Desulfurization Pump Corrosion Repair: Step-by-Step Case Study
Desulfurization pumps in steel plants face severe corrosion and erosion from acidic slurry and gypsum particles. This article presents a real-world repair case from a steel plant in Xinjiang, detailing step-by-step procedures, material choices, and critical tips to extend pump life and reduce downtime.
Understanding the Corrosion Challenge in Desulfurization Pumps
In flue gas desulfurization (FGD) systems, pumps continuously circulate limestone slurry to absorb sulfur dioxide. The slurry typically has a pH between 5 and 6, temperatures around 60–80°C, and contains hard gypsum particles. This combination creates a dual mechanism of corrosion and erosion. Over time, pump casings develop pitting, grooves, and eventually through-wall leaks. Traditional repair methods like welding or patching often fail quickly because they do not address the root cause or withstand the harsh conditions.
The case study involves three LC550/750 desulfurization pumps at a sintering plant. These pumps, made of Cr30 alloy, had been in service for six years. The operator had tried external fiberglass wrapping, which lasted only one week. The goal was to find a repair method that could be performed on-site without disassembling the entire pump, provide long-term erosion resistance, and cost less than replacing the casing.
Key Pump Parameters
- Material: Cr30 alloy
- Medium: Desulfurization slurry with gypsum
- pH: 5.5
- Temperature: ~70°C
- Service life before repair: 6 years
Step-by-Step Repair Procedure
The repair utilized advanced carbon nano polymer composite materials. These materials are designed for high adhesion to metal substrates, excellent chemical resistance, and outstanding erosion resistance. Unlike welding, they require no hot work and can be applied with simple tools. The process is as follows:
1. Surface Preparation
Proper surface preparation is critical for coating adhesion. The damaged areas were grit blasted to remove all corrosion products, old coatings, and contaminants. The goal is to achieve a clean, rough surface with a minimum Sa 2.5 cleanliness level (near-white metal). After blasting, the surface was thoroughly cleaned with anhydrous ethanol to remove dust and grease. Any oil or moisture would compromise bonding.
2. Application of Primer
A two-component epoxy-based primer (SD3000) was mixed according to the manufacturer’s ratio and applied evenly to the prepared surface. This primer enhances adhesion and provides an initial corrosion barrier. It was applied with a brush, ensuring full coverage of the affected area.
3. Filling and Rebuilding
The main repair material (SD7400 carbon nano polymer composite) was mixed and applied to fill grooves, pits, and eroded areas. This paste-like material can be sculpted to restore the original profile. The recommended thickness is 2–3 mm. Thicker layers may interfere with impeller clearance, while thinner layers may not withstand erosion. Care was taken to avoid contact with wear rings and other close-tolerance areas.
4. Curing
After application, the repaired areas were heated using infrared lamps to accelerate curing. The temperature was carefully controlled to avoid cracking (too high) or excessively long cure times (too low). During curing, the pump must not be disturbed or vibrated. Full cure was achieved within a few hours, allowing the pump to be returned to service quickly.
Critical Success Factors and Common Pitfalls
Based on this and similar repairs, several factors determine the longevity of the repair:
| Factor | Recommendation | Pitfall to Avoid |
|---|---|---|
| Material Selection | Use carbon nano polymer composites specifically formulated for slurry erosion and chemical resistance. | Do not use general-purpose epoxy or polyester fillers; they degrade quickly in acidic slurry. |
| Surface Cleanliness | Achieve Sa 2.5 blast profile, remove all dust and oil with solvent. | Skipping degreasing or leaving rust will cause disbondment. |
| Coating Thickness | Maintain 2–3 mm thickness; measure with a wet film gauge. | Excessive thickness can cause cracking or interference; too thin leads to rapid wear. |
| Curing Conditions | Follow manufacturer’s temperature and time guidelines; use IR heating if needed. | Disturbing the pump or uneven heating can ruin the repair. |
Results and Long-Term Benefits
The three pumps were repaired within 24 hours without removing the casings from the piping. This minimized production downtime significantly. After the repair, the pumps have been running stably with no signs of new corrosion or leakage. The previous fiberglass wrap failure was completely resolved.
Cost analysis showed that the total repair cost was only one-third of replacing the pump casings. Moreover, the carbon nano polymer lining is expected to last 2–3 times longer than traditional repair methods, reducing the frequency of maintenance interventions. This translates to lower lifecycle costs and improved environmental compliance due to fewer unexpected outages.
Advantages of Carbon Nano Polymer Technology for Pump Repair
- Excellent adhesion to metals like Cr30, even in wet environments.
- High resistance to acids, alkalis, and abrasive particles.
- No hot work required, reducing safety risks and downtime.
- Can be applied on-site without specialized equipment.
- Extends equipment life and lowers total cost of ownership.
Preventive Maintenance Tips for Desulfurization Pumps
While this repair method is highly effective, prevention is always better than cure. Regular inspections should be conducted to detect early signs of erosion or pitting. Monitoring slurry pH and temperature can help optimize operating conditions. Additionally, maintaining proper water chemistry and avoiding excessive solids concentration will reduce wear. Combining these practices with advanced polymer coatings can significantly extend the service life of desulfurization pumps.
This case study demonstrates that with the right materials and procedures, even severely corroded pump casings can be restored to like-new condition, ensuring reliable operation of critical FGD systems in steel plants.
