Process for the continuous manufacture of tubular composite or multi-layer membranes comprising a porous sub layer (support layer), mainly determining the mechanical strength of the membrane, and adjacent to the support layer a second layer of a material of different chemical nature (separation layer), mainly determining the separation properties of the membrane, winding a respective flat sheet composite membrane lengthwise or spirally around a mandrel or shaft, into a tube or hose, the separating layer of the composite membrane facing to the inside of the tube or hose, gluing or welding the edges which may overlap or form a butt seam, and applying to said seam or overlapping area from the inside of the tube or hose a sealing material which can be solidified, and finally solidifying said sealing material.