High Temperature Hydrogen Attack (HTHA) is the progressive degradation of components made from carbon and low-alloy steels exposed to hydrogen at elevated temperatures for extended periods of time. Hydrogen atoms diffuse into the steel and react with carbon to form methane that builds up inside submicron intergranular cavities on the grain boundaries. These methane molecules are too large to diffuse back out, and so the resulting methane pressure builds up inside these cavities, inducing extra stress in the surrounding material that causes these cavities to grow and ultimately coalesce with other cavities to form cracks on the grain boundaries. This grain boundary damage will ultimately lead to failure of the component if left unchecked, usually through fusion line cracking at welds. HTHA is a serious problem in the petrochemical and refining industries and has led to a number of high-profile failures with fatalities and catastrophic environmental and financial consequences. Predicting, detecting, and preventing HTHA is thus of great importance and is the focus of the present work.