What HDG Specification Changes were Published in 2022?
ASTM A385/A385M-22, Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip)
ASTM A385 received a substantial number of updates to tackle topics such as steel chemistry, methods to avoid excessively thick coatings, vent hole plugs, and thermally cut edges.
See below list of changes published in the 2022 revision along with the associated rationale:
- Paragraph 3.2 was expanded to provide awareness to the specifier regarding accuracy and recommended use of MTRs when evaluating the chemical composition of steel for galvanizing using a cast or heat analysis.
- Paragraph 3.5 was revised to list available methods to limit coating thickness when galvanizing steels of reactive steel chemistry to address industry concerns regarding thick galvanized coatings and potential for flaking during field handling.
- Paragraph 3.7 was revised after several galvanizers expressed concerns regarding the 2017 inclusion of over-pickling in sulfuric as a method to remedy low coating thickness for Al-killed steels. Over-pickling is not considered best practice as it cannot be measured/confirmed and results in poor quality when mixing steel compositions in an assembly. Additionally, the phrasing incentivized the specifier to request over-pickling as opposed to utilizing proper steel selection, while also indicating blasting and over-pickling are equally suitable solutions.
- Paragraph 3.7 was also expanded to discuss abrasive blast cleaning before hot-dip galvanizing as a method successfully used to achieve two different outcomes: reducing HDG coating thickness or increasing HDG coating thickness, where the difference in outcome is the result of the initial steel chemistry.
- It is well known thermal cutting techniques increase hardness and change diffusion properties of steel, making it very difficult to form a coating of typical quality and aesthetics along the cut edge, particularly among flame cut edges. Paragraph 8 now includes available methods to improve the coating quality of cut edges which are often necessary to achieve a surface condition acceptable for painting, powder coating, or Architecturally Exposed Structural Steel (AESS).
- Paragraph 12.5 was added to address the use of zinc and aluminum vent/drain hole plugs as this common practice had never been mentioned in ASTM standards before. Guidance was also developed to address concerns over galvanic corrosion when using aluminum plugs.
ASTM A153/A153M-23, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware
A revision to Note 6 was voted on and accepted to address the acceptance of parts susceptible to residual buildup of zinc (e.g. 90 degree elbows or tees). This is relevant for projects where the number of test articles for inspection is very small compared to the lot size. The change informs a specifier that, statistically speaking, it is possible to run into a few unusable parts or outliers even if the lot passes and galvanizing best practices are followed. The following change is expected to be published sometime in 2023:
NOTE 6—Since this specification is applicable to items that are centrifuged or otherwise handled to remove excess bath metal (see 1.2), irregular coating distribution is not normally encountered. Drainage problems not related to part design, which manifest themselves as local excess coating thickness that would interfere with function or as edge tears or spikes that present a safety hazard because of their sharpness, are grounds for rejection under the terms of 5.1. On part geometries with cavities and recesses, a buildup of zinc may result. Responsibility for remediation of these parts should be agreed to between the galvanizer and the customer.
ISO 1461:2022, Hot dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods
Overseas in Europe, our EGGA colleagues have been busy also. ISO 1461 was last updated in 2009 and the 2022 update includes the most extensive set of revisions since the first publication. While primarily used outside North America, AGA members are known to galvanize to this standard for small subsets of customers. The most significant changes for the galvanizer are related to the requirements for ultra-low silicon steels, appearance, and renovations (touch-up and repair). However, it is still the case that galvanizing to A123 will typically lead to a final quality which meets or exceeds ISO 1461.
AGA has revised the existing knowledgebase article comparing the requirements of ISO 1461 vs A123 to address the differences between the standards:
© 2023 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.