Integrity Management of Offshore Process Piping and Equipment with Sand Production – Part I: The Pinhole Incident

Abstract

Abstract Sand production is becoming a growing issue for oil and gas operators around the globe. Operators are faced to increase production of oil and gas, which may cause or worthen sand production, while insuring integrity management of process piping and equipment. As a result of higher than expected sand production in a specific field, a pinhole failure was observed on a 12″ Schedule 160 elbow downstream of a Multiphase flow meter (MPFM) that contained a venturi section that caused a localized increase in flow velocities. State-of-the-art Computational Fluid Dynamics (CFD) based erosion prediction procedure was utilized to determine the root cause of failure and help operators with integrity management of the associated piping systems and equipment. Data used for verification of erosion model included wall thickness losses and sand production data in a separator downstream. Additionally, CFD simulations of erosion rates in 12″ elbows were used for evaluating simplified erosion models that are being used to determine Integrity Operating Window (IOW) of piping that are currently installed downstream of the MPFM. The results in the paper include a comparison of wall thickness measurements and erosion rates of the piping downstream of the MPFM with predicted erosion rates. The CFD predicted erosion pattern and wall thickness losses downstream of the MPFM were comparable with the observed erosion rates. The geometry of MPFM and downstream section was too complicated to model with simplified mechanistic models, but the results of CFD and the mechanistic models were more conservative for isolated elbows downstream where wall thickness data were available with ultrasonic thickness (UT) measurements. The results indicate that simplified mechanistic model of Shirazi, et al. (1995, 2016) was sufficient to support developing sand erosion IOW prediction tool and determining condition monitoring locations, provided that a practical process for wall thickness measurements at critical locations is in place for verifying the outcomes and fine tuning the models on regular and as needed basis.