Creep Property and Correlation of Diffusion-Welded Alloy 800H Tubes for Printed Circuit Heat Exchangers and Steam Generators

Thermal creep tests were conducted on diffusion-welded Alloy 800H tubes at 700 °C under various hoop stresses between 70 and 140 MPa using an in-situ creep measurement system. The tube-type creep specimens obtained from diffusion-welded Alloy 800H plates at 1150 °C and 10 MPa for 2 h achieved a uniform thickness with only 1.8% variation. The primary and secondary creep regimes were clear in the stain curves, while tertiary creep and subsequent material rupture were not observed due to the premature leakage of Ar gas at the interface of diffusion welding. The acquired creep strain data do not match well with the reference creep data of the Alloy 800H, which requires further work to explain the whole details. In such a context, a modified Garofalo correlation was used to fit the acquired creep data resulting in the meaningful parameters for primary creep strain and secondary creep rate. The Ar gas leakage at the interface of diffusion welding was confirmed by leakage test and microstructure investigations. The current study points to the requirement for a better diffusion welding process for Alloy 800H for use in printed circuit heat exchangers and steam generators. Graphic Abstract: [Figure not available: see fulltext.]