Uncertainty budget development and evaluation of temperature measurements in Algerian natural gas pipelines

Algeria has one of the largest natural gas transmission networks in Africa, transporting gas from the Hassi R'Mel field to domestic and European markets via pipelines. In this demanding industrial context, the accuracy of gas temperature measurements at compression and metering stations is of paramount importance to ensure operational efficiency, safety, and infrastructure integrity. It determines the calculation of the compressibility factor Z and thus the exact determination of the volumes of gas traded. This article presents a rigorous evaluation of temperature measurement uncertainty at the gas processing module (MPP-IV) of Hassi R'Mel, for two operating conditions (January and July 2022). The metrological approach adopted is based on the GUM guide (ISO/IEC 98-3), taking into account the thermodynamic specificities of Algerian natural gas and extreme Saharan climatic conditions. A complete measurement model of fourteen uncertainty sources is established for an instrumental configuration representative of Sonatrach stations, comprising a Class B PT100 probe mounted in a thermowell, a 4–20 mA transmitter, and a SCADA system, for two contrasting seasonal regimes. The results show that the tolerance of the Class B PT100 sensor is the dominant contribution in both seasons (68.4% in winter, 57.0% in summer), whereas solar radiation, whose effect is attenuated along the thermowell, contributes 0.3% and 2.5%. The calculated expanded uncertainties are ±0.8726°C in winter and ±0.9555°C in summer, exceeding the regulatory limit of ±0.5°C set by ISO 17089-1/AGA-7 by factors of ×1.75 and ×1.91 respectively. A graduated corrective strategy is proposed, prioritising the replacement of Class B PT100 sensors by Class AA sensors combined with three supporting measures, which reduces the expanded uncertainty to ±0.388°C in winter and ±0.456°C in summer, satisfying the regulatory threshold in both seasons.