A pressure vessel for containing a mechanical device operable to convert heat to mechanical or electrical power, comprising: a high temperature section, the high temperature section having a first end and an open second end, a sealing flange, the sealing flange having a first end and a second threaded end, the first end bonded to the open second end of the high temperature section, and a low temperature section having an open threaded first end, the open first end in sealing engagement with the second threaded end of the sealing flange. Also provided are a Stirling engine and a method of hermetically sealing a pressure vessel of a Stirling engine.