Compression spring constitutive relationship, bolt pretension and flange contact with consideration of the nonlinearity of the gasket. From the results of finite element calculation from both inside and outside edge of the flange axial displacement difference (i.e. relative deflection) is then divided by the inner and outer flange diameter difference. Will take over the combined flange, gasket, bolt as a system of pre tightening, operating, 3-D nonlinear finite element simulation design and hydrostatic test condition and to the integrity and tightness was evaluated.
The conclusion is drawn as follows: 1 the selection of bolt preload is very important. One of the feasible methods is to select the proper preload by the Water formula and the finite element calculation and its strength and seal, and the 2 combined flange stress has similar distribution rule under different working conditions. Stress along the circumference of the flange to cyclical changes, the maximum stress discontinuities on the structure of the two flange connection, the flange stress strength evaluation; 3 due to the deflection of the flange bolts happen to combined tension and bending deformation. At the same time, there axial tensile stress and bending stress, and bending force can not be ignored; the gasket stress along the circumferential direction with only minor fluctuations, along the width from the inside to the outside gradually increases, this is due to the flange of the stiffness is much larger than that of the gasket, and the occurrence of deflection caused by flange 4 larger diameter, angle is large, and angle with pressure increase and change. The greater the flange angle, the more uneven distribution of the gasket stress along the width of the gasket, resulting in the narrow width of the effective seal, and even the outer side of the gasket. Therefore, the assessment of flange sealing need to be investigated from two aspects of the gasket stress and flange angle. Flange sealing rely solely on the analysis is not enough, still need to test, test leak rate is within the allowable range; 5 phosgene absorption tower combined flange at low temperature work has not yet been considered in cold shrinkage, temperature and low temperature performance data, wait for the following research.
The flange gasket under three working conditions of operation, design and hydrostatic test rap values and 2.52.75 4.125MPa according to the calculation and DN200 flange gasket under various conditions of minimum pressure stress the absolute value for the minimum pressure of 20.5MPaDN600 flange gasket stress absolute value respectively when fumed over pumping values, respectively. According to this criterion, indicating that the combination flange can meet the general requirements of the seal.
Flange angle deflection due to the three coordination deformation by 2010 ASME VIII a stiffness refers to the number and limited angular rotation of flange bending of bending deformation occurs in the bolt assembly load, internal pressure (operation) and a gasket counter force under the action of the flange body, a gasket non-uniform compression and bolts. For integral flange and angle limit of not more than 0.3 on flange rotation limit, the appearance is on the body of the flange bending stiffness is proposed, but the fundamental purpose is to guarantee the close of the flange; because of the greater the corner flange, gasket along the width of the pressure should stress distribution is not uniform, and even lead to the outboard gasket stress and crushing, the effective sealing width, increase the leakage rate. Therefore, the flange seal must be guaranteed from two aspects of the limitation of the gasket stress and the flange angle. Table 23 lists the corner of the combined flange under different conditions.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)