固定管板式换热器的危险工况分析和管、壳应力在设计中的作用

本文在前文的基础上,阐明危险工况(或称可能出现的危险工况)和真正危险工况之间的区别和联系,仅由操作条件只能列出危险工况而无法得出真正的危险工况,真正的危险工况不仅和操作条件有关,而且和换热器的结构条件和各部件相对尺寸有关。 根据换热器的具体结构条件、各元件相对尺寸和危险工况,管板、管子或壳体应力的最大值都有可能首先超过各自的强(刚)度校核条件。所以,在设计时不论管板、管子或壳体都应由各个危险工况求出其可能出现的最大应力值并校核满足,不能以并非最大的应力值进行校核,更不能因管子或壳体应力(特别是带有膨胀节时)绝对值较低而认为其强度不会成为问题,甚至不予计算。

Analysis-of Severe Services of Fixed Tube sheet Heat Exchanger and Applications of Tube Shell Stress in Design

This paper, based on the former paper, describes the differences and correlation between severe services (or so called possible severe services) and true severe services. From the analysis of operation conditions, only severe services, but not true severe service, can be obtained. The severe services relate not only to operation conditions, but also to both the structure of heat exchangers and the size of their elements. According to the structure of the heat exchangers and to the relative sizes and severe services of every elements, the maximum stress of tube sheet, tube or shell probably first exceeds their allowable stress limit respectively. Therefore, the possible maximum stress of tube sheet, tube and shell should be calculated first with their respective severe service. Then, all of them should be below these allowable stress limit respectively .It is inadequate to check the stresses that do not reach their maximum values. Moreover, it is wrong to think the strengths of tube and shell are enough and the calculation is unnecessary because of their low absolute stresses (especially, when expansion joint is used).