[en] A ring channel is formed in the tubeplate around the heat exchange tube, which is connected to the pipe with a valve outside of the tubeplate. A testing liquid unit and/or an alarm system for the leakage of the working medium into the ring channel may be connected to the pipe. In case of joint leakage it will be possible to determine the condition of the joint and to estimate its service life from the time change in the parameters of the testing liquid. The designed device may be used for heat exchangers in nuclear power. (J.C.)