Nickel alloy 725 is a precipitation-hardened Ni–Cr–Mo–Nb superalloy widely deployed in subsea and hydrogen-containing service environments, where hydrogen embrittlement poses a critical safety risk. This thesis investigates how surface condition governs hydrogen uptake, subsurface hydrogen penetration, and mechanical degradation in Alloy 725 under controlled cathodic electrochemical charging conditions. Five surface states were examined: a 2000-grit SiC ground reference, an electrical discharge machined surface retaining its thermally modified recast layer, a shot-peened surface carrying a compressive residual stress field, a thin gold film deposited by DC magnetron sputtering, and an electrodeposited nickel coating applied from a Watts-type bath. All specimens were pre-charged for 24 hours in a glycerol–phosphoric acid electrolyte at 50 °C; a subset of ground specimens was additionally charged for 72 hours to establish the time–response relationship for hydrogen-induced ductility loss.