Stainless steel flange stud tip section creep variable

DataTime:[2016-5-18]

With neck butt welding of stainless steel flange connection within the flange surface temperature of 573 k load. Stainless steel flange and stainless steel pipe outside surface without applying thermal insulation layer, considering the air layer between the flange and bolt hole air layer, fluctuation on the surface of the stainless steel flange surface heat transfer effect the temperature distribution of the system. External surface of the stainless steel flange, bolt and nut and air contact parts, applying equivalent convective heat transfer coefficient, air layer and the upper and lower flange bolt hole air layer between the exert their equivalent coefficient of thermal conductivity.
Along the gasket by radial temperature gradually reduce outside introversion, temperature difference between inside and outside about 16 k.
On both ends of the bolt temperature from the intermediate section to reduce gradually, and along the outer diameter of flange cover to gradually reduce from the inside-out. Nut and flange interface in the highest temperature, this is because the temperature of the bolt and nut first is passed by the flanges here, in addition, flange material coefficient of thermal conductivity is bigger than bolt hole equivalent coefficient of thermal conductivity of air layer. Gasket stress along the radial distribution of the comparison operation conditions, the gasket seal pressure should not be below mP = 9 for gasket coefficient, take 3; P for the internal pressure, take 3 MPa).
After gasket stress is more than 9 mpa, will not leak. But because the gasket will occur under high temperature creep, compression is more and more big, the amount of springback ability worse and worse. When creep variable is small, but if the gasket stress is greater than the mP, gaskets should not leak, the hydraulic flange without hot tight; But when the worm variables is larger, the gasket stress may be less than mP, gasket leakage will happen at this time, need to consider the hot tight. Operating conditions of bolt stress distribution along the length direction of the inner stress distribution, stress distribution along the length direction plate flange lateral. In length to 0, and 100 mm respectively stud two points, the inside of the cross section at the top and bottom section length of 0 and 100 mm respectively stud section at the top and bottom section of the lateral of the two points. Blind flange on the maximum stress occurs in the nut and the upper and lower flange near the contact position, less stress on both ends.

Contrast is bolt due to bending moments, the inner tension and the lateral pressure, the pre-tightening force and bending moment under the joint action of the medial tensile stress is larger, the lateral smaller. After add internal pressure butt welding flange bolt stress distribution in whole with a preloaded consistent, but the stress increase. Flat welding flange on both ends of the stress increased obviously after heating, other position slightly increased.

Source: Yaang Pipe Industry Co., Limited (www.yaang.com)

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