A bit of time while I await re-charging of my battery saw... so I can continue cutting a 12" trunk. "Timber!" - well, maybe tomorrow?
1 - 8 x 1/4 tubes situated - around the flue tubes, through the water and steam. Does this quick (15 seconds) sketch help?
2 - Ceramic burners (radiant burners): From top to bottom:
8 1/2" x 5 1/2"; 4in diameter; 2in square; 4in x 5/8in.
But also there are radiant burners per: Bekeart Brochure - even as small as will fit larger model boilers and locos. These are made from wire mesh or woven wires (knitted fabrics, etc.) in FeCrAlloy, or Nichrome. And I have udes regular burners with wire mesh of old electric element wire to make radiants that glow orange in the regular blue gas flames following guys who do that on small gauge locos.
3 - To the boiler, based on your materials.
* The main flue tube (most critical item):- the flue is 25.4mm dia with a1.65mm wall - Compressive stress limit is 825psi: AT 50 psi the calculated hoop stress (considering stress concentration factor for the cross tubes) = 1406psi = NO GOOD: but of NWP is reduced to 30psi: Compressive hoop stress becomes 863psi against a spec of 921psi = OK.
THEREFORE I recommend this boiler has a NWP NOT EXCEEDING 30 psi. - Which means the safety valve shall prevent any overpressure at 32psi. (Hydraulic test at 60psi for certification).
* the cross tubes are 15.9mm dia with a wall thickness of 1.7mmm. Compressive hoop stress permitted = 921psi, and hoop stress is 172psi (as there are no penetrations in these tubes, the SCF = 1) = OK for NWP = 30psi:
* The shell: the boiler casing is 76mm o/d with a 1.3 wall -Hoop stress 2982psi for NWP = 30psi, but permitted stress = 4389psi, so OK:
* I was going to make the ends from 1.5mm. - SO you can have a circle of up to 1.65in. (41.9mm) without stays or other support. (CUT a circle this diameter, and fit it anywhere in the end plate without overlapping a tube, or stay, and the design fails). Your plan is for a 1" annulus between the outer shell and main flue, so you cannot fit a 1.65" circle anywhere there: So that is OK for 30 psi NWP.
- But remember, the flue will fail the calculations against the stress permitted by the regulations if you want to certify the boiler for more than 30psi. So even though other parts won't fail, you would encroach on the factor of safety determined by the Federal Government - and fail the certification.
I hope this helps you understand what you can do with these materials in making a boiler.
I also posted a point in #12 about how the 15.9mm cross tubes block most of the gas passage for up the flue. Draw a circle 22mm diameter, now draw the cross tubes (16mm wide) and shade-in with a pencil. The gap at the sides is hardly enough for a candle flame to pass through, never mind the exhaust gases from the burner you'll need to power an engine. You idea of drilling solid 1/4" copper seems OK, except copper is so soft it will just collapse while you are trying to do that. I advise you just buy some copper tube. (I use regular 1/4" or 6mm central heating tube on boilers for 30psi like this one).
I hope this is useful?
If I have made any errors, I hope some reader can advise as I would not want anyone doing the wrong thing with steam boilers. - I am never offended by people correcting me. (there is always a first time?).
Enjoy being a boilermaker!