Condition Monitoring of Subsea Pipe Components in a Future Subsea Production Facility

Abstract

Traditionally, subsea systems have been designed to achieve a lifetime of 20 to 30 years without the need for maintenance. Still, experience has shown that failures may occur, leading to expensive interventions requiring partial or full production shutdown. This thesis evaluates which condition data that is necessary to collect when monitoring the condition of pipe components and pipe joints found in Statoil’s future subsea production facility. An evaluation of commercial technologies used for such collection has been done. The pipe components are defined as bends, injection points, flow reducers and headers, while the pipe joints are assumed to be non-welded. The necessary condition data was found to be pipe wall thickness, pipe diameter and crack propagation. An evaluation if the data collection is able to provide a sufficient description of the pipe components and joints current condition is further on reviewed. Finally, to which extent there will be compliance between the measured condition and the current state of the components and joints have been evaluated. Three commercial technologies have been evaluated after recommendations from Statoil. These are ClampOn’s Corrosion Erosion Monitor and Sensorlink’s Ultramonit for material loss, and Mistras Physical Acoustic’s monitoring system for crack propagation. The monitoring equipment manufactured by ClampOn and Sensorlink utilize ultrasonic technology. Both are designed for monitoring new and existing subsea pipelines, but have at present limited experience. Sensorlink’s Ultramonit is applicable for all the defined subsea components, and is stated to have an accuracy in the range of ±0,1 mm and ±0,2 mm when used subsea. ClampOn’s Corrosion Erosion Monitor can be used on pipe bends and flow reducers, and is considered to provide a sufficient description of the monitored components in general. However, no scientific research was found available on its accuracy when used subsea. Mistras Physical Acoustic’s monitoring system utilizes acoustic emission and can be placed on all of the defined pipe components. A sufficient description of the components’ state cannot be achieved with their monitoring system as it is not possible to obtain information of the size or geometry of the crack. Any scientific research of the compliance between the measured condition and the current state of the monitored pipe components was not found to be available.