We've got 3 1/2" rigid conduit on the old Detroit. Been there since '89 or so. Stainless steel flex pipe (before stainless steel flex pipe was cool) It's been maintenance free except for replacing a hanger that broke. The rigid conduit is about 3/16" thick.....little heavy.

Have several pieces of 4 1/2" thinwall conduit on the newer trucks or tractors. You have to build it up a little to make a 5" stretch clamp tighten up on it.

The galvanizing doesn't hurt anything. Probably helps life some.