第六章防腐方法CorrosionControl 经典.pptVIP

第六章 防腐方法Corrosion Control It has been estimated that a quarter of all corrosion problems could be prevented easily by using well established techniques. By retarding either the anodic or cathodic reactions the rate of corrosion can be reduced. Various corrosion control measures are available, one or more of which might be appropriate. Three ways of Corrosion Control Conditioning the Metal This can be sub-divided into two main groups: Coating the metal, in order to interpose a corrosion resistant coating between metal and environment. Alloying the metal, to produce a more corrosion resistant alloy. Conditioning the Corrosive Environment Removal of Oxygen By the removal of oxygen from water systems in the pH range 6.5- 8.5 one of the components required for corrosion would be absent. Corrosion Inhibitors A corrosion inhibitor is a chemical additive, which, when added to a corrosive aqueous environment, reduces the rate of metal wastage. Electrochemical Control Cathodic and anodic protection This is the control of metal potentials to reduce the corrosion rate. It is suitable for immersed and underground conditions for plant, recirculatory systems and natural environments. This can be done by either using sacrificial electrodes or using an impressed current. 第一节 电化学保护Electrochemical Control 1.Cathodic Protection 1.History Davy found that he could preserve copper in seawater by the attachment of small quantities of iron, zinc or tin. The copper became, as Davy put it, “cathodically protected”. It was quickly abandoned because by protecting the copper its antifouling防污的 properties became retarded, reducing the streamline of the ships, as they began to collect marine growths. The most rapid development of cathodic-protection was made in the United States of America and by 1945, the method was well established to meet the requirements of the rapidly expanding oil and natural gas industry, which wanted to benefit from the advantages of using thin-walled steel pipes