High-Temperature Corrosion and Oxidation
On boiler and furnace surfaces, hot gas, ash and chlorine-sulphur compounds in the fuel chemically consume the metal. When erosion is also present, wall thinning accelerates sharply.
Symptoms
- Thick, layered, easily spalling oxide and ash deposits
- Uniform or pitted wall loss under the deposit
- Rapidly increasing tube failures in biomass and waste-fired boilers
- Local damage at weld seams and transition zones
Typical Parts
Chlorine and alkali salts in the fuel form low-melting deposits that break down the protective oxide layer and continuously consume the metal. Sulphur compounds cause sulphidation. The rate rises steeply with temperature.
Which Process for Which Case?
Temperature, fuel chemistry and whether the work must be done on site determine the choice.
| Solution | Material System | Typical Thickness | When Is It the Right Choice? |
|---|---|---|---|
| Arc spray (on site) | Ni-Cr and Ni-based alloy wires | 0.3–1 mm | Large boiler surfaces, fast on-site application during outages |
| HVOF | Cr₃C₂-NiCr, Ni-based alloys | 150–350 µm | Tubes and parts that can be coated in the workshop; erosion + corrosion together |
| Ceramic sealer / densifier | Ceramic-based sealing | Thin film | Limits ingress of the environment through the pores of metallic coatings |
| Weld overlay | Ni-based (Inconel-type) filler | 1.5–3 mm | Most severe corrosion zones; when a metallurgical bond is required |
Values are typical ranges; the final choice is made after the part, base material and operating conditions have been seen.
If the fuel changed, the coating plan must change too
In plants switching from coal to biomass or waste fuel, the corrosion mechanism changes completely. A coating that worked before may be insufficient with the new fuel. Ash analysis and thickness measurements from recent outages are very useful for coating selection.
FAQ
How can tube life be extended in a biomass boiler?
Critical zones are identified by wall thickness measurement and protected with Ni-Cr based thermal spray or weld overlay. If required, pores are closed with a ceramic sealer.
Does coating reduce heat transfer?
Thin metallic coatings have a limited effect on heat transfer. Thick ash and oxide layers usually reduce heat transfer far more.
How long an outage does on-site work need?
It depends on the area and scaffolding. With measurements and photos we prepare a work schedule that fits your outage plan.
Let’s Talk About Your Part
Take a photo of the damaged area and send it by e-mail or WhatsApp, or call us directly. On the phone we identify the mechanism together and give a suitable process and a rough cost/lead-time indication in the same call.
- Close-up and overall photo of the damaged area
- Diameter / length or a technical drawing
- Operating conditions: temperature, medium, particles, speed