When boilers are taken out of service for any length of time, corrosion may occur on the internal surfaces of the boiler unless certain precautions are observed. During periods of idleness, boilers may be laid up by one of two methods – wet lay-up or dry lay-up. The choice of method is dependent on how long the boiler is to be out of service and how quickly the boiler may be required back in service for regular steaming purposes in an emergency, etc.
The dry method is preferable when a boiler is to be out of service for 3 months or more and will not be required for an emergency purpose. The boiler should be drained, thoroughly cleaned and carefully inspected to insure all is in good order. The boiler should then be thoroughly dried internally by means of a light fire. Close attention should be given to complete drying of non-drainable superheater tubes.
Absorbents, such as silica gel can be used in dry storage. Silica gel may be obtained in convenient packages to permit good distribution. The packages of silica gel should be placed on wood or metal trays and distributed throughout the boiler at a rate of approximately 4 pounds of silica gel for each 100 cubic feet of air space. The silica gel should be placed in the boiler immediately after the drying-out process. If the boiler is an HRT or locomotive type, a single tray resting on top of the flues or in the bottom of the shell will be adequate. In a multi-drum water boiler, a tray should be placed in each drum. If the boiler is idle for a considerable period of time it should be opened every 5 or 6 months and the silica gel examined. If necessary, the silica gel can be reactivated by placing it in an oven for several hours or by blowing hot air through it until moisture is no longer given off.