What condition enhances the risk of hydrogen blistering in vessels?

The presence of acidic substances significantly enhances the risk of hydrogen blistering in pressure vessels due to their corrosive nature. Hydrogen blistering occurs when hydrogen gas, generated by corrosion reactions, gets trapped beneath the metal surface, leading to the formation of blisters. Acidic environments often accelerate the corrosion process of steels and other alloys, resulting in higher hydrogen production. This is because acids can react with the metal, facilitating the release of hydrogen at an increased rate.

In contrast, low operating pressure typically does not contribute to this risk, as blistering is more associated with the local pressures created by accumulating hydrogen. The absence of water also tends to diminish the risk, as water is essential for galvanic corrosion processes that lead to hydrogen generation. Lastly, insulated thermal barriers can help maintain temperature stability within a pressure vessel, potentially mitigating localized overheating that might aggravate corrosion processes. Thus, the relationship between acidic substances and increased corrosion makes the presence of these materials a key factor in elevating the risk of hydrogen blistering.