Articles Stuck Together / Contact Marks
Also called: contact marks · touch marks · stuck bundles
Appearance
Dull grey patches with straight, geometric edges that match the footprint of another piece — and the same mark appears on both mating faces. After the pieces are pulled apart the zinc in the patch may be torn, scored or missing, sometimes with a raised lip or drag mark at its edge. The straight edge is the tell: a contact mark has a geometry, because it is the shadow of another piece of steel. Reactive-steel grey has a chemistry instead — it is cloudy, follows the section, and is usually thicker rather than thinner.
Root cause
Articles touching one another during immersion, in the bath, or on withdrawal — too little spacing on the jig, nested or bundled sections, pieces resting on each other. Molten zinc cannot flow through a contact face, so little or no coating forms there, while zinc bridging the gap freezes and welds the pieces together. Pulling them apart then tears whatever coating did form. This is load design and jigging: the galvanizer's own fault, not the steel's and not the fabricator's.
Acceptance verdict
Judged on what the contact face is left with, not on how it looks — and A123 decides this case by name: marks from tongs and other handling during galvanizing are not cause for rejection UNLESS they expose base metal beyond the renovation limits. Contact marks are the same mechanism. A dull mark still meeting thickness is an appearance matter; bare metal at the contact faces is renovated per A780 within the limits — each area over 25 mm in one dimension only, at most 0.5% of the accessible surface and 256 cm2 per metric ton — and beyond them the article is re-galvanized.
Same test. ISO 1461 does not require uniform appearance, so a contact mark that meets the local thickness requirement is acceptable. Thin or bare contact faces are non-conforming — repairable within ISO 1461 renovation limits (total at most 0.5% of the surface, each area at most 10 cm2, repair at a minimum average of 100 um unless otherwise agreed), beyond them re-galvanize.
This is the question the standards actually answer — describe the defect, then decide: accept, repair, or reject.
Repairable?
Yes — within the standard's renovation limits, using ASTM A780 methods: zinc-alloy solder, zinc-rich paint, thermal spray. Repair only within the size and total-area limits set by the governing standard; beyond them the article is re-galvanized.
Remedy at the plant
Fix it in the load, not after the kettle. Space articles on the jig so no two faces can touch, wire or bar them apart, never nest angles or channels inside one another, and review the bundle design for the section being run — withdraw slowly enough that pieces cannot swing together. Once the mark is there the only route is to measure the contact face and renovate per ASTM A780 within the governing standard's renovation limits; past those limits it is re-galvanized.
Remedy at design
Mostly plant-side, but design can help: provide jigging and lifting holes so the galvanizer can hang articles individually instead of bundling them — often the same holes that serve venting and draining.
Clause references
- ASTM A123/A123M-24
- ASTM A780/A780M-20
- ISO 1461:2022
- ISO 14713-2:2020
Standard designations are the property of ASTM International and ISO. This page states the acceptance outcome for this condition — it reproduces no standard text or tables. Verify against the current edition at astm.org · iso.org.