meilinda nurbanasari | Itenas - Academia.edu (original) (raw)

Papers by meilinda nurbanasari

Engineering Failure Analysis

Journal of Failure Analysis and Prevention, 2019

A failure analysis was carried out on an A213 T91 secondary superheater tube after 4 months of ov... more A failure analysis was carried out on an A213 T91 secondary superheater tube after 4 months of overhaul. The failure caused the 600-MW coal power plant was shut down. The investigation consisted of visual inspections, microstructure analysis, Vickers hardness test, x-ray diffraction, and ash fusion temperature test and ash content analysis. The failed tube had a thin-lip rupture with sharp edges and experienced a decrease in hardness in the area of lip rupture. The microstructure analysis shows the coarse carbide and some isolated voids. Corrosion products were detected in slag deposits, and nonuniform thin oxide layer in the inner wall of the tube was observed. It is concluded that the main failure of the failed tube was due to the formation of slag deposits on the outer surface of the tube wall. This formation has resulted in simultaneously occurring phenomena, which was the localized flue gas erosion followed by the rapid overheating of the tube. The formation of slag deposits was in consequence of the use of coal with lower ash fusion temperature than required coal ash fusion temperature for the power plant.

Journal of Failure Analysis and Prevention, 2019

Your article is protected by copyright and all rights are held exclusively by ASM International. ... more Your article is protected by copyright and all rights are held exclusively by ASM International. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to selfarchive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Case Studies in Engineering Failure Analysis, 2017

The Forced Draft Fan (FDF) blade in a 300 MW coal fired power plant that experienced catastrophic... more The Forced Draft Fan (FDF) blade in a 300 MW coal fired power plant that experienced catastrophic failure has been investigated. There were two main locations of the blade damage, namely damage at the root of the blade and the other one is at the third of the blade height. The FDF blade has been run for 5 years and before its failure, the FDF experienced high vibration (14 mm/s). The forced draft fan is an axial flow fan horizontally in front of the boiler and the fan is single stage. Visual inspection, metallographic analysis, chemical composition and hardness test were carried out to find the cause of the failure. It is concluded that the material of the blade is cast Al-Si alloy (A356.0) that fits the requirements for FDF blade application, the failure of the third of the blade height is owing to the external particles collide to the leading edge of the blades causing erosion and notch. That notch acted as initial crack. The failure at the root blade was caused by broken fragments of the others damaged blades entered in between casing (stator) and the blade (rotor) so they obstructed the blade rotation.

I would like to express my greatest gratitude to Professor Panos Tsakiropoulos for his valuable g... more I would like to express my greatest gratitude to Professor Panos Tsakiropoulos for his valuable guidance and encouragement he provided during my study, and for giving me the opportunity to study on interesting topic in tungsten hot working tool steels. I also gratefully acknowledge to Dr. E.J. Palmiere for his support and important suggestion in every aspect of my study. I would like to thank Directorate of Higher Education, Indonesian Government and Institut Teknologi Nasional, Bandung, which helped greatly for their financial support to accomplish my study. I am also grateful to many members of technical staffs within the Sorby Centre, IMMPETUS and the Department of Materials Science and Engineering in general for all of their assistance during my study. I thank also to my friends in the department who encouraged me. Most importantly, I would like to express my deepest thanks to my parents, my husband, Setiyo Suprastiyoko, and my lovely daughters, Shafira Sari and Nadhira Ratnasari for their endless encouragement, support and love.

2020 International Conference on Power, Energy, Control and Transmission Systems (ICPECTS), 2020

Coal-Fired Power Plant Boiler 600 MW has been operated more than 20 years. Secondary superheater ... more Coal-Fired Power Plant Boiler 600 MW has been operated more than 20 years. Secondary superheater outlet (SSH Outlet) tube bursts had been occurred on this unit. Long-term overheated failure mode was observed at failed tubes on three occasions which was on September 2017, April 2018, and December 2019. The design tubes are called SA-213 T91. On April 2018 and December 2019, the powerplant operator has joined hand with two different public university research institute which are called institution-1 and institution-2 to conduct tests to find the root cause of the failure by hardness test, microstructural examination, creep test and the remaining life analysis. The results of the hardness test on the fail tube on April 2018 and December 2019 were 170.84±1.98 Harness Vickers (HV) and 168–219 HV respectively compared to the new material hardness which are on the average of 258HV. On April 2018, creep tests were resulted that expected time to failure on 750°C and 72.93Mpa was 3.6hours; on...

International Journal of Engineering Research and Technology, 2020

Ash handling unit is one of the crucial part of the operation of a coal fired power plant (CFPP).... more Ash handling unit is one of the crucial part of the operation of a coal fired power plant (CFPP). This paper focused on the investigation of shackle chain failure in ash handling unit of a 600 MW CFPP. The failure caused disruption to the operating system of the CFPP. To improve the chain system in order to prevent similar failure in the near future, the metallurgical failure analysis was conducted on failed shackle chain through crack observation using optical and electron microscope and Vickers hardness test. Crack surface observation of failed shackle chain using Scanning Electron Microscope (SEM) revealed that the failure of shackle chain was primarily due to the fatigue failure which was proven by the presence of beachmarks. In addition, there were two initial cracks which were caused by pitting corrosion. The clearance (gap) occurred in the bolt connection system caused the fatigue load which in turn resulted in failure to the CFPP operation. This research suggested preventive measures to be taken to avoid similar problem in the future.

International Journal of Engineering and Technology, 2017

Evaluation and remaining life assessment of separator and demister for 55 MW geothermal power gen... more Evaluation and remaining life assessment of separator and demister for 55 MW geothermal power generation plant have been conducted. The equipment has been used for 27 years and has stopped operating due to the failure of steam turbine. Before it is operated back, the condition of separator and demister needs to be evaluated and their remaining life assessment has to be calculated to anticipate the future repair. The methods used for evaluation were UT phased array, thickness measurement, chemical composition, hardness test and deposit composition analysis. The remaining life assessment was calculated in correlation with thickness reduction. The results showed that the chemical composition and hardness of materials met the standard of SA 516 Gr 70. No evidence of internal defect was found in both equipment. The demister in all part is still in good condition and its remaining life was beyond 20 years. In separator, the reduction in thickness extremely occurred on top head and cone. The remaining life of top head separator was below 1.2 years and cone separator was not more than 4.7 years. Deposit analysis taken from demister gave evidence the presence of sulfur, silica, iron oxide, and sulfide iron.

Key Engineering Materials, 2019

Bearing cooler coils connector of 175 MW hydropower plant experienced premature leaks after one y... more Bearing cooler coils connector of 175 MW hydropower plant experienced premature leaks after one year operation and caused an unscheduled shutdown. To avoid the same failure in the future, the leaking bearing cooler coils connector was investigated. Nondestructive tests, such as chemical composition analysis, hardness test, metallographic test, characterization of the filler brazing by scanning electron microscopy – energy dispersive X-ray spectroscopy were conducted. The results confirmed that the bearing cooler coils connector consisted of two types of material namely the flange material which was made of stainless steel 304 and the pipe material which was a Cu/Ni 90/10 and were joined together using brazing process. It was a clearly evidence that leaks occurred in the brazing area and the leakage was due to improper brazing process. It was shown by the excessive gap and a lot of porosity.

MATEC Web of Conferences, 2015

This paper reported the evaluation of a 50 MW steam turbine shaft that has exceeded the designed ... more This paper reported the evaluation of a 50 MW steam turbine shaft that has exceeded the designed lifetime (30 years). The inspection of turbine is a mandatory for safety and continued reliable operation. The shaft was made of nickel-chromium-molybdenum alloy steel. The turbine operated in the range temperature of 500-600 o C, and creep was considered to be a major damage mechanism. The remaining life assessment of the turbine shaft was also conducted using replication technique. The replica samples were taken from 125 position distributed along the turbine shaft. The microstructural analysa of replicas showed that creep had occurred, which was indicated by the cavities formation at the grain boundaries. After evaluation and assessment, it can be concluded that the turbine shaft still can be used however it needs to be re-inspected within 6 months. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits distribution, and reproduction in any medium, provided the original work is properly cited.

International Journal of Minerals, Metallurgy, and Materials, 2015

The microstructure and the stability of carbides after heat treatments in an H23 tool steel were ... more The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures (1100°C and 1250°C), followed by water quenching and double-aging at 650°C, 750°C, and 800°C with air cooling between the first and second aging treatments. Martensite did not form in the as-quenched microstructures, which consisted of a ferrite matrix, M 6 C, M 7 C 3 , and MC carbides. The double-aged microstructures consisted of a ferrite matrix and MC, M 6 C, M 7 C 3 , and M 23 C 6 carbides. Secondary hardening as a consequence of secondary precipitation of fine M 2 C carbides did not occur. There was disagreement between the experimental microstructure and the results of thermodynamic calculations. The highest double-aged hardness of the H23 tool steel was 448 HV after austenization at 1250°C and double-aging at 650°C, which suggested that this tool steel should be used at temperatures below 650°C.

Case Studies in Engineering Failure Analysis, 2014

The turbine blade in a steam turbine has an important role to convert the kinetic energy of the s... more The turbine blade in a steam turbine has an important role to convert the kinetic energy of the steam into mechanical energy [1-3]. Blade failure in a steam turbine is a prevalent occurrence and has a strong correlation with the forces acting on the blade, which are centrifugal forces, centrifugal bending, steady steam bending, unsteady centrifugal forces due to lateral shaft vibration and alternating bending [4]. Working environment of turbine blade in corrosion during operating and lay up also has a big contribution to the blade failure [5,6]. Previous investigations [5,7-9] reported that fatigue, stress corrosion cracking and corrosion fatigue were general causes that often lead to the blade failure. This paper reported the investigation of the first stage blade failure in a steam turbine, which has been operated for 12 years. The steam turbine of a 55 MW consists of five stages of turbine stator and rotor. The type of blade used in the first stage in this investigation was single T root blade assembled in slot disc of rotor. Fig. 1 shows the investigated blade, and blade terminology used in this paper. Each blade was integrated in its top by a shroud. The shrouds contact to each other that strengthen the rigidity, decrease the bending and twisting distortion and the friction occurred between the shrouds caused by blades vibration could absorb the vibration power [10]. The blade failure of the first stage was observed initially using non-destructive inspection (dye penetrant) when the steam turbine being repaired. The result found that all blades had cracks at the tang and the crack at the fillet for the blades with broken tang. The main objective of this paper was to find out the cause of failure of the first stage blade.

Transactions of the Indian Institute of Metals, 2014

The H23 tool steel contains high concentration of carbide forming elements, which affect the micr... more The H23 tool steel contains high concentration of carbide forming elements, which affect the microstructure and mechanical properties. This present study described the microstructure and mechanical properties of the as cast H23 tool steel. The steel was prepared by vacuum induction melting. The microstructural investigation used XRD and electron microscope. The nano hardness and elastic moduli of matrix and carbide were also measured. The results show that the as cast microstructure consisted of ferrite matrix and M 6 C, MC and M 23 C 6 carbides. The eutectic M 6 C carbides had two different morphologies owing to different growth mechanisms. There was agreement between the experimental results and the calculated solidification path for the H23 tool steel regarding the presence of carbides in the microstructure. The nanohardness and elastic moduli of ferrite matrix and M 6 C carbides were respectively 4.2 ± 0.2 and 10.6 ± 1.2 and 198.3 ± 10.2 and 253.5 ± 11.7 GPa.

Advanced Materials Research, 2014

Solidification behaviour of a H21 tool steel has been studied. The aim of this work is to give be... more Solidification behaviour of a H21 tool steel has been studied. The aim of this work is to give better understanding of the as cast microstructure of the steel. The investigated H21 tool steel was made using induction vacuum furnace with air cooling. The microstructure observation was carried out using optical and electron microscopy. X ray diffraction and nanohardness were also used for phase and carbide identification. The results show that the as cast microstructure consisted of ferrite and coarse primary M6C carbide that is rich in tungsten. The nanohardness of ferrite was 5.1 ± 0.3 GPa and there was inhomogeneity in as cast microstructure, which is indicated by the nanohardness values from bulk grain to grain boundary precipitates varied between 4.8 to 8.9 GPa. Comparison between prediction and experimental results shows that the calculated phase diagram was not in agreement with the solidification microstructure of the H21 tool steel.

Advanced Materials Research, 2014

The cementite precipitation behavior in the martensite and banite of the H21 tool steel under hig... more The cementite precipitation behavior in the martensite and banite of the H21 tool steel under high temperature axisymmetric compression test and double temper was investigated. The main purpose on this work is to develop a better understanding regarding the transformation mechanism of bainite and martensite in a H21 tool steel. The selected deformation temperatures were 1100 oC and 1000 oC and the double temper process was carried out at 650 oC for 1 hour respectively. The results showed that the cementite was sensitive to the stress. The applied stress has affected the Fe3C precipitation behaviour by decreasing the number of variants carbides in tempered martensite and decreasing the number of a single variant carbides in tempered lower bainite. The results were in agreement with a displacive mechanism of martensite and bainite transformation. It was also found that hot deformation temperatures selected in this work have the same contribution in decreasing number of variant carbide...

ISIJ International, 2014

Carbide precipitation in a H21 tool steel during conventional heat treatment was studied. The aim... more Carbide precipitation in a H21 tool steel during conventional heat treatment was studied. The aim of this work was to study the exact microstructure and for better understanding of carbide formation during double tempering process of the H21 tool steel. The steel was austenised either at 1 100°C or 1 250°C for 1 hour, and water quenched. Double tempering was performed at 650, 750 and 800°C for 1 hour with air cooling in the first and second temper for each austenising temperature. The results showed that the double tempered microstructure consisted of tempered martensite, lower bainite and carbides. The current study confirmed previous findings and contributed to existing knowledge that depending on the tempering temperature, the types of carbide formed during double tempering were M2C, Fe3C, M6C and M23C6 carbides. The present study findings add substantially to our understanding of the carbide formation sequence in the H21 tool steel during double tempering. No secondary peak hardening was observed, and the highest hardness (505 HV) was obtained after austenising at 1 250°C and double tempering at 650°C, which implies that the double tempering of the H21 tool steel should be carried out below 650°C.

Materials Science and Engineering: A, 2013

An axisymmetric compression test was used to study the effect of hot deformation and double tempe... more An axisymmetric compression test was used to study the effect of hot deformation and double tempering on the microstructure and hardness of a H21 tool steel. The compression tests used a constant true strain rate of 0.01 s À 1 , and were performed in the temperature range 1000-1100 1C after austenising at temperatures of either 1100 or 1250 1C. The double tempering was carried out at 650, 750 and 800 1C, with air cooling in between the first and second temper. An overview of the flow curves and the characterisation of microstructures showed no evidence of dynamic recrystallisation. The increase in flow stress with decreasing austenising and deformation temperature was attributed to dislocation movement and the presence of fine and dispersed carbides causing a Zener pinning effect. Without double tempering, the highest hardness was measured after austenising at 1250 1C, followed by deformation at 1000 1C and water quenching (617 HV). No secondary hardening phenomena occurred after double tempering for samples that were first subjected to hot deformation, and the highest double tempered hardness (354 HV) occurred after a double temper at 650 1C following an austenising temperature of 1250 1C and subsequent deformation at temperature of 1000 1C.

Journal of Failure Analysis and Prevention, 2014

The leakage of a supercritical boiler tube has been investigated. The leakage was observed during... more The leakage of a supercritical boiler tube has been investigated. The leakage was observed during a working pressure hydrostatic test under 40.1 MPa. The internal geometry of the investigated leaking tube was multi-lead ribbed tube. Various methods for investigation namely radiography, microstructural analysis using optical and scanning electron microscopes, Vickers hardness testing and chemical analysis were conducted to investigate the main cause of leakage. The results revealed that the material tube met the standard for supercritical boiler tube (ASTM A 213 Grade T12). From the microstructural analysis, there was a crack, which initiated from the outer wall adjacent to the weld metal and propagated to the inner wall of the tube. The crack was due to a weld defect known as ''excessive melt through'' which is due to overheating during the welding process in joining the tubes. It is suggested that control of welding process parameters must be accomplished during fabrication to make a furnace wall, and placing strip of steel between the tubes to reduce the fit-up gap should be considered.

Advanced Materials Research, 2014

The effects of hot axisymmetric compression to break down the primary carbide network of the H23 ... more The effects of hot axisymmetric compression to break down the primary carbide network of the H23 tool steels were studied. This current study only focused on one strain rate of 0.01 s-1. The samples were deformed at 3 different temperatures (1000, 1050 and 1100 °C) with solutioning temperatures 1100 and 1250 °C, respectively. Afterwards, the samples were cooled by water quenching. The techniques used in this current study for investigation were the optical and electron microscopes and Vickers hardness test. The results show that hot axisymmetric compression had broken down the primary carbide network in the direction perpendicular to the compression axis and the carbides became finer. Although the highest hardness (274 HV) was achieved after solutioning at 1250 °C, followed by deformation at 1000 °C, however the microstructure analysis indicated that the optimum hot axisymmetric compression condition was solutioning at 1250 °C and deformation at 1000 °C.

Engineering Failure Analysis

Journal of Failure Analysis and Prevention, 2019

A failure analysis was carried out on an A213 T91 secondary superheater tube after 4 months of ov... more A failure analysis was carried out on an A213 T91 secondary superheater tube after 4 months of overhaul. The failure caused the 600-MW coal power plant was shut down. The investigation consisted of visual inspections, microstructure analysis, Vickers hardness test, x-ray diffraction, and ash fusion temperature test and ash content analysis. The failed tube had a thin-lip rupture with sharp edges and experienced a decrease in hardness in the area of lip rupture. The microstructure analysis shows the coarse carbide and some isolated voids. Corrosion products were detected in slag deposits, and nonuniform thin oxide layer in the inner wall of the tube was observed. It is concluded that the main failure of the failed tube was due to the formation of slag deposits on the outer surface of the tube wall. This formation has resulted in simultaneously occurring phenomena, which was the localized flue gas erosion followed by the rapid overheating of the tube. The formation of slag deposits was in consequence of the use of coal with lower ash fusion temperature than required coal ash fusion temperature for the power plant.

Journal of Failure Analysis and Prevention, 2019

Your article is protected by copyright and all rights are held exclusively by ASM International. ... more Your article is protected by copyright and all rights are held exclusively by ASM International. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to selfarchive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".

Case Studies in Engineering Failure Analysis, 2017

The Forced Draft Fan (FDF) blade in a 300 MW coal fired power plant that experienced catastrophic... more The Forced Draft Fan (FDF) blade in a 300 MW coal fired power plant that experienced catastrophic failure has been investigated. There were two main locations of the blade damage, namely damage at the root of the blade and the other one is at the third of the blade height. The FDF blade has been run for 5 years and before its failure, the FDF experienced high vibration (14 mm/s). The forced draft fan is an axial flow fan horizontally in front of the boiler and the fan is single stage. Visual inspection, metallographic analysis, chemical composition and hardness test were carried out to find the cause of the failure. It is concluded that the material of the blade is cast Al-Si alloy (A356.0) that fits the requirements for FDF blade application, the failure of the third of the blade height is owing to the external particles collide to the leading edge of the blades causing erosion and notch. That notch acted as initial crack. The failure at the root blade was caused by broken fragments of the others damaged blades entered in between casing (stator) and the blade (rotor) so they obstructed the blade rotation.

I would like to express my greatest gratitude to Professor Panos Tsakiropoulos for his valuable g... more I would like to express my greatest gratitude to Professor Panos Tsakiropoulos for his valuable guidance and encouragement he provided during my study, and for giving me the opportunity to study on interesting topic in tungsten hot working tool steels. I also gratefully acknowledge to Dr. E.J. Palmiere for his support and important suggestion in every aspect of my study. I would like to thank Directorate of Higher Education, Indonesian Government and Institut Teknologi Nasional, Bandung, which helped greatly for their financial support to accomplish my study. I am also grateful to many members of technical staffs within the Sorby Centre, IMMPETUS and the Department of Materials Science and Engineering in general for all of their assistance during my study. I thank also to my friends in the department who encouraged me. Most importantly, I would like to express my deepest thanks to my parents, my husband, Setiyo Suprastiyoko, and my lovely daughters, Shafira Sari and Nadhira Ratnasari for their endless encouragement, support and love.

2020 International Conference on Power, Energy, Control and Transmission Systems (ICPECTS), 2020

Coal-Fired Power Plant Boiler 600 MW has been operated more than 20 years. Secondary superheater ... more Coal-Fired Power Plant Boiler 600 MW has been operated more than 20 years. Secondary superheater outlet (SSH Outlet) tube bursts had been occurred on this unit. Long-term overheated failure mode was observed at failed tubes on three occasions which was on September 2017, April 2018, and December 2019. The design tubes are called SA-213 T91. On April 2018 and December 2019, the powerplant operator has joined hand with two different public university research institute which are called institution-1 and institution-2 to conduct tests to find the root cause of the failure by hardness test, microstructural examination, creep test and the remaining life analysis. The results of the hardness test on the fail tube on April 2018 and December 2019 were 170.84±1.98 Harness Vickers (HV) and 168–219 HV respectively compared to the new material hardness which are on the average of 258HV. On April 2018, creep tests were resulted that expected time to failure on 750°C and 72.93Mpa was 3.6hours; on...

International Journal of Engineering Research and Technology, 2020

Ash handling unit is one of the crucial part of the operation of a coal fired power plant (CFPP).... more Ash handling unit is one of the crucial part of the operation of a coal fired power plant (CFPP). This paper focused on the investigation of shackle chain failure in ash handling unit of a 600 MW CFPP. The failure caused disruption to the operating system of the CFPP. To improve the chain system in order to prevent similar failure in the near future, the metallurgical failure analysis was conducted on failed shackle chain through crack observation using optical and electron microscope and Vickers hardness test. Crack surface observation of failed shackle chain using Scanning Electron Microscope (SEM) revealed that the failure of shackle chain was primarily due to the fatigue failure which was proven by the presence of beachmarks. In addition, there were two initial cracks which were caused by pitting corrosion. The clearance (gap) occurred in the bolt connection system caused the fatigue load which in turn resulted in failure to the CFPP operation. This research suggested preventive measures to be taken to avoid similar problem in the future.

International Journal of Engineering and Technology, 2017

Evaluation and remaining life assessment of separator and demister for 55 MW geothermal power gen... more Evaluation and remaining life assessment of separator and demister for 55 MW geothermal power generation plant have been conducted. The equipment has been used for 27 years and has stopped operating due to the failure of steam turbine. Before it is operated back, the condition of separator and demister needs to be evaluated and their remaining life assessment has to be calculated to anticipate the future repair. The methods used for evaluation were UT phased array, thickness measurement, chemical composition, hardness test and deposit composition analysis. The remaining life assessment was calculated in correlation with thickness reduction. The results showed that the chemical composition and hardness of materials met the standard of SA 516 Gr 70. No evidence of internal defect was found in both equipment. The demister in all part is still in good condition and its remaining life was beyond 20 years. In separator, the reduction in thickness extremely occurred on top head and cone. The remaining life of top head separator was below 1.2 years and cone separator was not more than 4.7 years. Deposit analysis taken from demister gave evidence the presence of sulfur, silica, iron oxide, and sulfide iron.

Key Engineering Materials, 2019

Bearing cooler coils connector of 175 MW hydropower plant experienced premature leaks after one y... more Bearing cooler coils connector of 175 MW hydropower plant experienced premature leaks after one year operation and caused an unscheduled shutdown. To avoid the same failure in the future, the leaking bearing cooler coils connector was investigated. Nondestructive tests, such as chemical composition analysis, hardness test, metallographic test, characterization of the filler brazing by scanning electron microscopy – energy dispersive X-ray spectroscopy were conducted. The results confirmed that the bearing cooler coils connector consisted of two types of material namely the flange material which was made of stainless steel 304 and the pipe material which was a Cu/Ni 90/10 and were joined together using brazing process. It was a clearly evidence that leaks occurred in the brazing area and the leakage was due to improper brazing process. It was shown by the excessive gap and a lot of porosity.

MATEC Web of Conferences, 2015

This paper reported the evaluation of a 50 MW steam turbine shaft that has exceeded the designed ... more This paper reported the evaluation of a 50 MW steam turbine shaft that has exceeded the designed lifetime (30 years). The inspection of turbine is a mandatory for safety and continued reliable operation. The shaft was made of nickel-chromium-molybdenum alloy steel. The turbine operated in the range temperature of 500-600 o C, and creep was considered to be a major damage mechanism. The remaining life assessment of the turbine shaft was also conducted using replication technique. The replica samples were taken from 125 position distributed along the turbine shaft. The microstructural analysa of replicas showed that creep had occurred, which was indicated by the cavities formation at the grain boundaries. After evaluation and assessment, it can be concluded that the turbine shaft still can be used however it needs to be re-inspected within 6 months. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits distribution, and reproduction in any medium, provided the original work is properly cited.

International Journal of Minerals, Metallurgy, and Materials, 2015

The microstructure and the stability of carbides after heat treatments in an H23 tool steel were ... more The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures (1100°C and 1250°C), followed by water quenching and double-aging at 650°C, 750°C, and 800°C with air cooling between the first and second aging treatments. Martensite did not form in the as-quenched microstructures, which consisted of a ferrite matrix, M 6 C, M 7 C 3 , and MC carbides. The double-aged microstructures consisted of a ferrite matrix and MC, M 6 C, M 7 C 3 , and M 23 C 6 carbides. Secondary hardening as a consequence of secondary precipitation of fine M 2 C carbides did not occur. There was disagreement between the experimental microstructure and the results of thermodynamic calculations. The highest double-aged hardness of the H23 tool steel was 448 HV after austenization at 1250°C and double-aging at 650°C, which suggested that this tool steel should be used at temperatures below 650°C.

Case Studies in Engineering Failure Analysis, 2014

The turbine blade in a steam turbine has an important role to convert the kinetic energy of the s... more The turbine blade in a steam turbine has an important role to convert the kinetic energy of the steam into mechanical energy [1-3]. Blade failure in a steam turbine is a prevalent occurrence and has a strong correlation with the forces acting on the blade, which are centrifugal forces, centrifugal bending, steady steam bending, unsteady centrifugal forces due to lateral shaft vibration and alternating bending [4]. Working environment of turbine blade in corrosion during operating and lay up also has a big contribution to the blade failure [5,6]. Previous investigations [5,7-9] reported that fatigue, stress corrosion cracking and corrosion fatigue were general causes that often lead to the blade failure. This paper reported the investigation of the first stage blade failure in a steam turbine, which has been operated for 12 years. The steam turbine of a 55 MW consists of five stages of turbine stator and rotor. The type of blade used in the first stage in this investigation was single T root blade assembled in slot disc of rotor. Fig. 1 shows the investigated blade, and blade terminology used in this paper. Each blade was integrated in its top by a shroud. The shrouds contact to each other that strengthen the rigidity, decrease the bending and twisting distortion and the friction occurred between the shrouds caused by blades vibration could absorb the vibration power [10]. The blade failure of the first stage was observed initially using non-destructive inspection (dye penetrant) when the steam turbine being repaired. The result found that all blades had cracks at the tang and the crack at the fillet for the blades with broken tang. The main objective of this paper was to find out the cause of failure of the first stage blade.

Transactions of the Indian Institute of Metals, 2014

The H23 tool steel contains high concentration of carbide forming elements, which affect the micr... more The H23 tool steel contains high concentration of carbide forming elements, which affect the microstructure and mechanical properties. This present study described the microstructure and mechanical properties of the as cast H23 tool steel. The steel was prepared by vacuum induction melting. The microstructural investigation used XRD and electron microscope. The nano hardness and elastic moduli of matrix and carbide were also measured. The results show that the as cast microstructure consisted of ferrite matrix and M 6 C, MC and M 23 C 6 carbides. The eutectic M 6 C carbides had two different morphologies owing to different growth mechanisms. There was agreement between the experimental results and the calculated solidification path for the H23 tool steel regarding the presence of carbides in the microstructure. The nanohardness and elastic moduli of ferrite matrix and M 6 C carbides were respectively 4.2 ± 0.2 and 10.6 ± 1.2 and 198.3 ± 10.2 and 253.5 ± 11.7 GPa.

Advanced Materials Research, 2014

Solidification behaviour of a H21 tool steel has been studied. The aim of this work is to give be... more Solidification behaviour of a H21 tool steel has been studied. The aim of this work is to give better understanding of the as cast microstructure of the steel. The investigated H21 tool steel was made using induction vacuum furnace with air cooling. The microstructure observation was carried out using optical and electron microscopy. X ray diffraction and nanohardness were also used for phase and carbide identification. The results show that the as cast microstructure consisted of ferrite and coarse primary M6C carbide that is rich in tungsten. The nanohardness of ferrite was 5.1 ± 0.3 GPa and there was inhomogeneity in as cast microstructure, which is indicated by the nanohardness values from bulk grain to grain boundary precipitates varied between 4.8 to 8.9 GPa. Comparison between prediction and experimental results shows that the calculated phase diagram was not in agreement with the solidification microstructure of the H21 tool steel.

Advanced Materials Research, 2014

The cementite precipitation behavior in the martensite and banite of the H21 tool steel under hig... more The cementite precipitation behavior in the martensite and banite of the H21 tool steel under high temperature axisymmetric compression test and double temper was investigated. The main purpose on this work is to develop a better understanding regarding the transformation mechanism of bainite and martensite in a H21 tool steel. The selected deformation temperatures were 1100 oC and 1000 oC and the double temper process was carried out at 650 oC for 1 hour respectively. The results showed that the cementite was sensitive to the stress. The applied stress has affected the Fe3C precipitation behaviour by decreasing the number of variants carbides in tempered martensite and decreasing the number of a single variant carbides in tempered lower bainite. The results were in agreement with a displacive mechanism of martensite and bainite transformation. It was also found that hot deformation temperatures selected in this work have the same contribution in decreasing number of variant carbide...

ISIJ International, 2014

Carbide precipitation in a H21 tool steel during conventional heat treatment was studied. The aim... more Carbide precipitation in a H21 tool steel during conventional heat treatment was studied. The aim of this work was to study the exact microstructure and for better understanding of carbide formation during double tempering process of the H21 tool steel. The steel was austenised either at 1 100°C or 1 250°C for 1 hour, and water quenched. Double tempering was performed at 650, 750 and 800°C for 1 hour with air cooling in the first and second temper for each austenising temperature. The results showed that the double tempered microstructure consisted of tempered martensite, lower bainite and carbides. The current study confirmed previous findings and contributed to existing knowledge that depending on the tempering temperature, the types of carbide formed during double tempering were M2C, Fe3C, M6C and M23C6 carbides. The present study findings add substantially to our understanding of the carbide formation sequence in the H21 tool steel during double tempering. No secondary peak hardening was observed, and the highest hardness (505 HV) was obtained after austenising at 1 250°C and double tempering at 650°C, which implies that the double tempering of the H21 tool steel should be carried out below 650°C.

Materials Science and Engineering: A, 2013

An axisymmetric compression test was used to study the effect of hot deformation and double tempe... more An axisymmetric compression test was used to study the effect of hot deformation and double tempering on the microstructure and hardness of a H21 tool steel. The compression tests used a constant true strain rate of 0.01 s À 1 , and were performed in the temperature range 1000-1100 1C after austenising at temperatures of either 1100 or 1250 1C. The double tempering was carried out at 650, 750 and 800 1C, with air cooling in between the first and second temper. An overview of the flow curves and the characterisation of microstructures showed no evidence of dynamic recrystallisation. The increase in flow stress with decreasing austenising and deformation temperature was attributed to dislocation movement and the presence of fine and dispersed carbides causing a Zener pinning effect. Without double tempering, the highest hardness was measured after austenising at 1250 1C, followed by deformation at 1000 1C and water quenching (617 HV). No secondary hardening phenomena occurred after double tempering for samples that were first subjected to hot deformation, and the highest double tempered hardness (354 HV) occurred after a double temper at 650 1C following an austenising temperature of 1250 1C and subsequent deformation at temperature of 1000 1C.

Journal of Failure Analysis and Prevention, 2014

The leakage of a supercritical boiler tube has been investigated. The leakage was observed during... more The leakage of a supercritical boiler tube has been investigated. The leakage was observed during a working pressure hydrostatic test under 40.1 MPa. The internal geometry of the investigated leaking tube was multi-lead ribbed tube. Various methods for investigation namely radiography, microstructural analysis using optical and scanning electron microscopes, Vickers hardness testing and chemical analysis were conducted to investigate the main cause of leakage. The results revealed that the material tube met the standard for supercritical boiler tube (ASTM A 213 Grade T12). From the microstructural analysis, there was a crack, which initiated from the outer wall adjacent to the weld metal and propagated to the inner wall of the tube. The crack was due to a weld defect known as ''excessive melt through'' which is due to overheating during the welding process in joining the tubes. It is suggested that control of welding process parameters must be accomplished during fabrication to make a furnace wall, and placing strip of steel between the tubes to reduce the fit-up gap should be considered.

Advanced Materials Research, 2014

The effects of hot axisymmetric compression to break down the primary carbide network of the H23 ... more The effects of hot axisymmetric compression to break down the primary carbide network of the H23 tool steels were studied. This current study only focused on one strain rate of 0.01 s-1. The samples were deformed at 3 different temperatures (1000, 1050 and 1100 °C) with solutioning temperatures 1100 and 1250 °C, respectively. Afterwards, the samples were cooled by water quenching. The techniques used in this current study for investigation were the optical and electron microscopes and Vickers hardness test. The results show that hot axisymmetric compression had broken down the primary carbide network in the direction perpendicular to the compression axis and the carbides became finer. Although the highest hardness (274 HV) was achieved after solutioning at 1250 °C, followed by deformation at 1000 °C, however the microstructure analysis indicated that the optimum hot axisymmetric compression condition was solutioning at 1250 °C and deformation at 1000 °C.