Analysis of Failure Mode and Construction Improvement of Spray Tubes in Boiler Desuperheater

2013 ◽  
Vol 331 ◽  
pp. 79-83 ◽  
Author(s):  
Zhong Bing Chen ◽  
Ming Sheng Chi ◽  
Li Feng Zheng ◽  
Ji Xiong Shen ◽  
Heng Hai Lei
Keyword(s):  
Thermal Stress ◽  
Failure Mode ◽  
Fracture Zone ◽  
Fatigue Cracks ◽  
Surface Cracks ◽  
Thermal Mechanical Fatigue ◽  
Mechanical Fatigue ◽  
Thermal Fatigue Cracks ◽  
Alternating Bending ◽  
Fast Fracture

With macrographic examination, SEM observation and fracture quantitative analysis technology, the fracture fractography of a spray tube with both the mechanical stress and the thermal stress in a boiler desuperheater of a power plant was interpreted, and the failure mode and the cause were researched. Results showed that rupture of the spray tube was due to the fatigue, and further, the thermal mechanical fatigue. The alternating bending stress and thermal stress were main factors of the fracture failure. The shallow surface thermal fatigue cracks in tube inner wall were induced by thermal stress. When the thermal mechanical fatigue crack grew up steadily to the shallow surface cracks zone, fast growth occurred and the local fast fracture zone generated which had different fractographies with final fast fracture zone of the normal fatigue fracture.

Thermal Mechanical Fatigue and Creep Interaction in Turbine Housing Divider Wall Design

2016 ◽  
Author(s):  
Wei Guo ◽  
Henry Guo
Keyword(s):  
Thermal Shock ◽  
Large Deformation ◽  
Failure Mode ◽  
Internal Combustion Engines ◽  
Wall Region ◽  
Turbine Wheel ◽  
Shock Testing ◽  
Thermal Mechanical Fatigue ◽  
Mechanical Fatigue ◽  
Turbine Housing

Turbochargers are commonly used to boost internal combustion engines for both on and off high way applications to meet current emission regulations and performance requirements. Divider wall turbochargers have two exhaust gas inlets and twin scrolls with the divider cast wall connected. Turbochargers with divider wall feature could conserve an engine’s exhaust pulse kinetic energy for great turbine wheel efficiency. It is widely used in 6-cylinder engine applications. Turbochargers with divider wall configuration operate in very hostile conditions with high temperature and great thermal gradient. Using thinner divider wall feature benefits aerodynamic performance, but with the configuration turbine housing may show cracks and large deformation during thermal cycling. In order to achieve the balance between mechanic and aerodynamic, design study of a reasonable divider wall is required. This paper first presents the initial design with thinner divider wall, which experienced severe cracking problem in the divider wall location during the engine thermal shock testing. In order to capture the failure mode at divider wall region, finite element analysis (FEA) with thermal mechanical fatigue (TMF) and creep interaction is performed. The simulation repeats the failure mode very well which shows this numerical analysis method is convincing and fast for further study. Base on the failure case and successful cases, TMF with creep interaction simulation criteria is proposed. The criteria could be used as the reference for the further design, and the design should be controlled within the criteria limit. Based on the methodology and the criteria, the new design is analyzed and the simulation result shows the risk is low. Engine thermal shock testing is done for the final validation. This design has acceptable cracks and no large deformation at divider wall location under the testing condition. TMF and creep interaction gives a right and fast methodology to capture the failure mode at divider wall. Meanwhile it provides a knowledge base for the turbine housing divider wall design.

Assessment of thermal behavior of a cooling system to reduce thermal fatigue cracks in aluminum injection molds

2020 ◽  
pp. 75-86
Author(s):  
Sergio Antonio Camargo ◽  
Lauro Correa Romeiro ◽  
Carlos Alberto Mendes Moraes
Keyword(s):  
Thermal Fatigue ◽  
Cooling System ◽  
Fatigue Cracks ◽  
Cooling Water ◽  
Thermal Conditions ◽  
Thermal Gradients ◽  
Ansys Software ◽  
Cooling Systems ◽  
Thermal Fatigue Cracks ◽  
Number Of Cycles

The present article aimed to test changes in cooling water temperatures of males, present in aluminum injection molds, to reduce failures due to thermal fatigue. In order to carry out this work, cooling systems were studied, including their geometries, thermal gradients and the expected theoretical durability in relation to fatigue failure. The cooling system tests were developed with the aid of simulations in the ANSYS software and with fatigue calculations, using the method of Goodman. The study of the cooling system included its geometries, flow and temperature of this fluid. The results pointed to a significant increase in fatigue life of the mold component for the thermal conditions that were proposed, with a significant increase in the number of cycles, to happen failures due to thermal fatigue.

scholarly journals Fatigue Crack Initiation and Propagation at High Temperature of New-Generation Bearing Steel

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Zhiwei Wu ◽  
Maosheng Yang ◽  
Kunyu Zhao
Keyword(s):  
Fracture Surface ◽  
Failure Mode ◽  
Electron Backscatter Diffraction ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Optical Microscope ◽  
Bearing Steel ◽  
Fatigue Properties ◽  
New Generation ◽  
Scanning Electron

The new generation of bearing steel has good comprehensive properties, which can satisfy most of the requirements of bearing steel in a complex environment. In the presented work, fatigue properties of 15Cr14Co12Mo5Ni2 bearing steel have been investigated by means of rotating bending fatigue tests on smooth bar specimens after carburization and heat treatment. Optical microscope, scanning electron microscopy, electron backscatter diffraction, and Image-Pro Plus software were used to analyze the fracture, microstructure, and carbides. The results suggest that the fatigue strength at room temperature and 500 °C is 1027 MPa and 585 MPa, respectively. Scanning electron micrographic observations on the fracture surface of the fatigue specimens at 500 °C show that fatigue cracks usually initiate from voids in the carburized case and oxide layer on the surface of steel. The failure mode in the carburized case is a quasi-cleavage fracture, and with the increase of crack propagation depth, the failure mode gradually changes to fatigue and creep-fatigue interaction. With the increase of the distance from the surface, the size of the martensite block decreases and the fracture surface shows great fluctuation.

Heat Resistance of Ferritic Stainless Steels with 15% Chromium for Automobile Exhaust System

2011 ◽  
Vol 239-242 ◽  
pp. 1799-1803
Author(s):  
Hua Bing Li ◽  
Zhou Hua Jiang ◽  
Qi Feng Ma ◽  
Dong Ping Zhan
Keyword(s):  
High Temperature ◽  
Grain Boundaries ◽  
Thermal Fatigue ◽  
Fatigue Cracks ◽  
Exhaust System ◽  
High Temperature Strength ◽  
Temperature Oxidation ◽  
Ferritic Stainless Steels ◽  
Automobile Exhaust ◽  
Thermal Fatigue Cracks

The high-temperature strength and thermal fatigue properties of Fe-Cr-Nb-Mo ferritic stainless steel (FSSNEW) developed for automobile exhaust system were investigated. The results show that the high-temperature tensile strength and yield strength of FSSNEW are better than or equal to those of the presently applied ferritic stainless steels. The thermal fatigue cracks nucleate at the V-notch. The inclusions along grain boundaries become prior regions for initiation of the cracks. The inclusions distributed at the defects make the formation of cracks in the materials easily through the effects of cycle thermal stress and thermal strain. The length and propagated rate of thermal fatigue cracks increase with the maximum tested temperature increasing. When the maximum temperature arrives at 900°C, the high-temperature oxidation is serious along the grain boundaries, which aggravates the cracks propagating along the grain boundaries. The principle mechanism of stress assisted grain boundary oxygen (SAGBO) embrittlement can be applied to illustrate the effects of external stress on aggravating the damage caused by environmental factors. Therefore, the high-temperature oxidation is the main reason for the propagation of thermal fatigue cracks. The FSSNEW is satisfied for the applied requirement of high-temperature strength in the hot side of the automobile exhaust system.

A Method for the Analysis of the Growth of Short Fatigue Cracks

1995 ◽  
Vol 117 (4) ◽  
pp. 408-411 ◽  
Author(s):  
A. J. McEvily ◽  
Y.-S. Shin
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Material Constant ◽  
Plastic Zone Size ◽  
Surface Cracks ◽  
Zone Size ◽  
Short Cracks

A method for the analysis of the fatigue crack growth rate for short cracks has been developed and is applied to the case of fatigue crack growth of short surface cracks in a 1045 carbon steel. The method entails three modifications to standard LEFM procedures. These modifications include the use of a material constant to bridge between smooth and cracked specimen behavior, consideration of the plastic zone size to crack length ratio, and incorporation of the development of crack closure. Comparisons are made between calculations based upon this approach and experimental data.

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