One of the many benefits of hot-dip galvanizing is that coating integrity is readily apparent: zinc will metallurgically bond only to clean steel. Coating uniformity is visible as the work is withdrawn from the molten zinc bath. Surface preparation is of paramount importance in providing optimum quality zinc coatings.
There are a variety of products used for marking and identification that are not removed during the chemical cleaning phases of the galvanizing process, including paint, grease and oil-based markers. Therefore, it is advisable to use other forms of identification including:
- Temporary identification – detachable metal tags (metal barcode tags are also available) or water-soluble paint or markers
- Permanent identification – stamping, weld beads, and deep stencil marking
The most common form of temporary identification is the use of detachable tags. Whether barcode tags or stamped/stenciled tags, these are often preferred as they stay affixed to the part throughout the process, but can be removed once the steel is delivered to the job site. Because they are still readable after all phases of the galvanizing process, tags can facilitate turnaround time and eliminate lost parts while not affecting the aesthetics of the steel once erected.
Another increasingly popular temporary identification method is the use of water-soluble paint or markers. The markings will dissolve during the chemical cleaning process at the galvanizer’s plant. Unlike other markings, which cannot be removed during the cleaning process, this ensures a fully coated part, but the markings will not be visible after withdrawal from the galvanizing bath. Often this is acceptable and even preferred; however, sometimes identification is still needed when delivered to the job site, and thus this temporary marking method would not be recommended.
- Stamping the surface of the item using die-cut deep stencils or a series of punch-marks toward the center of the piece. The marks should be placed in a consistent position on each member and should be a minimum of 1/2” (13 mm) high and 1/32” (0.8 mm) deep to ensure readability after galvanizing.
- A series of weld beads to mark letters or numbers directly onto the fabrication. It is essential that all weld flux be removed in order to achieve highest-quality galvanized coatings.
- Deep stenciling a steel tag (minimum #12 gauge) or a metal barcode tag and firmly affixing it to the fabrication with a minimum #9 gauge steel wire. The tag should be wired loosely to the work with a gap of 1/8” (3 mm) so that the area beneath the wire can be galvanized and the wire does not freeze to the work when the molten zinc solidifies. If desired, tags may be seal-welded directly onto the materials.
In order to lower costs and minimize turnaround times, abrasive-blast-cleaning required to remove marking products not removed by chemical cleaning solutions should be performed at the fabrication facility.