PCS Corrosion Science and Prevention Flashcards

In electrochemical corrosion, what four components must be present simultaneously for the corrosion cell to function?

Answer: Anode, cathode, electrolyte, and metallic path

A complete corrosion cell requires an anode (where metal is lost), a cathode (where reduction occurs), an electrolyte (ionic conductor), and a metallic path connecting anode to cathode.

Which form of corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte?

Answer: Galvanic corrosion

Galvanic corrosion occurs when two dissimilar metals form an electrochemical couple in an electrolyte, causing accelerated corrosion of the more active (anodic) metal.

What type of corrosion occurs in low-oxygen areas such as lap joints, gaskets, and under deposits?

Answer: Crevice corrosion

Crevice corrosion develops in confined spaces where oxygen is depleted, creating an oxygen concentration cell that accelerates localized attack within the crevice.

Zinc-rich primers provide corrosion protection to steel primarily through which mechanism?

Answer: Cathodic (sacrificial) protection by acting as the anode

Zinc-rich primers protect steel cathodically because zinc is more active than steel in the galvanic series, so zinc corrodes sacrificially to protect the steel substrate.

What is the primary cause of osmotic blistering in coatings applied over steel in immersion service?

Answer: Water-soluble salts trapped under the coating film

Soluble salts (chlorides, sulfates) beneath a coating draw water through the semi-permeable film via osmosis, creating blisters filled with a corrosive electrolyte solution.

Which test method is used in the field to detect soluble salt contamination on a prepared steel surface before coating?

Answer: Bresle patch method (ISO 8502-6)

The Bresle patch method (ISO 8502-6) extracts soluble salts from the surface using a latex cell filled with deionized water, which is then measured with a conductivity meter.