Changfeng Chen

Effect of environmental factors on corrosion behaviour of L360QCS pipeline steel in H2S/CO2 environments

Abstract The present research investigated the effect of H2S/CO2 partial pressure, sulphur deposition and corrosion inhibitor on the corrosion behaviour of L360QCS pipeline steel in H2S/CO2 environments by immersion tests, scanning electron microscope analysis and electrochemical measurements. The results show that the corrosion rate (CR) of L360QCS steel decreased first and then increased with increasing p H2S and p CO2.The CR is closely associated with the protectiveness of corrosion film. Sulphur deposition can cause an acceleration of the corrosion of steel in H2S/CO2 environments. Furthermore, the CR increased obviously with increasing p H2S and p CO2 in sulphur deposition environments. After addition of continuous corrosion inhibitor, the CR decreased significantly in H2S/CO2 environments. Prefilming corrosion inhibitor could enhance the inhibition effect in the presence of continuous corrosion inhibitor.

Study on Synergistic Mechanism of Inhibitor Mixture Based on Electron Transfer Behavior

Mixing is an important method to improve the performance of surfactants due to their synergistic effect. The changes in bonding interaction and adsorption structure of IM and OP molecules before and after co-adsorbed on Fe(001) surface is calculated by DFTB+ method. It is found that mixture enable the inhibitor molecules with higher EHOMO donate more electrons while the inhibitor molecules with lower ELUMO accept more electrons, which strengthens the bonding interaction of both inhibitor agent and inhibitor additive with metal surface. Meanwhile, water molecules in the compact layer of double electric layer are repulsed and the charge transfer resistance during the corrosion process increases. Accordingly, the correlation between the frontier orbital (EHOMO and ELUMO of inhibitor molecules and the Fermi level of metal) and inhibition efficiency is determined. Finally, we propose a frontier orbital matching principle for the synergistic effect of inhibitors, which is verified by electrochemical experiments. This frontier orbital matching principle provides an effective quantum chemistry calculation method for the optimal selection of inhibitor mixture.

Synergistic effect of mixing cationic and nonionic surfactants on corrosion inhibition of mild steel in HCl: Experimental and theoretical investigations

We studied the inhibition performances of IMB (imidazoline quaternary salt (IM) and benzotriazole (BTAH)) and IMO (IM and octyl phenol ethoxylates (OP)) mixtures as inhibitors of L245 steel placed in 10 vol% HCl solution at 298 K using experimental methods and theoretical calculations. We found that the mixtures adsorb on the steel by an endothermic spontaneous process, and the adsorption model follows Langmuir isotherm. The mixtures exhibit good synergistic inhibition effect, and the inhibition efficiency enhanced in turn (IMB < IMO). The relationship between synergistic effect of organic inhibitors and their energetic position of molecular frontier orbitals was discussed.

Dissolution of interdendritic σ phase in cast Ni–Fe–Cr alloy

Abstract Various sizes, fractions and morphologies of interdendritic σ phase in the as cast N08028 alloy due to different solidification conditions are characterised. Dissolution behaviours of the secondary phase in both the as cast and the forged alloys are investigated during heat treatment at 1100, 1150 and 1200°C. A recently developed analytical model, subjected to necessary modification, is applied to describe the dissolution process of σ phase in the alloys with and without prior hot deformation. A recipe derived from transformed fraction is applied to evaluate the effective activation energy for dissolution. It has been found that, the prior hot deformation accelerates the dissolution process, which can be attributed to the decreased particle size and the reduced effective activation energy.

Roles of carbon dioxide and steam on the hydrogen embrittlement of 3Cr tube steel in synthetic natural gas environment

ABSTRACT The hydrogen embrittlement behaviour of 3Cr has been investigated under mixed H2 with CO2 at different strain rates, hydrogen partial pressures, and in the presence/absence of steam. The slow strain rate test results show that the HE susceptibility of 3Cr increased with increasing hydrogen partial pressure, and the plasticity of 3Cr obviously decreased in the presence of steam. The effect of strain rate was negligible in H2/CO2 environment but showed a significant difference in H2/CO2/steam environment. The fracture was a ductile fracture mode in N2 environment and a brittle fracture mode in H2/CO2/steam environment. The reason for the severe plasticity loss of 3Cr in H2/CO2/steam environment was probably that the steam has a preferential adsorption onto the 3Cr surface compared with H2 and CO2. Consequences in CO2 combined with H2O to form H2CO3, which accelerated the anodic dissolution of 3Cr, and the physical adsorption of H2 on steel was enhanced.