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ASTM standards undergo a revision process at minimum every five years, and occasionally significant changes are brought forward and discussed. Below are recent updates from ASTM regarding standards applicable to the hot-dip galvanizing industry with involvement from AGA and member galvanizers.

ASTM A385/A385M

Revisions to ASTM A385/A385M, Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip), were approved in March 2022 with added language to address improved quality along thermally cut edges, proper use of vent/drain plugs, and the appropriate use of mill test reports to predict steel reactivity.

A summary of key changes includes:

  • Paragraph 3.2 – added cautionary language to manage expectations when evaluating silicon and phosphorus levels (as listed on mill test report), recycled steel, or test pieces to predict steel reactivity and/or initial appearance on a project.
  • Paragraph 3.5 – additional mitigations described for avoiding excessive coating growth when galvanizing reactive steel chemistries: abrasive blasting before galvanizing and further optimization of vent/drain holes.
  • Paragraph 3.7 – removed “over pickling in sulfuric acid” as a potential option to increase coating thickness on steels which have difficulty achieving the minimum coating thickness requirements (e.g., aluminum-killed steels) based on feedback from AGA member galvanizers over the years. Added a brief explanation of why abrasive blast cleaning before galvanizing increases coating thickness for steels of low reactivity while limits coating thickness for reactive steels.
  • Paragraph 8.4 – new paragraph describing aesthetic limitations and available methods to improve the appearance of thermally cut edges (e.g. grinding) on projects involving Duplex Systems, Architecturally Exposed Structural Steel, or other elevated aesthetic requirements.
  • Paragraph 12.5 – new paragraph describing the appropriate specification of vent/drain hole plugs.

Overall, these changes are expected to benefit the galvanizer by aligning expectations and educating the specifier on common topics which are typically misunderstood. Be on the lookout - the standard is expected to be published later this year and will be available for purchase through ASTM directly.

ASTM D6386

A new 2022 revision of ASTM D6386, Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting, is now available for purchase through ASTM with changes that open up the recommendations for blast media used to prepare HDG surfaces for painting.

The beginning of Paragraph 5.4.1 now states:

5.4.1 Sweep Blasting—Abrasive sweep or brush blasting in accordance with procedures described in SSPC Surface Preparation No. 16, which uses a rapid nozzle movement will roughen the galvanized surface profile. The abrasive material must be chosen with care to provide a stripping action without removing excess zinc layers, removal of up to 25 microns (1 mil) is acceptable. One of the materials that has been used successfully is aluminum/magnesium silicate. Particle size should be in the range of 200 to 500 μm (8 to 20 mils). Other materials that can be used are soft mineral sands with a MOH hardness of five or less, organic media, such as corn cobs or walnut shells, corundum, limestone or cast zinc shot. The use of abrasive media with Mohs hardness 5 or greater or a bulk density over 200 lbs/ft3 is capable of producing roughened galvanized surfaces with increased peak heights, but additional mitigations may necessary by the blaster to significantly reduce the risk of damage. Depending on the value of hardness for the abrasive medium, blasting pressure may need to be determined for the appropriate nozzle to work-piece distance, geometry of the component, and blasting medium. […]

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