When laying up a boiler in a dry state, which substance is NOT used as a desiccant?

When laying up a boiler in a dry state, the primary goal is to protect the boiler components from moisture, which can lead to corrosion and deterioration. Desiccants are substances used to absorb moisture from the air and maintain a dry environment.

Caustic soda, also known as sodium hydroxide, is not typically used as a desiccant in this context. While it has hygroscopic properties and can absorb moisture, its primary purpose in boiler applications usually involves controlling pH and reducing corrosion rather than acting solely as a moisture absorber during the lay-up process. The use of caustic soda can also pose risks due to its caustic nature and potential to cause chemical reactions if not handled properly.

In contrast, other substances mentioned are commonly used desiccants. Silica gel is a standard drying agent that effectively absorbs moisture and is often used during boiler lay-ups to ensure a dry environment. Calcium chloride is another efficient desiccant that absorbs moisture from the air. Sodium bicarbonate can be employed in various contexts, but it is less effective as a desiccant compared to silica gel or calcium chloride.

Thus, the nature and role of caustic soda distinguish it from the other substances listed, making it the choice that is not used