The Failure Analysis Of Stirred Vessels Mechanical Seals And The Study Of Their Monitoring System

The stirred vessel is one of the core equipments in petroleum chemical, chemical fiber, pharmacy and other industries. Shaft seal is the key factor that influences the properties of stirred vessels. At present, most of the stirred vessels adopt mechanical seal as the shaft sealing system. But the mechanical seal of the stirred vessel often runs out prematurely, which seriously affects the enterprise production. Traditional cauldron-using machinery sealing device monitoring system is unable to do real-time monitoring on the operation of the mechanical seal and send out alarm signal in the early time of failure, which results in complete failure. This article studies the failure analysis and the monitoring system of stirred vessel mechanical seal, so as to improve the operation reliability of the stirred vessel mechanical.A fault tree (FT) of the stirred vessel mechanical seal is established with excessive leakage as the top event, which gets the all-round failure paths and basic failure reasons of the stirred vessel mechanical seal. Through the fault tree analysis:the seal face leakage influences excessive leakage of the stirred vessel mechanical greatestly; Design and use factors of failure account for larger proportion, manufacturing and installation factors account for smaller proportion; Improper selection or operation of barrier seal ways is a common problem in the application of the stirred vessel mechanical. Put forward the general solutions corresponding to basic failure reasons of the stirred vessel mechanical seal.A numerical calculation model of the leakage rate of contacting mechanical seal faces, which considers the influence of the whole stress deformation on the sealing rings, is put forward, so as to study the influence law of the main factors of seal face leakage. The seal face leakage increases along with sealing medium pressure, differential pressure of the seal faces, surface roughness, and decreases with the increasing of spring pressure.Based on the above model, the leakage rate on seal faces of a stirred vessel mechanical seal is calculated with ANSYS and MATLAB softwares and verified to be accurate by test. The influence law of sealing medium pressure, differential pressure of the seal faces, surface roughness and spring pressure to the leakage rate of seal faces are studied to provide theoretical reference for the the research on failure mechanism of the stirred vessel mechanical seal. The influence of differential pressure and surface roughness to the leakage rate is significant.With ANSYS finite element numerical calculation method, this article analyzes the stress distribution on the seal faces in various loading stages under different barrier seal ways of constant pressure and constant pressure differential respectively. Then the maximum pcV values of seal faces during the process of running are calculated. Choose the maximum pcV values of seal faces, after stable wearing, during the process of running as the index to judge the wear conditions of end faces, the contacting wear state of seal faces under the constant pressure barrier seal way is better than that under constant pressure differential barrier seal way. An operation suggestion of the barrier seal way is given:stabilize the seal medium pressure before operate the stirred vessel mechanical seal.Based on a sensitive leak tube, a monitoring system of leakage for the stirred vessel mechanical seal is invented. By analyzing the impacts of liquid level transmitter’s measuring precision, sensitive leak tube specifications and calculation level interval to the leakage rate calculation deviation, this article gives a selection method of sensitive pipe specifications and liquid level calculation time interval. The leakage rate monitoring and alarm procedure and barrier liquid automaticly replenishing procedure are designed with LAB VIEW software as the development platform. Constructing the test bench of the leakage rate monitoring and alarm to test the performance of the monitoring system, the correctness of the leakage rate monitoring and alarm procedure is verified.The research content of this article is helpful to the guidance of design, manufacture, use and maintenance of stirred vessel mechanical seal, perfects the theory study of failure analysis on the stirred vessel mechanical seal, which has important scientific research and engineering practical significance to the improvement of the reliability of the stirred vessel mechanical seal.