Abstract
Tubes in industrial water heaters, steam boilers, and condensers of turbines are fitted in the holes of adjoining drums or head plates by expanding the tube ends. These are slightly enlarged by means of small revolving rolls. In one large steam condenser many thousands of such tube joints have to be rolled, and in high-pressure boilers these joints must remain tight under several thousands of pounds pressure at high temperatures. The investigation reported in this paper, of the conditions under which tube joints are expanded and made pressure-tight, was undertaken at the suggestion of R. A. Bowman, manager of condenser engineering, of the South Philadelphia Works of the Westinghouse Electric and Manufacturing Company, early in 1942. The pressure of the revolving rolls creates a radial plastic distribution of stress in the tube wall and around the hole in the adjoining heavy steel plate. After the tube end has been rolled, a system of residual stresses remains locked up near the joints which is essential for its pressure tightness. These plastic states of stress have been investigated for various types of the stress-strain characteristics of the tube metal and steel of the head plates. Simple rules are used for computing the stresses in a moderately thick-walled tube under external and internal pressure, either in the elastic or in the plastic state of stress.
