Ten Years in the Water: Observation and Detailed Evaluation of a Riser after Extensive Service Life

Abstract

Life extension of existing assets is an important aspect of offshore oil and natural gas operations in the Gulf of Mexico. As part of an effort to evaluate existing riser systems, Anadarko launched an inspection and testing program to investigate risers retrieved following well abandonment after a service life of nearly 10 years in the water. To assess the pipe and connections, 12-3/4′ T95, Anadarko and Vallourec performed visual inspection of the full pipe body length (internal and external), ultrasonic inspection, and wet magnetic particle inspection. The original testing was repeated on the post service pipe and connection. For both sealability and fatigue testing one side of the connection was left in the "in service" condition, while the other side was broken out and made-up again. Sealability testing followed the ISO13679/API 5C5 CALIII protocol. Fatigue testing repeated the original stress level, and was cycled to failure. The pipe and connection performed very well under the post service testing and evaluation. Overall corrosion and defects in the pipe were very low, and within service parameters. The connection evaluation also showed very good results. The most important evaluation/observation was of the internal and external seal. The field broken connections had signs of galling and rust. However, further evaluation of the damage, as well as review of the connections not broken out during riser pulling, pointed towards handling damage during pulling operations. Review of photographs taken during pulling operations showed no signs of degradation from the environment or galling. Further inspection of connections that were broken out at the testing facility indicated no damage to the connections. The fatigue testing results were also positive, indicating significant remaining life, had the riser been left in service. This represented a rare opportunity to evaluate the state of the threaded and coupled risers after such a long service life, along with assessing the remaining longevity of the riser system. It was a chance to observe and measure the effects of actual service life as opposed to calculated service conditions on the pipe and connections. The findings provided valuable insights into the future usability of similar riser systems.