Boiler tube corrosion causes material wastage, which eventually will lead to equipment failure due to hoop stress or the replacement of the material if the mechanism is not identified. The extent and type of corrosion impacting boiler tubes can vary widely and is driven by a number of operational conditions. High temperature corrosion leading to boiler tube wastage does not follow the rules of wet chemistry and so is often misunderstood.
Also, mechanisms such as fly ash erosion can couple with corrosion by removing oxide scales, thus accelerating wastage rates from boiler tube corrosion. As another example, some corrosion phenomena, such as coal ash corrosion, only occur at specific temperature ranges. The following is a list of factors that can affect the rate and mechanism of thinning in boilers due to corrosion:
- Tube skin temperature.
- Corrosive gas composition due to fuel type.
- Flue gas stoichiometry.
- Boiler design.
- Moisture content of fuel.
- Erosion due to fly ash or sootblowing, which aggravates corrosion rates.
In order to address the problem of boiler tube corrosion, the boiler must be readily inspected with UT to identify thinning areas. If areas are losing thickness due to corrosion, corrective actions can be implemented. Based on the condition of the tubes, operational conditions, and the operator’s equipment maintenance run-time objectives and budget, there are several solutions, including:
- Ceramic cladding application with UTEx 6-040 or 6-041.
- MetalsprayTM with HVAS or HVOF processes.
- Corrosion resistant weld overlay.
- Boiler tube replacement.
IGS undergoes a unique research process for each potential application in order to understand the corrosion or erosion mechanism and recommend the optimal material and application process solution to solve the operator’s problem. The IGS Technology Center provides analysis of failed boiler tube sections and diagnoses the corrosion and/or erosion mechanism.