水下采油树30CrMo钢/625合金异金属腐蚀机理试验研究

针对水下采油树在海水和内部流体长期作用下极易发生腐蚀的问题，借助高温高压反应釜，对流花11–1油田水下采油树的30CrMo钢/625合金的电偶腐蚀和堆焊金属腐蚀分别进行了腐蚀浸泡模拟试验，采用扫描电子显微镜和能谱分析仪分析了腐蚀产物膜的微观形貌和化学成分，并分析了30CrMo钢和625合金的异金属腐蚀机理。研究发现，水下采油树的30CrMo钢与625合金接触时，30CrMo钢易发生较严重的均匀腐蚀，且接触位置及堆焊焊缝处30CrMo钢存在较严重的沟槽腐蚀。水下采油树不同金属接触腐蚀的原因包括电偶腐蚀和缝隙腐蚀，堆焊修复后热影响区金相组织的不均匀性也会加剧缝隙腐蚀。研究结果表明，水下采油树应尽量避免不同金属接触形成异金属电偶腐蚀体系，修复已发生局部腐蚀失效的水下采油树时应合理选择堆焊材料并进行全覆盖堆焊，避免异金属腐蚀风险。 

An Experimental Study on the Heterometallic Corrosion Mechanism of 30CrMo Steel/625 Alloy for Underwater X-Trees

Underwater X-trees are prone to ongoing corrosion under the action of seawater and internal fluids. To address the problem, simulation experiments for the galvanic corrosion and surfacing metal corrosion of 30CrMo steel/625 alloy for the underwater X (Christmas) tree of the Liuhua 11–1 Oilfield were conducted by means of high temperature high pressure reaction kettle; the micromorphology and chemical composition of corrosion product film were analyzed by scanning electron microscope and energy spectrum analyzer, respectively, and analyzed the heterometallic corrosion mechanism of 30CrMo steel/625 alloy. The studies suggested that 30CrMo steel side of the heterometallic contact surface of the underwater X-tree was more likely to suffer a more severe uniform corrosion, and the 30CrMo steel at the contact position and the surfacing weld had more serious groove corrosion. The causes of heterometallic corrosion in the X-tree include galvanic corrosion and crevice corrosion. After surfacing repair, the unevenness of the metallographic structure in the heat-affected zone also exacerbates the crevice corrosion. The research results showed that the underwater?X-tree should try to avoid the heterometallic corrosion caused by the contact of different metals. Best practices now suggest that when repairing a underwater?X-tree with local corrosion failure, the surfacing material should be properly selected and adopted fully covered surfacing to avoid the risk of heterometallic corrosion.