Simple Guidelines for Hot Dip Galvanization Inspection  

Hot dip galvanizing is a highly trusted industrial process where a zinc coating is applied to steel and iron. This involves dipping steel or iron, both fabricated and unfabricated, into a molten zinc bath at about 840 degrees Fahrenheit. Galvanization is critical to many industries because it helps enhance the durability of the base metal without getting rusted or corroded. Just like many other manufacturing processes, however, hot dip galvanized metals must be inspected as per certain standards and specifications.  

Hot dip galvanization inspection is a simple and quick process that primarily scrutinizes coating appearance and coating thickness.  Appearance, thickness, adherence, and uniformity can be determined by some uncomplicated physical and laboratory tests.   Every country has its own standards for the inspection of hot dip galvanized products, covering required minimum coating thicknesses, composition of the used zinc metal, testing methods to be followed, and much more.   

A large majority of inspections for hot dip galvanized metals are carried out immediately after the application and cooling of the coating. These inspections take place before the finished products leave the galvanizing facility, to ensure compliance with specifications. However, ongoing field inspections are also conducted after the commissioning of hot-dip galvanized steel structures.   

As mentioned earlier, coating thickness is a critical element during the inspection of hot dip galvanized products.  Optical microscopy and magnetic thickness gauge are the two methods for the measurement of hot-dip galvanized steel’s coating thickness. Magnetic thickness gauge is a simple, non-destructive method that can be categorized into the following three types.  

  • Pencil gauge: This method utilises a pencil-like container with a spring-loaded magnet. The accuracy of this inspection depends significantly on the skill of the inspectors.  
  • Banana gauge: Coating thickness can be measured in any position without gravity interference or recalibration.  
  • The easiest to use, and the most accurate method is a digital thickness gauge. This method also allows performing averaging calculations and data storage.  

Surface condition is as important a parameter as galvanization thickness, while evaluating galvanization quality.  During the inspection of the coating’s finish quality, many different surface conditions are observed. The finish can get affected by multiple factors, only some of which can be controlled by the galvanizer. Ideally, a good coating quality demands a finish that is uniform, smooth, and continuous.  However, the acceptability of a coating relates to its long-term corrosion performance.   

In addition to visual inspections and coating measurements, a few other inspections may also be performed for hot-dip galvanized products. Inspectors conduct these tests when they have concerns about the quality of the coating.  

  • Adherence test for testing the adherence of the coating using a stout knife  
  • Embrittlement test, if there is suspicion about the structure’s potential embrittlement 
  • Bending test to evaluate whether the galvanized structure can withstand bending without peeling or flaking 
  • Passivation testing to find out whether chromate is present in zinc surfaces 

This was just a brief overview of inspection of hot dip galvanized metals and its different methodologies. If you are looking for comprehensive inspection services for your hot dip galvanized products, please contact us immediately at Coating Management Solutions. We are a third-party inspection agency with a track-record of serving a wide spectrum of industries across Australia.