Coating grade selection, mass verification, bend test mandrel sizing, and QC sampling for galvanized sheets and structural steel
◉ IS 277:2003, IS 2629:1985, IS 4759:1996 STYLE CHECK · NOT A REGULATORY SUBMISSION TOOL
⚠ Indicative tool only. IS 277 (Sixth Revision, 2003, with Amendment 1/2005 incorporated) covers plain/corrugated sheets and coils; IS 4759 (Third Revision, 1996) covers structural steel, castings, and threaded products; IS 2629 (1985) is the process standard both explicitly cross-reference for the galvanizing bath itself. Note IS 277 has since been superseded by a Seventh Revision (2018) not reviewed here — verify current applicability. Marine/industrial atmosphere service requires increased coating mass by agreement between galvanizer and purchaser (IS 4759 Note 1) — directly relevant for coastal tank terminal components.
Identification
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IS 277 — Sheet/Coil Coating Grade & Mass (§7.3, Table 2)
Recommended coating grade by thickness (§7.3): 0.18–0.28mm→200, 0.30–0.55mm→220, 0.63–1.0mm→275 (min. for roofing), >1.0mm→350. GC grade is exempt from the bend test when intended for corrugation (Amendment 1).
Result
Recommended coating grade—
Min. average mass (triple-spot)—
Min. single-spot mass—
ComplianceNot evaluated
Grade
600
450
350
275
220
200
180
120
Min avg triple-spot (g/m²)
600
450
350
275
220
200
180
120
Min single-spot (g/m²)
510
380
300
235
190
170
155
100
IS 277 — Bend Test Mandrel Diameter (Table 3)
180° bend around the mandrel; no peeling or flaking of zinc coating permitted. Mandrel diameter is expressed in the standard as a multiple of sheet thickness. Not applicable to GC grade sheets intended for corrugation (Amendment 1) or GPH/GCH grades.
Result
Mandrel diameter multiplier—
Required mandrel diameter—
IS 4759 — Structural/Fabricated Item Coating Mass (Table 1)
Values shown are for normal/rural atmosphere. For marine or industrial atmosphere service, the minimum coating mass shall be increased by agreement between the galvanizer and purchaser (Note 1) — directly relevant for coastal tank terminal structural components.
Result
Minimum coating mass—
ComplianceNot evaluated
IS 4759 — QC Sampling Plan (Table 2)
Units shall be selected at random (see IS 4905:1968). Acceptance number reference: IS 2500 (Part 1):1992.
Result
Sample size to select—
Acceptance number (max defectives)—
Lot Size
Sample
Accept No.
Up to 25
3
0
26–100
5
0
101–150
8
1
151–500
13
1
501–1000
20
2
1001–10000
32
3
10001 and above
50
5
IS 2629 — Galvanizing Process Reference
Recommended practice, not a numeric specification — reference parameters only. Degreasing: alkaline solution 85–90°C, immersion 1–20 min depending on soiling. Pickling (HCl, with inhibitor): room temperature. Pickling (H₂SO₄, 100–150 g/L, with inhibitor): best results at elevated temperature (per acid supplier guidance). Fluxing: room temperature to 80°C. Dry galvanizing pre-dip drying: ~120°C, must not exceed 150°C (flux decomposes above this). Galvanizing bath: molten zinc, working temperature commonly 450°C (range 440–460°C), should not ordinarily exceed 475°C to avoid excessive attack on the work. Aluminium addition (dry process): ~0.005% to brighten appearance and reduce ash/dross.