PURPOSE: To provide a welded part to avoid a formation of empty interstitial spaces with a gap, existing between a wall of a corresponding housing seat located in a panel for a heat exchange element and a pipe, which must have harmful and dangerous consequences for the element and a plant where they are used.

CONSTITUTION: This method is achieved by a work process which provides a combined heating and internal pressurization step for a pipe 5 under a value which realizes a metal creep condition of metal with which a pipe is made. A deformation arising from the method enables a pipe 5 completely welded on a wall 4 under a fully controllable condition. Further, a controlled deformation of a pipe realizes a stress given by a pressurization in a secure limit in order to preserve its structural safety of a panel 2, thereby the method is properly applicable to the panel 2 made especially from graphite, ceramic, or other ductile materials.