Verification And Safety Evaluation Of Preload Force Calculation Method For Flanged Bolted Joint System Of Fixed Tube Plate Heat Exchanger

Flange bolt connection structure is one of the most important sealed connection structures in petrochemical industry.Due to the differences in environment,temperature and pressure,connector is prone to leakage and other failures which will result in seal failure,property damage and casualties.Most of the leakage accidents of daily operation happen at the flange bolt connection part,thus reasonable fastening of flange bolt is critical for the safety operation of pressure vessel.This paper takes the flange bolt connection structure and parameters of the tube-plate and the heat-fixing tube-plate heat exchanger(hydrogen preheater)provided by a petrochemical enterprise in Lanzhou as the research object,treat bolts,flanges and a gasket as a whole.The pre-tightening force of the heat exchanger bolt is calculated by the flange bolt pre-tightening calculation method using another method of EN13445 Appendix G flange design(hereinafter referred as EN method).The bolts,flanges and gaskets were simulated and verified by using the finite element analysis software ANSYS Workbench to verify the rationality of the preload force.Combined with the safety evaluation theory,the structure is analysed for failure and safety,and corresponding maintenance recommendations are given.In this paper,through the combination of theoretical analysis,simulation and safety evaluation,the rationality of the calculation method of the pre-tightening force of the target flange bolt structure is verified.It has a certain guiding effect on the maintenance and repair of the same type of heat exchanger.The EN method is a method for calculating the conventional flange gasket bolt structure of a flange-a gasket-flange type.The target flange of this paper is an unconventional flange bolt structure,moreover,in the structure,the tube sheet has a heat exchange tube bundle passing through the hole thereof to reduce the strength of the tube sheet,but the tube bundle is connected with the tube sheet and the baffle plate to fix the flange bolt structure.Therefore,this paper regards the tube sheet as a flat cover structure,so that the bolt does not bear the shell-side medium pressure,and finally the target flange is regarded as a standard long-neck flange-gasket-flat cover flange bolt structure for preload force calculation.The CAD Inventor software was used to establish the model,and the flange bolt structure of the actual fixed tube plate heat exchanger and the flange bolt structure after the flat plate were respectively established.The calculated flange screw preload force is applied to the model and simulated by ANSYS Workbench.The results show that the two models are similar in thermal-structural coupling field analysis and their strength and tightness can guarantee the safety operation.It is indicated that the flange bolt structure of the fixed tube plate heat exchanger can be calculated by the EN method.Through the strength failure and the leakage failure,the failure analysis of the target flange bolt structure is carried out,and the failure accident tree model is established.The safety inspection table is made by the expert score analysis of the importance of each event structure.Some certain safety maintenance proposals are proposed for the failure factors of the flanged bolt connection of the fixed tube plate heat exchanger.