My new design uses 1/4" wall boiler shell, furnace shell, and 1/4" tube plates.
also uses 36, A178 boiler tube in the hexagonal pattern.
I've done some calculations it has 16.25 square feet of heating area just shy of 1 square foot of gas flow area on the bottom tube plate, and will hold 29 gallons of water, 2/3 of the tubes are under water. This is still before I go chopping holes in it
Looks good. Keep in mind that with that thin of shell, you're going to need weld-o-lets for all of your fittings as the shell will be too thin to just thread them directly into it.
Also, if you're going with that thin of shell I would take a close look at boiler water treatments, because there isn't much room for corrosion.
Very good drawings by the way. I wish I had paid attention in architectural design when we started doing the CAD stuff.
Thanks, I like designing and drawings things just as much as building them.
Anyway, Wisconsin's chief boiler inspector got back to me. Our boiler code applies only to buildings. The state DNR has control over all watercraft and they have no provisions on boilers.
YAY! I can build my own.
In designing my own boiler I'm going to deviate slightly from the code (fire up the flak guns)
the only thing I mean to change is having the top and bottom tube plates sit atop the boiler and furnace shell (similar to my first drawing) the reasoning behind this is simple, I'm building it myself and I'll never get the top tube plate a perfect circle to fit the inside of the boiler shell which, being just a section of pipe, may not be a perfect circle, same goes for the bottom tube plate and the base plate. I'm not trying to incite a rebellion or anything I just don't see any reason to pay the extra $ If I don't have to, for something that seems a little overkill.
Thank you all again for the design tips and pointers.
Also looks like I'll be employed in a week or two so maybe construction will begin in a month or so, on the engine at least.
Josh
Last edited by Spanky on Thu Mar 01, 2012 6:11 pm, edited 1 time in total.
Edit: Removed old post as I have settled on my final basic* boiler design.
Uses .25" boiler shell, top tube plate, and base plate .375" furnace shell and bottom tube plate. It still uses the 36 A178 OD 1.25" .095" wall boiler tube in the hexagon pattern.
I did calculations on it 16 square feet of heating area, will hold 28 gallons of water, and will weigh approx 165 lb empty.
*basic meaning before I cut holes for firebox doors and the various pipe fittings.
I will edit and post pictures when I have the time.
Question for Fred (or anyone else) since I know you have been following this post:
I wonder why the code wants tube sheets to be positioned and welded inside the shell? I've always done it that way on 1/8 and 1/5 scale locomotive boilers. Indeed, the sched. 80 pipe I have used was never exactly round but it only took me a few minutes with my killer disk grinder to make the tube sheet fit close enough for a good TIG root weld.
I'm guessing that it has something to do with the sheer forces on the weld as the shell expands under pressure. Or it may have to do with the way riveted tube sheets were done although, as I think of it, the full scale units I've worked around have had formed lips on the tube sheets so that the riveted joint was under mostly sheer loads in the axial direction of the boiler.
I'm neither a boiler designer nor a decent welder so I've always tried to follow tradition and the advice of real welders but I'm curious.
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
Sorry, to cut in... But here's my final design (still no holes)
iso
front
Just some quick questions about hole placements.
Where should the pressure gauge fitting be located? I want to say right out the top...
Where should the sight glass fittings be located? Again common sense leads me to think top (steam) fitting needs to be as close to the top tube plate as possible, and the bottom (water) fitting needs to be just a little above the bottom tube plate.
How close to the base plate is the blowdown valve supposed to be located?
How many hand holes are needed and where is a good location for them?
Josh, the 1/4 inch thick shell is OK for thickness, but I would strongly recommend you use the ASME minimum of 5/16 inch plate thickness for the tubesheets and bottom ring. As to putting the sheets inside the shell and furnace tubes, this is not really difficult. You can make these sheets with a perimeter gap of 1/8 to 3/16 inch (sheet diameter 1/4 to 3/8 smaller than shell ID) and still get a good full penetration weld. As Mike states in the last post: "it only took me a few minutes with my killer disk grinder to make the tube sheet fit close enough for a good TIG root weld.+
Why does the ASME Code require tube sheets to be positioned and welded inside the shell? Welds often have enough composition difference and often imperfections that can weaken the joint. With the tubesheet not placed within the shell, but placed on the end of the shell, the weld alone holds the tubesheet to the shell, and it is in pure tension, (or tension plus bending, which is worse). If there are imperfections in the weld, or the weld experiences cracking (a common occurrence in many pressure vessel welds) the joint can fail catastrophically. With the tubesheet placed completely within the shell ID, the weld can loose much of its strength, but will still block the tubesheet being driven to failure due to shear stress. The weld could basically turn into "Swiss cheese" and still its presence would block the potential for pressure to drive out the tubesheet.
Attachments
THESE ARE BEST, SOME USE SCHEDULE 80 THREADED "HALF COUPLINGS" WELDED TO SHELL
threadolets.jpg (13.19 KiB) Viewed 8382 times
E PLURIBUS UNUM
Prohibited Weld.jpg (21.17 KiB) Viewed 8382 times
A-105 Thread-o-lets.jpg (32.64 KiB) Viewed 8382 times
"I'm not trying to incite a rebellion or anything I just don't see any reason to pay the extra $ If I don't have to, for something that seems a little overkill."
Good choice of words Josh, that is, the last word in your statement....
Attachments
ford boiler explosion.jpg (46.89 KiB) Viewed 8380 times
Boiler_Explosion_old.jpg (76.03 KiB) Viewed 8380 times
He's right, Josh. There is a reason for doing things a certain way. Hard experience, often bad. And a hydro test doesn't catch everything.
As a related example, the FAA has a wonderful publication on certain things NOT to do when building a home built airplane. Some of them seem quite innocuous until you think them through and then they make your face turn white.
The energy release from even a very small boiler is amazing. When I was a young tad living in the country we put our garbage in a hole in the ground and burned it every so often. In spite of some awareness on the family's part, a jar of some liquid stuff would end up in there and the resulting kablooie would nearly empty the hole. I always stood back a ways when tending the fire.
A short Google expedition with the words. "Boiler explosion" is educational.
If you think you are too small to make a difference, try sleeping with a mosquito.
Dalai Lama
My point of view is this... the boiler code was written in 1914 when they had little knowledge of welding techniques, used inferior quality steel and riveted boilers together. Material processing has changed dramatically since then, the boiler code hasn't. (evident in the hydro testing method) The top tube plate is not just held on by the weld joining it to the boiler shell, it's also connected with 36 tubes. These tubes main purpose is of course to provide area for gas flow, they also serve structurally to "check" any tendency for the top tube plate to "pop" out. They are connected to the bottom tube plate of course, where the pressure is acting in a different manner than the top. At the top of the boiler the pressure inside wants to push out and explode the vessel, at the bottom the pressure wants to force the bottom tube plate into the furnace and implode the vessel. These forces although not completely balanced (area differences between top and bottom tube plates) would not be sufficient to overcome the structure of a well constructed and maintained boiler. Going back to the antiquated boiler code, for a prime example of how much things have changed, look no further than your shop's air compressor. It is no doubt constructed of 1/16" steel rolled into a tube, welded along the seam and then similarly welded along the top and bottom joints, those "cups" forming the top and bottom are not set inside the tanks shell but the vessel will still hold 300+ psi. So long as proper care is shown to my boiler (which being built by me is quite likely) and all relief valves function there is no reason that this design would not last. As for your attached pictures the top appears to be a domestic use boiler for home heating, I do not see this as relevant as these receive poor attention at best. And as my boiler is not of riveted construction this one can also be branded irrelevant.
