The offshore subsea pipelines transporting well fluids require thermal insulation to gain the synergy between efficient mechanical design and thermal performance of the flowlines. This heat loss minimisation becomes a primary requirement for offshore fields with demanding hydrate formation requirements. Usually, the rigid pipelines will be designed as thermally efficient single pipelines with wet insulation coatings or pipe-in-pipe systems with dry insulation between the inner and outer pipes, but the connecting spools/jumpers in both the rigid pipeline systems will be designed with wet insulation coating thickness reaching many multiples of pipeline steel thickness. The technical challenges become more pronounced as the subsea pipeline development reaches deeper water with higher pressure and temperature requirements. Subsea rigid pipeline systems wet insulation coatings include Polyethylene, Polypropylene, and Polystyrene based coating systems.

Some operator-specific design guidelines require for the pipelines with wet insulation coatings, the magnified effect of hydrostatic pressure as the external pressure to be used in local buckling (collapse and combined), and propagation buckling calculations on the pipelines and spools. As per this premise, the thicker the wet insulation coating, the higher the pressure magnification factor. This approach will increase the required steel wall thickness compared to the case without such effects. The available methods for such assessment include analytical methods (Lame, Love, OTC 11042 methods) and numerical FE methods. The objective of the paper is to show the comparison of the analytical and numerical methods in the calibration of the external hydrostatic pressure magnification factor (HPMF) at the steel and coating interface.

This paper shows the benefit of using FE based approach for the pressure magnification factor assessment which shows that the magnification factor due to wet coatings is negligible. This behavior is attributed to FEA capturing the stiffness contributions of coatings accurately in the resistance calculations compared to analytical formulations.