Understanding the 2024 Revision of ASTM A123/A123M
In May 2024, ASTM International approved a significant revision to ASTM A123/A123M, "Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products." Published in July 2024, this update represents the first major revision since 2017 and introduces important clarifications that address long-standing interpretation questions from specifiers, inspectors, galvanizers, and fabricators. Understanding these changes ensures proper specification, inspection, and acceptance of hot-dip galvanized coatings in accordance with current industry standards.
ASTM A123/A123M serves as the primary specification governing hot-dip galvanized coatings on fabricated iron and steel products including structural shapes, plates, bars, castings, forgings, and assembled fabrications. The specification establishes minimum coating thickness requirements based on material category and steel thickness, along with finish, appearance, and adherence criteria that ensure coatings provide effective corrosion protection throughout the intended service life.
Overview of Key Changes in the 2024 Revision
The 2024 revision of ASTM A123/A123M addresses four primary areas requiring clarification:
- Minimum average coating thickness requirements for forgings and castings
- Formal definition of "intended use"
- New appendix providing guidance on Table 1 interpretation
- Clarifications regarding steel thickness measurement protocols
These changes do not fundamentally alter the specification's technical requirements but provide essential guidance on proper interpretation and application of existing provisions, particularly regarding coating thickness determination and acceptance criteria.
Minimum Average Coating Thickness for Forgings and Castings
One of the most significant technical additions in the 2024 revision addresses coating thickness requirements for steel forgings and iron castings incorporated into galvanized fabrications.
Background on Specimen-Level Requirements
ASTM A123 establishes coating thickness requirements at two hierarchical levels: the specimen level and the individual measurement level. A "specimen" represents a distinct component or section of a fabricated assembly designated for coating thickness testing. For single-part articles, the entire part constitutes one specimen. For multi-component assemblies, each major element (beam, column, brace, plate) may represent a separate specimen.
Prior to the 2024 revision, the specification stated that the minimum average coating thickness grade for any specimen shall be one coating grade below that required for the material category and thickness specified in Table 1. However, the specification did not explicitly address minimum average coating requirements for forgings and castings, leading to inconsistent interpretation and application.
New Provisions for Forgings and Castings
The 2024 revision clarifies that steel forgings and iron castings shall meet the same minimum average coating thickness requirements as other material categories. When forgings or castings are incorporated into a fabricated assembly, they are treated as distinct specimens for coating thickness measurement and evaluation purposes.
This clarification ensures that forgings and castings—which may exhibit different surface reactivity characteristics compared to rolled steel products—receive adequate coating thickness evaluation appropriate to their material properties and geometry. Galvanizers must ensure these components achieve coating thickness meeting or exceeding the minimum average grade requirements, just as they would for structural shapes, plates, or other material categories.
Definition of "Intended Use"
The 2024 revision introduces a formal definition for the term "intended use," addressing a long-standing ambiguity in the specification's finish and appearance requirements.
Historical Context
Previous versions of ASTM A123 included provisions stating that excess zinc deposits or rough surface conditions are not cause for rejection unless they "interfere with the intended use of the product" or "make it dangerous to handle." However, the specification provided no definition of "intended use," creating potential for disagreement between galvanizers, fabricators, and inspectors regarding which surface conditions constitute interference with intended function.
New Definition and Application
The 2024 revision defines "intended use" as follows:
"The normal function for which a product is designed, manufactured, or marketed, excluding aesthetic considerations unless appearance has been specifically identified as part of the product's intended function in the purchase order or contract documents."
This definition establishes several important principles:
Functional vs. Aesthetic Considerations: Under the revised definition, "intended use" focuses primarily on functional performance rather than appearance. Surface roughness, zinc buildup in corners, or color variation do not constitute interference with intended use unless they prevent the product from performing its designed function or create a safety hazard during handling, installation, or maintenance.
Contractual Specification of Appearance Requirements: If appearance is important to the project, it must be explicitly specified in the purchase order or contract documents as part of the product's intended function. Without such specification, appearance characteristics beyond those ensuring adequate coating coverage and safety are not grounds for rejection under ASTM A123.
Dangerous-to-Handle Provision: The specification retains provisions addressing coating conditions that create handling hazards—such as sharp zinc spikes, edge tears, or projections that could cause injury during fabrication, shipping, or installation. These conditions remain cause for rejection or remediation regardless of intended use considerations.
This clarification helps establish more consistent and objective evaluation criteria, reducing disputes and promoting mutual understanding between stakeholders regarding acceptable coating characteristics.
New Appendix: Guidance on Table 1 Interpretation
Perhaps the most extensive addition in the 2024 revision is a new appendix providing detailed guidance on interpreting and applying Table 1, which establishes minimum coating thickness requirements based on material category and steel thickness.
Common Interpretation Questions
ASTM subcommittee A05.13, which maintains the A123 specification, regularly receives support requests from specifiers, inspectors, and galvanizers seeking clarification on Table 1 application. Common questions include:
- How should coating thickness requirements be determined for products with multiple thicknesses (tapered sections, structural shapes with varying flange and web thickness)?
- What steel thickness value should be used when measured thickness is not practically available?
- Can nominal thickness or drawing dimensions be used instead of measured thickness?
- How should expanded metal mesh products be evaluated?
Steel Thickness Determination Principles
The new appendix establishes clear protocols for determining the appropriate steel thickness value for coating grade selection:
Standard Practice: Measured Steel Thickness
The specification's general requirement calls for using actual measured steel thickness before galvanizing to determine the applicable coating grade from Table 1. Measured thickness accounts for mill tolerances and variations that may result in actual steel thickness differing from nominal or specified dimensions—differences that can be significant for the galvanizing process and coating formation.
Alternative Method 1: Post-Galvanizing Measurement
When pre-galvanizing steel thickness measurement is unavailable or impractical, one alternative method involves measuring the part thickness after galvanizing to approximate the steel thickness. Since typical galvanized coating thickness ranges from 3.5 to 5.0 mils (85 to 125 microns), this introduces minimal error compared to measuring the steel directly, particularly for components exceeding 1/8 inch (3.2 mm) in thickness.
Alternative Method 2: Nominal Thickness or Drawing Dimensions
For specimens where direct thickness measurement is inaccessible or impractical (such as closed hollow sections, interior surfaces, or assembled components restricting measurement access), the appendix permits using nominal steel thickness or dimensions from project drawings to approximate steel thickness for coating grade determination.
This provision recognizes practical measurement limitations while maintaining the specification's fundamental principle that coating requirements should reflect actual material characteristics. However, this approach should be used judiciously, with awareness that nominal dimensions may differ from actual thickness.
Tapered Designs
For products with tapered cross-sections where steel thickness varies continuously, the appendix clarifies that steel thickness measurement should be obtained from the location of the thinnest steel section. This ensures coating requirements are based on the most reactive portion of the component, which typically requires the thinnest minimum coating to provide adequate corrosion protection relative to its mass and expected corrosion rate.
Structural Shapes with Variable Thickness
Hot-rolled structural shapes such as wide-flange beams, channels, and angles commonly exhibit different thicknesses between flanges, webs, and legs due to manufacturing processes. The appendix specifies that for these shapes, steel thickness measurement should be obtained from the thinnest steel section—typically the web for wide-flange sections or channels.
This provision addresses practical galvanizing considerations. Thinner sections heat and cool more rapidly during galvanizing, potentially exhibiting different coating growth characteristics. Additionally, thinner sections have lower thermal mass and may be more susceptible to distortion. Basing coating requirements on the thinnest section ensures these critical areas receive adequate coating thickness.
Expanded Metal
For expanded metal products, the appendix clarifies that steel thickness is determined using the measured sheet thickness value—the thickness of the original sheet material before expansion—rather than attempting to measure strand thickness or other dimensional characteristics resulting from the expansion process.
Practical Implications for Stakeholders
The 2024 revision provides important guidance affecting multiple stakeholders in the galvanizing specification chain:
For Engineers and Specifiers
Understanding these clarifications enables more accurate specification of hot-dip galvanizing requirements and helps prevent specification ambiguities that could lead to disputes. When appearance is a project requirement, engineers should explicitly identify this as part of the product's intended function in contract documents rather than assuming aesthetic considerations are implicitly included in ASTM A123 requirements.
For projects involving forgings, castings, tapered sections, or variable-thickness structural shapes, specifiers should be aware that coating requirements will be determined based on these clarified measurement protocols, potentially affecting coating thickness expectations and inspection procedures.
For Galvanizers
The clarifications regarding steel thickness determination provide clear guidance on selecting appropriate coating grades when faced with products exhibiting multiple thicknesses or when measurement limitations exist. Galvanizers can apply these protocols consistently, reducing the need for case-by-case judgment calls that may vary between facilities or personnel.
The "intended use" definition helps establish more objective criteria for coating acceptance, potentially reducing subjective disputes over surface appearance while maintaining focus on functional coating performance and safety.
For Inspectors
Coating thickness inspection and acceptance should follow the measurement protocols outlined in the new appendix, ensuring consistency with the specification's intent. Inspectors should recognize that for multi-thickness products, coating requirements are based on the thinnest section, and alternative measurement methods may be appropriate when direct measurement is impractical.
Understanding the "intended use" definition helps inspectors distinguish between coating characteristics that genuinely interfere with product function or safety versus aesthetic preferences that fall outside ASTM A123's scope unless contractually specified.
For Fabricators
Fabricators should recognize that design decisions affecting steel thickness distribution—such as tapering, use of variable-thickness sections, or incorporation of forgings and castings—may influence coating thickness requirements and evaluation procedures. Early consultation with galvanizers during design development can help optimize fabrication details for successful galvanizing while meeting project coating requirements.
Minimum Average Coating Grade Requirements: A Clarification
The specification maintains its established principle that the minimum average coating thickness grade for any specimen shall be one coating grade below that required for the material category and thickness in Table 1. This provision accounts for normal variation in coating thickness across a specimen while ensuring adequate average coating thickness for corrosion protection.
For example, if Table 1 requires Grade 65 (2.5 mils or 65 microns) for a particular material category and thickness, the minimum average for any specimen would be Grade 55 (2.1 mils or 55 microns). Individual measurement locations may fall below this average, provided they meet the specification's minimum single-spot requirements and the specimen average meets the minimum average grade requirement.
This hierarchical approach—with requirements at both the individual measurement and specimen average levels—provides flexibility to accommodate normal coating thickness variation while ensuring overall coating adequacy for corrosion protection.
The 2024 revision of ASTM A123/A123M represents a significant step forward in clarifying long-standing interpretation questions affecting hot-dip galvanizing specification and inspection. By establishing formal definitions, providing detailed measurement protocols, and addressing specific material categories, this revision enhances consistency and reduces ambiguity in applying the specification across diverse project types and stakeholder organizations.
These changes do not alter the fundamental technical requirements that have made ASTM A123 the industry-standard specification for hot-dip galvanized coatings on fabricated steel products. Rather, they provide essential interpretive guidance enabling all parties—engineers, fabricators, galvanizers, and inspectors—to apply the specification more consistently and effectively.
Projects specifying hot-dip galvanizing should reference ASTM A123/A123M-24 to ensure compliance with current industry standards. Understanding these revisions enables stakeholders to specify, produce, and inspect galvanized coatings with confidence that they meet established requirements for corrosion protection, functionality, and safety. Read more on this topic in the original AGA resource on the 2024 Revision of ASTM A123.
