Abstract: To set up sealing between two parts, having the possibility of relative rotation to a limited extent around a determined axis, a concertina element is used. This concertina element has two rigid, end tubular sections, fixedly joined in an impervious way with respective zones of each of said parts and an intermediate tubular part between said end tubular sections, and is capable of changing shape under torsion around said axis, to an extent that is at least equal to said extent. Thus, all risks of leakage between the two parts are removed.

Abstract: The invention relates to a method and to apparatus for tightening and slackening bolts by hydraulic tensioning. The apparatus comprises a tightening system (60) applied to the bolts to be tightened and/or slackened, controlled by a central unit (24), via the intermediary of a control device (26) and a hydraulic pump (28). Transducers (19 and 18) permit respectively measurement of the effective strain of the bolt and the pressure effectively applied to the tightening system (60). A correlation between the effective strain of the bolt and the pressure effectively applied is thus effected for obtaining a very good precision of the strain. Application is to mechanical construction in the nuclear environment.