Modelling of the thermal cycles during the circumferential arc welding of components with cylindrical and spherical shapes has been carried out using a bilinear degenerated shell element adapted for the thermal analysis. The analysis was conducted for the cases of butt welding of a thin cylindrical pipe to thin cylindrical pipe, a thin spherical end to thin spherical end and a thin spherical end to a thin cylindrical pipe. In all the three cases, the thickness of the components, the diameter of the components and the heat input were kept the same in order to compare the results. Various phenomena associated with welding, like temperature dependent material properties, distributed arc heat input, heat losses through convection and radiation and latent heat were accounted for in the model. The circumferential and axial thermal profiles in various sections and the thermal cycles at various locations for the three cases were compared. The graphs show that the thermal results for the three cases are almost similar during the heating cycle near the weld and significant differences are found during the cooling phase. The temperatures on the sphere side are found to be higher compared to the cylinder side as the amount of metal is less and the surface area for the heat losses is also less in the spherical side. The FEM program and the thermal results are discussed in detail.