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IS 4736:2003 is the Indian Standard (BIS) for hot-dip galvanized coatings on structural steel and other allied products - specification. This standard covers the specification for hot-dip galvanized coatings applied to structural steel shapes, plates, and bars to provide corrosion protection. It details the required zinc coating mass, thickness, adhesion, and appearance criteria based on the thickness of the base steel.
Specifies the general requirements for hot-dip galvanized coatings applied to fabricated structural steel and other products.
Overview
Status
Current
Usage level
Frequently Used
Domain
Materials Science — Aluminium and Non-Ferrous Metals
! Surface preparation is critical; ensure steel is properly pickled and free from mill scale, rust, and grease before galvanizing to avoid bare patches.
! Hot-dip galvanizing involves immersing steel in a zinc bath at around 450°C, which can cause distortion or warping in thin or asymmetrical structural sections.
! This standard does not apply to threaded fasteners (nuts, bolts), which are covered under IS 1367 (Part 13).
ISO 1461:2022International Organization for Standardization (ISO), International
HighCurrent
Hot dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods
Specifies general properties and test methods for hot-dip galvanized coatings on fabricated iron and steel articles.
ASTM A123 / A123M - 17(2023)American Society for Testing and Materials (ASTM), USA
HighCurrent
Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products
Covers requirements for hot-dip zinc coatings on iron and steel products made from rolled, pressed, and forged shapes, castings, plates, bars, and strips.
BS EN ISO 1461:2022British Standards Institution (BSI), United Kingdom / European Committee for Standardization (CEN), Europe
HighCurrent
Hot dip galvanized coatings on fabricated iron and steel articles. Specifications and test methods
The UK and European adoption of ISO 1461, making it technically identical in content.
AS/NZS 4680:2006Standards Australia / Standards New Zealand, Australia/New Zealand
HighCurrent
Hot-dip galvanized (zinc) coatings on fabricated ferrous articles
Provides specifications for hot-dip galvanized coatings applied to general fabricated ferrous articles, closely aligned with ISO 1461.
Key Differences
≠IS 4736 specifies coating requirements as mass per unit area (g/m²), whereas ISO 1461 and ASTM A123 primarily specify coating thickness (µm), although providing mass equivalents.
≠The criteria for repairing uncoated areas are not explicitly quantified in IS 4736 ('small bare patches'), while ISO 1461 limits individual repair areas to 10 cm² and total repair to 0.5% of the surface area.
≠ASTM A123 categorizes coating thickness requirements by the type of steel product (e.g., structural shapes, pipe, bar) in addition to material thickness, a level of detail not present in IS 4736.
≠IS 4736 specifies sampling plans for inspection based on lot size in Annex A, which differs from the 'control sample' methodology and specific sample numbers defined in ISO 1461.
≠IS 4736 includes the 'Preece Test' (copper sulphate test) for uniformity of coating, a method considered obsolete and not included in modern standards like ISO 1461 or ASTM A123.
Key Similarities
≈All standards require the minimum coating mass/thickness to be directly related to the thickness of the base steel, ensuring thicker steel sections receive a more substantial protective coating.
≈The fundamental galvanizing process is consistent across all standards, including pre-treatment steps (cleaning, pickling, fluxing) followed by immersion in a molten zinc bath.
≈All standards include provisions for visual inspection, requiring the coating to be continuous, adherent, and free from major defects like bare patches, blisters, and sharp points that could cause injury.
≈IS 4736, ISO 1461, and ASTM A123 all permit the renovation of small damaged or uncoated areas using approved methods like zinc-rich paint, thermal zinc spray, or zinc alloy solder.
Parameter Comparison
Parameter
IS Value
International
Source
Coating Mass (Steel > 6 mm thick)
610 g/m² (min average)
85 µm mean thickness (equivalent to 610 g/m²)
ISO 1461:2022
Coating Mass (Steel 3 to 6 mm thick)
460 g/m² (min average)
70 µm mean thickness (equivalent to 505 g/m²)
ISO 1461:2022
Coating Mass (Steel 1.6 to 3 mm thick)
345 g/m² (min average)
55 µm mean thickness (equivalent to 395 g/m²)
ISO 1461:2022 (for 1.5 to 3 mm)
Maximum Individual Repair Area
Not explicitly quantified, refers to 'small bare patches'.
10 cm²
ISO 1461:2022
Maximum Total Repair Area
Not explicitly quantified.
≤ 0.5% of the total surface area of the article.
ISO 1461:2022
Adhesion Requirement
No flaking or peeling when cut with a stout knife (Stripping/Pivoting Test).
Generally assumed satisfactory; a cutting/prying test is used only if adhesion is in doubt.
ISO 1461:2022
Minimum Zinc Purity in Bath
Refers to IS 209 (e.g., ≥98.5% for Prime Western Zinc).
The zinc in the bath shall contain not less than 98.0 % zinc by weight.
ASTM A123 / A123M - 17(2023)
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Min zinc coating mass (steel thickness > 5 mm)610 g/m²
Min zinc coating mass (steel thickness 2 mm to < 5 mm)460 g/m²
Min zinc coating mass (steel thickness 1.2 mm to < 2 mm)340 g/m²
Equivalent thickness for 610 g/m² coating85 microns
Equivalent thickness for 460 g/m² coating65 microns
Purity of zinc required (as per IS 209)98.5%
Tables & Referenced Sections
Key Tables
Table 1 - Mass of Zinc Coating on Steel Articles
Key Clauses
Clause 5 - Coating Requirements
Clause 6 - Sampling and Criteria for Conformity
Clause 7 - Test Methods (Thickness, Adhesion, Uniformity)