ME Corrosion and Degradation 2

Question 1

Stress corrosion cracking (SCC) requires the simultaneous presence of:

Accepted Answer

A susceptible material, a specific corrosive environment, and tensile stress

Answer

High temperature, high pressure, and fatigue loading

Answer

Impact loading and an acid environment

Answer

Compressive stress and neutral pH electrolyte

Question 2

Hydrogen embrittlement in high-strength steels is caused by:

Accepted Answer

Atomic hydrogen diffusing into the lattice and reducing ductility and toughness

Answer

Hydrogen oxidizing the steel surface

Answer

Hydrogen gas bubbles forming at grain boundaries

Answer

Reaction with atmospheric moisture

Question 3

Cavitation erosion occurs in hydraulic components when:

Accepted Answer

Vapor bubbles form and collapse violently near the surface, causing pitting

Answer

High velocity particles impact the surface

Answer

Corrosive fluids slowly dissolve the surface

Answer

Fretting wear occurs at contact surfaces

Question 4

The Evans diagram (mixed potential theory) predicts the corrosion potential and corrosion current by finding:

Accepted Answer

The intersection of the anodic and cathodic polarization curves

Answer

The maximum oxidation potential only

Answer

The pH at which corrosion ceases

Answer

The minimum electrolyte conductivity for corrosion

Question 5

Crevice corrosion occurs in tight gaps (under fasteners, gaskets) because:

Accepted Answer

Oxygen depletion inside the crevice creates an anodic region relative to the outside surface

Answer

The crevice is exposed to higher oxygen levels

Answer

The crevice has lower temperature

Answer

Higher pH inside the crevice dissolves the passive film

Question 6

The Pilling-Bedworth (PB) ratio predicts a protective high-temperature oxide scale when:

Accepted Answer

PB ratio is between 1 and 2 (compact, adherent, protective scale)

Answer

PB ratio is less than 1 (porous, non-protective scale)

Answer

PB ratio is greater than 2 (compressive buckling, non-protective)

Answer

PB ratio equals 0