Assessing toughness correlation methods for S690 steels based on complete and incomplete CHarpy transition curves

Abstract

Modern structural integrity assessment codes such as BS 7910 and FITNET have been increasingly utilised throughout design, fabrication and operation stages of metallic infrastructure. When defects are present, these codes describe an engineering critical assessment which requires the input of material fracture toughness. The standard fracture toughness test method - crack tip opening displacement (CTOD) test is both time consuming and costly to measure toughness. Instead, it is more common to determine the fracture toughness based on the correlation with Charpy impact toughness test results, which are relatively quick and inexpensive to obtain. However, existing correlation methods are empirically based on the test results in the past from the steel grades at that time and may not represent the modern high strength grades of steel with large thickness. This often leads to overly conservative engineering critical assessment output. To further validate the toughness correlation methods, this paper compares the Charpy energy based toughness estimates with CTOD test results, focusing on high strength steel grade S690 including base metal, welds and heat affected zone, with a thickness ranging from 10 mm to 160 mm. In addition to the method using complete Charpy ductile-to-brittle transition curves, the formulae proposed in the FITNET report and procedure for incomplete datasets are also examined. The outcome of this study provides judgement on the validation and potential conservatism induced by toughness correlation for high strength steels. This also helps with further developing the procedure of converting Charpy impact energy into material fracture toughness in structural integrity assessment codes.

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ORCID for Y. Wang: orcid.org/0000-0001-5619-7795

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