Link between unaccounted for gas in transmission networks and flow-meters accuracy

One of the main issues in natural gas transmission networks is represented by the so-called Unaccounted-for-Gas (UAG), that is the amount of gas related to the unavoidable measurement and estimation errors in the balancing equation of the network. In particular, accuracy of flow-rate measurement in transmission network pipelines is a very crucial issue due to the numerous related metrological criticalities. This paper is aimed at evaluating the influence of the flow-meter accuracy on UAG. To this aim, the rangeability limits of the flow-rate measuring device in delivery points characterized by large fluctuation of gas flows have been investigated, together with the effect of the drift of the instrument due to the absence of punctual periodic calibrations. From the analysis carried out, it was found that about 12% of the average daily flow rates measured at DSO measuring plants is below the minimum flow rate of the meter and that a significant correlation between monthly UAG and registered rangeability faults of flow-meters has been found.