API RP 571, under "Caustic Corrosion" (also referred to as Caustic Stress Corrosion Cracking or Caustic Cracking), notes that this form of damage is:
“Most commonly associated with the injection points of caustic (e.g., NaOH) in crude units, particularly upstream of desalter vessels and heat exchanger circuits.”
“This damage occurs due to the combination of caustic environment and tensile stress, especially in carbon steel and low alloy steels.”
“Stress relief heat treatment of welds can mitigate susceptibility.”
(Reference: API RP 571, 3rd Edition, Section 4.2.2.3)
Thus, among the options, caustic injections in crude units are the most typical area of concern, making option C the correct answer.
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