Drift Estimation in Offshore Process Measurand

摘要

The importance of effective measurement of process measurands in offshore oil and gas processing facilities cannot be over emphasized. Due to environmental influences, aging, vibration, wear and tear, etc over-time, these measurement systems experience drifts, giving misleading information about the process variables. In this study it was desired to evaluate the drift in 3 pressure Gauges at an offshore platform. Periodic inspections were performed on the Gauges over a 6-month period. Results showed zero and minor drifts in the measurands after 1-month and 3-monthsusage, respectively. However, after 6-months usage, significant drifts were recorded, corroborating the rule-of-thumb for pressure measurands. The drift models were linear with R~(2)= 1.0 for measurand less than 6 months of instrument usage, and R~(2)< 1.0 for usage periods ≥ 6 months. Recalibration results showed instability for input pressures ≥50% gauge range, and hence faster convergance for input pressures ≤ 50% of gauge range. Validation results showed variance and standard deviation 3685Psi (25.407MPa) and 60.7Psi (0.418MPa) , respectively for Gauge 3 at 4000 Psi (27.579MPa) input pressure. To restore the Gauges, recalibrations by error convergence and validations by replications were performed.