酸性湿气腐蚀中O2与H2S交互作用机制

O2-H2S coexisting acid humidity corrosion occurred in some industrial fields, such as cargo oil tanks of crude oil tankers, storage tankers and nature gas pipelines etc. We found that corrosion scale formed in such environment was composed of several substances, including iron oxyhydroxide, iron oxide, iron sulfide and elemental sulfur etc., and corrosion scale had a close relation with corrosion rate and corrosion morphologies, which indicated that there existed an interaction between O2 and H2S in acid humidity corrosion. The application aims to investigate corrosion mechanism in H2S system and O2 system as well as O2-H2S coexisting system, and further to establish the correlation among gases contents, substances and structures of corrosion scale, corrosion rate and corrosion morphologies in O2-H2S coexisting acid humidity environment, by thin condensate film corrosion experiment in acid humidity environment, including thin condensate film condition change experiment by dry-wet transformation, and analyzing substances and structures of corrosion scale as well as electrochemical performance by several methods. The research results have important theoretical significance in clarifying the interaction mechanism between O2 and H2S in acid humidity corrosion, and can furthermore provide theoretical support to corrosion control and corrosion resistant steels development in the corrosive environments, such as cargo oil tanks of crude oil tankers et al.

原油船货油舱、储罐和天然气管线等工业领域中存在O2和H2S共存的酸性湿气腐蚀环境。我们研究发现在这种环境中形成的腐蚀产物由羟基氧化铁、铁氧化物、铁硫化物及元素硫等多种物质组成，该腐蚀产物与钢的腐蚀速率和腐蚀形态之间存在密切的联系，这表明这种酸性湿气腐蚀中存在着O2和H2S的交互作用。本项目通过酸性湿气薄液膜腐蚀实验，利用干湿交变改变薄液膜状态，采用多种方法对腐蚀产物组成结构及腐蚀电化学性能测试分析，研究酸性湿气H2S体系和O2体系及O2和H2S共存体系的腐蚀机制，探索O2和H2S共存条件的气体含量、腐蚀产物的组成结构、腐蚀速率和腐蚀形态之间的相关性。研究结果对阐明酸性湿气腐蚀中O2与H2S交互作用机制有重要的理论意义，为原油船货油舱等环境腐蚀控制及耐蚀钢的开发奠定理论基础。

在原油船货油舱储运及石油天然气管线钢运输中，O2和H2S酸性湿气腐蚀是普遍存在的，其严重影响原油船及输油管线的安全和服役寿命。本项目对合金钢在O2与H2S酸性湿气环境下进行腐蚀模拟实验，旨在研究钢的腐蚀机理与锈层演变机制：（1）研究了酸性湿气腐蚀环境中O2含量对腐蚀锈层的影响机制。酸性湿气腐蚀环境中，较高O2含量可增加锈层中非晶态产物含量，降低锈层中晶态产物的含量。5vol%O2腐蚀条件下锈层的比表面积有很大的增长，其对腐蚀性粒子扩散有更高的阻碍作用。锈层中的非晶成分能够有效提高锈层致密性、锈层电阻Rrust和电荷转移电阻Rct；（2）研究了酸性湿气腐蚀环境中H2S含量对腐蚀锈层的影响机制。酸性湿气腐蚀环境中，锈层的物相组成随着H2S含量的升高变得复杂。硫化氢含量低时，锈层疏松多孔易脱落。随着H2S含量的升高，锈层出现分层，锈层厚度升高和内部锈层致密度增强，锈层内部氧含量升高，并且锈层保护性能降低；（3）研究并明确了干湿交替酸性湿气环境中腐蚀锈层演变机制。在干湿交替酸性腐蚀过程中，锈层比表面积(SSA)随腐蚀时间增加而增加。腐蚀过程中，当锈层SSA低于临界值时，腐蚀电流随腐蚀时间增加而增加。当锈层SSA达到临界值时，锈层由单层膜向双层膜结构转变，且内层膜中γ-FeOOH含量随腐蚀时间逐渐降低；（4）研究并提出了酸性湿气O2和H2S共存对腐蚀速率和腐蚀形态影响机制。在O2-H2S环境下，腐蚀初期钢基体表面生成一层以马基诺矿为主要成分的腐蚀产物薄膜。随着腐蚀产物的进一步沉积，锈层对粒子扩散的抑制作用变得更强，最终形成以马基诺矿和FeOOH为主要成分的内锈层，以马基诺矿和磁黄铁矿为主要成分的外锈层。