Abstract
The production fluids from the reservoirs of the Ichthys Gas Field, located 220 kilometers offshore from the North West coast of Western Australia in average water depths of 250 m, will be gathered using a number of 18" production flowlines, with a design temperature of 135°C. The flowlines are between 10 and 16 km long and are insulated with high integrity multi-layer polypropylene (MLPP) coating and injection moulded polypropylene (IMPP) field joints. Standard subsea pipeline corrosion protection utilizing bracelet anodes poses risk of water ingress at the anode connection points which could compromise the integrity of the coating. To mitigate this risk, secondary corrosion protection was designed to utilize anodes only on the inline structures in the system and on anode skids at discrete locations along the flowlines. This paper presents a system approach for manual calculation of the attenuation along the flowline sections assuming uniform and localised coating damage scenarios. The solution is compared with boundary element analysis results and used to demonstrate that all the flowlines have sufficient protection potentials for a 40-year design life.
