Corrosion Protection

Belt Conveyor Structure

CORROSION PROTECTION

A variety of methods can be employed for corrosion protection. In many cases, conveyors operate in environments where corrosion is not a significant issue, provided that a corrosion allowance is factored into the thickness of structural members exposed to the elements. A common practice is to increase the thickness of structural members by 3 mm to account for potential corrosion.

However, belt conveyors are frequently placed in industrial settings, exposed to process water, saltwater splash zones, corrosive bulk materials, ultraviolet light, and other elements that may cause deterioration. In potentially corrosive environments, such as marine settings or when handling corrosive materials, corrosion protection must be specifically tailored to the situation. Typically, corrosion can be mitigated by applying a suitable surface protection method, such as a paint system or galvanising. In extreme cases, constructing the conveyor structure from corrosion-resistant materials like aluminum, stainless steel, or timber should be considered.

Regardless of the chosen corrosion protection method, care should be taken to avoid design details that promote deterioration. Features that allow water or conveyed materials to accumulate can accelerate corrosion. The attachment of dissimilar metals may also lead to corrosion through galvanic action. Additionally, abrasion from moving components can strip protective coatings, exposing the underlying material to corrosion.

Connections in corrosive environments require special attention. Slip-critical bolted connections necessitate particular preparation, including the removal of paint at the joint. The compatibility of bolted connections with the corrosion protection system of the structural members should also be considered.

Paint
The most common corrosion protection method is painting the conveyor structure. Paint application techniques range from simple wire brushing and a single coat of paint to more advanced methods, such as sandblasting, acid etching, and the application of high-build epoxy paint systems. The level of protection depends on the expected lifespan of the conveyor and the severity of the corrosive environment. Guidelines for proper surface preparation and suitable paint systems for various conditions can be found in the Steel Structures Painting Council (SSPC) manuals.

Advantages of paint:

• Widely available and easy to apply
• Less expensive compared to other corrosion protection systems
• Can be easily repaired in the field
• Available in a variety of colors

Disadvantages of paint:

• Provides a relatively shorter lifespan for corrosion protection
• Scratches may allow unnoticed deterioration beneath the paint
• Cannot coat interior surfaces of pipes or tubes

Galvanizing
Galvanizing is another widely used surface protection method in which steel components are dipped in molten zinc or a zinc alloy, forming a corrosion-resistant coating. In most environments, galvanizing offers longer-lasting protection than paint. Because of the galvanic action between the steel and zinc, minor scratches will self-heal, maintaining corrosion resistance.

When preparing steel for hot-dip galvanizing, careful consideration must be given to the design. Completely enclosed air spaces, such as pipe columns with end plates, can explode during the process due to heat expansion. Properly placed vent holes must be included to allow gases to escape while also ensuring that they do not collect water or material during operation.

Galvanizing offers long-term protection and can coat interior surfaces that are inaccessible to paint. However, repairing galvanized steel in the field is challenging, and the heat involved in the process may distort lighter structural members.

Corrosion-Resistant Steels
For high levels of corrosion resistance, conveyor frames can be constructed using corrosion-resistant materials such as stainless steel or weathering steel.

• Stainless Steel: This material offers excellent corrosion resistance across various environments. Available in multiple grades, stainless steel maintains its resistance through its entire thickness, meaning that scratches do not compromise its protective properties. However, stainless steel is costly, and its use is typically reserved for situations where extreme corrosion resistance is required.
• Weathering Steel: Designed to develop a protective surface oxidation layer, weathering steel forms a barrier against further corrosion. If scratched, the steel regenerates its protective layer. However, initial oxidation may stain nearby surfaces, and welding techniques must be chosen carefully to ensure compatibility with weathering steel properties.

Alternate Materials and Methods
In some cases, alternative materials may be used to mitigate corrosion-related deterioration. Cathodic protection systems can be implemented for steel structures, though they are not commonly used in conveyor construction.

• Aluminum and Light Metals: These materials offer corrosion resistance in many environments, making them particularly suitable for smaller or lightweight conveyor components. While aluminum is significantly lighter than steel, it lacks the same strength and stiffness. Many aluminum alloys undergo heat treatment, so welding techniques must be carefully selected to avoid reducing strength in critical areas.

Regulations may restrict the use of aluminum, magnesium, and titanium alloys in underground mining operations where fire or explosion hazards exist. These metals can react with rusty steel upon impact, potentially triggering a thermite reaction capable of igniting methane gas.

By carefully selecting appropriate corrosion protection measures, conveyor structures can achieve long service lives, even in highly corrosive environments.

Preventing rainwater from being trapped

Here are some key tips and methods to prevent rainwater from being trapped in holes when designing a conveyor structure:

1. Provide Proper Drainage Holes – Ensure all hollow sections and boxed structures have adequately sized and strategically placed drain holes to allow water to escape.
2. Use Sloped Surfaces – Design surfaces with a slight incline so water naturally runs off instead of accumulating in flat or recessed areas.
3. Avoid Horizontal Surfaces with Pockets – Minimize areas where water can pool, such as flat plates with holes or recessed bolt holes.
4. Seal Welds and Joints – Where possible, use continuous welds instead of stitch welds to prevent water from seeping into crevices and accelerating corrosion.
5. Avoid Closed or Hollow Sections Without Venting – If using hollow structural members, provide vent holes to prevent water entrapment, ensuring they do not collect dirt or debris.
6. Galvanizing and Coating Considerations – Ensure any protective coatings or galvanizing processes account for potential water entrapment, using well-placed openings to facilitate drainage.
7. Rounded or Beveled Edges – Instead of sharp or flat edges, using rounded or beveled designs can help direct water away from sensitive areas.
8. Use Water-Resistant Fasteners and Materials – Employ stainless steel or coated bolts and fasteners that resist corrosion even if exposed to trapped moisture.
9. Regular Maintenance and Inspections – Design the structure with accessibility in mind to allow periodic checks and clearing of any blockages in drainage holes.