powder coatings

Galvanized steel versus powder coatings for outdoor environments

Thursday, April 13, 2017

Chipping, fading and corrosion are common concerns when deliberating over the use of galvanized steel coating or powder coating for outdoor furnishings, such as handrails and guardrails, bike racks, playground equipment and park benches. Both coatings; however, are quite different in how they protect components and how they are manufactured. Here, Larson Electronics offers guidance on their unique advantages.

Galvanized Steel Coatings (HDG)

Galvanization is the practice of dipping steel in hot, molten zinc, and a ‘metallurgical bond’ should form between the zinc and steel. This process helps steel-based structures last longer (about 50 to 100 years) at a corrosion rate of 1/30 of bare steel, and is low-cost in terms of maintenance and first-time and lifetime costs.

“Galvanization offers cathodic protection for steel,” notes Andrew Holland of Larson Electronics. “When exposed to moisture from outdoor environments, zinc corrodes very slowly, protecting the base metal – even if small parts of the surface succumb to rust. This streamlines maintenance, as reapplication of coatings is not needed with the zinc layer present.”

Powder Coatings

Powder coating is an organic process that involves barrier-layer protection. An electrostatically charged coating is applied to the surface – specifically a positive charge to the dry powder (thermoplastic or thermoset polymer). This bonds with the negatively charged surface of the base component, creating a rich protective layer.

There are copious benefits of this coating. For instance, it takes about 20 minutes to complete and layers don’t hinder the flexibility of the base item. This helps components endure vibration, chipping, fading corrosion and rough weather. Aesthetically, Holland notes that powder coating is applicable to products that require coloured finishes or textures.

When exposed to outdoor or marine environments, powder coatings can resist corrosion, abrasion and chemicals – but only up to a certain threshold,” adds Holland. “Compared to paint, this type of protection is exponentially more reliable. To ensure protection, powder coatings must be maintained properly by applying paint over the exposed or chipped surface.”

For more guidance, ISO 12944 is an international standard on corrosion protection of steel structures by protective paint systems. It consists of several parts. Holland says that for marine locations, such as coastal areas, users must refer to category C5-M. ISO 12944 guidelines for C5-M marine environments recommend the application of zinc-rich primer, epoxy intermediate or polyurethane to ensure durability for at least 15 years.

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