Weight Control, Performance Monitoring, and In-Situ Inspection of the TLWP
Authors: Peters D.J.H. , Zimmer R.A. , Hein N.W. , Wang W-J. , Leverette S.J. , Bozeman J.D. 
Published: October 2008

An integrated system has been set up for the Jolliet Tension Leg Well Platform(TLWP) which includes precision monitoring of the weight distribution and center of gravity. These factors are, in turn, reconciled with measured tension leg loads and regulated by a load management/ ballast control system. The weight control system was initiated in conceptual design and maintained throughout all phases of the project design, fabrication and installation. This procedure is monitored and supplemented with the Jolliet Performance Monitoring System(JPMS), which includes recording of TLWP performance and input meteorological and oceanographic (metocean) driving forces. In addition to its use in recording routine performance data in support of the load management system, the JPMS will record special storm data sets for use in verifying model test results and analytical tools used in TLP design. Finally, a detailed in-situ inspection program is put in place for the tendons, template, hull and deck, to ensure the long-term safe operability of the TLWP. Again, this program is tied into the overall performance monitoring and load management systems, with the intention of defining the performance or load history of the vessel should a flaw or crack be found during routine inspection. This will allow for definition of crack growth history and prediction of remaining component life.

Introduction

The monitoring of vessel performance on a routine basis, in conjunction with the controls of the weight distribution and center of gravity, and routine inspection of components for defects or failures are critical tasks in the long-term safe operation of the Jolliet Tension Leg Well Platform(TLWP). This paper describes an integrated system set up in the early stages of design to accomplish these tasks and outlines procedures to be used during the in-service operation of the TLWP. An additional benefit from the extensive monitoring and recording systems described below will be realized in the improvements made in future designs through the verification of model test.

Weight Control

The continual estimation of a floating vessel?s weight and center of gravity is critically important throughout its design and into initial operation. This is particularly true for the TLWP. The term weight control describes the efforts used throughout the project to estimate weight and its consequence on the TLWP design and performance. During conceptual and preliminary design, weights were estimated for equipment and steel by the appropriate discipline engineers. These were fed into a Target Value Table (Table 1) in which weights plus TLWP pretension and ballast were totaled to yield the displacement or buoyant force requirement for the hull. The term target value referred to the fact that the values were targets or goals which could change as long as the total displacement of the hull was held constant for a particular design iteration. During detailed design, the purchased equipment weight estimates came from the vendors. When the equipment weight was delivered, it was weighed and the associated accuracy estimated. The steel weight estimates came from the detailed structural design drawings. A weight control engineer was added for the duration of the project to provide coordination and consistent reporting of these estimated weights.