A fixed tubesheet type heat exchanger with semi-ellipsoidal heads which is dealt with in this paper has been adopted for refrigerant heat exchange process in LNG Plant. Since the conventional design standards, e.g. ASME Sec VIII Div.1 and TEMA, are not meant to be used for such a special type of heat exchanger, FEA should be performed to determine minimum required thickness of the tubesheet.
The elastic design procedure uses a stress classification methodology to guard against failure due to gross plastic deformation. According to the design standards, mechanical stresses in the tubesheet due to tube-side and/or shell-side pressure are defined as the primary membrane and bending stress and are evaluated by comparing with allowable values of the primary stress. For the special type of heat exchanger, however, stresses in the tubesheet obtained by FEA are actually complex combination of primary and secondary stresses. Application of this conventional design approach to the FEA-calculated stresses in tubesheet may lead to over-conservative design.
In helping to establish reliable and economical design of the tubesheet for such a special type of heat exchanger, authors conducted FEA investigation employing axisymmetric analysis model. Considering the geometric parameters, such as thickness of a tubesheet, heads type and shell dimension, the characteristics of tubesheet stresses was investigated and an appropriate stress classification was proposed.