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The Study of the Welding Technique for Big Diameter Bent Pipes Forming

Author: ShiFeng
Tutor: LiYunTao
School: Tianjin University of Technology
Course: Materials processing
Keywords: Welding Technology Large diameter elbow Forming Tensile test Crack tip opening displacement Simulation
CLC: TG457.6
Type: Master's thesis
Year: 2010
Downloads: 69
Quote: 0
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Abstract


The large caliber bends (big diameter bent pipes) refers to the diameter in 508mm, wall thickness of more than 8mm bending tube member. Large diameter elbow as important components of the pipeline system, widely used in workers apply for machinery, power machinery, and boilers, petrochemical, aerospace, plumbers Shen and other pressure vessels. Pipe bending technology at home and abroad is curved, bent over Shen Sinoma hot or not can be divided into cold bending and bending. The bending process is a complex too Shen elastic, plastic deformation over Shen. So bending over Shen Zhongrong easily cracks caused by the outer wall, the inner wall wrinkling, cross-sectional distortion, resulting in a serious accident. In view of this, we butt big caliber elbow forming that first according to the requirements for sheet metal bending, then choose the welding process and welding parameters for two parts bent pieces butt shaping. Further study the performance of welded joints of large diameter elbow, while its numerical simulation by means of ANSYS software. Curved pieces of wood material, size and use requirements analysis, manual arc welding primer, submerged arc welding process of filling and capping butt shaping. Microstructure of the welded joints of testing, analysis showed that: the presence of a large number of acicular ferrite, granular bainite in the microstructure of the base metal, a small amount of pearlite; microstructure of the heat affected zone is granular Bayesian body; capping microstructure of ferrite and a small amount of pearlite; fill welding microstructure of ferrite, a small amount of pearlite; the root welding organization for ferrite, pearlite. Tensile test, fracture scan test, the crack tip opening displacement tests on large diameter bend formability. Tensile properties of the test showed that: the location of the fracture of the welded joints, mostly in the area of ??the base metal, the welding quality, and tensile strength values ??are in line with the standards. The analysis showed: weld fracture morphology showing a large number, depth dimple fracture impact absorbed energy; parent material at the fracture morphology of the tensile specimen fracture scanning by smaller dimples gather from the shallow depth of the dimple, the relatively small number of impact absorbed energy below break welds. Crack tip opening displacement fracture toughness test results show that the welded joints: CTOD in of minus 20o weld at the mean of 1.39, while the the CTOD mean of the base metal at 0.82 and greater than 0.15. The welded joints of high strength steel having more excellent low temperature toughness in the material, a welding process is good. ANSYS software, two programs were used to simulate the temperature and stress field of large diameter bend. The first scenario: weld welded by a welding. The second option: weld welded by the multi-pass welding. Simulation Shen in life and death cell technology, the first weld zone unit \Then analyzed and solved to obtain the distribution of temperature and stress field. The results show that: the two programs to get the distribution of temperature and stress field of the same, that all welding is completed, the maximum temperature point at the top of the welding material material, temperature from the middle to the ends gradually reduced; maximum residual stress points in the fusion line at the residual stress value from the middle to the ends gradually reduced.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding process > Welding of a variety of metal materials and components > Pipe welding
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