MARS TLP - lntegration and Installation

Abstract

This paper focuses on the experience gained during the development and use of the novel aspects of the integration and installation of the MARS TLP project. These include:- The use of a Specialized Lifting Device [SLD] to place the MARS TLP topsides on the hull at lngleside, Texas. The design, construction and operation of the SLD are described. The scope and timing of the integration work are presented, and the interfaces with other aspects of the project discussed. The MARS foundation consists of 12 driven piles, one for each of the 12 tendons, which connect direct to the tendon with no foundation templates. A driveable connector was developed and tested, these were built into each pile. Soilcyclic behaviour, relevant to tension pile design, was investigated in an extended series of laboratory tests. The piles were placed in 2940' waterdepth using acoustic positioning and driven to grade using a hydraulic hammer with an underwater power-pack. Detailed installation engineering and preparations included model tests of the TLP and Balder while moored together and simulation of critical aspects of their positioning, including failure of mooring lines and positioning tugs. The tendons were barged to location in 750 ton packages containing 12 segments, nominally 240 feet long each, which were lifted and secured to the deck of the SSCV Balder. Theindividual segments were stalked together in assembly towers over either side of the SSCV using pressure actuated mechanical connectors. After all 12 tendons were assembled and hung off on both sides of the vessel, the TLP was moored to the stem of the Balder using a combination of surface lines and an array of tugs for positioning control. Fully assembled tendons were sequentially passed over slacked mooring lines and hung off on the TLP. Using special chain jacks, tendons were stabbed into their foundation pile receptacles with the assistance of ROV's, latched and tensioned to a balanced condition using a combination of chain jack stroke and ballasting. Introduction The MARS TLP configuration is described in the preceeding papers of this session [Refs I to 5]. The MARS TLP hull and deck modules were integrated at lngleside, Texas beginning in September 1995. A shore based Specialised Lifting Device [SLD] was used to place the modules on the hull. Hook-up and commissioning of the structure and suystems was brought to a high level of completion prior to sailaway. The TLP sailed away from lngleside on April 24th, 1996. Manufacture of the tendons and piles began in 1994, final fabrication being performed at Aransas Pass, Texas. Installation of foundation and TLP was planned to take place in a single operation to minimise mobilisations of the SSCV Balder. The TLP was moored to the SSCV during tendon transfer and stabbing. Pile installation began on March 29, 1996, the TLP arrived on site on April 29th, 1996, and installation was completed on May 19th 1996. First Oil began to flow on July 8th, 1996. A bar chart indicating the main activities is shown In Figure 1.

Centrifuge Model Tests on Anchor Piles for Tension Leg Platforms

“…One method to connect the tendons of Tension Leg Platforms (TLPs) to the foundation piles is to drive the piles with the tendon bottom receptacle attached to the piles. This method was first used on the Mars TLP (Garside et al, 1997). Because it is a free-head pile, this direct-connect method may result in lateral deflections that exceed the criteria on which RP2A (1993,2000) is based (see Matlock, 1970).…”