If the pipe is stiff enough to hold its shape to near circular when handling and installation of buried pipe. Generally, the elasticity modulus of steel is 207 GPa. The materials with lower moduli must have thicker walls to provide equivalent stiffness. Steel pipe lends itself to installation by microtunneling for its longitudinal strength and relatively smooth outer surface. For easy to install, it is necessary to increase ring stiffness actually. http://www.navetc-group.com/valve/