Tech Specifications

Steel Selection

Carbon, silica, phosphorus and manganese are the main elements to consider when selecting steel for a project involving hot-dip galvanizing. The concentration ranges in which these elements must be found are well defined in the ASTM A385 standard. Respecting these selection parameters will ensure that the zinc coating obtained during the galvanizing process will offer effective, resistant and durable protection during the useful life of the galvanized part.

Some steels, such as high strength steels, may be subject to embrittlement during galvanizing. Although not very frequent, it is important to consider the recommendations of the ASTM A143 standard when selecting the steel in order to minimize the risks related to embrittlement. It's challenging to provide exact guidance on steel selection without knowing the commercially available steel grades. There are 4 basic elements to consider as they are shown to affect the galvanized coating.

• Carbon in excess of about 0.25%.
• Silicon in the range of 0.04% to 0.15% or above 0.22% can produce galvanized coating growth rates.
• Phosphorus in excess of 0.04%.
• Manganese in excess of about 1.3%.

Galvanizing DEsign

The hot-dip galvanizing process involves the complete immersion of steel parts and structures in a pool of molten zinc. As a result, the design of assemblies intended for galvanizing differs significantly from that of structures and assemblies that are painted.

In order for a part to be galvanized, it must have the capacity to be racked onto a beam - something that should be considered during the design phase. In addition, the design of steel structures and assemblies with ventilation and drip holes that meet ASTM A385 criteria is critical for safe immersion in the kettle and for quality galvanizing.

VENT HOLES:
The primary purpose of these holes is to allow air to be evacuated from within and around the part, while the secondary purpose is to prevent pressure buildup and localized uncoated surfaces caused by trapped moisture or cleaning solutions. Vent holes should be located at the highest point and drain holes at the lowest point to ensure proper coating coverage and avoid unwanted explosions!

DRAINING HOLES:
To ensure effective galvanizing, it is important to provide free and unimpeded flow of cleaning solutions and molten zinc through the part. Poor drainage design can lead to complications and poor coating quality. It is important to follow best design practices for drainage in common fabrications such as gusset plates, stiffeners, end-plates, and bracing. Holes should be placed in cropped corners or as close to corners as possible, and stiffeners, gussets, and bracing should be cropped a minimum of 3/4 inches. End-plates should have holes at least 1/2 inches in diameter placed as close to interior corners as possible or in the web within 1/4 inches of the end-plate.

Chart 1. - Drainage holes for overlapping surfaces - steel thickness less than or equal to 1/2" (1.25 cm)

DISTORTION PREVENTION

Some applications require the assembly of steel parts of different sizes and thicknesses, while others require large quantities of welds, creating many residual thermal constraints in the assembly.

In such cases, the application of the recommendations stated in the ASTM A384 standard makes it possible to orient the design and fabrication in such a way as to minimize the risks of deformation and distortion that would occur during the galvanization process. A design that respects the spirit of the ASTM A384 standard combined with the know-how and expertise of the galvanizer are the key ingredients to the recipe of success for flawlessly galvanized product.

POST-GALVANIZING