Synopsis An analysis for predicting stresses, strains and rotations at all levels of load and for predicting the strength of members under combined torsion–shear–flexure loads is presented. Equilibrium and compatibility are considered and the analysis predicts the phenomenon of ‘shear relief’, whereby the torsional strength of an over-reinforced beam is enhanced by a small shear load. A torsion–shear–flexure interaction surface is proposed which is actually a combination of two surfaces. An equation defining the space curve formed by the intersection of these two surfaces is derived. Use of this equation indicates the portion of the interaction surface that is appropriate for a particular combination of loads. The proposed interaction surface is compared with test results available in the literature and good correlation is noted.

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The Terra Nova FPSO will be the first Floating Production facility operating in the harsh environment of the Grand Banks. Unique design solutions have been applied to enable the FPSO to quickly disconnect from its mooring in order to avoid iceberg collision and operate subsea and topside process facilities efficiently in sub-zero temperatures. The ongoing integrity of the asset will be assured by implementing effective engineering, maintenance and inspection strategies, balanced with the requirements of production and marine operations in difficult environmental conditions. This has uncovered some unique challenges. The paper addresses the Design Basis along with the integrity and maintenance strategies that have been developed to cost-effectively manage the overall facilities' integrity and the control 'tools' that are being implemented. Facilities Description / Basis of Design Location and Field Layout. The Terra Nova field is the second largest discovery in the Jeanne d'Arc basin on the Grand Banks off Eastern Canada. The field is located in 94m of water, 350km ESE of St. John's, Newfoundland and 35km SE of the Hibernia platform. In addition to significant storm conditions (100 year Hs of 16m) the area is vulnerable to sea ice, icebergs and prolonged periods of fog, (Fig. 1). The Graben and East Flank areas of the field have estimated recoverable reserves of 300-400 million barrels, (Fig. 2). These areas will be developed by 24 subsea wells; 14 producers, 7 water and 3 gas injectors. The initial development will consist of six wells. The Far East area of the field has a high probability of development. Potential for growth to 48 wells has been built into the design. Subsea Equipment. The initial Terra Nova field development consists of seven Hinge Over Subsea Templates (HOSTs) installed in excavated glory-holes. An additional five HOSTs will complete the future development of the field, (Figs.3&4). Each HOST system, configured for 2 to 5 well templates has been installed from a conventional drilling rig and is flexible for future expansion. Each template is supported on a central conductor, drilled and cemented in position. The subsea manifolds contain hydraulically actuated switching valves for directing each well flow to either the production or test header and to allow pigging. The manifolds can be retrieved independently of the trees. A standard wellhead design has been used, with horizontal Xmas trees located on the HOST template. Each wellhead consists of a 3-hanger tree, with 7" monobore tubing sealing in the tree spool. For standardisation purposes, common subassemblies have been used for production and injection trees. Flowlines and Risers. The HOST manifolds are connected back to the FPSO by 13 flowlines and 11 flexible risers. These have the following diameters and design pressures:Production/test 9/10" ID 29.0 MPaWater injection 7/10" ID 45.2 MPaGas injection 9" ID 45.2 MPaGas lift 5/5½" ID 29.0 MPa In addition to the flowlines and risers, subsea equipment is connected by four composite electro-hydraulic umbilicals. An electro-hydraulic multiplexer control system is used, with open-loop hydraulics.

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The Terra Nova FPSO will be the first floating production installation to operate in the unique and harsh environment of the Grand Banks. In order to avoid the threat of icebergs the FPSO will be able to quickly disconnect from its mooring and to proceed under its own power. The FPSO is therefore required to be certified as both an offshore installation and as a ship. The paper focuses on initiatives implemented to ensure fitness for purpose of the installation within a complex regulatory climate while reducing commercial risk related to the broad geographic and technical spread of development activities. The paper also provides an overview of the Terra Nova development and discusses prominent technical challenges encountered.