When sludge settles at the bottom head of a vessel, what corrosion mechanism is likely to occur?

When sludge settles at the bottom head of a pressure vessel, concentration cell corrosion is likely to occur. This form of corrosion arises due to variations in the concentration of electrolytes, typically caused by stagnant fluids that can lead to localized differences in chemical activity.

In this case, the accumulation of sludge creates layers of trapped liquid, which can result in areas of different concentrations of dissolved ions within the bottom head of the vessel. The settled sludge can hinder proper fluid circulation and create zones where oxygen or other corrosive agents are either more or less abundant. This disparity in concentration leads to differential corrosion rates over the surface of the material, primarily affecting the areas that are less conducive to oxygen diffusion, often resulting in concentrated electrochemical reactions that accelerate corrosion.

By understanding this mechanism, operators and inspectors can recognize the significance of managing sludge in vessels and implement appropriate inspection and maintenance strategies to mitigate potential corrosion issues effectively. The awareness of concentration cell corrosion ultimately supports the integrity and longevity of pressure vessels in service.