Inspection of HDG
Similar to any manufacturing process, hot-dip galvanized steel requires an inspection of the finished product to ensure compliance with applicable specifications. The inspection process requires a clear understanding of galvanizing specification requirements and measurement techniques to make an accurate assessment.
A key feature of hot-dip galvanized (HDG) products is longevity – decades of maintenance-free performance. The time to first maintenance for galvanizing is directly proportional to the zinc coating thickness. Therefore, coating thickness is the most important component in determining a galvanized coating’s quality. However, coating thickness is only one inspection criteria. Other key requirements include adherence, appearance, and finish.
Inspection of hot-dip galvanized steel is fairly simple, as any uncoated areas are easily identifiable. The requirements for hot-dip galvanized coatings are found in three ASTM specifications A123, A153, and A767. Differences in appearance as well as surface imperfections can occur, however, in most instances this is not cause for rejection of the material and does not affect the long-term protection. Inspection is most effectively and efficiently conducted at the galvanizing facility where questions can be asked and answered quickly.
AGA Inspection of Galvanized Steel App
The AGA has created a comprehensive app to aid in the inspection of hot-dip galvanized steel. The app is a visual guide to identifying various surface conditions present after hot-dip galvanizing. Each image in the app is accompanied by text identifying the industry term for the surface appearance and detailing how and why it occurs, and whether or not it is accepted according to the specification. In addition to the visual interpretation of surface conditions, the app also contains critical specification (ASTM, ISO, AASHTO) information to assess compliance with coating thickness requirements as well as how to conduct repairs.