SURF products

Bend stiffeners

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.


Polyurethane bend stiffeners are used to add support to flexible pipes, umbilicals and cables. They are typically positioned at vulnerable interfaces where a significant change in stiffness occurs such as when being connected to rigid structures or a floating production system where there is a requirement to control the minimum bend radius of the pipe.

Three types of stiffener are generally available, dynamic, intermediate and static. These are typically conically shaped PU mouldings with a cylindrical bore that slips over the pipe, umbilical or cable.

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

Balmoral bend stiffeners accommodate a variety of interfaces on client hardware engaging and locking into grooves or bolting directly onto flanges while, in special cases, Balmoral will design bespoke steelwork to accommodate client hardware. In certain circumstances Balmoral also offers split bend stiffeners allowing a retrospective installation providing a greater window for client installation.


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 14m in length.

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.


Balmoral bend stiffener FEA analysis

Balmoral bend stiffener FEA analysis interface structure


Bend stiffener design analysis

Balmoral uses the proprietary package ‘Orcabend’, an industry standard for many years, to generate the 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.