At what pressure should the drum vents be opened during a prolonged shutdown to prevent vacuum formation?

To prevent vacuum formation in a steam drum during a prolonged shutdown, it is essential to maintain a pressure that is higher than atmospheric pressure. Opening the drum vents at an appropriate pressure helps to equalize the pressure inside the drum with the atmospheric pressure, thus preventing any potential vacuum that could cause structural damage or impact the integrity of the drum.

The correct pressure for opening the drum vents, in this context, is 170 kPa. This pressure is sufficient to ensure that the internal pressure of the drum remains above atmospheric levels while allowing for any potential pressure fluctuations that may occur during temperature changes or other operational conditions. It is also a safe margin above ambient conditions, giving a buffer to avoid any risk of creating a vacuum as external temperatures drop or as the steam cools and condenses.

The other pressure values presented do not effectively provide the same level of safety against vacuum formation. Setting the vents at lower pressures, such as 200 kPa, 150 kPa, or 100 kPa, may not adequately protect the drum against potential vacuum situations, depending on external temperature conditions and other factors. Thus, maintaining the vents at 170 kPa plays a crucial role in operational safety during shutdown conditions.