Do the Math-Spiral Welded Steel Pipe is a Good Bet

This paper will address that the mathematics of helix, including the calculus derivation of a curve length in space to determine the length of a helix in one revolution; this derivation demonstrates the length of spiral seam per unit length of pipe, and provides the basis for other geometric relationships that include the pipe diameter, coil width, coil splice and helix or spiral seam angle. The paper will also present pressure vessel derivations for principal hoop and longitudinal stress including the Barlow and PA (pressure-area) formulas. From engineering mechanics of materials, knowing the stresses on a solid body under rotation, stresses on spiral weld seams and coil splices can be calculated. The results of this investigation provide for an interesting discussion because they indicate that spiral weld seam stress is typically very low compared with the hoop stress of a pipeline.