Since the mid-1990s, degradation mechanisms have been identified in feeder piping at CANDU stations. One of the major forms of degradation has been pipe wall thinning that is attributed to the phenomenon of Flow Accelerated Corrosion (FAC). More recently, highly localized wall thinning has been discovered in the vicinity of feeder pipe welds. The Canadian CANDU industry has managed FAC wall thinning by means of regular thickness measurements of susceptible locations, the assessment of thinning rates to predict the wall thickness changes between planned outages and accurate calculation of minimum acceptable thickness. To date, there have been no instances of pipe failures in Canada due to FAC wall thinning though several feeder pipes have been replaced when their predicted wall thicknesses fell below the pre-established minimum thickness criteria. From a regulatory perspective there is the concern that, in the absence of an adequate ageing management program, the ultimate failure mode of a locally thinned pipe would be a sudden rupture without adequate prior warning by leakage. This paper describes the experiences of the Canadian CANDU industry in the degradation of feeder piping and how it has been managed. The paper also briefly discusses Canadian regulatory expectations for industry management practices to ensure a safe operation of degraded feeder piping.

Speaker Biographical Information

Mr. Carroll is a Technical Specialist working in the Operational Engineering Assessment Division of the Canadian Nuclear Safety Commission. His responsibilities include reviewing licensee submissions related to inspection, assessment and repair of nuclear power plant pressure boundaries. Prior to joining the CNSC, Mr. Carroll held engineering positions with a NDE inspection company, a petroleum pipeline operator and an engineering consulting company. His worked focused on inspection and fitness-for-service assessments for structures and pressure retaining components.

Keywords :

CANDU Degradation, FAC, Feeder Piping, Flow Accelerated Corrosion, Regulatory