Bundles and towed installation

36

Bundles and towed installation

INSULATION AND HEATING SYSTEMS

THERMAL INSULATIONLIMITATIONS

THERMAL INSULATION LIMITATIONS

ƒ Thermal conductivity ƒ K-values – 0.025 W/m/K (0.015 BTU/hr/ft/F) ƒ U-values – 1 to 5 W/m²/K (0.2 to 0.9 BTU/hr/ft²/F) ƒ Operating temperature ƒ Above 100 °C (212 °F) ƒ Hydrostatic resistance ƒ Deeper than 100 m (330 ft) ƒ Crushing and creep during lifetime – use of P-I-P ƒ External impact resistance ƒ Handling or installation ƒ Thickness and density – net buoyancy ƒ Costs

Insulation applied to bundles, pipelines and risers has a number of competing limitations. Thermal conductivity can be quoted as a U-value, or, more usefully for a pipeline or riser, as a k-value. The former is based on area so requires a reference diameter for tubulars. This is usually the outside diameter of the steel, but can be the inside diameter or occasionally the outside of the insulation. The more logical k values are linear, defined along the length of the riser or pipeline. The best insulation can often achieve the values shown above. However, the other factors need to be taken into consideration. Lower U-values indicate better insulation. However, lightweight foams have very good thermal properties but are very poor at resisting collapse from the external hydrostatic pressure. They are also poor at resisting high operating temperatures. They require a pipe-in-pipe solution. It is possible to withstand operating temperatures greater than 100 q C (212 q F) but solid PU or PP, denser foam or syntactics may be needed for this. These materials have poorer insulation qualities.