Buoyancy modules are widely used ancillary equipment aiming to shape riser systems to resist harsh offshore environments. Due to their thermoset polymeric nature, they are sensitive to the manufacturing parameters as well as subject to water absorption along their service life. To overcome the challenges of polymer-based buoyancy module, this paper explores the design of metallic buoyancy modules that can be 3-D metal printed. An initial material selection is performed to identify suitable material candidates for the optimization algorithm. Steel and aluminum materials are considered and evaluated on a representative case combining density, mechanical stress and buckling criterion. Then a topology optimization algorithm called ‘Adaptative Bone Mineralization’ is applied on the best candidate material, adapting their modulus of elasticity at each iteration according to the current stress distribution, load case definition and boundary conditions. The optimized design incorporates additional requirements related to additive manufacturing processes. Results of the optimization algorithm are presented in a progressive order of complexity starting from the optimization of an angular section of 11.25 degrees opening with symmetrical boundary conditions up to a quarter of half-shell buoyancy module fully optimized in 3D. The optimization process log, capturing the volume fraction and the maximum stress at each iteration, is presented and compared with the selected set of criteria. Impact of the manual reconstruction process of the buoyancy module is assessed and the buckling stability is evaluated as a post-treatment. Two-dimensional and three-dimensional topologically optimized buoyancy modules are presented and comply with the strict mass requirement, stress criterion and buckling stability achieving deep water depth. This novel design approach to create deep water metallic buoyancy modules achieves the tailoring of the buoyancy module's internal structure to maximize the buoyancy performance while ensuring its structural integrity.

Anchor flanges are interface items which are used to connect pipelines to subsea in-line and end termination structures. They are forged and tend to be long-lead items; therefore, the design of an anchor flange should be completed at a very early project stage, possibly even during the tender phase. An optimised, analytical method for preliminary design would result in reduced design time overall and have beneficial cost implications. The analytical notch methods (i.e. Neuber’s and Glinka’s) that are presented utilise linear-elastic stress concentration factors to make realistic predictions of the ultimate load carrying capacity of an anchor flange in the non-linear regime. The linear-elastic stress concentration factor values are calculated with simple analytical formulae and graphs. The analytical notch methods are deployed to predict the anchor flange limit load and peak plastic strain and thereby ensure that the plastic strain remains within the allowable limits of design codes. The cost and time saving associated with the analytical notch methods, and the accuracy that is maintained, are assessed by comparison with the predictions results obtained from detailed finite element analyses.

Since Deepwater field developments started around year 2000, Deepwater Buoyancy has been dominated by syntactic foam and has not evolved significantly since then. Some Deepwater applications like towed Bundle, Steel Lazy Wave riser and Hybrid Riser towers require large amounts of it, both for temporary (installation aids) use and permanent use, becoming a significant part of the cost associated to those systems. In parallel, the present market conditions is pushing Oil companies to develop new technologies and to promote cost reduction initiatives. In this context, Subsea7 and Matrix, Composites & Engineering have developed a new concept of buoyancy, so called low cost buoyancy. This paper will present the Buoyancy concept, will provide insight on the qualification tests successfully passed, and present typical application where the low cost buoyancy is intended to be used.