Bundles and towed installation

Bundles and towed installation

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Similarly, once we get into deeper water than around 100 m (330 ft), we need stronger insulation or need to protect with pipe-in-pipe. Again, syntactic products may be needed to achieve the crushing resistance. All foams will tend to crush and creep with time. Any collapse of foam will degrade the thermal behaviour. It may be necessary to design the thermal behaviour for conditions at the end of life. For drilling risers, or pipelines installed using reel laybarges, the strength of the insulation may be important. Damage can occur either from impact or abrasion at rollers. Any water able to penetrate into the insulation will degrade its thermal properties. Better thermal behaviour may be achieved by applying thicker layers. However, the thickness and density of the insulation may be important when assessing the net buoyancy in seawater. Although not usually a deciding factor, it needs to be allowed for during the design. Risers may need additional buoyancy or weighting to help response in seas. Pipelines may need trenching or burial for stability. It is common for insulation and buoyancy to be manufactured from similar material so the solution can be combined in a single layer. The over-riding limitation is the total cost of procurement and installation. Some syntactic products are extremely costly.

INSULATIONSOLUTIONS

INSULATION SOLUTIONS

ƒ Use of multiple layers ƒ Inner layer to withstand high temperatures ƒ Middle layer provides insulation properties ƒ Outer layers for impact and handling ƒ Extreme depths ƒ Dense syntactic foams ƒ Use of pipe-in-pipe – insulation driven ƒ Presents significant engineering issues ƒ High operating temperatures ƒ Installation of heat exchanger to cool product

It is common to manufacture insulation in multiple layers. Each layer is optimised to resist the design condition. At extreme depths, syntactic foams are usually adequate. Normal design caters adequately for collapse resistance under combined external pressure, tension and bending loads. Where severe thermal problems demand a very efficient system, pipe-in-pipe may be required to resist the hydrostatic collapse pressures, protecting an efficient but structurally-weak foam insulant. However, this presents significant engineering issues for risers. It may even be cost-effective to cool product down at the wellhead to limit the line temperature or install subsea cooling loops.

INSULATIONSYSTEMSUSEDFORBUNDLES