Risk Assessment of Gray Cast Iron Pipelines

Abstract

Tokyo Gas has been supplying gas to 9 million customers in the Tokyo metropolitan area in Japan since 1885, using 45,000 km of distribution pipelines. One of the old materials for the low pressure distribution pipelines is gray cast iron (GCI) pipe, which was used for construction until the 1970s, often break and cause gas leakage due to the lack of ductility; therefore, these GCI pipelines have a potential risk. To reduce the risk induced by breaks in GCI pipes and improve the safety level, Tokyo Gas (TG) has been conducting a program to repair or replace the aged-GCI pipes with liners or polyethylene pipes. In urban areas, however, measures such as repair or replacement are highly time- and cost-consuming, which is against the trend in the gas industry. Therefore, in order to reduce the risk induced by breaks in GCI pipes with minimum cost, TG has been developing a method for assessing the risk of GCI pipes. Presented in this paper is a revised method to assess the risk of GCI pipes by accurately evaluating the likelihood of breaks and the consequences induced by the gas leakage with detailed information on the environment where the pipe is buried.