Lessons Learned from a 24-in. DIP Inspection

The City of Phoenix (city) launched an assessment program for its force main assets in 2015. In 2020, as part of the city’s ongoing efforts to understand and minimize risk associated with buried infrastructure, Black & Veatch was hired to perform a comprehensive condition assessment of the force main associated with Lift Station 43 (LS 43). LS 43 Force Main is a triple barrel force main, with each barrel comprised of 1.5 mi of 24-in. ductile iron pipe DIP, referred to as Barrels 1, 2, and 3. Two of the three force main barrels were assessed (3.0 mi total). DIP tends to fail through corrosion, causing initiation and growth of localized defects. Based on the city’s objective of identifying the location and approximate depth of pitting in every foot of the inspected pipes, remote field electromagnetic (RFEM) technology was identified as the primary inspection technology. Barrel 1 was inspected first. During the inspection, a construction anomaly was identified, preventing the RFEM inspection tool from flowing freely through the pipeline and requiring extraction by excavation. The anomaly was assumed to be present throughout all force main barrels, and the RFEM inspection tool was subsequently modified to allow passage. Barrel 3 was then successfully inspected using the modified tool until the last 5 ft when the tool became stuck again. This document will review inspection planning, execution, and tool recovery. Significant operational challenges must be overcome to insert, track, retrieve, and obtain high-quality data when deploying the 22-in. outer diameter inspection tool through a 24-in. inner diameter pipe. Lessons learned from planning and executing the inspections will be discussed.