Failure Analysis for Cracking and Deflection Deformation of Pressure Pipe-line in Synthesis Ammonia Equipment
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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.Cite
Abstract The mechanical behaviour of end cracking during one-sided SAW was computer-simulated by thermal elastic analysis with the introduction of a dummy element. Experiments on small sized specimens and on-site large specimens have been carried out. The rotational deformation, the mechanism of formation of the end cracking and factors affecting it were investigated. It was concluded that for preventing the formation of end cracks, the end opening displacement and the rate of end opening should be reduced as far as possible. Theoretical analysis and on-site large specimen experiments showed that end cracking can be effectively prevented only if the arrangement of tack welds over the weld end is appropriate, and the stiffness and restraint of slit tab plate are moderate. By the aid of the above mentioned study, end cracking was successfully avoided in over 130 specimens of 12, 14, 16, 18 and 20mm thickness with weld length more than 1000m.
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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.
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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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Brittleness
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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.
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Pressurizer
Gate valve
Leakage (economics)
Hydrostatic test
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Jacking
Section (typography)
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Leakage (economics)
Internal pressure
Hydrostatic test
Discontinuity (linguistics)
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