Galvanizing

Home Galvanizing

Hot-Dip Galvanizing Process

Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent premature rust and corrosion.

Most common method: Hot-dip Galvanization.

Supreme Galvanizing

Figure 3. Batch Hot-Dip Galvanizing. American Galvanizers Association (2015) Zinc Coatings: A comparative Analysis of Process and Performance Characteristics, p.2

Surface Preparation

Degreasing/Caustic Cleaning

First the steel is immersed in an acid degreasing bath or caustic solution in order to remove the dirt, oil, and grease from the surface. After degreasing, the steel is rinsed with water.

Pickling

The steel is then immersed in an acid tank filled with either hydrochloric or sulfuric acid, which removes oxides and mill scale in a process called “pickling.” Once all oxidation has been removed from the steel, it is again rinsed with water.

Fluxing

The purpose of the flux is to clean the steel of all oxidation developed since the pickling of the steel, and to create a protective coating, to prevent the steel from any oxidizing, before entering the galvanizing kettle.

Proper Drainage and Venting

Crucial to the Galvanizing Process.

The primary reason for vent and drain holes is to allow air to be evacuated, permitting the object to be completely immersed into cleaning solutions and molten zinc. Proper sizing and location of the holes make it safer to galvanize and provide an optimal finish. The secondary reason for venting/drainage is to prevent damage to the parts.

Proper Drainage for common fabrications:

Supreme Galvanizing

Figure 9. Cropped Gusset Plate Corners. American Galvanizers Association (2015) Design Guide: The Design of Products to be Hot-Dip Galvanized After Fabrication, p.10

Venting for tubular fabrications & hollow structures:

Supreme Galvanizing

Figure 12. Vent Hole Options. American Galvanizers Association (2015) Design Guide: The Design of Products to be Hot-Dip Galvanized After Fabrication, p.12

Supreme Galvanizing

Figure 13. Vent holes should be visible on the outside of any pipe assembly to provide internal vent verification. American Galvanizers Association (2015) Design Guide: The Design of Products to be Hot-Dip Galvanized After Fabrication, p.13

Corrosion protection in not only for exterior purposes but also interior.

Specifications

Hot-Dip Galvanized steel requires an inspection of the finished product to ensure compliance with the applicable specifications. Inspection is conducted at the galvanizing shop prior to shipment of the product.

The most common specification used: ASTM A123 – Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products. See the American Galvanizers Association for more details on Specifications.

The coating thickness is an important requirement in the specification and effectiveness of hot-dip galvanizing as a corrosion protection system. There are many tools that can be used, however the Electronic or Digital Thickness Gauge (Elcometer) is the most accurate and easiest to use. Measuring coating thickness is only one of the many specification requirements in the inspection process.

Supreme Galvanizing Diagram-06

Figure 5. Time to First Maintenance of Hot-Dip Galvanized Coatings. American Galvanizers Association (2015) Zinc Coatings: A comparative Analysis of Process and Performance Characteristics, p.3

Common Uses of Galvanizing Steel

Galvanizing not only provides excellent corrosion protection and durability, it is also low maintenance, economically beneficial, has a low environmental impact, and improves aesthetics.

The list below shows specific items that are typically galvanized:

Anchor Bolts Buildings Beams Brick ties
Brick Ledges Columns Dock Levelers Equipment Supports
Fencing Flagpole Bollards Cranes
Electrical Boxes Handrails Gates Girts
Faraday Cages Fish Ladders Flood Control Gates Flow Restrictions
Fasteners Guardrail Guardrail Posts Gates
Gas Turbine Skids Generator Housings Generator Support Platforms Hopper Structures
HVAC Supports Lattice Towers Light Poles Light Brackets
Ladders Lintels Mechanical Screens Overhead Cranes
Penstock Pipe Bridges Pipe Supports Platforms
Purlins Railings Relieving Angles Reinforcing Steel
Roof Hatches Sheet Piling Pole Arms Railings
Structural Steel Sign Supports Posts Bridge
Yard Equipment Steel Stairs Coal-handling Equipment Sheet Piling
Catwalks Steel Grating Steel Stairways Solar-panel Supports
Conveyor Supports Trench Covers Transmission Poles Solar Control Boxes
Corner Guards Truck Scales Tubular Towers Tower Ladders
Trash Racks & Booms Truck Lifts Walkways Tower Supports
Wine Mill Towers Valve Stands

American Galvanizer’s Association (2015). HDG In Use. Retrieved from http://www.galvanizeit.org/hdg-in-use/bridge-and-highway.