scope:

This Technical Report describes the principles of, and general requirements for, the traceable calibration of automatic hydrocarbon-dew-point chilled-mirror instruments using the indirect automatic weighing method (method B) described in ISO 6570:2001 to determine the potential hydrocarbon liquid content of natural gas, or similar gas. The calibration procedure is intended for use by chilled-mirror instruments in downstream applications transferring processed natural gas.

If the gas composition is constant, the manual weighing method (method A) described in ISO 6570:2001 is also applicable.

NOTE 1 Whether or not a gas composition is constant is difficult to establish. A process gas chromatograph (GC) measuring calorific values within 0,1 % is absolutely no guarantee for a constant hydrocarbon liquid drop-out content. Information up to C₁₂ is required to verify that the gas composition is constant.

NOTE 2 The application of this calibration procedure in the upstream area is not excluded a priori, however, currently there is no experience using this procedure in an upstream environment. The usability of data on the potential hydrocarbon liquid content of natural gas for verification, adjustment or calibration of hydrocarbon-dew-point chilled-mirror instruments is based on the condensation behaviour of natural gases. Information on the condensation behaviour of natural gases and the various measuring techniques to determine properties, like hydrocarbon dew point and potential hydrocarbon liquid content, related to the condensation behaviour of natural gases are given in Annex A.

NOTE 3 Unless otherwise specified, gas volumes are in cubic metres at 273,15 K and 101,325 kPa.