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Copper, zinc, stainless and specialty metals · Lesson 4 of 4

Copper, zinc, stainless and specialty metals: defects, verification and case study

Rust spots on stainless, cracked zinc folds, white rust, underside pitting, copper runoff stains, springback and fingerprints: cause, fix and evidence for each, then an illustrative coastal job worked through as RFIs.

You will be able to: Diagnose common specialty-metal defects from their evidence, name the likely cause from a published source, choose a corrective option and record what a reviewer needs.

10 min · 11 slides · 7 questions

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Inspect before it ships

Check each metal against its own card: stainless for rust specks and the angle, copper for prints and thickness, zinc for cracks, radius and white bloom, lead-coated copper for edges.

Record each check on the card, so the evidence ships with the bundle.

Shop inspection cards, one per metalFour inspection cards. Stainless: no rust specks, no scratches with paper or film on, angle checked for springback. Copper: no fingerprints or scratches, thickness at or above the maker minimum, gloves used. Zinc: no cracks at folds and radius not sharp, rolling direction consistent, no white bloom and film on. Lead-coated copper: coating intact, cut edges treated as copper, no edge draining onto zinc.Stainless steelNo rust specks (picked-up steel)No scratches; paper or film onAngle checked for springbackCopperNo fingerprints or scratchesThickness at or above maker minimumGloves used in handlingZincNo cracks at folds; radius not sharpRolling direction consistentNo white bloom; film still onLead-coated copperCoating intact on the facesCut edges treated as copperNo edge draining onto zinc

Four inspection cards. Stainless: no rust specks, no scratches, paper or film on, angle checked for springback. Copper: no fingerprints, no scratches, thickness at or above the maker minimum. Zinc: no cracks at folds, radius not sharp, rolling direction consistent, no white bloom, film on. Lead-coated copper: coating intact, edges treated as copper.

Checks drawn from SSINA, Outokumpu, Revere, RHEINZINK, VMZINC and AFS's compatibility screening.

Sources

Videos for this lesson

What this video shows: IMOA webinar on contamination in welded fabrications (grease, carbon-steel contamination, heat tint) and the cleaning, pickling and passivation sequences that restore the surface. Specialist work, not a shop step.

Video: Selecting Passivation Techniques for CRA to complete Fabrication by IMOA, on YouTube. AFS checked its description against this lesson.

Glossary

White rust
Unstable zinc hydroxide that forms on zinc with too much water and too little carbon dioxide, instead of the stable grey patina (VMZINC).
Passivation
A chemical treatment of stainless steel covered by ASTM A967 and A380; SSINA notes nitric passivation does not remove embedded iron. It is specialist work, not a shop step.
Underside corrosion
RHEINZINK calls it hot water corrosion: when the underside of zinc is exposed to moisture combined with high temperatures over a long period, with no air exchange, no carbonate layer forms there and the zinc eventually pits.