Research for pipe wall thinning management improvement. Part 4. Discussion on implementation of local thinning criteria and leakage risk assessment for pipe wall thinning management

As one of the major activities of the JSME research committee for the improvement of pipe wall thinning management, latest knowledge concerning pipe wall thinning phenomena and state of the inspection technologies of wall thickness have been surveyed and reviewed. Although a complete management of pipe wall wastage consists of prediction, inspection, and evaluation, survey of the evaluation part has been running late compared to the prediction and inspection parts. On the other hand, many overseas countries adopt local thinning criteria that calculate minimum thickness according to the thinning area because pipe wall thinning phenomena caused by flow accelerated corrosion (FAC) and liquid drop impingement (LDI) decrease pipe wall thickness locally. Additionally, 'Risk-Informed In-service Inspection (RI-ISI)' has been introduced and developed by the Electric Power Research Institute (EPRI), etc. in the USA. This paper focuses on the study of domestic and overseas codes that adopt local thinning criteria, the examples of local thinning analysis applying these codes and the risk assessment procedure which was developed by EPRI. In EPRI's RI-ISI procedure, leakage risk due to pipe failure is evaluated by consequence categories and pipe failure potential. Finally, future issues are discussed in order to adopt local thinning criteria and risk management in Japan. (author)