In process and chemical engineering apparatuses like stirrer vessels, tanks, or autoclaves are often equipped with welded on coils at the outer surface. These coils are used for the heating and cooling of the respective vessel contents. For that purpose a heat carrier fluid flows through the pipes. Figure 1 shows the cross section of three typical stirrer vessel wall constructions. Compared to double-walled vessels, vessels with welded on coils allow smaller wall thicknesses and hence, are more economic. Furthermore, a good heat transfer inside of the coil is possible even though high viscous heating or cooling fluids are applied.