What are the causes of severe corrosion in centrifugal fans?

Severe corrosion in centrifugal fans is typically caused by multiple factors, involving environmental conditions, process media, operational practices, materials, and design aspects. The primary causes and detailed analysis are as follows:

I. Environmental and Medium Factors
Corrosive Gases/Particulate Matter

If the air processed by the fan contains acidic gases (such as sulfur dioxide, hydrogen chloride), alkaline substances, or chloride ions (commonly found in chemical processing, electroplating, wastewater treatment, and similar industries), direct chemical corrosion occurs.

Excessive humidity or condensation accelerates corrosion, particularly when gas temperatures fall below the dew point. Condensate adhering to impeller or casing surfaces creates an electrolyte environment.

High-Temperature, High-Humidity Environments

Elevated temperatures accelerate chemical reaction rates, while moisture promotes electrochemical corrosion. Significant temperature fluctuations in the medium, leading to frequent condensation, exacerbates corrosion.

Particle Abrasion

Dust and solid particles (e.g., coal ash, grit) in the airflow cause abrasive corrosion (erosion) on fan surfaces. This damages protective layers (e.g., passivation films) on metal surfaces, exposing fresh metal and accelerating corrosion.

II. Inappropriate Material Selection
Inadequate Corrosion Resistance of Metal Materials

Common carbon steels (e.g., Q235) are highly susceptible to rusting in corrosive environments. Failure to select suitable materials based on medium characteristics (e.g., stainless steel 316L, titanium alloys, fiberglass-reinforced plastic) significantly increases corrosion risk.

Stainless steel may also experience pitting corrosion in specific environments (e.g., stress corrosion cracking induced by chloride ions).

Failure of Protective Coatings

Poor quality, improper application, or aging/peeling of anti-corrosion coatings (e.g., epoxy resin, polyurethane) or plating (galvanizing, powder coating) exposes the base material directly.

III. Design and Structural Defects
Localized Liquid or Dust Accumulation

Design flaws in fan housings or impellers create dead corners prone to accumulating moist dust or liquids, forming localized corrosion cells that accelerate corrosion.

Blocked drain holes or absence of drainage structures cause condensation retention.

Galvanic Corrosion

Direct contact between dissimilar metal components (e.g., stainless steel bolts connecting carbon steel housings) creates potential differences in electrolyte environments, triggering electrochemical corrosion.

Stress Concentration and Fatigue

Weld seams, bolt holes, and similar locations are prone to stress corrosion cracking, particularly in corrosive environments.

IV. Operational and Maintenance Issues
Frequent Start-Stops or Low-Load Operation

Long-term operation below design conditions may cause unstable internal airflow, exacerbating localized wear or condensation.

Failure to promptly remove dust or dry the unit after shutdown allows residual corrosive substances to continue acting.

Lack of Regular Maintenance

Failure to promptly clear accumulated dust or water, or inspect coating damage.

Failure to periodically repair or replace anti-corrosion coatings or cathodic protection systems (if installed).

Improper Cleaning Methods

Cleaning fans with strong acids or alkalis, where residual cleaning agents corrode metal surfaces.

V. Special Corrosion Types
Microbial Corrosion

In wastewater treatment, agricultural ventilation, and similar environments, bacterial metabolites (e.g., hydrogen sulfide produced by sulfate-reducing bacteria) may induce biofouling.

High-Temperature Oxidation

In high-temperature environments (e.g., boiler induced draft fans), metal surfaces may undergo oxidation and spalling, reducing material corrosion resistance.

Solution Recommendations
Optimize Material Selection

Select corrosion-resistant materials based on medium composition, temperature, and humidity (e.g., stainless steel, duplex steel, composites, or rubber/plastic lining).

Improve Design

Eliminate structural dead zones and optimize airflow pathways; incorporate drainage holes; insulate dissimilar metal contact points.

Enhance Surface Protection

Apply high-performance anti-corrosion coatings (e.g., fluorocarbon coatings, ceramic coatings) or thermal spraying (e.g., aluminum spraying, zinc spraying with sealing treatment).

Standardize Operation and Maintenance

Regularly clean fan interiors and maintain dryness; perform purging or drying during shutdowns; establish corrosion monitoring protocols (e.g., periodic thickness measurements, coating inspections).

Environmental Control

Install pre-filtration devices (e.g., scrubbers, dust collectors) to remove corrosive particulates; control medium temperature and humidity to prevent condensation.

Cathodic Protection

For large critical fans, consider sacrificial anodes or impressed current cathodic protection.

Summary
Corrosion in centrifugal fans results from the combined effects of environmental media, materials, design, and maintenance. Solutions require comprehensive measures including controlling media corrosivity at the source, selecting appropriate materials, optimizing structures, and enhancing protection. Establish regular inspection and maintenance protocols to extend equipment lifespan.