Recently, corrosion of piping of petrochemical plants has been a problem. Apparatuses which degenerate comparatively fast are inspected periodically, while piping lias been overlooked since the corrosion rate is very slow. However, there is a danger that the corrosion of the piping causes leakage of internal fluid because the piping has been used for a long time. Inspection of piping needs enormous works like removal of heat insulation material around the piping. There are some problems to carry out the inspection such as cost, time and danger for workers. This research supports decision-making on selection of inspection parts in order to reduce these problems. Although the inspection parts exist innumerably in large scale plants, this system can presume the parts required inspection and improve the hitting ratio of the inspection parts. The performance of proposed system which uses graph theory to decide the partial order relation of each of inspection parts is successfully demonstrated by using an actual case database.