Risk Assessment and Repair Priority of PCCP with Broken Wires

Condition of existing buried pipelines with prestressed concrete cylinder pipe (PCCP) from standpoint of number of broken wires can now be determined accurately using the remote field eddy current/transformer coupling (RFEC/TC) non-destructive test method. The test provides the owner with information about wire break locations and the number of broken wires in each location. The purpose of this paper is to evaluate the risk of rupture for the reported number and location of broken wires for a pipe subjected to specified pressures, and to determine the repair priority for pipes with broken wires. PCCP derives strength from prestressing wires, and loss of prestress due to wire breakage poses a risk of pipe rupture that depends on the number of broken wires, location of broken wires, original pipe design, and maximum pressure likely to occur in the future. Risk of failure of a pipe is evaluated by comparing the maximum pressure expected in the line with the pressure required to cause rupture. The pressure required to cause rupture in a pipe with broken wires is calculated by computing the pressure that causes tensile softening of concrete in the circumferential direction, and exceeds the bending capacity of the outer core in the longitudinal direction and rupture strength of the steel cylinder. The calculation accounts for interlocking and arching effect of cracked concrete and for soil resistance against radial movement. Application of the above technique to the risk assessment and repair priority of several prestressed concrete pipelines with broken wires is discussed.