If laying up a boiler for a short time, what concentration of caustic soda should be maintained in the boiler water?

When laying up a boiler for a short period, maintaining a proper concentration of caustic soda (sodium hydroxide) in the boiler water is essential to prevent corrosion and other forms of degradation. A concentration of 400 ppm is often recommended for effective alkalinity in the water.

At this concentration, caustic soda helps in neutralizing acidic species that can contribute to corrosion. It also works to form a protective layer on metal surfaces within the boiler, reducing the risk of damage while the boiler is out of operation.

Lower concentrations might not provide sufficient alkalinity to effectively control pH levels and protect the metal components of the boiler, while higher concentrations beyond 400 ppm could lead to other operational issues, including foaming or carrying over of chemicals during the operation. Therefore, maintaining caustic soda at 400 ppm strikes a balance between effective protection and operational safety during the temporary layup of the boiler.