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HTHA differs fundamentally from hydrogen embrittlement. Whereas hydrogen embrittlement is reversible and occurs at ambient temperatures, HTHA is permanent, temperature-dependent, and involves chemical reactions between dissolved hydrogen and internal carbides.

High-Temperature Hydrogen Attack (HTHA) was first identified in the 1940s and 1950s in refinery hydroprocessing units. The term “HTRI crack” emerged from early collaborative research at the Heat Transfer Research Institute (HTRI) in California, where investigators documented intergranular cracking in carbon steel heat exchangers exposed to hydrogen at 400–500°C. However, “HTRI crack” is a misnomer; the correct metallurgical phenomenon is HTHA, and the term is now discouraged except in historical reference. htri crack