Failure Analysis of the Stacker Crawler Chain Link

Stacker ARs 2000 presents the final link in the system for continuous overburden removal in the open pit mine "Kostolac" Serbia. Its superstructure leans on three crawlers of the same length, width and height. During the stacker's travel from the erection site to the open pit mine, three crawler chain links fractured, presenting an indication of the problems that were to occur during exploitation. In fact, after only 1000 working hours (about three months), 30 chain links sustained fractures resulting in direct and indirect costs due to the downtime that substantially diminished the effects of the overburden removal system. The goal of the study presented in the paper was to diagnose the cause of chain link breakdown occurrence. Working stresses in the chain link are defined by applying FEM. Experimental investigations define the chemical composition, the tensile properties, the impact toughness and the macro and microhardness. Metallographic examinations are conducted additionally. Based on the results of the numerical-experimental analysis, it can be concluded that chain link breakdown is predominantly caused by (a) substantial deviation of the mechanical properties of the material with respect to those prescribed by the standard and (b) the existence of macro and microcracks in the material structure

Failure Analysis of the Tower Crane Counterjib

Failures of the cranes' structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (x1425C) counteijib. The crane is used for assembly works at the hydropower dam. The counteijib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect

Failure Analysis of the Stacker Crawler Chain Link

Stacker ARs 2000 presents the final link in the system for continuous overburden removal in the open pit mine "Kostolac" Serbia. Its superstructure leans on three crawlers of the same length, width and height. During the stacker's travel from the erection site to the open pit mine, three crawler chain links fractured, presenting an indication of the problems that were to occur during exploitation. In fact, after only 1000 working hours (about three months), 30 chain links sustained fractures resulting in direct and indirect costs due to the downtime that substantially diminished the effects of the overburden removal system. The goal of the study presented in the paper was to diagnose the cause of chain link breakdown occurrence. Working stresses in the chain link are defined by applying FEM. Experimental investigations define the chemical composition, the tensile properties, the impact toughness and the macro and microhardness. Metallographic examinations are conducted additionally. Based on the results of the numerical-experimental analysis, it can be concluded that chain link breakdown is predominantly caused by (a) substantial deviation of the mechanical properties of the material with respect to those prescribed by the standard and (b) the existence of macro and microcracks in the material structure

Failure Analysis of the Tower Crane Counterjib

Failures of the cranes' structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (x1425C) counteijib. The crane is used for assembly works at the hydropower dam. The counteijib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect

Residual strength assessment of cracked welded spherical storage tank

Dva sferna rezervoara za amonijak (zapremine 1000 m3) su ispitana 1998. i 1999. tehnikama bez razaranja (NDT) u skladu sa Propisima za periodičnu kontrolu. Ovi rezervoari su izrađeni 1979. od čelika StE 460 prema DIN, mikrolegiranog Cr-Ni-Ti, debljine 30 mm. Uočen je veliki broj poprečnih prslina u metalu šava i uzdužnih prslina u zoni-uticaja-toplote (ZUT) i po liniji stapanja unutrašnjih zavarenih spojeva. Da bi se procenila zaostala čvrstoća oba rezervoara, ploče 500 x 500 mm, su isečene radi hemijskog, metalurškog i mehaničkog ispitivanja. Ova ispitivanja su obuhvatala detaljno određivanje žilavosti standardnih Šarpi epruveta na instrumentiranom klatnu i ispitivanja mehanike loma na standardnim SEN(B) epruvetama za ocenu žilavosti loma. Na osnovu rezultata Šarpi ispitivanja i ispitivanja mehanike loma ocenjena je preostala čvrstoća sfernih rezervoara sa prslinama.Two spherical storage tanks for ammonia (volume 1000 m3) have been tested in 1998 and 1999 by Non-Destructive Techniques (NDT) in accordance with the Periodic Inspection Regulations. These storage tanks have been constructed in 1979 of St.E460 steel according DIN, Cr-Ni-Ti microalloyed, 30 mm thick. The large number of transverse cracks in weld metal and longitudinal cracks in heat-affected-zone (HAZ) and along fusion line of inner welded joints have been detected. In order to assess the residual strength, of both storage tanks, plates 500 x 500 mm were cut for chemical, metallurgical and mechanical testing. These testing included detailed toughness testing of standard Charpy specimens on instrumented pendulum, and fracture mechanics testing on standard SEN(B) specimens for fracture toughness evaluation. Based on results of Charpy and fracture mechanics testing residual strength of cracked storage tanks has been assessed

Residual strength assessment of cracked welded spherical storage tank

Dva sferna rezervoara za amonijak (zapremine 1000 m3) su ispitana 1998. i 1999. tehnikama bez razaranja (NDT) u skladu sa Propisima za periodičnu kontrolu. Ovi rezervoari su izrađeni 1979. od čelika StE 460 prema DIN, mikrolegiranog Cr-Ni-Ti, debljine 30 mm. Uočen je veliki broj poprečnih prslina u metalu šava i uzdužnih prslina u zoni-uticaja-toplote (ZUT) i po liniji stapanja unutrašnjih zavarenih spojeva. Da bi se procenila zaostala čvrstoća oba rezervoara, ploče 500 x 500 mm, su isečene radi hemijskog, metalurškog i mehaničkog ispitivanja. Ova ispitivanja su obuhvatala detaljno određivanje žilavosti standardnih Šarpi epruveta na instrumentiranom klatnu i ispitivanja mehanike loma na standardnim SEN(B) epruvetama za ocenu žilavosti loma. Na osnovu rezultata Šarpi ispitivanja i ispitivanja mehanike loma ocenjena je preostala čvrstoća sfernih rezervoara sa prslinama.Two spherical storage tanks for ammonia (volume 1000 m3) have been tested in 1998 and 1999 by Non-Destructive Techniques (NDT) in accordance with the Periodic Inspection Regulations. These storage tanks have been constructed in 1979 of St.E460 steel according DIN, Cr-Ni-Ti microalloyed, 30 mm thick. The large number of transverse cracks in weld metal and longitudinal cracks in heat-affected-zone (HAZ) and along fusion line of inner welded joints have been detected. In order to assess the residual strength, of both storage tanks, plates 500 x 500 mm were cut for chemical, metallurgical and mechanical testing. These testing included detailed toughness testing of standard Charpy specimens on instrumented pendulum, and fracture mechanics testing on standard SEN(B) specimens for fracture toughness evaluation. Based on results of Charpy and fracture mechanics testing residual strength of cracked storage tanks has been assessed

Procena čvrstoće zavarenih spojeva na tankim cilindričnim ljuskama oslabljenim aksijalnom prslinom, modifikovanom rei metodom

U radu su analizirani modifikovana REI metoda i mogućnost njene primene na zavarene spojeve tankih cilindričnih ljuski, ne uzimajući u obzir specifičnost zavarenih spojeva (heterogenost strukture, zaostale napone i geometrijske nepravilnosti), a sve sa ciljem dobijanja dovoljno tačne i jednostavne inženjerske procedure za određivanje sila rasta prsline (SRP) u zavarenim spojevima u kojima su prisutni zaostali naponi i geometrijske nepravilnosti. U radu su prikazane modifikacije radi uprošćenja REI metode i mogućnosti izrade odgovarajućeg programa u cilju brže primene procedure.The modified REI method and possibility of its application to the welded joints of this cylindrical shells have been analyzed in the paper, without taking into consideration specificity of welded joints (heterogenity of structure, residual stresses and geometric irregularities), in order to obtain quite correct and simple engineering procedures for determination of crack grow forces in welded joints in which there are residual stresses and geometric irregularities. The modifications for REI method simplification and possibilities of producing suitable program in order to speed up application of procedure have been reviewed in the paper

Procena čvrstoće zavarenih spojeva na tankim cilindričnim ljuskama oslabljenim aksijalnom prslinom, modifikovanom rei metodom

U radu su analizirani modifikovana REI metoda i mogućnost njene primene na zavarene spojeve tankih cilindričnih ljuski, ne uzimajući u obzir specifičnost zavarenih spojeva (heterogenost strukture, zaostale napone i geometrijske nepravilnosti), a sve sa ciljem dobijanja dovoljno tačne i jednostavne inženjerske procedure za određivanje sila rasta prsline (SRP) u zavarenim spojevima u kojima su prisutni zaostali naponi i geometrijske nepravilnosti. U radu su prikazane modifikacije radi uprošćenja REI metode i mogućnosti izrade odgovarajućeg programa u cilju brže primene procedure.The modified REI method and possibility of its application to the welded joints of this cylindrical shells have been analyzed in the paper, without taking into consideration specificity of welded joints (heterogenity of structure, residual stresses and geometric irregularities), in order to obtain quite correct and simple engineering procedures for determination of crack grow forces in welded joints in which there are residual stresses and geometric irregularities. The modifications for REI method simplification and possibilities of producing suitable program in order to speed up application of procedure have been reviewed in the paper

Failure of the bucket wheel excavator buckets

Buckets are a vital substructure of all digging machines, and are intended for the realisation of the fundamental machine function - soil excavation. This paper presents the results of the experimental-numerical investigation of the cause of the bucket wheel excavator SRs 470 buckets failure. The chemical composition and mechanical properties, the impact toughness, hardness, tendency to cracks and the microstructure were determined using appropriate tests. Experimental examinations of working and residual stresses were performed using strain gauges. The superposition of the experimentally determined working and residual stresses and the calculation of the total principal stresses were conducted using the originally developed procedure presented in this paper. The bucket working stress state was calculated by applying the linear finite element method. Conclusions based on the investigation results show that the main reasons for the buckets failure were the 'design-in defects' - oversights made during the procedures of geometrical shaping and material selection. Furthermore, high values of residual stresses, as well as the cold cracking observed on the welded joint of the knife and the bucket body, suggest that the 'manufacturing-in defects' also played a significant role in the failure. The superposition of influences of the 'design-in defects' and the 'manufacturing-in defects' has conditioned the appearance and propagation of long-term fatigue cracks, leading to the total destruction of the buckets. The fact that buckets' failure appeared due to oversights made during geometrical shaping, material selection and manufacturing further points to the importance of the critical approach implementation during the design phase of the earthmoving machines working devices

Reliability of critical welded joints in responsible support structures of bucket wheel excavator

Structural reliability and integrity include analysis of state, diagnostics of structural behaviour and compliance, life assessment and revitalization of structures. Aside to assessment based on flaws detected by non-destructive methods, these disciplines also include stress state analysis. Detailed distributions of displacement, deformation and stress are acquired determining “weak” locations. This approach is important for structures exposed to complex dynamical loads as bucket wheel excavators. Fatigue research deals with welded joints as critical locations in welded structures. Under variable loads, stress concentration effects are pronounced not only by geometry and shape, but also by flaws. Flaws originate in design and construction, or in the technology, inspection and testing. Multiple parameters become critical compared to base material. Reliability is observed with more complexity as the probability of proper functionality of responsible welded joints in prescribed working conditions and operating life. The relationship between probability of failure and the degree of overlapping and shape of critical and working stress spectra are clarified and enable reliability determination in responsible welded joints.Navedeni su: Editor