External Cleaning - Boiler Tubes

Tubes may be externally cleaned by various methods. The specific method is usually determined by the accessibility of the tubes and the purpose for which they are to be cleaned. Readily accessible tubes may be cleaned by wire brushing or grit blasting. Grit blasting is preferred if defects are suspected and a close inspection is required, since all deposits can be removed and the bare metal exposed. Refractory should be protected from grit blasting.

All radiant surfaces should be cleaned. Cleaning only a portion of the radiant surfaces may promote overheating of the cleaned surfaces. Scaled or fouled surfaces will obstruct heat transfer and cause the clean surfaces to absorb more heat. Usually, it is physically impossible to clean the economizer or convection tubes by wire brushing or grit blasting because of tube arrangement. Other methods, such as the use of a steam lance or a stream from a water hose or high-pressure water equipment, may be used. In such instances, cleaning is performed primarily to remove external deposits and improve the heat transfer. Before resorting to steam or water cleaning of the tubes, careful consideration should be given to possible damage to the refractory insulation and brickwork, particularly in a service where a fuel with a high sulfur content is used. In addition, for stainless steel tubes consider using a soda ash solution as detailed in 6.1.9 and maintaining the chloride content of the water at less than 50 ppm. These will minimize potential stress corrosion cracking of the tubes from cleaning operations.