Corrosion, galvanic action and service life: methods and worked application

An eight-step review method; screening pairs with the Design Center and reading it against the sources; choosing separation; zinc-loss arithmetic, an area-ratio example and a site checked against four warranty and category documents.

You will be able to: Run a documented corrosion and service-life review on a flashing detail: define the site, map contact and drainage paths, screen pairs, choose separation, check warranties and record assumptions, with three worked examples.

A documented review in eight steps

This course's review has eight steps: define the site, list the metals, map the contact and drainage paths, screen the pairs, choose separation, check each warranty, record the assumptions, and send requests for information.

It is a teaching method built from the sources in these lessons, not a published standard.

1: Define the site: exposure evidence, the distance to salt water measured on the plan, and local electrolyte sources
2: List the metals: every metal, coating, fastener and substrate in the detail
3: Map the paths: where parts touch or share a fastener, and where water runs from one part onto another
4: Screen the pairs: avoid, caution, compatible, review or not covered, noting which part is small
5: Choose separation: insulate, coat the more noble part, place the joint out of the damp, or drain runoff away
6: Check warranties: each product's distance condition and exclusions, with the document's date
7: Record assumptions: service-life assumptions as the designer's own, each with its source
8: Send requests for information for every fact the record lacks

This course's review method, built from the sources in these lessons. It is a teaching sequence, not a published standard.

Sources

ISO 9223:2012 Corrosion of metals and alloys - Corrosivity of atmospheres - Classification, determination and estimation (committee page; scope only, full text paid) - ISO (ISO/TC 156)
Stainless Steel in Contact with Other Metallic Materials (Materials and Applications Series, Vol. 10, 2009) - Euro Inox
UFGS 07 60 00 Flashing and Sheet Metal (08/23, Change 1 05/25), a Department of Defense guide specification - U.S. DoD / Whole Building Design Guide

Glossary

Contact path

A place where two metals touch or share a fastener, giving the electrical connection a galvanic couple needs.

Drainage path

The route water takes from one part onto another; copper-bearing water running onto aluminum or zinc can corrode it with no contact at all.

Screening

A first look at a metal pair that returns avoid, caution, compatible, review or not covered; it is not an approval and does not replace the maker's guidance.

Separation

Breaking the metal path or keeping moisture off: insulating the parts, coating the more noble part (never only the anode), placing the joint out of the damp, or draining runoff away.

Request for information

A written question for the designer or maker about a fact the record lacks, such as a stainless grade or aluminum alloy that AFS marks "AFS to confirm".