The generalized diagram of fracture toughness for pipeline steels

Transit oil and gas pipelines usually exhaust their design service life after 30-40 years. Embrittlement is one of the most dangerous consequences of metal aging. Standard linear fracture toughness K-IC testing of pipeline steels is possible only at a sufficiently low temperature (-196 degrees C) when the pipe wall thickness satisfies plane strain conditions. In this case there arises the problem of calculating K-IC values at operational temperatures, by means of the results of low-temperature small specimen testing. The aim of the present work is building up the concept of a generalized fracture toughness diagram for different pipeline steels within the absolute temperature range 77 <= T <= 293 K. Nine different pipeline steels in "as-received" state were tested. A linear relationship between yield stress and Brinell hardness HB was revealed within the temperature range mentioned above. The generalized correlation between relations of K-IC,K-T/K-IC,K-243 and HBT/HB243 was found. Here subscripts "T" and "243" correspond respectively to any temperature and a phase transition temperature of 243 K. The correlation described makes it possible to propose a new simplified method for different pipeline steels fracture toughness estimations. (C) 2012 Elsevier Ltd. All rights reserved.