Titanium Stress Joint for a TLP Tendon System

Abstract

This study presents the technical feasibility of replacing a connector and flex-joint with a titanium stress joint and a collet connector as components of a tendon system for a Tension Leg Platform (TLP). A detailed analysis of this new tendon system is presented for 2,000 feet of water depth in the Gulf of Mexico. The main conclusion of this study is that this new approach is feasible and replaces effectively the flex-joint used in previous TLP tendon designs. The new system has no moving parts, long fatigue life and works even better for the deep water cases. INTRODUCTION Figure 1 shows the general layout of a TLP platform with a tendon system anchored to the foundation template. The purpose of this study is to demonstrate the technical feasibility of replacing the connnector and flex-joint used in conventional TIP tendon design, with a titanium stressjoint and collet connector tha thas a stinger. The titanium stress joint provides the required flexibility for the maximum angular offset at both ends of the tendon. The collet connector provides the latching capabilities of the tendon to the receptacle of the foundation template. A stress joint connection at the bottom or top receptacles induce high bending moments at both ends of the tendon due to the lateral motion of the TLP. The stinger increases significantly the strength of the connector to resist high bending moments. The new tendon system uses the stinger approach at both ends of the tendon. Hutton and Jolliet, the only two TLP platforms installed as of 1992, use a flex-joint at both ends of the tendon system. Hutton TIP uses at the bottom a Vicker's connector design with a collet locking system that engages the male stinger into the female receptacle located on the ocean floor. The Murdock flex-joint is built into the anchor housing. The fabrications of these joints use alternate layers of elastomer and partial spheres of stainless steel reinforcements to provide the required axial and angular spring area to accommodate a maximum angular offset of 16.6 degrees. The design of the tendon system for Snorre TLP follows very closely the design adopted for Hutton. Jolliet follows a different design with a different latching mechanism at the bottom. Figure 2 shows the approach used in Jolliet for the bottom connection. The fabrication of the receptacle for the bottom tendon connection uses a load ring forging that has a cone shaped rolled plate skirt. The load ring assembly is welded into a structural stiffener fabrication which makes up the foundation template. The shroud of the connector has a slot that allows the lateral engagement of the male back flange of the tendon. The load ring and skirt assembly match the outward orientation of the tendon receptacle slot. The flex-joint is a ring built into the bottom part of the tendon. Several layers of elastomer bearings and metal sheets define the flex-joint. The fabrication of thetop tendon connection receptacle also uses a load ring forging with a cone shaped rolled plate skirt.