Automated device for taking off residual mechanical pressure to raise reliability of NPP pipelines
Connection of all the devices of nuclear energy facilities requires a large number of pipelines. The overall length of all the NPP pipelines can reach hundreds of kilometers, and their cost can be up to 10 % of the station's cost.
Pipelines at NPPs are influenced by different damaging factors: high pressure inside pipelines, vibrations, ionization radiation, high temperature, etc. Destruction of most important pipelines endangers safe exploitation of a nuclear station. Conducting of expensive repairs requires complete halt of a nuclear reactor, which leads to large financial expenses.
In this regard, there is a need to implement a set of procedures, aimed at ensuring the reliability of the pipelines of nuclear power plants, specifically their welded joints. They, in view of the peculiarities of the technological process, are subject to the greatest destruction due to the appearance of residual stresses and residual deformations in them during welding, leading to the occurrence of surface cracks. In addition, during operation, the operating voltages will add up with residual stresses, which can lead to an increase in the strength of the metal and cause cracks.
At the Department of Automation, Control and Diagnostics of MEPhI Obninsk branch, a first year Master's degree student D.I. Chulkov under the guidance of Ph.D., Associate Professor S.I. Minina is developing an automated device for removing residual pressures in welded joints of NPP pipelines after they have been performed by ultrasonic hardening.
The essence of the method is that, due to the effect of ultrasonic oscillations, arising at the end of the acoustic ultrasonic waveguide, its pressed against the surface of the welded joint leads to a hardening. As a result, the crystal structure of the metal changes during plastic deformation. In a welded joint this allows to remove the surface residual stresses due to the fact that the energy necessary for their return to the initial stable energy state after deformation is transferred to the dislocations.
MEPhI scientists carried out a number of experimental works confirming the efficiency of this method and, based on their results, proposed an automated device for removing residual stresses in welded joints of pipelines after they had been performed by ultrasonic hardening. Figure 1 shows a schematic representation of the mechanism of an automated device.
"The developed automated device is designed to increase the reliability and extend the life of welded joints of the circulation pipelines of nuclear power plants, however, it can also find wide application in industries with high requirements to the reliability of welded pipeline connections and it is necessary to carry out procedures aimed at prolongation of service life of welded joints of pipelines. Examples of such areas are chemical, gas or oil industries," S.I. Minin noted.
Provided by National Research Nuclear University
