Khalil Ranjbar | Shahid Chamran University - Ahwaz (original) (raw)

Papers by Khalil Ranjbar

International Journal of Materials Research, 2016

Materials & Design, 2010

Failure of a tubular heat exchanger made up of copper based alloys in a steam power plant was inv... more Failure of a tubular heat exchanger made up of copper based alloys in a steam power plant was investigated. Tubes were made initially from yellow brass, and there after replaced by Cu-5Ni alloys. Circulating water from cooling tower was used as coolant, to condense the hot steam inside the steel shell. The velocity of cooling water was found to be very low, causing accumulation of deposits, reduction of diameter and some times complete blockage of tubes. The causes of failure were investigated performing various tests such as chemical analysis, XRD, optical, and SEM examination. Study revealed that tube material suffering from extensive dealloying and impingement attack.

Powder Metallurgy and Metal Ceramics, 2011

ABSTRACT An extensive scanning electron microscopy and image analysis is carried out on Alumina a... more ABSTRACT An extensive scanning electron microscopy and image analysis is carried out on Alumina and Zirconia Dispersed Alumina (ZDA) ceramic composites containing controlled amounts of tetragonal, monoclinic, and cubic zirconia phases. ZDA powders are prepared through a partial chemical route and sintered at 1600°C for 2 h in air. Zirconia nanoparticles reduce alumina matrix grain size by more than six times. Intricate relationships are revealed between zirconia allotropes and different microstructural parameters such as matrix grain size and its distribution, abnormal grain growth, zirconia particle size distribution, pore size, fracture mode, interparticle distance, etc. Keywordsalumina dispersed zirconia composites–microstructural evaluation–particles

Engineering Failure Analysis, 2007

An analysis was made on the failure and shut down of boiler cold and hot reheater tubes by chemic... more An analysis was made on the failure and shut down of boiler cold and hot reheater tubes by chemical analysis of sediments, metallographic examinations, XRD, SEM and EDX studies. The mode of operation, maintenance, and feed water chemistry were also checked. It is concluded that the bad maintenance and feed water chemistry are the main causes of the failure, leading to various types of corrosion mechanisms, which are identified and discussed in this study.

Engineering Failure Analysis, 2011

The present study describes origin and failure mechanisms of air cooled heat exchangers tubes, in... more The present study describes origin and failure mechanisms of air cooled heat exchangers tubes, in a gas pressure boosting station. Hydrocarbon gas was circulating within aluminum finned tubes and cooling was done by forcing ambient air over the exterior of the tubes, made of carbon steel A-214 material. The hydrocarbon gas was contained traces of H 2 S and substantial level of CO 2 . The investigation was carried out in a station located in southern part of Iran. The process involved condensation of water and hydrocarbon along the length of tubes, resulting in a wet gas multiphase flow situation. Such type of coolers is also called composite coolers. The failure of tubes was characterized on the bases of all the available evidences and metallurgical examinations, such as analysis of tube materials, feeding gas, condensate water, and the residue inside the tubes. The processing was also simulated by Hysis-3.1 software, in order to evaluate and compare various parameters such as gas flow rate, liquid water and hydrocarbon formation, in actual and design condition. The air cooled tubes showed highest corrosion rate and was experienced leakage regularly. The results indicated that, low velocity assisted sweet corrosion caused severe pitting inside the tubes, and led to failure.

Metallurgical and Materials Transactions A, 2016

The Canadian journal of cardiology

Journal of Materials Engineering and Performance, 2015

Journal of Failure Analysis and Prevention, 2015

The Canadian journal of cardiology

The Canadian journal of cardiology

American Ceramic Society Bulletin

Alumina powders dispersed with monoclinic, tetragonal, and cubic zirconia were prepared by evapor... more Alumina powders dispersed with monoclinic, tetragonal, and cubic zirconia were prepared by evaporating a colloidal dispersion of alumina powders in solutions containing zirconium and yttrium salts. The dried and calcined powders were compacted, sintered, and characterized. The results demonstrated a clear toughening effect by the zirconia on the alumina ceramics. The alumina containing 20-wt%-yttria-stabilized tetragonal zirconia had the maximum toughness.

Journal of Alloys and Compounds, 2015

ABSTRACT In the present investigation, friction stir processing (FSP) was utilized to incorporate... more ABSTRACT In the present investigation, friction stir processing (FSP) was utilized to incorporate Multi Walled Carbon Nano Tubes (MWCNT) and nanosized cerium oxide particles into the matrix of Al5083 alloy to form surface reinforced composites. The effect of these nanosized reinforcements either separately or in the combined form, on microstructural modification, mechanical properties and corrosion resistance of FSPed Al5083 surface composites was studied. A threaded cylindrical hardened steel tool was used with the rotation speeds of 600 and 800 rpm and travel speeds of 35 and 45 mm/min and a tilt angle of 5°. Mechanical properties and corrosion resistance of FSPed samples were evaluated and compared with the base alloy. The maximum tensile strength and hardness value were achieved for the hybrid composite containing a mixture of CNTs and cerium oxide in the volume ratio of 75–25, respectively, whereas a significant increase in pitting resistance of the base alloy was obtained when cerium oxide alone was incorporated. The corrosion behavior of the samples was investigated by potentiodynamic polarization tests and assessed in term of pitting potential and passivation range. Microstructural analysis carried out by using optical and electron microscopes showed that reinforcements are well dispersed inside the nugget zone (NZ), and remarkable grain refinement is gained. The study was aimed to fabricate surface composites with improved mechanical properties and corrosion resistance simultaneously.

Materials Science and Engineering: A, 2011

Commercially pure Al is severely deformed through semi-constrained groove pressing up to four pas... more Commercially pure Al is severely deformed through semi-constrained groove pressing up to four passes. Mechanical properties and microstructure of the samples are studied using mechanical tests, transmission and scanning electron microscopy and X-ray line profile. The yield stress and tensile strength increase by a factor of 2.3 and 1.5, respectively, compared to the annealed state, after the third pass and decrease slightly afterward. The Hardness saturates at about 40 VHN at last stages of pressing. Fracture surface morphology demonstrates that the fracture mode is ductile even after four passes. Results show that finer and more dislocation free cells are observed after the fourth pass. An average grain size of about 300 nm is obtained after the final pressing. The results are compared with that of the previous works conducted on Al through fully or partially constraint groove pressing.

Journal of Failure Analysis and Prevention, 2013

Pumps are a key and crucial part of many industrial units which usually are endangered by metallu... more Pumps are a key and crucial part of many industrial units which usually are endangered by metallurgical, mechanical, and chemical damages. The most important mechanisms of failure in pumps are cavitation, erosion, and corrosion which directly are influenced by pump's materials, type of fluent, and operation condition. The aim of this study was to investigate the role of material selection in the main failure mechanisms of a power plant booster pumps. To observe the kind and micro structure of pumps optical microscopy and image analyses software were used. Morphology of the pumps' body is investigated by scanning electron microscopy. Electrochemical tests and water analyses are done for measurement of corrosion rate as well as amount of particles in feed water. Moreover, tensile testing was carried out to compare the mechanical properties of body alloy with standard alloy. The results revealed that cavitation and erosion were the most significant mechanisms. On the other hand, the data from analyses and observations clarified that the material which chosen for pumps alloy was improper which was accompanied with lack of fabrication technology.

Journal of Failure Analysis and Prevention, 2012

The failure of a multistrand wire rope used in drilling rig hook is investigated in this case stu... more The failure of a multistrand wire rope used in drilling rig hook is investigated in this case study. The wire rope failed during the raising of the rig and caused some serious damage to the rig structure. Throughout its short time of service, the wire had been used a few times for rig up and rig down. The failure investigation is performed by metallurgical examinations and computational analyses utilizing the finite element method. The wire rope was made of AISI 1095 steel. Its chemical composition, ferritepearlite structure, and high hardness indicate that the wire is a type of extra extra improved plow steel (EEIPS) grade. The morphologies of fractured surfaces indicate tensile overloading of wires. Finite element analysis confirms the overload in core and strands, and compressive contact stresses between wires, and between wires and sheave surface. The results show that high tensile stresses due to the overload and small ratio of sheave-to-rope diameter were responsible for the failure. Fig. 15 Stresses of a section of the wire rope: (a) maximum principal and (b) minimum principal J Fail. Anal. and Preven.

International Journal of Minerals, Metallurgy, and Materials, 2012

An alloy of Al-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstructural changes due ... more An alloy of Al-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstructural changes due to Ti-B refiner and Sr modifier additions were studied. Apart from usual refinement and modification of the microstructure, some mutual influences of the additives took place, and no mutual poisoning effects by these additives, in combined form, were observed. It was noticed that the dimensions of the iron-rich intermetallics were influenced by the additives causing them to become larger. The needle-shaped intermetallics that were obtained from refiner addition became thicker and longer when adding the modifier. It was also found that α-Al and eutectic silicon phases preferentially nucleate on different types of intermetallic compounds. The more iron content of the intermetallic compounds and the more changes in their dimensions occurred. Formation of the shrinkage porosities was also observed.

Engineering Failure Analysis, 2013

and sharing with colleagues.

Engineering Failure Analysis, 2012

and sharing with colleagues.

International Journal of Materials Research, 2016

Materials & Design, 2010

Failure of a tubular heat exchanger made up of copper based alloys in a steam power plant was inv... more Failure of a tubular heat exchanger made up of copper based alloys in a steam power plant was investigated. Tubes were made initially from yellow brass, and there after replaced by Cu-5Ni alloys. Circulating water from cooling tower was used as coolant, to condense the hot steam inside the steel shell. The velocity of cooling water was found to be very low, causing accumulation of deposits, reduction of diameter and some times complete blockage of tubes. The causes of failure were investigated performing various tests such as chemical analysis, XRD, optical, and SEM examination. Study revealed that tube material suffering from extensive dealloying and impingement attack.

Powder Metallurgy and Metal Ceramics, 2011

ABSTRACT An extensive scanning electron microscopy and image analysis is carried out on Alumina a... more ABSTRACT An extensive scanning electron microscopy and image analysis is carried out on Alumina and Zirconia Dispersed Alumina (ZDA) ceramic composites containing controlled amounts of tetragonal, monoclinic, and cubic zirconia phases. ZDA powders are prepared through a partial chemical route and sintered at 1600°C for 2 h in air. Zirconia nanoparticles reduce alumina matrix grain size by more than six times. Intricate relationships are revealed between zirconia allotropes and different microstructural parameters such as matrix grain size and its distribution, abnormal grain growth, zirconia particle size distribution, pore size, fracture mode, interparticle distance, etc. Keywordsalumina dispersed zirconia composites–microstructural evaluation–particles

Engineering Failure Analysis, 2007

An analysis was made on the failure and shut down of boiler cold and hot reheater tubes by chemic... more An analysis was made on the failure and shut down of boiler cold and hot reheater tubes by chemical analysis of sediments, metallographic examinations, XRD, SEM and EDX studies. The mode of operation, maintenance, and feed water chemistry were also checked. It is concluded that the bad maintenance and feed water chemistry are the main causes of the failure, leading to various types of corrosion mechanisms, which are identified and discussed in this study.

Engineering Failure Analysis, 2011

The present study describes origin and failure mechanisms of air cooled heat exchangers tubes, in... more The present study describes origin and failure mechanisms of air cooled heat exchangers tubes, in a gas pressure boosting station. Hydrocarbon gas was circulating within aluminum finned tubes and cooling was done by forcing ambient air over the exterior of the tubes, made of carbon steel A-214 material. The hydrocarbon gas was contained traces of H 2 S and substantial level of CO 2 . The investigation was carried out in a station located in southern part of Iran. The process involved condensation of water and hydrocarbon along the length of tubes, resulting in a wet gas multiphase flow situation. Such type of coolers is also called composite coolers. The failure of tubes was characterized on the bases of all the available evidences and metallurgical examinations, such as analysis of tube materials, feeding gas, condensate water, and the residue inside the tubes. The processing was also simulated by Hysis-3.1 software, in order to evaluate and compare various parameters such as gas flow rate, liquid water and hydrocarbon formation, in actual and design condition. The air cooled tubes showed highest corrosion rate and was experienced leakage regularly. The results indicated that, low velocity assisted sweet corrosion caused severe pitting inside the tubes, and led to failure.

Metallurgical and Materials Transactions A, 2016

The Canadian journal of cardiology

Journal of Materials Engineering and Performance, 2015

Journal of Failure Analysis and Prevention, 2015

The Canadian journal of cardiology

The Canadian journal of cardiology

American Ceramic Society Bulletin

Alumina powders dispersed with monoclinic, tetragonal, and cubic zirconia were prepared by evapor... more Alumina powders dispersed with monoclinic, tetragonal, and cubic zirconia were prepared by evaporating a colloidal dispersion of alumina powders in solutions containing zirconium and yttrium salts. The dried and calcined powders were compacted, sintered, and characterized. The results demonstrated a clear toughening effect by the zirconia on the alumina ceramics. The alumina containing 20-wt%-yttria-stabilized tetragonal zirconia had the maximum toughness.

Journal of Alloys and Compounds, 2015

ABSTRACT In the present investigation, friction stir processing (FSP) was utilized to incorporate... more ABSTRACT In the present investigation, friction stir processing (FSP) was utilized to incorporate Multi Walled Carbon Nano Tubes (MWCNT) and nanosized cerium oxide particles into the matrix of Al5083 alloy to form surface reinforced composites. The effect of these nanosized reinforcements either separately or in the combined form, on microstructural modification, mechanical properties and corrosion resistance of FSPed Al5083 surface composites was studied. A threaded cylindrical hardened steel tool was used with the rotation speeds of 600 and 800 rpm and travel speeds of 35 and 45 mm/min and a tilt angle of 5°. Mechanical properties and corrosion resistance of FSPed samples were evaluated and compared with the base alloy. The maximum tensile strength and hardness value were achieved for the hybrid composite containing a mixture of CNTs and cerium oxide in the volume ratio of 75–25, respectively, whereas a significant increase in pitting resistance of the base alloy was obtained when cerium oxide alone was incorporated. The corrosion behavior of the samples was investigated by potentiodynamic polarization tests and assessed in term of pitting potential and passivation range. Microstructural analysis carried out by using optical and electron microscopes showed that reinforcements are well dispersed inside the nugget zone (NZ), and remarkable grain refinement is gained. The study was aimed to fabricate surface composites with improved mechanical properties and corrosion resistance simultaneously.

Materials Science and Engineering: A, 2011

Commercially pure Al is severely deformed through semi-constrained groove pressing up to four pas... more Commercially pure Al is severely deformed through semi-constrained groove pressing up to four passes. Mechanical properties and microstructure of the samples are studied using mechanical tests, transmission and scanning electron microscopy and X-ray line profile. The yield stress and tensile strength increase by a factor of 2.3 and 1.5, respectively, compared to the annealed state, after the third pass and decrease slightly afterward. The Hardness saturates at about 40 VHN at last stages of pressing. Fracture surface morphology demonstrates that the fracture mode is ductile even after four passes. Results show that finer and more dislocation free cells are observed after the fourth pass. An average grain size of about 300 nm is obtained after the final pressing. The results are compared with that of the previous works conducted on Al through fully or partially constraint groove pressing.

Journal of Failure Analysis and Prevention, 2013

Pumps are a key and crucial part of many industrial units which usually are endangered by metallu... more Pumps are a key and crucial part of many industrial units which usually are endangered by metallurgical, mechanical, and chemical damages. The most important mechanisms of failure in pumps are cavitation, erosion, and corrosion which directly are influenced by pump's materials, type of fluent, and operation condition. The aim of this study was to investigate the role of material selection in the main failure mechanisms of a power plant booster pumps. To observe the kind and micro structure of pumps optical microscopy and image analyses software were used. Morphology of the pumps' body is investigated by scanning electron microscopy. Electrochemical tests and water analyses are done for measurement of corrosion rate as well as amount of particles in feed water. Moreover, tensile testing was carried out to compare the mechanical properties of body alloy with standard alloy. The results revealed that cavitation and erosion were the most significant mechanisms. On the other hand, the data from analyses and observations clarified that the material which chosen for pumps alloy was improper which was accompanied with lack of fabrication technology.

Journal of Failure Analysis and Prevention, 2012

The failure of a multistrand wire rope used in drilling rig hook is investigated in this case stu... more The failure of a multistrand wire rope used in drilling rig hook is investigated in this case study. The wire rope failed during the raising of the rig and caused some serious damage to the rig structure. Throughout its short time of service, the wire had been used a few times for rig up and rig down. The failure investigation is performed by metallurgical examinations and computational analyses utilizing the finite element method. The wire rope was made of AISI 1095 steel. Its chemical composition, ferritepearlite structure, and high hardness indicate that the wire is a type of extra extra improved plow steel (EEIPS) grade. The morphologies of fractured surfaces indicate tensile overloading of wires. Finite element analysis confirms the overload in core and strands, and compressive contact stresses between wires, and between wires and sheave surface. The results show that high tensile stresses due to the overload and small ratio of sheave-to-rope diameter were responsible for the failure. Fig. 15 Stresses of a section of the wire rope: (a) maximum principal and (b) minimum principal J Fail. Anal. and Preven.

International Journal of Minerals, Metallurgy, and Materials, 2012

An alloy of Al-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstructural changes due ... more An alloy of Al-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstructural changes due to Ti-B refiner and Sr modifier additions were studied. Apart from usual refinement and modification of the microstructure, some mutual influences of the additives took place, and no mutual poisoning effects by these additives, in combined form, were observed. It was noticed that the dimensions of the iron-rich intermetallics were influenced by the additives causing them to become larger. The needle-shaped intermetallics that were obtained from refiner addition became thicker and longer when adding the modifier. It was also found that α-Al and eutectic silicon phases preferentially nucleate on different types of intermetallic compounds. The more iron content of the intermetallic compounds and the more changes in their dimensions occurred. Formation of the shrinkage porosities was also observed.

Engineering Failure Analysis, 2013

and sharing with colleagues.

Engineering Failure Analysis, 2012

and sharing with colleagues.