Fast Reactors and Accelerator Driven Systems Knowledge Base
Conference Article: Creep-fatigue evaluation on butt welded joints of type 304 SS
Wada, Y.; Asayama, T.; Hasebe, S.; Kasahara, N. (Power Reactor and Nuclear Fuel Development Corp., Oarai, Ibaraki (Japan). Oarai Engineering Center)Abstract
n high temperature plant systems such as thermal power generation and petro-chemical
complexes, various weldments are used for pressure vessels and piping. Usually in
structural design methods for weldment of conventional pressure vessels and piping
systems, load controlled stresses are dominant, and to protect early failure in
weldments tensile and creep strengths of each welded joint have not to be lower than
the standard values of base metal. While under cyclic deformation controlled stress
such as thermal loading in LMFBR, creep-fatigue phenomenon caused by reversal
loading and residual stress relaxation is dominant. Therefore, a creep-fatigue evaluation
method of Type 304 ss butt welded joints has to be investigated under cyclic thermal
loading. For a study of this effect, the strain concentration factor Kepsilon. Kepsilon =
Max[1+(qwq-1)(1-2 gammaysigmay/E εn), Kepsilon0], which is derived from the
generalized elastic follow-up concept as the plastic strain redistribution, was applied,
and in the Kepsilon factor the metallurgical discontinuity effects. Qw and gammay were
considered. The elastic follow-up increment factor for weldment. Qw is equal to 2
under uni-axial mechanical loading. And under bi-axial thermal loading in shell-type
structures, it is clarified that 1.5 as the qw value can be applied. As the yield ration
gammay, the value of 0.8 is the best for Type 304 ss weldment. As for the creep
damage estimation, the simplified procedure based on the time fraction rule is
discussed, and it is investigated how the creep damage of weldment can be evaluated
by using mechanical properties of base metal (design standard values). The initial value
of stress relaxation is determined by the cyclic stress-strain relation of base metal and
the above Kepsilon value. Stress relaxation during strain hold can be analyzed by using
creep strain behaviour of base metal. Finally the allowable creep-fatigue life can be
estimated by using the design curves.
view the full text of this article
(10 pages, format: PDF, size= 478kB)
key words: Fast Neutron Spectrum Systems, Nuclear Technology