ASTM A123 & ISO 1461 — New Editions:
What Changed and Why It MattersCorrected

Table 1 in the 2024 edition runs to six steel-thickness brackets (bounded at 1.6, 3.2, 4.8, 6.4 and 16.0 mm — the metric equivalents of 1/16, 1/8, 3/16, 1/4 and 5/8 in) across seven material categories, including Reinforcing Bar and Forgings & Castings. The 2024 revision added minimum coating thickness requirements for forgings and castings.

What matters here is that the numbers did not move. The required coating grade for structural shapes did not go up. Structural shapes above 6.4 mm required Grade 100 under the 2017 edition as well, so there is no step change in required zinc deposit and no shift in consumption or pickup benchmarks. An earlier version of this article said otherwise; see the correction at the top.

Note that both of those categories carry blank cells in the thinnest brackets — reinforcing bar in the first four, forgings and castings in the first three. A blank is not a zero and not an oversight to be filled by analogy: Table 1 gives no grade there, so the requirement has to come from the standard itself or from agreement with your galvanizer.

This matters for inspection discipline. A galvanizer or inspector who was taking fewer readings on large assemblies is now explicitly out of compliance with the measurement protocol.

The 2024 edition caps renovation two ways at once, and specifies the required repair coating thickness by method.

The dual cap (percentage of surface AND cap per weight of piece) closes a loophole that allowed large pieces to have disproportionately large bare areas simply because the percentage calculation was favourable. The explicit 75–100 μm window for zinc-dust paint repair is new and directly references the method requirements in ASTM A780/A780M.

For duplex system projects — HDG followed by liquid paint or powder coat — the preparation regime is no longer left to interpretation. D7803 includes the critical outgassing protocol that prevents pinholes in powder topcoats over freshly galvanized steel: §6.1.2 requires the pre-bake oven to be capable of heating the work to 30 °C (65 °F) higher than the curing oven — a differential, not an absolute surface temperature — and §6.1.3 holds the work there long enough to reach oven temperature, typically one hour, so all moisture and entrapped gases are expelled.

Appendix X1 — Determination of Material Categories and Steel Thickness — is new in the 2024 edition (Summary of Changes, item 12). It is short and text-only, and it does two jobs.

Category assignment. Its worked examples turn mainly on the boundary between Structural Shapes and Plate: rolled beams are structural shapes, but beams fabricated from plate (plate girders) are plate; rolled angles are structural shapes, but angles fabricated from welded plate are plate; poles made from bent plate are plate, not structural shapes. It also settles two long-running questions — bar grating belongs to "strip and bar", handrail to "pipe and tubing".

Steel thickness. The appendix directs you to the measured thickness rather than the nominal, warning that nominal values for pipe, tube and plate can put an article in the wrong Table 1 row. Where the pre-galvanizing thickness is unavailable, measure after galvanizing to approximate it, or fall back to project drawings. On tapered designs, and on structural shapes whose flanges, webs or legs differ, take the measurement at the thinnest section. For expanded metal, use the measured sheet thickness.

The appendix is non-mandatory, but it is the reference to settle category disputes against — and the grade difference between two plausible readings is real money.

All instances of "gage" were changed to "gauge" throughout the document. Missing metric designations were added to several referenced ASTM specifications. The arrow direction in Figure 3 (lot acceptance flowchart) was corrected. These are editorial corrections with no technical significance.

The old rule was relative — it produced different repair thicknesses depending on how thick the surrounding coating was. On a thin sheet with 50 μm coating, a repair at "30 μm thicker" would only be 80 μm. The 2022 rule sets a single figure of 100 μm mean, which is more protective and more consistently enforceable — though note it is a default, not an absolute: clause 6.3 allows a different thickness by agreement, for instance where it would better match a thinner surrounding coating. The duplex carve-out is a practical addition for painted galvanized work.

In ISO 1461:2022, cast iron and steel castings are not assessed against the wrought-steel minimums: Table 3 carries a separate casting row group with its own values. This is a current-edition provision rather than a documented 2022 change — the Foreword's list of main changes does not mention castings, so treat the rows below as what the standard requires today, not as something that moved.

Castings present different chemistry and surface condition challenges. The lower mean minimum for castings >6 mm — 80 μm against the 85 μm for steel of the same section — reflects the difficulty of achieving uniform coverage on complex casting geometries, and the ≤6 mm row means thin castings are not judged against a steel-based criterion that does not suit them. If you are inspecting castings to the steel rows, you are applying the wrong line of the table.

This clause did not exist in ISO 1461:2009. It addresses a real problem that has existed in the industry for years but had no standard framework: modern aluminium-killed, ultra-low-silicon steels — particularly those used in laser-cut fabrications — sometimes cannot achieve the Table 3 minimum for their actual section thickness, regardless of bath chemistry or process adjustments. The steel chemistry itself prevents the necessary alloy layer growth.

In practical terms: an 8 mm plate of ultra-low-reactivity steel is now assessed against the 3–6 mm row (70 μm mean) rather than the >6 mm row (85 μm mean). This requires the mill test certificate (MTC) to confirm the Si and Al values, making incoming steel verification at the galvanizing plant more important than ever.

ISO 1461:2022 clause 4.2 requires that the bath "shall primarily contain molten zinc", and that the total of the other elements identified in ISO 752, EN 1179 or EN 13283 — excluding tin and iron — shall not exceed 1,5 % by mass. As with castings above, this is a current-edition requirement rather than a documented 2022 change: the Foreword does not list bath composition among the main changes.

It is worth being precise about how this compares with ASTM. A123/A123M-24 clause 5.5 requires the working volume of the bath to average not less than 98,0 % zinc by weight, and its Note 3 permits trace additions of aluminium, nickel and tin provided that bulk chemistry holds. The two are close in intent but are not arithmetically equivalent, because the ISO limit excludes tin and iron from the count while the ASTM figure is a straight zinc percentage.

Lamellar zinc products (such as those used in automotive fastener coatings) have increasingly been applied for repair in the field. The 2022 edition formalises this, removing uncertainty about compliance when these products are used for renovation.

The last of the six changes the Foreword lists is to the informative Annex E, which covers the corrosion resistance of galvanized coatings: the information has been updated, and a reference to ISO 9224 — Corrosivity of atmospheres — Guiding values for the corrosivity categories — has been added for longer-term corrosion resistance. Annex E is informative, so nothing here changes an acceptance criterion; it changes where you are pointed for service-life estimates.

The specification advice is unchanged by the re-attribution: stop using C5-I or C5-M in new documents. Use C5 for very high onshore environments and CX for offshore or extreme environments — citing ISO 12944-2:2017 as the authority, not ISO 1461.