Integrity Assessment and Repair Techniques of Flexible Risers

Abstract

Deep water oil and gas exploitation in Brazil remarkably increased the utilization of flexible pipes in conjunction with floating production systems. In Campos Basin nowadays oil and gas transfer, water and gas injection and well control and monitoring are carried out almost entirely by flexible pipes, including risers, flowlines and umbilicals. Periodic inspections have detected a considerable incidence of damage in the top section of risers, which may affect their structural integrity and eventually induce different failure mechanisms. These include mostly external sheath damage, corrosion and/or fatigue-induced damage to the tensile armours and torsional instability. These damages are generally originated during installation or, more frequently, during operation due to contact with another riser or the platform structure. In order to mitigate the progression of these damages, besides periodic inspections, repair techniques were developed for both emerged and submerged riser sections. Apart from the inspection program, surface monitoring procedures, such as nitrogen injection, pressure monitoring and flow measurements in the annular space are being implemented, for a continuous flexible riser integrity assessment. This paper describes and evaluates these techniques, as well as reports the results obtained from field experience.