A method of fabricating a conduit comprises steps of attaching a first tubular-outboard-ply-end of a tubular outboard ply to a first inner collar portion of a first collar with a second weld and attaching a second tubular-outboard-ply end of the tubular outboard ply to a second inner collar portion of a second collar with a fourth weld. The method also comprises steps of inserting a tubular inboard ply into the tubular outboard ply, threadably interconnecting the first inner collar portion and a first outer collar portion of the first collar, and threadably interconnecting the second inner collar portion and a second outer collar portion of the second collar. The method further comprises steps of attaching a corrugated inboard ply to the first outer collar portion with a first weld and attaching a corrugated inboard ply to the second outer collar portion with a third weld.