Steel has to be wisely selected for optimal coating. The following information is based on ASTM A-385. The relative corrosion resistance of an aesthetically normal or abnormal coating is, all in all, equal.
The quality and durability of galvanized coatings depend, among other things, on the correct selection of steel based on its physical and chemical properties, and on compliance with design and assembly standards for structures intended to be galvanized. Our customer service team will be delighted to help you with your galvanizing projects.
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.
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.
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!
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)
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.
Although the look that galvanizing confers on steel structures is highly prized, it is also possible to paint galvanized steel.
The development of duplex systems combining hot-dip galvanizing and painting, or hot-dip galvanizing and electrodeposition powder coating, opens the way to the use of galvanized steel in a multitude of applications ranging from architectural aesthetics to extending the life of galvanic protection in certain hostile and corrosive environments.
The ASTM D6386 and D7803 standards cover the key elements required for the development of durable, high-performance duplex systems.
The following is a list of questions commonly asked by our clients. Please contact us if you have a question about our process that is not answered below.
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