Materials & Testing
Clamp Body
The clamp body is cast from an epoxy resin composite providing a tough, rigid component which is also advantageously buoyant.
Circumferential Strap & Tensioning System
The strap and tensioning assembly are supplied in titanium. Titanium is highly suited to this application as it is highly corrosion resistant, making it suitable for an extended subsea service life while exhibiting highly elastic porperties for a metal. The elasticity allows for a significant amount of extension provided by the strap during tensioning. The subsequent change in riser diameter will not generate large variations in the clamp surface contact pressure.
Our clamp has no loose parts and is hinged to enable a rapid installation directly onto the riser. It is usually pre-lubricated behind the titanium band to reduce any potential loss of tension due to the capstan effect.
The requirement to prevent unscrewing of the fastenings after installation is satisfied by the use of two locknuts which prevent the socket head cap screws from rotating following tensioning.
The multi-jaw configuration ensures that "as manufactured" tolerances are readily accommodated.
The Internal Clamps supplied by us are subjected to a comprehensive test programme which can be tailored to suit a client's specific requirements which typically include:
- Buoyancy checks
- Weight checks
- Clamp strap capacity checks
- Coefficient of friction checks
Foam Core
The foam core is manufactured from a composite syntactic foam with three main constituents:
- Base polymer
- Glass microspheres
- Macrospheres
The resulting material has a nominal density which varies according to the specific water depth of the application. An additional allowance is made to the Final Module Buoyancy to cover losses during the design life. An allowance for marine growth may also be added to the Final Buoyancy Module. This new value is known as the Initial Module Buoyancy.
External Skin
The external skin can be moulded or sprayed in a suitable high performance polymer. This is a tough, inert, impact resistant material which is suitable for an extended marine service. The colour of the skin is yellow as standard.
The polymer skin although non-toxic is marine growth resistant. The material is neutrally buoyant with a density of approximately 1000kg/m3
The buoyancy modules can be marked for installation purposes by stencilling directly onto the external skin.
Fastening System
The buoyancy element halves are secured around the internal clamp with endless EVA coated securing straps secured together by tensioning assemblies which enable the straps to be tightened, thereby securing the buoyancy modules in position.
The tensioning assemblies are manufactured from a highly corrosion resistant material such as UNS S32760 or similar, subject to availability.
All buoyancy elements and the syntactic foam contained within them are subjected to a rigorous programme of qualification and process control testing including the following:
- Density checks
- Hydrostatic crush pressure testing
- Water absorption testing
- Buoyancy loss checking
- Full scale buoyancy testing
- Full scale hydrostatic testing
- Fit-up and assembly testing.
Hydrostatic Testing
This is probably the most common and regular form for testing undertaken by our engineers. To assist with the thorough and comprehensive testing of buoyancy modules, we have installed a suite of pressure vessels including one of the largest hyperbaric test chambers in Europe and one in the USA capable of simulating 3500msw.
To complement this impressive test facility, a fully equipped control and quality assurance laboratory enables routine quality assurance testing to be carried out quickly and accurately.