PCS PCS Corrosion Science and Prevention 2 — Questions and Answers
Question 1: According to NACE/AMPP standards, what maximum soluble salt level (expressed as equivalent NaCl) is generally acceptable on steel before immersion-service coating application?
- 50 µg/cm²
- 20 µg/cm² (Correct answer)
- 100 µg/cm²
- 5 µg/cm²
Correct answer: 20 µg/cm²
Industry practice and many specifications limit soluble salt contamination to 20 µg/cm² equivalent NaCl or less on steel destined for immersion or severe service coating.
Question 2: What type of corrosion results from cyclic loading of a metal structure in a corrosive environment, leading to crack initiation at lower stress levels than in air?
- Erosion corrosion
- Corrosion fatigue (Correct answer)
- Exfoliation corrosion
- Filiform corrosion
Correct answer: Corrosion fatigue
Corrosion fatigue is the synergistic effect of cyclic mechanical stress combined with a corrosive environment, causing crack initiation and propagation at stresses well below the normal fatigue limit.
Question 3: In cathodic protection (CP) systems, what is the minimum protective potential (Cu/CuSO4 reference) for buried or submerged steel as specified by NACE SP0169?
- -0.50 V
- -0.85 V (Correct answer)
- -1.10 V
- -0.65 V
Correct answer: -0.85 V
NACE SP0169 specifies that a minimum protective potential of -0.85 V measured with a Cu/CuSO4 reference electrode indicates cathodic protection of buried or submerged steel.
Question 4: Which atmospheric category in ISO 9223 represents the most severe corrosion environment (offshore/tropical industrial)?
- C1
- C3
- C5
- CX (Correct answer)
Correct answer: CX
ISO 9223 category CX (formerly C5-M extreme marine) designates the most corrosive atmospheric environment, typically found at offshore platforms or tropical industrial locations.
Question 5: What is the corrosion mechanism known as 'undercutting' in relation to coated steel?
- Coating applying too thin at cut edges
- Corrosion spreading laterally beneath the coating from a defect (Correct answer)
- Mechanical damage from abrasion underneath
- Osmotic blistering from below
Correct answer: Corrosion spreading laterally beneath the coating from a defect
Undercutting (or filiform creep) is lateral corrosion migration beneath the coating film from a defect such as a scratch or holiday, progressively delaminating the coating from the substrate.
Question 6: Which standardized test method subjects coated steel panels to a continuous salt fog to evaluate coating corrosion resistance?
- ASTM B117 (Correct answer)
- ASTM D4541
- ASTM D3363
- ASTM D2247
Correct answer: ASTM B117
ASTM B117 is the Standard Practice for Operating Salt Spray (Fog) Apparatus, widely used to evaluate coating corrosion resistance under accelerated salt fog exposure.
PCS PCS Corrosion Science and Prevention 2
According to NACE/AMPP standards, what maximum soluble salt level (expressed as equivalent NaCl) is generally acceptable on steel before immersion-service coating application?