The Steamboating Forum

Just bouncing this idea out there to see what comes back...

Making a rectangular waterwall firebox for a watertube and trying to maximize heating surface while minimizing difficult welds in tight spaces;

Square 2"x2" tubing, astm a178 if available, vertical sections welded directly to one another with a common header top and bottom made of 2x2" with the side that the tubes are welded into it effectively cut away, making a "U" shaped tube or deep channel. I would think that the walls of the tubes welded together would make stays unnecessary and the "U" headers would be ok as well.... Thoughts?? Fred?

What you suggest can be done, and would behave very similar to a typical stayed sheet. I would think two parallel flat plates, with staybolts joining them would be easier to make, with easy welding. Applying ASME rules to the assembly you are suggesting would require some special calculations, My preferred method for similar assemblies is to use round tubes, swaged to a smaller diameter where they are inserted into the drums. This allows tight tube spacing, while still maintaining space for welding between tubes.

Fred, the swaged tubes/pipes sounds like an interesting way of getting closer tube spacing. How can this be done? Just hardened half-round die blocks and a hydraulic press?

- Bart
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To extend this idea, make it a curved water wall. That way you don't need all those stays and such. Then reverse the construction such that the water is outside the tubes and run the combustion gasses inside the tubes. Then surround the remaining water with a cylindrical case. In other words, a VFT.

(Sorry. I just couldn't resist.)

Bart, to make swaged tube ends you have the right concept, just add "heat", "Graphite lube" and "Big hammer"

The attached sketch shows the two major components, a die made from 2 inch round stock, and a tube holder which has a split and pinch bolt to firmly clamp the straight tube section. Clamp the tube in place, heat the end to red heat, bring down the die and smack it with a blow from the hammer. The long arms hold proper alignment, and are necessary. I tried using hydraulic press, but quick forming is necessary. A big vise can be used instead of the pinch bolt, but a split round tube holder is necessary. If the tube is short, just a base support may work, but I had to make the tube holder for tubes over 12 inches long (7/8 OD x 0.065 wall mild steel tubes), otherwise they would sometimes buckle or damage the unformed end.

I was also playing with doing this on the lathe, with something like a pipe /tube cutter, fitted with a big blunt roller rather than a sharp tube cutter, work here pending further experiments, that day job keeps getting in the way.

Actually, I like Mike's concept better, as evidenced by the boiler in my boat.

Haha thanks Mike.

I'm going for a rectangular sectioned firebox to maximise the use of available area and maximise grate space.

Fred, thank you very much for the info on the tubes! Might go this route as it would be a lot lighter than what I was thinking.

Note that if you're using pipe for the vertical water wall, you can get the same effect as swaging by turning some adapters so you can weld in smaller nipples into the ends of the water wall tubes.

- Bart

Fred, how small did you reduce the 7/8" tube to?