Measuring Zinc Coating Thickness of Hot-dip Galvanized Steel
Coating thickness is tested by using a magnetic thickness gauge. There are three types of magnetic thickness gauges: pencil-style, banana-style, and electronic. Electronic thickness gauges are the most common and the most accurate. Information on how to measure the thickness with magnetic gauges is contained in ASTM E376, and the minimum coating thicknesses and sampling requirements are contained in the appropriate specification for the product (ASTM A123, A153, or A767). A single measurement of coating thickness is not sufficient to evaluate whether the galvanized coating adheres to the specification (ASTM A123, A153, A767) requirements. Each specification calls out sampling size and averaging techniques to develop a true picture of compliance.