<p>The investigations of the effects of intrinsic thermotransport and weld cooling rate on the mass transport of hydrogen in carbon steel welds during deposition and desorption were extensions of the author’s previous study from 2021. Intrinsic thermotransport arises from different jump frequencies of hydrogen atoms on neighboring atomic planes along a temperature gradient. The major effect of intrinsic thermotransport in rapidly cooled welds is a large accumulation of hydrogen in the heat affected zone (HAZ) during deposition that exceeds that for non-thermotransport in the previous study. Changes in cooling rate significantly affect hydrogen concentration profiles of the as-completed welds due to changes in cooling time, temperature gradient variation rate, and type of microstructure formed in the HAZ. Depending on the cooling rate, the final microstructure of the HAZ was assumed to be 100 pct martensite, one of three different mixtures of ferrite-pearlite and martensite, or 100 pct ferrite-pearlite. The results of the intrinsic thermotransport and weld cooling rate studies together with the results of the previous study were used to design a critical experiment for gaining evidence concerning the role of thermotransport in the mass transport of hydrogen during weld deposition. The results of simulations per the designed critical experiment predict the experiment would likely gain evidence identifying the role of thermotransport.</p>