There is increased interest in compact heat exchanger (CHX) application for nuclear service given the high thermal efficiency and compactness of CHXs. Dense microchannels with high surface area are created by joining a stack of etched plates through diffusion bonding. Diffusion bonding changes the mechanical properties of the base material, which demands for new set of allowable stress for design purpose. Existing nuclear code ASME Sec. III, Div. 5 do not provide any recommendation regarding diffusion bonded alloy properties. Hence, there is a need to develop allowable stresses of diffusion bonded alloys and respective weldments for primary stress evaluation. In this paper, one of candidate material in Sec. III., alloy 800H, was selected for diffusion bonding trials.  Preliminary results obtained from a series of tensile and creep tests suggest that the diffusion bonded material is weaker than the base metal 800H. These experiments are used in determining the allowable stresses of the diffusion bonded 800H material. In this paper, a table of allowable stress which includes S~mt~, S~o~, S~t~, S~y~ and S~u~ for diffusion bonded Alloy 800H are presented and compared against the base metal. A strategy is proposed to extrapolate short term creep tests for longer creep life and estimate the onset of tertiary creep strain.


Allowable Stress Development of Diffusion Bonded Alloy 800h for Section Iii

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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