Figure 10: FLEXASSURE Ready for Field Usage
Wire Breakage Response Above Offshore Background Noise
For a real offshore situation a certain amount of background noise due to currents, waves, riser clashing and internal fluid flow will be present. As such, effects could not be simulated during the laboratory tests, and the background noise from an in-service riser was measured during the offshore test for comparison with the laboratory results. The wire break signals are compared against the background noise in Figure 9. The failure threshold level is represented as the red horizontal line, and for each sensor the ratio between the signal recorded during each wire break and the failure threshold level is given. Also plotted is the riser tension at the point each wire broke. Most of the wire break events are well above the failure threshold level based on background noise. The clearest signal is 81 times the failure threshold level. After 14 wires have been broken, the recorded responses increase significantly.
Summary – System Ready for Field Application
According to the laboratory and offshore tests, armour wire failure can be clearly detected by the collection of sensors used with the FLEXASSURE flexible riser monitoring system. As a considerable number of armour wires are expected to break before the riser actually fails, a catastrophic failure can be prevented. 2H Offshore considers that the integrity management of flexible risers is greatly improved with the FLEXASSURE system and that the data interpretation software is now ready for long-term offshore field usage. The FLEXASSURE system is the result of over 15 years of experience in monitoring risers using standard off-the-shelf products developed and deployed by 2H on numerous offshore developments (see Figure 10). In conclusion, the system provides essential data for the safe and reliable operation of flexible riser systems. n
1. Marinho MG, Santos JM, Carneval RO, Integrity Assessment and Repair Techniques of Flexible Risers, 25th International Conference on Offshore Mechanics and Artic Engineering, Hamburg, Germany, 2006, paper OMAE 2006-92467.
EXPLORATION & PRODUCTION – VOLUME 8 ISSUE 1
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