S. L. Jiang

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.

Corrosive Wear Behaviors of Carbon Steels in Oil-Water Fluid

Carbon steel (CS) is the most common material used in oil production. Based on surface wetting state, the corrosive wear behavior of CS in oil-water fluid was investigated. The surface wetting state of the metal in oil-water fluids with different water cut and flow velocity was measured using a specially constructed device. Wear loss, corrosion loss, and corrosive wear loss of the CS samples in different oil-water fluids were measured by a reciprocating corrosive wear tester. The damage morphology of the CS samples was observed using scanning electron microscopy (SEM) and the element distribution on the surface was detected by energy-dispersive X-ray spectroscopy (EDS). The results indicated that the surface water wetting rate of the metal increased with water cut and decreased with flow velocity in the oil-water fluid. Wear, corrosion, and corrosive wear behavior of the CS was related to the surface wetting film and surface reaction film. In this test range, the synergetic action is negative and chlorine embrittlement occurs in the fluid with high water cut and low velocity. The damage mechanism of the CS was abrasive wear with selective corrosion.

Tribocorrosion Behavior of 304 Stainless Steel in 0.5 mol/L Sulfuric Acid

The tribocorrosion behavior of 304 stainless steel was studied through comparing the damage behavior of 304 stainless steel in dilute sulfuric acid to that in distilled water by a reciprocating tribotester. The re-passivation behavior, the surface and sectional morphological features, as well as the change of microhardness of samples were studied, and the tribocorrosion mechanism was also discussed. The experimental results reveal that the damage of stainless steel in dilute sulfuric acid was caused by the steel’s mechanical removal and electrochemical dissolution. The wear mechanism of stainless steel is abrasive wear, which mainly consists of micro-cutting and peeling. The synergetic action between corrosion and wear is notable. The corrosive environment leads to the embrittlement of the surface layer, and the wear destroys the passivation film and causes galvanic corrosion.