**5. Corrosion causes in steel cables**

Steel cable is a collection of twisted and wounded metal strands to form a helix shape to support and lift loads.

Steel cables are used to provide suspension bridge supports, lift the elevators, and serve as additional reinforcement for infrastructure. The design of steel cable that is wrapping the multiple strands around the stable core provides strength, flexibility, and ease of handling, but also constrains the implementation of corrosion protection

**Figure 21.** *Impressed Current Cathodic Protection.*

techniques. Steel cable corrosion not only reduces the strength but also accelerates cracks and fatigue, ultimately reducing the elasticity.

The steel cables are prone to pitting corrosion due to the presence of strong chlorides in the atmosphere. The strong chloride ions penetrate the oxide layer and the protective layer on the surface of steel cables, to electrochemically react with the internal metal matrix. The absorption of hydration energy of chloride ions into the pores and cracks on the steel cable surface, during this electrochemical reaction, replaces the oxygen with the chlorination layer. The chloride displaces the insoluble oxide present as a passive layer and initiates a corrosion electrochemical reaction. This generates the pits on the surface of the steel strands. A deeper and sharper pit will result in greater pitting local stress and shorter fatigue life. The pitting of steel cable is hard to predict because of its complex nature, involving the type of attack corrosion, attacked material, and environmental conditions.

As stated in earlier sections, galvanic corrosion, also known as bimetallic corrosion, occurs when dissimilar metals are in contact with the presence of an electrolyte. The two main factors affecting the rate of galvanic corrosion are the distance between the two metals in the galvanic series and the relative surface areas of the different metals. The further apart the two metals are in the galvanic series, the greater the risk of galvanic corrosion.

If the anodic metal has a smaller surface area than the cathodic metal, the difference in surface area causes the rate of corrosion of the anodic metal to increase. Conversely, if the anodic metal has a much larger surface area than the cathodic metal, it may be sufficient to discount the effects of galvanic corrosion.

For example, when a steel cable is clamped with aluminum, both materials being apart in the galvanic series, aluminum will get corroded, and lead to failure of support.

Steel cable corrosion can be divided into three types of corrosion, that is, external, internal, and fretting corrosion.
