Study On Protecting Technique For The Stray Current Corrosion

The stray current corrosion has puzzled shipbuilding industry for a long time over the world.Therefore, to study causes of the stray current corrosion, put forward a solving solution and avoid unnecessary losses, has important practical significance and application value.46000DWT vessels in Dalian Ship Yard suffered stray current corrosion. Based on this engineering practice, this thesis discusses the mechanism of stray current corrosion and electrostatic field theoretically, and finds out the causes of the corrosion by on-site observation and theoretical analysis, which are current leak and potential gradient. According to the causes, we propose methods by increasing the number of sacrificial anodes and using metal field plate respectively to protect vessels and offshore structures from stray current corrosion. Sacrificial anode cathodic protection has been applied widely in engineering, so this thesis doesn't study it any more. By using the model test and numerical calculation (BEM) , we verifies the effectiveness of the solution with a metal field plate.First, we design and make the equipment and establish electric field in the laboratory, which is causes by the stray current and have potential gradient, and then observe the potential changes before and after using the metal plate. By changing the material properties, geometric size, grounding mode of the metal plate, and the distance between the metal plate and positive electrode, we conduct several groups of tests in the laboratory respectively. Second, we model the electric field, which coincide essentially with the above tests by using BEM, verify the effectiveness of the method using metal shield plate to eliminate the potential gradient, and quantitatively calculate the influencing factors of the stray current corrosion.The results of the model tests and numerical calculation show that, using metal shield plate can eliminate the potential gradient and protect vessels from suffering stray current corrosion. And this thesis also makes clear the influencing factors of the stray current corrosion, and proposes the scheme to avoid stray current corrosion finally.