Integrity assessment of regulation system pipeline elements in hydroelectric generating set a6 of hydro power plant 'Djerdap 1'

Abstract

Vertical Kaplan turbines with nominal power of 176 MW manufactured in Russia are installed in 6 hydroelectric generating sets at hydro power plant 'Djerdap 1' (Kladovo, Serbia). Most of the components are made of materials in accordance to GOST and ASTM standards. During rehabilitation of hydroelectric generating set, the analysis of the current state and integrity assessment of turbine regulation system pipeline required non-destructive tests on parent material and welded joints between pipes and pipes-elbows. The purpose of the regulation system, comprising of the pipeline for the turbine regulator oil supply, is to open and close vanes of the guide vane apparatus and to regulate the position of runner blades and their number of revolutions. Internal pressure in the regulation system is p = 4 MPa. Structural integrity is a recent scientific and engineering discipline which in broader sense comprises state analysis and behaviour diagnostics, service life assessment and rehabilitation of structures, meaning that beside the usual situation where structural integrity assessment is required when flaws are detected by non-destructive testing, this discipline is also includes stress state analysis. This approach is especially important for welded structures, since cracktype flaws can originate from welding and from unfavourable service conditions. In this paper, the results of non-destructive tests referring to the lack of penetration in roots of butt-welded joints between pipes and pipes-elbows, as well as tensile test results of technical specimens with reinforcements and in specimens with parallel machined sides and standard dimensions, are presented in order to carry out the integrity assessment of the turbine regulation system pipeline of hydroelectric generating set A6 at hydro power plant Djerdap 1. Results of analytical strength calculation of butt-welded joints between 2 pipes, and pipe-elbow with a lack of penetration in the root are also presented.