Which of the following methods is used in dry lay-up techniques?

The method used in dry lay-up techniques is heated air. This technique is designed to prepare and preserve various types of equipment, such as boilers or heat exchangers, by keeping them dry and preventing corrosion when they're not in service. Heated air helps to maintain a consistent temperature around the equipment, which reduces humidity levels and minimizes the risk of moisture-related damage. This is crucial in maintaining the integrity of the equipment during long periods without operation.

In contrast, steam injection is typically associated with wet lay-up techniques, where the presence of moisture is intended to protect metal surfaces. Oxygen saturation refers to the process of introducing oxygen into the system, which can promote corrosion, making it unsuitable for dry lay-up. Chilled water is generally used in cooling applications and does not apply to the dry lay-up process, as it would not effectively prevent moisture accumulation. Thus, heated air is the most appropriate choice for maintaining a dry environment around the equipment during lay-up.