This study investigates the effect of gas flow rate on the corrosion rate of Inconel 617 alloy under two controlled atmospheres: He + 100 ppm O2 and He + 100 ppm CH4. Corrosion experiments were conducted at 950 °C for 20 h, with gas flow rates set at 50, 100, 200, and 300 mL/min. The corrosion rates were evaluated based on mass change measurements and gas-phase compositional analysis. For oxygen-containing atmospheres, the results revealed that alloy weight gain increased with flow rate, reaching saturation at 100 mL/min. In contrast, methane exhibited a different behavior: the alloy mass initially decreased with increasing flow rate but reversed and increased at 300 mL/min. This discrepancy arises from the distinct reaction mechanisms of the gases. Oxygen drives a contact oxidation reaction, where direct contact with the alloy surface is necessary for oxidation. Higher flow rates enhance oxidation until saturation, beyond which flow rate has no further impact. Conversely, methane induces carburization through carbon deposition, governed by the interplay between methane decomposition rate and carbon deposition probability, leading to non-linear mass change trends. In summary, when choosing the minimum flow rate of helium containing O2, it should be ensured that the oxygen consumption per unit time is at least 40% of the initial concentration. When choosing the minimum helium gas flow rate of helium containing CH4, it is sufficient to ensure that methane does not become depleted within a given time period.