Методические особенности конечно-элементного исследования прочности трубопроводов водо-водяных энергетических реакторов с учётом локальных утонений от воздействия эрозионно-коррозионных процессов

Abstract

The methodological features pertinent to strength analysis of the pipelines used in the secondary coolant circuit of nuclear power plants (NPPs) with taking into account local thinning caused by flow accelerated corrosion processes are addressed. The geometric features of pipelines are essential not only for assessing the flow accelerated corrosion intensity in metal, but also for the final strength assessment, in particular, in analyzing the strength of pipelines with walls containing local thinning spots. The pipeline structure lifetime prediction accuracy depends directly on the strength analysis of pipeline elements in which local thinning spots have occurred, especially if these elements themselves have a complex shape. Elbows, sockets, adapters (transitions), and shell rings can be referred to such elements. All of them are thin-walled structures having a complex shape. Software systems like ERCO and PELBOW are best suited for numerically studying them. These computer programs are based on the shell finite element method, using which the thickness at each finite element node can be specified either in the form of certain dependencies or (in some cases) manually. In accordance with the 3D finite element theory of thick-walled shells, a pipeline section can be approximated by a mesh of finite isoparametric 3D elements of a thick shell. The flow accelerated corrosion wear (FACW) depends essentially on the chemical composition of steels. Domestically produced Grade 10Kh9MFB steel is compared with foreign Grade P91 steel (that is close to the former in chemical composition and in performance characteristics), which has positively proven itself and widely applied for making NPP pipelines, with a view to recommend Grade 10Kh9MFB steel for use.