Acoustic monitoring of prestressed concrete pipe

Abstract

The Bureau of Reclamation has made extensive use of Prestressed Concrete Pipe (PCP) in several of its major water projects. Widespread corrosion and failure of the reinforcing wire on over 6 miles of PCP used for the Central Arizona Project was found in 1990. This pipe had been in service less than 15 years which is significantly shorter than its expected design life. It was apparent that if wires continued to fail, catastrophic rupture of the pipe would result. Repair methods were developed to restore the prestressing forces to a deteriorated pipe section. This would extend its service life; however, locating the deteriorated areas in a buried pipeline was difficult. Numerous technologies were tested inside and outside the pipe in attempts to locate the distressed areas. None of the techniques tested could reliably locate areas of distress, however, one method has shown great promise. The use of hydrophones (underwater microphones) to detect the sound caused by the failure and subsequent slippage of the reinforcing wire has been demonstrated to be quite effective. The development of this technology is described, from initial field testing using a single pair of hydrophones, to the system currently being used for the continuous monitoring of a 2-mile pipeline. This system uses an array of 12 hydrophones and a sophisticated computer system to detect sounds in the pipeline, classify them as either wire-related sounds or extraneous sounds, and, based on the location of the wire-related sounds, map areas of pipe deterioration.