Architectural galvanizing in the spotlight
Little has changed in almost 187 years in the hot-dip galvanizing industry to protect steel structures against corrosion. However, on the aesthetic front there has been a sea change in the way in which galvanized products are being presented, explains Nick Karakasch, retired principal of Total Corrosion Consultants, Melbourne, Australia.
Designers are increasingly calling for an ‘architectural finish’ to steel structures, creating in effect a new product which needs specific consideration from the outset. The bare metallic finish and natural texture of uncoated galvanized surfaces is often selected for architectural work based on its impact as a self-finish. As a result, this brings into play a whole new set of considerations which can affect the visual qualities of the finished product.
Galvanizing has a track record in not all but most atmospheric environments, where service life up to 25 years-plus is commonplace. In some instances, particularly in dry rural environments, 110 years has been achieved. There are also documented case histories of transmission towers in windswept coastal regions around the world lasting up to 75 years before requiring maintenance.
The prime purpose of galvanizing is to provide corrosion protection for steel. Throughout the world it is commonly referred to as either hot-dip or static galvanizing. Both descriptions are covered by the internationally-recognised standards ISO 1461, Australian Standard AS/NZS 4680 and USA ASTM A123. However, it is important to understand that these standards only address product description and process method and do not cover an increasingly-significant element of aesthetic appearance of the work piece, fusing to the steel rather than forming a separate metal surface, commonly referred to as adhesion at the atomic level.
It is not always possible to judge that the alloy metal created will be acceptable. Variations in steel composition can result in notable differences in appearance, even though these may be well within standard specifications required for protective properties. The use of some steels can also make the creation of the desired effect less likely, due to vagaries in the way in which they accept the galvanizing process. With knowledge that architectural appearance is required, the steel fabricator together with the galvanizer can take extra precautions to achieve uniform appearance and normal alloy weight.
Historically, choosing a galvanized product was relatively simple. For the first 100 years or so it was the only product available; today many zinc-based products are on the market via differing processes which can and have confused the consumer. It is vitally important to understand what is on offer, particularly where long-term protection is the expectation, otherwise, materials with lower performance qualities may be unwittingly chosen.
Read more of this article in the latest issue of Protective Coatings Expert