Failure analysis of a multiplier from a Kaplan turbine

This paper presents the failure analysis of a multiplier from a Kaplan turbine. The failed component was the pinion. The failure occurred during normal operation by cracking and consequent fracture of several teeth. Taking into account the results obtained in the destructive examination, the cause of the fracture was found to be an improper carburizing of the pinion material.     

Failure analysis of the combat jet aircraft rudder shaft

This paper analyzes failure causes of the combat jet aircraft rudder shaft (RS) which occurred during the flight mission. A finite element method (FEM), utilized to determine the stress state of the RS subjected to hinge moment ultimate load, resulted in the high stress concentration sites around the rivet holes. The longitudinal crack was initiated from the corrosion pit in the zone of the rivet hole, where the fatigue beach marks were observed. The inner surface of the RS was heavily corroded. Moreover, pitting corrosion has destroyed approximately 50% of the wall thickness. Based on the presented results it was concluded that the failure of the RS had a character of fatigue combined with heavy corrosion. Therefore, it is recommended that the RS should be redesigned; the material changed into more corrosion resistant one and the maintenance procedure changed in order to avoid future similar failures.     

Failure of two overhead crane shafts

The failure analysis of two overhead crane shafts is presented: the failure of an overhead crane drive shaft and the failure of an overhead crane gearbox shaft, due to rotating-bending fatigue. The fracture of the overhead crane drive shaft originated in small radius fillet between two different diameters of the shaft. A new shaft was made with a larger-size fillet, resulting in reduced stress concentration in this region. The failure of the overhead crane gearbox shaft originated at the intersection of two stress raisers, at the change in shaft diameter and in the keyway corner. A new shaft was made with a larger-size fillet and a larger size radius of the keyways corner to minimize stress concentration in this section. In both cases the installed couplings were replaced by gear couplings in order to allow parallel and angular misalignment as well as to avoid additional load due to misalignment. The analysis shows that the fatigue life can be significantly increased with a simple change in the structural details.     

Failure analysis of Ti6Al4V gas turbine compressor blades

The failure mechanism of Ti6Al4V compressor blades of an industrial gas turbine was analysed by means of both experimental characterisations and numerical simulation techniques. Several premature failures were occurred in the high pressure section of the compressor due to the fracture of the blade roots. Metallurgical and mechanical properties of the blade alloy were evaluated. A 2D finite element model of the blade root was constructed and used to provide accurate estimates of stress field in the dovetail blade root and to determine the crack initiation in the dovetail.

The results showed no metallurgical and mechanical deviations for the blade materials from standards. SEM fractography showed different aspects of fretting fatigue including multiple crack initiation sites, fatigue beach marks, debris particles, and a high surface roughness in the edge of contact (EOC). The numerical model clearly showed the region of highest stress concentration at the front EOC of the blade root in the dovetail region, correlated closely with the experimentally characterised fatigue crack region. It was concluded that this failure has occurred due to the tight contact between the blade root and the disk in the dovetail region as well as low wear resistance of the blade root.     

Failure analysis of steam turbine last stage blade tenon and shroud

This paper presents an analysis of the cause of steam turbine blade fractures. Recently, several L-0 blades 28.5 (725 mm) long of a steam turbine fractured 5 in. (125 mm) from the blade root platform, causing the forced outage of the turbine. A finite-element analysis (FEA) of the blade was carried out in the beginning of the last decade to calculate the natural frequencies and de vibratory stresses on the blade. A telemetry test was also conducted. The current investigation analyzed the operational data during the last two years, reviewed the results of previous studies, conducted metallurgical investigations, and identified the mechanical and metallurgical modes of the failure. The results of the investigations showed that improper welding of the shroud to the blade was the principal cause of blade fracture.     

Failure analysis of a high-speed pinion shaft

The failure of a high-speed pinion shaft from a marine diesel engine was investigated. The shaft, which had been in service for more than 30 years, failed shortly after a service operation in which the bearings were replaced. Examination of the shaft revealed cyclic fatigue as the failure mechanism, with a substantial distribution of nonmetallic inclusions near the fracture initiation site. Fracture mechanics analysis indicated that the inclusions would be unlikely to have served as failure initiation sites if only stresses acting on the shaft were induced by normal service loads. Further examination of the bearing elements revealed an abnormal wear pattern, consistent with the application of elevated bending loads to the shaft after bearing replacement. The root cause of failure was determined to be an increase in service stresses after bearing replacement along with the presence of significant nonmetallic inclusions in the pinion shaft.     

汽轮机叶片断裂失效分析

利用电子显微镜对汽轮机叶片断裂原因进行分析,结果是疲劳断裂。     

Failure of a 17-4 PH stainless steel sailboat propeller shaft

In this study, a 17-4 PH precipitation hardening stainless steel propeller shaft failed in use when installed in a sailboat working in a marine environment. Failure analysis was conducted on the propeller shaft. Results indicate that the failure was caused by the fracture of the propeller shaft by torsional fatigue and stress corrosion cracking (SCC). SCC progressed transgranulary in the martensitic matrix.     

透平膨胀机故障分析与处理

结合实际操作经验 ,主要介绍我公司 15 0 0m3/h空分设备透平膨胀机发生的几起常见故障原因 ,进行分析及处理。     

Fracture analysis of wind turbine main shaft

Shaft fracture at an early stage of operation is a common problem for a certain type of wind turbine. To determine the cause of shaft failure a series of experimental tests were conducted to evaluate the chemical composition and mechanical properties. A detail analysis involving macroscopic feature and microstructure analysis of the material of the shaft was also performed to have an in depth knowledge of the cause of fracture. The experimental tests and analysis results show that there are no significant differences in the material property of the main shaft when comparing it with the Standard, EN10083-3:2006. The results show that stress concentration on the shaft surface close to the critical section of the shaft due to rubbing of the annular ring and coupled with high stress concentration caused by the change of inner diameter of the main shaft are the main reasons that result in fracture of the main shaft. In addition, inhomogeneity of the main shaft micro-structure also accelerates up the fracture process of the main shaft. In addition, the theoretical calculation of equivalent stress at the end of the shaft was performed, which demonstrate that cracks can easily occur under the action of impact loads. The contribution of this paper is to provide a reference in fracture analysis of similar main shaft of wind turbines.     

空气透平压缩机轴振动值高的分析及处理

介绍了DH-80-20型空气透平压缩机轴振动值高的现象,详细分析了原因,阐述了所采取的处理措施,总结了在检修过程中积累的经验和教训。     

Failure analysis of a ceramic ball race bearing made of Y-TZP zirconia

Full ceramic ball bearings have some advantages compared to conventional steel bearings. They have for instance higher stiffness and hardness, lower density and reduced friction. Because they need less lubrication than steel bearings and owing to their wear and corrosion resistance they are generally materials of choice for pharmaceutical and food industries.In this work a full ceramic bearing that was used in a small mixer in the pharmaceutical industry is investigated. The bearing, consisting of two ZrO₂ rings and silicon nitride balls in between, was damaged during service because of premature wear. A failure analysis is performed by fractography and Raman spectroscopy, and it is shown that a stress induced phase transition from the tetragonal to the monoclinic phase was the reason behind the failure of the ZrO₂-rings.     

Failure analysis of a cast steel railway wheel

The failure analysis of a broken railway pearlitic cast steel railway wheel, which was involved in a train derailment, has been investigated. The fractographic results near the fracture origin of the wheel have been compared to the regions of stable (fatigue) and unstable crack propagation of cast steel fracture toughness samples. The macro and microfractographic features of the broken wheel did not show any evidence of the occurrence of a fatigue mechanism, indicating that its fracture was caused by transgranular cleavage fracture, as a consequence of the train derailment.     

Failure analysis of rolling mill stand coupling

The failure analysis of two slipper couplings showed that both couplings fractured as a result of fatigue. In both cases, the fracture started in the corner between the paddle and the coupling body and propagated around the corner. Both fractures are caused by deficient design of the fillet between the paddle and the coupling body with high stress concentration. In order to extend actual service life, three design modifications have been considered. Numerical analysis showed that redesign of coupling by stiffener between the paddle and the coupling body reduces maximum local and actual service life of couplings can be improved from finite to infinite.     

Failure analysis of drillstrings

The cost of drilling a well is measured in tens of millions of dollars. The incidence of downhole failure of the drillstring can increase this figure dramatically. The focus placed on cost reduction in the early 1990’s – when the oil price was much lower than today’s levels – resulted in some scrutiny of drilling operations, amongst other areas. Drillstring failure was a natural part of this.

Despite the earlier attention, failure of drillstrings remains to this day an undesirable feature of oilwell drilling. The costs associated with lost time (to recover the drillstring from the well or to sidetrack; and recommence drilling) and the material cost of the damaged drillstring elements can be very high. This is especially true where the failing drillstring is not detected at the wash-out stage and complete separation subsequently takes place downhole.

Premature failures commonly fall into two general groups: at the threaded connections or in the body of the drillpipe at the internal taper.

This paper presents a number of case studies from the authors’ own work that collects the results of investigations on failed drillstrings and components spanning over a decade of activity in the North Sea. Improvements in relation to design practice, manufacture, use and inspection are also discussed.     

28000m~3/h空分设备配套汽轮机运行故障分析

简介了28000 m3/h空分设备配套汽轮机的相关参数和流程,详细分析汽轮机在运行中出现的轴封汽管路堵塞、真空度波动大、真空度低和主蒸汽流道结垢等现象和原因,提出了相应的优化整改措施,确保汽轮机稳定运行。     

Failure analysis of a crankshaft made from ductile cast iron

This paper describes the failure analysis of a diesel engine crankshaft used in a truck, which is made from ductile cast iron. The crankshaft was found to break into two pieces at the crankpin portion before completion of warranty period. The crankshaft was induction hardened. An evaluation of the failed crankshaft was undertaken to assess its integrity that included a visual examination, photo documentation, chemical analysis, micro-hardness measurement, tensile testing, and metallographic examination. The failure zones were examined with the help of a scanning electron microscope equipped with EDX facility. Results indicate that fatigue is the dominant mechanism of failure of the crankshaft. It was observed that the fatigue cracks initiated from the fillet region of the crankpin-web. The absence of the hardened case in the fillet region and the presence of free graphite and nonspheroidal graphite in the microstructure of the crankshaft made fatigue strength decrease to lead to fatigue initiation and propagation in the weaker region and premature fracture.     

Failure analysis of automotive battery parts

In the injection molding process defective pieces are sometimes detected, showing weak points which break easily. In this work, the possible causes of these failure points are evaluated. Thermal analysis techniques were applied to the material to better understand the degradation that takes place with relation to the transformation process. Simulations were made to determine the possible causes of deterioration and at the same time reproduce the effects of this fragility. The creation of the weak points was simulated and their origins were determined.     

Failure analysis of bursting on the inner pipe of a jacketed pipe in a tubular heat exchanger

In order to identify the causes of a bursting incident that occurred on the inner pipe of a jacketed pipe in a tubular heat exchanger for synthesis of high pressure polyethylene, series of characterization analysis were conducted. Metallurgical structure and chemical composition of the pipe’s metal matrix were inspected by metallographic microscope (MM) and photoelectric direct reading spectrometer; scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) were applied to observe the microscopic morphology and micro-area composition on the ruptured surface; compositions of the coolant, i.e. the circulating cooling water were examined by inductively coupled plasma-atomic emission spectrometry (ICP-AES), ion chromatography (IC) and Fourier transform infrared spectroscopy (FTIR). In addition to these, finite element analysis (FEA) was employed to study the erosive effect of on the pipe. Analysis results revealed that interaction between corrosion and erosion both led by scaling, was the main cause that accelerated its thinning and eventually resulted in its premature failure. Finally countermeasures and suggestions were proposed.     

Failure analysis of a cracked concrete gravity dam under earthquake

A dynamic contact model for simulating the interaction of two surfaces divided by a dam crack, and a simplified reinforcing steel constitutive model for simulating the effect of earthquake-resistant reinforcement on a cracked dam are developed in this study. After the verification of the dynamic contact model and the reinforcing steel constitutive model by illustrations, the JINANQIAO roller compacted concrete (RCC) gravity dam is investigated with two case scenarios: a straight crack case and a curving crack case scenarios, including their dam–foundation–reservoir interaction, respectively. Emphasis is paid to analysing the failure process of the cracked dam with and without reinforcement. Results show that the cracked dam maintains a large safety margin, and the curving crack is beneficial to the improvement of earthquake resistance. Commonly applied steel reinforcement measures can effectively decrease the sliding displacement and the joint opening of the cracked dam; however, the layout of the reinforcing steel and its quantity to be used needs particular consideration.