Bend Stiffeners Protection for Risers and Umbilicals

When a flexible pipe or cable connects to a rigid structure (like an FPSO turret, an offshore wind monopile, or a subsea manifold), there is a sudden transition in stiffness. Without protection, the natural movement of the ocean would force the pipe to bend sharply at this connection point, violating its Minimum Bending Radius (MBR).

A Bend Stiffener is a conical polyurethane device designed to provide a gradual transition in stiffness. By tapering from a thick, rigid base to a thin, flexible tip, it distributes the bending stresses over a longer length of the pipe rather than allowing them to concentrate at a single point.

Why Polyurethane is the Standard Material

Just as with buoyancy modules, Polyurethane (PU) is the material of choice for Bend Stiffeners, but the specific requirements are different. While buoyancy needs low density, stiffeners require high dynamic fatigue resistance.

Customizable Modulus: Manufacturers can chemically engineer the PU to have specific elasticity. The base of the stiffener is often harder and more rigid, while the tip is softer to match the flexibility of the cable.

Fatigue Life: Subsea Bend Stiffeners must endure millions of bending cycles over a 20+ year lifespan. High-grade elastomers are used because they do not suffer from work-hardening or brittle fracture under constant cycling.

Environmental Resistance: The PU material is impervious to seawater and resistant to marine growth, ensuring the cone maintains its mechanical properties for decades.

Key Applications

1. FPSO and Dynamic Risers

In deepwater oil and gas, Floating Production Storage and Offloading (FPSO) vessels are constantly moving. The risers carrying oil from the seabed enter the vessel through a turret. Bend Stiffeners are essential here to prevent the steel or flexible risers from kinking as the ship heaves and surges.

2. Offshore Wind Farms

This is a rapidly growing sector. Array cables connect wind turbines to each other. These cables exit the foundation through J-Tube." A dynamic Bend Stiffener is typically installed where the cable exits the J-Tube to protect it from the constant swaying of the tower and the action of the currents.

Conclusion

The Subsea Bend Stiffener is a vital component in the protection of offshore assets. By utilizing the unique properties of Polyurethane to manage stiffness transitions, these devices ensure that the connection points between the seabed and the surface can withstand the relentless energy of the ocean environment.