Offshore Pipeline Case-Study: State-Of-The-Art Comparison Between Different ILI Technologies for Challenging Metal Loss Diagnosis and Remaining Lifetime Assessment

Abstract This paper describes the history of an offshore pipeline that failed from an internal corrosion defect that was not detected by the MFL-A technology. After the failure, the pipeline was inspected with different technologies such as MFL-A, MFL-C, IEC, and Ultrasonic Wall Thickness Measurement. The authors discuss different detection capabilities, inspection variables, data analysis process, inspection results, and integrity management. Internal corrosion is one of the main failure mechanisms of rigid pipelines. Accordantly to the U.S. Department of Transportation [3], between 1998 and 2017 approximately 12% of pipeline incidents were caused by internal corrosion. To detect, measure and evaluate the corrosion anomalies, the ILI technologies are the most accurate approach to define the maximum operating pressure and manage their integrity [13]. The industry offers different types of technologies, such as Ultrasonic Wall Thickness Measurement, Axial and Circumferential Magnetic Flux Leakage, and Internal Eddy Current. Corrosion defects offer different levels of complexity for detection and sizing depending on the nature of the corrosion phenomenon and its morphology. All technologies have advantages and limitations; therefore, it is important for operators to identify the priorities to select the most appropriate technology based on needs. The decision of which technology or combination of technologies should be used is the main task and responsibility of the Integrity Manager, and involves technical, commercial, and operational factors. The paper proves that some ILI technologies are not able to correctly identify and measure specific nature and geometry of corrosion anomalies. It intends to create a guideline for operators to correctly choose the ILI technology and be able to properly manage the integrity of rigid pipelines, defining its maximum operating pressure and evaluating the necessity for repair. The authors intend to share with the industry the technical particularities in the data comparison from the last two inspections carried out to pipeline with Ultrasonic Wall Thickness Measurement, with special focus on challenging anomalies due to its location, geometry, and size. This Offshore pipeline case is turned public to share the knowledge gathered through many inspections and engineering analysis conducted during life extension assessment of the pipeline.