Supercritical carbon dioxide CO2 has been proposed as working fluid in various types of power plants, thanks to its potential higher efficiency and cost reduction with respect to well-known technology of steam cycles. However, the high operating temperature and pressure conditions pose significant concerns in terms of compatibility of supercritical CO2 with the high-temperature sections of the power block. Typically, to address this problem, experiments are proposed, where samples of different materials are kept in contact with the supercritical CO2 in a pressure vessel in order to test the material compatibility. This research deals with designing an innovative openable pressure vessel capable of withstanding the high temperatures (700 °C) and the pressures (100 bar) typical of those power plants. The results obtained by analytical calculation and the finite element method are consistent. The results obtained with both methods are generalizable and the methodology is applicable to any removable pressure vessel that must withstand 100 bar of pressure and a temperature of 700 °C, application field that is outside the ASME B&PV Code Section VIII division 1, standard usually used for the design of nonnuclear pressure vessels. It is important to emphasize that the use of a removable container allows to reduction of the costs of compatibility tests since otherwise, after each test, the pressure vessel would be disposed of. In addition, this allows a reduction of the environmental impact due to the fact that the new container will not be disposed of after each use.