Bend stiffeners

Balmoral bend restrictors

Balmoral bend stiffeners are fully accredited by Bureau Veritas to API 17L standards using specifically formulated polyurethane materials and are engineered to suit project operational parameters.

Bend stiffeners are used to support flexible pipe, umbilicals and cables when connected to rigid structures or a floating production system where there is a requirement to control the minimum bend radius of the pipe. They are usually attached at either the topside or seabed connection.

In dynamic applications bend stiffeners require to have sufficient fatigue resistance to control the in-service bend radii and sustain the cyclic loads to the end of the specified life whereas in static applications they protect against gross over-bending.

Stiffeners are typically conically shaped polyurethane mouldings with a cylindrical bore that slips over the pipe, umbilical or cable.

Manufacturing and materials

BOE has invested heavily in the technology and infrastructure to produce what are thought to be the largest bend stiffeners in the world. The upgraded capability allows the company to produce stiffeners in excess of 15m long.

A key aspect of the BOE bend stiffener/restrictor development program has been to negate the significant health and safety issues associated in traditional elastomer stiffener supply. The material systems used in BOE products meet the increasing demand for minimum hazard at all stages of manufacture and use.

BOE does not use carcinogenic aromatic amine cross-linkers and uses only ‘stripped’ prepolymers, ie, materials that are essentially free of volatile and toxic TDI. Additionally, BOE bend stiffeners comply with Norwegian Product Regulation 2.3 which bans the use of toxic mercury catalysts.

Bend stiffener options

Dynamic bend stiffener

Dynamic bend stiffener

Dynamic bend stiffeners provide localised stiffening for umbilicals and flowlines in demanding applications. They are designed to protect the minimum bend radius (MBR) inflicted by flexing while under axial loads and also to prevent fatigue failure.

The end steelwork on dynamic stiffeners is custom-designed and fully encapsulated to connect with the matching project hardware.

Balmoral’s proprietary manufacturing capability means that stiffeners of virtually any size can be produced.

Static bend stiffener

Static bend stiffener

Balmoral static stiffeners provide overbend protection during installation and overboarding procedures. They support and control the minimum bend radius on flexible pipe and cable at the end fitting and mid-line joints.

The standardised Orcabend design and modular tooling means that static stiffeners can be offered on a very quick turnaround.

Split bend stiffener

Split bend stiffener

These Orcabend-designed products are generally produced for retrofitting on to umbilicals, cables and flowlines already in service.

Split stiffeners can be used on a number of end fittings and are usually strapped or bolted in place.

Balmoral SolGuard UV protection coating

Balmoral SolGuard® UV protection coating

The vast majority of offshore elastomer products are used subsea where UV degradation is not an issue.

However, a limited number of moulded products are deployed above the surface and by far the most critical in terms of performance and consequences of failure are bend stiffeners.

To overcome this issue, Balmoral developed its unique SolGuard UV protection system which effectively creates an overcoat layer preventing UV penetration through to the underlying bend stiffener.

Design analysis

Balmoral uses the proprietary package ‘Orcabend’, an industry standard for many years, to generate a profile for the active conical section of the stiffener.

Information that is critical to bend stiffener design includes:

Tension and angle data from the riser analysis
Temperature
Interface detail
Riser end-fitting profile
Diameter and stiffness
Minimum bend radius
Riser analysis fatigue data

Balmoral’s FEA package is used to verify the Orcabend design and analyse the end-fitting structure. This process can also provide thermal analysis if required.

Balmoral bend stiffeners are comprehensively flex-fatigue tested and Lloyds approved.

A combination of Orcabend and FEA technologies allows split stiffeners to be designed for retro fitting.

Stiffener interface structure

A smooth transition is required between the rigid flange and the flexible cone of the stiffener. BOE’s design achieves this by creating both rigidly bonded and un-bonded areas that provide deflection and minimum stress in these localised areas.

Balmoral bend stiffener design analysis
Balmoral bend stiffener design analysis

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