Abstract
Because thermowells are prone to fatigue damage in petroleum cracking gas pipelines, in this paper, the LES method is used to simulate the flow around thermowells through two-way thermal-fluid-solid coupling, the internal causes of thermowell damage are explored, and measures for improving the thermowell safety are proposed. According to this study, when high-speed, high-temperature gas passes the thermocouple bushing, the main factors affecting the structural safety of the thermocouple bushing are the alternating stress caused by the vortex falling off, the thermal stress cycle due to the temperature gradient, and the pressure gradient impacted by the gas. Furthermore, this paper proposes improving the thermowell safety by installing the interference devices and optimizing the installation angle. The improvement measures were studied by conducting a two-way thermal fluid-structure coupling simulation. The results of this study show that after installing the interference device and optimizing the installation angle the displacement deformation of the thermowell and the equivalent stress is reduced by 57.2% and 72.1%, respectively, which indicates the safety improvement of the thermowell structure and the effectiveness of the method. The research contents of this paper can provide guidance for the installation and use of thermocouple bushing.
Highlights
In the petrochemical industry, the temperature of petroleum cracking, as an important monitoring and control parameter, is usually measured by a thermocouple
Aiming at the fracture damage of thermowell in the application of petroleum cracked gas pipelines, a bidirectional thermo-fluid-solid coupling model for the thermocouple thermowell was established, and the analysis of thermowell dynamic characteristics based on bidirectional fluid-solid couplings was conducted. e interference device installation and the installation angle optimization were introduced to improve the safety of the thermowell structure and applied to the petroleum cracking gas pipeline of an enterprise
E specific conclusions are as follows: (1) e influence of gas compressibility cannot be ignored; the vortex shedding in the wake of the thermowell, the thermal stress due to high temperature, and the pressure generated by the gas are the direct causes of damage to the thermowell
Summary
The temperature of petroleum cracking, as an important monitoring and control parameter, is usually measured by a thermocouple. Erefore, to simulate the real operating conditions and explore the internal mechanism of thermowell damage, two-way thermal-fluid-solid coupling calculations are required. Gengwang et al [12] used the LES method to conduct thermal-fluid-solid coupling numerical simulations of T-shaped pipelines in petroleum, chemical industries, nuclear power, and other pipeline systems and explored the causes of thermal fatigue of pipelines. E petroleum cracked gas pipeline transports high-temperature and high-speed gas, and gas temperature and compressibility affect the force and deformation of the thermocouple thermowell [16,17,18,19,20]; not considering their influence, the calculation results would be inconsistent with the reality [21, 22]. From the aspects of temperature field, pressure field, and gas compressibility, the surface stress and wake field changes of the thermowell were studied, and the causes of the thermowell breakage at the welding point were explored. en, because the thermowell is prone to breakage in practice, the corresponding structure was improved, and the improved structure model was numerically simulated to analyze its influence on the thermowell. e research results are of great significance to the safe applications of thermowells in industrial fields
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