Written so a buyer's own inspector can follow it without our help. If you can check the work properly, we would rather you did.
Most galvanizing inspection goes wrong in one of two ways. Either nobody measures anything and a certificate is accepted on trust, or somebody rejects a consignment for an appearance issue that no standard actually treats as a defect.
This page is the middle path: what to measure, where, how many times, and what genuinely constitutes a reason to reject. It is deliberately written so you can run it without us.
What the standard actually requires — and what it does not.
| Genuine defect | Not a defect |
|---|---|
| Uncoated areas — bare steel visible | Dull grey or matte finish from reactive steel chemistry |
| Blisters in the coating | Colour variation between members or between heats |
| Flux deposits left on the surface | Minor surface roughness |
| Gross dross inclusions | Ash or zinc spots that are firmly adherent |
| Lumps, runs or spikes that stop the piece assembling | Darkening or weathering with age |
| Coating that fails an adhesion check | White bloom that brushes off and leaves adequate coating |
ASTM A123 requires a coating that is continuous, smooth and uniform, free from uncoated areas, blisters, flux deposits and gross dross inclusions, and adherent for the service life. Appearance is not a rejection criterion in itself. A grey coating is usually thicker than a bright one, not worse — see why coating peels for the metallurgy.
The standard check is a stout knife test: apply a stout knife to the coating at an angle, under firm pressure, and try to lift it. A properly formed coating will not peel or flake ahead of the blade. Paring away a sliver is not a failure — lifting the coating off in a layer is.
Do this on a limited area, not across the piece. It is destructive by nature and the tested spot may need repair to ASTM A780 afterwards.
Every batch leaves with a galvanizing inspection report carrying the coating thickness readings. Third-party inspection by SGS, Bureau Veritas, TÜV, DNV, Intertek or your own nominated agency is supported at your cost, and because fabrication and galvanizing are both on our floor at Howrah, that is one visit rather than two.
Where a state utility specification requires NABL-accredited type-test reports dated within a stated period, that is arranged against the order.
Answered from our own line, not from the standard's cover page.
With a calibrated magnetic dry film thickness gauge, taking multiple readings across a reference area rather than at a single spot, and including corners, edges and weld toes rather than only flat faces.
No. It is normally the result of steel chemistry — silicon in the reactive range grows the alloy layers to the surface, leaving no bright free zinc. The coating is usually thicker than a bright one, not thinner. Appearance is not a rejection criterion in itself.
An adhesion check. A stout knife applied at an angle under firm pressure should not lift the coating off in a layer. Paring a sliver away is normal; delamination ahead of the blade is a failure.
Enough to establish an average over a reference area rather than to prove a point — and they should include the difficult geometry. Standards are written as minimum averages, so a report should state how many readings were taken and where.
Yes, and we would rather they did. Inspection by SGS, Bureau Veritas, TÜV, DNV, Intertek or your own agency is supported at your cost, and fabrication and coating are witnessed in the same place.
Tell us the standard, the coating requirement and the component, and we will confirm in writing what we can hold and how we will certify it. Galvanizing is on our own floor, so the answer comes from us and not from a sub-contractor.
Request a quotation Galvanizing job work