PURPOSE: To make the tightening force excellent even in a high temperature operation by a method wherein at least either a tube plate or a flange is made of the material with larger thermal expansion coefficient than that of a clamping bolt.

CONSTITUTION: A tube plate 3 is made of stainless steel while both flanges 1A, 1B and a clamping bolt 4 are made of carbon steel. Therefore the tube plate 3 is thermally expanded by the temperature of fluid running into the tube in operation up to the amount of 11 while the clamping bolt 4 is thermally expanded by the same up to the amount of only 12. At this time, the thermal expansion coefficient of the stainless steel being larger than that of the carbon steel, the gaskets 2 shall be subject to the compression by the amount of 1/2 thermal expansion of the difference between the two thermal expansion coefficients i.e. 11-12(Δ1).