Investigation of Mechanical Restraint Joint Leaks on 48-inch Prestressed Concrete Cylinder Pipe

Concrete Pressure Pipe joints are restrained for thrust by welding or by using mechanical joint restraint devices. This paper presents the findings of a leak investigation conducted on a 48-inch (122 cm) Prestressed Concrete Cylinder Pipe utilizing the Snap Ring mechanical retrained joint system. In the summer of 2001 during field hydrostatic pipe testing of the Sandy Point Pump Station in College Station, Texas, several 48-inch (122 cm) pipe joints sprang leaks before achieving the specified test pressure. Preliminary investigation of the pipe showed that the Snap Ring joints leaked at a pressure less than the specified test pressure and less than the rated pressure capacity of the Snap Ring. A more thorough investigation then followed to determine the cause of the observed leaks. As a part of the investigation, two pipe joints were removed in a preserved condition and transported to the pipe manufacturer Hanson Pipe & Products plant in Grand Prairie, Texas for further evaluation. At the plant, the joints were subjected to hydrostatic pressure tests followed by a complete forensic evaluation. The investigation showed that the failure was due to the inappropriate field assembly and installation of the Snap Ring pipe joints.