Tension Leg Platform (TLP) tendons typically are installed for the life of the platform and incorporate elastomeric flex bearings. The Allegheny TLP, owned and operated by ENI Petroleum, was installed in Gulf of Mexico Green Canyon Block 254A, in 1999. It was designed for a service life of 20 years and currently ENI wants to extend the operating life of the platform. A baseline inspection showed significant degradation of the top tendon connector (TTC) flex bearing and it was concluded that the flex bearings needed to be replaced if the platform was to continue to operate safely.
SBM and BHGE came up with a solution for replacing the TTC including the flex bearing, which was accepted by ENI. This involved ballasting the TLP to reduce the tendon pretensions, installing a temporary buoyancy module, and using a hydraulic tool, first of its kind in the world, to take the load off of the old TTC and gradually release the tendon to free stand. The tool was then retrieved with the old TTC, onboard the installation vessel. A second identical tool with the new TTC was then lowered on to the porch and the tendon stretched to the lock-off position by the tool and locked in position with the new TTC. This was done on all six (6) tendons and the platform was de-ballasted to the original tendon pre-tensions. Development of the tendon de-tensioning tool required new designs, extensive shop testing, and planning.
The final offshore campaign took place during July 2018 and was completed in three (3) weeks. This represented a successful conclusion to a three (3) year effort. This paper highlights lessons learned in completing a complex first time ever project and makes recommendations for the design of future TLP’s.