A team of scientists of the State Research Centre JSC “RPA “CNIITMASH” (belonging within JSC Atomenergomash, a machine-building division of ROSATOM) presented a tests bench for fine-tuning the underwater welding technology and told about the research progress in this area. The presentation was made within the frames of the International Science Conference “Welding and related technologies for manufacture of special-purpose and critical equipment”. The work is performed under the order of Leningrad NPP for new VVER-1200 units; the General Contractor is LLC Special Design and Technology Bureau of Applied Robotics (SKTB PR), specialists of CNIITMASH and LLC APS RADIS were also engaged in the project.
In the course of research on the subject “Development and agreement of a technology for repair of a cooling pool lining by means of automatic robotic underwater welding, CNIITMASH is developing a unique technology of underwater welding, as well as welding materials having specific welding technological properties - cored wire suitable for works underwater. For elaboration of the wire composition and fine-tuning of the underwater welding technology the test bench was installed in the Welding Technology Center of CNIITMASH. The first stages of the technology fine-tuning were carried out in a container filled with water involving the application of the self-protected welding powder wire of various manufacturers, as well as solid wire, with and without shielding gas.
Moreover, CNIITMASH experts participated in development of process equipment capable to sustain radiation and active medium of the NPP cooling pool. LLC APS RADIS specialists designed the underwater welding system fully providing implementation of the developed technology, which will enable to eliminate potential defects. This is only one working member of a five-axis robot, the gripper of which can locate the crack grinding and crack ultrasonic detection systems (The systems are developed by the General Designer LLC SKTB PR). The employees working at new units of VVER-1200 of Leningrad NPP, who are going to inspect the cooling pool condition in-situ, will be trained at the similar test bench.
The test bench was designed by the team of scientists for testing of the welding system. The bench consists of the transportation system moving the welding machine in various directions, and a water pool. The tests bench makes it possible to simulate the water pressure at a different depth. Here the synergetic welding modes will be adjusted by means of simulation of all possible scenarios of defect growth in the pool.
“Work in the frames of this research involves many difficulties. One of them is the development of welding materials, special cored wires not yet having any equivalent in Russia. The infringement search has shown that not only materials, but all technical solutions that would be used in the course of underwater welding repairs of NPP cooling pools, met novelty requirements in the territory of the Russian Federation. In particular, currently we solve the problem of selection of materials and chemical elements serving to form of a stable shielding gas bubble required for quality welding,” says the project coordinator, Senior Researcher of CNIITMASH Institute of Welding Mr. Sergey Volobuev. “Formerly the underwater repair works were performed either in special chambers using the dry method, or with stick electrodes through diving. Both methods do not suit for works in agthe gressive media and limited space of the cooling pool, therefore we decided to undertake a research of other possibilities.”
The technology and installation for underwater welding potentially have a large area of application. In particular, they may be used in ship-building, in the course of deep water welding, laying subwater pipelines, various repairs of port infrastructure facilities and in the other spheres.