What is ASTM A239?

What is ASTM A239?

ASTM A239 is a standard practice established by ASTM International, officially titled "Standard Practice for Locating the Thinnest Spot in a Zinc (Galvanized) Coating on Iron or Steel Articles." This standard outlines a method for identifying the thinnest areas in zinc coatings applied to iron or steel products, ensuring uniformity and adequate corrosion protection.

Purpose of ASTM A239

  • Identify Thin Spots: Assists manufacturers and inspectors in locating areas where the zinc coating may be insufficient.

  • Testing Method Only: Serves as a procedure for detecting and measuring the thinnest spots but does not specify minimum thickness requirements.

This standard is commonly applied to products such as electrical metallic tubing (EMT), structural steel components, rigid conduit pipes, and other zinc-coated iron or steel articles.

General Overview

ASTM A239 provides guidelines for a testing method that helps highlight thin spots in zinc coatings. By following this practice, areas susceptible to corrosion due to inadequate zinc coverage can be identified, allowing for corrective actions before the product is used.

Limitations of ASTM A239

  • Does Not Specify Minimum Thickness: The standard offers a testing method but does not define acceptable coating thickness levels. Minimum requirements are usually specified in other standards like:

    • ASTM A123: For hot-dip galvanized coatings.

    • ETL/UL 797: For EMT conduits.

  • Not Predictive of Service Life: While effective for assessing coating uniformity, it does not predict the durability of the coating under service conditions.


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Practical Use Example

For an EMT conduit, manufacturers like ALEX may use the ASTM A239 practice to assess the uniformity of the zinc coating. If thin spots are detected, they can decide whether further inspection or rework is necessary based on the results.

Summary

  • ASTM A239 is a testing method designed to locate thin spots in zinc coatings on iron or steel articles.

  • It complements other standards by ensuring coatings are uniform and capable of providing sufficient corrosion protection.

  • The test is considered destructive, as it may reduce the zinc layer where applied, so it's used carefully.

For more detailed information, you can refer to the https://www.astm.org/a0239-21.html on the ASTM International website, and purchase from ASTM.