Vertebrae Bend Restrictor

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A vertebrae bend restrictor (VBR) is designed to protect a subsea control line umbilical from bending stresses that can occur during normal offshore installation and operation. It offsets the action of applied loads which could kink or buckle the internal conduits of an umbilical, cable, flexible riser pipe or MUX line.

The vertebrae have omni-directional freedom until the locking bend radius (LBR) is reached where the ball and socket of the VBR are fully engaged. The LBR of each VBR is the radius at which the lock, or “lock up,” occurs. At that point the segments of the VBR will lock on each other increasing the effective stiffness of the cable it protects to withstand specified loads applied to the device without violating the specified minimum bend radius (MBR). The VBR will accommodate lines 0.5inch (13 mm) to 16 inches (406 mm) in diameter and is made from either polyurethane or steel depending on the need.

The steel vertebrae bend restrictor (SVBR) is designed to prevent damage to the umbilical control line that it supports at higher loads than its polyurethane counterpart. SVBR assemblies, like their polyurethane counterparts, protect the control line to a customer specified minimum bending radius (MBR).

The SVBR Assemblies are comprised of male and female type segments that fit into each other.  The male segment pair is locked inside the adjacent female segment pairs, thereby reducing the number of fasteners required to complete the assembly. SVBR assemblies are equipped with polyurethane stress wafers that work to evenly distribute the stress during loading.

ABCO Subsea’s hybrid vertebrae bend restrictors are made from both steel and polyurethane segments and provide the benefits of both materials in deep water, high load applications. Hybrid VBRs use steel segments near the VBR assembly’s structural support interface, where most loading occurs. Farther from the VBR assembly’s interface, polyurethane segments are used to take advantage of the near neutral buoyancy of the polyurethane.

As opposed to an entirely steel VBR assembly, the hybrid concept results in cost savings of 5-30% for ABCO Subsea’s customers. Additionally, the polyurethane segments reduce the overall weight of the hybrid VBR assembly compared to an entirely steel VBR assembly, and the polyurethane segments are easier to handle and assemble, reducing installation vessel schedules.

ABCO Subsea designed and produced its first hybrid VBR assembly in 2009 after a customer approached the company about a challenging deep water environment