WSSC Reliability Management

Abstract

A PCCP Reliability Management program was developed for the Washington Suburban Sanitary Commission (WSSC) to address deterioration of the 96 Potomac Transmission Main. The reliability program consisted of developing repair and monitoring recommendations that created the best value while maintaining a safe and reliable water delivery system. Reliability recommendations were based on both state-of-the-art forensics and performance analysis, including evaluation of the feeder's consequence-of-failure and delivery-redundancies. Together, these data allowed the development of an unprecedented large scale PCCP reliability program. The program enhanced investment while addressing both life and property safety through technologies not previously used for this purpose. Pipeline Reliability was directly influenced by the level and quality of assessment data obtained. An understanding of the pipeline's condition was at a level not previously seen in the industry. Assessment methods used consisted of nondestructive technologies (NDT) both common and un-common to PCCP evaluations. The technologies include: visual, magnetic, Sonic-Ultrasonic (SU), and Acoustic assessments, including Performance-Analysis based on the NDT data. The uncommon technologies used were the Sonic Ultrasonic and Performance-Analysis. The Sonic Ultrasonic NDT allowed the identification of both early and advanced stages of pipe deterioration. Degradation measured, from on-set to advanced, are: 1) de-lamination at the pre-stress wire, 2) micro-cracking at the outer core, 3) de-lamination at the embedded cylinder, and 4) micro-cracking at the inner core. These data complement both the magnetic and acoustic assessments by identifying the stages of deterioration leading to pipe failure. Performance Analysis uses the data produced from the NDT (magnetic, SU, acoustic, and visual) to predict pipe performance with loss of pre-stress. The advantage here is pipe performance is measured by structural Safety Factors. This allows easy prioritization of the myriad of suspect pipe (low safety-factor pipe are more vulnerable than pipe with high safety-factors). Further, this approach has been refined for cost efficiency. For WSSC, 15 select suspect spools were used to develop 15 Performance Curves. From these 15 curves all suspect pipe were evaluated and safety factors developed, 90 spools in all. This technology allowed every suspect pipe to be individually evaluated and performance to be understood relative to each other. This reliability approach allowed resources to be used where and when needed, resulting in the best return on investment while offering the continued safe and reliable operation of the 96 Potomac Transmission Main.