A new flash tube device adapted specifically for use with hot erosive flow streams is provided. This flash tube uses an extension cone fixed to the outlet of a choke to create an extension choke to insure that the shock wave occurs within the extension choke, thereby decreasing the flow velocity to a subsonic level, reducing the kinetic energy of the flow as it leaves the extension choke. By moving the shock wave into the extension choke, this device dramatically improves the working life of the flash tank, allowing for easier separation of fluid/solids and vapor in the flash tank.