Silver soldering rod for boiler

[Nikhil Bhale]

BUT the end plates do not work at 1/16in thick.

Hi,
Thanks for the calculations. I guess I will have to buy a 3mm copper plate and form end plates.
One more thing to learn.

Regards
Nikhil

 

[Steamchick]

Re: phosphorous based alloys. In the presence of sulphur products from the fuel, the brazing filler containing phosphorous is prone to high corrosion.
I guess that with a model boiler (not full time duty cycle, just a couple of hours "whenever") that corrosion would be relatively insignificant? Especially kit not used with high sulphur coal or oil as a fuel...
K2

 

[Lloyd-ss]

Hello,
I am going through other sites on internet for information.
What I could gleen from them is " A coal fired boiler produces a hot Sulphur bearing atmosphere that destroys joints made with copper phosphorus alloys.".

So I think phoscopper rods are not used on steam locomotive boilers nowadays.

I looked up the link and it cannot be delivered to India. I will look for other source for this book.

Regards
NikhilView attachment 149781

Nikhil and Steam,
I found a very similar reference about sulfur and sulfides reacting with, and degrading silver brazed joints that had phosphorous in the filler metal. So, if you are firing your boiler with coal or crude oil, the phosphorous-containing filler metal is not good.

There are several older threads on the forum regarding brazing copper boilers and they mostly seem to end up endorsing the silver-copper-zinc filler metals. Actual hard documentation as to why those are the choices is pretty much non-existent, except references to hobbyist books that may or may not have a documented reason for the filler metal choice.

I tried to look up the Brazing Filler Metal section of the ASME boiler specs, but that is all copyrighted, too, and costs quite a bit to get access to. If I was still working, I could have done that at work. Maybe somebody here is working somewhere that has a full ASME subscription.

Personally, I am quite confused also, but a lot of people on the forum have built boilers without mishap, so maybe that is most readily available (and reliable?) information. There are quite a few smart people here.
Lloyd

Edit, Ha Ha, I found a price for the full print book set of the ASME 2023 Boilers and Pressure Vessel Standards. A paltry $20,000. The portion that contains brazing filler metals might be less than $1,000. A bargain, ha ha, again.

 

[Lloyd-ss]

Hi Nikhil.
A quick calculation of the 2 1/2 in tube - with penetrations - and the boiler - except for end plates should be just OK for NWP = 3 bar (45psi).
BUT the end plates do not work at 1/16in thick.
They must be at least 1/8in thick.
Sorry, but that is what the numbers say.
K2

Hi Steam,
Just covering your back, LOL, so I did just the hoop stress calcs for copper using 8,500 psi as the yield for the copper tube. For the 2.5" dia tube with .065" wall I got that the tube starts to yield at 450 psi. I think(?) the 8,500 psi number is ok for hot copper, but could be totally wrong. So the tube that Nikhil will be using has a 10 to 1 safety factor for the working pressure of 45psi max. I will take you at your word that the 10 to 1 is a reasonable SF for the boiler. I normally use 3 to 1 yield for room temperature small steel pressure vessels for compressed air, but I can definitely see where 10 to 1 makes sense for something with as many variables as a hot copper boiler. Just going with my gut feel on this. And with the weight I have gained since retirement, my gut feel might be a lot smarter than it used to be, LOL.

BTW, I did not do any calcs for the end plates. Were you calculating for flat or domed end plates?
Thx,
Lloyd

 

[Steamchick]

Hi Lloyd.
I use information from old versions of ASME along with information that Kozo Hiraoka presents in his interpretation of the ASME regs for model boiler design in the US of A.
K2

 

[Lloyd-ss]

Hi Lloyd.
I use information from old versions of ASME along with information that Kozo Hiraoka presents in his interpretation of the ASME regs for model boiler design in the US of A.
K2

That is good to know. Thank you.
Lloyd

 

[krypto]

Some links:

https://www.amazon.com/Gas-Fired-Boilers-Engines-Crowood-Metalworking/dp/1785008765/
http://www.midfedmodeng.altervista.org/Documents/Boiler Test Code 2018 - Volume 1.pdf
http://www.midfedmodeng.altervista.org/Documents/Boiler Test Code 2018 - Volume 2.pdf
It would be prudent to start with a low pressure boiler for learning and then go for the high pressure boiler. What PM engines are you steaming?

 

[Nikhil Bhale]

What PM engines are you steaming?

Hi,

I have a PM research #1 horizontal and #5 vertical engines.
Yes you are right. I will start with low pressure boilers first. I was thinking a 3 bar boiler. But after Steamchicks calculations I think a 2 bar boiler will be much safer.

regards
Nikhil

 

[Steamchick]

Lloyd, Nikhil, Try this, if it will attach? - Just some pertinent notes from Experts. Not the latest, but close.
ASME-II-PART-D-METRIC-2019-www.fouladline.com
I made a few notes for myself: attached. (Can be extracted from the internet). And some UK documents pertinent to obtaining approval to use the models within the control of an appropriate Model Engineering society.
I do not agree with all the UK stuff. e.g. it suggests inner firebox wrappers should be thinner than the outer. As the compressive strength of copper is so much lower than the tensile strength:
https://www.azom.com/properties.aspx?ArticleID=597I find this a little strange, as the inner firebox wrapper in many cases is in compression... : e.g. the case of a cylindrical firebox in a vertical boiler? Or a semi-cylindrical inner roof of a loco firebox? BUT I am also aware that many answer this with "So and so's boiler is like that and has been used for many years and not failed". - or "is a design that has been around for many years"... In these case it is very likely that the factor of safety is compromised, and does not equate to that used in ASME or other Regulations for New designs.
So I caution the standards used when designing boilers. Meeting an "obsolete" standard does not necessarily mean the boiler is a danger to users, nor necessarily safe, but may mean it cannot stand scrutiny by an inspector, insurance assessor, etc. - which may only be scrutinised after a catastrophic failure, at which point the designer and maker must accept liability for their "innocent error". Lloyd, I think you will appreciate more than us non-US citizens what "liability" means in court?
If there are any professionals who can advise further, I will appreciate your help. I have only come to this level of understanding through help from some experts on this site. (Thanks!) and from Kozo's magazine article.
There is a lot missing from many texts.
Take care, do the best you can.
K2

N.B. (from the web).

Property	Minimum Value (S.I.)	Maximum Value (S.I.)	Units (S.I.)	Minimum Value (Imp.)	Maximum Value (Imp.)	Units (Imp.)

Compressive Strength

45

330

MPa

6.5267

47.8625

ksi

Tensile Strength

210

390

MPa

30.4579

56.5647

ksi

ASME de-rates the permissible strength of annealed copper due to the required safety factor and deterioration at elevated temperature, using:
Max allowable stress (tensile) @100F = 6700psi,
Max allowable stress (tensile) @400F = 3000psi,
I.E.
Max allowable stress (tensile) @40psi (Steam) = 4157psi,
Max allowable stress (tensile) @100psi (Steam) = 3142psi,

AND ASME requires a stress concentration factor of 3.3 to be applied to calculations of all cases where the copper surface has penetrations, regardless of the applied reinforcement.

 

[Lloyd-ss]

Lloyd, Nikhil, Try this, if it will attach? - Just some pertinent notes from Experts. Not the latest, but close.
ASME-II-PART-D-METRIC-2019-www.fouladline.com........................

snip ...............

Excellent stuff. Thank you so much! I appreciate not only the information, but the time it took to ferret it out, analyze, and comment. As always, much appreciated.
Lloyd

 

[Zeb]

Something I see interesting from a high level risk analysis perspective. If the greatest variable in a newbie build is the solder joint quality, it seems like having a wall on the thin side would tip the operator of an impending failure. This would be as opposed to having everything overly built and having a joint fail catastrophically. Those very handy empirical tests someone made showed excessive bulging before any type of failure occurred.
I've spent a lot of extra time making sure my engines run at very low pressure, with some compromises on tolerances. I like the boiler build videos above because she shows how things didn't go quite right. I would have made worse mistakes had I not watched it, as most people only show the best of their work.

 

[Lloyd-ss]

Something I see interesting from a high level risk analysis perspective. If the greatest variable in a newbie build is the solder joint quality, it seems like having a wall on the thin side would tip the operator of an impending failure. This would be as opposed to having everything overly built and having a joint fail catastrophically. Those very handy empirical tests someone made showed excessive bulging before any type of failure occurred.
I've spent a lot of extra time making sure my engines run at very low pressure, with some compromises on tolerances. I like the boiler build videos above because she shows how things didn't go quite right. I would have made worse mistakes had I not watched it, as most people only show the best of their work.

I agree 100%. It is very good practice to build a "safe" failure point into any type of pressure vessel. A pressure relief valve, an over-pressure plug, an o-ring installed with excessive clearances, etc, etc. A failure in a hydraulic system will normally just cause an oily mess, but the kinetic energy stored in a boiler or air reservoir is pretty scary. As Zeb said, if previous builders took the time to show their embarrassing mistakes, we might as well learn from them.
Lloyd

 

[Steamchick]

I make my own mistakes - plenty of them - and rarely learn anything except how to get it wrong. But good teaching from those who know "the right way" helps me a lot. Then I try and pass on "the right way".
Sorry, if I don't present my mistakes. Too many to list.
K2

 

[abby]

Apologies for not reading all of this post but to see 1/8" thick copper quoted for boiler end plates on what amounts to a tiny boiler working at almost no pressure (45 psi) as overkill .
Too much negativity can put newcomers off a very rewarding and enjoyable hobby.
The casting of metal and the use of machine tools is no more dangerous than driving a motor vehicle , with the obvious proviso that you take care and understand what you are doing.
I would bet that more people are hurt in the kitchen than in the workshop but do we really need to tell people to be careful with knives or hot fat ?

 

[Richard Hed]

Apologies for not reading all of this post but to see 1/8" thick copper quoted for boiler end plates on what amounts to a tiny boiler working at almost no pressure (45 psi) as overkill .
Too much negativity can put newcomers off a very rewarding and enjoyable hobby.
The casting of metal and the use of machine tools is no more dangerous than driving a motor vehicle , with the obvious proviso that you take care and understand what you are doing.
I would bet that more people are hurt in the kitchen than in the workshop but do we really need to tell people to be careful with knives or hot fat ?

No apology necessary. IN our "permissive" society, it is becoming to the point that a paper cut will require an ambulance to the hospital, a fart in church will require a city wide emergency shutdown. It's good that covers are required on gears, belts and other dangerous, open points that can pull clothing or jewelry into them and hamburgurize a person but it might be just as well to teach people that they are NOT made of steel, we are not supermen.

 

[minh-thanh]

Apologies for not reading all of this post but to see 1/8" thick copper quoted for boiler end plates on what amounts to a tiny boiler working at almost no pressure (45 psi) as overkill .
Too much negativity can put newcomers off a very rewarding and enjoyable hobby.
The casting of metal and the use of machine tools is no more dangerous than driving a motor vehicle , with the obvious proviso that you take care and understand what you are doing.
I would bet that more people are hurt in the kitchen than in the workshop but do we really need to tell people to be careful with knives or hot fat ?

I quite agree with you
But on the other hand, for a newbie and for the steam engine he has worked on, the information in the topic should also be considered.
For example, That engine is made in the best way, everything is smooth...it can run at 0.5 , 0.7 or 1 bar pressure then it will be quite okay with a 1 mm thick boiler
But if That engine is not machined carefully, it is not smooth, there is too much friction...then with a 1mm thick boiler it will be a problem. Because the engine will need a much higher pressure to run and that pressure may be more than the boiler can handle.
I think the most important thing is still what pressure the engine can run at (max and min), and then consider the boiler construction.

 

[Steamchick]

Of course all opinions are equally correct.
But I know someone (a professional person, Caught by something that failed because it had not been correctly built by the previous person) who only has half the flesh on one arm from a steam blast when a wrong part broke. May be a one-in-a-million accident, but it gave him 9 months recovery before he could work again. So with all steam vessels at pressure we should caution new people, without the experience or training, just as we teach our children that "sharp knives must be used with care". Etc.
When any of us write in this open forum, we must give our best professional opinions, as while there are many with some degree of expertise, there are also some people without experience who read - and may blindly follow - our advice.
I respect all opinions presented here, but may not agree with all opinions.
Therefore I trust You all to correct my errors, but sometimes "agree to disagree".
In the case of thickness of copper for this boiler, if my calculations are wrong please correct me. But please do not challenge the Engineering without proper justification. It is hard fact for a boiler to be approved to a National Regulations.
EXAMPLE: I ride motorcycles, and in the UK it is the law to wear a helmet on public roads. Having met a guy - who just survived a low speed crash in a field when not wearing a helmet, but who just banged his head the wrong way and now only has the mental capacity of a 3 year old, I tell anyone "Please wear a helmet at all times riding the bike". I call it responsible teaching, so the innocent can learn from others mistakes.
Thanks for your opinions, I shall continue to advise the risks and countermeasures as I understand them.
K2

 

[Steamchick]

Hi Abby, Without demeaning anything, ("a tiny boiler working at almost no pressure (45 psi) as overkill ."), Nikhil is now considering a 2 bar boiler instead of a 3 bar boiler. Minh Thanh usefully suggest considering the pressure required to run the chosen (largest proposed?) engine as well as the steam demand. - Then we can comment on Nikhil's design for a boiler.
But, considering the original design proposal of 1.16in thick copper for a 3 bar boiler, the main 2 1/2" tube is OK, but the same thickness FLAT ends are not OK when un-stayed, if you follow the Regulation standards. Of course, if you reinforce the end plates with ribs, or make them domed then that is a different consideration. Or you can ignore the standards, if you are happy to take that risk. But I cannot recommend that to a new builder of boilers. The standards are there to give us limits - to stay safe.
For example, using a simple guide (K.N.Harris) that Nikhil already has, and is referencing:
P = 2T x t / D. (P = Pressure, T - boiler wall thickness, t = permitted stress, D = diameter of metal).
- so D = 2T x t /P:
Hence, for T = 0.0625in, P = 45 psi, and s = 3125 psi (K.N.H. value, ASME would permit about 4050psi limit stress for this pressure):
D = 2 x 0.0625 x 3125 / 45 = 8.68in.
Hence a spherical (domed) end plate of radius <4.3in would be OK at 1/16in thick, un-stayed, for 3 bar NWP.
Is that an easier task for the "new coppersmith" than making an end plate from thicker material, or adding stays? Personally. I think not, as there is considerable risk of thinning the "dome" so it is weaker than desired. And who would know? OK for an ornamental Tea-pot or coffee pot for hot water not under pressure, made by an expert (well practiced) copper-smith, but not for a first-timer making a 3 bar boiler, IMHO.
Seriously, what do you suggest? I am willing to learn if I am wrong. I am interpreting writings of experts, but may be in error, as I am an amateur e.g. am I wrong to consider the "worst case" limiting stress value that is in the books?
Cheers.
K2

 

[krypto]

Has anyone here made their own boiler for model steam engines?

Minh Thanh, any of the PM engines you mention should be able to turn-over on a very little amount of pressure, say a few PSI if built correctly. You need higher boiler pressure to perform work.

For myself, for low-pressure (<30 PSI) steam it's very easy for me to inexpensively (compared to DIY) source Jensen electrically heated toy boilers so that's what I use for the small engines. I have a PM #5 in my horde of unbuilt kits and their 3" boiler should be able to run it. For the PM #1 and other kits a bigger boiler is required, so for that engine I will need to make a gas-fired boiler, more for the volume of steam produced than a higher working pressure. Again, Quinn (Blondihacks) on Youtube has made build videos for both the PM #1 and a gas fired boiler to run it. The boiler build is especially good as the first rendition was a failure at test time and much was learned through this.

 

[Steamchick]

Hi Krypto. I guess you may be surprised how many have made their own boilers. I have designed and built 6, and repaired or reconstructed another half dozen over the last 25 years or so.
The "recent" experience has been that to obtain certification, I need to present certain calculations to the Inspector.
Also, when I first did the sums (in the 90s), there was very little covered except in the K.N.Harris book. I have since (mid-2010s) found the ASME Regs, and various technical papers and even university papers discussing various aspects of stress in pressure vessels. I try to use the "latest" standards, but because of the cost of new ASME, etc. I use older versions as they become available free on the inet.
But as an engineer designing pressure vessels in the early 1980s, I did calculations that are not covered in the Regs. This was before computer modelling FEA was commonplace, so very empirical in parts.
One thing that wasn't obvious in the pressure vessel regs was how to calculate stresses and the appropriate compressive stress limits for design of copper steam boilers. I am still in the search of that "holy grail", and many (official) people won't discuss it.
But I have scrapped badly designed boilers, and reassessed all my boilers to my latest understanding. In most cases, when I do a thorough analysis by calculation, "old" designs and "simple" boilers fail the Regulations, as the Regulations are a bit more stringent now than a century ago, whence many designs were standardised.
I therefore offer what I know to any/everyone who wants it. - There are some who want to make models to suit Engineering standards.
I suggest that every locomotive driver wants the surety that his locomotive boiler between his thighs is not going to suddenly release enough steam to cook flesh. It is very rare for boilers to explode, but I have seen failures - usually a joint fails inside the boiler and there is a sudden huge cloud of hot fog generated around the boiler. But better to design and build these things to standards so they are as safe as we like in the 2020s.
Ask if you need anything else? Anyone can directly message me if you want to discuss a design, or something.
Cheers
K2