What should be done to all blowdown valves after a 15-minute cooldown period?

After a 15-minute cooldown period, all blowdown valves should be retorqued to prevent leakage. This procedure is crucial because the temperature change can lead to thermal contraction of the materials involved, which may alter the tightness of the valve connections. Retorquing ensures that the gaskets and seals are properly compressed, enhancing their effectiveness and preventing any potential leaks that could result from the cooling process.

Maintaining the integrity of the valve connections is essential for the overall safety and efficiency of the system, as leaks can lead to not only operational issues but also safety hazards. This step is a critical part of routine maintenance and is particularly important in pressurized systems where reliability is paramount. In contrast, the other options, such as replacing valves or painting them, do not directly address the immediate need to ensure that the valves are securely fastened following the cooldown. Cleaning might be necessary as part of regular maintenance, but it is not the priority at this stage.