Abstract
An offshore jacket complex from the late sixties consisting of 5 platforms is protected by a conventional sacrificial anode system. Recent surveys have indicated that extending end service life with a minimum of 20 years requires a significant retrofit effort in the near future. Since replacement of individual anodes on a like-for-like basis would be very expensive, a retrofit option based on remote impressed current anode sleds was considered offering very considerable cost savings.
Remote ICCP anode sleds are relative easy to install but the design of such a CP system is more challenging. Correct positioning of the sleds is critical for obtaining proper protection and avoiding overprotection. In this particular project the availability of target locations was limited because of various subsea pipelines connected to the platforms and two large jack-up zones that should remain accessible.
The feasibility of using an ICCP system was therefore investigated through computational modeling. First the as-is CP status of the complex was simulated taking into account the current condition of the sacrificial anodes as observed during the latest survey. Secondly, an ICCP system was included in the model and different anode sled positions were investigated until an optimal design was obtained. The remaining life of the anodes was re-calculated such that the amount of anode sleds was kept to a minimum. Through modeling the CP effectiveness of the combined system was validated and a cost-effective solution was proposed.
