Introduction

Cathodic protection is a widely used technique to prevent corrosion of metal structures in various industrial applications. The process involves making the metal structure cathodic with respect to a more easily corroded metal or an inert anode. This results in a flow of current, which causes the metal to be protected from corrosion. However, cathodic protection can also lead to the generation of hydrogen gas, which can cause hydrogen embrittlement.

Technical Background

When cathodic protection is applied, a voltage is applied to the metal structure, which is more negative than the equilibrium potential of the metal in the electrolyte. This negative potential causes a flow of electrons from the anode to the cathode. At the cathode, hydrogen ions are reduced to form hydrogen gas. This is a normal process in cathodic protection, but at high potentials, the amount of hydrogen generated can be excessive and lead to hydrogen embrittlement.

Hydrogen embrittlement occurs when hydrogen diffuses into the metal and interacts with the metal lattice. This can reduce the ductility and fracture toughness of the metal, making it more susceptible to cracking and failure. The severity of hydrogen embrittlement depends on factors such as the material, the level of hydrogen exposure, and the applied stress.

History

Hydrogen embrittlement was first observed in the mid-19th century in steel rails used in railway tracks. The rails were observed to fracture suddenly, even though they had not been subjected to excessive loads. It was later discovered that the rails had been exposed to hydrogen gas, which had caused them to become brittle and prone to fracture. Since then, hydrogen embrittlement has been observed in various other metals and alloys.

Mitigation Strategies

To mitigate the risk of hydrogen embrittlement in cathodic protection, several strategies can be employed. One approach is to limit the amount of hydrogen generated at the cathode by using lower cathodic potentials or adding inhibitors to the electrolyte. Another approach is to use materials that are less susceptible to hydrogen embrittlement, such as high-strength alloys or titanium.

Post-processing techniques can also be used to remove or reduce the amount of hydrogen in the material. For example, annealing or heat treatment can be used to diffuse the hydrogen out of the metal. Additionally, hydrogen diffusion barriers can be applied to prevent hydrogen from entering the metal in the first place.

Conclusion

In conclusion, cathodic protection is an effective method to prevent corrosion of metal structures, but it can also lead to the generation of hydrogen gas and subsequent hydrogen embrittlement. To mitigate the risk of hydrogen embrittlement, it is important to limit the amount of hydrogen generated at the cathode and use materials that are less susceptible to hydrogen embrittlement. Regular inspections and proactive corrosion management are crucial to detecting any signs of hydrogen embrittlement or other types of corrosion damage.

References:

• H. Wang, J. Zheng, Q. Zhang, & Y. Wei. (2019). Mitigation of hydrogen embrittlement of a 7B04 aluminum alloy by controlling the microstructure. Materials & Design, 170, 107675.
• M. W. Kendig & R. G. Buchheit. (2003). Hydrogen embrittlement. Corrosion: Understanding the Basics, 305-324.
• J. R. Scully & H. Zhu. (2010). Hydrogen embrittlement and hydrogen-induced cracking. ASM Handbook, 13B, 1085-1101.