Design/methodology/approach - Fourier-transform infrared spectrometry and electron impact mass spectrometry were used to characterize the chemical structures and compositions if five NAs. The corrosivities of the NAs were assessed by stagnant NA corrosion (NAC) tests. An attempt was made to identify any correlation between the chemical composition of the NAs and their corrosiveness.

Findings - The acidic species in all five NA samples were saturated aliphatic and naphthenic acids and the amount of aromatic and unsaturated acids was negligible. A relationship between the carboxylic acid distribution and the molecular weight was obtained. Most of the carboxylic acids in five NAs contained 0-3 ring structures. NAs with lower molecular weight and fewer ring structures usually were more corrosive.

Originality/value - The findings have important implications for assessing the corrosivity of acidic crude oils from various resources.