Nickel base alloy 718 is a precipitation hardened material. Due to its properties alloy 718 is one of the most favorite materials used in oil and gas industry. Mechanical and corrosion behavior of the material depend strongly on its microstructure. One of the microstructural elements considered to have a detrimental effect on the material resistance to stress corrosion cracking is the delta-phase precipitation. The mechanism of that phenomenon is yet not fully understood.Therefore the aim of the present work is to investigate the influence of delta-phase precipitates on the pitting performance of alloy 718. Electrochemical measurements were performed in various chlorides containing solutions at different temperatures. Two materials with different heat-treatment were used for this study. Those material variations were aged at 760°C and 870°C for 8 hours respectively to obtain microstructures with different delta phase content. The corrosion behavior was evaluated by measuring the mass loss and analyzing the current potential curve. Special attention was also paid to the passivation effect. Deviations in corrosion performance of different microstructures were observed in all of the experiments. Specimens with an increased content of delta-phase precipitates were shown to be more active in the corrosion process. Among all of the studied parameters temperature was found to have the most significant effect on the pitting corrosion behavior. The electrochemical measurements were performed on samples which were charged with hydrogen for 24 hours before the actual experiment. It is assumed that similar to austenitic stainless steel 304 or 310 [1] solved hydrogen decreases the passivation of nickel base alloy 718.Keywords: nickel-base alloy 718 pitting corrosion hydrogen delta-phaseReference: [1] Yang Qi (2000). Effect of Hydrogen on Passivity and Corrosion Related Behavior of Stainless Steels. Ph. D. Thesis. Edmonton Alberta: Canada.