(Hydrogen embrittlement of carbon steels is most likely to occur at temperatures of:)

Comprehensive and Detailed Explanation From Exact Extract:

According to API RP 571, hydrogen embrittlement (HE) of carbon steels is a low-temperature damage mechanism. It occurs when atomic hydrogen enters the steel lattice, reducing ductility and toughness and potentially causing cracking or delayed failure.

API RP 571 clearly differentiates HE from high-temperature hydrogen damage mechanisms (such as HTHA). Hydrogen embrittlement is most severe at ambient to moderately elevated temperatures, typically below about 200 °F (93 °C), where hydrogen mobility and trapping promote embrittlement.

At higher temperatures, hydrogen tends to diffuse out of the steel and embrittlement effects diminish.

Referenced Documents (Study Basis):

API RP 571 – Section on Hydrogen Embrittlement

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