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Hot-dip galvanizing is one of the most economical, maintenance-free corrosion protection systems available. Like any other 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 both specification requirements and compliance measurement techniques to make an accurate assessment.

For hot-dip galvanized products, a key feature is durability and decades of maintenance-free performance.  However, to plan for the extension of a products service life and facilitate long-term budget planning, the estimated time to first maintenance in atmospheric exposures can be seen in the chart below. 

Time to first maintenance chart

For any environment, the service life of hot-dip galvanized steel is directly proportional to the thickness of the zinc coating.  Thus, coating thickness is an important requirement in the specification and effectiveness of hot-dip galvanizing as a corrosion protection system.

Measuring coating thickness is only one of the many specification requirements in the inspection process. Other requirements include adherence, appearance, and finish.

The requirements for hot-dip galvanized coatings are found in three ASTM specifications; A123/A123M, A153/A153M, and A767/A767M. The difference between these specifications is the type of steel product covered by each. A123/A123M covers structural steel, pipe and tubing, flat bar, and wire. A 153/A 153M includes small castings, nails, nuts, bolts, washers, and small parts centrifuged after galvanizing to remove excess zinc.  And A767/A767M covers reinforcing steel bars. In Canada, the specification CSA G 164 covers the requirements for all hot-dip galvanized articles, and ISO 1461 is the standard used in Europe. In all cases, the inspection of hot-dip galvanized products is conducted at the galvanizing plant prior to shipment of the article.

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