We can view rust as the nemesis of steel structures and components.
This reddish-brown iron oxide forms when steel is exposed to moisture and oxygen. It gradually weakens the metal, compromising its structural integrity.
Scientific research shows us that rust (corrosion) affects the mechanical properties of steel due to the formation of pits (small cavities).
Understanding how to prevent rust is crucial to extending the lifespan of industrial equipment. This article explores some of the key methods to prevent steel rusting, including coatings that protect steel, design considerations, environmental controls and more.
Coatings to prevent rust
We’ll start by focusing on the various coatings that can help to prevent rust and protect steel.
Galvanisation
Galvanisation involves applying a protective zinc coating to steel surfaces. The zinc acts as a sacrificial anode, corroding before the steel and providing protection even when the coating is slightly damaged.
Hot-dip galvanising creates a metallurgically bonded zinc layer that can protect steel for decades in many environments. This method is particularly effective for outdoor structures, fencing and agricultural equipment.
Paint systems
Anti-corrosion paint systems typically consist of multiple layers. There are primers, which contain rust-inhibiting compounds such as zinc phosphate; intermediate coats, which provide thickness and enhanced protection; and topcoats, which offer weather resistance and desired appearance.
Modern epoxy-based paints offer excellent adhesion and chemical resistance, while polyurethane topcoats deliver superior UV protection and colour retention.
Proper surface preparation is essential when applying a paint system. This typically includes cleaning, degreasing and removing any existing rust through mechanical or chemical means.
Oil-based treatments
Oil coatings create a hydrophobic barrier that prevents moisture from reaching the steel surface. They include penetrating oils that displace moisture and provide temporary protection, and heavier oils and greases that offer longer-lasting protection. These treatments are particularly helpful for tools and machine parts.
There are also specialised rust-preventive oils that contain additives like vapour phase inhibitors. Oil-based treatments need to be reapplied regularly, especially in high-humidity environments and for frequently handled items.
Dry coating methods
Dry film lubricants and corrosion inhibitors offer protection in a different way. PTFE (polytetrafluoroethylene, or ‘Teflon’) coatings provide a non-stick, corrosion-resistant surface, while molybdenum disulfide coatings offer both corrosion protection and lubrication.
There are also graphite-based coatings that can withstand high temperatures while preventing rust – these are suitable for machinery and tools in hot industrial environments.
Dry coating methods are ideal for precision manufacturing components used in environments where oil might attract contaminants or interfere with functionality. They are also commonly used in electronics and aerospace applications.
Powder coating
Powder coating involves applying dry powder to steel electrostatically, before curing it under heat to form a hard finish. It creates a thick, uniform coating that is highly resistant to chipping and scratching.
Powder coating is available in a broad variety of colours and textures, ticking the boxes for aesthetics.
Two more advantages of powder coating is that it is excellent for covering the edges of metal structures compared to liquid coatings, and that it is more environmentally friendly, with minimal VOC (volatile organic compounds) emissions.
Powder coating is ideal for components used in industrial systems, as well as outdoor furniture, appliances and architectural elements, providing an effective barrier against moisture and oxygen.
Design considerations
Rust formation can also be avoided with the intelligent design of metal machinery and structures. In order to avoid rust, the design should seek to avoid water traps and ensure proper drainage, as well as give components adequate ventilation.
Structural design should also eliminate crevices where moisture can accumulate. To prevent direct contact between dissimilar metals, spacers should be used. It also helps for all areas of steel structures to have access points that allow for inspection.
Environmental control
Managing the environment around steel components is also a consideration. Correct environmental control can dramatically reduce corrosion risk.
It is generally recommended to keep relative humidity below 50% when possible, and to control temperature to avoid condensation. Exposure to industrial pollutants and salt spray should be avoided, and during storage or shipping, desiccants – substances that absorb moisture from the air to keep objects dry – can be used in enclosed spaces.
Cathodic protection
For large structures, especially those underground or underwater, cathodic protection systems can be highly effective.
These systems shift the electrochemical potential of the steel, preventing the corrosion reaction from occurring. This approach is commonly used for pipelines, storage tanks and marine structures.
Arresting the rust
Ultimately, preventing rust comes down to employing the correct methods for each steel structure and component; utilising coatings, designing products with corrosion prevention in mind and paying heed to the demands of each environment.
