PCS Corrosion Science and Prevention Flashcards

What type of corrosion is characterized by thin, thread-like filaments of corrosion product growing beneath a coating film, often starting at cut edges?

Answer: Filiform corrosion

Filiform corrosion forms worm-like threads of corrosion product under coatings, typically initiating at scratches or edges in humid environments, particularly on aluminum and steel.

Which factor most significantly increases the corrosion rate of steel in an atmospheric environment?

Answer: Chloride deposition rate

Chloride deposition rate is the dominant factor accelerating atmospheric corrosion because chlorides are highly hygroscopic and form a persistent, conductive electrolyte on the steel surface.

When applying a thermal spray zinc (TSZ) coating for corrosion protection, which property makes it superior to paint-applied zinc-rich primer in aggressive marine environments?

Answer: Higher purity zinc providing more consistent cathodic protection with no organic binder to degrade

Thermal spray zinc coatings contain nearly pure zinc with no organic binder, providing long-term, consistent cathodic protection without the risk of binder degradation that limits paint-applied zinc primers.

What does 'passivation' mean in the context of corrosion science for metals like stainless steel?

Answer: Formation of a thin, stable oxide layer that inhibits further corrosion

Passivation is the spontaneous or induced formation of a thin, adherent oxide film on a metal surface that acts as a barrier, greatly reducing the metal's corrosion rate.

Which type of inhibitive pigment in a coating primer reacts with the substrate or electrolyte to slow the anodic corrosion reaction?

Answer: Zinc phosphate

Zinc phosphate is an inhibitive pigment that reacts with moisture and the steel substrate to form a passivating phosphate layer, slowing anodic dissolution at the coating-metal interface.

In NACE/AMPP corrosion control, what is the primary advantage of combining a coating system WITH impressed current cathodic protection (ICCP) on a buried pipeline?

Answer: The coating reduces current demand so less power is needed to achieve full protection

A good coating dramatically reduces the bare metal area exposed to the electrolyte, lowering the cathodic protection current required and making the combined system far more economical and effective.