High Temperature Hydrogen Attack (HTHA) is a degradation mechanism that affects steels exposed to hydrogen at high temperatures and pressures, leading to cracking and failure, particularly in welds and stressed areas. HTHA occurs when hydrogen atoms react with carbon in the steel, forming methane gas that accumulates and weakens the material. This is a serious concern in industries like petroleum refining, petrochemical production, and chemical facilities where hydrogen is used. To prevent HTHA, engineers must carefully select materials based on operating conditions and consult resources like the Nelson Curves, which provide guidance on safe material selection. Detecting and managing HTHA requires careful monitoring and inspection, as it can be a subtle and complex phenomenon.