The rupture of a natural gas pipeline may result in a major fire or explosion if the gas release is not quickly mitigated. When such a rupture occurs, negative pressure waves created in the fluid exhibit changing rates of pressure drop (ROPD) and low pressure. Both characteristics of the rupture are widely used as rupture signals (or parameters) to trigger automatic shutdown valve (ASV) closures when compared with preset threshold values. Although ruptures create unique wave patterns, it is still a challenge to detect them reliably and without false alarms due to various reasons. One challenge is wave attenuations, resulting in narrow detectable ranges. Another challenge is the existence of operational noises such as compressor shutdown and flow changes that cause an increase in the threshold values and interfere with detection. Lastly, the effects of initial operational conditions, pipeline configurations, and system controls also impact the ability to easily detect the unique pressure waves created by a rupture. Hence, rupture detection is site specific, and these influences must be understood for each individual system.
In this study, modeling is used to determine the preset threshold values from transient operations of a natural gas transmission line and to evaluate both maximum ROPD and minimum pressure values from ruptures along various locations in the pipeline. In addition, effects of rupture location on both maximum ROPD and minimum pressure values are assessed. Furthermore, a parametric study is performed to investigate the effects of initial operational scenarios on rupture detection at each specified rupture location.
Modelling results from both signals and noises, plotted in distance charts, are compared to assess the threshold setpoints (noises) and to identify the detectable ranges for both the ROPD method and low-pressure method. Using the transient modeling approach, this study aims to assess the applicability of each method, determine the rupture detectability, derive the detectable ranges, optimally place ASVs, and ensure compliance with federal regulations. The proposed approach is applicable to all natural gas pipelines even though the analysis results are site specific. Using a combination of ROPD and low-pressure signals, can increase the reliability and efficiency of rupture detection.
