Discussion on Improvement Aspect of Design-by-analysis Method of ASME-Ⅲ-5 Class 1 High Temperature Component

Abstract

Division 5 of the ASME code section Ⅲ (referred to as ASME-Ⅲ-5) provides design-by-analysis methods and evaluation criteria for Class 1 nuclear components working at high temperatures. It has a long history and is the main international design code for high temperature nuclear equipment. It took the lead in adopting the idea of stress classification and first introduced the concepts of primary stress, secondary stress and peak stress, which had a far-reaching impact on the development of subsequent other high temperature design codes. However, with the rapid development of computational methods, high-performance computer technology, commercial finite element software and high temperature inelastic analysis methods, the results derived from elastic analysis and the evaluation of stress classification used by ASME as a mainstream method exist the limitation of overly conservatism and thus insufficient design economy. This paper first introduced the definition of high temperature condition and the insignificant creep temperature, as well as the design loads, failure mechanisms, design-by-analysis methods, and evaluation criteria of ASME code for nuclear Class 1 components at high temperature. Then, by comparing the analysis methods and criteria of primary load limit and deformation control limit of ASME with other high temperature codes, such as R5, RCC-MRx and MONJU (with or without consideration of the time dependence of creep), the advantages and limitations of ASME analysis methods and criteria were explored. Each code has its distinct characteristic. British R5 code focuses on the reference stress method and the application of limit analysis. French RCC-MRx code is in the same lineage with ASME, but distinguishes between significant/insignificant creep and significant/insignificant irradiation effects. Japanese MONJU code distinguishes the long-term load from short-term load, such as seismic load. Long-term loads and short-term loads adopt different limits to avoid overly conservatism. It is concluded that the elastic analysis based on the stress classification traditionally adopted by the ASME code is excellent, but it cannot perfectly cope with the all the code-considered failure mechanisms due to its inherent characteristics. Therefore, several methods are proposed as alternative methods for the ASME-Ⅲ-5 improvement. The pointed-out directing improvement aspects of ASME-Ⅲ-5 enable to enhance the advancement, economy and safety of the development and use of ASME, with the scientific integration of the traditional design of pressure vessels and the new era of computational analysis technology. At the same time, this study also has important guiding value for the development and construction of Chinese independent design code in nuclear Class 1 high temperature pressure-bearing components.

Keywords

• asme code
• high temperature
• design-by-analysis
• primary load control limit
• deformation control limit