| The metal lens pad seal has a small effective contact area,can obtain a high contact stress,and is easy to realize a high-pressure seal.Therefore,the metal lens pad is widely used in a high-pressure pipe connection.However,in use,not only the internal pressure of the medium and the load of the bolt are used,but also the external bending moment load generated by the thermal deformation in the pipeline system often causes the leakage failure of the bolted pipe flange connection structure.In this paper,based on the consideration of internal pressure and preload of bolts,the mechanical behavior of bolted flange joints under external bending moments is studied.A simplified method for the theoretical analysis of metal lens pads under external bending moments is established.The sealing performance of the lens flange bolt connection structure under the action of the moment provides a reference.The main work and research results of this paper are as follows:External bending moments are experimentally studied through the lens mat flange connection structure of two adjacent bolt symmetry planes.The pressure drop method is used to measure the total of 14 kinds of metal lens pad flanges under different preloads with the change of external bending moment.Connection structure leakage rate changes.The strain changes in the whole process of preloading,pressurizing and external bending moments of the bolts were measured by affixing two strain gauges at intervals of 180° to each bolt polished rod section.At the same time,a three-dimensional finite element model corresponding to the experiment was established.The numerical simulation calculation of the flange connection structure of the metal lens pad under various working conditions was performed.Finally,a simplified method for the theoretical analysis of the metal lens pad under the external bending moment was established through theoretical derivation.Comparative analysis of the experiment,finite element simulation and theoretical derivation under different conditions of the bolt load changes,the results are basically consistent.According to the experimental results of the sealing performance of the metal lens pad flange connection structure under the action of external bending moments,it can be seen that the circumferential indentation of the metal lens pad shows an obvious phenomenon of uneven distribution,and the width of the indentation at the “pressurized” side is wider and “pulled”.The lateral indentation width is narrow;the relationship between the leakage rate LR and the external bending moment M is nonlinear,showing a two-stage change trend,when the pre-tightening force is 230 kN or 240 kN,the internal pressure is 2.0MPa,and the metal for DN50 Lens gasket bolt flange connection structure,when M <3.5kN · m,the leakage rate with the increase of the external bending moment showing a steady increase in the trend,when the external bending moment M> 3.5kN · m,the leakage rate of growth rate Obviously increased.The influence of the external bending moment on the contact stress distribution of the gasket was investigated.The results showed that the contact stress of the gasket before the external bending moment was evenly distributed in the circumferential direction of a narrow strip of the metal lens pad,with the increase of the external bending moment,The contact stress of the metal lens pad gasket shows a non-uniform distribution on the circumference,and the tendency of this uneven distribution becomes more and more significant with the increase of the external bending moment.The contact stress of the lens pad is the largest in the central area of the contact width and gradually decreases along both sides until it reaches zero.The contact stress of the spacer in the sealing contact area is not uniformly distributed in the radial direction,and the contact stress distribution area in the outer diameter direction of the lens pad is larger than the inner diameter direction.Contact stress distribution area. |
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