Influence of corrosion of buried metal facilities on cathodic protection

Nowadays, joint protection method is widely used to prevent corrosion of underground metal facilities in power plants. Joint protection refers to cathodic protection and coating protection for protected facilities at the same time. In the process of joint protection, people often only pay attention to the monitoring of cathodic protection, but ignore the detection of coating defects.


In fact, the underground metal facilities with anticorrosive coating are buried underground for a long time. After a period of use, the anticorrosive coating will fail. This is mainly because the coating continuously absorbs moisture from the soil in the process of use, which leads to the moisture absorption of the coating, and the soil stress and biodegradation will lead to the coating failure. For example, after absorbing moisture, the anticorrosive coating will obviously reduce its mechanical properties and be more vulnerable to soil stress damage. In the process of use, the adhesion between the coating and the substrate will also decrease, so there will be a variety of coating defects, such as blistering, cracking, peeling and so on.


In addition, the anticorrosive coating of underground metal facilities may be damaged in the process of transportation, installation and burying. Once the anticorrosive coating is peeled off or damaged, it will have adverse effects on cathodic protection.


Under the condition of cathodic protection, if the anticorrosive coating has peeling off, it can still cause the corrosion of the substrate. When the anticorrosive coating is damaged, such as the anti-corrosion coating beside the pinhole does not adhere to the pipe wall, cathodic protection shielding will occur.


Even if all exposed metal tube walls are protected by cathodic protection, the cathodic protection current still cannot reach the exposed metal just below the stripping layer. That is to say, when the anticorrosive coating is peeled off, the moisture in the soil can penetrate into the non stripped coating, forming local corrosion cell on the metal surface, and this corrosion process will not be controlled by cathodic protection. This is mainly because the total resistance of the interface between the coating and the metal will increase when the coating is peeled off, which hinders the cathodic protection current. At this time, the pipe ground potential of cathodic protection only reflects the situation of bare pipeline at the stripping position, and cannot truly reflect the original state of stripping.


Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing cathodic protection technology, engineering design, installation and technical services.