Slip Nut Top Tendon Connection
Authors: Pallini J.W. , Wald G. , Bozeman J.D. 
Published: October 2008

This paper summarizes the design, analysis, testing, and field installation of a threaded slip-type top tendon connection for a tension leg platform (TLP) which combines both conventional thread and slip technology. The connector can be latched and unlatched at any location along a mating threaded shaft, simply by applying hydraulic pressure and flow to an actuation tool that mates to the connector.

INTRODUCTION

ATLP is typically moored by tendons arranged in multiple groups at the platform corners. Each tendon is attached to the foundation template on the ocean floor and to the platform at the surface by mechanical connectors. These connectors must have strength and durability for long term service, and provide for ease of installation. Additionally, the top connection must have a means of precisely adjusting the distance between the TLP platform and the ocean floor template. Because of the problems in determining the exact tendon length and water depth, and the need to provide final trim adjustment during installation, the top connector could require as much as 10ft. of length adjustment.

Previous TLP tendon systems top connectors used a conventional threaded nut which terminated above the waterline inside the platform columns. This type of connection is directly accessible from the TLP platform for installation and maintenance. However, the Conoco Jolliet TLWP terminates the tendons below the waterline on the outside of the hull column. This configuration is not directly accessible and requires remote installation of the top connector. Due to the difficulty in remotely starting a large diameter threaded nut, the high torque requirements to rotate a large diameter nut down a threaded shaft, and the potential of damaging threads during installation, an improved top connector was designed.

Combining both conventional slip and thread technology, a threaded nut is segmented into slip segments which are retained within a housing or bowl. The slips are engaged and disengaged onto the threaded shaft by a hydraulically-operated actuation tool which interfaces with a drive mechanism on the connector. The top connector is installed by setting the slips in the retracted position and axially lowering the connector over the tendon shaft, until the connector lands into a mating receptacle. The actuation tool is then operated and the slip segments are engaged onto the threaded shaft. As the slips are driven inward towards the threaded shaft, the slip segments rotate to correctly 'time' thethreads between the slip segments and shaft. Once the thread leads are matched, the connector self-locks in the engaged position and assumes the characteristics of a conventional threaded nut.

DESCRIPTION

Connector Design

The slip nut connector, shown in Figures 1 and 2, has two sets of components. The first set supports the tendon loads and includes the slip segments, housing, elastomeric flex element, and back flange. The remaining components are not loaded by tendon tension and function only to actuate the slip segments and provide attachment points for the actuation tool and corrosion cap. The slip nut connector engages onto a threaded length adjustment joint (LAJ) which is welded to the tendon top section.