Helically corrugated metal pipe (CMP) is often the optimum choice of modern infrastructure projects. It is fabricated in the factory and be directly used when arrived at the job site. Compared with annular pipe, there is no welded or riveted seam along the longitude direction. It won't crack under heavy loads or vibrations. Diameter or span of helical CSP ranges from 300mm to 3600mm, which are relatively smaller than CMP formed by structural plates. Normal length is up to 7000mm and up to 15 000 mm for custom design.