Finite element analysis of prestressed concrete pressure pipes and its application in non-destructive testing

Nondestructive inspection of high-pressure water supply pipelines is in high demand due to their increasing maintenance costs. Breaks in the prestressing wires are often blamed for dangerous ruptures of the concrete pressure pipes. In this thesis, finite element analyses are performed to study the signal behavior of a patented non-destructive inspection technique for a prestressed concrete pressure pipe. Visual Basic script is used to automate the modeling, solving and post processing process in the finite element software MagNet 6. A Green's function method employing the superposition principle is proven to provide accurate results with much less computing time than direct finite element calculations. The induced eddy currents in the prestressing wires play an important role in synthesizing the break signals. A zero-forcing equalization algorithm is employed to study the signals from multiple wire breaks. The effect of the joint and its interference with break signals are also investigated. The frequency dependence, the spatial resolution and the signal sensitivity of the inspection technique are evaluated. The effects of detector lift-off and orientation on the voltage output are presented. Brief discussions are given to verify or interpret these calculation results.