Time-dependent allowable stresses for ASME code case N-47: a second look

Abstract

This report represents a partial assessment of the implications of new data and improved analytical techniques regarding possible revisions to the current allowable stresses in Code Case N-47. We analyzed available stress-rupture and time to tertiary creep data for type 304 stainless steel, type 316 stainless steel, and alloy 800H. The results show that the current Code Case allowable stresses for type 304 stainless steel appear to be appropriate. However, the stresses given in the Code Case for type 316 stainless steel appear to be too high by up to about 15 MPa in the long-time (>10,000 h) region at 704{sup 0}C (1300{sup 0}F). Moreover, our results indicate lower allowable stresses (by 5 to 20%) than those given in the Code Case for alloy 800H under a variety of loading conditions.