FPSO工艺水舱阳极快速消耗原因分析

Reasons for Rapid Consumption of Anodes in Process Water Tank of FPSO

目的研究FPSO工艺水舱中铝牺牲阳极消耗过快的原因。方法参照GB 17848—1999牺牲阳极电化学性能试验方法,对比水舱环境与普通环境下,在役阳极的电化学性能数据,并模拟水舱环境,监测阳极工作时实际的发生电流与工作电位等情况,据此分析牺牲阳极在工艺水舱中消耗过快的原因。结果在常温(25℃)、常温充空气、高温(65℃)充空气等条件下,阳极的电化学容量分别是2522.07、2464.29、1943.74Ah/kg,且高温(65℃)充空气环境下阳极的晶间腐蚀较其他两组试验严重许多,说明温度是影响阳极电化学容量的关键因素。在模拟工艺水舱环境下,实测的阳极发生电流最高可达100m A。将工艺水与海水1:5稀释后,实测的保护电流密度最高达45m A,说明工艺水中存在大量的去极化剂,是造成阳极快速消耗的又一重要因素。结论工艺水舱环境下,阳极发生严重的晶间腐蚀,严重影响了阳极的电化学容量,使阳极寿命缩短。工艺水成分中含大量去极化剂,使船舱所需的保护电流密度大大增加,促使阳极发生电流加大,亦缩短了阳极的实际服役寿命。

Objective To research the reason for rapid consumption of sacrificial anodes in process water tank of FPSO. Methods According to the test methods in national standard 17848-1999, through comparing water tank environment and common environment, the water tank environment was simulated based on data on electrochemical performance of anode on active service to monitor current and potential of the anode during working, to analyze the reason why the anodes in process water tank are consumed so fast. Results The electrochemical capacities of the anode were 2522.07, 2464.29 and 1943.74Ah/Kg respectively in 25 degrees Celsius, 25 degrees Celsius with air inflation and 65 degrees Celsius with air inflation. Besides, the intercrystalline corrosion of anode was the most serious in 65 degrees Celsius with air inflation. It showed that the temperature was the key factor that influenced electrochemical capacity. In the simulated process water tank environment, the anode current could go to 100 mA, but in diluted process water, one liter of process water was mixed with 5 liter of seawater, it only went to 45mA. It showed the process water contained plenty of depolarizer, which was another important factor for rapid consumption of the anode. Conclusion In the process water tank environment, the anodes has serious inter-crystalline corrosion which greatly affects the electrochemistry capacity of the anode and shortens its service life. The plenty of depolarizer in the process water increases the protection current density required by the cabin, increase the current anode and shortens the actual service life of the anode。