International Journal of Modern Research in Engineering & Management (IJMREM) ||Volume|| 2 ||Issue|| 3 ||Pages|| 13-17 || March 2019 || ISSN: 2581-4540
Failure Analysis of Boiler Tubes at LPGCL (Khanote) 1
Ahmed Abdullatif, 2Dr. Dur Muhammad Pathan, 3Dr.Muhammad Ishaque Abro 1,
M.E Research Student (Manufacturing engineering), Directorate of Post Graduate, M.U.E.T, Jamshoro 2, Professor, Department of Mechanical Engineering, M.U.E.T, Jamshoro 3 , Professor, Department of Metallurgy and Material Engineering, M.U.E.T, Jamshoro
------------------------------------------------ABSTRACT---------------------------------------------------------Failure of boiler tubes in a thermal power plant is a very common phenomenon. So run the plant safely it is imperative for every plant owners to investigate the reason of failure and find out the remedies to prevent frequent plant shut downs. This paper, therefore, aims to provide the failure analysis report of boiler tubes at Lakhra Power Generation Company limited LPGCL (Khanote). The investigation is comprised on visual examination, fractography analysis, microstructural investigations and chemical analysis of the tube material. Optical microscope, Scanning electron microscope (SEM), X-Ray diffraction (XRD) and electron dispersion spectroscopy (EDS) techniques were used. Results indicated that the major cause of failure was localized short-term overheating of the tube due to improper material used for manufacturing of boiler tube. The fracture appearance is called fish mouth opening.
KEYWORDS: Failure analysis, Boiler tubes, Thermal power plant, Lakhra Coal ---------------------------------------------------------------------------------------------------- ----------------------------------Date of Submission: Date, 18 February 2019 Date of Accepted: 24. February 2019 --------------------------------------------------------------------------------------------------------- -----------------------------I. INTRODUCTION According to Babcock and Wilcox failure of boiler tube is a common cause in any fossil fuel/coal fired boiler and to run the boiler on line and safely it is important to find the cause of failure and eliminate it [1]. Pakistan has only coal power plant in public sector. It uses coal that comes from Lakhra coal mines and the reason its name is Lakhra power plant. Coal fired boiler is being used in LPGCL power plant and it was installed in capacity of 150 MW. It comprises of 3 units with the rated capacity of 50 MW each. In the service of twenty two years many failure of boiler tubes were observed in the steam generation tubes. The failure mechanism for the tube was the hydrogen damage which makes the tube metal brittle and initiation and coalescence of inter-granular cracks resulted in the tube failure by using VE, SEM and EDS [2]. Super heater tube was analyzed by M.E, V.E and by empirical formula for operating temperature estimation. The failure caused by a local overheating temperature due to the clinker formation because of using low quality coal for combustion.[3]. A leakage in 304H tube due to stress corrosion cracking. M.E, SEM, XRD, and EDS were used for its failure analysis [4].EDX was used to investigate the cause of failure. The failure observed in form of fish-mouth open rupture in one tube and pinhole in another tube. The results showed that failure was caused due to presence of corrosive environment of sulfuric acid (H2SO4) [5]. II. METHODOLOGY Failed boiler tubes were carried out from the plant for visual examination. Subsequently, the specimens were cut along the cross section of tubes near the failures and away from failure regions for fractography analysis, metallography and chemical analysis. Scanning electron microscope (SEM), energy dispersion spectroscopy (EDS), and spark emission spectroscope (SES) were used for the failure analysis.
III. RESULTS AND DISCUSSION Visual Examination: Visual inspection was carried out by the naked eyes and photographs were taken by digital camera.
Fig1: Thin-lipped rapture and knife edge. And also known as fish mouth opening observed which reveals rapid over heating over the designed working temperature.
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Failure Analysis of Boiler Tubes at LPGCL… Chemical Analysis : According to the manufacturer, the steam generation boiler tube is made of 12Cr1MoV steel. Chemical analysis of the tube was carried out with Spark Emission Spectrometer (SES). Elements Carbon Silicon Manganese Chromium Molybdenum Vanadium
Measured 0.212 0.168 0.423 0.0153 0.0169 00
Required [6] 0.08-0.15 0.17-0.37 0.4-0.7 0.9-1.2 0.25-0.35 0.15-0.3
Elements Nickel Phosphorous Aluminum Copper Tungsten Iron
Measured 00 0.008 0.015 0.052 0.060 99.02
Required [6] ≤0.3 ≤0.35 -----
Table 1: shows the chemical composition of the tube and compared with the standard composition of the tube. [6] Fractography : Specimens were examined by Scanning Electron Microscope (SEM) after chemical etching in HCL, some fractographical images were taken by SEM, as shown below
Fig 2: Shows a large cavity/void on the surface of the specimen near the fracture.
. Fig3: Shows small sized micro-voids/dimples were observed on the surface of the specimen.
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Failure Analysis of Boiler Tubes at LPGCL‌
Fig 4: Some micro cracks on the surface of the specimen
Fig 5: An image taken by SEM at the tip of the specimen which shows the cracks propagation till the fracture. EDS Analysis
Table 2: EDS Analysis: in the mid of the crack which shows the presence of high silicon contents.
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Failure Analysis of Boiler Tubes at LPGCL‌
Table 3: EDS Analysis: reveals high contents of silicon as well as sodium contents.
IV. MICROSTRUCTURE ANALYSIS Optical Microscope : Microstructural examination was carried out by optical microscope after grinding, polishing and etching process. Some images were taken by optical microscope.
Fig6: Shows the microstructure of the sample at the center in which the black lines show the pearlitic zone. The microstructure is fine grained ferrite and pearlite structure. (Image was taken by OM at 200X)
Fig7: Shows the tip of the sample which shows the intergranular cracks propagation till the fracture (Image was taken by OM at 100X)
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Failure Analysis of Boiler Tubes at LPGCL… V: CONCLUSION 1. 2. 3. 4.
5. 6. 7.
The material composition is not the same as it was recommended by the manufacturer shown in the chemical analysis. Chromium and molybdenum are the main elements of the tube which are totally absent in the composition. High concentration of Silicon dioxide (SiO2) was found in the material near and in mid of the cracks. A fish mouth opening and knife edge i.e. thin-lipped rapture type failure was found which was caused by rapid over heating over the designed working temperature and rapid overheating take place because of poor circulation of water in the tubes. Presence of sodium, sulphur, oxygen, potassium which clearly points towards the disturbance in the water chemistry. Presence of oxygen causes oxidation, which results a wall thinning, which leads to fracture existence. The microstructure is a fine grained ferritic-pearlitic structure. The intergranular cracks are originated from the voids present in the microstructure.
REFERENCES [1] [2] [3] [4] [5] [6]
Babcock and Wilcox, Boiler tube Analysis, Babcock and Wilcox Power Generation group, 2005,p1. Neal Hanke: Evaluation of a Failed Water Wall Boiler Tube. J Fail. Anal. And Prevent. (2012) 12:11–15 M.M. Rahman a, J. Purbolaksono a, J. Ahmad b Root cause failure analysis of a division wall super heater tube of a coal-fired power station. Engineering Failure Analysis 17 (2010) 1490–1494 A.SaadAbou-elazm , I. El Mahallawi R. Abdel-karim , R. Rashad “Failure investigation of secondary super-heater tubes in a power boiler “Engineering Failure Analysis 16 (2009) 433–448 M. Mobin Æ A. U. Malik Æ M. Al-Hajri . Investigations on the Failure of Economizer Tubes in a HighPressure Boiler. J Fail. Anal. And Preven. (2008) 8:69–74 Chinese Standard: GB/T 17107–1997.
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