电解法处理船舶压载水对舱体用钢腐蚀行为的影响

来源期刊：金属学报2010年第9期

论文作者：刘光洲 王建明 张鉴清 曹楚南

文章页码：1093 - 1097

关键词：压载水； 电解处理； 低碳钢； 腐蚀； 电化学方法

Key words：ballast water； electrolytic treatment； low carbon steel； corrosion； electrochemical method

摘    要：采用开路电位-时间和电化学阻抗谱等测量方法,研究了3.5%NaCl水溶液中总余氯(TRC)含量对船用低碳钢Q235腐蚀行为的影响.结果表明,舱体金属腐蚀可以分为表面迅速氧化,表面形成氧化物覆盖层,覆盖层发生破损导致腐蚀3个阶段.TRC含量较低(如5和10 mg/L)时,压载舱壁金属的腐蚀略有增强.而当TRC含量较高时(如20 mg/L),则可以促进舱体金属表面钝化并形成致密腐蚀产物而堵塞氧化物覆盖层的破损,致使舱体金属的开路电位提高,电荷传递电阻增加,使舱体金属的抗腐蚀能力增强.电解法压载水处理在杀灭水生生物的同时对于压载舱壁金属腐蚀而言是安全的,且较高的TRC含量在提高杀灭效率、缩短杀灭时间的同时,并不会导致严重的舱壁金属腐蚀.

Abstract: In order to regulate discharges of the ships’ ballast water and reduce the risk of non-native species introduced from the ballast water,the international maritime organization (IMO) has developed international legislation,the ships’ ballast water should be treated before discharge, and electrolysis has been developed as a promising method for ballast water treatment.However, the oxidative species such as Cl₂,HClO and NaClO generated during electrolytic treatment may not only kill the non-native aquatic species but also accelerate the corrosion of the ballast tank steel. In this paper,the effect of the total residual chlorine (TRC) concentration in 3.5%NaCl solution on the corrosion of Q235 steel was studied using mainly the open-circuit potential-time measurement (E_OC-t) and electrochemical impedance spectroscopy (EIS).Four TRC concentrations,0,5,10 and 20 mg/L,which are around the concentration proved to be effective for removal of non-native aquatic species,were tested.Both the E_OC-t and EIS results suggested that the corrosion of the Q235 steel in 3.5%NaCl solution with or without TRC can be divided into three stages:rapid oxidation of steel, coverage of metal surface by oxide film,and breakdown of the oxide film and initiation of corrosion. The negative shift of E_OC and reduction of charge-transfer resistance (R_ct) of the steel immersed in the solutions containing low TRC concentrations such as 5 and 10 mg/L demonstrated that the corrosion of steel is slightly enhanced.The enhancement of corrosion is due to the increase of the depolarization concentration present in the solutions.But for solution with higher TRC concentration such as 20 mg/L,both the E_OC and R_ct increased,suggesting retardation of the corrosion process.The retardation of corrosion can be attributed to the passivation of the steel surface due to the strong oxidation of the active species and the formation of compact corrosion product that covers the corrosion sites.This means that increasing TRC concentration to 20 mg/L does not accelerate the corrosion of the tank steel. Therefore,higher TRC concentration for on-board electrolytic treatment is allowable,which is beneficial for shortening the treating process and improving the removal efficiency.