Design, Fabrication, And Installation Of Auger Lms And Tendons
Authors: Lohr C.J. , Bowen K.G. , Calkins D. E. , Kipp R.M. 
Published: October 2008

The Auger TLP is held on 1ocat ion by a combination of a Lateral Mooring System (LMS) and Tendons. The LMS is a catenary mooring system comprised of linear winches, wire, chain, submerged buoys and anchors as shown on Figure 1. It is used to position the TLP over specific well locations and to resist lateral environmental forces (Ref. 1). There are 12 steel tubular tendons mechanically latched, three per Column, to four individual foundation templates on the seafloor (Ref. 2). Each tendon is configured as shown on Figure 2. The tendons resist vertical motions and work in concert with the LMS to resist lateral environmental forces. The LMS was also used to hold the hull on location during mating operations in shallow water and while the tendons were connected to the superstructure and stabbed into the foundation templates at the Auger site.

This paper overviews the significant and/or unique features in the design, fabrication and installation of the Auger LMS and Tendons. Design considerations discussed include performance criteria, material selection, fatigue requirements, and full scale testing. Fabrication issues reviewed include the large number and location of vendors, general fabrication scenarios, significant problems encountered during manufacturing and the use of functional testing to verify acceptability of completed components. The extensive installation engineering and planning and the resulting development of several purpose-built pieces of installation equipment are described. An overview of the installation sequence and critical aspects of the installation are presented.

INTERACTION BEWEEN THE LMS AND THE TENDONS

Conceptual designs of the Auger TLP considered the LMS only for superstructure positioning during well operations and tendon installation. The LMS was considered non-critical for resisting extreme environmental events. However, due to the complexity of the tendon component designs, the tendon pipe size was fixed early in the TLP design cycle. The LMS component sizes were subsequently increased to account for an increase in superstructure size, increased wave forces, and to meet the requirements for minimum tendon tension.

The restoring force induced by the tendons, risers and platform set down is included in the LMS analysis. This restoring force is beneficial for the LMS response to the 100-year hurricane. However, the tendency of the tendons to pul1 the TLP back to center works opposite of the LMS for the operating condition where the TLP is moved over an outer well.

LMS DESIGN

The primary code used for LMS design and analysis was API RP 2FP1 (Ref. 3). Every component has a minimum breaking strength (MBS) of 2900 kips and is designed for a 30-year service life. The eight lines are symmetrically oriented at spacings of 45 degrees with the anchors located approximately 9200 feet from the TLP. Two anchors have been placed on the flanks of a salt diapir.

Line configuration and component sizes are based on the final platform size and response to the design environmental conditions. Chain length is based on the on-bottom stiffness requirements and is provided for abrasion resistance in the dip zone.