| Yes .. you're quite correct! I did get the calculation wrong. In hindsight the furnace tube should have been 12 gauge (0.104") wall as compared to a minimum wall for the shell of 0.05" assuming 100 psi DP.
I had assumed that the stiffening effect of the cross tubes would prevent collapse.
I guess the lesson I learned was.... calculate first, re-calculate and only then buy the materials!!
In answer to Kevins query, if my memory serves me right it was stick brazed and I do recollect just how difficult it was to get adequate heat in the right place with a large paraffin blowlamp. Also lost a few sets of eyebrows into the bargain! |