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Steel protection

Picture courtesy of Sherwin-Williams

Advances in modern surface treatment technology, including coatings and galvanizing, are optimising the protection of constructional steelwork and delivering the required durability at minimum cost. NSC takes a look at the protective systems sector.

Safeguarding structural steelwork with the correct protection will give a steel frame an improved performance as well as extend the life to first maintenance, thereby reducing ongoing maintenance costs

The key is to recognise the environment and what the structure is likely to be exposed to before deciding on the appropriate surface treatment.

If the steelwork is in a dry heated interior environment the risk of corrosion is insignificant and no protective coating is necessary.

However, a steel structure exposed to an aggressive environment needs to be protected with a high performance treatment and may need to be designed with maintenance in mind if extended life is required.

Coatings for steel structures have developed considerably in recent times in order to comply with industrial environmental legislation, and in response to customers wanting improved durability and performance.

One of the challenges that the sector has faced is the requirement for high quality paints that dry and cure more rapidly in order to allow for a faster application procedure.

The development of new fast-drying paints delivers reduced drying times and shorter re-coating intervals, which enables steel to be handled and transported offsite at a greater turnaround rate.

The application of an intumescent coating protects a steel-framed building in a fire scenario. Intumescent coatings can be divided into two broad families: thin film and thick film.

Thin film intumescent coating systems are mainly used in buildings where the fire resistance requirements are 30, 60 and 90 minutes. In recent times, a number of products have been developed which can provide 120 minutes fire resistance. All of these coatings can be applied either on site or offsite and can be used to achieve attractive surface finishes.

Thick film intumescent coatings are usually epoxy-based and typically have a much higher dry film thickness than thin film alternatives. These materials are tough and durable and can generally be used to protect against hydrocarbon and cellulosic fires. Aesthetic finishes are possible and they can also be supplied in the form of preformed casings. Thick film intumescent coatings can also be applied offsite.

The most commonly used method for applying a protective metal coating to constructional steelwork is hot-dip galvanizing.

This process involves immersing steel components in a bath of molten zinc (at about 450°C). The immersed surfaces are uniformly coated with zinc alloy and zinc layers that form a metallurgical bond with the substrate. The resulting coating is durable, tough, abrasion resistant, and provides cathodic (sacrificial) protection to any small damaged areas where the steel substrate is exposed.

Wedge Group Director of Sales & Marketing, David Fitzpatrick says: “Galvanizing provides long-term protection against corrosion and it is undertaken in a factory controlled environment rather than on site. The great thing about galvanized steel is that it can be transported straightaway without the need for drying time.

“The galvanizing sector is able to protect a range of steel products from nuts and bolts to 21m long beams. Longer items up to 29m can be achieved through double dipping if necessary for large construction projects. The nature of the coating also means that life to first maintenance can be in excess of 60 years depending on the environment it is being used in.”

Protective Coatings

Wedge Group Galvanizing

Jack Tighe Ltd

Joseph Ash Galvanizing,

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