A.I. Mohammed

Simultaneous determination of benzotriazole copper inhibitor and microbiocidal isothiazolinenones by high-performance liquid chromatography

Abstract A high-performance liquid chromatographic (HPLC) procedure for the separation and determination of the components of a formulation that contained sodium benzotriazole (copper inhibitor), 2-methyl-4-isothiazoline-3-one and 5-chloro-2-methyl-4-isothiazoline-3-one (microbiocide mixture) was developed. This mixture is used to protect and maintain a large water-chilling plant in Saudi Arabia. A UV spectrophotometric method was tried unsuccessfully as both sodium benzotriazole and the isothiazolinones had λmax at 275 nm, so an HPLC method was sought. Optimum conditions were established using a Hewlett-Packard RP C8 column to be methanol-water (40:60) containing 0.05 M KH2PO4 as the eluent at a flow-rate of 1 ml/min. The relative standard deviation of the method at the 95% confidence level was found to be 0.8, 0.7 and 2.4% for the respective components at concentration levels of 35, 115 and 50 mg/l, respectively.

Cyclic oxidation behaviour of a Ni‐Mo‐Cr alloy at 800°C

The oxidation behaviour of a wrought Ni‐Mo‐Cr alloy was studied under thermal cyclic conditions in air at 800°C for exposure periods of up to 1,000 h. The morphologies, microstructures and compositions of the oxide scales were characterized by scanning electron microscopy, energy dispersive X‐ray spectroscopy and X‐ray diffraction. Oxidation kinetics were determined by weight gain measurements. Results show that steady‐state oxidation was achieved within 1 h of exposure while partial scale spalling was observed after 400 h. The alloy grain boundaries intersecting the alloy surface showed preferential oxidation. They became depleted in Ni and enriched in Mo and Cr during transient oxidation. The scale initially formed at the surface was NiO which grew outwardly and laterally to cover the entire alloy. Upon continued oxidation, the scale developed into an outer NiO layer and an inner Cr2O3 layer while the presence of NiMoO4 was also observed within the scale.

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.

Corrosion study of SS304 and SS316 alloys in atmospheric, underground and seawater splash zone in the Arabian Gulf

ABSTRACT Bare stainless steel type 304 and 316 alloys were exposed to atmospheric, underground and seawater splash conditions in order to evaluate their corrosion properties. The exposure was undertaken for 15 months at the coastal and industrial city of Jubail located in the Arabian Gulf. The corrosivity of the environment was determined by testing the soil, groundwater, seawater and air quality. Corrosion rate of the exposed coupons was determined by weight loss method. The experimental results indicate that the both types of stainless steels corroded moderately in this environment. Primary factors influencing the corrosion process are thought to be high degree of variation in temperature and humidity combined with high chloride and sulphate concentrations. The corrosion rate of stainless steel is also compared with those reported for other international locations.

Failure analysis of catalytic steam reformer tubes

Purpose – To determine if the interim use of liquid waste as a fuel in a catalytic steam reformer unit had any deleterious effect on the long‐term life of the reformer tubes.Design/methodology/approach – Standard metallographic techniques were used to prepare representative samples obtained from various sections of the reformer tubes for metallurgical evaluation. Microstructural characterization was carried out in a scanning electron microscope equipped with an energy dispersive X‐ray spectrometer. Imaging and elemental analysis was used for the identification of the alloy material, corrosion products and other microstructural features.Findings – Hydrogen was produced in a catalytic steam reformer by cracking methane using natural gas as a fuel. Corrosion of reformer tubes occurred when natural gas fuel was replaced with a liquid waste. Use of liquid fuel waste accelerated the rate of oxidation at the outer tube surface. However, foreign species from the fuel were not transported into the tube material. T...

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.