PD ISO/TR 12148:2009

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols
5 Performance characteristics of automatic weighing
  method in accordance with ISO 6570:2001
  5.1 Working principle
  5.2 Functional requirements
  5.3 Measurement uncertainty
6 Performance requirements for a chilled-mirror-type
  instrument for hydrocarbon-dew-point determination
  6.1 Working principle
  6.2 Precision
7 Requirements/Points of interest to carry out a calibration
  7.1 Process gas
  7.2 Sampling system
  7.3 Selection of the PHLC reference value
  7.4 Compositional range of gases covered by the calibration
      procedure
  7.5 Calibration interval
8 Execution of calibration procedure
  8.1 General
  8.2 Method A - Change in trip point value
  8.3 Method B - Direct change of dew point value
  8.4 Which method should be used?
Annex A (informative) - Condensation behaviour of natural
        gas
Annex B (informative) - Example of a hydrocarbon-dew-point
        analysis
Annex C (informative) - Examples of a calibration
Annex D (informative) - Performance of different types of
        chilled-mirror instruments for hydrocarbon dew
        point determination
Bibliography

Specifies 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.

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 ISO6570:2001 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 ISO6570:2001 is also applicable.

NOTE1 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.

NOTE2 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 AnnexA.

NOTE3 Unless otherwise specified, gas volumes are in cubic metres at 273,15K and 101,325kPa.