利用动电位扫描(PDS), 电化学阻抗谱(EIS)和线性极化电阻法(LPR), 研究了石英砂沉积物覆盖下的X65管线钢在含氧盐溶液中的腐蚀行为及有机膦缓蚀剂乙二胺四亚甲基膦酸钠(EDTMPS)的作用效果. 通过丝束电极(WBE)对沉积物所导致的电偶效应进行了测试. 结果表明, 沉积物覆盖下的X65钢平均腐蚀速率变缓, 但伴随有局部腐蚀发生. 在溶液中加注35 mg/L的EDTMPS后, 裸露的X65钢电极的腐蚀速率在3 h内由0.17 mm/a降低并稳定在0.082 mm/a, 沉积物覆盖下的X65钢电极在6 h内腐蚀速率由0.051 mm/a降低到0.026 mm/a并保持稳定, EDTMPS对裸钢和沉积物覆盖下的碳钢均有良好的缓蚀效果. WBE电偶效应测试结果表明, 沉积物覆盖区域电位较低, 表现为阳极区并伴随有严重的局部腐蚀发生. 在注入35 mg/L缓蚀剂后, WBE平均电位迅速下降, 阳极区域逐渐减小, 在加入EDTMPS缓蚀剂24 h后, 最大阳极电流密度和阳极总电流分别从0.21 mA/cm²和0.056 mA降低至0.078 mA/cm²和0.021 mA. 监测数据表明, EDTMPS对沉积物覆盖所引起的电偶效应也有一定的抑制作用.

Localized corrosion such as pitting and mesa attack caused by the presence of solid deposits on a metal surface is defined as under deposit corrosion (UDC). UDC is frequently observed in oil and gas transition pipelines where sand, debris biofilm and carbonate deposit are present. Studies have found that the introduction of oxygen would accelerate the galvanic corrosion behavior between the deposit covered area and the area without deposit. Some experiments have been carried out and demonstrated that high concentration inhibitor should be used for the migration of UDC. However, the inhibition effect of the organic phosphonic inhibitor for UDC is rare in the previous studies. In this work, the evaluation of UDC behavior of X65 pipeline steel and the performance of corrosion inhibitor Ethylene Diamine Tetra (Methylene Phosphonic Acid) Sodium (EDTMPS) in the oxygen contained solutions are studied by using polarization dynamic scan (PDS), electrochemical impedance spectra (EIS) and linear polarization resistance (LPR) methods. The galvanic effect caused by the deposit is studied by using wire beam electrode (WBE). The measurement results show that the corrosion rate of deposit-covered electrode is lower than that of bare electrode, but localized corrosion is observed on the deposit-covered steel surface. After 35 mg/L EDTMPS is introduced into the solution, the corrosion rate of the bare steel decreased from 0.17 mm/a to 0.082 mm/a and the corrosion rate of the deposit covered electrode decreased from 0.051 mm/a to 0.026 mm/a. Protective films are observed on both deposit covered steel surface and bare steel surface after EDTMPS added. In the galvanic corrosion monitoring experiment by using WBE, the under deposit area has a lower potential and performs as the anodic area with serious localized corrosion. After 35 mg/L EDTMPS is injected, the average potential begins to decrease. The maximum anodic current density and the total anodic current respectively decrease from 0.21 mA/cm² and 0.056 mA to 0.078 mA/cm² and 0.021 mA. The electrochemical measurement results reveal that EDTMPS has an excellent inhibition effect for the corrosion of both bare electrode and deposit covered electrode. The WBE test illustrates that EDTMPS also has an inhibition effect on the galvanic corrosion caused by the covering deposit. However, EDTMPS cannot completely prevent the localized corrosion behavior on WBE surface.