Thanks codeeng, anyway the tolerances I'm interested are about tolerances of flatness and parallel of the two tubesheet's to which the manufacturer has to attain during manufacturing, if these measures are not specified on drawing of the designer. The heat exchanger in question is under PED and TEMA Module G. When checking the relevant standards EN and TEMA, have not found these two measures, but only refference is that tubesheet has to be flat and uniform thickness. This said a lot and no. So if anyone know the refferenced chapter of the relevant standard to which reffer please reply. Personaly have not good experience of "good engineering/manufacturing practice"-too much discussions. Preffered are exact numbers. Thanks.