Distributed riser buoyancy

Balmoral Distributed riser buoyancy

Operating what is probably the most advanced buoyancy manufacturing plant in the industry, Balmoral provides high quality, consistent modules which result in low water absorption and compression throughout their service life. Balmoral distributed buoyancy modules are fully accredited by Bureau Veritas to API 17L standards.

Dynamic applications normally involve an offshore floating production facility or terminal connected to another floating facility or fixed structure.

Flexible pipe and umbilicals require the use of buoyancy modules to reduce topside or tension loads and assist in achieving particular configurations which include steep, lazy, W-wave and pliant.

BOE distributed buoyancy modules generally consist of an internal clamping system and syntactic foam buoyancy elements. The buoyancy elements are supplied in two halves incorporating a moulded internal recess that is configured to transfer the forces from the buoyancy to the clamp and subsequently the riser. This recess also accommodates bending of the riser during service. The internal clamping system is fixed to the pipe and the two half modules are fastened around the clamp.

Deepwater projects require modules and clamps to be designed for operating depths in excess of 3000msw where substantially larger modules and extreme clamping loads are demanded.

BOE has been at the forefront of significant R&D efforts to meet this challenge and has developed a number of solutions for deep and ultra-deepwater environments.

Installation times

Balmoral provides installation tools with its distributed buoyancy modules which dramatically reduce installation times. When properly deployed a pair of Balmoral DBMs can be fully installed in under six minutes.

Distributed buoyancy configurations

Steep wave

Steep Wave

Lazy wave

Lazy wave

W-wave

W-wave

Pliant

Pliant

Design, engineering and materials

The densities and composition of the modules are based on operational requirements such as hydrostatic pressure, uplift, water ingress, riser diameter, length, etc. However, the main elements of the modules comprise microspheres and macrospheres encapsulated in a polymer syntactic foam matrix.

In higher temperature applications the buoyancy modules can incorporate convection channels.

Operating what is probably the most advanced buoyancy manufacturing plant in the industry, Balmoral provides very high quality, consistent modules which result in low water absorption and compression throughout their service life.

External finishing

BOE provides finishing options of rotationally moulded polyethylene, polyurethane elastomer or GRE external skins which offer the following benefits:
Abrasion and impact resistance
Enhanced water ingress performance
Marine growth resistance
High-visibility pigmentation
Customised graphics option
Distributed buoyancy cross-section

Distributed buoyancy cross-section

Clamping options

As the requirement for flexible risers and umbilicals progresses into ever deeper water, the performance of the clamping systems required to maintain the buoyancy, ballast or tethers in position has changed significantly.

On occasion, risers also have an insulating layer which in many cases will be subject to creep over the service life of the riser.

The range of variables encountered through the design life of the clamp includes variation in diameter due to changes in internal pressure, flexing of the riser/umbilical as well as temperature and tension fluctuation.

Whilst the clamps are fitted directly onto the outer layers of the riser/umbilical, they are normally required to transfer the clamping load through the outer layers to the internal armour layers. This load transfer is designed to prevent slippage between the layers - caused by in-service and deployment loads - with an acceptable safety factor.

Balmoral Offshore Engineering has designed a unique generation of clamps to ensure optimum performance for specific operating conditions.

Typical example of a three-piece clamp

Typical example of a three-piece clamp

High performance clamp

This one-piece product is designed for high clamping load situations to resist the axial movement of large buoyancy and ballast loadings. The high performance clamp is designed to control the contact pressure onto the flowline allowing the accommodation of large diameter expansion/contraction due to its low stiffness and excellent spring properties. The clamp is installed directly onto the flowline using a specialised tool allowing accurate loads to be generated while minimising installer fatigue.

The high performance clamp in summary:

Suited for high loading/large buoyancy applications
Riser outer diameter tolerance accommodated by hinge feature
Riser diameter variations during operation accommodated by excellent spring properties of clamp assembly

Intermediate clamp

Designed for intermediate load situations this one-piece clamp resists the axial movement of moderately large buoyancy and ballast loadings.

The intermediate clamp is engineered to control the contact pressure onto the flowline allowing it to accommodate large diameter contractions due to the low stiffness and excellent spring properties of the material.

The clamp can be installed directly onto a flowline with torqueing bolts or through the use of an installation tool to induce a load into the clamping strap.

The intermediate clamp in summary:

Best suited for intermediate loading applications where low clamping pressures are essential
Riser diameter variations are readily accommodated due to the excellent spring stiffness of the clamp assembly

Standard clamp

This three-piece device is designed to clamp directly onto flexible flowlines, risers and umbilicals to prevent a module assembly from sliding along the length of the flowline whilst allowing the module to rotate freely.

This clamp is best suited for umbilical or small diameter risers where low clamping pressures are required.

The standard clamp in summary:

Best suited for low clamping pressure applications
Riser outer diameter tolerance readily accommodated while retaining consistent clamping load to resist slippage

Integral clamp

The integrally clamped module removes the need for a separate clamping system by attaching directly onto flexible flowlines, rigid pipelines, umbilicals and risers. Custom designed pads placed within the recess of the module accommodate riser diameter expansion and contraction while generating consistent clamping loads to resist slippage.

These pads also allow the module to accommodate upper and lower deviations of the nominal outer diameter of the flowline. The module can be installed using hydraulic cylinders, removing the need for bolting modules together and minimising installer fatigue.

The integral clamp in summary:

Variation in riser outer diameter is readily accommodated while generating consistent clamping loads to resist slippage
The clamping load can be generated by hydraulic tool, minimising installer fatigue

Buckle mitigation buoyancy

If a pipeline is carrying high temperature product it is inevitable that expansion will occur along the steel pipe. Although the pipe may expand in diameter, most occasions see the pipe increase significantly in length. If both ends of the pipe are fixed this longitudinal expansion can potentially transform into a buckle situation with catastrophic results.

Balmoral buckle mitigation buoyancy

To mitigate this phenomenon designers incorporate pre-determined buoyant zones along the pipeline so that expansion, or buckle, is allowed to take place in a safe and controlled way. These buoyancy modules must maintain their integrity as the pipeline “bends” during installation and operation.

Balmoral distributed buoyancy modules are based on high performance syntactic foams which are designed to meet exacting performance, strength, and installation project requirements through life of field and in water depths of 100-4000msw.

In a typical 25 year design life, buckle mitigation modules may travel over 15km of sea bed as the pipe oscillates through expansion and contraction. For this reason the external shell must be highly abrasion resistant and materials such as polyethylene, elastomer or GRE are ideally suited to this purpose.

Balmoral’s unique range of clamping systems is used in conjunction with its distributed buoyancy products ranging from integral clamps, particularly suited to steel pipelines and umbilicals, to a patented composite clamp design for flexible flowlines as well as steel and composite stop collars.

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