Pradeep Vaidya, CEO of Innovative Coating Industries explains answer to the FAQs about hot-dip galvanising and cold galvanising of mild steel.

Frequently Asked Questions (FAQs)

How does galvanising protect steel from corrosion?
Zinc metal used in the galvanising 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.

What are the specifications governing hot-dip galvanised steel?
Structural steel (plate, wide-flange beams, angles, channels, pipe, tubing) are galvanised to ASTM A 123/A 123M. Fasteners and small parts that fit into a centrifuging basket are galvanised to ASTM A 153/A 153M. Reinforcing steel is galvanised to ASTM A 767/A 767M.

What is the difference between hot-dip galvanised fasteners and zinc-plated fasteners?
Hot-dip fasteners generally have about 10 times as much zinc on the surface and are suitable for use in all exterior and interior applications. Zinc-plated fasteners will provide a dissatisfactory anti-rust performance if used outside, especially when used to connect hot-dip galvanized structural steel members.

Where are galvanised steel products used?
First of all, the variety of things galvanised 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 and nuts. The industries that utilised hot-dip galvanised steel range from infra and EPC projects, water and wastewater treatment plants architectural steel structures (canopies, facades, exposed structural steel, lentils, reinforcing steel for concrete decks, exposed structural steel columns and barriers, pulp and 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 or petrochemical plants, off-shore constructions, (pipeline hardware manufacturing buildings, storage tanks, walkways) SILOS, tank farms, chemical and steam pipelines, FENCE poles, boats, trailers, stadiums, arenas, road crash guards, racetrack fences) pre engineered metal buildings and almost every mild steel fabrications.

What is the difference between hot-dip galvanising after fabrication and continuous hot-dip galvanised sheet?
The process steps are similar but the production equipment is very different. After fabrication galvanising is a more manual process where structural steel (fabricated plate, wide-flange beams, angles, channels, tube, pipe, fasteners) is suspended by wire, chain or hook from crane hoists and immersed in the cleaning solutions and zinc. Continuous sheet galvanising involves uncoiling sheet, passing it through the cleaning steps and molten zinc bath at speeds up to 500 feet per minute, drying and recoiling. The uses of after-fabrication galvanised steel are usually exterior in nature because the zinc coating is relatively thick (3.0 – 6 mils, 75 – 150 microns, 1.7 to 3.6 oz/sq. ft.) and will protect steel from corrosion in most severe and corrosive atmospheric conditions for 50 to 100 years. Galvanised sheet is suitable for interior applications because of the relatively thin coating (0.45 oz on each side), unless it is painted after galvanising.

What is cold galvanising?
There is no such thing as cold galvanising. The term is often used in reference to painting the mild steel fabrication or damaged galvanised structure or object with 99 per cent pure zinc-rich paint. Galvanising 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, weldedc, 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 galvanised zinc coating layer. Hence it is customary and mandatory to coat such areas with cold galvanising zinc rich paints.

Contact:

Pradeep Vaidya, CEO,
Innovative Coating Industries
MIDC, Pune
Thane: B-7 / 701,
Vedant Comlex, Vartak Nagar Naka,
Thane (West) – 400606
Mobile: 09820181738
Email: puvpromtech@gmail.com
Sonia Vaidya, Tech
Mktg Executive, Thane
Tele: +91-22-25883265,
9819813015
Email:soniavaidya30@gmail.com