An estimation procedure to evaluate limit loads of bi-metallic specimens. PART-1

Abstract

The integrity assessment of bi-metallic joints is an important issue for the nuclear industry. Recent international surveys of such welded joints have shown that there are several cracking problems, due to fabrication, ageing or corrosion. Thus there exists a strong need to develop simple methods to assess the fracture integrity of such bi-metallic joints. The current leak-before-break (LBB) methodology is based on evaluating the integrity of cracked nuclear piping, having mismatch in material properties, by considering the strength properties of the base material and fracture properties of weld material. This method generally yields safe results but it is highly conservative. At present FEM is considered as the best method to evaluate limit load and crack driving force for these mis-matched/bi-metallic structures. However, it is always useful to have some simplified estimation methods for engineering calculations. Therefore, an estimation method has been developed for evaluating the limit loads of mis-matched/bi-metallic specimens such as centre crack plate, three-point bend specimen and compact tension specimen. This article contains details of analytical procedures to evaluate limit loads of bi-metallic specimens. A simplified procedure to assess the fracture integrity of such bi-metallic specimens is explained in a related article.