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Damage mechanisms — failure atlas

Identify damage from symptoms (API 571 + ASME PCC-3)

The reference card every refinery materials engineer keeps printed. Search by symptom, drill into root cause + recommended NDT + mitigation, jump to the quantitative tool when you need numbers.

Pitting corrosion

Corrosion · API 571 §4.3.1
Symptoms / signs
  • Discrete deep cavities, often hemispherical
  • Often hidden under deposit
  • Cl⁻ stains around pit mouth
  • Through-wall in days under right conditions
Drivers / conditions
  • Chlorides > 50 ppm
  • Stagnant flow / under-deposit
  • pH 4-7 (peak)
  • Aerated water
Susceptible alloys
  • 304L (PREN ~18) — fails under any Cl
  • 316L (PREN ~25)
  • CS (general)
  • Aluminum (Cl pitting)
Recommended NDT
  • Visual + magnification
  • UT thickness scan
  • PT (penetrant)
  • Pit-depth gauge
Mitigation / control
  • Spec ≥ duplex 22Cr (PREN 35) for sea water
  • Cathodic protection
  • Velocity > 1 m/s avoids stagnation
  • Inhibitor + pH control
quantitative tool
Pitting potential E_p →
Sources: API 571 (damage mechanisms in refining + petrochemical), ASME PCC-3 (inspection planning), Roberge "Handbook of Corrosion Engineering" Ch. 7-10.