with a number of provisos. It is teasing out these provisos which is now my goal.

I don't think I will be MMA welding an SS boiler, there are things I do better than welding, talking underwater with a mouth full of marbles is one of them.

One thing I have discovered is that SS loses its shine in an ascerbic environment. ;D

Regards,
Ian

[44767]

Just a bit of an update. I was talking to a chap who was part of the committee dealing with the use of stainless steel for model boilers. He says that stainless steel was never intended to take the place of copper for small boilers. By small boilers he means under 50 litres. It is intended as an alternative to steel in the larger locomotives and traction engines. The material is 2205 which is a Sandvik product designed for this sort of use and has been endorsed by Sandvik. It would be most suited to a boiler with a round top fire box and straight sides as it is not easy to form so Belpaire type boilers would not really be suited to it.

Of course it still needs to be welded by ticketed welders as is the case for steel boilers. The material is much stronger than steel and so thinner plate can be used which in turn reduces the amount of weld needed at the joint making the welding cheaper to do.

Sure, stainless steel is not the best conductor of heat but being thinner material will negate that drawback and in any case the tubes can still be copper expanded into place.

As far as I am aware the rules are to be put in place as part of the Australian rules.

I hope this doesn't stir up the hornet's nest again,

Mike

[steam4ian]

G'day Mike

Thanks for your comments. I had a few seconds to look at the code at our club meeting recently. We had Les who was instrumental in the developing the code talk to us. I agree the material is Sandvik 2205 which seems to have a high resistance to crevice corrosion and chloride attack. Les is building a prototype boiler, almost finished but not yet tested so there is no established life of the material or designs yet.

The Code design is fairly prescriptive made up basically of simple elements with edge welding. It would really suit a marine type boiler like that for Sweat Pea/Sweat William. Only problem with a 5" loco would be the reduced heat transfer of 2205 vs copper.
Les mentioned using copper tubes is OK but they can only be expanded in. Brazing is a No No, I didn't ask about lead/tin based solder fills.

Time will tell, I don't think the boiler will fail catastrophically but may develop funny leaks.

Regards
Ian

[grahamo]

Hi
2205 is a "duplex" stainless steel, We worked with it some time ago, and it is very resistant to corrosion as discussed above.

As st/st's go it is also very difficlut to work with (we had to get whole pipe lengths annealed before bending and even then the tube bender would not take a repeat order!). It is very hard even compared to other stainless steels, eating cutting blades and hacksaws. I recall having some special welding procedures beyond the normal st/st procedures. I'll try to locate the procedures and let the forum know the differences.

Graham

[weldsol]

Hi Graham it was normal practice to use Super duplex filler wire (higher Cr content) for the root run as this was the high dilution area, also weld procedures used to have to have a G48 test ( held in acid at a given temp then weighed to check losses in material / weld)
If a G48 test is part of the requirement for a model boiler then the costs involved I think may put it out of reach (financially)
Paul