جستجوی مقالات مرتبط با کلیدواژه « خوردگی سایشی » در نشریات گروه « مواد و متالورژی »

One of the main problems in oil and gas pipelines is abrasion corrosion on the edges of the flow channel in the plug and ball valves. Under normal conditions, the gas is moving at a pressure of about 145 bar and an approximate speed of 70 feet per second; The suspended particles in the gas collide with the edges of the flow channel and cause severe erosion on them. Abrasion resistance of steels depends mainly on their surface properties and can be increased by increasing the surface hardness by friction stir processing (FSP). In this study, A216-WCB steel, which is used in the manufacturing of casting parts for valves, flanges and fittings, was processed using a friction stir process for one and three passes. The microstructure, hardness and wear properties of the processed area were investigated. The results showed that two distinct zones, the stir zone (SZ) and the thermo-mechanical affected zone (TMAZ), are formed in the processed zone. Due to the friction stir process, the ferrite grain size in the stirring region decreased from 25 microns to about 3 microns. The hardness of the stir zone increased from 165 Vickers to about 780 HV. Also, the abrasion resistance of the stirring area increased up to 2.5 times.

Damage caused by the two-phase gas-solid flow on the immersion tubes into the cyclone in cement industry that involved the environmental corrosive and abrasive factors is very important. In this work, the effect of particle flow and impact on the corrosion of the immersion tube was studied by the simulation of two-phase gas-solid into the cyclone. The results of gas-solid particle flow simulation and investigation on the particle abrasion on the immersion tube were shown that the impact of particle and shear stress is more in the upper half compared to the lower half. In addition, microstructural studies conducted by optical and scanning electron microscopies on the severely corroded sections of immersion tubes were shown that chromium carbide in the grain boundaries of austenite is formed and the cracks nucleated and growth along the grain boundaries of austenite. Formation of chromium carbide in the grain boundaries of austenite caused to decreasing the chromium from the areas adjacent to the grain boundaries, and as a result, intergranular corrosion occurred. Furthermore, the abrasion of the particle impact on the upper half of the immersion tube leading to severe corrosion based on the erosion corrosion mechanism.

In the present work, Alumina coating with an approximate thickness of 240 µm was applied via high velocity oxy-fuel (HVOF) method on a 4340 hot-work tool steel substrate. The morphology of the coating and the influences of the corrosive medium which contained hydro-chloric acid (5-15 vol.%) were studied using scanning electron microscope (SEM). Afterwards, the wear behavior of the coatings in dry and acidic wet environments were studied using a pin-on-disk wear apparatus and the wear mechanism was analyzed through SEM studies. The results of the wear tests showed that the wear rate in the 5% acidic medium was approximately the same as that of the dry test. Furthermore, the results showed that increasing the concentration of acid in the wear medium (up to 15%), leads to a continuous increase of the wear rate which was ascribed to increased corrosion rate. The dominant wear mechanism in all the tested situations was determined as sticking wear. As the wear rate increased, the wear surfaces showed increased roughness. Finally, hot corrosion experiments were carried on the coated specimens at the temperature of 880 ˚C. At this condition, the coating lasted for about 460 hours.