Bend restrictors prevent over-bending at the interface between flexible flowlines/umbilicals/cables and rigid structures by mechanically locking up.
They are normally used in static applications but, unlike bend stiffeners, only provide protection once the pipe has achieved the desired bend radius between the flexible line and rigid structures such as wellhead connections, J-tube exits, rigid pipe crossovers and PLET connections.
Designed in accordance with API 17L, BOE bend restrictors are manufactured in rigid structural polyurethane two piece units that are bolted together around the pipe.
Bend restrictor design analysis
BOE restrictors are designed using ‘Inventor/Ansys’, the recognised industry standard, using the following information:
- Flexible pipe OD
- Minimum bend radius
- Service life
- Length of coverage by angle or length
- Support structure details
- Flexible pipe min and max internal temperatures; operation and installation
- Flexible pipe min and max thermal conductivity value if pipe is heated
- Min and max installation air temperature
- Min and max seawater operation temperature
- Installation and operation shear force
- Installation and operation bending moment
- Flexible pipe stiffness if not taken into consideration in the bending moment and shear force loads
Balmoral offers a variety of options for bend restrictor end fittings (reaction collars) where a robust design is required to provide the smooth transfer of load from the project interface to the end of the restrictor string ensuring protection is maintained at all times.
Forged reaction flange
Using this method, Balmoral bend restrictors couple to the structure by means of a flanged (male) end fitting. Forged reaction flanges are manufactured using compliant material as a single body which is machine finished and requires no welding. They are supplied as split units and bolted together using B7M bolts.
Forged reaction flanges are coated with a standard marine grade paint system (NORSOK System 7B) and couple with the client’s end fitting. Balmoral does not supply the bolts to connect the reaction flange to the end fitting but this can be arranged if required.
PU reaction flange
PU reaction flanges are the connecting point between PU bend restrictors and the subsea termination interface; these are designed to match clients’ end fittings. The PU reaction flange design is based on the bend restrictor as both components share the neck and pin geometric sections and utilise the same material.
PU reaction collar
Using this method, bend restrictors couple to the structure by means of a PU fitting connected to a steel flange located within the groove of the end fitting. Steel flanges are supplied in two halves with a pitch circle diameter (PCD) to match the PU end fitting.
All the options above can be supplied in Balmoral’s standard welded assembly format.