Here are a few of my thoughts, hope they help!
1. Would iron pipe work to make the frame instead of welded angle iron? Any thoughts on pipe diameter?
Sure, why not?! My few steam table pans I use for various things have a 1/2" lip on them so I would go with something with a O.D. of 1" at most, at least for those parts supporting the pans.
2. How much of a lip do I need for the edges of the pan to sit on?
I think most pans have about a 1/2" lip/rim so if they are supported from the top then I'd personally try to support the entire lip of the pan.
3. The fittings on the corners will be taller than the pipe (rails) so I'll plan on using arch/rail gasket to fill that void.
Sounds like that could work.
4. Does the pan need any support in the middle or just around the edges?
No need for support in the middle in my experience. The pans are made to be supported only by that rim and made to hold more weight than the 1" or 2" of boiling sap will weigh; just think of a buffet table with a pan piled high with bacon and sausage! LOL.
Having said all that, keep in mind that IDEALLY (and ideals are hard to achieve in real life of course and you may already know all of this anyway), the heat should be concentrated on the very bottom of the pans to prevent scorching. When I started with steam table pans on a fry burner and two-burner Colman camp stove, I had issues with the sap scorching on the sides and turning my syrup pretty dark and having an off-taste. Some of the darker color also comes from boiling in batches as is done with multiple steam pans anyway.
Given that, I quickly moved to a system where I could support the pans from the BOTTOM and was able to shield the heat from escaping around to the sides. That also greatly increased the efficiency since I wasn't loosing precious heat to anywhere but where it really counted. To do that since it is tough given the radius of the corners, I made an angle iron frame which had the angle "upside down" (for lack of a better term) where the horizontal leg held the weight and the vertical leg was a lip that kept the pan in place.
Good luck!
Last edited by SyncroScott; 03-13-2019 at 10:45 AM.
-Scott
2017: Found a new addiction/hobby!: 6 taps, Coleman stove/turkey fryer, graduated to barrel arch, 1.75 gal
2018: Increased efficiency - 22 taps on 3/16 gravity vac, 10 buckets, homemade extended barrel arch w/ firebrick, warming pan, 20X30 baffled pan, small home-built RO, 11.5 gal
2019: Same as above now with AUF, home-built float pan, gas sap pump, fewer fire brick but more insulation, maybe a few more taps if the wife lets me. ;-)