基于子模型法的大型固定管板换热器有限元分析

FINITE ELEMENT ANALYSIS OF A LARGE FIXED TUBESHEET HEAT EXCHANGER BASED ON SUB-MODEL TECHNIQUE

大型固定管板换热器由于管子数量大,无法在有限元模型中建出所有换热管与管板的详细连接结构,得不到相关区域的真实应力分布,无法有效地进行应力强度评定。对某大型固定管板换热器,利用粗模型确定了管板布管区换热管与管板连接区的最大应力强度位置,进而建立了该位置换热管与管板详细连接结构的子模型。子模型中考虑了换热管与管板的焊接结构及其相互接触,分别对此区域进行基于应力分类法和极限载荷法的分析计算。结果表明:虽然基于应力分类法的焊缝及换热管应力强度评定不合格,但考虑到应力分布的非轴对称特性,基于极限载荷分析的直接法评定应更为合理。对子模型结构进行了极限分析并利用零曲率法确定了极限载荷,按相关标准进行了评定,表明结构满足强度要求。

As enormous number of tubes in large fixed tubesheet heat exchangers,it is difficult to model alI the tubes and tubesheet connections in detail for FEA.Therefore,it fails to yield an accurate stress field around the connecting region of tubes and tubesheet,which is essential for the effective stress intensity evaluation.Taking a large fixed tubesheet heat exchanger as example,the maximum stress intensity location is found for the tube layout region of the tubesheet according to the coarse model. Then the sub model is utilized in the predetermined maximum stress location.In the sub model,detailed connecting structure of the tube and the tubesheet are included,such as the weld metal and contact condition between the tube and tubesheet hole.Both stress classification and limit load analysis are preformed for the sub model structure.Although both the weld and the tube fail the evaluation based on stress classification,it is more reasonable to evaluate the connecting region with the direct route based on limit load analysis for the structure with non axisymmetric stress distribution.Limit analysis is carried out and limit load is determined by zero-curvature method.It is shown that the structure meets the strength requirement based on the relevant standards.