looking for advice on a boiler project

[HenryBanjo]

Hello,
im looking at building my first boiler and had a question. i want to use hold water heater (see pictures) for the copper, its been tested to 120 PSI before and doesn't leek. I was wondering if i would be better keeping it the way it is and adding all the fittings and putting a source of heat underneath or cutting it up and using the copper to build one from scratch.

I

I plan to do a simple pot boiler as its my first and gas fire it (or if i cut it up and make a new one maybe methalyated spirits/alcohol). the engines i plan to use it on are 2 little single acting engienes both 1/2" bore by 5/8 stroke and ild like it to be able to just run a elmers 33 but its not going to be designed for that engine (once i build that one im going to build a bigger boiler)
Im aiming to do it as cheap as possible since boilers anoying are built out of the most expensive materials as well as keep it nice and simple but i don't mind doing a bit of work on it.

 

[HenryBanjo]

UPDATE: I think the copper is 26 thou thick, although it is hard to tell without cutting into it

 

[LJ Peterson]

I built a hot water boiler using pipes in front of the flame source. With this I heat my shop and greenhouse.
What are your intentions with this project?

 

[HenryBanjo]

I built a hot water boiler using pipes in front of the flame source. With this I heat my shop and greenhouse.
What are your intentions with this project?

to power small steam engines

 

[Richard Hed]

to power small steam engines

As for myself, I would ALWAYs use a barrel type boiler, as the circle (or cylinder) is the strongest geometric form. A sphere is the strongest of all but not very practical.

 

[Gedeon Spilett]

If you really tested this boiler up to 120 PSI, without seeing any inflating or bulging, it cannot be 26 thou thick, or it is heavily stayed inside !
and yes a cylinder is to be preferred to a rectangular box...
for little elmer engines, you need 20-30psi to get them running very fast...

 

[HenryBanjo]

If you really tested this boiler up to 120 PSI, without seeing any inflating or bulging, it cannot be 26 thou thick, or it is heavily stayed inside !
and yes a cylinder is to be preferred to a rectangular box...
for little elmer engines, you need 20-30psi to get then running very fast...

I haven't tested it to 120 PSI, but it said that on the water heater. it was a bit hard to measure. i tried with my round anvil micrometers but I'm not sure of how accurate the measurement is. Ill cut it up so i can measure propery

 

[TimTaylor]

I worked with industrial scale steam systems most of my career, and will echo what others have said regarding the geometry vs. strength. Water heaters are designed to be used with water - if they fail, all you get is wet. A steam vessel, by contrast, stores a huge amount of energy, and failure can result in catastrophic damage. I'd suggest starting from scratch with some large diameter heavy wall copper pipe. There are lots of model boiler designs out there you might want to take a look at.

You'll want to hydro test it before putting it in service. ASME code specifies the minimum hydro test pressure as 1.3 x design pressure (or maximum allowable working pressure) x LSR. LSR = (material stress at operating temp)/(material stress at design temp). A good rule of thumb is a minimum of 1.5 times the design or maximum operating pressure, so for a boiler designed to be run at 100 psig, you'll want to hydro test at a minimum 150 psig. Any leaks, or distortion of the vessel geometry, are immediate red flags.

A major factor in boiler design is maximizing the heat transfer surface area, which is why most boilers will be either fire tube or water tube design. It also needs to be designed with either enough head space or a separate steam drum to prevent moisture carry over and wet steam, which can cause erosion and damage your engines. Good luck, and let us know how you plan to proceed.

 

[HMEL]

Hello,
im looking at building my first boiler and had a question. i want to use hold water heater (see pictures) for the copper, its been tested to 120 PSI before and doesn't leek. I was wondering if i would be better keeping it the way it is and adding all the fittings and putting a source of heat underneath or cutting it up and using the copper to build one from scratch. View attachment 136000
I View attachment 136001View attachment 136002
I plan to do a simple pot boiler as its my first and gas fire it (or if i cut it up and make a new one maybe methalyated spirits/alcohol). the engines i plan to use it on are 2 little single acting engienes both 1/2" bore by 5/8 stroke and ild like it to be able to just run a elmers 33 but its not going to be designed for that engine (once i build that one im going to build a bigger boiler)
Im aiming to do it as cheap as possible since boilers anoying are built out of the most expensive materials as well as keep it nice and simple but i don't mind doing a bit of work on it.

Heaters are designed differently than boilers. First you have to decide whether you are building a model boiler or something to supply steam. You have what looks to be a low pressure heater and without knowing the internal bracing it would not be wise to use it as a boiler. If building a scale boiler get plans. If you are just building a boiler options are greater. How comfortable are you with your skills, soldering, fit up, etc. What is you knowledge background on water quality, safety valves, low water cut off. This is stuff you can learn. And you can learn the skills to work with various materials. But you do need to know the materials to use and why. Boilers expand in all kinds of ways and this expansion can put thousands of pound of pressure on a joint in addition to the boiler pressure. Does not matter the size. So I would find me a set of plans that have been somewhat proven. And finally do not substitute materials unless you know they can withstand the corrosion and have a tensile strength required at your operating temperature. I suspect there are a few guys on this forum that have plans. Good Luck with your project
HMEL

 

[Steamchick]

Hi Henry, Tim says a lot in his post #8, and HMEL also says it all - "use a proven design" - but I'll add a few snippets as I have designed and made a few steam boilers.
The "Bible" I use to design boilers comprises 2 sources.
"Old" ideology - which worked but is NOT as safe as "Modern Regulations". (E.G. Model Boilers and Boiler-making: K.N. Harris).
And CURRENT regulations:
I know USA and Australia use basically the same thinking, and I GUESS, NZ regulations are the same? And you really should comply, as the Regulations are there for SAFETY reasons.
Putting it simply, EVERY single part of the boiler has to have the stress calculated at the "Normal Working Pressure", then that is related to Regulation limits. That sounds like "hard sums" for engineering, but in fact it has been made simple in the following article: "Safety of Copper Boilers" by Kozo Hiraoka: published in Live steam and outdoor railroading Nov-Dec 2006: available from the publishers as a back issue, for a few dollars.
REALLY, it is straightforward and easy to follow:
E.G. he has made a simple table of test pressures, to ease the "translation" of the Regulations:

e.g. at 100psi "Normal Working Pressure", the boiler must be tested at/above 277psi. - if NZ uses the same basis as ASME for the USA.
(Website controller: I hope my photos don't breach any Copyright laws? - delete if necessary).
E.G. For a basic cylinder - in copper - the wall thickness and INTERNAL pressure limits are shown in another table:

BUT if the cylinder has ANY holes in it, then another Regulation applies and requires the Wall THICKNESS to be 3.3 times the thickness shown on this table.
FURTHER:
COPPER does not stay "strong" as we get to STEAM temperatures, so in the "simple sums" of stress on every part of the boiler, you must consider the "MAXIMUM PERMISSABLE STRESS" defined by the Regulations: Here is a simple table for Stress in tension:

You can see that the Regulations permit a max stress at room temperature of 6700psi, but at 100psi (for the associated STEAM TEMPERAURE) that is limited to 3142psi.
So You can see a bit of "WHY?" copper steam boilers cost a lot of money: they have to have a lot of metal in them.

There are other factors that apply, - such as the simple one that a tube with Steam on the outside and "atmospheric pressure" on the inside will fail (collapse) at about 22% of the stress of the same tube with internal pressure (define in the table above). So I can help with your design as you work through it. Don't be shy of the sums, they are basic "schoolboy" sums. And they will ensure the design is safe and worth making.
If you have an engine size and performance in mind, then really, you should start with the "power" you want from the engine, which then translates as the pressure and quantity of steam you want, the burner size you NEED, etc.
So when you want to know about that, PLEASE ASK ME, because I have met many who do not "look before they leap" (Then get it wrong).
In the modern society where we live (and enjoy Hobbies!) we become automatically liable if something goes wrong (and the insurance does not pay-out!). As "Steam" can go wrong (very rarely!), with Horrid consequences, I just want you to stay safe with this project.
Finally, I ALWAYS advise joining a local "Steam" club, whether they make model engines, boilers, or full sized stuff, as they will probably include you in their Insurance when you have a finished and certified, tested boiler. Most clubs even have an Engineer responsible for examination and testing, and he can teach you how to make the boiler right.
Cheers!
K2

 

[TimTaylor]

Steamchick - great reply, and some good resources! I too have built several model copper boilers, from a simple HRT fire tube to a 2 drum water tube with an added basic single pass superheater section.

Safety is my main concern as well. Over almost 50 years I worked with industrial steam systems ranging from 150 psig to over 2000 psig. I have seen the results of a few system failures, including a 7 story boiler building that was completely demolished by the catastrophic failure of a 250 psig drum.

I tend to over design, and typically use ASTM B280 type K copper, which I know is way overkill. The extra wall thickness reduces heat transfer rate a bit, but that's easy to make up for by adding a little more surface area. Making sure all joints closely fit and using silver brazing is another step for added strength.

Maximum pressure vs working temperature can be easily calculated using the formulas in the ANSI B31 standard. Another good resource is a document from LLNL that can be found at this link:
http://www-eng.lbl.gov/~shuman/XENO... documents/LLNL_course_material/AppendixD.pdf

 

[Steamchick]

Thanks Tim,
I didn't know you are a Boiler Engineer! - Only the 3rd I have corresponded with.
I'll be honest - as that is a good starting point for me - I am an Engineer, but have not professionally done boiler work. Steel structures, High power busbars, Switchgear and associated pneumatics - but Steam Boiler work is just my hobby in retirement.
Is it OK if I correspond separately to this thread so I can level "my knowledge base" with your professional knowledge?
I have had a glance at your attachment. Very useful, except the Copper ratings (the only material I am familiar with in this context of Model Boilers) suggests 9000psi is a "Safe" limit. That conflicts with ASME (I am reading Kozo Hiraoka's magazine article) that says 6700psi at Room temperature (20deg.C). Then de-rates the Max Allowable Stress to 3142psi at a boiler temperature relating to steam at 100psi. This is the top pressure limit within ASME for Silver Soldered copper boilers.
I feel that is ASME specifies the "safe" limits as such, then following that strategy should be a good starting point for me.
But I have struggled to find other factors, that could re-define "safe" limits for boiler design, such as tubes in compression (de-rates to about 22% of the safe limit for tubes internally pressurised), tubes with holes penetrated in them (ASME statutory Stress Concentration factor of 3.3 used when determining the max. stress in the tube), etc.
I have "de-rated" a couple of boilers according to odd factors I have gleaned from the Internet, but it would be good to have another professional appraise my design strategy, if you are willing? Knowledge is good, but "with experience" is much better.
Thanks,
K2

 

[timo_gross]

Hello,

I found a plan that looked right size and basic enough to give it a try. It is for a small boiler with four water tubes ("sticking out from the bottom").
A tube with two endcaps, some bushings.

That is what I tried to make. It is basically a copy of the boiler I found on the internet.
I am not sure if I am allowed to upload the pdf, so I don*t.
Found it here http://www.plans-for-everything.com/downloads/steam_engines/SE NiggelBoiler.pdf

I deviated a little from mentioned plan. I made the main tube 2 mm larger in diameter and it is 15 mm shorter. Instead of M4 I used a M5 rod between the boiler caps. The tube has a wall thickness of 2 mm, the small tubes on the bottom I tried to make (sort of similar to the plan, bending them was a challenge).

I do not have a water glas or pressure gauge on the boiler. If there is no steam coming anymore, I just switch everything off and wait until everything is cold enough to open the filler cap.

I filled the thing as good as I could with water by submerging it into a bucket with water. Then plugged the holes and pressurized it up to 6 bar with compressed air.

The safety valve pops open at a little over 3 bar and closes at 2 bar.

I made boiler bushings from brass only the bushing below the water level is made from copper.
I would appreciate a comment if that is a usable approach, or if there is anything totally unacceptable.

Greetings Timo

 

[Steamchick]

Hi Timo,
Please can you advise the OD of the tube, and wall thickness of the tube you have used? Large and small. I'll do the sums. Be aware, the brass bushings will "de-zincify" with age. The remaining metal crumbles like a cookey! But took 25 years on some brass fittings on my Dad's boiler, which is why they need ANNUAL checks and testing at pressure. Copper and bronze bushes have no zinc so it cannot be dissolved by the steam and water.
Ta,
K2

 

[HMEL]

Hello,

I found a plan that looked right size and basic enough to give it a try. It is for a small boiler with four water tubes ("sticking out from the bottom").
A tube with two endcaps, some bushings.

View attachment 136476
That is what I tried to make. It is basically a copy of the boiler I found on the internet.
I am not sure if I am allowed to upload the pdf, so I don*t.
Found it here http://www.plans-for-everything.com/downloads/steam_engines/SE NiggelBoiler.pdf

I deviated a little from mentioned plan. I made the main tube 2 mm larger in diameter and it is 15 mm shorter. Instead of M4 I used a M5 rod between the boiler caps. The tube has a wall thickness of 2 mm, the small tubes on the bottom I tried to make (sort of similar to the plan, bending them was a challenge).

I do not have a water glas or pressure gauge on the boiler. If there is no steam coming anymore, I just switch everything off and wait until everything is cold enough to open the filler cap.

I filled the thing as good as I could with water by submerging it into a bucket with water. Then plugged the holes and pressurized it up to 6 bar with compressed air.

The safety valve pops open at a little over 3 bar and closes at 2 bar.

I made boiler bushings from brass only the bushing below the water level is made from copper.
I would appreciate a comment if that is a usable approach, or if there is anything totally unacceptable.

Greetings Timo

Not a good idea to wait until no steam comes out. You could end up warping the metal and destroy it. Low water cut off is what you need.
HMEL

 

[Steamchick]

Hi Timo,
I am travelling tomorrow, and won't be back until Monday. I have started to look at your design, but will get to it then.
Hope the delay isn't a bother.
This design is inherently strong, being all internal pressure on the tubes. It is pretty standard, going back as far as I can see to at least the 1960s. So I doubt I'll find anything worrying. But don't hold your breath, as Regulations (and safety ideology) have changed a bit in the last 20 years or so. (Ask the bullet makers: They use depleted Uranium, as lead poisoning causes brain damage! ).
K2

 

[Steamchick]

Hi Timo,
Just realised you had included the wall thickness of the main Boiler tube in your mail # 13. (STUPID Me!):
So put the data into my spreadsheet and:

1. S.E.Niggel's boiler shell (tube: 52mm OD x 50mm ID) => FOS 8.8 (ASME Want >8) = OK.
2. S.E.Niggel's water tubes: 6mmOD x 5mmID => FOS ~56 = OK.
3. Timo's boiler shell (tube: 54mm OD x 50mm ID) => FOS 17.2 (ASME Want >8) = OK.

To put it simply, as you have double the tube thickness, you Almost double the FOS. So (including the stress concentration factor of 3.3 for shell penetrations at the bushings = 3.3:- ASME specified) you have a "good" boiler. - I did some other checks, and feel I should mention:

• At 80 psi (551.6kPa) - YOUR thicker shell just fails the calculation, so would need a MAX NWP of 75psi... BUT, as the water tubes are only good WHEN FILLED WITH WATER TO PREVENT OVERHEATING your setting of 3 bar for the Safety relief valve is appropriate. (Regs say is must be blowing and not permit over-pressure > 48psi = 330kPa.).
• The water tubes may not fail the way you operate the boiler, but when it has JUST boiled away the last of the steam, the temperature will very rapidly rise - in fact the silver soldered joints at the water-tube to boiler shell interface will overheat even before the last of the water in the water tubes has boiled-out. The result is that you are eating into the FACTOR OF SAFETY... which means you are at risk of an uncontrolled steam leak at the silver soldered joint as the likely failure mode. (ASME says silver-soldered copper boiler joints shall not exceed 400deg.F, 205deg.C.). Without knowing really what is happening when you boil the boiler to dry, I can only guess that the heat on the main boiler shell when the water tubes are still just wet is actually superheating the steam in the boiler shell - and silver-soldered joints - but not exceeding 205deg. C temperature.
• The end plates: Min thickness specified on drawing = 2mm: So the un-stayed min circle permitted is about 35mm diameter. - Your un-stayed circle is about 25mm diameter, so is "Good".
• Stay-bolt diameter: MIN diameter (at thread root) of 3mm. - if made from Phosphor Bronze: Tensile yield strength: 380 MPa: Stainless steel: Tensile yield strength: 800 MPa - so your 5mm stay-bolt is GOOD.
• ASME Test pressure for a 45psi boiler would be about 6.5barg. (I guess your 6 barg may be the limit of your air-line?). Normally, I would have a hand feed-pump dedicated to the boiler - that is capable of the test pressure or higher. (But I always have a water gauge fitted anyway, so I can manage the water level when steaming).

In conclusion, the only thing that I cannot condone is the practice of "boiling -dry". So, PLEASE try and arrange a water gauge, so you do not boil-dry the SILVER SOLDERED JOINTS under any circumstances.
I assume you are running a spirt burner - as S.E.Nigel's design? Usual practice with spirit-fired boilers is to limit the fuel to prevent the water level getting too low.
I hope this is of interest?
If you feel comfortable, please post a photo of your boiler, burner, engine etc. set-up, as I am sure many will be keen to see what you have?
Thanks for permitting me the "fun" of checking the boiler,
Happy - and safe! - steaming!
Steamchick - K2.

 

[timo_gross]

Hi Timo,
Just realised you had included the wall thickness of the main Boiler tube in your mail # 13. (STUPID Me!):
So put the data into my spreadsheet and:

1. S.E.Niggel's boiler shell (tube: 52mm OD x 50mm ID) => FOS 8.8 (ASME Want >8) = OK.
2. S.E.Niggel's water tubes: 6mmOD x 5mmID => FOS ~56 = OK.
3. Timo's boiler shell (tube: 54mm OD x 50mm ID) => FOS 17.2 (ASME Want >8) = OK.

To put it simply, as you have double the tube thickness, you Almost double the FOS. So (including the stress concentration factor of 3.3 for shell penetrations at the bushings = 3.3:- ASME specified) you have a "good" boiler. - I did some other checks, and feel I should mention:

• At 80 psi (551.6kPa) - YOUR thicker shell just fails the calculation, so would need a MAX NWP of 75psi... BUT, as the water tubes are only good WHEN FILLED WITH WATER TO PREVENT OVERHEATING your setting of 3 bar for the Safety relief valve is appropriate. (Regs say is must be blowing and not permit over-pressure > 48psi = 330kPa.).
• The water tubes may not fail the way you operate the boiler, but when it has JUST boiled away the last of the steam, the temperature will very rapidly rise - in fact the silver soldered joints at the water-tube to boiler shell interface will overheat even before the last of the water in the water tubes has boiled-out. The result is that you are eating into the FACTOR OF SAFETY... which means you are at risk of an uncontrolled steam leak at the silver soldered joint as the likely failure mode. (ASME says silver-soldered copper boiler joints shall not exceed 400deg.F, 205deg.C.). Without knowing really what is happening when you boil the boiler to dry, I can only guess that the heat on the main boiler shell when the water tubes are still just wet is actually superheating the steam in the boiler shell - and silver-soldered joints - but not exceeding 205deg. C temperature.
• The end plates: Min thickness specified on drawing = 2mm: So the un-stayed min circle permitted is about 35mm diameter. - Your un-stayed circle is about 25mm diameter, so is "Good".
• Stay-bolt diameter: MIN diameter (at thread root) of 3mm. - if made from Phosphor Bronze: Tensile yield strength: 380 MPa: Stainless steel: Tensile yield strength: 800 MPa - so your 5mm stay-bolt is GOOD.
• ASME Test pressure for a 45psi boiler would be about 6.5barg. (I guess your 6 barg may be the limit of your air-line?). Normally, I would have a hand feed-pump dedicated to the boiler - that is capable of the test pressure or higher. (But I always have a water gauge fitted anyway, so I can manage the water level when steaming).

In conclusion, the only thing that I cannot condone is the practice of "boiling -dry". So, PLEASE try and arrange a water gauge, so you do not boil-dry the SILVER SOLDERED JOINTS under any circumstances.
I assume you are running a spirt burner - as S.E.Nigel's design? Usual practice with spirit-fired boilers is to limit the fuel to prevent the water level getting too low.
I hope this is of interest?
If you feel comfortable, please post a photo of your boiler, burner, engine etc. set-up, as I am sure many will be keen to see what you have?
Thanks for permitting me the "fun" of checking the boiler,
Happy - and safe! - steaming!
Steamchick - K2.

Hello,

Thank you very much that you had such a detailed look at it. It seems I got lucky not to be too flimsy. The empty boiler weights approx. 740g
I did not make the final burner yet and was using one of those kitchen gas torches for the first trials, also the complete lower part is not finished yet (too much other interesting stuff to do ).

Not sure if this is hijacking hte original post too much : But I felt it might also help HenryBanjo
to get some idea.

Video is not really showing the boiler, more its use. It can be seen in the corner of the frame.

https://www.youtube.com/shorts/mRojXrnoffk

Greetings Timo

 

[TonySteamHobby]

Timo, do you have any info on the boiler, ie working pressure, typical run time….

 

[timo_gross]

Timo, do you have any info on the boiler, ie working pressure, typical run time….

No not really collected any hard fact numbers, it is sufficient to drive a small thing like an Elmers Engines, or the Gerries Beam Engine.
Both engines run on compressed air well below 1 bar.
I would guess it also depends very much on the heat source and the insulation. (which are both not finalized yet)
I think this is not the best boiler for a "workhorse" engine, but good enough for "my toy" enginges they do not have to do work.
The running time is about 10 maybe 20 min and it stays well below 3 bar. (I get the safety valve only to open when I close the steam valve and wait a little)
Starting the heating with around 200 ml of Water. The total Volume as per CAD program is 290 ml.
I think the steam was fairly wet coming out of the boiler, some kind of overheating would be a good idea.

Maybe in the final setup I take the steam line once through the flame.


I hope that helps.

Greetings Timo