Statistical investigation of the weld joint efficiencies in the repaired WWER pressure vessel

Abstract

From a fatigue point of view, the second most important WWER (Water-Water Energetic Reactor) pressure vessel component (after closure studs) are the primary nozzles. These parts are included in the in-service inspection performed every 4 years when non-destructive testing techniques like ultrasonic, eddy-current and dye-penetration methods are applied. After the determination of the severity of fatigue crack, the progress of initial defects over time can be prevented by repair welding. Purposedetermination of values of the eight main mechanical properties of the welded nozzle after major repair, evaluation of statistical data for reliability and recommendations for the maintenance. Study designthe examination of the nozzle Du-500 revealed the presence of perpendicular crack on the outside surface in the base metal. The crack in the base metal has an angle of 72° with the horizontal plane which was repaired at normal (T = 20 °C) and elevated (T = 350 °C) temperatures by (i) automatic arc welding under the flux layer AN-42, and (ii) ceramic flux. The analysis was performed with 15 different batches of welded steel specimens and every single parameter each time was established by using 45 repetitions of the test procedure for the same type of specimen. Findingsthe study describes the specific case of defected nozzle's housing that was made of steel 15Cr2MoVA and after the crack repair along the length of nozzle diameter could potentially be further exploited. Value – the analysis of the welded specimens showed good agreement between the empirical and theoretical curves and can be used in lifetime and fatigue life predictions for WWER pressure vessels still applicable in power generation industry.