Pressure waves in pipelines develop any time there is a change in fluid velocity. If the change in velocity is large enough, the magnitude of a travelling pressure wave can exceed the Maximum Operating Pressure (MOP) of the piping. It is a violation of the Canadian and US regulations for petroleum pipelines (Canada – CSA Z662 4.18 and United States – ASME B31.4) to operate a pipeline at pressures in excess of 110% MOP even for short periods of time. In order to meet standards and regulations, transient analyses are undertaken to verify whether the pipeline MOP profile is susceptible to overpressures and to recommend solutions for such cases.
This paper presents the results of a working group on developing a standard for the suite of transient scenarios and methodology to be used for detailed transient hydraulic analysis. The work consisted of reviewing and analyzing historical transient studies and, abnormal operating conditions / overpressure events recorded by Control Centre; as well as, incorporating new learning from operational lines.
Methodology standardization focused on four areas: selection of inputs, model scope and criticality of pipeline sections, pipeline initial state, and worst-case upset scenarios. As a result, this paper describes the most prudent approach for each area or step of a pipeline transient analysis; including the evaluation of mitigation options if required. Finally, the use of this methodology is illustrated on a crude oil pipeline.