The hot dip galvanizing process per se consists of the immersion of the piece in molten zinc for a few minutes, at a temperature between 450±5 oC.. Hot dip galvanizing is generally applied to soft steel and steelwork, to crude iron or molten steel.

Metalwork as long as 9 m can be hot dip galvanizing in a double hot dipping process.

Requirements for metalwork which is to be hot dip galvanized:

The metalwork to be hot dip galvanized should have accessible surfaces and should be easy to handle. The mechanical rigidity of the piece will be maintained as much as possible, in order to avoid its distortion in the tank.

The surface of the raw metal should not have pores, fissures, retouches, non-metallic materials, paint, oil, or grease stains, cinders, oxides, other flaws which can persist after hot dip galvanizing, having a negative influence on the aspect and quality of the coverage. The pieces will be designed and made according to the specific requirements of hot dip galvanizing and SR EN ISO 1461-2009. In order to obtain a hot dip galvanizing layer with even thickness and quality, the elements that make up the steel should not exceed the following values: silicium (0.12%-0.25%), phosphorus (max.0.25%), carbon (max.0.2%). manganese (max.1.5%). For the steel that contains more than 0.04% Si, the thickness of the layer will reach the value of 0.08%Si. Between 0.08% Si and 0.17 Si, the zinc layer diminishes, growing again for values above 0.22%Si.

The alloyage used by BergBanat in the hot dip galvanizing tank also contains Ni, which enables it to increase its fluidity, with positive consequences on the thickness of the layer found on the piece. Under these circumstances, the surface becomes smoother and has an increased resistance against the wearing course.

Requirements for the zinc layer:

For proper hot dip galvanizing, the zinc used should have a purity of at least 98.5 %, according to SR EN ISO 1461-2009. The average thickness and the weight of the zinc layer per surface unit fit the values in Chart 1.

The minimal thickness of the coverage should be at least 80 microns of the prescribed value in the chart. The zinc layer should be continual on the entire surface. Uncovered spots, rust stains, acid, flux or ash stains are not allowed. The surface of the zinc layer should be smooth, with no swellings, blisters, scrubs or excessive coverage. The colour of the zinc layer can vary from shiny silver to matted grey, depending on the composition of the material. The flaws resulted from the hot dip galvanizing process can be repaired only with zinc or zinc-aluminum spray.

Resistance to corrosion

The zinc alloyage deposited after the hot dip galvanizing protects the surface of the pieces by means of the barrier created between the steel and the environment and by means of a cathodic protection (the zinc has a lower electro-chemical potential than the iron, so the former becomes anode, while the latter becomes cathode). It is a known fact that the zinc layer has the following under-layers: eta, zeta, delta, gama, alpha, each of them having a different degree of hardness and each of them being successively exposed to corrosion. The eta layer being the first one, it is exposed in the first hours after the hot dip galvanizing process. The products resulted from the corrosion are invisible at first, but later they turn white, they become soluble and can be washed off by the rain. The following layers are then exposed to corrosion, the speed of this process depending on such factors as: the frequency and duration of the exposure, the degree of moisture, the wind speed and direction, dust, the sun, the degree of pollution in the original environment of the piece. To give an example, it is a fact that the sulphur dioxide has a strong influence on the corrosion of zinc, and this is why the maximum level of corrosion is reached in winter, when the fuel used for heating gives off large quantities of sulphur dioxide.

Transportation and storage

In order to avoid the deterioration of the zinc layer, the pieces are handled with textile tie bands and laid down on wooden beams or rubber (plastic) buffers, so that the scratching or the alteration of the protective zinc layer can be avoided.

Carbon footprints, renewable resources, energy efficiency – suddenly sustainability has become a real hot topic, but what does it really mean? This booklet gives a brief overview of the important role galvanizing has to play in sustainable construction.

With the Earth’s natural resources at more of a premium than ever, the need to be environmentally aware when it comes to construction is a must.

Galvanizers Association has been a major contributor to the European Initiative for Galvanizing in Sustainable Construction. Many independent experts have contributed to this initiative including Prof. Tom Woolley, a well known advocate of green and natural building. The aims of the initiative were to help architects, specifiers, engineers, developers and their clients consider how to use galvanized steel in the context of sustainable construction.

“The galvanizing industry can undoubtedly make many improvements, but I welcome their willingness to address the issues and take a hard look at themselves to see whether they can contribute to the sustainability imperative.” Tom Woolley Professor at Graduate School of the Environment, Centre for Alternative Technology (CAT)

SO WHAT EXACTLY IS GALVANIZING?

In as simple terms as possible, Hot Dip Galvanizing is the process of coating steel with a layer of zinc. And the benefits? As well as providing long-term durability and protection from corrosion, a real benefit is the relatively low environmental burden associated with the whole process.

When clean steel is dipped into molten zinc a unique coating develops that creates a strong bond with the steel. This protective coating is tougher and more resilient than other coatings that only bond chemically or mechanically.

WHY GALVANIZE?

Galvanized steel is everywhere; in the lighting columns that brighten our roads, the high voltage pylons that power our homes, even in the cars and trucks that get us from A to B. In fact, anywhere that corrosion protection and long-life are essential, you’re likely to find galvanized steel.

While undeniably versatile, steel does have the unfortunate drawback of being susceptible to corrosion when left out in the open – amazingly many countries estimate 4% of GDP is lost to corrosion. That’s when employing galvanizing can make all the difference: long-term durability, a tough and resilient coating – the benefits are clear. What’s more, galvanizing also provides improved economies of scale by eliminating repeated on-site maintenance and replacement costs.

• A galvanized coating can provide more than 60 years of maintenance-free life

• The coating can be more robust than the steel it is trying to protect

• The coating is simple and easy to apply

• All parts of the steel are coated – external and internal

INSIDE A GALVANIZING PLANT

While galvanizing plants have been around since the late 1800s, it’s fair to say a lot has changed since then. Present day plants feature computer controlled processing technology that play an integral role in managing the process.

They are also being designed with their environmental performance and recycling in mind. For example, plants are designed to reuse water and waste heat throughout the galvanizing process. What’s more, galvanizing plants are continually implementing new ways to make them more efficient than ever.

HOW THE GALVANIZING PROCESS WORKS ?

The galvanizing process can essentially be split into two important stages: cleaning and galvanizing. The cleaning stage chemically washes the steel so that it is ready to react with molten zinc. The steel can then be submerged into a molten zinc bath to obtain the coating.

ZINC – THE NATURAL PROTECTOR

It’s fair to say zinc can be found pretty much everywhere. Not only is it naturally present in rock and soil, you will also find it in water, plants, animals and even the air. In fact, zinc is an essential mineral necessary for sustaining all life. Furthermore, it is highly abundant and can be indefinitely recycled.

Zinc protects steel against corrosion by both forming a physical barrier and through electrochemical protection. When it reacts with air, a surface film that is insoluble in rainwater forms a barrier. This prevents moisture and oxygen from reaching the steel and corroding it.

• Zinc is a natural component of the Earth’s crust and all living organisms need zinc

• Zinc is used in sun block products, shampoo and vitamin supplements

• 30% of all zinc comes from recycled sources

• Zinc for galvanizing contains a high proportion of recycled zinc.

STEEL – THE ADAPTABLE ALLOY

Steel is rightly considered a highly versatile material. It plays a major part in our modern lives, from our buildings and transport systems, to our home appliances and the tools we rely on in the workplace. Steel can be recycled continuously without significant deterioration to its quality, making it highly sustainable as very little is ever wasted. Ideal for construction, steel has many qualities that make it simple to work with. For starters, it is lightweight making it easy and quick to erect, it can also be pre-engineered to cut down the need for manpower. Then there’s the fact that steel is easy to modify or reshape whilst remaining stable at all times.

• Steel is one of the world’s most recycled materials. Over 90% of steel is recycled

• Steel is easy to use, modify and salvage from construction

• The flexibility of steel allows demounted structures to be rebuilt in whatever form is required.

WHAT ON EARTH IS SUSTAINABLE CONSTRUCTION ?

This planet may not be perfect, but let’s not forget it’s the only one we’ve got. That’s why it’s now more important than ever to choose building materials and products that are as sustainable as possible. However, with everyone talking about sustainable construction, how do you distinguish between genuine change for the better and ‘greenwashing’?

The Brundtland definition of sustainability (above right), if interpreted correctly, provides a very good benchmark from which to judge most human activities. In terms of building construction it implies that we should be extremely careful about using resources which are scarce and cannot be renewed. Whatever we do should be able to last a long time or be recycled and used again. In addition fossil fuel energy should be minimized and pollution controlled.

Excerpt from Brundtland Report – “Humanity has the ability to make development sustainable – to ensure that it meets the needs of the present without compromising the ability of future generations to meet their needs.”

SO WHY IS GALVANIZING SUSTAINABLE ?

Simply put, galvanizing protects steel from corrosion, lengthening its lifespan and eliminating the need for replacement steel at a cost to the environment. But that is really only half the story:

Low Life Cycle Energy : Galvanizing is energy efficient throughout its production and whole life cycle.

Resource Efficient : The galvanizing process uses natural resources considerately to ensure a relatively low environmental burden.

Recyclable : Whether it’s re-galvanizing, removal or reuse, galvanized steel is easily recycled. What’s more, it can also be recycled with steel scrap.

Long-life : Galvanizing protects against corrosion and prolongs the life of steel, greatly lowering both the environmental and economic cost.

Cost Efficient : The initial investment of using galvanized steel for long-term protection in construction can provide cost benefits for decades.

THE ADVANTAGES OF HOT DIP GALVANIZING COMPARED TO OTHER COATING PROCEDURES OF METAL SURFACES