Sea Technology

JUL 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 11 of 68 July 2017 / st 11 gas industry. One specific area is bend protection where a flex- ible tubular connects to a struc- ture. The normal movement or dynamic loading during opera- tion, or forces incurred during installation and retrieval, can cause catastrophic failure of the tubular at the termination point. Failure can be through collapse, rupture of internal lines or even rupture of the external layers, leading to escape of the con- tents of the pipe into the environment. This can be due to fatigue over time or an accident occurring that brings about instant failure. With the use of bend restrictors and stiffen- ers, such failure can be avoided. Bend stiffeners protect flexible pipelines from over-bend- ing or kinking. Stiffeners are used in more dynamic applica- tions where there is a constant wave or current motion, for example, where a pipe meets a ship or a platform. Here they are deployed to prevent over-bending at the termina- tion point, seeking to: maintain the manufacturer's recom- mended minimum bend radius (MBR) during the life of the project; provide a suitable load path from tubular to fixed structure; and reduce point loading at the termination to an acceptable level. Being designed and constructed from polyurethane means installation and maintenance are much simpler, more cost-effective and provide significantly lower whole-of-life cost while reducing the weight of the connectors, making it neutrally buoyant in water. Qualification and Compliance Bend stiffener manufacture must be compli- ant with API 17L, the industry standard for subsea equipment. This standard reviews manufacturing and procedures covering machining, welding, heat treatment, nondestructive evaluation (NDE) and coating. NORSOK standards, developed by the Norwe- gian petroleum industry to ensure adequate safety, value adding and cost-effectiveness for petroleum industry developments and operations, must also be adhered to for work within the North Sea. Cor- rosion protection also falls under NORSOK com- pliance. Industry Knowledge Sharing Trelleborg has historically been the supplier of choice in safety critical applications where failure of the key components is simply not an option. For example, many thousands of dynamic bend stiffen- ers have been supplied to projects across the globe with zero failures. The main driver for this is the rigorous design methodology, with key safety fac- tors an inherent part of the process. This same rigor is used in the design of renew- able products, but the key difference is that materials, tolerances and conservatism can be reduced due to the nature of the power cables compared to risers and um- bilicals. With the world looking increasingly for more sus- tainable forms of energy, Trelleborg devised equally reliable solutions for wind farms. One of these solutions is NjordGuard, a cable pro- tection system specifically designed for the renewables market, used to protect cables carrying electrical power generated by wind farms from the converter platform back to shore. The system also protects the interarray cables con- necting each wind turbine subsea. The entry and exit point for the power cables at each tur- bine will see significant loads due to a combination of wave height, water depth, storm conditions and tidal currents. These areas can see significant cable fatigue and damage, therefore, protection is required from each entry and exit point to the burial point. In some cases the burial point can be 20 to 30 m from the turbine base with a significant free span. Trelleborg's expertise in dynamic cable protection can overcome these issues using tried and tested design method- ology gained from years of oil and gas design. Reworking for Renewables Adapting the cable protection system for wind farms in- (Top and Bottom) Trelleborg successfully performed eight full-scale wet tests of Njord- Guard in ORE Catapult's con- trolled testing environment. Seabed view of NjordGuard attached to wind turbine. .

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