Ak. Bhaduri et al., TRANSITION-METAL JOINTS FOR STEAM-GENERATORS - AN OVERVIEW, International journal of pressure vessels and piping, 58(3), 1994, pp. 251-265
The transition metal joint (TMJ) between an austenitic stainless steel
and a chromium-molybdenum (Cr-Mo) ferritic steel used widely in steam
generators of power plants has for a long time presented problems rel
ating to premature failures in service. The direct (bimetallic) TMJ pr
esently in use is designed for a service life of about 200,000 h; but
such TMJs with iron-base weld metals have been failing in service with
in about one-third of their design lifetime, while their counterparts
with nickel-base weld metals fail within about one-half of their desig
n lifetime. The causes for such premature service failures of these TM
Js are discussed in detail, leading to the development of improved TMJ
s. One of the improved TMJs with a trimetallic configuration of austen
itic stainless steel/Alloy 800/Cr-Mo ferritic steel is discussed in de
tail, covering its development, characterisation and evaluation. Accel
erated performance tests in the laboratory have indicated a four-fold
improvement in the service life of the TMJ with this trimetallic confi
guration compared to the bimetallic configuration. The metallurgical d
etails of these studies are also discussed in this paper.