Corrosion Assessment Flashcards

When evaluating corrosion under insulation (CUI), which temperature range poses the HIGHEST risk for carbon steel?

Answer: 25°F to 250°F (-4°C to 121°C)

CUI on carbon steel is most active in the 25°F to 250°F range where moisture can accumulate and not fully evaporate.

A vessel exhibits uniform metal loss of 0.012 inches over a 2-year inspection interval. What is the calculated corrosion rate?

Answer: 0.006 in/yr

Corrosion rate = total loss divided by years = 0.012 divided by 2 = 0.006 in/yr.

Which type of corrosion is characterized by selective attack along grain boundaries of a metal?

Answer: Intergranular corrosion

Intergranular corrosion attacks the grain boundaries preferentially, often due to sensitization in stainless steels.

API 510 requires that remaining life calculations use which corrosion rate when both short-term and long-term rates are available?

Answer: The more conservative (higher) rate

API 510 specifies using the more conservative (higher) corrosion rate to ensure safe remaining life estimates.

What phenomenon occurs when two dissimilar metals are in electrical contact in a corrosive electrolyte?

Answer: Galvanic corrosion

Galvanic corrosion occurs when dissimilar metals are in electrical contact and immersed in an electrolyte, causing the more active metal to corrode preferentially.

During a pressure vessel inspection, localized thin spots are found. Per API 510, what minimum thickness concept is used to evaluate these areas?

Answer: Required minimum thickness (t_min)

API 510 compares actual measured thickness against the required minimum thickness (t_min) calculated from applicable design codes.

Which factor does NOT typically influence the rate of uniform corrosion in a pressure vessel?

Answer: Vessel wall color

Vessel wall color has no effect on corrosion rate; temperature, pH, and corrosive concentration are the primary influencing factors.