Inspection, Failure Risk Analysis, and Repair of Cooling-Water Lines in One Outage

In cooling-water lines of nuclear, coal-fired, and gas-fired power plants, large-diameter pipelines are used to convey water between the cooling towers and condenser heat exchangers. Several failures of cooling-water pipes raised the awareness of the risk of pipe failure and high costs of repair and loss of revenue from power generation. Inspection and repair of the distressed pipe pieces needs to be performed during planned outages. A power plant outage typically lasts between one and four weeks and occurs at three-or-more-year intervals. Since failure may result between inspection and repair time if a high risk pipe is left without repair, a program needs to be developed to inspect, assess the risk of failure, and repair of distressed pipes at high risk of failure during the same outage. This paper presents the results of a 108 in. diameter pipeline inspection, failure risk analysis, and repair of pipes during a two-week outage at the Tri-State power plant in Craig, Colorado. The cooling-water lines were inspected using electromagnetic inspection and on-site risk assessment of pipes with broken wires. Internal inspection and repair prioritization was performed at the beginning of the outage. CFRP and post-tensioning pipe repairs were designed prior to the outage, and a contractor was on standby so that the pipe pieces with the highest risk of failure could be repaired during the same outage. Four pipes were repaired using either internal CFRP lining or external post-tensioning within the scheduled time frame.