Analysis of current state and integrity evaluation for the air tank of the regulation system of turbine A6 at hydropower plant Djerdap 1

Abstract

Vertical Kaplan turbines with nominal power of 200 MW, made in Russia, have been installed at 6 hydroelectric generating sets of "Djerdap 1". Most of the components were made of steel in accor-dance with GOST and ASTM- standards. During the rehabilitation of the hydroelectric generating set A6 non-destructive testing methods were performed on parent material and welded joints of the main oil/air tank and air tank with the auxiliary oil/air tank, which acts as pressure accumulator in the regulation system, in order to carry out the analysis of the current state and integrity evaluation for the regulation system- of the turbine. Shells of all 3 tanks were made of steel Č 1205, while bottoms were made of russian steel St 20K Tests were also performed on pipeline elements (pipes and elbows). The results of non-destructive tests performed on air tank are presented in this paper Mechanical damages were detected by visual inspection at parent material of the shell and at the upper bottom, as well as discontinuous and incompletely welded joints on the inside and outside of the tank. Sur-face linear crack type indications were detected through magnetic particle testing at intersections of welded joints on the inside of the tank. Internal crack type defects were detected through ultrasonic testing of welded joints On the basis of test results the technology of reparatory welding / surface welding of parent mate-rial and welded joints was created, while on the basis of the analytical calculation of tank strength the evaluation of its integrity for the following 40 years of operation was obtained.