Tube-to-tube joint method

The method of making a tube-to-tube joint directly between a first tube and a cylindrical end of a second tube, and utilizing mandrel means and first and second die means, comprising the steps of:

• grasping the first tube with the first die means;
• moving the mandrel means and the first die means relatively axially together to form in one end of the first tube a radially enlarged first portion and to form a first shoulder at the junction between said enlarged first portion and the main body of the first tube;
• said enlarged first portion having an inner diameter slightly larger than the nominal outside diameter of one cylindrical end portion of the second tube;
• removing the mandrel means;
• grasping the second tube at said one cylindrical end portion thereof with the second die means;
• relatively axially moving together the grasped portions of the tubes to cause said end of the second tube to enter said enlarged first portion of the first tube and to abut and have movement arrested at said first shoulder and continued axial relative movement of the grasped portions of the tubes causing first and second annular portions of the inner wall of the second tube to bulge outwardly from a cylindrical shape to form an annular bead;
• forming in said first tube a second enlarged portion closer to said one end than said first enlarged portion and a second shoulder between said first and second enlarged portions;
• continued relative axial movement between the grasped portions of the tubes causing said first and second annular portions of the inner wall of the second tube to be compressed into mutual engagement;
• continued relative axial movement between the grasped tubes establishing fluidtight seal means between said annular bead of the second tube and said second shoulder of the first tube;
• and
• said fluidtight seal means capable of withstanding pressures of several atmospheres.