Overview

Background

The probability of pipeline failure is assessed, in this model, via an evaluation of four failure mechanisms. In three of those third party, corrosion, and incorrect operations the assessment focuses on the probability that the failure mechanism is active. The potential presence of the failure mechanism is assumed to directly correlate with failure potential under the assumption that all failure mechanisms can eventually precipitate a failure, even in very strong pipelines. In the fourth the design index the assessment looks not only at the potential for an active failure mechanism, but also at the ability of the pipeline to withstand failure mechanisms. This resistance to failure ( safety factor and integrity verifications variables) will play a role in absolute risk calculations when a time-to-fail consideration is required.

A significant element in the risk picture is the relationship between how a pipeline was originally designed and how it is presently being operated its safety margin. Although this may seem straightforward, it is actually quite a complex relationship. All original designs are based on calculations that must, for practical reasons, incorporate assumptions. These assumptions deal with the variable material strengths and anticipated stresses...