Numerical Investigation on Cathodic Protection of X80 Pipeline Steel in Marine Environment

Abstract Submarine pipelines are usually buried in sea mud, but part of the pipes will be exposed to seawater directly because of the change of seabed, the differences between sea mud and seawater result in different corrosion states. Generally, due to its large geometric size, complex medium, difficult to detect and other reasons, corrosion defects will cause greater harm to pipeline materials. A numerical analysis model of the outer surface corrosion of submarine pipelines was developed to simulate status of cathodic protection, furthermore, potential distribution and local density of current inside the defects was also analyzed and evaluated. The results indicates that: (1)The CP potential distributes more evenly in sea mud when the same sacrificial anode is used, and the cathodic protection current density needed to meet the anti-corrosion requirements is much larger in seawater than in sea mud.(2)Compared with sea mud, the polarization potential of the sacrificial anode in seawater is more negative, and the CP potential at the edge of anodes is the most positive in both sea mud and seawater. Furthermore, in seawater, the dissolution rate of sacrificial anodes closer to the seabed is lower, and anodes dissolve much faster at the inner surface, while it is just the opposite in sea mud.(3)Cathodic protection cannot ensure complete and effective protection at defect points. At defect bottom, the cathodic protection current is partially shielded, reducing the effectiveness of CP system on corrosion protection of pipelines. Moreover, the shielding effect of defect point on cathodic protection current has a great deal with the geometric shape of defect points, with decreasing width and increasing depth, the shielding phenomenon becomes more obvious.(4) Numerical simulation technique based on the finite element model provides a new method to solve this problem and plays a positive role in assessing anti-corrosion status and the service life of anodes.