The principal of heat fusion is to heat two surfaces to a designated temperature and then fuse them together with the application of force. The pressure causes flow of melted material which causes mixing thus fusion. When polyethylene pipe is heated, the molecular structure is transformed from a crystalline state into an amorphous condition. When fusion pressure is applied, the molecules from each pipe end mix. As the joint cools, the molecules return to their crystalline form, the original interfaces are gone, and the two pipes have become one homogeneous pipe. The joint area becomes stronger than the pipe itself in both tensile and pressure conditions.
High-density polyethylene (HDPE) is a polyethylene thermoplastic made from petroleum. HDPE is far more flexible than Ductile and PVC pipe in traditional applications and does not require restraints. It lasts longer and does not corrode from the water inside the pipeline or the ground conditions around the pipe.
HDPE pipe is corrosion resistant, flexible and has many uses and applications including trenchless installations for both water lines and sewer rehabilitation.