What type of corrosion often occurs at bolts and nuts?

The type of corrosion that typically occurs at bolts and nuts is crevice corrosion. This form of corrosion arises in areas where there are stagnant or trapped electrolytes, which can occur in the narrow gaps between bolts and nuts, or between the nut and the surface it is fastened to. The presence of these crevices can create conditions that lead to a localized depletion of oxygen, reducing the effectiveness of protective oxide layers and allowing for accelerated corrosion processes.

Factors such as moisture, dirt, and other contaminants can accumulate in these crevices, further promoting corrosion in those restricted spaces. This localized corrosion can result in more significant damage than general corrosion, which affects the entire surface uniformly.

In the context of pressure vessels, understanding the nuances of different corrosion types is crucial for ensuring structural integrity and preventing leaks or failures in critical components.