Rigid couplings used in straight runs should be supported similar to welded or flanged piping. Refer to: ANSI B31.1, ANSI B31.9, NFPA 13. Rigid couplings do not provide longitudinal movement. However, a gap exists between pipe ends and should be considered when calculating axial displacement. Rigid couplings are recommended in areas of concentrated weight and where flexibility is not desired, to hold plumb and pitch.