Monotube Flash Boiler Design

[Richard Hed]

I'll be interested to see your designs and builds,....hope you post them.

Toy, I am presently building four machines: a Stuart horizontal, a Stuart verticle and two Corliss/Ray machines. I have been building the Corliss for 40 years, mostly because I did not have the tools to continue them till three years ago (or is that four now?), and I am putting a Bridgeport back together. I make only small progress because I am also working on a relief shift in which I rotate every two days. It's exceptionally easy work with comprably low pay--the problem is the spinning dizzyness of the graveyard shift once a week.

One of the Corliss' I bought from a dieing machinist fourty years ago, it was not complete but about 70%. His workmanship was not the best. The second Corliss I bought as a kit forty years ago for $200--a steep sum in those days. That's the one I am presently slowly working on. since I spend a lot of time in the Philippines, I don't really get much time to work on it but am making slow progress.

As far as designs go, I have no plans except for maybe two: One will be like the Corliss but a reduced complexity. It has Corliss steam valves but the exhaust has a different arragement. It's called the "Improved Greene" Which one can find vids of but not any plans. The second one, is something that I am slowly gathering info on which I hopw will use poppet valves for the steam input and maybe a uni-flow exhaust.

I have several engines I would like to build from JDW and Elmers, Atkinson, and others, the stranger the engin is, the better as I like to see how odd mechanisms work--always a possibility to incorporate something into a design.

Until I get the mill re-assemble, I am haveing to use the lathe for milling operations as far as I can which naturally doesn't proceed very quickly. I have too many tools that I need a mill to make easily, else it takes a lot longer on th e lathe or is not possible at all. At the moment I am turning the four steam/exhaust packing glands but can only go so far till I need a file or a mill. I prefer the mill as it's a lot of filing. Also, i need two drill holes in each gland and I do not trust my drill for that.

 

[Richard Hed]

x

 

[Toymaker]

one problem with the flat plate spiral "radiation plate" boiler is its small surface area from which to absorb heat, you'll be much better off with a spiral tube, in fact lots of spiral tubes. Thats the game with all boilers and heat exchangers, surface area, surface area, and last but not least surface area.

The purpose of the flat plate spiral isn't to absorb all the heat coming out of the burner's exhaust, as most of the hot exhaust gases will simply bounce off the disk's flat surface and proceed into the rest of the boiler's spiraling monotube with it's total surface area of 1466 sqr in. Rather, the disk's purpose is to absorb the radiant heat which might otherwise be mostly lost.

It isn't possible to make a tightly wound spiral using 5/8" copper tube. I've considered using lots of parallel tubes of smaller diameter, which could be rolled into tighter spirals, but making the two junctions between the 5/8" tube and the bundle of smaller tubes would be quite the challenge, and parallel tubes increase the risk of overheating the working fluid as uniform flow through all the parallel tubes cannot be controlled.

If you have what you believe is a better, workable solution, I'm open to suggestions.

 

[Toymaker]

I believe steamchick is correct. Even ignoring the thermal expansion issue the flat plate design internal side pressure is going to be very high. Say a 8 inch diameter plate will have 50 square inches or 25,000 lbs of force on the side walls (given a 500 psi pressure )and this coupled with the lower yield strength at the higher temperatures is more then likely to come apart. Now the question is just how fast will it come apart. By the way that is not including the force on both sides of the disk so you are looking at twice the generated stress of value of one side. More likely 50,000 lbs of linear stress. You can no longer use the hoop stress equations of tubes because of the flat walls.

Thanks for your concerns,...I will try to address them.

Disk diameter is mostly 5.5" (it's a spiral, so not a perfect circle) which means it has a 24 sqr in surface area.
Total force on the flat plate: 24 sqr in X 500 psi = 12,000 lbs.

The spiral walls have a total length of 1300mm with a 1mm width; therefore total area of the wall's edge brazed to the flat plates = 13 sqr cm = 2.015 sqr in.

Tensile force on the walls from one flat surface: 12,000 lbs / 2 sqr in = 6,000 psi

Total tensile force on walls from both surfaces = 12,000 psi

Ultimate Tensile Strength of annealed copper at 200 C: 26,000 psi

Of course all the above calculations assume the flat plates will remain flat, and the force vectors will all be straight up and down,...but we both know those flat surfaces will bulge into dome shapes above the channel length as pressure inside the disk builds up to 500 psi. At that point the force vectors on the once flat plates wont be straight up and down anymore, and the channel shape will more closely resemble that of a tube with flattened sides. So, for strength purposes, do I treat the disk as a coiled tube or a box-shaped channel? Most likely, something in between.
Using only tube calculations as in post #35 results in what I consider very acceptable numbers, but the numbers above are no so appealing.

Your thoughts?

 

[NapierDeltic]

Off course, I know forged is better than machined; copper is better than brass/ bronze; thinner, uniform walls better than thick when comes to thermal and mechanical stress.
But have you thought of making radiation disk from solid, CNC machined material - meaning brass? You could dimension the walls with the safety factor you want, front side would have the spiral channel milled and the back would be only a lid -flange like. Bolts could be not only on the rim but uniformly distributed on entire area and threads cut in what remains as "meat" after milling spiral. The lid itself could be from copper plate, as thick as it takes. Rim could be reinforced with an additional ring of different material, for sealing and uniform distribution of forces.
In fact, being washed by liquid, local variation of temperature would be quite small, and the entire disk would work somewhere 185 deg.C and 32bar or psi equivalent.
I'm just questioning...

 

[HMEL]

Thanks for your concerns,...I will try to address them.

Disk diameter is mostly 5.5" (it's a spiral, so not a perfect circle) which means it has a 24 sqr in surface area.
Total force on the flat plate: 24 sqr in X 500 psi = 12,000 lbs.

The spiral walls have a total length of 1300mm with a 1mm width; therefore total area of the wall's edge brazed to the flat plates = 13 sqr cm = 2.015 sqr in.

Tensile force on the walls from one flat surface: 12,000 lbs / 2 sqr in = 6,000 psi

Total tensile force on walls from both surfaces = 12,000 psi

Ultimate Tensile Strength of annealed copper at 200 C: 26,000 psi

Of course all the above calculations assume the flat plates will remain flat, and the force vectors will all be straight up and down,...but we both know those flat surfaces will bulge into dome shapes above the channel length as pressure inside the disk builds up to 500 psi. At that point the force vectors on the once flat plates wont be straight up and down anymore, and the channel shape will more closely resemble that of a tube with flattened sides. So, for strength purposes, do I treat the disk as a coiled tube or a box-shaped channel? Most likely, something in between.
Using only tube calculations as in post #35 results in what I consider very acceptable numbers, but the numbers above are no so appealing.

Your thoughts?

You need to double the 12000 lbs to account for the other side of the disk. You can deduct the area from the supporting walls forming the walls of the spiral. Not sure how to handle the spiral walls because internally they will balance out except for those on the out side exposed to atmosphere. However 26,000 lbs force is still a big number. What I have seen done in annular round spaces is to fabricate a heat exchanger bundle of tubing that forms a circular pattern with the tubes running horizontal to the axis. You might be able to fabricate that if you can form the bend radius acceptable to the material you choose. Based on the color of the flame front in your pictures you will be seeing temperatures in excess of 1500 degrees F. It is not an easy design project. Then of course there is the other option to build one and test it. But in any event you will have to account for thermal expansion of the material as well as internally generated forces.

 

[Steamchick]

Hi Toymaker,
I see where you are coming from re: "Ultimate Tensile Strength of annealed copper at 200 C: 26,000 psi".
But, I understand that for the last 100 years or so, people who know better than I only use 1/8th of the tensile strength of copper for their pressure vessels. I.E. a Factor of safety of 8.
Which is why ASME (in their wisdom) use a MAXIMUM PERMITTED STRESS of 3000psi at 400deg. F. in their Regulations for the USA, which have been adopted as a standard in other countries as well.
If you choose to use a different value, as you are "outside Regulations for USA", then that is entirely your responsibility. But I fail to see how that avoids the physical properties of copper, and the rest of the Engineering worlds' recommendations for the use of Copper for pressure vessels at elevated temperature.
So, please consider a larger factor of safety than "1".
I.E. instead of your 26000psi (post #44) please use a value like ASME recommend. I think that changing from 1mm thick to 3.5~4 mm thick Copper is all that is needed for your design, but I'll let you do your calculations and make your own decisions, as you know the strength of your joints, other reinforcements, etc. as well as sizes of unsupported Copper plate that you propose to use in the brazed assembly.
I am sure that the owners of this site would not let us recommend or condone anything that is not considered "Safe" in the Engineering world, as the information is read by many who do not all have such a good or complete understanding of Engineering, and could mis-use "unsafe" recommendations without appreciating the risks of doing so. I certainly do not have any knowledge of the gas you are proposing, to know the risks if the radiation plate should develop a leak at all. I only know what happens when water enters the combustion chamber.
K2

 

[Steamchick]

Toymaker, I think you may need to do a bit of research, as your whole device may be bound by codes or Regulations of which I am unaware. Even when they do not "Apply in your country", they are based on the laws of physics, materials, and sound Engineering practice, so offer an excellent guide to designing devices such as yours. I am in the UK, but if I cannot find what I want in UK Regs and Codes I will use the best and nearest appropriate documents. Because they answer most of my questions when I don't know something. I think your "boiler" (Better to call it an "Heat-Exchanger"?) may be better considered within refrigeration codes and Regulations, because they must consider how the gases you propose are safely contained at their maximum temperature and pressures you plan. ( a refrigeration plant always has a Hot end as well as a cold end... Yours is just a system to cool a huge flame!).
keep at it, the answer is there somewhere.
K2
https://www.engineeringtoolbox.com/asme-boiler-vessel-code-d_8.htmlhttps://www.mass.gov/doc/2015-asme-boiler-and-pressure-vessel-code-section-i/downloadhttps://www.asme.org/codes-standard...refrigeration-piping-heat-transfer-componentshttps://archive.org/details/gov.law.asme.b31.5.2001

 

[Steamchick]

Hi Toy,
I searched for stress concentration in the corners of a rectangular tube subjected to internal pressure, and found this:

https://www.quora.com/What-is-the-f...tangular-shell-subjected-to-internal-pressure
The formula for stress in the case of a rectangular shell subjected to internal pressure is:$\sigma = P/t$Where:

• $\sigma$ is the stress
• $P$ is the internal pressure
• $t$ is the thickness of the shell
  It's important to keep in mind that this formula assumes that the shell is thin and that the stress is uniform across the thickness. Additionally, this formula is only valid for a rectangular shell with a uniform thickness. If the shell is not rectangular or the thickness is not uniform, the stress will be different across the shell and the formula will not apply.

Maybe this is the method of determining the stress in the top and bottom flat faces of the Radiation disc? - for each part of the rectangular channel.
K2

 

[peterl95124]

there's no way to "loose" radiant heat, it will bounce around in the boiler until absorbed. the notion that you can absorb as much as you want from a small plate with limited surface area isn't realistic. the rate at which a surface can absorb radiant heat depends on that materials emissivity and reflectivity, and there's little to no difference between copper tubing and a copper or brass or whatever plate, but you can work around this by increasing the surface area. you should also ensure that the entire works is jacketed by a highly polished (especially on the inside) reflective metal tube and insulate the outside.

 

[Toymaker]

there's no way to "loose" radiant heat, it will bounce around in the boiler until absorbed. the notion that you can absorb as much as you want from a small plate with limited surface area isn't realistic. the rate at which a surface can absorb radiant heat depends on that materials emissivity and reflectivity, and there's little to no difference between copper tubing and a copper or brass or whatever plate, but you can work around this by increasing the surface area. you should also ensure that the entire works is jacketed by a highly polished (especially on the inside) reflective metal tube and insulate the outside.

Peter, the boiler is constructed of two stainless steel "stew pots", one inside the other, with the inside pot having smaller dimensions than the outer pot thereby forming an air gap between the two shells; the air gap will be filled with insulation if needed. All the copper tubing slides loosely into the inner shell, allowing for expansion as the tubes heat. Having been made for cookware, all the metal surfaces on the pots are super shinny, almost a mirror surface. However, the burner uses Diesel fuel and although I've done my best to ensure complete combustion, no doubt all the metal surfaces exposed to exhaust gases will eventually turn black from unburned carbon deposits. Blackening the tube surfaces will likely prove beneficial, but blackening the inner shell surface is of course detrimental. You can see a bigger pic of the burner-boiler assembly in post #9.



Looking at the design above, it's clear that if not for the radiation disk, the exhaust gases would strike the flat bottom of the inner pot as they exit the burner, and much of the radiant heat would be absorbed by the inner pot, likely heating much of that area to a nice cherry-red temperature. No matter how good the insulation between the inner and outer pots, much of the otherwise useful enthalpy will escape to the outside world and be lost.

By placing the radiation disk directly in the path of the exhaust, it will absorb much, not all, but much of the radiant heat emitted by the burner and transfer that enthalpy into the working fluid flowing through it, and also act as a physical barrier between the exhaust gases and the bottom of the inner pot.

 

[Toymaker]

Off course, I know forged is better than machined; copper is better than brass/ bronze; thinner, uniform walls better than thick when comes to thermal and mechanical stress.
But have you thought of making radiation disk from solid, CNC machined material - meaning brass? You could dimension the walls with the safety factor you want, front side would have the spiral channel milled and the back would be only a lid -flange like. Bolts could be not only on the rim but uniformly distributed on entire area and threads cut in what remains as "meat" after milling spiral. The lid itself could be from copper plate, as thick as it takes. Rim could be reinforced with an additional ring of different material, for sealing and uniform distribution of forces.
In fact, being washed by liquid, local variation of temperature would be quite small, and the entire disk would work somewhere 185 deg.C and 32bar or psi equivalent.
I'm just questioning...

Actually, the idea of milling the entire disk from a single block of copper was one of my first thoughts,...but the price for a solid chunk of 3/4" x 6" x 6" copper, with shipping, is just over $350,...so that idea quickly went from 1st place to last.

I've also considered using a different material such as stainless steel which is easily brazed using one of several different silver based braze rods. Again, here too price is a strong influence as silver based braze is not cheap, and I'm not sure I can find any here in Thailand,...I may be forced to order it through eBay or wherever.

I do like your idea of adding bolts (stainless steel) through the thickness, which could be done on my current sheet copper design.

 

[Toymaker]

Taking a second look at overcoming the stress forces inside the spiral disk. (Note: si = square inches)

Disk diameter is mostly 5.5" (it's a spiral, so not a perfect circle) which means it has a 24 si surface area.
Total force on the flat plate: 24 si X 500 psi = 12,000 lbs.

The spiral walls have a total length of 1300mm. Increasing the wall thickness from 1mm to 2mm changes the total area of the wall's edge which is brazed to the flat plates from 13 sqr cm = 2.015 si to 26 sqr cm = 4.03 si.

Tensile force on the walls from one flat surface: 12,000 lbs / 4.03 si = 2,977 psi

Total tensile force on walls from both surfaces = 5,955 psi

At this point,...
Ultimate Tensile Strength of annealed T2 copper at 200 C = 26,000 psi
Yield Strength of annealed T2 Copper at 200 C = 7961 psi

Therefore, a 2mm wall thickness results in 4.37 times the Ultimate Tensile strength, and 1.3 times the Yield strength.

Now add 50 stainless steel M3 x 0.5 screws & nuts sprinkled uniformly around the disk surface. Each screw penitrates through the entire thickness of the disk. The 2mm thick wall is reinforced with the addition of a small 2mm thick scrap of copper resulting in small wall area of 4mm thickness, where each 3mm hole is drilled; this will help prevent any leakage. Will look a little like this:

50 M3 screws adds 420,300 psi to the total wall tensile force resulting in a total tensile strength of 426,255 psi.
That's 53 times the Yield strength needed and 16 times the Ultimate Tensile strength needed.

EDIT:
Although I'm confident this idea will work, fabrication is a nightmare, requiring brazing of joints inside the closed spiral. Using two overlapping pancake spirals wound from 5/8" tubing as discussed in post #56, is much easier to fabricate.

 

[peterl95124]

Peter, the boiler is constructed of two stainless steel "stew pots", one inside the other, with the inside pot having smaller dimensions than the outer pot thereby forming an air gap between the two shells; the air gap will be filled with insulation if needed. All the copper tubing slides loosely into the inner shell, allowing for expansion as the tubes heat. Having been made for cookware, all the metal surfaces on the pots are super shinny, almost a mirror surface. However, the burner uses Diesel fuel and although I've done my best to ensure complete combustion, no doubt all the metal surfaces exposed to exhaust gases will eventually turn black from unburned carbon deposits. Blackening the tube surfaces will likely prove beneficial, but blackening the inner shell surface is of course detrimental. You can see a bigger pic of the burner-boiler assembly in post #9.

View attachment 148075

Looking at the design above, it's clear that if not for the radiation disk, the exhaust gases would strike the flat bottom of the inner pot as they exit the burner, and much of the radiant heat would be absorbed by the inner pot, likely heating much of that area to a nice cherry-red temperature. No matter how good the insulation between the inner and outer pots, much of the otherwise useful enthalpy will escape to the outside world and be lost.

By placing the radiation disk directly in the path of the exhaust, it will absorb much, not all, but much of the radiant heat emitted by the burner and transfer that enthalpy into the working fluid flowing through it, and also act as a physical barrier between the exhaust gases and the bottom of the inner pot.

just use copper pipe wound in a spiral, two of them, one behind the other, and aligned so that the behind one gets all the radiation from the gaps in the front one (180-deg offset). if you're using 5/8 pipe then 5/8 gap sounds about right, if you're really worried use three spirals (120-deg offsets)

since you have a double wall container it doesn't matter that the inside of the inner one gets blackened, you want its outer (and the outer one's inner) surfaces to be reflective. Here's the funny thing about reflective surfaces, just like radiation is reflected off the surface, so too is internal heat inside the metal reflected back into the metal, weird but reflection is always symmetrical that way. the reflective surface on the outside of the inner shell keeps radiation inside the metal and its inner black coating enables it to be re-radiated back to the inferno, and the reflective surface on the inside of the outer shell helps keep radiation from being absorbed.

if the inside bottom of the inner pot gets blackened that will enable it to re-radiate all the heat it absorbs, and having a polished reflective outside will prevent most of it from re-radiating to the outside.

good luck what ever you decide !!!

 

[HMEL]

Taking a second look at overcoming the stress forces inside the spiral disk. (Note: si = square inches)

Disk diameter is mostly 5.5" (it's a spiral, so not a perfect circle) which means it has a 24 si surface area.
Total force on the flat plate: 24 si X 500 psi = 12,000 lbs.

The spiral walls have a total length of 1300mm. Increasing the wall thickness from 1mm to 2mm changes the total area of the wall's edge which is brazed to the flat plates from 13 sqr cm = 2.015 si to 26 sqr cm = 4.03 si.

Tensile force on the walls from one flat surface: 12,000 lbs / 4.03 si = 2,977 psi

Total tensile force on walls from both surfaces = 5,955 psi

At this point,...
Ultimate Tensile Strength of annealed T2 copper at 200 C = 26,000 psi
Yield Strength of annealed T2 Copper at 200 C = 7961 psi

Therefore, a 2mm wall thickness results in 4.37 times the Ultimate Tensile strength, and 1.3 times the Yield strength.

Now add 50 stainless steel M3 x 0.5 screws & nuts sprinkled uniformly around the disk surface. Each screw penitrates through the entire thickness of the disk. The 2mm thick wall is reinforced with the addition of a small 2mm thick scrap of copper resulting in small wall area of 4mm thickness, where each 3mm hole is drilled; this will help prevent any leakage. Will look a little like this:

View attachment 148076

50 M3 screws adds 420,300 psi to the total wall tensile force resulting in a total tensile strength of 426,255 psi.
That's 53 times the Yield strength needed and 16 times the Ultimate Tensile strength needed.

Me thinks my design will hold

The 12000 lbs is a vector force . Each of the side wall joints must distribute its force across the available wall area. Calculate that area and divide by 24000 lbs since there will be two apposing static vectors which will yield 12 tons of force. Your bolts are technically called stays and they require special calculations. Old steam engines had them in their boiler furnace above the fire box. I dont think your bolts will have the same thermal expansion as the walls and that will be a problem. But like I said you can always build and test.

 

[Toymaker]

just use copper pipe wound in a spiral, two of them, one behind the other, and aligned so that the behind one gets all the radiation from the gaps in the front one (180-deg offset). if you're using 5/8 pipe then 5/8 gap sounds about right, if you're really worried use three spirals (120-deg offsets)

since you have a double wall container it doesn't matter that the inside of the inner one gets blackened, you want its outer (and the outer one's inner) surfaces to be reflective. Here's the funny thing about reflective surfaces, just like radiation is reflected off the surface, so too is internal heat inside the metal reflected back into the metal, weird but reflection is always symmetrical that way. the reflective surface on the outside of the inner shell keeps radiation inside the metal and its inner black coating enables it to be re-radiated back to the inferno, and the reflective surface on the inside of the outer shell helps keep radiation from being absorbed.

if the inside bottom of the inner pot gets blackened that will enable it to re-radiate all the heat it absorbs, and having a polished reflective outside will prevent most of it from re-radiating to the outside.

good luck what ever you decide !!!

Thanks for the two pancake coils idea . With a slight modification, It's the best solution so far. Because the recommended minimum bending radius of copper tube is 3 times the diameter, each coil still leaves a 3.75" diameter "hole" in the center of the pancake spirals, which is nearly the size of the area I'm trying to cover.

However, by constructing the two pancake spirals you suggest, and placing one behind the other, but with their centers offset as shown below, the bottom coil tubes effectively cover the "hole" left by the top coil. As a bonus, the two coils effectively cover the entire bottom surface of the boiler.

The circle containing the two spirals (magenta) represents the diameter of the stainless steel pot. The red and blue spirals represent the pancake spiral coils.

 

[Toymaker]

The 12000 lbs is a vector force . Each of the side wall joints must distribute its force across the available wall area. Calculate that area and divide by 24000 lbs since there will be two apposing static vectors which will yield 12 tons of force. Your bolts are technically called stays and they require special calculations. Old steam engines had them in their boiler furnace above the fire box. I dont think your bolts will have the same thermal expansion as the walls and that will be a problem. But like I said you can always build and test.

Looks like we both posted (#55 & #56) at nearly the same time, but with you posting first.

Anyhow, my spiral disk idea was getting way too complex to actually construct; I'm scrapping that idea entirely in favor of using more tubing, (post # 56). Spiral tubing is much simpler to fabricate, adds much more surface area, and covers more of the bottom surface of the boiler where the burner's exhaust gases make their 180 degree turn.

 

[Bentwings]

Actually, the idea of milling the entire disk from a single block of copper was one of my first thoughts,...but the price for a solid chunk of 3/4" x 6" x 6" copper, with shipping, is just over $350,...so that idea quickly went from 1st place to last.

I've also considered using a different material such as stainless steel which is easily brazed using one of several different silver based braze rods. Again, here too price is a strong influence as silver based braze is not cheap, and I'm not sure I can find any here in Thailand,...I may be forced to order it through eBay or wherever.

I do like your idea of adding bolts (stainless steel) through the thickness, which could be done on my current sheet copper design.

I would think that TIG welding would be common there stainless TIG welds nice if you back purge. Before you embark on bolted or rivited assembly you may want to get a book called Roarks dress and strain . I has lots of information on bolted riveted connections as might be used in a boiler. You can get some idea by looking at rail road locomotives on just how many and approximate size fasteners might have to be even machinery manual has good information on bolted or riveted. connections . They are not as easy as they look . I did a lot of tank truck repair and weld standards were far higher than you might think . If a repair didn’t pass inspection you were in for a massive rework job . Often the inspector was standing right over you as you worked . There is not a lot of room inside tank trucks

 

[Toymaker]

I would think that TIG welding would be common there stainless TIG welds nice if you back purge. Before you embark on bolted or rivited assembly you may want to get a book called Roarks dress and strain . I has lots of information on bolted riveted connections as might be used in a boiler. You can get some idea by looking at rail road locomotives on just how many and approximate size fasteners might have to be even machinery manual has good information on bolted or riveted. connections . They are not as easy as they look . I did a lot of tank truck repair and weld standards were far higher than you might think . If a repair didn’t pass inspection you were in for a massive rework job . Often the inspector was standing right over you as you worked . There is not a lot of room inside tank trucks

My biggest obstacle to making the spiral disk was getting physical access to the inner walls that make up the spirals,...it proved quite a challenge as there's only 0.6" between the top and bottom flat plates, and once the plates are in place, only the outer wall is accessible to weld or braze.

None of that matters now as I've opted to use two overlapping spiral wound copper tubes as described in post #56.

 

[Toymaker]

Toymaker, I think you may need to do a bit of research, as your whole device may be bound by codes or Regulations

For this specific post, I'm putting our views of what is and is not safe from a physics viewpoint aside, and looking strictly at what is law. Also, I'm not a lawyer and I'm not providing legal advice.

Within the United States, so far as I'm aware, there are no federal laws requiring ASME codes or standards be followed, they are completely voluntary . However, some states have enacted laws requiring ASME and other organizational codes and standards be adhered to, so builders should consult their state laws.

In Thailand, where I live, the governing standards body is TISI (Thai Industrial Standards Institute). I cannot find any standards regarding boilers or even "steam".