Fracture Failure Analysis on Head of High Pressure Steam Pipe
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In order to find out the cracking causes of a head of high pressure steam pipe,the head was analyzed for the cracking morphology analysis,the fracture analysis and microstructure analysis.The results showed that the cracking failure character of the head was thermal fatigue. The main factor of the head cracking cause was the leakage of rain for a long time on high temperature head outer wall quench and produce thermal stress. Head forging process produce microstructure defects that promote the crack initiation and propagation. Combining with the actual situation,remedial measures were taken to avoid the similar failure accidents.Cite
Failure reason of vertically-cracking box of φ139.7 mm drilling pipe was studied through visual inspection,mechanical testing,metallographic examination,fracture surface analysis and considering loads added on it.Results showed that reason of failure was the Martensite layer caused by screw thread pair's severe friction.During drilling process,cracks were initiated from mansensite layer on the thread crest and brittle-vertically developed by the reason of its lateral absorbed-energy was much lower than longitudinal absorbed-energy.In the end,they lead box of drilling pipe to longitudinal-cracking failure.
Brittleness
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Structural failure of a high pressure orifice flange of an oil refinery is studied by using visual inspection, optical and electron microscopy, tensile tests, fractography and stress calculation. This flange was located at a high pressure (2700 KPa), elevated temperature (370 C°) feeding pipe line. Failure observed during a startup at the time of increasing pressure and temperature. The results of the analysis show that brittle fracture has acted as a main factor for failure of the structure and stress concentration together with corrosion have provided minor sources for the failure. These results indicate that brittle behavior of this flange can attribute to hydrogen embrittlement of the steel material.
Flange
Fractography
Refinery
Embrittlement
Brittleness
Environmental stress fracture
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The characteristics and causes of longitudinal cracking of IU X95 drill pipe with size ofφ101.6 mm×8.38 mm during using were analyzed.The results show that the drill pipe cracking was brittle,and the surface micro-crack suffered from contaminating of metal with low melting point,such as Pb and Sn,to result in poor property and crack extension easily.The dill pipe cracked when cracking extended to some degree under the action of temperature and tensile stress.
Drill pipe
Brittleness
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The causes of cracking and failures for N80Qnon-upset tubing are analyzed comprehensively by mechanical property tests,analysis of chemical compositions,microstructure and appearance of fracture.The results show that pin-end over tightening torque,pressure over-load and lowrising,high frequency vibration resulted from fracturing fluid during fracturing process are the main reasons of tube's pin-end cracking.
Upset
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Cracking happened in the welded seam between elbow and ascending pipe of a pressure pipe-line which have been used about two years,and deflection deformation of effusers belonging to the same pressure pipe-line were detected after three months.To get to the bottom of the failure cause of these two cases,this paper analyses the relative pressure pipe-line by using finite element analysis.The reasons causing cracking and deflection of the pressure pipe-line are found out and some useful conclusions are achieved.
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Fracture analysis and microstructure examination were used to investigate the crack of a stainless steel pipe installed on an aero-engine turbine.The results showed that the crack mode of the pipe was fatigue failure,which starting at the defect of the pipe side surface;the major cause of the pipe crack was defect in the welding place.
Pipe
Aero engine
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Flange
Cylinder head
Fillet (mechanics)
Metallography
Piston (optics)
Shrinkage
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A steam pressure pipe broke into pieces in the course of normal operation. The chemical composition and mechanical property analyses proved that the material of the pipe was good. However,the metallographic examination and fractographic observation showed that there were some defects in the weld joint of the pipe and the fixed bracket,where there was a zone of high stress concentration. Furthermore,mechanical analysis of the weld joint explained the reason why there was high peak stress and it indicated that the wall thickness of the pipe was too thin to endure the severe stress condition. In addition,the possibility of steam hammer or water hammer and their possible influence were discussed. Based on these analyses,it was concluded that the cracking occurred first in the weld joint between a steam pipe and a fixed bracket. And then it lead to the rupture of the whole pipe. The cracking resulted from poor quality of the welding and inapposite design of the pipe thickness as well as the structure of the joint.
Hammer
Pipe
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Two oil leaking failures of one type of aero-engine happened continuously, which were resulted from fracture of U-pipes at the joint connecting with the main pipe laying. Fix position, structure characteristics and assembly state of fracture U-pipes were inspected and the fracture surface was observed. And trial run of the same type of aero-engine was conducted. The results show that the fracture model of two pipes are the same high cycle fatigue fracture due to high original stress. Fatigue crack originated from welding line at inboard or outboard of U-pipes. The main cause of fatigue crack origination was excessive assembly stress. Bend stress resulted from shock and pulse of high pressure oil also have some effects on the crack origination. The welding defects existed in welding line promoted the origination of crack.
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