Y. G. Zheng

Resistance of Mo-bearing stainless steels and Mo-bearing stainless-steel coating to naphthenic acid corrosion and erosion-corrosion

Abstract Naphthenic acid corrosion (NAC) and erosion–corrosion (NAEC) behavior of Mo-bearing (0–7.0 wt.%) stainless steels have been investigated in laboratory to evaluate the essential role of Mo on their NAC and NAEC resistance. The NAC and NAEC resistance of a high-velocity-oxygen-fuel (HVOF) thermal sprayed Mo-bearing stainless-steel coating was also investigated in both laboratory and an oil refinery. It was found that increasing the Mo content remarkably enhanced the NAC and NAEC resistance of stainless steels. The Mo-rich areas or phases in the steels played an importance role in resisting the NAEC. The HVOF coating showed excellent NAC and NAEC resistance in laboratory tests. The 700-day field test in an oil refinery revealed that the coating can effectively prevent the carbon-steel substrate from erosion–corrosion during long-term exposure in oil-refining environment. The corresponding NAC and NAEC mechanisms of the stainless steels and the beneficial role of Mo were discussed by taking account of inherent susceptibility of metal elements to corrosion, possible effects of Mo on surface films, and Mo-induced change in microstructure and microhardness.

Effect of cavitation on corrosion behavior of 20SiMn low-alloy steel in 3% sodium chloride solution

The cavitation corrosion behavior of 20SiMn low-alloy steel in both distilled water and 3% sodium chloride (NaCl) solution was investigated using a magnetostrictive-induced cavitation facility. The micrographs of damaged surfaces were observed with a scanning electron microscope (SEM). The role of corro- sion was analyzed using polarization curves, electrochemical impedance spectroscopy (EIS), linear polarization resistance, and the corrosion potential with or without cavitation. Fur- thermore, the effect of cavitation on corrosion behavior of 20SiMn steel was compared to that of oxygen bubbling. The results showed that a fraction (0.05) of the damage arose from electrochemical corrosion and a fraction (0.59) arose from corrosion-induced erosion. Cavitation shifted the corro- sion potential in the positive direction and strongly enhanced the cathodic current density in the polarization curves. Cavi- tation also reduced the magnitude of impedance. The mor- phological examination revealed that the ferrite area and grain and ferrite-pearlite boundaries were preferential sites for cavitation attack as a result of the low hardness of ferrite. The mass loss came from the detachment of small pieces in the ferrite area in the early stage and from the removal of massive chunks by the propagation and connection of cracks in the following test period.

Corrosion inhibitor performances for carbon dioxide corrosion of N80 steel under static and flowing conditions

Abstract Inhibition for carbon dioxide (CO2) corrosion of N80 steel by quaternary alkynoxymethyl amine (IMC-80-Q) in 3% sodium chloride (NaCl) solution was investigated under static and flowing conditions using a modified rotating disk apparatus. The effects of flow velocity and concentration of inhibitor on inhibition performance were performed using a weight-loss test, scanning electron microscope (SEM) observation, and electrochemical techniques including electrochemical impedance spectroscopy (EIS), linear polarization resistance, and polarization curves. The results showed that flow velocity had strong effects on the inhibitor performances. Inhibition efficiency (η) and polarization resistance (Rp) exhibited the peak-value phenomenon at an inhibitor concentration of 150 mg/L when flow velocity was less than 5 m/s, in contrast with the 300 mg/L when flow velocity was higher than 5 m/s. Critical flow velocity in the uninhibited solution was between 4 m/s and 5 m/s.

Synergistic effect of ultrasonic cavitation erosion and corrosion of WC-CoCr and FeCrSiBMn coatings prepared by HVOF spraying

The high-velocity oxygen-fuel (HVOF) spraying process was used to fabricate conventional WC-10Co-4Cr coatings and FeCrSiBMn amorphous/nanocrystalline coatings. The synergistic effect of cavitation erosion and corrosion of both coatings was investigated. The results showed that the WC-10Co-4Cr coating had better cavitation erosion-corrosion resistance than the FeCrSiBMn coating in 3.5 wt.% NaCl solution. After eroded for 30 h, the volume loss rate of the WC-10Co-4Cr coating was about 2/5 that of the FeCrSiBMn coating. In the total cumulative volume loss rate under cavitation erosion-corrosion condition, the pure cavitation erosion played a key role for both coatings, and the total contribution of pure corrosion and erosion-induced corrosion of the WC-10Co-4Cr coating was larger than that of the FeCrSiBMn coating. Mechanical effect was the main factor for cavitation erosion-corrosion behavior of both coatings.

Ultrasonic cavitation erosion of high-velocity oxygen-fuel (HVOF) sprayed near-nanostructured WC-10Co-4Cr coating in NaCl solution

The high-velocity oxygen-fuel (HVOF) spraying process was used to prepare near-nanostructured WC-10Co-4Cr coating. The cavitation erosion behavior and mechanism of the coating in 3.5 wt.% NaCl solution were analyzed in detail. The results showed that the amorphous phase and WC grain were present in the coating. The cavitation erosion resistance of the coating was about 1.27 times that of the stainless steel 1Cr18Ni9Ti under the same testing conditions. The effects of erosion time on the microstructural evolution were discussed. It was revealed that cracks initiated at the edge of pre-existing pores and propagated along the carbide-binder interface, leading to the pull-out of carbide particle and the formation of pits and craters on the surface. The main failure mechanism of the coating was erosion of the binder phases, brittle detachment of hard phases and formation of pitting corrosion products.

Characterization of the Corrosion Product Films Formed on the As-Cast and Friction-Stir Processed Ni-Al Bronze in a 3.5 wt% NaCl Solution

An as-cast Ni-Al bronze (NAB) was subjected to friction-stir processing (FSP). The friction-stir processed NAB (FSPed NAB) exhibited better corrosion resistance in a 3.5 wt% sodium chloride solution. The corrosion product films formed on the as-cast and FSPed NAB were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and electron probe micro-analysis (EPMA). Uncorroded phases were retained in the films. The interfaces between these phases and their surrounding corrosion products allowed the chloride ions in and reduced the film protectiveness. For the as-cast NAB, the un-corroded phases were large in size or continuous in structure, resulting in continuous interfaces. Therefore, the film on the as-cast NAB exhibited relatively inferior protectiveness. The films on the as-cast and FSPed NAB were similar in composition with mainly copper chloride hydroxide Cu2(OH)3Cl in the outer layer, and Al2O3 and Cu2O with the incorporation of Fe and Ni in the inner layer. Stability of the fi...

Comparison of Corrosion and Cavitation Erosion Behaviors Between the As-Cast and Friction-Stir- Processed Nickel Aluminum Bronze

An as-cast nickel aluminum bronze (NAB) was treated by friction-stir processing (FSP). Immersion test and electrochemical measurements under cavitation erosion condition were carried out to investigate the long-term and short-term corrosion behaviors of the as-cast and as-FSP NAB. Cavitation erosion tests were conducted in both distilled water and 3.5 wt% sodium chloride (NaCl) solution. The immersion test indicated that the electrochemical impedance of the as-FSP NAB was much higher, while there was little difference between them in the short-term test. The cumulative mass loss of the as-cast NAB was about 1.5 and 2 times as large as that of the as-FSP in distilled water and 3.5 wt% NaCl, respectively. The higher corrosion resistance of the as-FSP was a result of the refined and homogenized microstructure. Improved mechanical properties and fewer galvanic corrosion sites are attributed to the higher cavitation erosion resistance of the as-FSP NAB.

Corrosion and Cavitation Erosion Behaviors of Friction Stir Processed Ni-Al Bronze: Effect of Processing Parameters and Position in the Stirred Zone

As-cast Ni-Al bronze (NAB) was subjected to friction stir processing (FSP). Different processing parameters including rotating rate, traverse speed, and processing passes were selected to investiga...

Effect of Heat Treatment on Erosion-Corrosion Behavior of Electroless Ni-P Coatings in Saline Water

To prevent premature failure of heat exchanger tubes enduring rapid seawater flow, amorphous electroless Ni-P coatings were prepared on copper-nickel alloy (CuNi 90/10) substrates. The influence of post-deposition vacuum heat treatment at different annealing temperatures (190, 300, 400, 500, and 600°C) on the erosion-corrosion resistance of the annealed coatings was examined by X-ray diffraction, scanning electron microscopy, potentiodynamic polarization, and electrochemical impedance spectroscopy. It was found that precipitation of a crystalline phase took place in the coating matrix at 400°C. The highest microhardness was achieved for coatings undergoing heat treatment at 400°C due to the formation of the stable Ni3P phase. Electrochemical results indicated that all the Ni-P coatings present passivity and better corrosion resistance than the uncoated CuNi 90/10 substrate. The Ni-P coating treated at 500°C demonstrated the best erosion-corrosion resistance, which represented the optimization of the balance between erosion and corrosion resistance.

Relationships between spray parameters, microstructures and ultrasonic cavitation erosion behavior of HVOF sprayed Fe-based amorphous/nanocrystalline coatings

Fe-based amorphous/nanocrystalline coatings were prepared on the AISI 321 steel substrate by the high-velocity oxygen-fuel (HVOF) thermal spraying technology. The effect of selected parameters (oxygen flow, kerosene flow and spray distance) on the cavitation erosion resistance (denoted as Rc) of the coating were investigated by using the Taguchi method. Statistical tools such as design of experiments (DOE), signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were used to meet the expected objective. It was concluded that the kerosene flow had greater influence on the Rc of the coating and followed by the spray distance and the oxygen flow, respectively. The optimum spray parameters (OSP) were 963L/min for the oxygen flow, 28L/h for the kerosene flow, and 330mm for the spray distance. The Rc of the coating increased with the increase of hardness or the decrease of porosity, and the hardness had a greater influence on Rc than the porosity. The Fe-based coating deposited under the OSP exhibited the best cavitation erosion resistance in distilled water. The cracks initiated at the edge of the pores and the interfaces between the un-melted or half-melted particles, and finally leaded to the delamination of the coating.