Research On Failure Mechanism Of Barrier Fluid Bar In Polypropylene Multizone Circulating Reactor

Multizone circulating reactor is presently the most innovative and advanced facility in the process of polypropylene production. The barrier fluid bar is one of the important components to adjust the polypropylene molecular weight, and its failure could cause polymer dispersion and affect product quality, which will bring serious economic losses. Thus, through a series of tests and theoretical work,the paper investigates failure mechanism and presents effective measures for the barrier fluid bar with high engineering value. The result of the study would be useful information to prevent the similar failure, ensure intrinsic safety, to reduce property losses and casualties, and to promote safety production.This paper takes barrier fluid bar as the research object. Fracture failure mechanism of barrier fluid bar has been investigated, including physical and chemical properties tests, numerical simulation analysis of gas-solid coupling and the characteristic analysis of vibration fatigue. The main contents of this paper are as follows:Firstly, materials of barrier fluid bar were verified on physical and chemical test, including fracture morphology analysis, chemical component analysis, mechanical property analysis and metallurgigraphic analysis. Results showed that, the initiation area of fatigue crack located on the welding transition zone of the barrier fluid bar and plug with stress concentration phenomenon. And mechanical properties of barrier fluid tube failed to meet the standard criteria, such as high hardness on the external surface and low toughness, which causing crack initiation easily. Cone part plasticity was lower than the criteria with welding porosity, which could accelerate the crack propagation.Secondly, stress analysis of barrier fluid bar was under taken on fluid-solid coupling. Through simulating different operation conditions, the results showed that, periodic exciting force produced by granular flow presented a greater influence on the stress level of barrier fluid bar. Maximum equivalent stress was located in the welding transition zone which was consistent with the actual failure location. And the existence of local stress concentration brought about the weakest part of the structure.Thirdly, failure behaviors of barrier fluid bar were investigated on vibration fatigue. Combined test with simulation, the experimental and simulated values of the natural frequency were compared for the feasibility of the simulation; the natural frequency and vibration frequency were compared with these of the analysis results of vibration harmonic response, it was concluded that resonance phenomenon would happen easily under 6.726 Hz. The lowest fatigue life location was near the welding transition zone by fatigue life evaluation, which showed that the weakest part of barrier fluid bar with crack by cyclic loading led to fatigue failure after a period of operation.Finally, comprehensive analysis of fracture failure was implemented with preventive countermeasures. The results showed that flow induced vibration initiated by granular flow caused the barrier fluid bar fracture. Mechanical properties were uneven, and stress concentration existed on the welding, which created the conditions for crack initiation, meanwhile resonance phenomenon aggravated vibration fatigue damage.