Measurement of Natural Gas Emission Rates from Belowground Pipelines

Emissions from natural gas pipeline systems result mainly from fugitive methane (CH4) leaks of the aged pipelines in the infrastructure. The growing concern over climate change and the need to reduce greenhouse gas emissions has prompted gas companies and federal organizations to recognize the need for accurate methodologies of gas emission estimation. The U.S. Environmental Protection Agency's annual inventory estimates of the methane emissions from underground gas pipes are based on early tests from 1992 to 1994 performed by excavating and isolating a known number of underground leaks and measuring the flow rates in the isolated leaking pipes. This paper presents a new methodology for measuring gas emission from underground pipeline leaks to provide updated estimates with increased accuracy. The new approach consists of capturing the gas emissions at the soil surface, rather than excavating and isolating the leaking pipe. The leak rate is measured at the surface using a Hi-Flow Sampler device. This approach allows one to perform a significantly larger number of tests without the need to excavate the soil, interrupt the service, and cut and isolate the pipe sections for leak measurements. Field measurements in controlled test sections and at gas utility sites in various cities were performed using both the old method of excavating and isolating the pipe and the new approach of surface measurements. The tests were performed in sites with various leak sizes, pipe material, operating pressures, and soil types. The results from both methodologies correlated and demonstrated the applicability of using the Hi-Flow Sampler to measure pipeline gas emissions.