Technical Article · Standards & Compliance
A complete practitioner's guide to the 2024 ASTM and 2022 ISO revisions — covering every change to coating thickness requirements, repair rules, material categories, and steel provisions
If you work with hot-dip galvanized steel — whether as a fabricator, specifier, galvanizer, inspector, or procurement manager — two standards govern the quality of every coating you buy, sell, specify, or accept: ASTM A123/A123M and ISO 1461. Both were revised: ASTM in 2024, ISO in 2022. Both moved in the same direction.
This article explains, change by change, what is different in the new editions compared to the editions they replaced (A123/A123M-17 and ISO 1461:2009). It covers the numbers that changed, the rules that were tightened, the new provisions that did not exist before, and the practical consequences for anyone involved in galvanizing work.
If you are still specifying or accepting work against the 2017 or 2009 editions, this article is for you.
ASTM A123/A123M-24 was approved May 1, 2024 and published July 2024. It supersedes A123/A123M-17. This is the primary American standard for batch hot-dip galvanizing of structural steel, plate, bar, pipe, and wire products. The 2024 revision contains twelve documented changes in the official Summary of Changes. The ones that matter operationally are grouped below.
This is the most significant change in the 2024 edition. The old Table 1 had four steel-thickness brackets and covered Structural Steel, Plate/Strip/Bar, Pipe/Tube, and Wire. The new Table 1 has six thickness brackets and adds two entirely new material categories: Reinforcing Bar and Forgings & Castings.
| Material Category | Steel Thickness | Old Min. (A123-17) | New Min. (A123-24) |
|---|---|---|---|
| Structural Shapes | ≥ 6.4 mm | 85 μm | 100 μm ↑ |
| Structural Shapes | 3.2–6.4 mm | 75 μm | 85 μm ↑ |
| Structural Shapes | 1.6–3.2 mm | 55 μm | 75 μm ↑ |
| Plate, Strip & Bar | ≥ 6.4 mm | 85 μm | 75 μm |
| Pipe & Tube | ≥ 3.2 mm | 75 μm | 75 μm |
| Wire | ≥ 6.4 mm dia | 85 μm | 85 μm |
| Reinforcing Bar | All | Not in old edition | New category — own minimums |
| Forgings & Castings | All | Not in old edition | 100 μm (all thicknesses) |
The headline number: The minimum average coating thickness on Structural Shapes ≥6.4 mm rose from 85 μm to 100 μm. For a galvanizer processing heavy beams, columns, and angle sections — the dominant product type in most plants — this is an 18% increase in the minimum zinc deposit required. It is not a rounding error; it is a meaningful specification increase that affects zinc consumption, cost modelling, and pickup percentage benchmarks.
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 old edition stated renovation was acceptable up to 0.5% of total surface. The new edition adds a second cap 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 (minimum 30 °C surface temperature, approximately 1 hour hold) that prevents pinholes in powder topcoats over freshly galvanized steel.
Appendix X1 is new in the 2024 edition. It provides illustrated examples and guidance to help galvanizers and specifiers determine which Table 1 material category applies to a given product. This was a persistent source of confusion in A123/A123M-17, particularly for products on the boundary between Structural Shapes and Strip-Bar. The appendix is non-mandatory but practically valuable.
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.
ISO 1461:2022 was published in August 2022. It is the fourth edition of this standard and supersedes ISO 1461:2009. It is the governing standard for hot-dip galvanizing in Europe, the Middle East, Asia, Africa, and all global markets that follow ISO specifications. The changes are fewer than in ASTM A123, but several are significant for daily production and inspection work.
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 new rule sets a universal floor of 100 μm, which is more protective and more consistently enforceable. The duplex carve-out is a practical addition for painted galvanized work.
In ISO 1461:2009, cast iron and steel castings were assessed against the same thickness minimums as wrought steel. ISO 1461:2022 breaks castings out as a separate row group in Table 3 with their own values.
| Article Type | Section Thickness | Local Min. (μm) | Mean Min. (μm) |
|---|---|---|---|
| Steel articles | > 6 mm | 70 | 85 |
| Steel articles | 3–6 mm | 55 | 70 |
| Steel articles | 1.5–3 mm | 45 | 55 |
| Steel articles | < 1.5 mm | 35 | 45 |
| Castings | > 6 mm | 70 | 80 (new — was 85) |
| Castings | ≤ 6 mm | 60 | 70 (new row) |
Castings present different chemistry and surface condition challenges. The slightly lower mean minimum for castings >6 mm (80 μm vs. the 85 μm for steel) reflects the difficulty of achieving uniform coverage on complex casting geometries, while the new ≤6 mm casting row addresses thin castings that were previously assessed against an unsuitable steel-based criterion.
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.
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.
For specifiers writing corrosion protection specifications: stop using C5-I or C5-M in new documents. Use C5 for very high onshore environments and CX for offshore or extreme environments.
| Topic | ASTM A123/A123M-17 (old) | ASTM A123/A123M-24 (new) | ISO 1461:2009 (old) | ISO 1461:2022 (new) |
|---|---|---|---|---|
| Min. thickness — structural ≥6 mm | 85 μm | 100 μm ↑ | 85 μm (mean) | 85 μm (unchanged) |
| Castings — thickness requirement | Same as structural steel | 100 μm (all thicknesses, new category) | Same as structural steel | Separated: 80 μm mean >6 mm, 70 μm mean ≤6 mm |
| Renovation (repair) thickness | Not specified in standard | 75–100 μm (zinc-dust paint); Table 1 min. for metallizing | "30 μm thicker than adjacent coating" | 100 μm mean minimum (absolute) |
| Max. repair area | 0.5% of total surface | 0.5% AND ≤256 cm²/metric ton | 0.5% of surface; max 10 cm² per spot | 0.5% of surface; max 10 cm² per spot (unchanged) |
| Ultra-low-reactivity steels | No provision | No provision | No provision | Clause 6.5: Si ≤0.01% + Al >0.035% → next lower thickness category |
| Duplex prep requirements | Not in A123 scope | Clause 6.4.1: D6386 (paint) and D7803 (powder) are now normative requirements | Referenced via ISO 14713-2 | Updated ISO 14713-2 cross-reference maintained |
| Bath composition minimum | ≥98.0% Zn by weight | ≥98.0% Zn by weight (unchanged) | Not explicitly stated in 2009 body | Non-Zn elements (excl. Sn, Fe) ≤1.5% |
| Approved repair methods | Zinc solder, zinc-rich paint, thermal spray | Same (unchanged) | Zinc solder, zinc-rich paint, thermal spray | + Lamellar zinc pigment (added) |
| Corrosivity categories | C1–C5 | C1–C5 (unchanged) | C5-I / C5-M (obsolete split) | C5 / CX (per ISO 12944-2:2017) |
Many international contracts and project specifications include a clause along the lines of: "galvanizing shall conform to ASTM A123 or ISO 1461, whichever is more stringent." Under the old editions, this almost always resolved to roughly the same requirement for structural steel — both specified 85 μm on sections ≥6 mm. With the 2024 ASTM revision, that has changed.
| Scenario | ASTM A123/A123M-24 | ISO 1461:2022 | More Stringent |
|---|---|---|---|
| Structural shapes (beams, columns, angles) ≥6 mm | 100 μm | 85 μm | ASTM A123/A123M-24 |
| Plate, strip, bar ≥6 mm | 75 μm | 85 μm | ISO 1461:2022 |
| Forgings and castings (all thickness) | 100 μm | 80 μm mean (>6 mm) | ASTM A123/A123M-24 |
| Repair area maximum | 0.5% AND ≤256 cm²/metric ton | 0.5% of surface | ASTM A123/A123M-24 (dual cap) |
| Repair coating minimum | 75–100 μm (zinc-dust paint) | 100 μm mean | ISO 1461:2022 (no upper cap on repair thickness) |
For the most common specification scenario — heavy structural steel using the "more stringent" clause — ASTM A123/A123M-24 now governs more often than the 2017 edition did. Any galvanizer or specifier using the "whichever is more stringent" formulation needs to re-evaluate their project requirements with the new edition numbers in hand.
Standards revisions are not abstract. The 100 μm minimum for structural shapes in ASTM A123/A123M-24 has a direct and calculable effect on zinc consumption, and therefore on cost, for any plant running ASTM-spec structural work.
The ISO 1461:2022 changes are less costly in themselves — the coating thickness minimums for steel are unchanged, and the new castings row and ultra-low-reactivity provision actually provide more flexibility, not less. The cost impact of ISO 1461:2022 is mostly administrative (updated documentation, new MTC review procedure for Al-killed steels).
Both revisions represent the galvanizing industry maturing its quality framework — more granular thickness requirements, tighter repair rules, and explicit handling of situations (ultra-low-reactivity steels, duplex preparation) that previous editions left to interpretation or custom practice.
For ASTM A123/A123M-24, the practical impact is significant for structural galvanizers: the 100 μm minimum on heavy sections is a real increase that must flow through into pricing, zinc budgets, and QC systems. For ISO 1461:2022, the impact is more about clarification and modernisation — the renovation rule change and the ultra-low-reactivity provision are the substantive operational changes.
Neither revision invalidates well-run galvanizing operations. They raise the documented minimum bar and close gaps that existed in the previous editions. Galvanizers who already produce consistently above the minimums will notice little difference in production. Those who were running close to the old 85 μm floor on structural work will need to adjust.
Update your specifications, update your certificates, update your training. The standards have moved — your documentation should move with them.
