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15 NACE INTERNATIONAL: VOL. 56, NO. 4 MATERIALS PERFORMANCE APRIL 2017 The FPSO model shows the sacrificial anodes on the chain connectors and turret. Photo courtesy of BEASY. Continued on page 16 be based on the design code used, or based on damage experienced at similar structures. The simulation starts at year zero and predicts the protection provided to the structure and the current delivered by the individual anodes. The simulation continues step by step, calculating at each step the consumption of the anodes (and the reduction in size)— including the assumed degradation of coatings until the design life is reached. If the anode is consumed during the simula- tion, it is determined that it no longer contributes to the protection of the struc- ture. During the time-stepping process, the ICCP settings are adjusted to main- tain the protection potentials at the set point as the structure ages. In this way, the model simulates the actual behavior of the ICCP system. One recent project used a modeling study from the software package to verif y that its CP system met the design goals. The study 3 involved an offshore develop- ment based on an FPSO unit w ith f low lines and subsea systems. Protection was prov ided by an ICCP system, and certain structures and appendages were pro- tected by sacrif icial anodes—located on the chain connectors, moon pool, and turret. One of the factors considered in the design is the inability to guarantee elec- trical continuity between the chain con- nectors and the turret. As a result, an electrical resistance between the chains and the turret is factored in. In the FPSO case study, the simulation provided data on the CP protection pro- vided to the FPSO structures over time and the consumption of individual anodes. With this information, areas where protection may not be maintained and imbalances in the anode consump- tion could be identif ied and used to improve and optimize the design. Model predictions of the protection were generated, thus enabling the vessel's start, mid-life, and end-life potentials to be viewed. These models demonstrated a decrease of protection, which occurs as the asset ages. The model showed that at the end of life, the requirement that pro- tection potentials be more negative than –950 mV could not be satisf ied. The model also showed accelerated consumption of sacrif icial anodes on the chain connectors. This accelerated con- sumption was caused by interference cur- rents from the ICCP system which, due to resistance between the chain connector and turret, created an IR drop between these components. This resulted in stray current from the anodes on the chain connector, and accelerated mass loss as a result. The model predictions of anode depletion can also be useful for integrity management of the vessel, and in www.FarwestCorrosion .com Rectifiers Anodes Reference Electrodes Coatings Backfill Test Instruments Casing Fillers Remote Monitoring Isolators C.P. Engineering C.P. Installation 9 Locations Nationwide 888-532-7937 The Most Complete Corrosion Prevention Site on the Web And More... Use Your Smart Phone to Visit Our Website... Information on corrosion control and prevention