储罐底板阴极保护有效性及屏蔽行为研究

Study on Cathodic Protection Effectiveness and Shielding Behavior of Storage Tank Bottom Plate

储罐罐底板的腐蚀问题是影响储运安全的关键问题,目前常用阴极保护技术对储罐底板进行腐蚀防护。但是由于底板腐蚀、沉降以及施工等问题,底板与地面不可避免地存在缝隙,成为阴极保护的死角。针对储罐底板缝隙腐蚀及阴极保护屏蔽问题,自行构建矩形缝隙结构模拟储罐底板缝隙,根据电位测试和腐蚀形貌研究了阴极保护对缝隙腐蚀的影响,通过电位测试明确了缝隙对阴保电流的屏蔽作用,并进一步建立了缝隙内电位分布的预测模型。结果表明:缝口金属表现为全面腐蚀状态,而缝内金属为局部点蚀状态,当施加阴极保护后,增大了缝隙内外阴阳极的电位差,加剧了缝内金属的点蚀。在不同的阴极极化水平条件下,温度越高,缝隙结构对阴保电流的屏蔽作用越小。建立了缝隙电位分布模型,结果表明温度越低,外加阴保电位越大,外加阴保电流贡献度越小,矩形缝隙的屏蔽作用越大。

The corrosion of the bottom plate of storage tank is a key problem affecting the safe operation of storage tank,and cathodic protection technology is commonly used to protect the bottom plate of storage tank from corrosion.However,due to the corrosion,settlement and construction of the floor,there is inevitably crevice between the bottom plate and the ground,which becomes a dead corner of cathodic protection.Aiming at tank bottom plate crevice corrosion and cathodic protection shielding problem,a rectangular aperture structure simulating tank bottom plate crevice was built,in which the effect of cathodic protection on crevice corrosion was studied by potential test and corrosion morphology,and the shield effect of crevice on cathodic protection current was also researched.Finally,the model of potential distribution in the crevice was put forward.The results showed that the metal in the opening was in the general corrosion state,while the metal in the deepest crevice was in the local pitting corrosion state.When cathodic protection was applied,the potential difference between the inside and outside the crevice was increased,and the pitting corrosion of the deepest crevice in the seam was intensified.At different cathodic polarization levels,the higher the temperature was,the less the crevice structure shielded the cathodic current.The crevice potential distribution model was established,and the results showed that the lower the temperature was,the greater the external negative protection potential was,the smaller the contribution of external negative protection current was,and the greater the shielding effect of rectangular crevice was.