As winter begins to loosen its grip and Spring arrives in most of the US, boilers that are used for comfort heating may no longer be needed until the cooler weather returns in the Fall. Often most offline boilers are stored improperly during the Spring and Summer months. Boilers are most susceptible to corrosion and oxygen attack when they are offline. To protect offline equipment, proper layup procedures must be implemented.
01Wet Storage — For Outages Under 30 Days
Boilers that will be out of service for less than 30 days may implement a wet storage procedure. To wet store a boiler, the boiler should have the steam outlet valved off along with the flue stack. The boiler should be flooded with chemically treated water.
Lone Wolf recommends maintaining a minimum sulfite residual of 100 ppm and phenol alkalinity level greater than 400 ppm. The offline boiler should be tested weekly to ensure that the proper chemical levels are being maintained. If the chemical levels are below the recommended range, adding additional chemical may be necessary to maintain sufficient chemical protection. Consider using an external pump to circulate water throughout the boiler to ensure sufficient mixing of the boiler chemicals.
02Dry Storage — For Full-Season Layup
Boilers that are going to be offline for an entire season should be dry stored. To dry store a boiler, the boiler should be drained and dried out to minimize moisture in the boiler. The steam outlet and flue stack should be closed to keep any residual moisture out of the water side of the boiler.
A squirrel cage fan along with a 110-watt light bulb may be utilized to keep moisture from accumulating on the water side surfaces of the offline boiler.
03Vapor-Phase Corrosion Inhibitors (VpCI)
A preferred method of dry storing a boiler is to utilize a vapor phase corrosion inhibitor from Cortec. To use a vapor phase corrosion inhibitor, the boiler should be drained, and the steam outlet and flue stack should be closed. After the boiler is drained, sufficient boiler lizards should be added to the boiler and the hand holes should be closed.
Cortec's Boiler Lizard® contains vapor-phase corrosion inhibitor powder in a polyvinyl alcohol (PVA) water-soluble bag. The powder formulation is free of phosphates, heavy metals, nitrites, and free amines. Designed for dry lay-up of boilers, the Boiler Lizard® protects metals in enclosed spaces. The VpCIs vaporize and adsorb on the metal surfaces, reaching all recessed areas and interior cavities.
04Prepare Before Shutdown, Not After
Proper storage of offline boilers is often overlooked until there is a serious corrosion issue and it's too late to take appropriate action. There is nothing more heartbreaking than to see a well-treated boiler with serious corrosion issues from improper layup procedures. The best plan to avoid corrosion in offline steam systems is to implement layup procedures prior to shut down, not after the boiler is already off.