Seeking info

[sutty]

Ken, I did note the size of the tubes on the stove site, some of the stoves heaters below the feed pipe and some ran the tube through the burner. Also the holes in the burner head seemed to be about 4/5 mm and around 16 of them. I’ve been searching through to see it I could see the jet size, it’s bound to be there somewhere. It seems as though the fuel flow is controlled by the long wick in the feed tube.
I have about 6 or 7 nozzles, they’re quite small but easy enough to make.

regards sutty

 

[Steamchick]

Hi Sutty, I am going to guess at a a few sizes here...
Supposing you need a 1kw burner:
IF you were using an LPG supply at say 10psi, you would want about a 0.25mm jet.
But if at only 32mBar, maybe a 0.5mm jet? But your alcohol vaopour is at an even lower pressure, and different density/calorific value, so I would not be surprised if it needed between a 1 and 2 mm dia jet?
Now typically, you need 250 x the CSA of the jet for the mixer tube: ~11 x the diameter... so a 1/2" tube is reasonable. The air hole/gap CSA needs to be at least 1.25 x the tube CSA - so typically, start at a gap from jet (holder?) to tube of about half the ID of the mixer tube... or side drilled holes with CSA around 30~50% larger than the tube CSA. = 2 x 10mm dia holes is a starting point... (You can mask off if too much air?).
When the mixer tube >3 1/2 " long gets to the burner, you need the holes in the burner to be no more than about 1mm dia - in my guess - and as many as needed to have 4 x the CSA of the mixer tube. You can have a couple of rows, maybe 1 pointing flame straight up, and one row pointing radially outwards?
The tuning is a case of:
# Getting the gas-air to ignite, If it won't, it is probably too lean: mask half the air hole and then open up to the optimum flame point.
# getting flames that are blue, with virtually no yellow. - If yellow, you need more AIR, or less gas.
# getting flames that sit on the burner holes, - if they blow off the holes then they probably won't work in the boiler, when things get hotter and pressure rises. So CHECK in the mock-up firebox: The burner holes are too small. Try just the next size or drill and hope... Maybe drill every 4th hole 1 size up, then another 1/4 of the holes, etc. until you get a workable burner for the conditions of the burner (gas, air, firebox and flue, etc.).
# Avoiding flash-back: This happens when the gas+air pressure is below the speed of the flame front and the flame dashes back to the jet! AAARRRGGGHH!! Not what is planned! The burner holes are too large.
# CHECKING the whole burner flame will fit inside the firebox - use the mock-up, or the actual firebox tube and top and flue tube.
A good burner will run perfectly well in the firebox without excessive flame or smell, and without extra air. If all the air comes in from the air hole there is no "extra" air to cool the boiler, so it will be at its best.
Hope this works for you?
K2

 

[sutty]

Cheers Ken, Edd wasn't too impressed with the math work. A lot of trial and error but we're getting there now here's a link to e short vid on you tube, still looking to modify it, we made the tubes from steel for cost reasons but the propper one will be brass or copper tube, we got a better burn with 8mm tube instead of 12mm and less wick and a shallower burner head, 12 instead of 22 with a slightly narrower bore. the flame cleans up a bit with more pre-heat.



Regards sutty and Edd

 

[Steamchick]

Hi Sutty I am just back from a week cruising the Adriatic, Ionian and Mediterranean seas. Or about 1300 miles thereof...
Some interesting sites to see. Look up the castle walls of Valletta (Malta), Kotor (Montenegro) and Dubrovnik (Croatia). Spectacular engineering to build those structures.
I was without Internet and mobile phone for days on end! That was relaxing! 67p just to send or receive a single SMS text message in Montenegro! £57 for 100 Mb of data for 24hrs. But silence is golden!).

Viewed your burner. SUCCESS.Well done. Maybe a bit more tuning? And perhaps change the configuration so the main burner pre-heats the fuel? Of course more pressure from more preheat will give higher velocity at the jet (up to a limit) and higher velocity will draw in more air making the flames more intense, more like the small blowlamp you are using as the temporary preheater. That small flame is the ideal form with light blue cone then a darker cone surrounding it. All the air if taken through the nozzle air holes, whereas you still need some burner air through the middle of your burner.
Don't be disheartened if the last 10% of tuning takes 90% of the effort! That's the way of life.
I suggest the next step is to tune it inside the mock-up firebox and flue, as that will really change the pressures around the burner and change the flame structure.
If you struggle with air intake at the jet with the firebox enclosing the burner (increased burner back-pressure) I can give you design parameters for a venturi that increases the efficiency of the air intake at the jet.
Next I need to reconnect my PC... limited to a tablet just now.
Keep up the good work!
K2

 

[HMEL]

Hi sutty !​

That seems to be a difficult question.
I think the Thickness of the boiler depends on the pressure you want it to produce
I think boiler making depends a lot on the engine - how big is the engine? How much pressure does it need to run? .... , with the same size but too much friction it needs 5 bar instead of just 2 bar ...
When I make "boiler" (I make it very simple , and my engine is also very simple)
I make the engine first, then try engine with compressed air, if the engine runs with 1 -> 2 bar pressure then I will make the boiler and try with about 8 bar pressure - is the maximum pressure of my compressor , if it is ok then I set the valve safe about 5 bar

Yes, there is a minimum wall thickness. It is determined by the design pressure. The operating pressure is below the design pressure. Once the pressure is known the stress on the materials is calculated. The materials are adjusted for the strength required by increasing thickness or choosing a different material. Capacity is a function of size. But as the area increases so does the force on the walls increase. For instance 12 psi on 12 square inches is 1700lbs force. !2 psi on 24 square inches yields around 7000 lbs force.
Because we can not always accurately calculate where these stresses are applied a boiler is built and then pressurized to a value much higher then the design. If it holds together and does not deform it can be considered ok. This has to be done under very strict rules. And there is no salvaging the unit if it fails so most of us call that a destructive type test.

One of the most destructive failures I have seen was from failure of the pressure parts.
Most hobby type boilers are small enough that the risk is minimal but the potential is always there. So I recommend designs that have been proven unless you like to experiment.

 

[Steamchick]

Hi Sutty & Minh-thanh,
Boiler design is not quite so simple. I many countries there are Regulations. e.g. UK, Europe (EEC,ECE) USA, Canada, Australia, Japan, etc. and these have very well-defined rules for boiler design and manufacture - above a certain size. The BEST engineers are consulted, and insurance companies, and anyone with knowledge of the boilers are also consulted, so products made to Regulations are safe to use as designed, and when manufactured to specific standards. Model makers generally work to such standards of fit, jointing, materials, etc.
Some principles that have changed boilers since the early 20th century.
# Riveting has been abolished as the manufacture of rivetted boilers is very hard to control successfully.
# Silver Soldered copper boilers are generally limited to 100psi due to the "natural loss of tensile strength" of silver soldered copper joints at the elevated temperature for steam at 100psi. (205deg.C. or 400deg.F.) At below 100deg.F. ASME code permits a max tensile stress of 6700psi. BUT at 400deg.F this is down to a MAX permissible stress of 3000psi. (!!).
# Hoop stress calculations are conducted for boiler shells containing internal pressure. BUT these must limit the stress to <1/8th of the yield stress for copper AT THE TEMPERATURE of the steam at NWP (Normal Working Pressure). At below 100deg.F. ASME code permits a MAX tensile stress of copper boiler shells to be 6700psi. BUT at 400deg.F this is down to a MAX permissible stress of 3000psi. (!!).
# ADDITIONALLY: where there are penetrations in the shell a factor for stress concentration MUST be included in the calculations: this is a statuary value of 3.3 for USA Regulations (ASME Code) and others who follow those codes. So the MAX permissible stress at 100psi becomes 3142psi / 3.3 = 952psi (!!).
# ANY penetration must also be reinforced to resist stress concentrations. This generally means the hoop stress calculation determines a very thick shell! - far thicker than many "Old" boilers. But the Regulations are based on having boilers that WILL NOT FAIL in service. (unless made badly, using poor materials, etc.).
# Further, because the min tensile strength of copper at room temperature is:
Mechanical Properties Metric English
Tensile Strength, Ultimate 210 MPa 30500 psi (ASME code limits Tensile stress to 6700psi.: FOS = 4.55)
Tensile Strength, Yield 33.3 MPa 4830 psi
Elongation at Break 60 % 60 %

MIN compressive strength: 45 MPa 6535psi (ASME FOS 4.55 reduces the LIMIT to 1436psi.)

So, if you do the calculations, for a tube in compression (e.g. a flue tube with exhaust gas inside and boiler pressure water or steam on the outside), with a tube that has penetrations (e.g. a cylindrical firebox inner jacket with a firing hole) then you have a max stress defined for 100psi as ... NOT A LOT!
So, (Minh-Thanh) please check some calculations appropriate to making safe boilers.
Without knowing your designs I cannot comment otherwise.
K2

 

[Richard Hed]

Hi Sutty & Minh-thanh,
Boiler design is not quite so simple. I many countries there are Regulations. e.g. UK, Europe (EEC,ECE) USA, Canada, Australia, Japan, etc. and these have very well-defined rules for boiler design and manufacture - above a certain size. The BEST engineers are consulted, and insurance companies, and anyone with knowledge of the boilers are also consulted, so products made to Regulations are safe to use as designed, and when manufactured to specific standards. Model makers generally work to such standards of fit, jointing, materials, etc.
Some principles that have changed boilers since the early 20th century.
# Riveting has been abolished as the manufacture of rivetted boilers is very hard to control successfully.
# Silver Soldered copper boilers are generally limited to 100psi due to the "natural loss of tensile strength" of silver soldered copper joints at the elevated temperature for steam at 100psi. (205deg.C. or 400deg.F.) At below 100deg.F. ASME code permits a max tensile stress of 6700psi. BUT at 400deg.F this is down to a MAX permissible stress of 3000psi. (!!).
# Hoop stress calculations are conducted for boiler shells containing internal pressure. BUT these must limit the stress to <1/8th of the yield stress for copper AT THE TEMPERATURE of the steam at NWP (Normal Working Pressure). At below 100deg.F. ASME code permits a MAX tensile stress of copper boiler shells to be 6700psi. BUT at 400deg.F this is down to a MAX permissible stress of 3000psi. (!!).
# ADDITIONALLY: where there are penetrations in the shell a factor for stress concentration MUST be included in the calculations: this is a statuary value of 3.3 for USA Regulations (ASME Code) and others who follow those codes. So the MAX permissible stress at 100psi becomes 3142psi / 3.3 = 952psi (!!).
# ANY penetration must also be reinforced to resist stress concentrations. This generally means the hoop stress calculation determines a very thick shell! - far thicker than many "Old" boilers. But the Regulations are based on having boilers that WILL NOT FAIL in service. (unless made badly, using poor materials, etc.).
# Further, because the min tensile strength of copper at room temperature is:
Mechanical Properties Metric English
Tensile Strength, Ultimate 210 MPa 30500 psi (ASME code limits Tensile stress to 6700psi.: FOS = 4.55)
Tensile Strength, Yield 33.3 MPa 4830 psi
Elongation at Break 60 % 60 %

MIN compressive strength: 45 MPa 6535psi (ASME FOS 4.55 reduces the LIMIT to 1436psi.)

So, if you do the calculations, for a tube in compression (e.g. a flue tube with exhaust gas inside and boiler pressure water or steam on the outside), with a tube that has penetrations (e.g. a cylindrical firebox inner jacket with a firing hole) then you have a max stress defined for 100psi as ... NOT A LOT!
So, (Minh-Thanh) please check some calculations appropriate to making safe boilers.
Without knowing your designs I cannot comment otherwise.
K2

What about welded steel? Tell us about boilers made of welded steel. Which kind of welding is best?

 

[sutty]

Hi Sutty I am just back from a week cruising the Adriatic, Ionian and Mediterranean seas. Or about 1300 miles thereof...
Some interesting sites to see. Look up the castle walls of Valletta (Malta), Kotor (Montenegro) and Dubrovnik (Croatia). Spectacular engineering to build those structures.
I was without Internet and mobile phone for days on end! That was relaxing! 67p just to send or receive a single SMS text message in Montenegro! £57 for 100 Mb of data for 24hrs. But silence is golden!).

Viewed your burner. SUCCESS.Well done. Maybe a bit more tuning? And perhaps change the configuration so the main burner pre-heats the fuel? Of course more pressure from more preheat will give higher velocity at the jet (up to a limit) and higher velocity will draw in more air making the flames more intense, more like the small blowlamp you are using as the temporary preheater. That small flame is the ideal form with light blue cone then a darker cone surrounding it. All the air if taken through the nozzle air holes, whereas you still need some burner air through the middle of your burner.
Don't be disheartened if the last 10% of tuning takes 90% of the effort! That's the way of life.
I suggest the next step is to tune it inside the mock-up firebox and flue, as that will really change the pressures around the burner and change the flame structure.
If you struggle with air intake at the jet with the firebox enclosing the burner (increased burner back-pressure) I can give you design parameters for a venturi that increases the efficiency of the air intake at the jet.
Next I need to reconnect my PC... limited to a tablet just now.
Keep up the good work!
K2

Cheers Ken, Glad you enjoyed your hol, we've spent quite a few holidays in Malta, one of our favourite places.
Still working on the fine tuning of the burner but like you say it's a challenge. I joined the Classic camp stove forum to find out more about Turm stoves, can't find much about the jet or orifice sizes, the later stoves ran the vaporising pipe through the burner head but that might restrict the airflow up the flue.
Going to have to think about that one. I'd be interested in the venturi info though when have a spare moment.

Best regards sutty

 

[Richard Hed]

Cheers Ken, Glad you enjoyed your hol, we've spent quite a few holidays in Malta, one of our favourite places.
Still working on the fine tuning of the burner but like you say it's a challenge. I joined the Classic camp stove forum to find out more about Turm stoves, can't find much about the jet or orifice sizes, the later stoves ran the vaporising pipe through the burner head but that might restrict the airflow up the flue.
Going to have to think about that one. I'd be interested in the venturi info though when have a spare moment.

Best regards sutty

Camp stove forum? Can you send me a link?

 

[HMEL]

What about welded steel? Tell us about boilers made of welded steel. Which kind of welding is best

Welding is a certification process. The welding method itself has to be qualified and the joint tested. Names are given to the position in which its made and the materials used. The welder does a coupon weld and then is tested by testing the pieces he welded together.
He or she is then certified to do the weld. Paperwork must be filed for the inspector.
The welds may also have to be x-rayed to search for imperfection. If so many welds fail then the number of tests has to be increased. The process is as important as the calculations. On a practical level the weld has to have penetration and no porosity in it. So the weld process can be of any type as long as it is certified and tested. And if the inspector is not satisfied he can require a weld removed and sent to a laboratory to be mechanically tested.
This subject is not often talked about but on commercial boilers under construction or repair in the field it can be a major management process just to keep up with the inspections and paper work.

 

[Richard Hed]

Welding is a certification process. The welding method itself has to be qualified and the joint tested. Names are given to the position in which its made and the materials used. The welder does a coupon weld and then is tested by testing the pieces he welded together.
He or she is then certified to do the weld. Paperwork must be filed for the inspector.
The welds may also have to be x-rayed to search for imperfection. If so many welds fail then the number of tests has to be increased. The process is as important as the calculations. On a practical level the weld has to have penetration and no porosity in it. So the weld process can be of any type as long as it is certified and tested. And if the inspector is not satisfied he can require a weld removed and sent to a laboratory to be mechanically tested.
This subject is not often talked about but on commercial boilers under construction or repair in the field it can be a major management process just to keep up with the inspections and paper work.

Well, that's certainly interesting. I understand why it would need to be certified especially for commercial boilers, however, I would thimpfk that welding would be the very best way to make a steel boiler. Also, for small boilers, I would thimpfk pressure tests would be adequate.

 

[Steamchick]

Richard, HMEL knows more than I! - Thanks HMEL.
In the UK a steel welded boiler must be certified if over 3 bar-litres. (To the best of my knowledge). Material wall thicknesses must be a minimum of the metal thickness calculated for the strength of the boiler to resist the pressure, plus 3mm for the corrosion allowance. Welds must start and end on disposable tabs. Copper boilers use a factor of "zero" for the corrosion thickness. Model boilers in copper have traditionally had a factor of safety of 8 for the design stress versus UTS. I guess the same applies to welded steel boilers but need to check on that as I don't know.
I have employed Lloyds certified welders on contract jobs that required such and their welds looked "text-book perfect". Yes, paperwork is part of the job. Along with records of the approved component materials (controlled stock) and welding materials, current, gas, etc. ALL welds were visually inspected by the inspector.
K2

 

[Steamchick]

Continued: A few notes that are relevant to boiler making (UK):

The Code of Practice produced by the Model Engineering Liaison Group (MELG) on the Examination & Testing of Miniature Steam Boilers 2018 recommends in the section on design verification, that
• The constructor of a boiler to other than a recognised design available through the model engineering trade and/or press shall produce design drawings and demonstrate to the satisfaction of the inspector, either by calculation or by well-proven example, that the design and materials used have adequate strength.
• If no working pressure is stated on the drawings, or published accompanying text, the boiler shall be treated as a new design and calculations shall be produced and validated.
• If a boiler is being made to a published or established design but is intended to be used at a higher pressure than that specified by the designer, it shall be treated as a new design. The decisions taken by boiler Inspectors shall be taken as final (see section 19).
• Consideration should be given to the use of a build record sheet.

Also:
To calculate the right thickness of metal to be used for the boiler barrel, the following formulae can be recommended;
P = D x F x WPTS x R x C x T x 2
Where P is plate thickness in inches
D is boiler diameter in inches
F is the safety factor. (this is between 6 and 10 but usually a factor of 8 is used)
WP is the working pressure in lb/in²
TS is the tensile strength of copper (a suggested figure is 25,000 lb/in²)
R is the riveting allowance (this is when a rolled and riveted barrel is used. Single row 0.5, double row 0.7, and for riveted and silver soldered 0.8. It is suggested that all copper boilers include this figure as an added safety factor.)
C is the corrosion allowance (no allowance is usually made for copper)
T is the temperature allowance (copper diminishes in strength at high temperatures. An allowance of 0.8 for pressures between 60-100 lb/in² and 0.7 for pressures from 110 to 150 lb/in²)

and:

The design and construction of welded steel boilers is covered by BS2790.

The boiler barrel should, wherever possible, be made from ASTM A106 grade B. This is hot finished seamless refinery tube as used in the oil industry and is normally easy to obtain. If the required diameter is not available the Notified Body may give approval for API 5L to be used (oil industry line pipe). Otherwise, it would be necessary to have a barrel roller and welded by specialist contractor such as Deepdale Engineering. This will need to be supplied with material certificate and evidence of satisfactory x-ray examination of the seam. Current practice is to re-roll the tube after welding to minimise fatigue of the joint. It is wise to have welded longitudinal barrel seams ultrasonically examined for fatigue cracks when the boiler is stripped for thorough examination.
The design drawings need to specify the weld preparation to be use on each joint by referencing to the figures in BS2790.
The welding must be carried out by a welder who has current approval to BS EN287:2011 for the joints used in the boiler. The welding rods must be specified on the drawings and be suitable for the materials used. Certificates of Compliance should be supplied for the rods.
When using the normal type of locomotive boiler foundation ring (BS2790 pt2 1973 fig37a) it is necessary to have the firebox crown fully supported by stays. This means that the use of girder type crown stays is not permitted.
The steam pipe inside the boiler, after the regulator, must be made from a non-corroding material (copper or 316 Stainless steel).

But there are similar (stricter?) regulations for USA, etc.?
K2

 

[Steamchick]

Other notes concerning "insurance" for the UK...

Extract from a letter from an inspector:
Beware of Boilers with Incorrect Documentation.
In my capacity as a boiler inspector I was recently asked to inspect and issue a boiler certificate for a new 7.25" gauge locomotive which had been purchased by one of our members. The locomotive had been purchased form a professional builder and the builder had purchased the boiler from a well-known maker.
I arrived to find a shiny new loco with its proud owner. I was given a large envelope of documents. Welder approval certificates, material test certificates and a boiler drawing. I then found the boiler certificate, signed by the boiler maker and witnessed by the locomotive builder. No mention of compliance with the Pressure Systems Safety Regulations nor was there a CE mark or reference to the involvement of a notified body (The boiler was trivially over 50 Bar Litre).
We located the boiler marking, covered by the footplate, and again there was no CE mark as required by the regulations. I had no option but to refuse to issue a boiler certificate. Having discussed my findings with the insurance broker who organised for me to meet with the HSE, this matter is now under investigation by the authorities.
I would advise all members that if they have a boiler which was made by a "professional" boiler maker or a "professionally" built locomotive and it was completed after 30th May 2002 it must be CE marked and in the sizes our members operate have evidence of the involvement of a notified body.
If you are operating a boiler without the certification required by the Pressure Systems Safety Regulations you will almost certainly be operating without boiler insurance.

So "Buyers beware".
I understand that Ebay and others on the web have special rules concerning the sale of items that have or need certification, so please check, check, check!

K2

 

[Weldsol]

Continued: A few notes that are relevant to boiler making (UK):

The Code of Practice produced by the Model Engineering Liaison Group (MELG) on the Examination & Testing of Miniature Steam Boilers 2018 recommends in the section on design verification, that
• The constructor of a boiler to other than a recognised design available through the model engineering trade and/or press shall produce design drawings and demonstrate to the satisfaction of the inspector, either by calculation or by well-proven example, that the design and materials used have adequate strength.
• If no working pressure is stated on the drawings, or published accompanying text, the boiler shall be treated as a new design and calculations shall be produced and validated.
• If a boiler is being made to a published or established design but is intended to be used at a higher pressure than that specified by the designer, it shall be treated as a new design. The decisions taken by boiler Inspectors shall be taken as final (see section 19).
• Consideration should be given to the use of a build record sheet.

Also:
To calculate the right thickness of metal to be used for the boiler barrel, the following formulae can be recommended;
P = D x F x WPTS x R x C x T x 2
Where P is plate thickness in inches
D is boiler diameter in inches
F is the safety factor. (this is between 6 and 10 but usually a factor of 8 is used)
WP is the working pressure in lb/in²
TS is the tensile strength of copper (a suggested figure is 25,000 lb/in²)
R is the riveting allowance (this is when a rolled and riveted barrel is used. Single row 0.5, double row 0.7, and for riveted and silver soldered 0.8. It is suggested that all copper boilers include this figure as an added safety factor.)
C is the corrosion allowance (no allowance is usually made for copper)
T is the temperature allowance (copper diminishes in strength at high temperatures. An allowance of 0.8 for pressures between 60-100 lb/in² and 0.7 for pressures from 110 to 150 lb/in²)

and:

The design and construction of welded steel boilers is covered by BS2790.

The boiler barrel should, wherever possible, be made from ASTM A106 grade B. This is hot finished seamless refinery tube as used in the oil industry and is normally easy to obtain. If the required diameter is not available the Notified Body may give approval for API 5L to be used (oil industry line pipe). Otherwise, it would be necessary to have a barrel roller and welded by specialist contractor such as Deepdale Engineering. This will need to be supplied with material certificate and evidence of satisfactory x-ray examination of the seam. Current practice is to re-roll the tube after welding to minimise fatigue of the joint. It is wise to have welded longitudinal barrel seams ultrasonically examined for fatigue cracks when the boiler is stripped for thorough examination.
The design drawings need to specify the weld preparation to be use on each joint by referencing to the figures in BS2790.
The welding must be carried out by a welder who has current approval to BS EN287:2011 for the joints used in the boiler. The welding rods must be specified on the drawings and be suitable for the materials used. Certificates of Compliance should be supplied for the rods.
When using the normal type of locomotive boiler foundation ring (BS2790 pt2 1973 fig37a) it is necessary to have the firebox crown fully supported by stays. This means that the use of girder type crown stays is not permitted.
The steam pipe inside the boiler, after the regulator, must be made from a non-corroding material (copper or 316 Stainless steel).

But there are similar (stricter?) regulations for USA, etc.?
K2

in addition to what you have said every piece of material used i.e. boiler barrel / any plate material and any bar material such as used for stays and steam dome ring must have a test cert,
When I did my Shay boiler I was requested to stamp the certification numbers on all parts that were used (proof of traceability) by the inspector.
On the welding certification this is not a cheap thing to do. If you do an ASME 9 6G position (EN287fixed axis at 45 deg) that will cover you for all positions including pipe /plate and fillet welds.
If you go for just a 1G plate test piece (welded in the flat position) then you are not covered for pipe and so on.
To cover for pipe you had to do a 3G (vertical butt) and a 2G (horizontal Butt)
Also you are only coded for the process used in the test piece. so if you used MMA (stick) for the test you cannot use a TIG root on your boiler.
So if you do a fixed position pipe that's one test at approx, £400
If you went the plate route that would require two tests
If you then add into that different welding methods you can see it is not cheap.
Also you are only covered on a thickness range so this also has to be considered
So when someone says they are coded to ASME or EN287 the question is on what ?

Re Material thickness for model boilers in the UK the minimum is 1/4" (if you want to run it in public and get it insured)
Paul

 

[Richard Hed]

in addition to what you have said every piece of material used i.e. boiler barrel / any plate material and any bar material such as used for stays and steam dome ring must have a test cert,
When I did my Shay boiler I was requested to stamp the certification numbers on all parts that were used (proof of traceability) by the inspector.
On the welding certification this is not a cheap thing to do. If you do an ASME 9 6G position (EN287fixed axis at 45 deg) that will cover you for all positions including pipe /plate and fillet welds.
If you go for just a 1G plate test piece (welded in the flat position) then you are not covered for pipe and so on.
To cover for pipe you had to do a 3G (vertical butt) and a 2G (horizontal Butt)
Also you are only coded for the process used in the test piece. so if you used MMA (stick) for the test you cannot use a TIG root on your boiler.
So if you do a fixed position pipe that's one test at approx, £400
If you went the plate route that would require two tests
If you then add into that different welding methods you can see it is not cheap.
Also you are only covered on a thickness range so this also has to be considered
So when someone says they are coded to ASME or EN287 the question is on what ?

Re Material thickness for model boilers in the UK the minimum is 1/4" (if you want to run it in public and get it insured)
Paul

1/4" is tremendously thick for a toy model. Of course the larger the boiler is, the thicker it must be, sure, but how big is one of these toy model boilers?

 

[Weldsol]

1/4" is tremendously thick for a toy model. Of course the larger the boiler is, the thicker it must be, sure, but how big is one of these toy model boilers?

The reason for the 1/4" is down to the corrosion limit set by the likes of the Southern Federation and insurance companies That is why steel is not used for anything under 5" gauge and even then there are problems with water space versus grate size.
There is nothing stopping you building a thin section boiler to use yourself on your private land and you wouldn't require to be a coded welder or be insured as it will be your life in danger. But say you were running your "Toy" and a visitor turned and there was a failure then you are liable for any injury or damage to said visitor.
that's the whole reason for test certs for materials / welders/ insurance etc
paul

 

[Richard Hed]

The reason for the 1/4" is down to the corrosion limit set by the likes of the Southern Federation and insurance companies That is why steel is not used for anything under 5" gauge and even then there are problems with water space versus grate size.
There is nothing stopping you building a thin section boiler to use yourself on your private land and you wouldn't require to be a coded welder or be insured as it will be your life in danger. But say you were running your "Toy" and a visitor turned and there was a failure then you are liable for any injury or damage to said visitor.
that's the whole reason for test certs for materials / welders/ insurance etc
paul

Oddly enough, most modellers use tiny boilers of copper, but I don't intend to build a tiny model. I intend to build a model that will power about 5-10 HP. I have built a prototype which has subsequently been torn down. I could not get some pin holes out of it. however, I brought it up to 100 psi in a test. It was fun and scary. I used stick welding and could not remove the slag from the small connections on the inside of the small pipe welds. Now I have wire-feed and TIG, and this will enable better welds in both cases. I thimpfks that stick welding is the worst of the three methods. However, some peeps believe that wire-feed does not give good enough penetration so that leaves TIG. TIG is my choice anyway, it is penetrating and completely combines the two metals and even with the ability to build up as many layers as necessary for a good weld and strong joints.

The design is water tube, I would NEVER do a fire tube, not even for a copper model. The design (I realize a photo would be nice but the prototype was build about 18 years ago in the dark ages -- even before cruize control, and certainly before I had a digital camera) is two horseshoe shaped (U-shaped) pipes with a cross pipe at the two ends communicating the hot water. these parts are 4" diameters and 3/8ths min. thickness, no seam. From the bottom horse shoe are many smaller "heater" pipes communicating to the second horse shoe about 30" above. there are two (the original prototype had three lines of pipes) lines of pipe communicating to the top horse shoe. The inside line crosses over to the other side of the horseshoe at the top making a cathedral top.

From the top horse shoe two lines of pipe are attached at an upward angle to a larger and thicker walled "gatherer" pipe, 8" diameter which has a take-off for the engine. These small communicator pipes are 1" ID, seamless and I thimpfks 1/8 or thicker.

At the time I didn't know about the super heaters so in the new design, I will add these to enable dry steam--not a difficulty to do.

by the way, my calculations for strength was a minimum of 500psi. Can anyone tell me if I'm wrong? I always want to have everything "overbuilt" but not so much that it is unmanageably heavy.

 

[Weldsol]

Oddly enough, most modellers use tiny boilers of copper, but I don't intend to build a tiny model. I intend to build a model that will power about 5-10 HP. I have built a prototype which has subsequently been torn down. I could not get some pin holes out of it. however, I brought it up to 100 psi in a test. It was fun and scary. I used stick welding and could not remove the slag from the small connections on the inside of the small pipe welds. Now I have wire-feed and TIG, and this will enable better welds in both cases. I thimpfks that stick welding is the worst of the three methods. However, some peeps believe that wire-feed does not give good enough penetration so that leaves TIG. TIG is my choice anyway, it is penetrating and completely combines the two metals and even with the ability to build up as many layers as necessary for a good weld and strong joints.

The design is water tube, I would NEVER do a fire tube, not even for a copper model. The design (I realize a photo would be nice but the prototype was build about 18 years ago in the dark ages -- even before cruize control, and certainly before I had a digital camera) is two horseshoe shaped (U-shaped) pipes with a cross pipe at the two ends communicating the hot water. these parts are 4" diameters and 3/8ths min. thickness, no seam. From the bottom horse shoe are many smaller "heater" pipes communicating to the second horse shoe about 30" above. there are two (the original prototype had three lines of pipes) lines of pipe communicating to the top horse shoe. The inside line crosses over to the other side of the horseshoe at the top making a cathedral top.

From the top horse shoe two lines of pipe are attached at an upward angle to a larger and thicker walled "gatherer" pipe, 8" diameter which has a take-off for the engine. These small communicator pipes are 1" ID, seamless and I thimpfks 1/8 or thicker.

At the time I didn't know about the super heaters so in the new design, I will add these to enable dry steam--not a difficulty to do.

by the way, my calculations for strength was a minimum of 500psi. Can anyone tell me if I'm wrong? I always want to have everything "overbuilt" but not so much that it is unmanageably heavy.

Sorry I should have put the1/4" thickness was for the boiler shell and not including the fire tubes which you can calculate the min thickness (I think the reasoning behind that was if a fire tube failed it would put out the fire)
Re what welding process is better is all down to how good you are with that process, as all three that you mentioned are being used in industry now on components far greater than what you want to make just for an example the picture below is a section from a 60 odd mm wall thickness tube approx 9" dia, it is an offshore drill tube in totally non magnetic stainless steel all welded with hotwire TIG this was done back in 2004
Paul

 

[Richard Hed]

Sorry I should have put the1/4" thickness was for the boiler shell and not including the fire tubes which you can calculate the min thickness (I think the reasoning behind that was if a fire tube failed it would put out the fire)
Re what welding process is better is all down to how good you are with that process, as all three that you mentioned are being used in industry now on components far greater than what you want to make just for an example the picture below is a section from a 60 odd mm wall thickness tube approx 9" dia, it is an offshore drill tube in totally non magnetic stainless steel all welded with hotwire TIG this was done back in 2004
Paul

View attachment 140792

Thanx for that. I thimpfks that water tube systems are all-round safer as the "body" of the system is NOT a barrel. That barrel system has to be calculated for the surface of the barrel which amounts to HUGE total pressures. But with a water tube system, the pressures are calculated for the individual tubes and it is not multiplicative of the length of a tube. I do not know the exact formulation for the pressure calculations however, if we do a pretend tube infinitely long, and have , say a 1" ID and 100 psi, then it makes sense that the pressure is NOT infinite! We would need to take a small section of the tube, I thimpfks it would be approximately a length proportional to the diameter, and use that for some kind of calculation for the local pressure--not at all like the barrel type calculations used for fire tube systems.

On the system I am designing, there are three sizes of tubes: 1" ID, 4" ID and 8" ID. Each has it's own calculations and the thickness of the sections has to be correct. For the 8" section, I calculate the "total" surface pressure as one would do for the barrel system. This 8" tube is only 30" long. this is over kill, but it is also the most dangerous section and only make the thickness a bit more. It is well known that if a smaller heat exchanging tube breaks, it will only be a small split which would put out the fire. My biggest problem is getting seamless tubing, as that is a necessity. (I've got it all now, however.)