Hot Dip Galvanizing – Characteristics and Costs
Hot dip galvanizing
Hot dip galvanizing is an anticorrosive treatment of steel that is applied by immersing the products, after a series of pre-treatments, in a bath of molten zinc.
The differences and characteristics
Unlike paints, where we are talking about a polymer film, in the case of hot dip galvanizing we are talking about a metal, namely zinc. Already this first difference highlights extremely different performances: the painting can be easily damaged already in the simple and simple loading and unloading operations or on site handling, while for zinc, due to its very metallic nature, it has an enormously superior resistance to shocks. and abrasions, moreover the hot galvanizing protects both the external and internal surfaces.
Another fundamental difference between galvanizing and painting is the adherence of the protective layer. It is one of the main positive characteristics of hot dip galvanizing, with the exception of galvanizing, all anticorrosive treatments consist of a layer that acts as a barrier between the steel and atmospheric corrosive agents, this is not enough if for any reason, a abrasion or a simple scratch to allow corrosive agents to creep between the protective layer and the steel forming rust.
This process does not take place for hot galvanizing, since it is not a simple covering film, in fact during the immersion in the molten zinc a real iron-zinc alloy is formed which, as such, is tenaciously clinging to the steel and is removable only with a robust mechanical action or with strongly acid solutions, for this reason even if it were to be able to scratch the zinc layer for its entire thickness, atmospheric corrosive agents could not proceed further penetrating under the zinc layer being, as said, alloyed with steel.
Another consideration to make is that with aging paints, in addition to being subjected to the aggression of UV rays, become permeable to water and high aggressive substances, zinc instead maintains its characteristics absolutely unchanged throughout its cycle of life.
The life cycle of hot dip galvanizing
The zinc layer, if exposed directly to pollutants and atmospheric agents, progressively transforms into oxidized compounds, of which a part participates in the protective action and a part is removed by the mechanical action of the rains.
This phenomenon is repeated continuously for many years until the zinc is completely consumed; however, it must be said that, when this has occurred, the steel structures will still be perfectly intact as they have never been attacked by the corrosion that begins only when the steel actually remains uncovered. In fact, zinc performs its function even if reduced to a very thin layer.
To understand how long it takes the zinc layer to wear out, you need to know its thickness and corrosion rate. The thickness of zinc is generally a function of the thickness of the steel and can vary, for structural steels greater than 5-6 millimeters, between 85 and 150 microns and beyond.
The corrosion rate can vary between 0.1 and 2 microns per year in the most common use scenarios while, in extreme conditions, it can even go beyond this limit.
On the basis of these data, excluding extreme or rare usage scenarios, it can be said that the duration of protection offered by hot dip galvanizing can vary from a minimum of 40 years to well over a century.
What can be hot dip galvanized?
Anything that is made of steel can be hot dip galvanized. It is possible to galvanize large and small structures: Pillars, coatings, trusses, pipes, emergency stairs, fences, gratings, lattices, poles, street furniture, ski lifts, scaffolding, tanks, bolts, etc., the list would be endless because, like said, everything that is steel can be galvanized, the main limit is set by the size.
Hot-dip galvanizing price: Is the cost of galvanizing excessive?
Even if most of the steel structures that could also be galvanized and are not, the reason is certainly not the cost of galvanizing, since it remains in the same order of magnitude as painting, as regards the immediate but is of great importance. long shorter in relation to the duration and therefore to the absence of maintenance over time.
The colors of the galvanizing … is it possible to obtain other colors besides the classic gray?
The answer of course is no! But it is possible to apply paints of any color, finish and brilliance to the galvanizing. The result of this operation, which certainly has a higher cost than galvanizing alone, is to obtain an even higher protection, and therefore a duration. At this point, the two anticorrosive treatments develop such a synergistic effect that the duration of the protection far exceeds the sum of the durations of the two treatments, if considered individually. The useful life of the product is further increased and always without the need for maintenance.
Is it worth hot-dip galvanizing?
Hot-dip galvanizing protects steel structures for a time that often exceeds the useful life cycle of the structures, is eco-sustainable and preserving from corrosion keeps the design characteristics unaltered, collaborating in the general safety of a work. It also has a low initial cost and comparable to other anticorrosive systems and since it does not require maintenance for decades, it greatly reduces the cost of a work over time.
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