Williams Gas Pipeline has tasked the Operations Support group with improving pipeline system operation without capital expenditure. In order to measure how well the pipeline is operating from an efficiency standpoint as well as to monitor performance, a metric was developed to quantify how efficiently the various pipelines or pipeline segments are operated. Tracking the total fuel consumed is not an accurate measure of pipeline efficiency as the amount of fuel consumed will vary depending on the amount of compression utilized to transport varying amounts of gas. The Pipeline Efficiency Rating (PER) was created to provide a simple numeric value that represents the pipeline operational efficiency independent of the amount of gas transported. The PER was designed such that it should be comparable from one time period to another and present the answer to the question: "how efficiently has the pipeline been operating?"
The PER associated with Transcontinental Gas Pipeline (Transco) is currently limited to the section of Transco's pipeline between Station 85 and Station 200, and is applied to flow data from the previous two calendar years. The PER considers the impact of utilizing electric and steam-driven units, the cost of gas, the effect of linepack changes, and the effect of a varying inlet boundary pressure.
All meter location mileposts and daily flow data are collected, along with linepack information and the cost of gas for the next calendar year and the current cost of electricity. The inlet boundary point's historical pressure values are collected along with fuel consumed by compressors within the metric's boundaries. A third order curve fit is applied to a plot of fuel consumed versus volumetric work of the pipeline. The amount of volumetric work performed by the system is an input into the above equation to determine the amount of fuel consumed by the system. The PER is the inverse ratio of actual fuel used to the predicted amount of fuel from the historical operating data. If less fuel is actually used to perform the same of amount of volumetric work, then the PER is above 100% and the system is performing more efficiently than the historical norm. If more fuel is actually used than the predicted amount, then the PER is less than 100% and the system is performing less efficiently than the historical norm.
The historical data revealed that the PER hovered around 100%, as designed. Past performance was within ±10% of the historical baseline over 80% of the time, and within ±20% of the baseline over 97% of the time.
Operations Support has been tasked with improving the efficiency with which Williams operates its pipeline systems. In order to do this, a quantifiable means of measuring how efficiently the systems are presently operating must be developed. This paper will describe the various factors that went into developing this metric, some of the challenges faced and requirements considered, and the final equation and historical results.
