EVALUATION OF THE STRUCTURAL RELIABILITY OF CRACKED STEAM GENERATOR TUBES BASED ON THE FAILURE DIAGRAM ASSESSMENT

Thais M. W. Ouverney¹; Renato S. Horta¹; Alexandre S. Francisco¹; Luciano P. Moreira¹

¹ Universidade Federal Fluminense

doi:10.20906/CPS/CILAMCE2017-0266

Resumo

In the structural reliability evaluation of Steam Generator Tubes (SGTs) subjected to crack-type defects, it is possible to perform analyses based on the plastic collapse, as well as on elastic-plastic fracture mechanics and even on linear elastic fracture mechanics. Due to the austenitic microstructure of the SGT materials, very high fracture toughness values are found in these materials, and the most of the integrity criteria are based on limit load analysis, where plastic collapse is the prevailing mode of failure. In spite of the failure mechanism of SGTs be mostly dominated by plastic collapse, a weak effect of elastic-plastic fracture takes place in the failure. One way for addressing this effect is evaluating the structural reliability based on the Failure Assessment Diagram (FAD), which is a two-criteria approach that considers the linear elastic fracture mechanics and the plastic collapse as two extreme forms of cracked component failure, while for elastic-plastic material, the failure will occur in an intermediate state. The recent tendency in safety assessment of structures containing defects is to consider the uncertainty of structural parameters. In the present paper, we perform a structural reliability evaluation of SGTs based on the FAD methodology by using the Monte-Carlo simulation. An engineering case is evaluated in order to compare the traditional limit load analysis with the FAD methodology, considering Alloy 600, Alloy 690, and Alloy 800 materials.

Palavras-chave: Structural reliability; Fracture mechanics; Monte-Carlo simulation