Flexible hang-off arrangement for a catenary riser

Abstract

Flexible hang-off arrangement is provided for a catenary riser suspended from an offshore or inshore platform, which includes floating or fixed platforms, vessels or/and buoys. The bending loads in the top segments of the said riser are reduced by incorporating a pivot at the riser hang-off. Pressure containing welded, bolted, rolled or swaged pipe spools transfer fluids, including hydrocarbons between the riser and the platform. Along significant spool lengths the tangents to the center lines of said spools are orthogonal to and offset from the tangent to the center line of the riser at the hang-off. The said pressure containing spools include arbitrary looped, spiral and helicoidal designs that are subject to torsion.

1 . Riser-deflection spool assembly, whereas:
 said riser, including a catenary riser is suspended using a pivoting arrangement from an offshore platform, including fixed platform, including an articulated platform, including a compliant platform, including a floating platform, including a floating vessel, including a floating buoy,   said pivoting arrangement transfers tension in said riser to the structure of said platform, including a core of a turret structure that might use approximately fixed orientation with regard to the geographical directions, while said platform utilizing said turret might be allowed to rotate freely around said core of said turret,   said pivoting arrangement allowing means to transfer directly to said platform, including said turret of said floater relatively small fractions of bending moments applied to said riser at the said pivoted points of said riser suspension,   said riser being also connected to said platform relatively flexibly using pressure containing piping spools,   said pressure containing piping spools being arranged spatially in manners that expose a significant percentage of the total length of said pressure containing piping spools to torsional deformations resulting from any combination of in-plane and out-of-plane bending of said riser relative to said structure at the location of said pivoting arrangement,   said combinations of in-plane and out-of-plane bending resulting in corresponding combinations of relatively free in-plane angular deflections and out-of-plane angular deflections of the axis of said riser at said location of said pivoting arrangement,   said pressure containing piping spools comprising components connected by reliable pressure containing means, including welding, including bolted flanges, including subsea connectors and including plastically deformed durably rolled connections, including cold rolled connections and including swaged connection,   said pressure containing piping spools including spools involving coiled shapes of spools, including circular spiral shapes and including polygonal spiral shapes.   
   
   
       2 . Said pivoting arrangements according to  claim 1  including ball joints, including flexjoints, including universal joints, including bellmouths, including hawse pipes, including chutes, including I-tubes, including J-tubes, including fairleads, including pulleys, including any combinations of shackles and chain links, connecting links and pad-eyes. 
   
   
       3 . Said riser, said pressure containing piping, including said deflection spool assembly and said platform piping according to  claim 1  incorporating and being interconnected utilizing piping elements featuring minimum radii of curvature of pre-determined minimum values, including those of predetermined ratios of bent radii to the nominal pipe diameters, including those of five times nominal piping diameters. 
   
   
       4 . Said pressure containing piping, including said deflection spool assembly being subject to torsional deformations according to  claim 1  being constructed of steel alloys used in riser and pipeline engineering, including high strength alloys, including corrosion resistant alloys including other steel alloys. 
   
   
       5 . Said pressure containing piping, including said deflection spool assembly being subject to torsional deformations according to  claim 1 , utilizing corrosion resistant materials, including alloys, including being constructed of corrosion resistant materials, and including utilizing corrosion resistant materials for internal cladding, and including utilizing corrosion resistant materials for internal plating, etc. 
   
   
       6 . Said pressure containing piping, including said deflection spool assembly being subject to torsional deformations according to  claim 1  being constructed of high strength steel alloys. 
   
   
       7 . Said pressure containing piping, including said deflection spool assembly being subject to torsional deformations according to  claim 1  being constructed of relatively low shear modulus and high yield and ultimate tensile material, including titanium alloys. 
   
   
       8 . Said pressure containing piping, including said deflection spool assembly being subject to high torsional deformations according to  claim 1  being constructed so that low torsional stiffness of the pipe cross section results, while the maximum design pressures are reliably contained, which includes utilizing fiber reinforced plastic materials. 
   
   
       9 . Said pressure containing piping, including said deflection spool assembly according to  claim 1  being subject to any combination of high torsional and high bending deformations being constructed so that a combination of low torsional stiffness of the pipe and of low bending stiffness of the pipe results, while the maximum design pressures are reliably contained, which includes fiber reinforced plastic materials. 
   
   
       10 . Said pressure containing piping, including said deflection spool assembly being subject to high torsional deformations according to  claim 1  comprising more than one layer, including multilayer constructions that might incorporate cladding, and including multilayer constructions that might incorporate plating, and including layers that might be swaged together, including any combinations of layers that might be interlocked, including any combinations of layers that might be bonded together and including any combinations of layers that might be not bonded. 
   
   
       11 . Said deflection spool assembly according to  claim 1  featuring riser system that is suspended from a platform, including a floating platform and a floating vessel, utilizing shape type interaction to transfer high loads between the components of the system, including a use of receptacle baskets, and including a use of connectors, which includes a use of a single connector, in particular collet connectors and a collet connector. 
   
   
       12 . Said deflection spool assembly according to  claim 1  utilizing design means of protection against vortex induced vibrations, including devices that shield selected parts of the system from the action of currents and waves and including vortex suppression devices. 
   
   
       13 . Said deflection spool assembly according to  claim 1  utilizing the rotational flexibility of said deflection spool assembly in order to reduce dynamic bending stresses in said catenary riser that result in increasing fatigue life of said riser.