API RP 571 explains under Condensate Corrosion (CO# Corrosion):
"In condensate systems, carbon dioxide dissolves in the water forming carbonic acid, which leads to localized corrosion, including grooving and under-deposit attack, especially at low points like the bottom of horizontal piping."
"This is most commonly observed in steam condensate return lines, and the damage is localized due to stratification." This matches the scenario described, where internal grooving at the bottom of steam condensate piping is characteristic of CO#-induced corrosion. Hence, option A is correct.

From API RP 571 Section 5.1.2.1 and RP 941:
"High strength low alloy steels (HSLA) are more susceptible to hydrogen embrittlement, especially during cold work, forming, or welding. These materials, due to their higher tensile strengths, are more prone to cracking when exposed to hydrogen, particularly during fabrication or post-weld heat treatment operations." Therefore, Option A (High Strength Low Alloys) is the correct answer due to their known susceptibility during manufacturing and processing.

API RP 571 on Naphthenic Acid Corrosion (NAC):
"NAC results in thinning, especially in areas of high velocity and turbulence. Standard UT or radiographic inspection followed by UT thickness monitoring is typically used to detect wall loss."
"Advanced techniques like angle-beam or eddy current are not typically required." So, option A correctly reflects the most effective and widely used method.

API RP 571 describes under Caustic Corrosion:
"One of the significant contributing factors is caustic accumulation in low-flow or stagnant areas, especially in heat-traced lines or around steam injection points."
"Localized heating can concentrate caustic solutions, promoting corrosion even in carbon or stainless steels." Thus, option C (heat-traced equipment) is the correct and technically accurate choice.

API RP 571 - Polythionic Acid Stress Corrosion Cracking:
"Polythionic acid SCC may be mistaken for wet H#S damage because both involve cracking in austenitic stainless steels under certain conditions." Thus, option D is correct.