In wet flue gas desulphurisation, probes and sensors sit in limestone-gypsum slurry moving at several metres per second. Unprotected stainless steel erodes and corrodes quickly, and once the element wears the control loop loses the measurement it depends on. Spraying a dense tungsten carbide (WC) coating by plasma or HVOF changes the failure mode: the slurry sees a 1200 HV carbide surface instead of soft stainless steel.
Coating Specification
| Parameter | Value |
|---|---|
| Coating material | WC-10Co4Cr (corroded-grade carbide) |
| Process | Plasma / HVOF spraying |
| Hardness | ≥ 1100 HV0.3 |
| Thickness | 0.30–0.50 mm |
| Medium resistance | pH 1–14 slurry, chloride-bearing |
| Effect | Probe life extended from months to years |
Why WC-CoCr Works in Slurry
- Abrasion – gypsum crystals and fly ash particles cannot cut the carbide phase at slurry velocities.
- Corrosion – the CoCr binder was chosen over plain Co because it survives acidic, chloride-bearing media.
- Signal stability – geometry stays within tolerance, so pH, density and flow readings remain calibrated.
- Lower operating cost – fewer probe replacements and fewer unplanned shutdowns of the absorber.
Related services: pump impeller WC coating and anti-corrosion surface treatment for steel structures.
Frequently Asked Questions
How long does a WC-coated FGD probe last compared with bare 316L?
In typical limestone-gypsum slurry, an uncoated 316L probe thins through within months. A 0.3-0.5 mm WC-10Co4Cr layer at 1200 HV extends probe life to several years, with replacement limited by plant overhaul cycles rather than wear.
Can other slurry-exposed internals be coated the same way?
Yes. Agitator blades, pump impellers, dampers, pH electrode guards and circulation piping in the absorber area are routinely protected with the same carbide system.
