A Statistical Analysis of the Notch Toughness of 9% Nickel Steels Obtained from Production Heats

Abstract Storage tanks for liquefied natural gas are constructed from 9% nickel steel. A collection of over 600 production heat sheets from producers in Europe, Japan, and the United States was assembled and analyzed to establish the trend in changes of composition and mechanical properties which have taken place in the production of these steels over the past 15 years. Generally, enhancement of the toughness of 9% nickel steels has been attained by lowering impurity levels. In fact, Charpy notch toughness values at 77K (−196°C) far in excess of the ASTM minimum requirement of 27 J are now consistently obtained in production. Two approaches were used in developing multiple regressions for Charpy toughness from the 627-heat data base. One approach involved the formulation of second-order expansions of the original predictor variables, while the second was a less formal approach wherein possible predictor variable combinations were generated from metallurgical considerations. Both multiple regressions accounted for approximately two-thirds of the variability in Charpy notch toughness values about the mean (112 J) of the data base.