Calculations and Data Interpretation
Formula to calculate corrosion rate (simplified)?
CR = (K * ΔW) / (A * T * D)
This metal forms a green patina over time.
Copper
Marine environments accelerate corrosion due to this ion.
Chloride
Corrosion that occurs uniformly over the surface.
Galvanizing involves coating steel with this metal.
Zinc
Units for corrosion rate?
mm/year or mpy
Stainless steel resists corrosion due to this protective feature
Passive Oxide Layer
RH stands for…
Relative Humidity
Corrosion in small, localized pits.
Pitting
What is the main difference between anodic and cathodic protection?
Anodic protection makes the metal passive, cathodic protection supplies electrons to prevent oxidation
If a steel coupon loses 0.5 g over 30 days in a 50 cm² area, what info do you need to calculate CR?
Area, time, density, constant K
Name one alloying element that increases corrosion resistance in steel.
Chromium or Nickel
The type of corrosion often found under paint or coatings in high humidity.
Crevice Corrosion
Corrosion that occurs in shielded areas or cracks.
Crevice Corrosion
Why is surface preparation critical before painting?
o remove oxides, grease, and contamination for proper adhesion
If a material shows a decreasing corrosion rate over time during long-term exposure, what could this indicate?
Formation of protective corrosion products or passivation layer slowing further corrosion
How does surface roughness affect corrosion behavior of metals?
Rough surfaces increase surface area and crevices, which can trap moisture and pollutants, accelerating corrosion.
Explain why cyclic wet/dry conditions are more damaging than constant immersion for metals.
They promote oxygen replenishment and localized corrosion (pitting and crevice)
Define “galvanic series” and its significance in corrosion.
Ranking of metals by electrochemical potential; predicts which metal will corrode when coupled
Why can misapplied coatings sometimes increase corrosion instead of preventing it?
Trapped moisture or poor adhesion can create crevices and accelerate localized corrosion