Marine Oil Jacket Platform Of Impressed Current Designing Optimization For Cathodic Protection

Our country has designed and built kinds of oil platforms in the 1980s. So far, there have been 600 platforms, and more than 95% those are fixed jackets. The sacrificial anode for corrosion protection method is widely used in the steel structure under offshore oil platform. For the large jacket with 200 meter depth in the South China Sea,1000 tons of sacrificial anode is needed. On the one hand, the consumption of sacrificial anode refining on energy and resource is so huge, the waste water, waste gas and waste residue generated from the smelting anode production process will cause serious pollution on the environment. On the other hand, sacrificing anodic dissolution releases large amounts of heavy metal ions, which will cause a potential ecological pollution on Marine. If the impressed current method is adopted, the above problems will disappear. This topic starts with the ocean oil jacket 200 meters depth as a prototype to carry out optimization design for impressed current cathodic protection in the South China Sea.There are many installation methods of impressed current, we roughly divided them into the far type auxiliary anode system, tensile auxiliary anode system and fixed auxiliary anode system. The remote type anode system construction is simple, convenient installation, and especially suitable for the depth ocean oil jacket platform in corrosion control. The far type auxiliary system is not only suitable for the old platform prolong for their lives, but also suitable for the new platform in cathodic protection.The methods of impressed current cathodic protection system design optimization are numerical simulation and shrinkage ratio model. Numerical model method is more convenient, it only needs to change the designed model in computer, and the designing optimization for the model can be realized. But the calcium sediments deposition and coverage on the steel surface in the Cathodic polarization process are dynamic, so the cathode surface potential and current density function in the boundary conditions will be constantly changing over time. If only at a certain moment based on potential and current density function to describe the whole process of cathodic polarization, the results will not be able to guarantee the reliability and credibility. However, the shrinkage ratio model does not exists the above shortcomings, and shrinkage ratio model can copy the complex geometry platform, at the same time it does not use any electrochemical data of polarization curve of the materials, saving time and reducing cost and so on. This experiment start with the ocean oil jacket platform of South China Sea 200 meters water depth as a prototype to build a 100:1 shrinkage ratio model, at the same time put a single seat far type auxiliary anode or double seat far type auxiliary anode, through changing the relative position or the angle of the auxiliary anode in the jacket platform to carry out design optimization of cathodic protection.This article main research conclusion includes:1) Under the stationary and the flowing state in the seawater, single seater far type auxiliary anode can realize the corrosion control of the entire jacket platform for South China Sea 200 meters depth of the water jacket model simulation.2) When single seater auxiliary anode and double seater ipsilateral auxiliary anode moves to the model, the surface electrical potential first decreased and then increased, presenting "U" shape. But double seater lateral side and double seater longitudinal side jacket optimization design model, as the auxiliary anode move to the model, the surface electrical potential gradually increase.3) When carry out impressed current cathodic protection optimization design for jacket model, the bigger protection current, the greater the model surface electrical potential, meaning the potential distribution in the model surface is uneven, proning to overprotection and none protection problems; On the other hand, using the small protection current, the potential distribution presents uniformity.4) When auxiliary anode moves to jacket model from far to near, the the different regions of the model surface are affected, the protection potential will change. But a different position influence degree is disparity, the biggest polarization area has the greatest influence, the opposite is minimal.5) Under the same protection current density, the surface electrical potential jacket model in double auxiliary anode is small than a single seat auxiliary anode, the potential distribution is more uniform.