EN 13445における疲労評価の概要

抄録

An overview of the fatigue assessment rule prescribed in the pressure vessels design code EN13445　was summarized．The fatigue assessment rule consists of two parts;simplified and detailed assessment procedures．Both parts include the assessment procedure for welded and unwelded components．Due to complexity of the description of the assessment procedures，it is not easy to understand the whole view of the code．Then，this manuscript tried to figure out the overview of the code．In particular，differences in the rule between welded and unwelded components and simplified and detailed procedures were focused．This code provides different design fatigue curves for the welded and unwelded components．The curve for unwelded components depends on the tensile strength of material，while multiple curves are prescribed for welded components in order to assess various joint configurations．Specimens simulating welded joint were used to determine the curves for welded components，while plane polished specimens were used for unwelded components．Correction factors are considered to incorporate the effects of component thickness，temperature，mean stress and surface roughness，although the effects of surface finish and mean stress for welded components are included in the design fatigue curve．Some conservative corrections are included in the design fatigue curve used for the simplified assessment procedure．The use of the multiple design fatigue curves and correction factors enables the safety margin to be optimized．Another major characteristics of the code is the use of the structural stress to represent fatigue damage driving force．The structural stress represents the local stress enhanced by gross structural discontinuities，although which does not includes the notch effect．It was concluded that the code can give reasonable assessment result by the relatively detailed and well organized assessment procedure．