Finite Element Analysis and Comparison of Two USX Inlet Models

摘要

USX inlet header is the key part of quench boiler of cracked gas for ethene plant. It is loaded byinternal pressure, pipe load and moment, thermal loads. The quite uneven temperature field in theUSX can result in high thermal stress. Proper design of the USX is very important for safety andeffectiveness of the USX. Two USX inlet header models are analyzed and compared based on thefinite element results.Temperature field in the USX and heat conduct in still steam layer between two tubes of the USX arecalculated by FEA. Plane 77 element and solid 90 element are used for the still steam layer andchannel cover structure of the USX respectively. A 3D FE model is established for the USX inletheader to take into consideration of non-symmetry of the loads and coherence of element and meshof FE for temperature and stress calculation. The elements of the still steam in the models fortemperature field calculation are deleted, and then the solid 90 element of the structure is changed tosolid 95 element for calculating the stress field. Elastic FEA and Elastic-plastic FEA with two kindsof simplified stress-strain relationships of the material are carried out. Thermal loads and mechanicalloads are taken into consideration in FEA calculation.The results of the FEA calculations show that the stresses in the new USX inlet header are muchlower than those in the original one. The stresses and strains in both models meet the requirements ofASME T-1310 and T-1332. But the accumulated creep and fatigue damage over the service life of theoriginal USX, including hold time and strain rate effects, should be considered, if there aretemperature and load cycles in the USX. The new USX inlet header has been safely used in a etheneplant for two years.