centrifugal pump shaft failure

The chemical analysis, mechanical tests such as tensile, micro-hardness, and impact tests in addition to microstructural analysis such as optical microscopy and Scanning Electron Microscopy (SEM), Investigation on the premature failure of suspension coil spring of a passenger car, which failed within few months after being put into service, has been carried out. Manufacturing flaws are rarely the cause of shaft failures. The shafts were manufactured onboard, from AISI 304 stainless steel. Failure Analysis of Centrifugal Pump Shaft and Impeller My company two sets of oil refinery atmospheric vacuum tank centrifugal pump for the cantilever centrifugal pump, the design of the pump shaft material requirements for the 35CrMo, quenched and tempered, hardness HB = 269 ~ 302. Consequently, failure occurs in some shafts due to fatigue initiated in the stress concentration area. 42. testing, (d) residual stress measurement by X-Ray diffraction (XRD) and (e) instrumental chemical analysis. If approximately 25 vol % lower bainite appears in 673 K tempered martensite of the steel, a 1700 M Pa yield-stress grade steel with high toughness and moderate ductility levels can be attained. Shaft bent due to damage - through shipment, operation, or overhaul: Dismantle pump and inspect shaft. However, you may not have a good understanding of the reasons why centrifugal pump shafts break. The basic shaft design will address torque as the primary dynamic because torque is the most important design element (speed and power are integral factors of torque). Foreign matter in the impeller (only for the centrifugal pump). Fractography examinations revealed that the fracture mode is due to mechanical fatigue. Failure analysis has been conducted to find out the root cause of failure. Hard chromium coating technique is used to extend the service life of water pump and improving the resistance of wear and corrosion. d) Pump and drive unit misaligned. A finite element simulation was conducted in order to determine the stress topology and to identify possible critical areas. The scope of the investigation has covered among others: erosion damage recognition, tests of the investigated pumps operating conditions, spectral analysis of pressure fluctuation generated by the pump blade system as well as strength analysis of the pump shaft and the frequencies of its natural bending and torsional vibrations. Centrifugal pump composition is relatively simple, which mainly composed of four parts: prime mover, impeller, pump shell, and shaft seal device. Both Mechanical Seal and Magnetic Drive Centrifugal pumps can suffer from running dry if the pump hasn’t been designed to combat it. Comparative material analysis was carried out on samples of shaft from other pumps in service (which has not failed) to manifest that proper heat treatment of the shaft material can bring about desired mechanical properties of component and procrastinate the failure. The water after cooling either the Rolls in a rolli… [3]A collection of pump shaft failures like, corrosion failures on shafts, igue fat failures on shaftsand s haft sleeve failuresare analyzed [4] . Google Scholar. The suction line is clogged – remove the obstructions. There isn’t enough room to bend the shaft that far. Fax 843-559-2740 DOWNLOAD PDF DOWNLOAD as DOCX DOWNLOAD as PPTX. SLEEVE / SHAFT WEAR When mechanical seals fail, they tend to spin on the shaft, or shaft sleeve. The design also addresses temperature, corrosion, metallurgy, bearing location, bearing size, cantilevered components (impellers and couplings), expected axial and radial hydraulic forces, keyway (… Further, it discusses guidelines for improving reliability and reducing failure… Routine inspection of bearings, shaft sealing and impeller clearance can help reduce the need for a breakdown maintenance. 13. Failure Mode Effect and Criticality Analysis Failure Mode Effect and Criticality Analysis (FMECA) defined as that technique which is frequently used to enhance reliability of a centrifugal pump. Bent shaft. Centrifugal pump composition is relatively simple, which mainly composed of four parts: prime mover, impeller, pump shell, and shaft seal device. Chemical analysis was carried out. The second leading cause of pump breakdowns is bearing failures. # Stuffing box leaks excessively:- 01. Prajapati, B.P. This article reviews the major failure modes that are found in centrifugal pumps.In general, pump failures result in operational changes that reduce efficiency or may result in a breakdown of the pump. Crack initiation might also occur during post forging quenching. Global Failure rate Pump Failure rate (f/h) Pump A 0,000281128 Pump B 0,000169465 Applying equation 5 to calculate the reliability value for the NGL centrifugal pump system at two years for non More about that in a previous post: "How Do Laser Aligned Pumps Become Misaligned During Operation?". 14. Fracture initiated at the keyway on the propeller side as it was predicted from the finite elements analysis. Selected results were gathered during investigation of centrifugal pumps used in a sea water cooling system of one of Diesel power stations are presented in the paper. Patel, N.V. Patel. 44. Historical data was collected, visual inspection was performed and a photographic file was created. Having in-depth knowledge about the common problems and their different deciding factors that may be killing your centrifugal pump performance is a smart thing to do. Fax 864-295-6990 Imbalance causes problems while the centrifugal pump is running. Pump not primed (not full of liquid) 2. Then, knowledge of the recent development of a steel having the mixed structures for low-temperature ultrahigh-strength applications is also reported. The causes of such failure could be classified based on (a) faulty design or misapplication of the materials, According to the type of exit chamber and suction mode, it can be divided into the snail pump and guide vane pump. Pump failures result in operational changes that reduce efficiency or result in a breakdown of the pump. The Charpy impact energy is 3 J, far below the standard requirement of 54 J. Due to rattling and vibration, the key developed numerous fatigue cracks and eventually failed by crack linkages. Report DMCA . If you are author or own the copyright of this book, please report to us by using this DMCA report form. The study found that the hardness of the shaft varied radially from the core to the surface. When a shaft breaks prematurely, many people blame the manufacturer. Fatigue^ Heat treatment^ Machinery failures^ Shafts. A detailed study was carried out to determine the cause of the component failures. Download Failure Analysis Of Centrifugal Pump Shaft. SATURDAY Any irregularity in these parts will cause a drag on shaft. Though this has happened, it’s more likely that the bearings fail before the shaft. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The beater heads manufactured following the recommended heat treatment exhibited better performance (life increased by 4 times) compared to the earlier ones. However. The vibration harmonics place extra stress on the shaft of the pump. John's Island, SC 29455, Phone 843-559-3945 It could take several rounds of investigation to identify the true root cause of a packing issue. Multistage Centrifugal Pump in a Power Plant due to Shaft Crack Based on ODS and FEA 27thInternational Pump Users Symposium George R. Brown Convention Center Houston, TX September 12 -15, 2011 By: Maki Onari Mechanical Solutions, Inc. Whippany, NJ 07981 USA Tel: (973) 326-9920 www.mechsol.com 241 • Two multistage barrel type pumps for each 1200 MW Unit were installed in … failure. Pump develops cavitation when the available NPSH is increased CHECKLISTS OF CAUSES OF PROBLEMS 1 Pump does not develop any head, nor does it deliver liquid Possible Causes 1. Type: PDF; Date: December 2019; Size: 340.8KB; This document was uploaded by user and they confirmed that they have the permission to share it. Contact Us, Phone 864-295-3810 A radial-flow centrifugal pump uses a rotating impeller to create centrifugal force on a fluid, creating energy that results in flow. The investigation has shown that the fractures were caused mainly by the resonance between pump shaft torsional natural vibrations and those following from the pressure fluctuations related to the frequency of the shaft rotational speed and the number of impeller blades. 877-835-0714 For high head and low volumes the most commonly used pumps are Vertical turbine pumps. In some cases, depending on the amount of oil in the bearing housing, a slinger or flinger may be required to properly lubricate the bearing. The microstructure in the bend area and the straight section contained tempered martensite and ferrite. The pump bearings start to wear, and the shaft begins to move laterally. Dirt or grit in sealing liquid, leading to scoring of shaft or shaft sleeves 40. 43. And finally, a bit more about shafts. This article reviews the major failure modes that are found in centrifugal pumps.In general, pump failures result in operational changes that reduce efficiency or may result in a breakdown of the pump. their field of application is continuously expanding. The non-uniform hardness of the shaft surface is one of the causes of shaft failure, ... Consequently, it is not unexpected to suffer from degradation. Flaws can shorten the lifetime of shafts and cause them to fail prematurely. The impeller is made of cast iron ISO-200, and the shaft is made of 42CrMoA. But the key here is “inside the pump.” It’s possible to misalign the pump and driver and break the shaft on either side of the outboard bearing. The chemical compositions for the shafts were as per recommendation. Centrifugal pump considerations The centrifugal pump family includes radial-flow types (the most common) and axial-flow types. Microstructure was examined by means of light microscopy. Figure 1. The lesson here is simple: Don’t run centrifugal pumps at near shut-off or wide open unless you like buying shafts. Moreover. The microstructure of one of the shafts was ferritic–pearlitic and its mechanical properties were inferior to the recommended values. The last two failed pieces were received for analysis. Since centrifugal pumps are one of the world’s most widely used type of pump, their operational parameters and also their vulnerabilities are well known. Shafts operate under a widely range of service conditions can be classified into various corrosive environments and a temperature range Shafts is affected by many of loads such as (tension, torsion, compression, bending), ... Heat treatment on a welded shaft can protect the shaft from fatigue failure [5][6][7]. The connection mode of impeller and shaft is interference connection, keeping the … Data collected through the survey were subsequently analyzed. For a mechanical seal pump, running dry could lead to pump cavitation and therefore seal damage. Vibration. Some of the factors that tend to cause impeller imbalance include the following: For more information about the top three causes for centrifugal pump shafts to break contact the professionals at W. P. Law, Inc. Chemical analysis, microstructural characterisation, fractography, hardness measurement, tensile and Charpy impact tests were used for the analysis. Rotating part rubbing on stationary parts. The guidelines below might help or at least eliminate some of the more usual problems we experience in a callout: The centrifugal pump is not primed – re-prime the pump and check that the pump and suction line is full of fluid. However, this investigation reveals that both the key and the shaft failed due to materials processing issues. In table 4 the failure rate for both pump are shown. bjective was to identify the cause and location of DMW failure during service operation in power plants. The austenitizing temperature as well as tempering temperature of heat treatment was found lower at the manufacturer’s end. Manufacturing and metallurgical process flaws are one cause for centrifugal pump shafts to break. The pump bearings start to wear, and the shaft begins to move laterally. A detailed failure analysis was carried out including design calculations, visual inspection, dye penetrant inspection, magnetic particle inspection, hardness test, microstructural analysis, and fractography. The average hardness is 154 HB after annealing, and 235 HB after normalizing and tempering. According to heat treatment simulation results, hanger material was supposed to be supplied under annealing condition where the hardness fulfils the standard requirement. The centrifugal pumps served as cooling pumps are used in a heavy load diesel engine. A good agreement between predicted lifetime and inservice operating life was found. 15. failure of the rotor shaft during operation of the centrifugal pump is still reported. Incorrect fitting of the stuffing box. However, the truth is that shaft breakage is often a result of the operating conditions of the pump. Mechanical seal failure has an effect on many different parts of a pump, including the pump shaft. new applications often bring about new problems. Failure Analysis and Prevention 2. the safe design of the shaft. If you are have a pump problem chances are it is something that is on this list. Council of Scientific and Industrial Research (CSIR), New Delhi, Investigation of Torsional Fatigue Failure of a Centrifugal Pump Shaft, Improving working life of automobile water pump shaft by hard material, Failure analysis of a centrifugal pump shaft experiencing plastic deformation using the exact and finite element method, Fracture analysis of a cooling water pump shaft. As you remove the rings from the stuffing box, try to keep the rings in removal order to best determine the failure mode. The most common centrifugal-pump lubrication-application system is the oil bath fed by a bottle oiler. Consequently. If a shaft is sound, overstress can only be produced by overload, or if the load was the design criterion, overstress could be the result of inadequate design. In this review, an attempt has been made to present the effect of the morphology (shape, size and distribution) of the ductile second phase on improved mechanical properties of ultrahighstrength low-alloy steels having mixed structures, This review first discusses the effect of the morphology of the second-phase bainite on mechanical properties of high-strength low-alloy steels with mixed structures of martensite and bainite, in which great improvement in the mechanical properties of the steel has been associated with the morphology of the bainite. Hanger material is ASTM A182 Grade F22 Class 1. In order to decrease the bonnet cracking susceptibility, tempering as a heat treatment was recommended for decreasing the hardness and preventing premature failure. The major o, Failure analysis of a tool steel (AISI A2) beater head of an impact crusher and development of suitable heat treatment process to improve its performance have been presented. Toll-Free 800-476-4515 Major Failure Modes of Centrifugal Pumps. For longest coupling life, ensure the pump is laser aligned and a… Tensile test results show a tensile strength of 1015 MPa which is far beyond the minimum, A catastrophic failure of a gate valve bonnet at wellhead facilities has been presented and investigated in the current research. While this list may seem exhaustive, keep in mind 90% of all centrifugal pump problems are on the suction side of the pump. Shafts fail when the induced stress - either direct or shear - in some plane exceeds the corresponding strength of the material. Misalignment can be caused by improper installation of the pump and motor, pipe strain, even bent shafts. The investigation consisted of visual inspection, fractography, chemical analysis, characterization of microstructures using optical, Seven out of 12 pieces of hangers for superheater pipe were failed after one year in service. Bearing damaged. Most of the hydraulic equipments in Romania are operating from more than 30 years. Other system problems such as cavitation, and operating outside the best efficiency point for the pump can cause excessive vibration as well. Cut-out section of a centrifugal pump, illustrating the main components. Some users do not fill enough water before the pump is started. Contact Us, Effective March 13, 2021 Metallography Microstructure and Analysis. Up to 50% of damage to rotating equipment is directly related to misalignment. Fax 864-879-1 046 Imbalance. The significant conclusions are as follows: an ultra-high strength steel of 1900 M Pa yieldstress grade with a high toughness level can be obtained when about 60 vol % lower bainite is associated with 473 K tempered martensite of 0.60% C-1.80% Ni-0.80% Cr-0.25% Mo steel. Inherent material defect in association with deficient processing led to the failure of the spring. 43. Materials are subjected to full annealing treatment at 900°C, and normalizing at 955°C followed by tempering at 675°C. Impeller key broken or missing 5. The pieces were measured in order to record their general features and a 3-D model was generated. Microstructural investigations revealed that the failure mechanism of the bonnet is hydrogen-induced cracking (HIC) due to the presence of hydrogen, stress, high hardness and presence of corrosive medium containing chloride and sulfide simultaneously. Insufficient seal liquid. Further examinations were conducted by heat treatment simulations to explore properties after heat treatment. it is impossible to foresee the problems that may turn up in the future. Its vibration results from the displacement of its shaft from its neutral position due to some external forces, both mechanical and hydraulics, generated when the shaft rotates. To find out how seal failure affects the pump shaft, I talked to one of our most experienced service technicians. Save to your local. Since centrifugal pumps are one of the world’s most widely used type of pump, their operational parameters and also their vulnerabilities are well known. Microstructural examination showed characteristic microstructure of coarse austenite. 23. The authors of this study are not aware of any published books and papers on the relationship of the cavitation erosion of pump rotating components with the phenomenon of the resonance vibrations of the pump shaft [3,4,[6], Structure - property co-relation; suitable filler material; welding conumable, In this project work, dissimilar metal welds (DMW) consisting of low alloy steel and 304LN Stainless steel buttered with SS and Ni alloys were investigated for power plant applications. The main goal of research was to explain the reason of occurring fractures in pump shafts. After approximately seven years of operation, one of the service water pumps failed when its shaft gave way. Failure description of impeller. The key, if fails, can be easily replaced to resume the operation of the pump. 8:00 am - 12:00 pm It increased hardness (64 HRC) as well as heterogeneity of the matrix as depicted by the micro-hardness profile, and decreased the toughness (3 J) since coarse carbide networks are very hard and brittle. Contact Us, Phone 864-879-1045 Check rings for the following: Embedded Solids See if the solids are embedded in all the rings. This paper presents a pump shaft failure case and its fatigue life estimation using a new formalisation of the theory of critical distances (TCD) recently proposed by Susmel and Taylor [1-3]. An analysis of the premature failure of two counter shafts used in centrifugal pumps for lifting slurry has been carried out. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. The centrifugal pump structure can be divided into horizontal and vertical centrifugal pumps according to the position of the shaft. Major Failure Modes of Centrifugal Pumps. WITS 2050, South Africa Received 10 June 1999; accepted 26 October 1999 The last two failed pieces were received for analysis. The problems commonly encountered in a centrifugal pump are leakage, excessive noise, excessive heat, suction clog no-pumping, and damage of its components. All rights reserved. It has been found that oil quenching and tempering at suitable temperatures provide optimum microstructure and hardness, ... A shaft is a part usually cylindrical shape responsible for the transmission of power. c) Bearings worn. The shaft’s purpose is to transmit the rotational motion and power (torque) from the driver to the pump shaft components, mainly the impeller(s). 800-660-7569 Failure Analysis and Prevention, InTech (2017), 10.5772/intechopen.70672. 37. Phone 803-461 -0599 structure[ A tempered bainitic microstructure was observed for shaft B\ shown in Fig[ 2"b#[ No, signi_cant inclusions or segregations were found^ only a few pores were observed on the polished, surface[ The presence of pores are below the level of concern[ The material used for the machining, of the shafts was almost clean\ only a few oxide inclusions of D3 _ne ratings were observed[, Figure 3 shows the microstructure of the distorted region along the axis and along the transverse, direction at the key region "indicated by  in Fig[ 1# of shaft B[ Lapping of thin layers and some, smearing of metal was found near the key region "Fig[ 3"a##[ Microstructural analysis of Fig[ 3"b#, indicated the presence of plastic ~ow lines[ It is also observed that the cracks had initiated from, Fig[ 3[ Optical micrographs for shaft B at key region "marked by  in Fig[ 1# "a# along the axis and "b# along the, An SEM fractograph for shaft A is shown in Fig[ 4[ The fracture surface of the broken shaft, showed that the fracture was by fatigue "Fig[ 4"a## and the cracks initiated from the locking key, sites[ The apparent striations observed in Fig[ 4"b# are actually likely to be fractured pearlite[, Figure 4"c# shows that the cracks had initiated from the keyway region[ Propagation of secondary, cracks was also observed\ as shown in Fig[ 4"d#[ A cavity of size approximately 299Ð399, Similarly shaft B also failed by fatigue[ The presence of striations in Fig[ 5 supports the view of, fatigue failure[ Here also\ the crack had initiated from the distorted key region where some plastic, Cylindrical specimens for tensile tests were prepared from shaft B along the longitudinal direction[, The test was performed with a strain rate of 09, :s[ The stressÐstrain diagram is shown in Fig[ 6[, The yield strength\ UTS and ) elongation were found to be 429\ 649 MPa and 11[44 respectively[, The YS and UTS values were below the recommended level whereas ) elongation satis_ed the, The results of the impact tests along the longitudinal and transverse directions are given in, Hardness values were obtained from the curved surface\ as well as from the transverse cut surface[, A number of readings at various locations across the cross section of the shafts were taken in order, to determine the variation of hardness\ if any[ No appreciable variation in the hardness values was, detected across the cross section[ The average hardness values for shafts A and B were 069 and, Chemical analysis showed that the shaft was made of EN13 steel which is a recommended, material for such applications[ The shaft was of a ferriticÐpearlite nature\ whereas for this type of, shaft the _nal microstructure should be tempered martensite ð4Ł[ Proper tempering should be done, after solution followed by oil quenching and rough machining[ The impact energy obtained was, far lower than the speci_ed level[ The hardness value was found to be 069 HV\ which is also lower, than the recommended value for such applications[ According to speci_cation\ the hardness value, should be 239Ð399 HV ð3\ 4Ł[ Visual examination and fractographic study of the failed shaft, Fig[ 4[ SEM fractograph for shaft A showing "a# fatigue failure\ "b# apparent striations\ "c# crack initiation region and, Fig[ 5[ SEM fractograph for shaft B showing fatigue striations[, disclosed that cracks had propagated from one of the keyways and failure was by fatigue[ From, the above discussions\ it is clear that the heat treatment of the shaft was not properly done[, Shaft B was also made of EN13 steel\ con_rmed by chemical analysis[ The microstructure was, predominantly tempered bainite[ The hardness value was found to be 139 HV\ still below the, recommended level\ while the impact energy was as per recommendation "40 J# ð3\ 4Ł[ Though the, Fig[ 6[ StressÐstrain diagram for shaft B[, impact value satis_ed the requirement for the present application\ there was a lack of hardness, and strength which might be a prime cause for the ultimate failure of shaft B[, Again\ one of the keyways near the fracture surface was heavily deformed[ Visual as well as, microscopic analysis of the fracture shaft disclosed that the crack had initiated from the distorted, region\ shown in Fig[ 0[ Analysis of SEM fractographs con_rmed the above[ The microstructure, of the plastically deformed region shows "Fig[ 5# that the crack originated from the deformed, region and propagated radially towards the centre[ Here pulleys were assembled on the shaft by, means of shrink _tting\ which resulted in a stress raiser under bending stress[ Improper _tting may, also result in friction between the shaft and the pulley[ Friction produces wear of the shaft\ resulting, in wear induced surface roughness and fretting\ all of which might promote nucleation and growth, of cracks[ Friction can also activate metal ~ow as a result of plastic deformation[, The shafts "consisting of ferriteÐpearlite for A and tempered bainite for B# were made of EN13, steel[ The materials did not show signi_cant inclusions or segregation[ Only a few pores were, noticed on the polished surfaces[ Fractography observations revealed the signature of fatigue, failure for both cases[ The mechanical properties of the shaft materials were found to be inferior\, though the impact energy for shaft B satis_ed the requirements[ Cracks were found to have, originated from the key area of the shaft[ For shaft A\ improper heat treatment produced an, undesirable microstructure and thus resulted in a low CVN toughness and low hardness of the, shaft material[ This was the primary cause of failure[ For shaft B improper heat treatment resulted, in low values of strength and hardness which made the material more prone to failure[ Again\ the, shaft and pulley were not properly _tted\ which led to fretting between the two components and, The authors would like to thank Mr S[ Das and Dr S[ Ghosh Choudhary\ for their help, and many stimulating discussions[ They are also grateful to Prof[ P[ Ramachandra Rao for, encouragement and permission to publish this work[, ð2Ł Woolman J\ Mottrum RA[ The mechanical and physical properties of the British Standard EN Steel\ vol[ 1[, ... From the published literature on drive shaft failures, mechanical design aspects are not generally studied while materials processing/performance issues are heavily focused in failure investigations. Shaft bent due to damage - through shipment, operation, or overhaul: Dismantle pump and inspect shaft. 41. … shows the representative microstructures in the longitudinal direction for shafts A and B[ The microstructure in the transverse direction was essentially the same[ The microstructure is, Fig[ 4[ SEM fractograph for shaft A showing "a# fatigue failure\ "b# apparent striations\ "c# crack initiation region and "d# secondary cracks[, Fig[ 0[ Schematic diagram of the failed centrifugal pump[, Fig[ 2[ SEM micrograph of "a# shaft A\ showing ferriticÐpearlitic microstructure and "b# shaft B\ showing tempered bainitic microstructure[, All figure content in this area was uploaded by G. Das, Engineering Failure Analysis 5 "0888# 156Ð165, Failure analysis of counter shafts of a centrifugal pump, G[ Das\ A[N[ Sinha\ S[K[ Mishra "Pathak#\ D[K[ Bhattacharya, National Metallurgical Laboratory\ Jamshedpur 720 996\ India, Received 03 August 0887^ accepted 01 September 0887, An analysis of the premature failure of two counter shafts used in centrifugal pumps for lifting slurry has, been carried out[ Chemical analysis\ microstructural characterisation\ fractography\ hardness measurement\, tensile and Charpy impact tests were used for the analysis[ The chemical compositions for the shafts were, as per recommendation[ The microstructure of one of the shafts was ferriticÐpearlitic and its mechanical, properties were inferior to the recommended values[ For the other shaft the microstructure was tempered, bainite^ although the impact energy satis_ed the speci_cation\ the other properties "hardness\ UTS# were, inferior[ It was concluded that the improper heat treatment was the prime cause for the premature failure, A shaft is a metal bar usually cylindrical in shape "solid or hollow#\ used to support rotating, components or to transmit power or motion by rotary or axial movement[ Shafts operate under a, broad range of service conditions including various corrosive environments and a wide temperature, range[ Shafts may be subjected to a variety of loads such as tension\ torsion\ compression\ bending, or a combination of these[ Shafts are also sometimes subjected to vibratory stress ð0\ 1Ł[, Shafts are made of various materials according to their applications and requirements[ EN13, "AISI:SAE3239# steel is one of the common shaft materials[ This is a medium carbon\ low alloy, steel[ It is used where high strength and toughness are required for thick sections[ It combines deep, hardenability with ductility\ toughness and strength ð2\ 3Ł[ It also has good fatigue resistance[ This, steel can be case hardened without di.culty and _nds many applications ð4Ł[ Its properties can be, tailored by varying heat treatment schedules to get a good combination of mechanical properties, and microstructure ð5\ 6Ł[ Hardening can be done by oil quenching "up to 64 mm diameter# or by, water quenching "for larger sections# ð7Ł[ After hardening by either process\ tempering is carried, G[ Das et al[ : En`ineerin` Failure Analysis 5 "0888# 156Ð165, out to reduce internal stresses and to optimise mechanical properties[ Impact energy is one of, several mechanical properties which is governed by the tempering treatment[ It has been found, that impact toughness may di}er for various microstructures though their hardness value may be, This paper presents the analysis of failure of two EN!13 shafts used in centrifugal pumps for, lifting slurries in a power plant[ The failed shafts were made of EN13 steel[ The shafts were of 5, cm "shaft A# and 6 cm "shaft B# diameter and were required to work for at least three years of, continuous operation[ Shaft A failed only after 05 days and shaft B after 09 days of operation[ A, schematic diagram of the entire pump is shown in Fig[ 0 and the location of fracture is indicated, by arrow marks[ For both the cases\ the breakage of the shafts was found to be in the centre of, the pulley[ The tensions of the belts were given as per the recommendation of the belt manufacturer[, Prior to failure\ no abnormal vibration was observed in the bearings associated with the shafts[, Also after the shaft failure\ the bearings were found to be in good condition[ In Fig[ 0 the motor\, hydro!coupling and bearings 4 and 5 are mounted on one base whereas bearings\ 6 and 7 and the, The microstructure of the shaft material was analysed by optical microscopes and a JEOL 739, scanning electron microscope "SEM# equipped with an energy dispersive X!ray "EDX# analysis, facility[ The composition of the shaft material was determined by using a standard spectrometer, analyser as well as by using SEMÐEDX[ The samples for microstructural studies were prepared in, the usual metallographic manner both in the transverse and longitudinal direction of the shaft, axis[ They were polished and etched with 4) nital "nitric acid in ethanol#[ Fractography of the, broken shafts was carried out by SEM[ Hardness testing was performed using a Vickers Hardness, testing machine under 29 kg load[ Tensile tests were carried out on cylindrical specimens as per, ASTM standards by using a servo hydraulic INSTRON machine[ Standard sized specimens for, Charpy impact tests were made in longitudinal and transverse directions from both the shafts[ The, specimens were then tested in a Wolpert instrumented impact testing machine using 099 and 049, J hammers to get impact toughness values[, Visual examination of the failed end gave the appearance that both the shafts failed by fatigue[, A macroscopic view of the failed region of shaft B is shown in Fig[ 1[ Signs of smearing and, distortion at the key edge were observed[ Both the shafts failed at the end where the pulley is _tted, The chemical analyses for both shafts A and B are listed in Table 0[ SEMÐEDX analysis also, showed a similar composition for both shafts[ It con_rmed that they were made of EN13 steel[, Figure 2 shows the representative microstructures in the longitudinal direction for shafts A and, B[ The microstructure in the transverse direction was essentially the same[ The microstructure is, Fig[ 1[ Macroscopic view of failed end of shaft B[, Fig[ 2[ SEM micrograph of "a# shaft A\ showing ferriticÐpearlitic microstructure and "b# shaft B\ showing tempered.

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