# Measurement Uncertainty and Compliance Evaluation Applied to Natural Gas Moisture
###### Abstract  
The reliability of natural gas moisture measurements is crucial in preventing corrosion in pipelines and equipment, ensuring burning efficiency and mitigating operational risks, and is often mandated by standards and regulations. An important quality parameter that aids in conformity assessment, particularly in risk assessment, is measurement uncertainty. The assessment of measurement uncertainty, based on the Law of Uncertainty Propagation, depends on the mathematical model used to calculate this physicochemical property. This study aimed to compare different algorithms for calculating moisture content in natural gas, estimate and validate the measurement uncertainty based on the algorithms implemented in the Portable Moisture Analyzer (PM880) equipment, a portable hygrometer manufactured by Panametrics in Wilmington, NC, USA, and evaluate compliance with Brazilian legislation using guard bands as a decision rule. The moisture results in natural gas varied by a maximum of 1% among the three approaches presented. Furthermore, based on the dew point and pressure results, the expanded uncertainties of moisture were about 20%, which did not compromise the risk assessment for the consumer, as the moisture results were well below the specification value. Consequently, the upper tolerance limit of 58.4 ppmv H2O was established. consumer's risk; Portable Moisture Analyzer; PM880; ppmv H2O; dew point; specification limit; acceptance limit 2020 IEEE/RSJ International Conference on Intelligent Systems (IEEE), Vol., No., No. D1142 [2] and ISO 18453 [3], the design and cost of these installations are influenced by the need for accurate knowledge of the water content at the dew point and the contractually required water content, as natural gas pipelines have specifications that limit the maximum permissible water vapor concentration. For instance, a standard pipeline specification in the Petrobras offshore production system is a maximum moisture content of 60 ppmv. The water dew point in gas refers to the temperature, at a specified pressure, at which liquid water will begin to condense from the water vapor present. Consequently, water concentration levels can be measured based on natural gas systems' dew point and pressure. As stated in ISO 6327, \"the partial pressure of water vapor in gas samples is the saturated vapor pressure corresponding to the observed dew point, provided that the gas in the hygrometer is at the same pressure as the gas at the time of sampling\" [4]. Therefore, to conduct moisture measurements in gas, it is essential to establish a correlation between the water dew point and the water content. [PERSON] and [PERSON] improved gas quality management, proposing a procedural framework for accurately determining the moisture of natural gas using dew point temperature indicators found in fuel certificates [5]. Studies conducted on hygrometers, generally, have shown to be an area of interest by researchers. One classic study evaluated the uncertainty in measuring the dew point of natural gas using the traditional cooling mirror condensation hygrometers [6]; another one compared various hygrometers used for measuring moisture in gases that are utilized with varying frequency in the natural gas industry [7]; the last study centers around hygrometers being used for measuring water vapor (moisture) in natural gas, focusing on their response to co-exposure to ethylene glycol [8]. [PERSON] et al. [9] compared eleven hygrometers at natural gas facilities in Spain utilizing various measurement techniques (including chilled-mirror, electrolytic sensors, spectroscopic analyzers, and polymeric and metal oxide humidity sensors). Chinese researchers have developed an optimized Gaussian process model that effectively evaluates parameters to predict the water dew point in natural gas dehydration units, enhancing the efficiency and accuracy of the dehydration process [10].