Metropolitan Water District of Southern California PCCP Condition Assessment and Comparison and Blind Test of RFTC and P-Wave

Abstract

The Metropolitan Water District of Southern California (Metropolitan) has 163 miles of prestressed concrete cylinder pipe (PCCP) within its distribution system. Metropolitan’s PCCP pipelines were installed between 1962 and 1985, vary from 42 to 201-inches in diameter and operate at pressures up to 300 psi. Eighty percent of Metropolitan’s PCCP is 78-inch diameter or larger. In 1996, Metropolitan initiated a PCCP condition assessment program. The early internal inspections included visual, sounding, and limited Impact Echo. Corrosion and electrolysis test records were compared to inspection findings. Corrosion mitigation systems were installed and repairs were conducted as needed. In 2000, Metropolitan added Remote Field Transformer Coupling (RFTC) to its PCCP condition assessment tools. As of June 2009, Metropolitan completed RFTC inspections in 99 percent of Metropolitan’s PCCP, second RFTC inspections in 70 percent, and third inspections in 11 percent. Metropolitan has repaired approximately 130 PCCP pipe sections as a result of the RFTC testing. In 2004, Metropolitan used P-Wave in the Rialto Pipeline; three months after RFTC testing identified several pipe sections with excessive wire breaks. The P-Wave inspection was conducted prior to repairs triggered by RFTC wire break predictions. The P-Wave inspection was conducted to determine if it provided results similar to RFTC. Metropolitan verified actual wire breaks in one pipe section during the repairs. In 2009, Metropolitan scheduled side-by-side RFTC and P-Wave inspections in four PCCP pipelines, totaling 3 miles. Two pipelines were scheduled to have several PCCP pipe sections removed shortly after the inspection for a treatment plant upgrade. The removal of pipe sections for the plant upgrade presented an opportunity to conduct a blind test of RFTC and P-Wave. One pipeline contained a pipe section with wire breaks detected by RFTC in 2002 that Metropolitan verified in 2003. One pipeline included a reach that was previously inspected using both methods in 2004, providing an opportunity to compare second inspection results. This paper provides an overview of Metropolitan’s PCCP condition assessment program, a comparison of RFTC and P-Wave wire break predictions from the side by side inspections in four pipelines, and the results of the blind tests. 1 Engineer, Materials and Metallurgy Team, Infrastructure Unit, Metropolitan Water