Types of Corrosion

腐蚀类型

1. General (Uniform) Corrosion

1. 全面（均匀）腐蚀

- Metal loss occurs uniformly over the exposed surface

- 金属在整个暴露表面均匀地发生损失

- Governed by overall electrochemical kinetics rather than local chemistry

- 由整体电化学动力学而非局部化学环境所控制

- 常见于暴露在大气或水环境中的碳钢

- Typically managed by corrosion allowance, coatings, or inhibitors

- 通常通过腐蚀余量、涂层或缓蚀剂来控制

2. Pitting Corrosion

2. 点蚀

- Highly localized anodic dissolution at discrete points

- 在离散点发生高度局部化的阳极溶解

- Initiated by breakdown of passive films (often due to chlorides or deposits)

- 由钝化膜的破裂引发（通常由氯化物或沉积物引起）

- Cathodic area is large relative to anodic pit → high local corrosion rate

- 阴极区域相对于阳极点蚀坑较大 → 局部腐蚀速率很高

- Major failure mechanism for stainless steels and duplex alloys

- 是不锈钢和双相合金的主要失效机制

- Small pits can penetrate full wall thickness rapidly

- 小的点蚀坑能快速穿透整个壁厚

3. Microbiologically Influenced Corrosion (MIC)

3. 微生物影响腐蚀

- Corrosion accelerated by microbial metabolic activity

- 由微生物代谢活动加速的腐蚀

- Sulphate Reducing Bacteria (SRB) produce sulphides → H₂S generation

- 硫酸盐还原菌产生硫化物 → 生成硫化氢

- Creates localized acidic and reducing environments

- 造成局部酸性和还原性环境

- Often manifests as deep pitting under biofilms or deposits

- 通常表现为生物膜或沉积物下方的深点蚀

4. Galvanic Corrosion

4. 电偶腐蚀

- Occurs when dissimilar metals are electrically connected in an electrolyte

- 当不同金属在电解液中电气连接时发生

- Less noble metal becomes anodic and corrodes preferentially

- 较不活泼的金属成为阳极并优先腐蚀

- Severity depends on Galvanic series separation, Area ratio (small anode / large cathode = severe attack)

- 严重程度取决于电偶序差异、面积比（小阳极 / 大阴极 = 严重腐蚀）

- Common failure in bolting, fasteners, mixed-material piping

- 常见于螺栓连接、紧固件、混合材料管道中

5. Erosion–Corrosion

5. 冲刷腐蚀

- Combined effect of mechanical wear and electrochemical corrosion

- 机械磨损和电化学腐蚀的综合作用

- High-velocity fluids or solids remove protective films

- 高速流体或固体去除保护性膜层

- Accelerated metal loss at elbows, tees, valves, chokes

- 在弯头、三通、阀门、节流处金属损失加速

- Damage pattern is directional and often horseshoe-shaped

- 损坏形态呈定向性，常为马蹄形

6. Crevice Corrosion

6. 缝隙腐蚀

- Localized corrosion in shielded regions with restricted mass transfer

- 发生在传质受限的屏蔽区域的局部腐蚀

- Differential oxygen concentration creates anodic crevice interior

- 氧浓度差导致缝隙内部成为阳极

- Common under gaskets, flanges, deposits, and lap joints

- 常见于垫片、法兰、沉积物及搭接接头下方

- Often more severe than pitting due to stable acidic micro-environment

- 由于稳定的酸性微环境，通常比点蚀更严重

7. Stress Corrosion Cracking (SCC)

7. 应力腐蚀开裂

- Synergistic interaction of Tensile stress (applied or residual), Specific corrosive environment and Susceptible material

- 拉应力（施加的或残余的）、特定腐蚀环境和敏感材料三者协同作用

- Leads to brittle cracking with little plastic deformation

- 导致几乎没有塑性变形的脆性开裂

- Cracks may grow sub-surface and remain undetected

- 裂纹可能在表面下扩展且难以探测

8. Hydrogen Induced Cracking (HIC) / Sulphide Stress Cracking (SSC)

8. 氢致开裂 / 硫化物应力开裂

- Associated with hydrogen ingress into steel

- 与氢渗入钢中有关

- Common in H₂S-containing environments

- 常见于含硫化氢的环境

- Hydrogen accumulates at inclusions → internal cracking

- 氢在夹杂物处聚集 → 导致内部开裂

- SSC requires tensile stress; HIC can occur without applied stress

- 硫化物应力开裂需要拉应力；氢致开裂可在无外加应力时发生

- Major concern for carbon steel in sour service

- 是碳钢在酸性服役环境中的主要关注点

9. Fatigue Corrosion

9. 腐蚀疲劳

- Corrosion-assisted crack initiation and propagation under cyclic loading

- 在循环载荷下，腐蚀促进裂纹萌生和扩展

- Common in vibrating piping, rotating equipment, offshore structures

- 常见于振动的管道、旋转设备、海上结构

- Surface corrosion pits often act as crack initiation sites

- 表面腐蚀点蚀坑常作为裂纹萌生点

10. Corrosion Under Insulation (CUI)

10. 保温层下腐蚀

- External corrosion caused by trapped moisture beneath insulation

- 由保温层下积聚的湿气引起的外部腐蚀

- Affects both carbon steel and corrosion-resistant alloys

- 影响碳钢和耐腐蚀合金

- Most severe in temperature ranges enabling wet/dry cycling

- 在能使干湿交替发生的温度范围内最为严重