杂散电流对剥离涂层下金属腐蚀行为影响的研究

发布时间：2018-03-01 09:29

本文关键词： 交流杂散电流直流杂散电流阴极极化剥离涂层剥离深度　出处：《中国民航大学》2017年硕士论文　论文类型：学位论文

【摘要】：目前,埋地管线通常采用防腐层和阴极保护联合防止其腐蚀。当防腐层存在缺陷失效时,容易与金属基体形成剥离缝隙,土壤中的腐蚀性介质通过缺陷口进入缝隙,使剥离区金属发生严重腐蚀。对于管道的实际敷设环境来说,大地中广泛存在着杂散电流,而杂散电流的流入势必会对剥离涂层下埋地管道的腐蚀行为产生更加不利的影响。本文采用矩形涂层剥离模拟装置利用电化学方法进行了有无阴极极化时杂散电流对剥离涂层下金属腐蚀行为影响的实验研究,通过测试杂散电流存在时剥离缝隙内金属各点的极化曲线和电化学阻抗谱(EIS),并观察缝内金属的腐蚀形貌,分析杂散电流对剥离涂层下金属腐蚀行为的影响规律,结果表明:(1)自然腐蚀状态下,在相同实验时间内,剥离缝隙内金属的自腐蚀电位随着涂层剥离深度的增加有先正移再负移的趋势,腐蚀电流密度有先减小再增大的趋势;施加阴极极化后,剥离缝隙内金属的自腐蚀电位比未进行阴极极化时明显负移,且腐蚀电流密度明显变小,阴极极化能使剥离涂层下金属得到一定保护;当阴极极化电位为-1.0V时,剥离涂层下金属的保护深度达到最大值为90mm,且该极化电位下剥离缝隙内金属的腐蚀电流密度较小,对缝内金属的保护效果较好。(2)有交流杂散电流存在时,剥离缝隙内金属的自腐蚀电位变化幅度比自然腐蚀状态下要大,缝内金属的腐蚀电流密度比自然腐蚀状态下也大很多;当交流干扰为1V~5V时,无论有无阴极极化,剥离缝隙内金属的腐蚀速度均较低;当阴极极化电位为-1.2V时,剥离涂层下金属的保护深度达到最大值为80mm,且该极化电位下剥离缝隙内金属的腐蚀电流密度较小,相比于其他阴极极化情况极化电位为-1.2V时对缝内金属的保护效果较好。(3)有直流杂散电流存在时,当干扰电压小于3V时,剥离缝隙内金属在施加阴极极化后的腐蚀电流密度均小于未进行阴极极化时的腐蚀电流密度,且在极化电位-0.9V~-1.2V的范围内,剥离缝隙内金属所受到的保护程度是相同的;当干扰电压较大(≥3V)时,极化电位为-1.0V和-1.2V时剥离缝隙内金属的腐蚀电流密度较小,金属的腐蚀速度较为缓慢;在直流干扰1V~10V范围内,当阴极极化电位为-1.2V时,剥离涂层下金属的保护深度能够达到最大值为80mm,相比于其他阴极极化情况极化电位为-1.2V时对缝内金属的保护效果较好。综上所述,无论腐蚀体系是否被阴极极化,杂散电流干扰下剥离涂层下金属的腐蚀均比缝内金属的自然腐蚀严重的多;交流杂散电流与直流杂散电流的存在均减小了剥离缝隙内金属在不同阴极极化电位下的保护深度,将极化电位适当的负移会增加缝内金属的保护效果;除直流干扰为1V外,直流杂散电流下剥离涂层下金属的腐蚀速度要远大于交流杂散电流;施加阴极极化后,阴极极化能够明显增强交流杂散电流腐蚀下剥离缝隙内金属各点的耐蚀性,保护效果要强于直流杂散电流腐蚀。
[Abstract]:At present, anticorrosive coating and cathodic protection of buried pipeline is usually used to prevent the corrosion of joint defects. When failure of anticorrosion layer, easy to form stripping gap with the metal corrosion in the soil through the mouth into the defect gap, the stripping area of serious corrosion of metal. The actual environment in pipeline laying, widespread land a stray current, and the inflow of stray current will inevitably have a more negative impact on the corrosion behavior of buried pipelines under disbonded coating. This paper uses the rectangular coating stripping simulation device by electrochemical method were no experimental study on the effect of stray current on Corrosion Behavior of metal coatings under cathodic polarization when stripping, stripping the metal gap the polarization curves and electrochemical impedance spectroscopy test by stray current time (EIS), and to investigate the corrosion of metal in the gap, the analysis of stray current Effect of metal corrosion under disbonded coating results showed that: (1) natural corrosion condition, in the same experimental time, peeling off the metal inside the crevice corrosion potential with the coating stripping depth increased the positive shift again negative shift of the trend, the corrosion current density first decreases and then increases again; cathodic after polarization, peeling off the metal inside the crevice corrosion potential than the cathodic polarization obviously negative shift, and the corrosion current density decreases obviously, the cathodic polarization of the metallic coating obtained under certain peeling protection; when the cathodic potential is -1.0V, the depth of the protection of metal release coating reached the maximum value of 90mm, corrosion current the density is smaller and the polarization potential stripping gap metal, good protection effect on the metal. (2) the existence of AC stray current, the metal peeling inside the crevice corrosion potential amplitude ratio However, the corrosion condition should be large, the corrosion current density in metal joints than natural corrosion condition also is much larger; when the AC interference is 1V~5V, regardless of whether the cathodic polarization, the corrosion rate of metal strip in the gap was low; when the cathodic potential is -1.2V, the depth of the protection of metal release coating reached maximum the value of 80mm, the corrosion current density is smaller and the polarization potential stripping gap metal, compared to the other conditions for the protection of cathodic polarization potential effect on the metal in the good -1.2V. (3) the existence of stray current, when the interference voltage is less than 3V, the corrosion current density of metal stripping gap in applied after cathodic polarization was less than the corrosion current density without polarization, and the polarization potential of -0.9V~-1.2V within the range, degree of protection by the metal stripping gap is the same; when the interference voltage is Large (more than 3V), -1.0V and -1.2V when the polarization potential of the metal stripping crevice corrosion current density is small, the metal corrosion rate is relatively slow; in DC interference in the range of 1V~10V, when the cathodic potential is -1.2V, the depth of the protection of metal release coating can reach the maximum value of 80mm, compared to other cathode polarization polarization potential for the protective effect of the metal in the -1.2V on the better. In summary, regardless of whether the corrosion system of cathodic polarization, stray current corrosion under disbonded coating of metal was more serious than natural corrosion of metal in the gap; AC stray current and DC stray current are reduced to protect the metal stripping gap depth in different cathodic polarization potentials, the appropriate polarization potential negative shift will increase the protective effect of joint metal; except for 1V interference of DC, DC stray current release coating The corrosion rate of the underlying metal is much larger than that of the AC stray current. After cathodic polarization is applied, cathodic polarization can significantly enhance the corrosion resistance of the metal points in the stripping gap under AC stray current corrosion, and the protection effect is stronger than the DC stray current corrosion.

【学位授予单位】：中国民航大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE988.2

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