Coating defect

Steel surface imperfections

Weld spatter, rough welds, slivers, laminations and sharp edges. Some only appear after blasting removes the mill scale.

Steel surface imperfections: the surface as you see it, and a schematic cross-section.

Causes

Welding and cutting.
Rolling defects in the steel that blasting lifts into slivers.

Prevention

Specify a preparation grade for welds and edges (ISO 8501-3, P1 to P3) next to the cleanliness grade.
Grind spatter, slivers and sharp edges before final blasting.

How it is assessed

Visual and by touch: a gloved hand snags on slivers. A cleanliness grade such as Sa 2½ alone does not require their removal.

Telling it apart

Edge corrosion (thin film at edges): Edge corrosion is the result in service. The sharp edge that caused it is an imperfection to fix before coating.
Pinpoint rusting: Rust spots over the whole surface come from the profile or a thin film. Rust along a weld or a sliver points to the steel itself.

Repair

Grind or remove the imperfection, reblast the area and stripe coat it. The specification and the coating manufacturer have the final word on the repair procedure.

17 practice items in the members area mention steel surface imperfections (CIP 1: 10 · CIP 2: 5 · FROSIO written: 2).

Try it in an exam-style question. The free readiness check shows the question style, explains every answer and gives you a dated study plan.

Take the free readiness check See the tracks

About this page

Written from coating practice and the published rating standards, in our own words; the drawing is schematic. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.