Corrosion Inhibition of N80 Steel in 10% Citric Acid +1% Hf Solution

Purpose: This paper aims to explore the corrosion law of oil well acidizing fluid containing 10% citric acid +1% HF on N80 steel, and to seek effective corrosion inhibitor. Design/methodology/approach: The corrosion rate of N80 steel in acid was calculated by weight loss method and electrochemical test. The optimum ratio of oleic acid imidazoline (OAI), thiourea (TU) and cinnamaldehyde (CA) composite corrosion inhibitor was determined by orthogonal test. The surface corrosion morphology of N80 steel was observed by scanning electron microscope (SEM). The corrosion products were analyzed by X-ray diffractometer (XRD) and energy dispersive spectrometer (EDS). Findings: The corrosion rate of N80 steel is greatly affected by the temperature of citric acid, while the corrosion rate of N80 steel is slightly affected by temperature of HF. At 313 K, the compound acid produced corrosion inhibition effect, which gradually disappeared with the increase of temperature. At 368K, the corrosion rate of the compound acid reached the same as the sum of the corrosion rate of the two alone. OAI, TU and CA have synergistic effect on corrosion inhibition, and the optimal ratio is 0.4%:0.1%:0.4%. At 353 K, the corrosion inhibition rate of N80 steel can reach 99.04%. The composite inhibitor acts as a mixed type inhibitor and does not change the corrosion mechanism of N80 steel. The composite corrosion inhibitor prevents acid from corroding the steel sheet by forming a protective film on the surface of N80 steel. Originality/value: The corrosion inhibition characteristics of N80 steel in the system of 10% citric acid +1% HF and the corrosion inhibition effect of OAI, TU and CA composite corrosion inhibitor were studied. The results can provide a theoretical basis for the application of N80 steel in the low corrosion acid system in the process of oil well acidizing.