Use of bimetallic welds in nuclear reactors: Associated problems and structural integrity assessment issues

Abstract

The bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system in itself is the critical part of a nuclear reactor. Any failure of this system can lead to grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. The present paper is an effort towards identifying and understanding the problems affecting the BMWs and is as well an attempt to highlight the current issues in the structural integrity assessment of structures having these welds. The basic aim of this work is to provide a clear understanding of the current structural safety issues and their importance in underpinning the use of BMWs in modern nuclear reactors.

Mechanical Properties of Bimetallic Weld Joint Between Sa 516 Grade 65 Carbon Steel and Ss 304 L for Steam Generator Application

“…In steam generating power stations, the parts of boilers that are subjected to lower temperatures as in the primary boiler tubes and heat exchangers are made of carbon steels for economic reasons. Other parts, such as the final stages of the super heaters and reheaters operating at higher temperatures where increased creep strength and resistance to oxidation are required, are constructed with austenitic stainless steels [4]. The materials used are carbon steel SA 516 grade 65 that is used in reactor pressure vessel [1,2,18] and stainless steel type 304 L that is used in primary boiler tubes [4,7,8].…”

“…The lower nickel content of SS 309L improves resistance to sulphur attach at high temperatures. It is tough and ductile and can be readily fabricated and machined [1,4].…”

“…There have been several studies on the welding of carbon steels and stainless steels because the failure in bimetallic joints can occur before the components reach their design life [4,8].…”

“…These investigations have shown that large thermal stresses arise in these joints during temperature fluctuations owing to the difference in thermal expansion coefficients [1][2][3][4][5].…”

“…This carbon migration is also responsible for bimetallic weld join failure [16,17]. To avoid carbon migration buttering layer is to be deposit on carbon steel [4]. This paper discusses the effect of buttering layer on carbon steel on mechanical properties of bimetallic weld joint.…”