7/29/2019 Questions_Answers_About_Corrosion_Testing

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This document contains general information, no rights can be derived.Questions and Answers about Corrosion Testing, Stork SwL Laboratories, Page 1 of 3

Quest ions and Answ ers aboutCorrosion Test ing

By: Stork SwL Laboratories222 Cavalcade Street

Houston, TX 77009-3213www.storksmt.com/swl

What is corrosion?

It has been said that metallurgy is the study of the making of metals; and corrosion isthe study of the unmaking of metals.

Metals corrode because we use them in environments where they are chemicallyunstable. Only copper and the precious metals (gold, silver, platinum, etc.) are found innature in their metallic state. All other metals, including ironthe metal most commonlyusedare processed from minerals or ores into metals which are inherently unstable intheir environments. It is the tendency of these metals to return to a stable state.

How big a problem is corrosion?

According to a study by the U.S. Federal Highway Administration, the total annualestimated direct cost of corrosion in the U.S. is $276 billion, approximately 3.1% of theU.S. Gross Domestic Product (GDP). Corrosion of bridges, highways, and vehicles arepart of these costs.

What are the triggers for corrosion?

Galvanic corrosion occurs when dissimilar metals are electrically connected inthe presence of an electrolyte.

General corrosion is caused by a reaction with the environment, such asoxidation and chemical attack of the metallic surface.

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How is corrosion "diagnosed?"

Corrosion testing experts, like those at Stork Materials Technology laboratories aroundthe country, typically identify corrosion in three ways:

1. By visual examination. Uniform corrosion, pitting, crevice corrosion, pack rust,Lamellar corrosion and galvanic corrosion can usually be readily identified by anexpert on sight.

2. By visual examination with supplementary means. Erosion corrosion,cavitation, fretting corrosion, intergranular corrosion, exfoliation, and dealloyingmay need more than visual examination to identify. For example, dealloyingcorrosion usually takes place below the surface of a material and will be revealedafter that layer is scraped away.

3. By microscopy. Optical or electron microscopes are necessary to confirmenvironmental cracking corrosion, stress corrosion cracking (SCC), corrosionfatigue, and hydrogen embrittlement.

What can help slow or prevent corrosion?

Environmental testing Protective coatings Corrosion-resistant alloys Cathodic and anodic protection Use of corrosion inhibitors

Stork knows how.

Many Stork metallurgists, engineers, and chemists are experts in corrosionidentification, prevention, and treatment. If you have questions about corrosionregarding your materials, products, or parts, contact info.swl@stork.com and one of ourmetals professionals will be in touch with you soon.