SNV SN EN ISO 18453:2004 Natural gas - Correlation between water content and water dew point

ISO/TC 193, Natural gas, was established in May 1989, with the task of creating new standards, and updating existing standards relevant to natural gas. This includes gas analysis, direct measurement of properties, quality designation and traceability.
This document provides a reliable mathematical relationship between water content and water dew point in natural gas. The calculation method was developed by GERG; it is applicable in both ways, i.e. either to calculate the water content or to calculate the water dew point. Information relating to the thermodynamic principles is given in Annex A; information relating to the traceability, applications and uncertainties associated with this work is given in Annex B.
Some of the operational problems in the natural gas industry can be traced back to water content in natural gases. Even with low water vapour content in the gas, changing operating pressure and temperature conditions can cause water to condense and thus lead to corrosion problems, hydrates or ice formation. To avoid these problems, expensive dehydration units have been installed by natural gas companies. The design and cost of these installations depend on the exact knowledge of the water content at the dew point and the (contractually) required water content.
The instruments resulting from the improvements of moisture measurement equipment during the last decades focus on the determination of water content rather than on water dew point. Therefore, if the water content is measured, a correlation is needed for the expression of water dew point.
The GERG1) Group identified a need to build a comprehensive and accurate database of measured water content and corresponding water dew point values for a number of representative natural gases in the range of interest before validating the existing correlations between water content and water dew point.
It was subsequently shown that the uncertainty range of the existing correlations could be improved.
Therefore, as a result, a more accurate, composition-dependent correlation was successfully developed on the basis of the new database.
The aim of this International Standard is to standardize the calculation procedure developed by GERG concerning the relationship between water content and water dew point (and vice versa) in the field of natural gas typically for custody transfer.