Balancing Boiler Maintenance Costs and Benefits
March 2012 - MS
Properly maintaining boilers can provide multiple benefits for maintenance and engineering managers, including improved safety and reliability and the curtailed use of energy and water. As the costs for these utilities continue to rise for institutional and commercial facilities, the benefits of a preventive maintenance (PM) program targeting boilers will increase.
To deliver these benefits related to fire-tube and water-tube boilers, managers need to implement the essential steps of a boiler PM program. The focus here will be on fuel-fired steam systems because they are the most challenging boiler systems to maintain and run efficiently. Managers with hot-water systems can choose to adapt many of these techniques, scaling-down these suggestions to meet individual facility needs.
PM programs come with a price, so managers need to determine if the benefits outweigh the costs. The answer depends on facility needs. Most managers would agree that preventing failures decreases downtime, but other advantages also exist, including:
- improved safety and system reliability
- decreased cost of replacement
- improved inventory management
- predictive maintenance cycles
- energy and water savings
- minimized downtime during annual boiler inspection.
These benefits seem reasonable, so the question becomes, when should a manager implement a PM strategy? Generally, such a program provides the most benefit when the failure rate for system components increases and the overall cost of the program is less than the cost of a corrective reaction. Corrective costs can be difficult to quantify because they include intangible costs, such as lawsuits over the failure of life-safety or mission-critical items, and the loss of goodwill.
The graph on this page shows the cost curves for preventive and corrective maintenance. Notice that as time increases, the costs of a PM program drop exponentially. Similarly, but in reverse, the costs of a corrective maintenance program accelerate with time. Adding these two curves reveals a minimum cost point that indicates the optimum replacement age. But to understand these costs, managers first must understand the boiler system and the maintenance issues that surround its components.
Fire-tube and water-tube are the two most common types of fuel-fired boiler systems. Fire-tube boilers circulate hot gases through tubing submerged in water. Water-tube boilers allow hot gases to flow over water-filled tubes. Both technologies can produce steam, and both have about the same footprint for a given boiler horsepower.
The similarities generally end there. Fire-tube boilers range from 20 boiler horsepower (bhp) to 2,000 bhp, with pressures approaching 250 pounds per square inch for saturated steam. Conversely, water-tube boilers range from small residential units to utility-scale models. Because their small tubes are designed to better withstand pressure, system pressures can be 15-3,500 psi.
Each boiler part is susceptible to different types of maintenance issues, and testing methods vary. These issues, and the maintenance techniques designed to avoid them, are described in the U.S. Department of Energy's Operations & Maintenance Best Practices for Boilers, with the addition of several other recommendations. Many of these checks are done every one-four years by contracted professionals who specialize in boiler PM.