The pressure vessels are connected by pipelines to form a system. Thermal expansion of the pipeline imposes an additional load on the nozzle of the connected vessel. There are two methods to deal with the thermal expansion load of pipeline in the design of pressure vessel: the partition method and the integrated method. A new Load Release Factor Method (LRFM) is proposed in this paper based on theoretical derivation. A spherical head with central nozzle is taken as an FEM (Finite Element Method) analysis model. The results show that a conservative design will be obtained by the traditional partition method, and the integrated method is the closest to the actual situation in spite of the large amount of calculation. However, compared with the traditional two methods, the LRFM can not only ensure the design margin but also reduce the calculation. This paper could be a reference for the analysis of pipeline thermal expansion load in the vessel design.