Lining Xu

Effect of welding process on the microstructure and properties of dissimilar weld joints between low alloy steel and duplex stainless steel

To obtain high-quality dissimilar weld joints, the processes of metal inert gas (MIG) welding and tungsten inert gas (TIG) welding for duplex stainless steel (DSS) and low alloy steel were compared in this paper. The microstructure and corrosion morphology of dissimilar weld joints were observed by scanning electron microscopy (SEM); the chemical compositions in different zones were detected by energy-dispersive spectroscopy (EDS); the mechanical properties were measured by microhardness test, tensile test, and impact test; the corrosion behavior was evaluated by polarization curves. Obvious concentration gradients of Ni and Cr exist between the fusion boundary and the type II boundary, where the hardness is much higher. The impact toughness of weld metal by MIG welding is higher than that by TIG welding. The corrosion current density of TIG weld metal is higher than that of MIG weld metal in a 3.5wt% NaCl solution. Galvanic corrosion happens between low alloy steel and weld metal, revealing the weakness of low alloy steel in industrial service. The quality of joints produced by MIG welding is better than that by TIG welding in mechanical performance and corrosion resistance. MIG welding with the filler metal ER2009 is the suitable welding process for dissimilar metals jointing between UNS S31803 duplex stainless steel and low alloy steel in practical application.

Electrochemical Impedance Spectroscopy Study of the Corrosion of 3Cr Pipeline Steel in Simulated CO 2 -Saturated Oilfield Formation Waters

The formation and the growth of the corrosion film that forms on 3Cr steel surface in CO2 environments were characterized and investigated by scanning electron microscopy, energy dispersive spectrometry, quadrant back scattering detector, x-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy (EIS). A model for the formation of the corrosion film is proposed in this paper. The data obtained using the proposed equivalent circuit, which is based on this model, exhibits close agreement with the experimental EIS results, indicating that the proposed film formation model is reliable.

Electrochemical impedance spectroscopy study on the corrosion of the weld zone of 3Cr steel welded joints in CO2 environments

The welded joints of 3Cr pipeline steel were fabricated with commercial welding wire using the gas tungsten arc welding (GTAW) technique. Potentiodynamic polarization curves, linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS) were used to investigate the corrosion resistance and the growth of a corrosion film on the weld zone (WZ). The changes in electrochemical characteristics of the film were obtained through fitting of the EIS data. The results showed that the average corrosion rate of the WZ in CO2 environments first increased, then fluctuated, and finally decreased gradually. The formation of the film on the WZ was divided into three stages: dynamic adsorption, incomplete-coverage layer formation, and integral layer formation.

Interaction effect between Cr(OH) 3 passive layer formation and inhibitor adsorption on 3Cr steel surface

Passive layer formation and inhibitor adsorption on the 3Cr steel surface in the absence of an interface inhibitor, i.e. benzamide, has been investigated. Above a threshold of roughly 600 mM, benzamide rapidly adsorbed onto the substrate surface and significantly inhibited the formation of the passive layer.

Compare the Corrosion of 3%Cr Steel With X65 Pipeline Steel in Subsea CO2 Top-of-Line Corrosion Environment

CO2 Top-of-Line Corrosion (TLC) of carbon steel pipelines is a serious problem for subsea wet gas pipelines. A series of experiments were carried out in the high-pressure high-temperature condensation autoclave, in order to simulate the corrosion environment of TLC. The purpose of this paper was to compare the corrosion resistance of 3%Cr steel with API X65 pipeline steel in CO2 TLC environment. The composition and morphology of the corrosion scale were characterized by energy dispersive X-ray spectroscopy and scanning electron microscopy analyses. The results indicate that 3%Cr pipeline steel shows relative good resistance to CO2 TLC, with slight pitting at static condition, however, X65 suffers severe mesa corrosion. The analysis of composition and morphology revealed that the amorphous corrosion scales was formed on the surface of 3%Cr steel. The localized corrosion of 3%Cr steel may be related to the uneven filling of Cr compound under static condition.Copyright

Corrosion Behavior of Novel Cr2MoNbTi Pipeline Steel in CO2 Environment

CO2 corrosion is frequently encountered in oil and gas industry. The search for new sources of oil and gas has pushed the operational activities to harsher environment and this requires new tubing and pipeline materials which can endure tough circumstances. Low alloy steel containing Chromium, which fills the gap between carbon steels and corrosion resistant alloys in terms of cost and corrosion resistance, has aroused significant interest from steel enterprises and scholars. At present, these studies mainly focus on 3%–5%Cr steel, and little study concerns the 2%Cr steel, which is more economic and weldable. In this paper, novel Cr2MoNbTi steel was developed and the microstructure and mechanical properties were studied. Corrosion behavior of the Cr2MoNbTi steel immersed in the CO2-containing solutions, which corresponded to the environment of bottom-of-line corrosion (BLC), was studied using high temperature-high pressure autoclave. In addition, dynamic high temperature-high pressure condensation autoclave was employed to simulate the top-of-line corrosion (TLC) environment and the corrosion behavior of the Cr2MoNbTi steel under wet gas environment was investigated. The composition and morphology of the corrosion scale were characterized by energy dispersive spectroscopy and scanning electron microscopy analyses. The results show that the Cr2MoNbTi steel exhibited uniform corrosion and presented good resistance to CO2 corrosion compared with X65 pipeline steel.Copyright