ABSTRACT

Leak detection is critical to the safety of the environment and of increasing importance to those responsible and accountable for pipeline operations. The ability to detect and locate leaks in tight-line operation has been understood and advanced for quite some time. Slack-line leak detection, although acknowledged to be a more difficult task, is now more practical. Through the pipeline case studies presented herein, it will be demonstrated that it is quite practical to provide slack-line leak detection with reasonable thresholds and averaging times. The result is added leak detection protection for pipelines that must operate in slack or go through slack conditions during pipeline operation. As modeling performance improves and requirements become more stringent, the boundaries of what is possible and what is practical, regarding accuracy and resolution, are continually closing. This paper will explore the leak thresholds that are possible in slack conditions. To date, this area of leak detection has proven to be very difficult and, thus, ignored in most leak detection systems. Two pipelines, both located in the United States, are used as the basis upon which this analysis is performed. The first, ESMD, runs from East Sparta, Ohio to Midland, Pennsylvania and operates in slack line during start up and shut down. The second, BYST, runs from Byron, Wyoming to Silver Tip, Montana and operates in slack line throughout its steady state operation. The following topics will be addressed:

  • Topic A sensitivity study for the parameters that becomes important during slack line conditions. Additional parameters become important when a pipeline transitions into slack line operation. These parameters have a distinct impact on slack line leak detection performance, being more significant than their impact to tight line conditions.

  • Topic The determination of thresholds and associated averaging periods that are possible to achieve a balance between minimum thresholds and minimal false detections.

INTRODUCTION

Through empirical work, it has become apparent that the parameters that have been documented and accepted as forming the basis of tight-line leak detection are actually insufficient in leak detection operation in slack-line conditions. The analysis of two real-world case studies will clarify the additional parameters differentiating slack line leak detection. The following list attempts to identify these additional parameters and how they contribute to accurate slack-line leak detection.

Elevation Effects
  • Pressure Taps The elevation of the measurement of the pressure is important to leak detection in slack line conditions. The measured field pressure value is used to update the model pressure. The exact elevation of the pipe along with the pressure measurement is important because everyone (1) foot of error in elevation results in approximately 0.5 psi of error in pressure determination. In tight line leak detection this is not very critical because it results only in a small error in the pressure drop calculations, which can be easily compensated by tuning. However, in slack conditions, this elevation error directly affects two critical items: the determination of the onset of slack and

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