Which of the following is NOT a wet lay-up method?

The correct response identifies "dry fill" as not being a wet lay-up method. Wet lay-up is a procedure used in maintenance to preserve equipment, particularly in the context of boilers and other systems, by filling them with a liquid substance to prevent corrosion and other damage while they are out of service.

Hot deaerated fill involves using water that has been heated and had its dissolved gases removed, which is essential in wet lay-ups to minimize oxygen that could cause corrosion. Sodium nitrate is commonly utilized in wet lay-ups as a chemical additive to further inhibit corrosion during the preservation process. Nitrogen is also associated with wet lay-ups; it is used to create an inert atmosphere to prevent oxidation in the equipment.

In contrast, "dry fill," by its name, implies the absence of liquids. Since a wet lay-up necessitates liquid to perform its protective function, dry fill does not conform to the concept of a wet lay-up method. Thus, identifying dry fill as not being a wet lay-up method is accurate and highlights the fundamental requirement of the wet lay-up process itself.