A Risk-Based Design Approach for Uncased Pipe Under Roads and Railways

Abstract

A risk-based pressure design approach has been developed for uncased pipe under roads and railways. Similar to the approach currently used in Canadian Standard Association’s Standard Z662, the approach uses a set of hoop stress factors to calculate the minimum wall thickness from the pipe’s pressure, diameter, and specified minimum yield strength. The hoop stress factors were calibrated to meet specified reliability targets considering the risk factors specific to roads and railways, which include elevated probabilities of mechanical damage due to higher construction activity rates, safety impact on road users, and potential costs of traffic interruption in case of a pipeline failure. The hoop stress factors are defined as a function of the safety class, which is determined according to the approach described in a companion IPC paper. This paper describes the development approach and provides a comparison between its results and the designs obtained from the current CSA Z662 approach. An analysis confirming adequacy of the resulting wall thicknesses to withstand normal traffic loads is also presented. The approach is being proposed as an alternative to the hoop stress factors currently used in CSA Z662.