Description

ASME STP-NU-020 – Verification of Allowable Stresses in ASME Section III, Subsection NH for Alloy 800H

Databases summarizing the creep-rupture properties of alloy 800H and its variants were reviewed and referenced. For the most part, the database was judged to be adequate to meet the needs for time-dependent properties in the extension of alloy 800H in ASME Section III Subsection NH (III-NH, Components in Elevated Temperature Service) to 900°C (1650°F) and 600,000 hours. Procedures for analyzing creep and stress-rupture data for III-NH were reviewed and compared to the current procedure endorsed by the ASME Section II on Materials. The stress-rupture database for alloy 800H in the temperature range of 750 to 1000°C (1382 to 1832°F) was assembled and used to estimate the average and minimum strength for times to 600,000 hours.

Part II Weldments – Databases summarizing the tensile and creep-rupture properties of deposited weld metal and weldments for alloy 800H were reviewed and referenced. Procedures for analyzing creep-rupture data for temperatures of 750°C (1382°F) and higher were reviewed and used to estimate the weld strength reduction factors (SRFs) as a function of time and temperature for temperatures to 900°C (1650°F). The database was judged to be inadequate to meet the needs for the extension of the use of filler metal for alloy 800H in ASME Section III Subsection NH to 900°C (1650°F). Five appendices were included that 1) listed the data used in the evaluation of the SRFs, 2) provided the values for parametric constants in the models, 3) provided an example of the calculated SRFs for alloy 82, 4) recommended supplemental creep-rupture testing to expand the database and improve the estimation of SRFs for long-time service and 5) provided a summary of a parametric Finite Element Analysis (FEA) study of cross-weld samples.