不同環(huán)境介質(zhì)中X70鋼的交流腐蝕行為及腐蝕產(chǎn)物膜層分析

不同環(huán)境介質(zhì)中X70鋼的交流腐蝕行為及腐蝕產(chǎn)物膜層分析INVESTIGATION ON AC-INDUCED CORROSION BEHAVIOR AND PRODUCT FILM OF X70 STEEL IN AQUEOUS ENVIRONMENT WITH VARIOUS IONS

通過交流腐蝕模擬實(shí)驗(yàn)考察了X70鋼在4種環(huán)境介質(zhì)中的交流腐蝕行為，獲得了X70鋼在4種介質(zhì)中的腐蝕速率Kd。結(jié)果表明，腐蝕速率Kd (NaCl)＞Kd (Na2SO4)＞Kd (CaCl2)＞Kd (MgCl2)。采用SEM、EDS和XRD對(duì)腐蝕產(chǎn)物膜的表面/截面微觀形貌、元素和物相成分進(jìn)行了表征與分析，探討了X70鋼在相同交流電流密度下，不同介質(zhì)中腐蝕速率差異的原因：在Na2SO4和NaCl介質(zhì)中，腐蝕產(chǎn)物膜比較疏松，侵蝕性離子SO42-和Cl-的存在會(huì)加速X70鋼的腐蝕，Na+不會(huì)影響腐蝕產(chǎn)物膜的形成；在MgCl2和CaCl2介質(zhì)中，Ca2+和Mg2+的存在有利于形成保護(hù)性好的致密腐蝕產(chǎn)物膜。

During the past decades, more buried oil or gas pipeline failures have been attributed to AC interference, and finally, those corrosion failures were investigated and the AC current density was identified as the critical influence parameter. There is general agreement on AC current density as a chief factor in determining metal wastage condition or assessing the AC corrosion risk for any type of soil in the presence of AC corrosion. Different degrees of AC corrosion may occurred if long distance pipelines pass through different kinds of soil environment, however, the effect of soil ions on pipeline steel without cathodic protection is still not well understood. Therefore, it is imperative to study the AC corrosion behaviors of pipeline steel in different soil environment. In the AC corrosion simulation experiment, by investigating the AC corrosion behaviors of X70 steel in 4 kinds of environmental media, the corrosion rates ( Kd ) were obtained, whose order was Kd (NaCl) > Kd (Na2SO4) > Kd (CaCl2) > Kd (MgCl2). SEM, EDS and XRD were used to characterize and analyse the microscope morphologies, elements and phase compositions of the corrosion product films surfaces/cross-sections. Under the same AC　current density, the reasons of differences of　X70 steel’s corrosion rate in different media were discussed. The presence of corrosive ions SO42- and Cl- would accelerate the corrosion rate, Na+ would not affect the formation of corrosion product film in NaCl and Na2SO4 solution media, however, the presence of Ca2+ and Mg2+ were helpful to form protective corrosion product films in MgCl2 and CaCl2 solution media.

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