The standard “ASTM A780/A780M Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings,” developed by the American Society for Testing and Materials (ASTM), describes methods that can be used to repair damaged hot-dip galvanized coatings and uncoated areas remaining after the initial hot-dip galvanizing on hardware, structural shapes, and other products manufactured before hot-dip galvanizing.
Damage can occur as a result of welding or cutting (flames). In this case, the coating is primarily damaged by burning. This process can also be used to repair hot-dip galvanized coatings damaged by excessively rough handling during transportation or installation. Requirements for resurfacing uncoated areas remaining after the initial hot-dip galvanizing are included in the applicable material specification.
This application describes the use of three types of materials with the properties required for the repair of damaged galvanized coatings:
The material to be used in the repair must have the specified coating thickness, provide barrier protection and preferably be anodic to steel, and application of the coating must be possible under workshop or field conditions.
Hot-dip galvanizing is a form of galvanizing. It is the process of coating iron and steel with zinc, which forms an alloy with the surface of the base metal when the metal is immersed in a molten zinc bath at a temperature of approximately 450 degrees Celsius. In other words, hot-dip galvanizing is the coating process of fabricated steel by immersing it in a molten zinc bath. There are three basic steps in the hot-dip galvanizing process: surface preparation, galvanizing, and inspection.
During the surface preparation process, the produced steel is placed on a rack system that can be moved throughout the process. It then undergoes a series of cleaning steps: degreasing, pickling, and fluxing. Proper surface preparation is critical because zinc does not react with unclean steel. In the galvanizing process, after surface preparation, the steel is immersed in a molten bath containing at least 98 percent zinc. While immersed in the vat, the iron in the steel reacts metallurgically with the zinc, forming a series of zinc-iron intermetallic layers and an outer layer of pure zinc. The final step is coating inspection. A very accurate determination of the coating quality can be achieved by visual inspection, as the zinc does not react with the contaminated steel to leave an uncoated area on the part.
The ASTM A780/A780M standard also outlines procedures for:
ASTM A780/A780M is a critical standard that provides procedures for repairing damaged or uncoated areas of hot-dip galvanized steel coatings. This practice ensures that galvanized steel components maintain their corrosion-resistant properties after damage from handling, fabrication, or in-service. Maintaining the integrity of the zinc coating is crucial for extending the service life of the steel in various environments.
In short, the ASTM A780/A780M standard provides the following procedures:
This standard specifies several methods for repairing damaged galvanization:
This standard plays an important role in extending the service life of galvanized steel structures such as:
This standard helps maintain corrosion resistance, structural integrity, and overall safety by ensuring effective repair of damaged areas. ASTM A780/A780M is essential for the maintenance and longevity of galvanized steel. It provides industry-recognized methods for restoring zinc coating performance after damage and ensures compliance with corrosion protection standards. Whether zinc-rich paint, soldering, or metallization is used, compliance with this standard ensures reliable performance of galvanized steel components throughout their intended service life.
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