Which of the following can cause pitting of boiler materials?

Pitting of boiler materials is primarily influenced by the presence of certain corrosive agents in the water or steam used in the boiler system. Chlorides are known to be particularly aggressive and can lead to localized corrosion, often resulting in pitting.

In the case of oxygen, it is important to note that while it contributes to overall corrosion processes, especially in certain environments, it is not a direct cause of pitting like chlorides. The presence of oxygen in water can lead to general corrosion and establish a pathway for further corrosion processes, which may not manifest as pitting but can still compromise the integrity of the boiler materials.

Carbon dioxide can also cause corrosion, primarily through the formation of carbonic acid in the presence of water, which leads to corrosion that can weaken metal components but is less frequently associated with pitting compared to chlorides.

Hydrogen sulfide poses its own set of corrosion concerns, mainly through sulfide stress cracking and general corrosion, but is not specifically linked to pitting of boiler materials in the same manner as chlorides.

Therefore, while oxygen is indeed a contributor to corrosion in boiler systems, it is not accurately recognized as a primary cause of pitting, which is more commonly associated with the aggressive behavior of chlorides.