Corrosion-Resistant Axial Fans: Materials, Coatings and Coastal or Chemical Duty

A fan that corrodes loses balance, blade profile, and casing integrity long before it fails outright, and corrosion is often the reason a fan that performed well on the test bench gives trouble within a few years on site. Choosing corrosion resistance means matching material and coating to the actual environment: salt air, chemical fume, condensation, or process moisture. This guide compares the main options and the details that decide whether a coating lasts.

Start With the Environment

Corrosion depends on what the fan sits in and what passes through it. Separate the two.

• External environment. Coastal salt, industrial atmosphere, chemical plants, humidity, rain, and condensation act on the outside of the casing, the motor, the fasteners, and the supports.
• Internal environment. The air or gas being moved acts on the impeller, hub, casing interior, and, if the motor is in the airstream, the motor.

A fan in a clean warehouse exhausting to a coastal roof faces a harsh external environment and a mild internal one. A fan in a chemical plant may face aggressive fumes inside and outside. State both in the specification.

ISO 12944 Corrosivity Categories

ISO 12944 defines corrosivity categories for atmospheric environments, from C1 for very low corrosivity up to C5 for very high, with CX for extreme. Fan suppliers commonly quote coating systems by category and by expected durability, for example a casing coating described as C4. Coastal and industrial environments often fall into C4 or C5. Choose the category from the site, not from the brochure, and state the durability you expect.

Material Options Compared

Material	Strengths	Limits
Hot-dip galvanised steel	Good general protection, widely used for casings	Zinc coating can be attacked by some chemicals and by damage at cut edges
Painted carbon steel	Low cost, flexible in shape and coating	Coating breakdown exposes steel; needs maintenance
Stainless steel	Excellent resistance to many atmospheres	Cost, and chloride environments can cause pitting on lower grades
Aluminium	Light, good in many atmospheres, common in impellers	Attacked by strong alkalis and some chemicals; galvanic problems with steel
Fibre-reinforced plastic (FRP)	Excellent chemical resistance	Temperature limits, lower stiffness, static charge, and impact damage

Stainless steel is not one material. Grade matters: a higher-alloy grade resists chlorides much better than a basic grade, so coastal and chemical duties usually call for the higher grade. Confirm compatibility with the actual chemicals, since resistance is specific to each.

FRP for Chemical Duty

FRP fans are used where fumes would attack metal. The polymer resin is chosen for the chemicals, and the fan can be built with a smooth, non-porous surface. Points to check:

• Temperature limit of the resin.
• Static electricity. FRP can accumulate static charge, so where flammable gas or dust is present, conductive constructions and earthing are used.
• Hazardous areas. AMCA 99 addresses metal and non-metal fans but does not address FRP, so special construction is required for spark-resistant FRP. See ATEX and spark-resistant axial fans.
• Mechanical strength at the required tip speed.

Coatings: What Makes Them Last

A coating is a system, not a paint. Durability depends on:

1. Surface preparation. Blasting to the right standard matters more than the topcoat.
2. Primer, build coats, and topcoat matched to the environment, with the specified dry film thickness.
3. Edge and weld treatment, since corrosion starts at sharp edges, welds, and crevices.
4. Application conditions, including temperature and humidity at the time of coating.
5. Repair procedure for damage during transport and installation.

Ask for the coating system, the thickness, and the standard, not only the colour.

Details Beyond the Casing

• Fasteners. Bolts, nuts, and washers corrode first if they are a lower grade than the casing, and galvanic action between different metals accelerates it. Use compatible, corrosion-resistant fasteners.
• Drainage. Water that pools inside a casing or on a horizontal surface corrodes the metal. Drain holes, sloped surfaces, and rain shields help.
• Motor protection. Motors for harsh environments use higher ingress protection, commonly IP55 or better, and suitable sealing, with coated or corrosion-resistant housings.
• Bearings and shaft seals. Sealed or protected bearings, and shafts with suitable finish, resist moisture and fumes.
• Balance. Corrosion and dust build-up change impeller balance and raise vibration, so inspection matters. See axial fan vibration and maintenance.

Coastal Sites

Salt-laden air attacks steel, damages coatings, and settles as deposits that hold moisture. Coastal fans benefit from a high-durability coating system, stainless or protected fasteners, drained casings, and sealed motors. Wash-down and inspection routines help, because salt deposits keep corroding until they are removed.

Chemical and Process Sites

Aggressive fumes, acids, alkalis, and solvents need material chosen against the specific chemical, concentration, and temperature. Where a corrosive gas passes through the fan, a motor in the airstream is exposed too, so consider a motor outside the airstream. Also consider whether the gas can condense inside the casing, creating a much stronger corrosive liquid than the vapour.

Where Our Range Fits

We manufacture axial fans with impeller diameters up to 1,600 mm, static pressure up to 2,400 Pa, and air volume up to 185,000 m³/h. Corrosion-resistant materials and coatings, including special constructions, are confirmed case by case, so tell us the environment and the chemicals before you specify.

What to Provide

1. External environment and ISO 12944 category, if known.
2. Internal gas composition, concentration, temperature, and moisture.
3. Whether condensation can form inside the fan.
4. Expected service life and maintenance access.
5. Any hazardous-area classification.
6. Motor arrangement and protection level.

Tell Us the Environment Before You Choose the Material

Send your site conditions and the gases or fumes involved, and we’ll confirm a suitable construction. Contact us for a free quote.

Frequently Asked Questions