FPSO Stray Current Interferences

Whenever impressed current is used offshore it is important to be aware of potential interference sites. In certain instances, cathodic protection currents can be picked up inductively on steel surfaces and subsequently discharged back through the seawater to another part of the structure. At the point of discharge localized corrosion can result. In order for this to occur the affected structure must be within the field gradient of the anode, and must be either electrically isolated or be connected through a high resistance path to the main cathodically protected structure. A good example of this is pipelines associated with fixed platforms, location of impressed current anodes must be such that the isolated pipelines do not lie within the close field of the anodes, otherwise there is a risk of current jumping from the pipeline riser to clamps attached to the structure. On an FPSO, this risk may exist on mooring components close to the hull, or on mechanical couplings associated with the risers within the turret structure. Modeling of anticipated voltage gradients at maximum rated anode output will facilitate prediction of potential problems.

Adapted from Cathodic Protection Strategies for FPSO's Jim Britton