ASTM D8488-22

SIGNIFICANCE AND USE 5.1 H2S measurements in natural gas are performed to ensure concentrations satisfy gas purchase contract criteria and to prevent pipeline and associated component corrosion. 5.2 Using TDLAS for the measurement of H2S in natural gas enables a high degree of selectivity with minimal interference from common constituents in natural gas streams. The TDLAS analyzer can detect changes in concentration with a relatively rapid response compared to other methods so that operators may take swift action when designated H2S concentrations are exceeded. 5.3 Primary applications covered in this test method are listed in 5.3.1 and 5.3.2. Each application may have differing requirements and methods for gas sampling. Additionally, different natural gas applications may require unique spectroscopic considerations. 5.3.1 Raw natural gas is found in production, gathering sites, and inlets to gas-processing plants characterized by potentially high levels of water (H2O), carbon dioxide (CO2), H2S, and heavy hydrocarbons. Gas-conditioning plants and skids are normally used to remove H2O, CO2, H2S, and other contaminants. 5.3.2 High-quality “sales gas” is found in transportation pipelines, natural gas distribution (utilities), and natural gas power plant inlets. The gas is characterized by a very high percentage of methane (90 to 100 %) with small quantities of other hydrocarbons and trace levels of contaminants. SCOPE 1.1 This test method is for the online determination of hydrogen sulfide (H2S) in natural gas using tunable diode laser absorption spectroscopy (TDLAS) analyzers also known as a “TDL analyzers.” The particular wavelength for H2S measurement varies by manufacturer, typically between 1000 and 10 000 nm with an individual laser having a tunable range of less than 10 nm. The H2S concentration ranges can be anywhere from 0-5 ppm(v) to 0-90 % by volume. 1.2 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard. TDLAS analyzers inherently output concentrations in unitless molar ratios such as ppm(v). Note 1: Weight-per-volume units such as milligrams or grains of H2S per cubic foot or cubic meter can be derived from ppm(v) at “standard conditions” or standard temperature and pressure. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.