Review of Cabling Techniques and Environmental Effects Applicable

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Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind Farm Industry – Technical Report Frond mattresses Frond mattresses can potentially increase protective cover over a surface laid section of cable by stimulating the deposition of sediments which are suspended and transported in the water column. When the sediments connect with the frond mattresses, they are forced to settle; this eventually forms a new sand bank. Before a frond mattress is selected for a particular application it would be essential to assess the appropriateness of the technique for the local conditions and it may be necessary to deploy a frond mattress at the site in advance of the cable protection project to ensure that the procedure would be successful. Figure 3.28 illustrates a frond mattress. Figure 3.28: Frond Mattress Protection Figure 3.29 illustrates how a frond mattress and a concrete mattress could be used in conjunction to protect cables and pipelines close to an offshore structure. Figure 3.29: Protection using a Frond Mattress in conjunction with a Concrete Mattress 62
Cable types and installation techniques Fronds are popular with environmental organisations as there is a perception that the indigenous substrate is being reinstated. However, experience has shown that situations such as storms, which create high energy situations on the seabed, have resulted in deposited materials around the fronds being stripped out. The installation procedure for the frond mattresses would be identical to that explained above for concrete mattresses. Uraduct Uraduct is manufactured using high performance polyurethane elastomer. The system comprises two cylindrical half shells which overlap and interlock to form close fitting protection around the core product such as cable, umbilical or flexible/rigid flowline. For ease of handling, the half shells are manufactured in lengths of up to 2.0 metres with flexing characteristics to suit the required minimum bend radius of the product or ancillary shipboard lay equipment. The half shells are secured in place using corrosion resistant banding located in recessed grooves to ensure a smooth external profile. A range of sizes is available to support product outside diameters ranging from 15mm to 450mm and beyond. Uraduct comes in varying sizes and stiffnesses to resist different levels of impact and is of particular use at cable crossing points or in areas close to structures, such as offshore wind turbine support structures or offshore oil and gas installations, where the risk from dropped objects is high. Uraduct is not commonly used along longer sections of cable which has been inadvertently surface laid on the seabed as it does not offer any further protection from trawling gear or anchors and only increases the target size. Articulated metal shell connectors Articulated metal shell connectors are typically used to provide cable sections with added mass and abrasion resistance in high energy environments such as a cable shore landings, which pass over rock outcrops and where other forms of cable burial are not possible. The articulated sections would be applied by surface divers in half sections which are then locked or bolted together to form a continuous pipe section. Directional drilling Directional drilling is employed by cable installation contractors when the topography of a landfall site makes it difficult to achieve a conventional landfall by trenching, or where there are environmental interest features that need to be avoided such as saltmarsh or chalk cliff. Directional drilling provides a very useful alternative, as it allows the cable installation to bypass the critical areas 63
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REVIEW OF CABLING TECHNIQUES AND EN
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Review of Cabling Techniques and En
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Abbreviations AIS Automatic Identif
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TTS Temporary Threshold Shift TWA T
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6 Good practice measures This secti
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7 Gaps in understanding Research fo
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References Introduction Sinden, G.
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Appendix A: Standards and codes of
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Printed in UK on recycled paper. De
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