ASME NTB-4:2021 pdf free download

ASME NTB-4:2021 pdf free download.Background Information for Addressing Adequacy oroptimization of ASME BPVC Section lll，Division 5 Rules for Nonmetallic Core Components.
The identified modes of failure for graphite are brittle fracture, fatigue, excessive deformation (including both elastic instability and irradiation-induced dimensional changes) and environmental effects such as irradiation and chemical attack.
The following are fundamental concepts for the code approach.
• It is possible to allocate probability-of-failure POF) targets to the graphite parts such that if the targets are met, the overall functional integrity of the assembly is ensured.
• The effects of loads on a part can be calculated and expressed as stress states in the part. Complex stress states can be reduced to an juivalcnt stress, which is equivalent to uniaxial stresses applied to test specimens.
• The nature of graphite implies that a probabilistic assessment method is better suited to the design of graphite parts than is a deterministic method.
• It is possible to characteri,c the marerials by a statistical treatment of the material specimen test results to produce a statistical distribution (referred to as the material reliability curve) and generate confidence intervals to ensure consen’atisim
• To ensure margin against brittle fracture, for a simple assessment, it is possible to determine stress values based on the POF targets and material test data so that when the part stresses are lower than these limits, adequate reliability of the part is ensured. For a full assessment, it is possible to calculate expected POF values for a graphite part based on material test data that arc directly comparable to the POF targets and ensure adequate reliability of the part.
• Environmental effects such as irradiation and oxidation can be incorporated into the method by considering the changes to the input material properties.
• To ensure the margin against fatigue fracture, the code requires protection against fatigue failure; but it does not specifically address guidance regarding failure of graphite parts due to fatigue- induced damage for the major operating cycles of the reactor(HI-IA-3 144)[22].