A Population Density Based Location Category System for Onshore Natural Gas Pipelines

The location class system used in current North American pipeline standards (ASME B31.8 and CSA Z662) is based on structure count included in a specified assessment area. Because the number of people occupying different structures can vary significantly, the population density can also vary significantly for the same location class. Given that the risk (in terms of human safety) imposed by onshore natural gas pipelines is directly proportional to the population density, the current location class system leads to a large variation in the risk level for pipelines with the same class. To achieve more risk consistent designs, a new location category system is proposed in this paper using actual population density data collected from over 19,000 km of gas pipelines in North America. The boundaries between different categories in the proposed system are directly based on population density rather than structure count. One of the key features of the new system is that it uses a separate category for pipelines in unpopulated areas, which are a significant majority of the pipelines included in the study. The implications of the new system are discussed by comparing the lengths of pipelines falling into each category with the lengths of pipelines falling into each location class for all the pipeline data analyzed.