Hot corrosion behavior of plasma and HVOF sprayed Co- and Ni-based coatings at 900°C

High temperature Co- and Ni-based metallic coatings were applied on samples of 310 stainless steel using plasma spray and high velocity oxy fuel (HVOF) methods. The samples were sprayed with Na₂SO₄, V₂O₅ and NaCl salt solutions and exposed in air at 900°C to cyclic conditions with an aim to simulate an environment typically encountered in oil refinery operation. Extent of hot corrosion damage was assessed using gravimetric measurements while microstructure of the coatings was examined using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. X-ray diffraction was used to determine phase constitution. The aim of this study was to evaluate and compare the performance of specific coatings in hot corrosive environments. Experimental results indicate that the presence of V₂O₅ and NaCl serves to enhance hot corrosion while Co-based coatings perform better than Ni-based coating.     

Surface mechanical characterization of sputtered nickel using nanoindentation

The surface of carbon steel (CS) samples was deposited with pure Ni for the durations of 2, 5 and 10 minutes using DC magnetron sputter deposition process. The aim was to examine the microstructure and surface mechanical properties of Ni coatings. Field emission scanning electron microscope coupled with an energy dispersive x-ray spectrometer and x-ray diffractometer were used to undertake materials characterization. Instrumented nanoindentation hardness, elastic modulus, adhesion and coefficients of friction of coatings were evaluated. Nickel coatings obtained were relatively uniform, continuous and adherent for all deposition times. Thickness of Ni coatings increased with deposition times. Coatings with lower deposition times showed relatively higher nanohardness, elastic modulus and creep which is thought to be due to its lower thickness. Coatings were found to crack and delaminate at relatively low applied normal force during micro-scratch testing. Coefficient of friction values of coatings was comparable with that found in the literature.     

Microstructural study of NiCrAlY electrodeposits

Pulse electrodeposition technique was used to co-deposit Ni with NiCrAlY powder on Ni-based high temperature alloy substrate. Pure nickel anode was immersed in a standard Watt’s bath containing fine particles of NiCrAlY powder that were entrapped during electrodeposition to form a NiCrAlY electrodeposit on cathode specimen surface. Diffusion heat treatment was conducted in argon at ≈1150°C and the samples were oxidized at 1000°C in air. Scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction were used to characterize the microstructure and identify the phases. Pulse electrodeposition resulted in dense and fine-grained deposit with the formation of Al₂O₃ oxide at the coating surface after exposure to high temperature.     

TEM Study of Scale Microstructures Formed on Ni–10Cr and Ni–10Cr–5Al Alloys with and Without Y Addition

A study was conducted to investigate the effect of Y addition on the isothermal-oxidation behaviors of Ni–10Cr, Ni–10Cr–0.5Y, Ni–10Cr–5Al, and Ni–10Cr–5Al–0.5Y alloys. The alloys were oxidized in air for 50 hr at 1000°C. The oxides formed on the alloys were characterized using primarily cross-sectional transmission-electron microscopy techniques along with light microscopy, scanning-electron microscopy, and X-ray diffraction. Although the Al-containing alloys showed comparatively better oxidation behavior, all alloys exhibited nonprotective scaling, as suggested by the thick oxides formed. The major component of the outer oxide was NiO. However, modified Y-containing alloys formed protective layers (i.e., -Cr₂O₃ for NiCrY and -Al₂O₃ for NiCrAlY) at the scale–alloy interface following the nonprotective scaling. The spalling resistance of the modified Y-containing alloys was better than their counterpart unmodified Y-free alloys, while their overall oxidation mechanism remained unchanged after Y addition.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> content on the oxidation behavior of Fe-Cr-Al-based ODS alloys

A study was conducted to investigate the cyclic oxidation behavior of two oxide dispersion strengthened (ODS) Fe-Cr-Al based alloys containing 0.17 wt.% and 0.7 wt.% Y₂O₃. The alloys were oxidized in air for 100 h at 1200°C based on a 24 h cycle period. X-ray diffraction (XRD) and analytical transmission electron microscopy (TEM) were used to characterize the structure, morphology, and composition of the oxide scales. Both alloys formed highly adherent and continuous layers of α-Al₂O₃ exhibiting a morphology indicative of inward scale growth. The role of Y₂O₃ was to promote adherence by segregating to the grain boundaries within the oxide. Concurrently, Y₂O₃ generated micro-porosity resulting in a scale of comparatively higher thickness in the alloy with 0.7 wt.% Y₂O₃.     

Electrochemical Deposition of Ni on an Al-Cu Alloy

Metallic coatings can be used to improve the wear and corrosion resistance of Al alloys. In this study, Ni was used as a candidate material for such a coating which was applied on the surface of Al 2014 alloy using electrodeposition in a standard Watt’s bath. A two-step heat treatment procedure was employed that served to increase the adhesion as well as hardness of Ni. Deposition was undertaken for different durations using both galvanostatic and potentiostatic techniques. The effect of deposition parameters such as surface finish, current, potential, temperature, pH level and duration on the microstructure, adhesion, and surface properties of the Ni deposit was studied. Materials characterization was performed using scanning electron microscopy, atomic force microscopy, and x-ray diffraction. Cross-sectional scanning transmission electron microscope images revealed the fine-grained (10 nm) structure of Ni initially deposited at the Ni-Al alloy substrate. Microhardness, adhesion, and corrosion behavior of the Ni deposit were evaluated. Experimental results indicate that deposition by galvanostatic technique on 1 μm surface finish at 45 °C with a pH level maintained at 3.6 represented the optimum conditions to generate a uniform Ni deposit on Al 2014. It was concluded that Ni deposition can be used to improve the surface properties of Al alloys.     

Use of X-ray powder diffraction for quantitative analysis of carbonate rock reservoir samples

Relative intensity ratio (RIR) method was used to determine the quantitative mineralogy of rock samples that were analyzed by X-ray powder diffraction (XRD). A total of more than 700 samples were tested from wells as deep as 7600 ft located at various carbonate reservoir locations in Arabian Peninsula. Pure mineral samples obtained from the same reservoir were employed as standards to determine relative intensity factors used in the calculations. The rock mineral was mainly composed of calcite, dolomite and anhydrite along with smaller quantities of quartz.     

Chemical modification of waste oil fly ash for improved mechanical and thermal properties of low density polyethylene composites

In this paper, oil fly ash (OFA), a by-product generated by the combustion of oil in power plants, was used as a filler for the preparation of low density polyethylene (LDPE) composite. Four different loadings of filler in the range 1–10%wt were used. Both mechanical and thermal properties were studied using tensile measurements and Differential Scanning Calorimetery. The effect of surface modification of OFA by functionalization with COOH group and the effect of polyethylene-grafted-maleic anhydride as a compatibilizer were also examined. Improvement in Young’s modulus and yield strength of OFA was obtained in the range 1–2% as a result of chemical modification and mainly in the range 5–10%w due to compatiblization. However, a decrease in toughness and elongation at break was also observed. In general, functionalization and compatiblization improved small strain mechanical properties and failed to do the same for large strain properties of composites. No considerable effect for fly ash on melting point, on-set temperature and crystallization peaks was observed. Coupling of functionalization and compatiblization can enhance modulus and tensile strength mechanical properties of composites of LDPE and waste ash.     

Corrosion of Bare and Galvanized Mild Steel in Arabian Gulf Environment

Corrosion performance of bare and galvanized mild steel in atmospheric, soil and splash zone exposure conditions was evaluated at a Khaleej Mardumah test station (KMTS) in Jubail Industrial City (JIC) located at Arabian Gulf coast. The samples were exposed for a period of 15 months. During the exposure, the environmental conditions were periodically monitored by analysis of air, soil, groundwater, and seawater samples. The corroded mild steel and galvanized steel samples were examined by SEM, XRD and XRF to identify the corrosion products and study their surface morphology. Weight loss method was employed to determine the corrosion rates. The experimental results showed that intense temperature and humidity variations as well as high chloride and sulfate concentrations in the region result in severe corrosion of bare mild steel especially under the splash zone conditions. A comparison with the corrosion data for other parts of the world shows that atmospheric and soil environments at the selected test site are significantly corrosive to mild steel. The splash zone, on the other hand, is much more corrosive to mild and galvanized steel than the other parts of the world.     

Failure of ethylene furnace outlet transfer line due to overheating

An outlet transfer line tube of an ethylene-cracking furnace failed after five years of service. The tube, made from Incoloy alloy 800H, developed cracks that penetrated the entire thickness. Optical and scanning electron microscopy, X-ray diffraction, and microhardness tests were used to evaluate the failed tube. It was found that the tube was considerably embrittled by high-temperature carburization, leading to intergranular fracture at the inner surface. Carburization appeared to have been caused by high-temperature exposure to the carbonrich atmosphere associated with the coke adhered to the inner surface. Additionally, the decrease in heat transfer due to the coke deposits caused the wall temperature to increase during service. However, at the outer surface, the tube fractured by a fatigue process that could result from the use of a counterweight to prevent sagging of the tube as a result of the coke deposition. Based on the results obtained, a short-term solution was to modify various process parameters to reduce the extent of coke deposition and/or increase the frequency of decoking and to discontinue the use of a counterweight. However, the long-term solution is to replace alloy 800H.