In refineries and processing plants, the enormous amount of piping is more complex in distribution than other types of equipment. In general, compared with other types of equipment in these industries, more difficulty in inspection planning is encountered. However, under-inspection or over-inspection can occur due to the lack of jurisdictional requirements on the inspection interval and method for piping, or the inspection interval being based only on piping service classifications in the existing regulations, such as API 570. This can result in unacceptable risks, along with costly loss of resources. To lessen the piping risk level, more and more companies have adopted and applied risk based inspection (RBI) methodology, leading to risk reduction and cost benefits since the last decade. This study applied RBI methodology to optimize the inspection strategy of the piping in a refinery and petrochemical plants in Taiwan. Two actual case studies were corroborated better with quantitative RBI methodology than without the methodology in terms of risk and cost reductions. (c) 2005 Elsevier Ltd. All rights reserved.