Nickel‐based alloys have an excellent corrosion resistance in high‐temperature sulfuric acid solutions. Some data on the effects of ferric and ferrous iron on the uniform corrosion rate are to be found in the literature. Based on the results of a series of immersion tests, a quantitative model is proposed for the uniform corrosion rate of a NiCrMo alloy at 98 °C as a function of sulfuric acid concentration, total iron content, and the ferrous to ferric ratio. The beneficial effect of iron, especially that of ferric iron, was demonstrated. The sulfuric acid concentration had only a weak influence on the uniform corrosion rate in the iron‐containing solutions. Scanning electron microscopy was applied to characterize selected samples after immersion testing. Depending on the sulfuric acid concentration, a completely uniform attack or partly localized attack was seen to lead to a similar mass loss. It is suggested that the oxide inclusions present in the microstructure were the most susceptible features to corrosion, leading to partly localized attack.