It is not uncommon for pipelines that transport clean, dry, natural gas to also carry some level of compressor oil, glycols, black powder, and other potential contaminants. The presence of these contaminants at a metering station can affect the measurement accuracy of any of the commonly-used metering technologies, including orifice meters, turbine meters, and ultrasonic meters. Maintenance of a meter station can involve periodically taking a meter run out of service for inspection and cleaning. However, with a better understanding of the impact of meter station cleanliness on measurement accuracy and information about the meter station condition that doesn’t require physical inspection, maintenance decisions can be improved.
Ultrasonic meters are known to be affected by the buildup of material inside the meter and surrounding pipe due to common pipeline contaminants. For this study, commercially-available multipath ultrasonic flow meters were installed downstream of piping that contained various levels of simulated dirt buildup with measured surface characteristics.
The project demonstrated the ability of multipath ultrasonic meters to detect changes in the condition of the upstream pipe caused by accumulated material. Identifying the severity of error in dirty meter runs allows facility operators to perform cost-benefit analyses that weigh the costs of pigging and cleaning meter runs against the potential impact of custody transfer errors and increased lost-and unaccounted-for gas totals.