Blade Fracture Research Articles

Research on operating characteristics of a centrifugal pump with broken impeller

The operating characteristics of a centrifugal pump with broken impeller malfunction was studied by tests and numerical simulation. One blade was cut 1/4 as a broken impeller. The energy characteristics, vibration, internal flow, pressure fluctuation, and radial force of the pump were studied in detail. The test results show that as for the pump with broken impeller, the head decreased by 9.85% and efficiency decreased by 1.06% under 1.0 Q0. The vibration increase amplitudes at the outlet flange are the maximum. The APF (axial passing frequency) of all monitoring points increased significantly, and a new frequency – 5APF appeared, except for the inlet of the pump. It can be found that the low-speed region of blade fracture surface is more obvious than other blades through numerical simulation. The radial force of the broken impeller increased obviously and became more concentrated. Due to the broken blade, the peak-to-peak magnitude of pressure fluctuation at the tongue and pump outlet increased by 4.7% and 9.5% respectively. The research results provide some reference for the malfunction diagnosis of centrifugal pump.

Numerical study on the flow characteristics of centrifugal compressor impeller with crack damage

The distribution and characteristics of internal flow field of the impeller with crack damage in service environment was investigated via numerical simulation with RNG k-ε turbulence model. The diffuser and volute are added based on the original impeller to simulate the internal flow field comprehensively. It was found that along the flow direction, the pressure, velocity, and temperature of the fluid increase continuously, and the maximum value appears near the outlet of the impeller. The maximum pressure and velocity in the crack area are distributed around the middle section and the trailing edge of the crack. Entropy production theory was applied in the study of internal flow, which reveals that the entropy production becomes larger around the crack. The further propagation of the crack is promoted by the opening force perpendicular to the entrance direction of the middle crack, the corrosion propagation at the rear edge of the crack, and the thermal deformation of the blade. The accelerated crack process will finally lead to the blade fracture accident.

Catastrophic failure of urea prill-tower fan

This work presents failure investigation of a prill-tower fan that was in service for about 20 years in a urea plant. All the fan-blades and the plummer blocks fractured catastrophically during the plant-operation, shocked the plant personnel, and caused a huge shutdown loss. Standard failure analysis procedure involving: site visit, visual inspection, microstructural analysis, fracture analysis, analytical stress calculation and FEM analysis was followed. The investigation confirms that the fan-blades having numerous dents and nicks were operating in a mild corrosive atmosphere of ammonium hydroxide. The fracture analysis suggests that a pre-existing dent on the trailing edge of a blade corroded to form a pre-crack that aligned perpendicular to the long axis of the blade. When the pre-crack grew to a critical size, a small chunk of the blade fractured from the vicinity and ejected towards the blade-tip by centrifugal force. Because of confined space around the fan and limited blade-tip clearance, this triggered a chain reaction of blade fracture and rattled the entire array of fan-blades. The analysis establishes that the plummer blocks failed due to mechanical imbalance of the fan-shaft caused by the blade failure. The investigation concludes that presence of dents and nicks on the fan-blades is the root-cause for this catastrophic failure. Grinding-off of the surface defects to eliminate stress raisers is recommended for averting such a failure in future.

Crack growth simulation in 13th row of compressor blades under foreign object damage and resonant vibration condition

In this study, the cracks growth rate in the 13th row of the T56 compressor blades was studied to investigate their fatigue life. For this purpose, the centrifugal and aerodynamic forces on the blade were calculated and then the resulting stress field was obtained by using finite element method. Then, the critical points of stress were determined and the initial semi-elliptical cracks were modeled at these points. After modeling of the initial crack, the stress intensity factor on the crack front was calculated by ANSYS software. Furthermore, the number of required cycles for the crack growth and blade fracture were calculated by applying Paris law to a certain value. After crack growth at this stage, a crack with new length was also modeled at the same point and all the mentioned stages for its growth, were repeated. In this paper, the modal analysis of the blade was conducted and normal frequencies with possible stimulation on compressor velocity were determined by Campbell Diagram. After determining the stress field at resonant frequency, all stages of crack growth were repeated under these conditions to calculate the fatigue life.

Evaluation of Steam Turbine Blades Surface Cracks Detectability by Nondestructive Methods

Abstract This article describes methods suitable for crack detection on low pressure steam turbine blades, not including the blade root. These cracks, which are initiated in the corrosion pitting, can cause serious damage to the steam turbine blade leading to its breakaway. Therefore, the detection of these cracks on the early stages of blade fracture is very important. Several methods for detecting of surface cracks (ultrasonic Rayleigh waves, eddy current with flexible array probe, etc.) has been tested on artificial flaws, which were manufactured into turbine blades. The comparison of all these methods is described as well as the evaluation of their advantages and disadvantages. Simulations of ultrasonic testing are also presented in this article.

First-in-Human Cutting Balloon Broken Blade Fracture Imaged Using Optical Frequency Domain Imaging/High-Definition Intravascular Ultrasound

A 62-year-old man underwent percutaneous coronary intervention for a heavily calcified left anterior descending coronary artery lesion ([Figure 1A][1]). Despite rotational atherectomy using a 2.0-mm burr, the lesion could not be fully dilated using a 3.0 × 10 mm Wolverine Cutting Balloon (Boston

Clinico-radiological Outcomes of Using Modified Stoppa Approach for Treating Acetabular Fractures: An Institutional Review.

IntroductionAcetabular fractures are complex intra-articular fractures. The extra-pelvic ilioinguinal (IL) has been the workhorse for the anterior approach and remains the gold standard. The major difference between the IL and the Stoppa approaches is that Stoppa allows for the avoidance of the middle window of the IL approach. Hence, the modified Stoppa approach (MSA) can be adopted by a comparatively less experienced surgeon with minimal complications. The purpose of this study is to evaluate the radiological and functional outcomes of patients operated on using the MSA.Materials and methodsPatients operated on by the MSA for acetabular fractures with a minimum of one year of clinical and radiographic follow-ups were reviewed. CT scans and radiographs were evaluated for the fracture pattern, time to surgery, operative time, blood loss, quality of reduction (Matta criterion), FO [Harris hip score (HHS) and Nach Merle d'Aubigné and Postel score (NMAPS)] and complications (perioperative and follow-up). Twenty-three of 26 patients with 45 acetabular fractures operated between January 2016 and November 2018 were included. Descriptive statistics were used for demographic data, and Pearson’s chi-squared statistic was calculated for the association between radiological and functional outcomes.Results Among the 23 patients, the mean age was 38.5 years (range: 15-65) with a male-to-female ratio of 18:5. The average time to surgery was 11.5 days (range: 2-32), operating time was 155 minutes (range: 90-243), and average blood loss was 650 ml (range: 500-1,250). A supplemental lateral window was used in 20 patients (87%), and three underwent the combined anterior and posterior [Kocher Langenbacks (KL)] approach. All cases were unilateral. The transverse fracture was the most common pattern (eight patients) followed by the associated both-column fracture in six and T-type, isolated anterior column fracture, and anterior column and posterior hemi-transverse fractures seen in three patients each. Iliac blade (high anterior column) fracture was seen in 14 cases and one patient had associated sacral type II fracture. Road traffic accidents accounted for 61% of the injuries and injury severity score (ISS) of >15 (polytrauma) was seen in more than 50% of the cases (associated with other organ injuries). The radiological outcome was anatomical in 52% of the cases, imperfect in 39%, and poor in 9%. The functional outcomes were good to excellent in 74% (HHS) and 79% (NMAPS) of the cases. The association and correlation between them were nonsignificant (p-value: >0.5). Two patients developed a superficial infection and three had iatrogenic obturator nerve palsy. One patient had a direct inguinal hernia, one had grade 3 bedsores, and two patients developed grade 2 arthritic changes during the follow-up. No case of vessel injury was encountered.ConclusionAdoption of the MSA for the treatment of acetabular fractures leads to a good-to-excellent anatomical reduction in most cases while providing direct visualization of the quadrilateral plate and posterior column. The learning curve is smaller for less-experienced surgeons in terms of complications and results. We recommend this technique as a viable alternative to the IL approach for anterior acetabular fixation.

Static Frequency Test and Leaf Fracture Analysis of Turbine Blades in a Power Plant

During the overhaul of a steam turbine of a power station, the frequency of the last twostages of the low-pressure rotor is tested and high-pressure rotor-regulated stage broken blades weresubjected to macroscopic inspection and analysis, chemical composition analysis, hardness test andmetallographic microstructure observation and analysis.The results of blade frequency measurementshow that the two stages of the low-pressure rotor can be safely and stably operated at the workingspeed. The results of broken blade analysis show that: due to the surface damage in the innersurface of the blade root, the blade vibration is aggravated, and the lower step of the concavegroove of the blade root is the stress concentration zone, where the fatigue crack source is generatedand gradually expanded, resulting in fatigue fracture of the blade; The fracture fatigue source zoneand the fatigue crack growth zone occupy approximately two-thirds of the entire fracture area,indicating that the blade fracture is a high-cycle fatigue fracture.

Investigation of the Trailing Edge Modification Effect on Compressor Blade Aerodynamics Using SST k-ω Turbulence Model

A gas turbine power plant in Thailand had the problem of compressor blade fracture in Stages 6–8, which was caused by housing damage. This gas turbine has a total of 15 stages. The housing damage reduced the lifetime of blades to an unacceptable level. This article shall report the solution and outcomes. Three-dimensional (3D) compressor blade models in the problematic stages were prepared by a 3D scanning machine to find a solution based on computational fluid dynamics (CFD), and then were completed for simulation by adding Stages 5 and 9 to become a multi-stage axial model. The latter models were modified by trimming the trailing edge by 1-, 5-, and 10-mm. Using ANSYS CFX R19.2 software, the CFD results of the trailing edge modification effect on flow using the shear stress transport (SST) k-ω turbulence model revealed aerodynamics inside the problematic stages both before and after blade modifications. Modifying the blade by 5 mm was suitable, because it had lesser effects on aerodynamic parameters: pressure ratio, drag, and lift coefficients, when compared to the modification of 10 mm. The larger the modification, the greater the effect on aerodynamics. The effects on aerodynamics were intensified when they were modified by 10 mm. The validation of base line blades was conducted for the overall compressor parameters that were compared with the measurable data. These results were accepted and gave positive feedbacks from engineers who practically applied our reports in a real maintenance period of gas turbine.

Influence Analysis of Blade Fracture of Ducted Propellers of offshore platforms on Flow Field

The flow field of ducted propellers in viscous flow is analyzed and calculated with CFD technology, and the flow field and surface pressure distribution of the ducted propeller of offshore platforms with the fracture in different positions of a certain blade are simulated. Firstly, the geometrical models of the ducted propellers are established with UG software and put into the girding caved up by the Gambit. Then the numerical simulations are carried out with CFD, by which the surface pressure distribution of the ducted propellers in open water are calculated using Moving Mesh method. Lastly, the flow field characteristics of ducted propellers with the fracture in different positions of a certain blade are compared, and the result data are analyzed and summarized to gain flow field change laws. The results can be applied in project for reference.

The Fracture Analysis of Turbine Rotor Blade

Failure of aeroengine Turbine Blade in Wing seriously threatens Flight Safety, We used the emergence and development of blade cracks to discuss the causes of blade fracture. The results show that due to intergranular oxidation, alloy dilution, and thermal stress, fatigue crack spreads through the blade and results in blade fatigue fracture. During blade usage and maintenance, We avoid over usage and overheating of the engine to decrease time of maximum capacity usage.

Fracture of wind turbine blades in operation—Part I: A comprehensive forensic investigation

AbstractThe structural integrity of rotor blades is crucial to ensuring continuous power production of wind turbines. Catastrophic blade fracture can cause significant economic loss and social impact and thereby should be prevented. It is important to understand the structural failure of rotor blades particularly during their normal operation. This study presents a comprehensive forensic investigation into fracture of 2 rotor blades in the field. The investigation is carried out synthetically taking into account interactive aspects associated with operational loads, materials, manufacturing processes, and structural design. The supervisory control and data acquisition data are analyzed to understand the turbine response with damaged blades. A detailed post‐mortem investigation is carried out at structural, subcomponent, and material levels both in field and in laboratory from a forensic perspective. Different manufacturing‐induced defects are examined using X‐ray computed tomography, and they are discussed in the context of the current manufacturing and design practices. Evidences from macroscopic failure features and microscopic fractographic morphologies are collected, analyzed, and correlated in order to identify the underlying mechanisms of blade fracture. Practices are recommended to improve structural integrity of rotor blades during their entire life cycles.

Vibration Traits and Mechanism Analysis of an Engine Blades Fracture Failure

For the failure of twice centrifugal wheel blade fracture of an engine, the paper obtained the vibration traits of the fracture failure by analyzing the gross trend, time domain wave type, axial trajectory map and frequency spectrum diagram of the vibration signals at the failure time. The failure mechanism was analysed systematically based on the failure analysis of the fracture vane, the vibration characteristic analysis and stress distributing research of the vane. Finally, the paper verified the failure mechanism through the vane dynamic stress measurement test.

MICROSTRUCTURAL CRITERIA FOR DETERMINING THERMO-MECHANICAL CONDITIONS OF OPERATIONAL VULNERABILITY OF THE WORKING BLADES OF HIGH-TEMPERATURE GAS TURBINE AVIATION ENGINES

The necessity of studying the structure of the blade material and corresponding in-service structural changes is attributed, on the one hand, to the fact that the structural changes may impair the performance of the material thus promoting the blade fracture. On the other hand, the structural changes can serve as diagnostic signs in determination of thermo-mechanical conditions of the blade destruction. Moreover, the structural changes in the blade material often determine the service life of the blades: aside of creep mechanism, in-service depletion of the blade lifetime in high temperature gas turbine engines of maneuvering aircrafts is attributed to complex thermo-mechanical loading of the blades which, in turn activates the mechanisms of fatigue and thermo-mechanical fatigue. Monitoring of the structural state of the blade material with equiaxed crystallization (ZhS6U, VZhL12U), directed and monocrystallization (ZhS26, ZhS32) and studying the features of structural changes attributed to the operational vulnerability of the turbine blade material are the main goals of the study. The features of changes in the morphology of the strengthening γ’-phase and carbide transformation in the blade material that occur in-service are considered. The results of monitoring the structural state of the blade material are compared with the results of testing the same samples under laboratory conditions simulating thermo-mechanical loading. Microstructural criteria are recommended for more accurate evaluation of thermo-mechanical conditions of operating vulnerability of the turbine blades of high-temperature aircraft engines.

Blade fracture analysis of a motor cooling fan in a high-speed reciprocating compressor package

Abstract This paper presents the root cause analysis of the blade fracture of the motor cooling fan in a reciprocating compressor package. The dynamic analyses results showed that the first-order torsional natural frequency of the fan was within ±5% of the fifth-order excitation frequency. In addition, the maximum dynamic stress of the fan operating in conditions of torsional resonance was 40.88 MPa, and exceeded the allowable stress of 36.12 MPa. Furthermore, the maximum dynamic stress occurred at the same locations where the cracks initially emerged. It was concluded that the excessive dynamic stress caused by the torsional resonance was the root cause of the fatigue fracture of the fan blade. Design improvements were implemented to adjust the natural frequencies of the fan, and included reducing the height of the blades, increasing the number of blades, and changing the weld locations. After the implementation of these modifications, the first-order torsional natural frequency of the new fan avoided the resonance regions, and the maximum dynamic stress of the new fan was 0.69 MPa, which was considerably lower than the allowable stress. No fracture problems occurred on the new fan.

Structural failure simulation of onshore wind turbines impacted by strong winds

The renewable energy industry is thriving in many countries against a global backdrop of growing environmental awareness. In particular, in Taiwan, wind is emerging as a potential source. The Taiwanese government has implemented the “Thousand Wind Turbines” project as a collaboration with the private sector to construct a wind power infrastructure. However, when Typhoon Soudelor hit Taiwan on August 7–8, 2015, the towers of 2.0 MW wind turbines close to Taichung harbor collapsed and falling blades damaged one of the collapsed turbine towers. This incident of wind turbine collapse was the second in the nation and was more extensive than the previous one. This study investigates the causes of this incident and the mechanical mechanisms of turbine tower collapse and blade fracture to support risk prevention and hazard-resistant design of future wind turbines. Relevant data are obtained to simulate wind turbine collapse. Next, mechanical analyses via finite element method are carried out to identify mechanisms of failure and structural weakness planes, with the ultimate purpose of summarizing potential causes of collapse. Improvement solutions on strong wind resistance of wind turbine towers and their benefits are discussed. Finally, this study gives the recommendations on weaker blades being a safety mechanism for the wind turbine tower, torque capacity of the pitch system as well as the required strength of joint bolts to be installed in steel structural connections, so as to withstand severe storms.

Steam turbine moving blade failure caused by corrosion fatigue – case history

Corrosion fatigue has been identified as one of the leading causes of steam turbine rotor blades failure. Despite of numerous research and development in the area of preventing sudden rotor blades failure due to corrosion fatigue, in the practice these failures continue to occur. This paper just describes one of number historical cases of rotor blade fracture that was caused by corrosion fatigue. It was an industrial turbine installed in fertilizer production plant Petrokemija Kutina, Croatia. The broken blades were belonged to the turbine stage located in the phase transition zone (salt zone) of the turbine. The paper also describes the analysis of the failure cause and the modification of the turbine stage that was failed.

Failure of a Rotating Blade of a 200 MW Steam Turbine LP Rotor and Options for Eliminating other Similar Breakdowns

This contribution deals with the analysis of the failure of a rotating blade of the third wheel (L-1 stage) of the LP rotor of a 200 MW turbine at the power station in Počerady. Material analysis of the blade showed that the cause of the blade fracture was the initiation and growth of a fatigue crack from a corrosion pit. Failures of low-pressure blades have occurred repeatedly on machines of the same design in the power stations of the ČEZ group in recent years and by a similar mechanism. Therefore, based on the knowledge obtained by EPRI (Electric Power Research Institute), ČEZ, a.s. has developed a methodology which can, in real conditions during checks of turbines, reliably detect the parameters of corrosion pits and predict the possibility of development of fatigue damage from these pits. The work summarizes the methodology and the conditions of its use with an emphasis on the fields of its application.

Failure Analysis of a Blade of Blast Furnace Top Gas Pressure Recovery Turbine

In the process of running of the blast furnace top gas pressure recovery turbine, abnormal noise and vibration from the gas turbine engine were noticed. One blade was found fractured from the middle during the overhaul inspection of this machine after running. In order to avoid the similar accident from happening again, comprehensive inspections on the failed blade have been carried out with the mechanical property testing, metallographic structure observation, chemical composition analysis, macro-fracture and micro-fracture analysis, and energy spectrum analysis. The analytical results show that many spherical particles are noticed in the area of crack initiation, and these spherical particles are similar to the blade material in chemical composition. After a series of tests, it was thought that these spherical particles are the remnant of molten metal that was firstly cooled in the process of blade casting, and they became the vulnerable part in the blade. When the blade rotates at relatively high speed, the synthesis of centrifugal and aerodynamic stresses may cause the occurrence of stress concentration in the vulnerable part inside of blade, causing the initiation and propagation of crack and subsequently resulting in the blade fracture.

Structural integrity of wind turbines impacted by tropical cyclones: A case study from China

This study presents a case study on wind turbines impacted by tropical cyclones in China. A quantitative investigation is conducted by integrating aerodynamic, aero-elastic and structural analysis to provide insights into structural integrity of wind turbines under extreme wind conditions. Local mean wind profiles at each turbine site are reconstructed using threedimensional CFD calculation considering terrain topography of the wind farm. Failure modes and failure locations of rotor blades and tubular towers are predicted using finite element analysis. “The lesser of two evils” principle in the turbine design is addressed regarding the criticality of blade fracture and tower collapse. Referring to the current IEC standard for wind turbine design, it is suggested that the partial safety factor associated with failure of turbine tower should be larger than, instead of equal to, the one for the rotor blade to reduce the risk of the total loss of wind turbines in extreme wind conditions.