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Resources/Cross-references/Galvanizing standards

Cross-references

Hot-dip galvanizing standards compared: ASTM A123 / A153 / A767, ISO 1461, IS 4759, JIS H 8641

Hot-dip galvanizing is specified by ASTM A123 (fabrications), A153 (hardware) and A767 (rebar) in the USA, EN ISO 1461 in the UK and EU, IS 4759 in India and JIS H 8641 in Japan. All set a minimum zinc coating by steel thickness or product type, about 85–100 µm (roughly 610–720 g/m²) for steel over 6 mm, but the thickness bands and units differ.

Cross-reference

Equivalent grades by region

LevelUSAASTM A123, ASTM A153, ASTM A767 (and ASTM F2329 for fasteners)UKBS EN ISO 1461; BS EN ISO 10684 (fasteners)EUEN ISO 1461; EN ISO 10684 (fasteners); EN ISO 14657 (reinforcement)インドIS 4759 (specification), IS 2629 (practice), IS 2633 (uniformity test)JapanJIS H 8641 (test methods JIS H 0401)
Structural steel and fabrications, over ~6 mm thickA123 is the most demanding at this thickness. IS 4759 places the 610 g/m² band at 5 mm, not 6 mm.ASTM A123 grade 100: 100 µm minimum average (structural shapes over 6.4 mm)BS EN ISO 1461: 85 µm (610 g/m²) mean, 70 µm (505 g/m²) local, steel over 6 mmEN ISO 1461: 85 µm (610 g/m²) mean, 70 µm localIS 4759: 610 g/m² minimum average, fabricated steel 5 mm and overJIS H 8641 HDZT 77: ≥77 µm (former HDZ 55, 550 g/m²), used for steel 6 mm and over
Steel ~3–6 mm thickASTM A123 grade 75: 75 µm (3.2–6.4 mm structural shapes, plate, strip and bar)BS EN ISO 1461: 70 µm (505 g/m²) mean, 55 µm local, over 3 mm to 6 mmEN ISO 1461: 70 µm (505 g/m²) mean, 55 µm localIS 4759: 460 g/m², 2 mm to under 5 mmJIS H 8641 HDZT 63: ≥63 µm (former HDZ 45, 450 g/m²)
Thin steel, ~1.5–3 mmThickness bands do not line up between standards; compare at the actual steel thickness.ASTM A123 grade 65: 65 µm (1.6–3.2 mm structural shapes, plate, strip and bar)BS EN ISO 1461: 55 µm (395 g/m²) mean, 45 µm local, 1.5–3 mmEN ISO 1461: 55 µm (395 g/m²) mean, 45 µm localIS 4759: 340 g/m², 1.2 mm to under 2 mm—
CastingsASTM A123 forgings and castings: 100 µmBS EN ISO 1461 castings: 80 µm (575 g/m²) mean at 6 mm and over; 70 µm (505 g/m²) under 6 mmEN ISO 1461 castings: 80 µm mean ≥6 mm; 70 µm under 6 mmIS 4759: 610 g/m², grey and malleable iron castings—
Bolts, nuts and threaded parts (centrifuged)Galvanized threads need allowance: EN ISO 10684 covers oversize-tapped nuts and undersize bolt threads. Galvanizing below M8 is not recommended.ASTM A153 Class C (over 3/8 in): 381 g/m² (53 µm) average; Class D (3/8 in and under): 305 g/m² (43 µm); ASTM F2329BS EN ISO 10684 (M8–M64, bolts to 10.9); BS EN ISO 1461 centrifuged threaded parts over 6 mm: 50 µm (360 g/m²) mean, 40 µm localEN ISO 10684; EN ISO 1461 centrifuged threaded parts over 6 mm: 50 µm mean, 40 µm localIS 4759 threaded work: 300 g/m² at 10 mm diameter and over, 270 g/m² under 10 mmJIS H 8641 HDZT 49 (former HDZ 35) is the class usually applied to bolts and nuts
Reinforcing barA767 also requires a chromate treatment after galvanizing.ASTM A767 Class I: 1070 g/m² (#4 [13] and larger), 915 g/m² (#3 [10]); Class II: 610 g/m²BS EN ISO 14657 (coating classes A, B, C)EN ISO 14657 (coating classes A, B, C)——

Read before comparing

  • Coating mass and thickness convert at the density of zinc: 1 µm of coating is about 7.2 g/m² (JIS H 8641 uses 7.2 g/cm³). So 85 µm ≈ 610 g/m² and 100 µm ≈ 720 g/m².
  • ASTM A123 grade numbers are the minimum average thickness in micrometres (grade 100 = 100 µm). It sets only minimums; there is no maximum coating thickness.
  • EN ISO 1461 gives two figures: a mean for the reference areas and a lower local minimum for any single area. ASTM A123 gives a minimum average per specimen; ASTM A153 gives both an average and an individual-specimen minimum.
  • JIS H 8641 was revised in December 2021 from coating mass classes (HDZ 35–HDZ 55, g/m²) to thickness classes (HDZT 35–HDZT 77, µm), in line with ISO 1461. Older drawings still call up HDZ 55 (= HDZT 77).
  • In India, IS 4759:1996 (reaffirmed) sets the coating mass; IS 2629 gives the recommended galvanizing practice and IS 2633 the uniformity (Preece dip) test. IS 4759 values are for normal atmospheres; heavier coatings are agreed for marine and industrial sites.
  • Thickness and mass values here are minimums for acceptance, not service-life predictions. Steel chemistry, especially silicon and phosphorus, can give much thicker coatings than the minimum.

よくあるご質問

Common questions

What is the difference between ASTM A123 and A153?

ASTM A123 covers fabricated products such as structural shapes, plate, pipe and assemblies. ASTM A153 covers hardware such as bolts, nuts, washers and small castings that are usually spun (centrifuged) after dipping, so its required coating is thinner.

Is ISO 1461 equivalent to ASTM A123?

They cover the same kind of work and are broadly similar, but not identical. For steel over 6 mm, ISO 1461 requires an 85 µm mean and A123 requires 100 µm for structural shapes; thickness bands, sampling and measurement rules also differ.

What is the minimum galvanizing thickness for structural steel?

For steel over 6 mm it is 85 µm mean (610 g/m²) under EN ISO 1461, 100 µm under ASTM A123 for structural shapes, 610 g/m² under IS 4759 (from 5 mm) and 77 µm (HDZT 77) under JIS H 8641.

What is HDZ 55 in the new JIS H 8641?

HDZ 55 (550 g/m² minimum) became HDZT 77 (77 µm minimum) when JIS H 8641 changed from coating mass to coating thickness in 2021. HDZ 45 became HDZT 63 and HDZ 35 became HDZT 49.

Which Indian standard covers hot-dip galvanizing?

IS 4759 specifies hot-dip zinc coatings on structural steel and allied products, including the minimum coating mass. IS 2629 is the recommended practice for the galvanizing process, and IS 2633 is the test for coating uniformity.

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Hot-dip galvanizingHot-dip galvanizing protects steel by immersing the cleaned, fluxed part in molten zinc at about 450 °C, forming zinc–iron alloy layers metallurgically bonded to the steel with a zinc layer on top.Zinc electroplatingZinc electroplating deposits a thin, even layer of zinc on steel from an electrolyte bath, usually 5–25 µm thick, and is normally sealed with a chromate passivate.Bolt property classesMetric bolts in the UK, EU, India and Japan all use the ISO 898-1 property classes (4.6, 8.8, 10.9, 12.9), while US inch bolts use SAE J429 grades and ASTM specifications.Rebar gradesRebar grades are named after their minimum yield strength: Grade 60 (420 MPa) in the USA, B500B or B500C (500 MPa) in the UK and EU, Fe 415 to Fe 600 in India and SD295 to SD490 in Japan.Structural steel gradesStructural steel grades in the USA, UK, EU, India and Japan line up by minimum yield strength: about 250 MPa (A36, S235/S275, E250, SS400), about 350 MPa (A572 Grade 50 / A992, S355, E350, SM490) and about 410–450 MPa (A572 Grade 60/65, S450, E410/E450, SM570).

References

Sources

  1. American Galvanizers Association: ISO 1461 vs ASTM A123 (A123 Table 1 grades)
  2. American Galvanizers Association: ASTM A153 for hardware
  3. American Galvanizers Association: ASTM A767 for reinforcing steel
  4. American Galvanizers Association: ASTM F2329 vs ASTM A153
  5. Galvanizers Association (UK): EN ISO 1461 coating requirements
  6. ISO 10684:2004 hot dip galvanized coatings on fasteners (scope preview)
  7. ISO 14657:2005 zinc-coated steel for the reinforcement of concrete
  8. IS 4759:1996 Hot-dip zinc coatings on structural steel and other allied products (Table 1), Bureau of Indian Standards — Read from a licensed copy; values are minimum coating mass for normal atmospheres.
  9. InfraLens: IS 2629 recommended practice for hot-dip galvanizing
  10. Nikkenren steel frame Q&A A-7-28: JIS H 8641 change from HDZ to HDZT
  11. Japan Road Association technical note on JIS H 8641:2021 class conversion

Values summarize published limits and typical data. The governing standard and the current edition control; check them before specifying.