FAQ's for Galvanizing
Zinc metal used in the galvanizing process provides an impervious barrier between the steel substrate and corrosive elements in the atmosphere. It does not allow moisture and corrosive chlorides and sulfides to attack the steel. Zinc is more importantly anodic to steel. This means it will corrode before the steel, until the zinc is entirely consumed.
There are four steps:
Pre-inspection – where the fabricated structural steel is viewed to ensure it has, if necessary, the proper venting and draining holes, overall design parameters which are necessary to yield a quality galvanized coating
Cleaning – steel is immersed in a caustic solution ( Degreasing Solution ) to remove oil. Grease, dust and dirt, This is followed by dipping in an acid bath (hydrochloric) to remove mill scale, rust, & finally dipped in bath of flux that promotes zinc & steel reaction, retards further oxidation (steel will not react with zinc unless it is perfectly clean)
Galvanizing – the clean steel is dipped into a kettle containing 4500C molten zinc where the steel. zinc metallurgically reacts to form three zinc-iron inter-metallic layers and one pure zinc layer
Final inspection – the newly galvanized steel is sight-inspected, followed up by measurement of coating thickness with a magnetic thickness gauge
Hot-dip galvanized steel resists corrosion in numerous environments extremely well. It is not uncommon for galvanized steel to last more than 70 years under certain conditions.
The corrosion rate of zinc and how long it will provide protection is a function of the coating thickness and the amount of corrosive elements in the atmosphere. For example, in rural settings where there is less automotive/truck exhaust and plant emissions, galvanized steel can easily last for 100 – 150 years without maintenance. Industrial and marine locations contain significantly more aggressive corrosion elements such as chlorides and sulfides and galvanized steel may last for 50 – 100 years in those cases.
Almost any and every type of Mild Steel fabrications for a variety of applications are Hot Dip Galvanized.
The galvanized coating appearance may either be bright and shiny resulting from the presence of an outer layer of pure zinc, or duller, matte gray as the result of the coating’s intermetallic layers being exposed. Performance is not affected. Coating appearance depends on the amount of zinc in the coating. Shining also results on the percentage of Aluminium in the Galvanizing bath as well as the Composition of flux.
Coating thickness depends on the thickness, roughness, chemistry, and design of the steel being galvanized. Any one or all of these factors could produce galvanized coatings of non-uniform thickness.
First of all, the variety of things galvanized is broad. Structural steel (angles, channels, wide-flange beams, I-beams, H-beams), grating, expanded metal, corrugated sheets, wire, cables, plate, castings, tubing, pipe, bolts & nuts. The industries that utilized hot-dip galvanized steel range from Infra & EPC Projects, water & wastewater treatment plants architectural Steel Structures (Canopies, facades, exposed structural steel, lentils, reinforcing steel for concrete decks, exposed structural steel columns & barriers, pulp & paper plants (structural steel, walkways, handrail), motor housings, electrical cabinets, frames, heat exchanger coils) : Transmission towers, distribution poles, substations, wind turbine poles), Signal Antennas, cell towers, rail transportation (poles, switchgear, miscellaneous hardware), chemical/petrochemical plants, Off-Shore constructions,(pipeline hardware manufacturing buildings, storage tanks, walkways) SILOS, tank Farms, Chemical & Steam Pipelines, fence poles, boats, trailers, stadiums, arenas, Road Crash Guards, racetrack fences) Pre Engineered Metal Buildings and almost every Mild Steel Fabrications..
Called duplex coatings, zinc and paint in combination (synergistic effect) produce a corrosion protection approximately 2 Times the sum of the corrosion protection that each alone would provide. Additionally, duplex coatings make for easy repainting, excellent safety marking systems, and good color-coding. Painting over galvanized steel that has been in service for many years also extends the life of the zinc coating.
Galvanized coatings can be easily and effectively painted, not only for aesthetics but also to extend the structure’s service life. The age and extent of weathering of the galvanized coating dictate the extent of surface preparation required to produce a quality paint system over galvanized steel. ASTM D 6386, Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting, should be refered for suggested surface preparation methods for galvanized coatings of varying ages.
There are no known studies to suggest zinc corrosion products cause any harm to the environment. Zinc is a naturally occurring element (25th most abundant element in the earth), and necessary for all organisms to live.
In order for zinc to develop its protective patina of zinc carbonate that is very stable and non-reactive, it requires a wetting and drying cycle like that produced by nature. Salt spray tests keep the zinc wet and essentially wash the zinc corrosion products off as they develop, inflating corrosion rate of zinc. This lab test is not reflective of real -Life performance of zinc coatings.
There is no such thing as cold galvanizing. The term is often used in reference to painting the Mild Steel Fabrication or damaged galvanized structure or object with 99%+ pure zinc-rich paint. Galvanizing by definition means a metallurgical reaction between zinc and iron to create a metallic bond between the zinc and the steel of approximately 3600 psi. There is no such reaction when zinc-rich paints are applied and the bond strength is only several hundred psi. Application of ZINC Rich Paints will Completely SEAL THE EXPOSED, SCRATCHED, WELDED, DAMAGED Surface (resulting from REMOVAL OF Zinc Layer on Mild Steel). Such damaged surfaces are VIRGIN and are much more prone to atmospheric Corrosion. Corrosion and Rusting are a SUB-SURFACE Phenomenon and will propagate under the Galvanized Zinc Coating layer. Hence it is Customary and Mandatory to coat such areas with Cold Galvanizing Zinc Rich Paints.
Yes. Zinc Rich Paints offer BEST ANTI CORROSION Properties to MS Structures compared to any other Primer + Paint Systems. Apart from Highest Anti Corrosion, Zinc Rich Paints also offer Aesthetic Finish Coating & eliminates use of Multiple Paint coating Applications.
Our ZINKOTE 20 GP and ZINKOTE 20 Premium Paints are manufactured using 99%+ PURE ZINC METAL DUST/FLAKES. As these are extremely Pure ZINC METAL based and blended with Instant Air Drying Pure Acrylic Resin, they offer a MUCH SUPERIOR & UNIQUE ANTI-CORROSION, compared to the normal ZINC PIGMENTS based paints.
When you are using Zinkote 20 Paints or Zinc Sprays for Cold Galvanizing, It is NOT NECESSARY to use any Zinc Phosphate / Chromate / Silicate based Primers. More-Over, Hot Dip Galvanizing is a Pure Zinc Molten Film Metal to Metal Bond Between Iron metal and Zinc Metal. Hence Zinc Rich Paints are very superior to Zinc Compound based paints, in terms of VERY LONG ANTI CORROSION LIFE of the GI & STEEL Fabricated Structures.
