Condition Assessment and Rehabilitation of the Windy Gap Pipeline—An Owner's Perspective

The Windy Gap Pipeline is a 9100-meter (30,000-foot) long, 2750 mm (108-inch) diameter pressure pipe. Approximately 7300 meters (24,000 feet) of this line is prestressed concrete cylinder pipe (PCCP). Given the problems experienced with numerous PCCP pipelines throughout the country, the owner, Northern Colorado Water Conservancy District, desired to perform a condition assessment on this portion of the pipeline. A phased condition assessment program was conceived to cost-effectively eliminate areas of concern that have historically been problems for PCCP. Initial testing indicated that the pipeline was surrounded by a relatively benign environment with no apparent distress or corrosion. However, wire testing results indicated highly variable properties with moderately strain aged wire. A remote field eddy current /transformer coupling assessment technique was employed to determine the extent of the wire problems on the pipeline. Results showed that 275 pipes had 5 or more broken wires, with 4 pipes containing over 50 broken wires. An external tendon repair was designed and constructed on 17 sections of pipe that were likely to fail. During the course of this project, several issues involving interpretation of test results, limitations of tendon repairs, and cost/benefit analysis of rehabilitation methods arose that highlight the challenges faced by PCCP owners relating to the emergence of new assessment technologies and rehabilitation methods.