Flexible riser systems are widely adopted by the industry as solutions to interconnect subsea equipment and pipelines to floating production units. Their unique ability to withstand motion and their ease of installation make flexible riser systems a favorable solution when compared to conventional rigid riser systems.
Historically, the integrity of flexible risers has been an issue and it is therefore critical that risers are designed and qualified according to the current continually challenging operating conditions. Flexible riser integrity management and complex riser qualification processes have consequently become the main focus for major operators in guaranteeing the safety of offshore operations to reduce the risk of human, environmental and material losses.
The industry has requested several qualification tests to verify the manufacture of the new flexible risers, e.g. a dynamic fatigue test, which is required to qualify the flexible pipe for deepwater installation.
A means of monitoring the flexible riser response is also required in order to record the integrity of the riser and assist operators in identifying and implementing suitable remedial action, ranging from inspection plans through to riser replacement, as necessary. Based on these requirements, Pulse Structural Monitoring developed an armour wire failure monitoring system and, after extensive testing including offshore tests, validated the system through a full-scale dynamic test cycled to damage 1.0 (safety factor 10), performed by Wellstream. This test continued for more than one year and validated the monitoring system that was able to detect 100% of the wire breaks.
This paper presents the results and conclusions from the blind test conducted to qualify the monitoring system. The results demonstrate that the monitoring system was able to detect the wire breaks caused during the full-scale dynamic test and would be a suitable solution to employ on flexible risers to detect failures in the field.
Flexible risers are responsible for oil and gas transportation of approximately 80% of Brazilian offshore production and are mainly used in highly dynamic loaded environments, where outstanding fatigue performance is essential. Flexibles are commonly used in today's harsh ultra deepwater developments and play an outstanding role in deepwater offshore operations worldwide. Given that the depths are increasing where flexibles operate, environmental conditions are becoming ever more challenging, and the engineering challenges in designing and manufacturing risers are also increasing. There are more than 1,200 flexible risers currently in use offshore Brazil whilst over 1,000 flexible risers are operational in the North Sea.
A complex engineering process takes place for the design and fabrication of flexible risers, based on presumptions about environmental loading conditions and the specific requirements of the application over its lifetime. As production expands into increasingly deeper water depths, more advanced riser designs and qualifications are required from offshore operators.