Purpose - The purpose of this paper is to evaluate the protective ability of mixtures of aniline and phenol as corrosion inhibitors for N80 steel in 15 per cent hydrochloric acid, which may find application as corrosion inhibitors in acidization jobs in the petroleum industry. Owing to scale plugging at well bore there will be a decline in the crude production and acidization operation has to be carried out in the oil wells, normally by using 15 per cent hydrochloric acid to remove the scale plugging and enhance crude production. If the acid alone is poured in the oil wells through tubular and casing, corrosion of the metal (N80 steel) structures takes place for which an inhibitor is also is used along with the acid. Design/methodology/approach - Different concentration ratios of the inhibitor mixtures of aniline and phenol were added to the test solution (15 per cent HCl) and corrosion inhibition of N80 steel in hydrochloric acid medium containing the inhibitor additives was tested by weight loss and potentiodynamic polarization measurements. Influence of temperature (ambient temperature to 333 K) and exposure period (6-24 h) on the inhibition behaviour was also studied. Corrosion products on the metal surface were analyzed by fourier transform infrared (FTIR) and a possible mechanism of inhibition by the compounds is suggested. Findings - Provides information about the protective ability of inhibitor mixtures containing aniline and phenol against corrosion of N80 casing steel in 15 per cent HCl medium. The results in the present study have shown synergistic effect of all the formulations tested. The formulation of the mixture containing 0.1 percent AL with 0.7 percent PH has shown a maximum efficiency (75 percent at ambient temperature) among other tested combinations in the acid medium. The inhibition efficiency exhibited by the inhibitor mixture (0.1 percent AL with 0.7 percent PH) in 15 percent HCl medium at 333 K and after 24 h - test was found to be 43 and 31 per cent, respectively. The inhibitors, in appropriate combinations may find some usefulness at still higher temperatures. Electrochemical measurements indicate that the additives are active towards both sides, i.e. cathodic and anodic. FTIR results of the inhibition product film (formed on the metal surface after the corrosion test) reveal the presence of the inhibitor molecules in the surface film on the metal. Aniline and phenol molecules of the inhibitor mixture undergo condensation after their addition to the acid solution and may result in formation of protective surface film on the metal consisting of diphenylamine (as also revealed by FTIR spectroscopy) which may also contribute to the corrosion inhibition apart from the inhibition offered by aniline and phenol separately. Research limitations/implications - Normal temperatures of oil wells will be about 363 K. The results presented in this paper refer to temperatures up to 333 K, which perhaps limits its usefulness in actual field conditions. However, further research work to test the inhibition potentiality of the compounds at higher temperatures (363 K and above) is in progress, and will be communicated at a later stage. Practical implications - The tested inhibitor mixtures containing aniline and phenol exhibited synergistic effect and a significant inhibition (75 per cent) at ambient temperature that also shows good inhibitive properties after longer exposure period (24 h) and higher temperature (333 K). Appropriate formulations of the compounds may also be effective at still higher temperatures and that may be worked out for possible application in oil wells as corrosion inhibitors for acidization job. Originality/value - This paper offers preliminary laboratory results of some inhibitor formulations on corrosion prevention of N80 steel casing and tubular in hydrochloric acid that may be of practical help to petroleum engineers for carrying out acidization jobs in oil wells after further investigations of the compounds at higher temperatures and actual field conditions.
