Qualitative Risk Assessment of Gas Pipelines by Using of Indexing System Method in GIS environment

Nowadays the urbanization is developing rapidly, and it leads to growing demand for gas; which resulted in denser pipeline network, by the following increase in the pipeline network congestion, accidents  will become inevitable. So Pipelines are a remarkable source of hazard for their adjacent society. Usually Indexing system method is used for pipe line risk assessment. This method assesses risk by using an index system, which includes a sum index and a leak impact index. Each index is made up of several sub factors which represent the major cause of failure in the network of gas pipelines. Using spatial analysis, changes in position, status and location of every factor in the vicinity of the pipeline can be checked and it helps to improve pipeline risk assessment. To increase accuracy of result, in this research, an indexing system method, is integrated with abilities of GIS. GIS can also be used as a calculating engine for produce risk scores. The developed model is implemented on a part with 52 km length of greatest Iranian hydrogen sulfide pipeline. The results show that the highest risk rating is 3 and the lowest number  is 42. 12 sections of pipeline have low or moderate relative risk due to low leak impact index and lower hazard after gas leakage in these sections. 42 sections of pipeline have  lower scores than 10 that show potential failure. In this regard, it is necessary to take measures to reduce risk. The implementation of this research in GIS, increase the accuracy of the risk calculation.