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首页> 外文会议>Eurocorr 2004 >Corrosion under disbonded coatings of cathodically protected pipelines
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Corrosion under disbonded coatings of cathodically protected pipelines

机译：阴极保护管道剥离涂层下的腐蚀

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摘要

The literature survey addresses two types of corrosion that occurred under disbonded coatingsof cathodically protected buried pipelines. The data analysed refer mostly to the chemical andelectrochemical conditions in the crevice at disbonding. The important points of this survey isthe idea that anodically polarised zones can be found under disbonded coatings, in spite ofthe cathodic protection. Geometry of the crevice (length to gap ratio, stagnation or flow) andpermeability of the coating to oxygen are important parameters. Oxygen permeable coatings(such as polyethylene) and multiple holidays are capable of producing large corrosion rate atdisbonding of a certain geometry.On the basis of a literature survey and of numerous field observations, an experimental set upwas developed to provide a better access to local data on potentials, current densities, pH,local chemistry, corrosion rates and corrosion products inside the crevice formed by adisbonded coating. Some parameters considered in this study are : organic coatingimpermeable (polyester) and permeable (polyethylene) to oxygen, resistive and conductivebulk solution, purging or establishing a flow of solution in the crevice. Corrosion rate wasmeasured by sensitive electrical resistance probes that gave quasi-instantaneous corrosion rateand by weight loss (cumulated corrosion rate). The test set-up allowed direct visualexamination, sampling of small volumes of local solution for pH and chemical analyses andelectrochemical measurements (local potential and current densities).The major result is the detrimental effects of coatings permeable to oxygen (such aspolyethylene which as extensively used for buried pipelines at a time) and the renewal of thesolution in the disbonded crevice (by purging or by a continuous flow). In thosecircumstances, corrosion rates in the range of 0.5 mm/y were measured in out tests.
机译：文献调查研究了在阴极保护的地下管道的脱层下发生的两种腐蚀。所分析的数据主要是指剥离时缝隙中的化学和电化学条件。这项调查的重点是，尽管有阴极保护，但仍可以在剥离的涂层下找到阳极极化区。缝隙的几何形状（长宽比，停滞或流动）和涂层对氧气的渗透性是重要的参数。透氧涂层（例如聚乙烯）和多个假期可以在一定几何形状的结合下产生较大的腐蚀速率。在文献调查和大量现场观察的基础上，开发了实验装置以提供更好的本地数据访问权限电位，电流密度，pH，局部化学，腐蚀速率和由脱粘涂层形成的缝隙内部的腐蚀产物的相关信息。本研究中考虑的一些参数为：有机涂层对氧气的不渗透性（聚酯）和渗透性（聚乙烯），电阻性和导电性大块溶液，吹扫或在缝隙中形成溶液流。腐蚀速率通过灵敏的电阻探针测量，该探针给出准瞬时腐蚀速率和重量损失（累积腐蚀速率）。测试设置允许直接目视检查，少量局部溶液的采样以进行pH和化学分析以及电化学测量（局部电势和电流密度）。主要结果是可渗透氧气的涂层（例如聚乙烯）的有害影响一次埋入管道）和更新解开的缝隙中的溶液（通过吹扫或连续流动）。在这种情况下，在外部测试中测得的腐蚀速率为0.5 mm / y。

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