21 - Rehabilitation-Risk Evaluation

Abstract

This chapter focuses on the various risk assessment methods used in pipelines industry. An informal approach to risk management can have the advantages of being simple, being easy to comprehend and to communicate, and being the product of expert engineering consensus built upon solid experience. However, an informal approach to risk management does not hold up well to close scrutiny, as the process is often poorly documented and not structured to ensure objectivity and consistency of decision-making. Successful risk assessment modeling involves a balance among various issues such as identifying an exhaustive list of contributing factors versus choosing the critical few to incorporate in a model; hard data and engineering judgment; uncertainty versus statistics; and flexibility versus situation-specific model. Three general categories of more formal pipeline risk assessment models can be found in use today. One of the simplest risk assessment approaches is the matrix decision analysis system, which ranks pipeline risks according to the likelihood and potential consequences of an event by a simple scale, such as high, medium, and low. The more rigorous and complex risk assessment is often called a Probabilistic Risk Assessment (PRA), in which initiating events are flowcharted forward to all possible concluding events, with probabilities being assigned to each branch along the way. The most popular pipeline risk assessment technique in current use is the "index model." In this approach, a relative weight is assigned to every important condition and activity on the pipeline, which includes both risk-reducing and risk-increasing items. This relative weight reflects the importance of the item in the risk assessment and is based upon statistics where available and upon engineering judgment where data are not available.