Research On Stress Relaxation Of The Floating Head Heat Exchanger Sealing System In A Atmospheric And Vacuum Distillation Unit

Flange sealing system is a kind of sealing structure, easy to remove the connection of the sealing structure, widely used in all kinds of equipment of petroleum chemical industry. The most active flange sealing system is exposed outside directly, without the thermal insulation, which leads to a great deal of energy waste. However equipping the flange sealing system with thermal insulation blindly may cause leakage accidents extremely easy. Therefore, the research of stress relaxation in flange sealing systems can provide a feasible method of heat preservation for the flange sealing systems lacking of heat preservation, which can save energy. To the flange sealing system with heat preservation system, it can provide a reliable forecast for flange sealing system in the behavior of the long-term stress relaxation, which can prevent accidents.The author chooses floating head of heat exchanger as research object, takes35CrMoA and40MnB material sample processing to set the stress relaxation experiments. Then, combining the measured data of the trial with the stress relaxation mechanism based on the relaxation, estimated the stress relaxation life of floating head heat exchanger in sealing system. Meanwhile, from different angle to estimate the floating head heat exchanger sealing system life, according to checked creep data of40MnB and35CrMoA steal combined with the stress relaxation mechanism based on creep. Taking the flange sealing system as a whole, comprehensively considered of the stress relaxation effect from bolts and gaskets, used the finite element analysis software establish the floating head heat exchanger model based on the three dimensions, analyzed the stress relaxation life of heat exchanger sealing system with heat preservation. Changing bolt material or size can prevent the leakage of the floating head heat exchanger with heat preservation. The author analyzed the improvement measure of heat preservation for flange sealing system.Stress relaxation test shows that, under40℃temperature,40MnB steel resistance to stress relaxation performance is poorer, stress as time down significantly; And35CrMoA under400℃temperature steel has a good high temperature performance and stress relaxation performance. Based on the relaxation of the calculation results and based on creep calculation results can match better and computation show that the40MnB bolts floating head heat exchanger with heat preservation may stress relaxation in three days and cause out, using35CrMoA bolts heat exchanger with heat preservation can keep effective seal for three years. The finite element analysis found that gasket seal stress was along with the development of the stress relaxation gradually reduce, from the zero moment as time down in a linear relationship. The stress relaxation development of40MnB material bolt flange seal system under the condition of thermal insulation can occur rapidly. Heat exchanger in50days or so may leak and fall to failure, while35CrMoA bolt flange sealing systems can keep for a long time effective seal (more than three years).Changing the bolt material with35CrMoA alternative40MnB found that the heat exchanger effective steal time extends greatly after changed the material bolts; Increased by40MnB bolt diameter, recalculation shows that, simply increase the bolt diameter can’t improve the flange sealing systems stress relaxation problem. Therefore, the selection of excellent performance of high temperature resistance and good stress relaxation performance materials is the basic way to solve the flange sealing systems stress relaxation.