Esmaeil Poursaeidi - Academia.edu (original) (raw)

Papers by Esmaeil Poursaeidi

Distortion or bend in a turbine rotor (especially HIP rotors) may be caused by a number of factor... more Distortion or bend in a turbine rotor (especially HIP rotors) may be caused by a number of factors, either singularly or in combination. In general, the causes of rotor bend can be classified invariably in two categories: Rapidly forming permanent rotor bends and/or Slower forming rotor bends, which could trip the turbines' emergency stop. One of the major modifying solutions for rapid repairing of bent rotors is hot spotting. For this purpose, after the initial tests (visual inspection, chemical analysis, nondestructive hardness), the hot spotting was performed seven consecutive times. The results of experimental investigations and experiences with different temperatures and times showed that, the 690 ± 20˚C and 210 S. are as an optimum temperature and time respectively, for hot spotting which can provide a noticeable straightening in bent areas, in addition to having no affects on mechanical properties. Also, this results were simulated by F.E.M in view of heat distribution in...

In this study, fatigue behavior of rock was analytically and numerically modeled. For this purpos... more In this study, fatigue behavior of rock was analytically and numerically modeled. For this purpose, three point of fatigue bending tests were carried out on Limestone specimens prepared from Urmia mine in Iran. Subsequently, the fatigue life and crack growth rate in Limestone were analytically (based on the nonlinear fracture mechanics) and numerically (based on finite element method; FEM) were modeled; the stress intensity factor of FEM models was calculated by J integral and crack tip opening displacement (CTOD). The obtained results showed that although, the analytical approach could fairly predict the fatigue behavior, the fatigue life and crack growth rate evaluated from finite element method had higher agreement with experimental data. In addition, the best results were obtained from FEM models based on J integral method.

One of the most important parts of the axial turbines is the blades of rotor, which are under ben... more One of the most important parts of the axial turbines is the blades of rotor, which are under bending, torsion and thermal stresses due to high combustion product temperature. In fact the combustion products have high temperature, since they are produced in the combustion chamber in gas turbines. Rotating blades of turbine will rotate with high rotational speed due to kinetic energy of the flow. In this paper, the process of designing gas turbine blades base on thermodynamics relations is reviewed. Moreover, this designing is developed by mathematical and thermo dynamical governing equations. The thermo dynamical analysis results are shown in temperature, pressure and velocity distribution graphs. In this research, temperature distribution of a second stage typical gas turbine rotor blade, under real conditions is computed by using computational fluid dynamics methods. Also the decreasing of temperature and increasing of heat transfer are reviewed as a result of blades height decrea...

Engineering Failure Analysis, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

E. Poursaeidi et al. / IJE TRANSACTIONS C: Aspects Vol. 32, No. 6, (June 2019) 872-876 873 TABLE ... more E. Poursaeidi et al. / IJE TRANSACTIONS C: Aspects Vol. 32, No. 6, (June 2019) 872-876 873 TABLE 1. Values of parameters used for coating Parameter Values Arc current [A] 315-310 [16, 17] Voltage [V] 42 [15, 18, 19] ] 1 Feeding rate [g.min 7 [19, 20] Spray distance [mm] 100 [18, 21] Injection angle [degree] 90 [18] 2. 2. Experiment Tests In order to assess the durability of plasma-sprayed bond coat under various thermal loading, two experiments were performed as follows. 2. 2. 1. Isothermal For studying the effect of being exposed to high temperature on bond coat oxidation, the heat treatment was conducted using a furnace for 24, 72, 120 and 192 hours with its temperature increased to 1070 °C. 2. 2. 2. Thermal Shock In this test, first, in order to oxides within the BC expand and TGO layer at BC/TC interface forms, the samples experienced isothermal loading for various time exposure (0, 24, 72 and 120h) and then, thermal shock test was performed. In this test, the temperature of sam...

Gas turbines casings are susceptible to cracking at the edge of the eccentric pin hole. This pape... more Gas turbines casings are susceptible to cracking at the edge of the eccentric pin hole. This paper describes the improvement of the transient thermal fatigue life of gas turbines casings through the application of pins. The repair technology under consideration involved drilling a number of holes in the gas turbines casing along the crack and inserting pins into them. The crack position and direction were determined using non-destructive tests. A series of finite element models were developed and tested in AStM-A395 elastic-perfectly plastic ductile cast iron. In some specimens, holes were drilled near the crack tips. Pins were inserted into the holes in some cases. Abaqus software finite element package and Zencrack fracture mechanics code were used for modeling. The efficiency of crack repair by the installation of pins was investigated along with the effect of the number of pins on crack repair efficiency. The result shows that the insertion of pins into holes drilled in the vici...

One of the important subjects in the analysis of compressor performance is estimating the surge l... more One of the important subjects in the analysis of compressor performance is estimating the surge limit. If the angle of attack changes for any reason, air jets separate from the blades and the cross-section area of the passing air becomes small and causes the alteration of the angle of attack in the next stage blades; this phenomenon is known as stall. When stall completed on a row, a pressure drop occurs at the rearward of that row. So, high-pressure air goes from the next row to the lower pressure area, which associated with a lot of noise and can cause the failure of the blades which is called surge. In this paper, the numerical simulation of surge in the first stage blades of the axial compressor of GEFrame 6 gas turbine has been done. Simulations are done with a 34 degree angle of attack and k-ѡ SST turbulence model has been used. Obtained velocity vectors indicate that during the surge, the reverse flow which is the most important characteristic of surge occurs and the flow ret...

Engineering Fracture Mechanics, 2020

Journal of Failure Analysis and Prevention, 2018

Since compressors have components rotating at high speed, the most common cause of failure in com... more Since compressors have components rotating at high speed, the most common cause of failure in compressors is their high cycle fatigue. In the present study, one of the rotating blades on the first row of an axial flow compressor was prematurely fractured. The crack position and direction were determined, using nondestructive tests. The results indicated that fatigue cracking initiated at two corrosion pits on the surface of the pressure side of the blade in response to corrosive compounds in the site atmosphere. The total life of the blade, from corrosion pit initiation to unstable fatigue crack growth, was calculated. The blade life had three stages: pit initiation and pit growth, pit transition to initial crack and stable crack growth reaching a critical value where the final fracture occurred. Pit growth and its transition to initial cracking were described. The time an equivalent pit requires to reach initial fatigue cracking was subsequently calculated. The number of cycles was calculated via two methods until initial cracking reached unstable growth. The first calculation was performed, using ZENCRACK fracture mechanics code. These results demonstrated that the rate of fatigue crack growth was at first slow and stable. After a period of time, the stress intensity factor reached a critical value where the crack began to propagate unstably. A MATLAB code was written based on Paris model as the second method for estimating fatigue life. The results obtained from drawing a comparison between these methods revealed that ZENCRACK crack shape simulation was in agreement with the fatigue beach marks.

Applied Thermal Engineering, 2014

ABSTRACT Stress analysis is essential for gaining an understanding of the factors affecting crack... more ABSTRACT Stress analysis is essential for gaining an understanding of the factors affecting crack on turbine casing arising from temperature gradients. Hence, making determinations of temperature distribution on gas turbine casing is the first step in stress analysis. The next step is comparison of results with available thermography data related to the casing. In addition, stress and distortion distributions are presented for three test levels of working load on the casing. Comparison of stress concentrations at the eccentric pin hole and observed cracks in these locations validated evaluations for stress distribution.

International Journal of Engineering, 2014

ABSTRACT The first row rotating blades of four axial-flow compressors fractured prematurely. Prev... more ABSTRACT The first row rotating blades of four axial-flow compressors fractured prematurely. Previous investigations had shown that the atmosphere of the site contained corrosive compounds which lead to an increase in possibility of pitting of the blades. It was also revealed that the crack was originated from two corrosion pits. Thus, this work is conducted to ascertain which of the fatigue or stress corrosion cracking (SCC) mechanisms is predominant in transition of pits into initial cracks. To this end, experimental, numerical and theoretical studies are considered. Replica testing, Scanning Electron Microscope (SEM) and fractography of the broken blade indicate that the pits join together and make one bigger pit under SCC mechanism which reduces the failure time. 3-D models of the pitting on the blade under existing forces are analyzed by ABAQUS software. The simulation results show the location of maximum stress concentration inside one of the pits which is compatible with the location of initial SCC crack. Theoretical and numerical analysis show that stress intensity range (ΔK) around the pits is smaller than threshold stress intensity range ( ΔKth); thus, cracks initiate and propagate at the mouth of the pits under SCC mechanism. Then, the pits join together and make one equivalent pit, so that ΔK reaches the ΔKth and finally crack propagates under fatigue mechanism.

International Journal of Engineering, 2016

This study investigated the effects of deposition techniques on the microstructural and tribologi... more This study investigated the effects of deposition techniques on the microstructural and tribological properties of Ti/TiN/TiCN/TiAlN multilayer coatings onto a Custom 450 steel substrate. The coatings were produced using cathodic arc physical vapor deposition (CAPVD) and plasma-assisted chemical vapor deposition (PACVD). The microstructural of the coatings was evaluated using (SEM), and phase formation was analyzed by (XRD). The mechanical properties of the coatings were examined by nano-indentation testing machine. Erosion behavior was studied using an erosion tester and the electrochemical behavior of the deposited films in 3.5% (wt) NaCl solution was investigated using potentiodynamic polarization. XRD analysis indicated that TiN, TiCN, and TiAlN featured different chemical compositions in each coating. Nano-indentation showed that the hardness of the CAPVD coating was 23.35 GPa and of the PACVD coating was 12.92 GPa. The coefficient of friction was 0.22 for the CAPVD and 0.17 for the PACVD coatings. Erosion testing was conducted using two abrasive powders at impact angles of 30° and 90°. The results showed that erosion rate at an impingement angle of 90° was greater than at 30° and the CAPVD coating showed better performance. The potentiodynamic polarization curves showed that the CAPVD coating provided better corrosion resistance than the PACVD coating.

Powder Technology, 2017

 Erosion tests were conducted in an erosion experimental bench using quartz powder.  Finnie ero... more  Erosion tests were conducted in an erosion experimental bench using quartz powder.  Finnie erosion model was calibrated on compressor blades material erosion tests.  Numerical simulations were employed to determine particle impact conditions.  The erosion rates were predicted over the IGV, rotor blade and stator vane surfaces.

Applied Thermal Engineering, 2016

Evaluation of shell temperature by using thermocouples. • Establish the transient thermal fatigue... more Evaluation of shell temperature by using thermocouples. • Establish the transient thermal fatigue life of a gas turbine casing. • Transient thermal stress analysis of a gas turbine casing. • Establish the stress intensity factor of a gas turbine casing.

Ceramics International, 2017

Ti(C,N)/TiAlSiN multilayer coating was deposited on GTD450 using the Cathodic Arc PVD method to p... more Ti(C,N)/TiAlSiN multilayer coating was deposited on GTD450 using the Cathodic Arc PVD method to protect compressor blades from erosion damage. The fracture and deformation mechanisms of coating were investigated. To better observe fracture and deformation events and thus the need to apply high loads, Vickers microhardness test was performed and imprint diagonals were measured. Then, using SEM analysis, indent surfaces were investigated to observe crack initiation and deformation patterns at different loadings. It was found that crack initiated at the coating top surface (top surface of TiAlSiN layer) at a loading range of 250-500 mN. Cross-section SEM images of indent surfaces at lower loads revealed shear sliding and radial cracking below the indenter in the coating-substrate interface (bottom surface of Ti(C,N) layer). To better understand coating fracture and deformation, a 3D FE model was used to determine stress distribution in the coating. FEM results showed that maximum Von Mises stresses occur beneath the indenter and its edges, causing shear sliding to take place. Also, maximum principal stresses at lower loads take place beneath the indenter at the coating-substrate interface. As load increases, the maximum principal stress zone changes and is transferred to the coating top surface. Maximum principal stress was produced during the unloading process at the coating top surface or median plane and may cause lateral cracking. Experimental and FEM results were in good agreement.

Engineering Failure Analysis, 2016

Abstract First-stage nozzles of gas turbines, which are the first elements after the combustion c... more Abstract First-stage nozzles of gas turbines, which are the first elements after the combustion chamber, encounter hot gases from the combustion process and have the task of directing the fluid path and increasing the velocity of combustion products. This paper reports on the incidence and failure of the first-stage nozzles of a gas turbine in September 2013 at a seaside pump-house located in the South-West of Iran. The nozzle was made of nickel-based superalloy Nimonic105. Due to nozzle failure, the turbine was damaged severely. The cause of nozzle failure was investigated. The results of visual inspection, XRD analysis of deposits on the blade airfoil, SEM images and EDAX analysis showed the characteristics of hot corrosion. Finite-element analysis (FEM) revealed that the cause of blade trailing edge failure was thermal stress leading to thermal fatigue, which accelerated nozzle blade failure in addition to the hot corrosion.

Local hardness increasing on the surface of the power plant rotor may result in severe damages. O... more Local hardness increasing on the surface of the power plant rotor may result in severe damages. One major solution for rapid repairing of the rotors is the adaptive tempering heat treatment. For this purpose, after identification of the damaged rotor, initial investigations and tests (such as visual inspection, chemical analysis, nondestructive hardness measurements and replica or on-site metallographic tests) were performed on the rotor journal. The results showed that, the occurrence of local phase transformation (i.e. tempered bainite to austenite and finally martensite) is the main factor. Finally, based on the aforementioned results, tempering heat treatment method was selected as a modifying solution for the following purposes: 1. Decreasing hardness in embrittled places (i.e. 400-690 HV) and, 2. invariable or admissible decrease of hardness in undamaged areas (250-300 HV). Experiments showed that by choosing the 680˚C/4hr as an optimum condition for tempering heat treatment, the two mentioned objectives can be met.

Engineering Failure Analysis, 2014

ABSTRACT Some gas turbines casings are very susceptible to involve cracking in critical points. A... more ABSTRACT Some gas turbines casings are very susceptible to involve cracking in critical points. According to studies, thermal fatigue specified as the main reason of creation of cracks. This approach is to predict the fatigue life of the detected crack on the edge of eccentric pin hole of a heavy duty gas turbine casing, which is one of the most probable positions for crack initiation and propagation. The crack position and direction was determined, by using non-destructive tests. Distribution of outer surface temperature was measured by using thermography method and for the measurement of inner surface ten thermocouples were installed inside the casing wall. The temperature data was applied as boundary condition in finite element simulation by using Abaqus software. Stress distribution of the casing was calculated in accord to engine work cycle and then, fatigue crack growth was predicted by using ZENCRACK fracture mechanics code. The analysis results showed that the crack growth rate will decrease gradually and after periods of time while stress intensity factor values will reach the Threshold value, the crack propagation will stop. CTOD and J-Integral methods were implemented for calculating the fracture mechanics quantities and Paris model was used to estimate the fatigue life.