API 571 Acidic Process Stream Corrosion 3

Question 1

Microbiologically influenced corrosion (MIC) in hydrocarbon piping systems is most commonly caused by which type of microorganism?

Accepted Answer

Sulfate-reducing bacteria (SRB)

Answer

Aerobic iron-oxidizing bacteria

Answer

Nitrifying bacteria

Answer

Acid-producing fungi

Question 2

What is the characteristic visual evidence of active MIC attack found during internal inspection of carbon steel piping?

Accepted Answer

Tubercles with underdeposit pitting and black sulfide deposits

Answer

Uniform wall thinning with smooth surface

Answer

Orange iron oxide streaks along flow direction

Answer

Laminar cracking parallel to the pipe surface

Question 3

Which temperature range is considered the primary zone of concern for Corrosion Under Insulation (CUI) on carbon steel equipment per API 583?

Accepted Answer

25°F to 250°F (–4°C to 121°C)

Answer

–50°F to 25°F (–46°C to –4°C)

Answer

250°F to 400°F (121°C to 204°C)

Answer

400°F to 600°F (204°C to 316°C)

Question 4

Austenitic stainless steel equipment under insulation (CUI) is primarily vulnerable to which form of degradation?

Accepted Answer

Chloride stress corrosion cracking and pitting

Answer

Uniform thinning from oxygen depolarization

Answer

Intergranular corrosion from carbide precipitation

Answer

Dealloying of chromium from the austenite matrix

Question 5

Which insulation type is generally considered most problematic for CUI due to its high water retention capacity and potential to leach chlorides?

Accepted Answer

Calcium silicate insulation

Answer

Aerogel blanket insulation

Answer

Cellular glass insulation

Answer

Polyisocyanurate foam insulation

Question 6

In galvanic corrosion, what area ratio condition produces the most severe attack on the anodic (less noble) metal?

Accepted Answer

Small anode area coupled to a large cathode area

Answer

Large anode area coupled to a small cathode area

Answer

Equal anode and cathode areas

Answer

Small anode and small cathode areas of equal potential

Question 7

Which metal coupling would produce the MOST severe galvanic corrosion on the active member in a seawater environment?

Accepted Answer

Carbon steel coupled to copper

Answer

Cast iron coupled to carbon steel

Answer

Zinc coupled to aluminum

Answer

Aluminum coupled to magnesium