Uncleaned Welding Slag & Spatter
Also called: slag line · weld spatter · uncleaned welds
Appearance
A hard crusty ridge tracing the weld toe with no zinc on it, rusting brown and bleeding stain onto the sound coating either side; hard spherical nodules scattered around the weld, either coated over as roughness or shed to leave uncoated points.
Root cause
Welding slag and spatter left on the steel before it reached the galvanizer. Slag is non-metallic: degreasing and acid pickling do not remove it, so molten zinc cannot wet the steel underneath and no coating forms along that line. Spatter either galvanizes over as roughness or, where poorly adherent, breaks away later and takes the coating with it. The condition is created at the welding bay, not at the kettle.
Acceptance verdict
Non-conforming where it leaves steel uncoated — coating continuity is required whoever caused it. But the ASTM chain settles who answers for it, in the standards' own words: A385 states that welding flux residues are chemically inert in normal pickling solutions, will not be removed by standard galvanizing cleaning, and are best removed at the time of fabrication — by grit or sand blasting or a wire needle gun. A123 makes A385 compliance mandatory in design and fabrication, and expressly says surface conditions caused by such fabrication deficiencies are not grounds for rejecting the galvanizing. Repairable per A780 within A123 renovation limits once the slag is ground off — each area over 25 mm in one dimension only, at most 0.5% of the accessible surface and 256 cm2 per metric ton; beyond them, clean and re-galvanize.
Uncoated slag areas render the article non-conforming — an uncoated area is a defined term, and renovation or re-galvanizing per Clause 6.3 is the remedy: 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. On responsibility, ISO 1461 speaks through its scope and its Annex: the standard itself sets no requirements on the surface condition of the steel as supplied — it says outright that surface condition affects the result and points to ISO 14713-2 for guidance — and its normative Annex A puts the duty to declare the basis metal's condition and any special pre-treatment needs on the purchaser. What the pickle cannot remove, the fabricator must.
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
Catch it at incoming inspection, not after the kettle — check weld toes for slag and spatter on receipt and send the work back or clean it before pickling. Once it is through the bath the fix is expensive: grind the slag away to bare metal, then renovate per ASTM A780 within the governing standard's renovation limits; past those limits the article is re-cleaned and re-galvanized.
Remedy at design
The fabricator removes all welding slag and spatter before the work ships for galvanizing — chip and wire-brush every weld, knock spatter off, or better, blast or needle-gun the welds, which is the method ASTM A385 itself names for flux residues precisely because pickling cannot remove them. Put it in the purchase order and the fabrication drawings. This is the most common condition blamed on the galvanizer that the galvanizer did not cause.
Clause references
- ASTM A385/A385M
- 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.