L52249 Failure Initation Modes of Pipe with High Charpy Transition Temperature

Abstract

This report presents a methodology that determines the lowest temperature where ductile fracture would occur for either sharp cracks or blunt corrosion flaws in older low-toughness line pipe base metals. It is applicable to either axial or circumferential flaws in pipes under quasi-static loading, i.e., normal operating conditions with no sudden transient loads. The results showed that ductile initiation of a surface crack can occur at a significantly lower temperature than the Charpy transition temperature. A master curve of transition temperatures for different pipe thickness and crack geometries was developed and validated on 1927 and 1948 vintage pipes. The master-curve of transition temperatures comes from accounting for thickness effects, loading-rate effects, and constraint effects (for a surface crack) on the transition temperatures of the flawed pipe relative to the Charpy transition temperature. These transition temperature shifts were empirically determined from hundreds of past full-scale tests and literally thousands of laboratory tests, and then checked against data developed on much older vintage line pipe steels, i.e., the 1927 and 1948 pipes in this project.