Maintaining Service Despite Wire Breaks: Condition Assessment of a Low Pressure PCCP System

The Ak-Chin Link pipeline is an 8.5-mi-long, 78″ and 84″ diameter prestressed concrete cylinder pipe (PCCP) near Maricopa, Arizona. This pipeline provides the entirety of irrigation supply for 16,000 acres of Ak-Chin Farms. Stantec (Engineer) recommended Ak-Chin Farms to complete an electromagnetic (EM) survey and visual and sounding inspection on the 40-year-old pipe. The 2017 EM survey revealed broken pre-stress wires, indicating a potentially compromised system. However, a thorough analysis demonstrated that despite wire breaks, the pipeline's steel cylinder is capable to withstand the low operating pressure and overburden loads. Therefore, a partial encasement repair solution was approved to extend the evaluation time. Other work in following years included expanding pipeline access (for future condition assessment), pipeline bonding for continuity, and installation of an impressed current cathodic protection (ICCP) system to protect further prestressed wire breaks. Five years later, the Engineer recommended another condition assessment to determine the pipeline deterioration rate specifically under partially encased pipe sections. Additionally, remote field testing (RFT) was used over 1.5 mi of the pipeline to identify the condition steel cylinder within the PCCP. This paper will not only discuss the results of the two condition assessments conducted in 2017 and 2022, but it will also explore the impacts of steel cylinder corrosion on pipe integrity, particularly within the context of the pipeline's low operating pressure capped at a maximum of 30 psi. Moreover, we will outline the procedure for establishing repair priority, leveraging the risk curves generated, and the degradation rate prevalent in each pipe segment. This project is a unique case study which highlights efforts to support Ak-Chin Farms to continue meeting their goal to sustainably feed the greater Southwest region.