An erect cylindrical pressure vessel, especially for a nuclear reactor, is constituted from cast-iron or cast-steel elements and is stressed by axially extending angularly spaced axial stressing elements and by axially circumferential peripheral stressing elements or cables. At least one of the axially stressing cables and at least one of the peripheral stressing cables serving for sustaining the operating load of the pressure vessel, i.e. the working elements rather than the addition or additional elements, is provided with a measuring device which triggers an alarm upon the detection of a change in the force developed at the respective stressing element or the length change thereof reaching 90% of the corresponding change at the pressure rating of the vessel.
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