Corrosion, galvanic action and service life · Lesson 4 of 4

Corrosion, galvanic action and service life: defects, verification and case study

Defects read as symptom, mechanism and evidence: fastener and crevice corrosion, copper-aluminum damage, rooftop-unit runoff, cut edges, treated wood and concrete; the evidence to capture; and an illustrative school re-roof case.

You will be able to: Diagnose a plausible corrosion defect from its symptom, name the likely mechanism and the evidence to capture, and work an illustrative school re-roof through the review to a list of requests for information.

10 min · 12 slides · 6 questions

All lessons in this module

Slide 1 of 12

Read a failure: symptom, mechanism, evidence

For each defect, write the symptom, the likely mechanism, the evidence that would confirm it, and who decides the fix.

Corrective design belongs to the designer or the system maker. This lesson names options, not approvals.

Sources

Stainless Steel in Contact with Other Metallic Materials (Materials and Applications Series, Vol. 10, 2009) - Euro Inox
Dissimilar Metal Corrosion in Roofing Installations (white paper page, published 06/2016) - Metal Construction Association

Glossary

Crevice: A tight, poorly drained gap, such as under a lid or washer, that stays damp and can greatly increase the risk of galvanic corrosion.
Cut-edge corrosion: Attack where the steel under a zinc coating is exposed at a cut edge, gouge or scratch; usually small because the bare area is small beside the zinc.
Condensate: Water that forms on cool surfaces, such as air-conditioning equipment, and can act as an electrolyte; copper-bearing condensate dripping on a galvanized frame can corrode it.
Nailer: The wood member that metal edge flashing is fastened to; copper-treated lumber in a nailer with moisture can corrode the metal, so a membrane is suggested between them.
Evidence record: Photographs, part and fastener identities, a water-path sketch, distance to salt water and the product documents, captured before repair and given to the designer or maker.