Study On The Water-Soluble Corrosion Inhibitor Used In H₂S/CO₂ System

A large number of water, hydrogen sulfide, carbon dioxide and other corrosive gases contribute to corrosion in oil and gas well, tubing, crude oil gathering and transporting systems to form H2S-CO2-H2O corrosion system. The injection of corrosion inhibitor is a cost-effective method of control corrosion of carbon steel. While the studies of corrosion inhibitors used in high content of H2S/CO2 system are few and the use of oil-soluble corrosion inhibitors are largely restricted in oil and gas fields with high water content. So in this paper, two water-soluble imidazoline corrosion inhibitors which exhibit excellent inhibition efficiency in high content of H2S/CO2 system were developed.In this paper, seven pyridine corrosion inhibitors and fifteen imidazoline quaternary-ammonium-salt were synthesized. Under the static condition, the corrosion rates of L360 steel were less than 0.076 mm·a-1 in H2S/CO2 system with methyl pyridine corrosion inhibitors. Their inhibition efficiency was 4-PB-AE> 2-PB-AE> 3-PB-AE> 0-PB-AE. When the length of carbon chain of hydrophobic group was 10,12,14,16,18, the inhibition efficiency was decreased with the increasing of the length of carbon chain of hydrophobic group. Two water-soluble imidazoline corrosion inhibitors NIMC(A) and Lx-2-IMC showed good inhibition effect. Their inhibition performance were equivalent to or better than the foreign inhibitor 1204. In oil refinery system, these two corrosion inhibitors showed antagonistic effects on neutralizer. Under the gas-liquid two phase conditions, these two corrosion inhibitors and methoxy propyl amine had significant synergistic effects.The mechanism of corrosion inhibitors were studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that the pyridine and imidazoline corrosion inhibitors in H2S/CO2 corrosion system present excellent anti-corrosion performance, the corrosion potential of L360 becomes more positive and the corrosion electricity density decreased, which prove that these corrosion inhibitors could be considered as mixed type inhibitors. Scanning electron microscope showed that inhibitors can adsorb on the surface of metal to form a dense corrosion protective film which mitigated the corrosion of metals.