ASTM D1945 Analysis of Natural Gas by Gas Chromatography

• Material type: Natural gases and similar gaseous mixtures.
• Purpose: Determining chemical composition for quality control, custody transfer, and process monitoring.
• Properties evaluated:  Concentration of hydrocarbon components (C1 through C6+) and non-hydrocarbon gases (N₂, CO₂, H₂S, He, O₂, H₂).
• Testing method:  Gas chromatographic separation and detection using appropriate columns and detectors.
• Result: Component concentrations reported in mole percent (% by mole) with recorded test conditions.
• Test limitations:  May be used for lean natural gases containing negligible amounts of hexanes and higher hydrocarbons, or for determination of one or more specific components as required.
• Use conditions: The method is of significance for providing data for calculating physical properties of the sample, or for monitoring the concentrations of one or more of the components in a mixture.
• Applications: Natural gas custody transfer, pipeline quality monitoring, LNG and CNG composition verification, gas processing plant operations, refinery gas analysis, utility and distribution companies, and research and development

What are the Uses of ASTM D1945 Testing?

ASTM D1945 testing provides a way for laboratories to evaluate the composition of natural gas samples. Engineers thereafter use the results to determine the purity of the gas, compute the fuel characteristics, and estimate the performance of the gas during processing. This standard-

• Determines the exact chemical composition of natural gas and similar gaseous mixtures.
• Ensures proper handling of custody transfers, streamlines pipelines, and maintains billing accuracy.
• Evaluates pipeline gas quality and pipeline safety requirements.
• Allows engineers to determine important gas properties like heat value, Wobbe index, relative density, and compressibility factor from the gas composition data.
• Helps engineers compare various types of gas sources and formulations.
• Supports Product Development and Quality Control during batch runs.
• Helps engineers select gas supplies for particular applications and end uses.

What Materials Can Be Tested Under ASTM D1945? 

It is a standard test method primarily for natural gases and other gaseous mixtures used in energy production and distribution. Typical substrates for ASTM D1945 testing include lean gas, rich gas, and gas mixtures from various sources. These gases provide key compositional data that is crucial for custody transfer, pipeline quality monitoring, LNG or CNG verification, and gas plant operations. 

Why is ASTM D1945 Important? 

Gas composition directly affects the heating value, combustion characteristics, and quality of natural gas that suppliers provide to consumers. This may cause processing equipment problems, including problems with fuel performance, pipeline integrity, custody transfer, or safety. Gas composition testing, as specified by ASTM D1945, enables manufacturers and operators to confirm that natural gas products meet end-use and regulatory requirements and to eliminate expensive operational problems before they enter the distribution system. 

ASTM D1945 Testing Process and Data Collection

The analyst selects representative gas samples and establishes the test parameters. After evaluating the specimens’ condition, the technicians insert the samples into the gas chromatograph. The operator maintains consistent temperature and flow parameters during the analysis. Finally, the analysts convert chromatographic peak data into composition values and compare the batch results with gas quality standards.  

Common Challenges and Troubleshooting

The sensitivity drift of detectors, contamination of the column and non-complete separation of gas components is a problem in testing. Sample handling and preparation protocols limit contamination and pressure variations, while troubleshooting – such as calibration, ensuring proper column conditions, and ensuring system leak integrity.

ASTM D1945 Analysis Results and Interpretation

The report summarizes the chemical makeup and computed characteristics of the natural gas samples.

• The analyst contrasts the measured values with the limitations that regulatory requirements and gas quality standards set.
• The lab records the particular test conditions and reports the gas’s composition in conventional SI units (mole percent).
• The analyst notes retention times, peak regions, detector response, chromatographic problems, and temperature sensitivity.
• The laboratory uses the gas’s determined composition to determine processing implications such as density, heating value, and combustion characteristics.
• Instead of giving the material a single overall performance value, the report describes observed differences and evaluates several gas batches against specification limits.

Link to ASTM D1945