Determination of Fracture Toughness and KIC-CVN Correlations for BM, HAZ, and WB in API 5L X60 Pipeline

Abstract

This paper presents a study to determine the fracture toughness for the API 5L X60 pipeline in the base metal (BM), the heat-affected zone (HAZ), and the welding bead (WB) by SE(B) specimens in the short transverse direction in an API 5L X60 pipeline. Also, a comparison of the KIC results from SE(B) specimens and KIC-CVN (Charpy V-notch) correlation equations using CVN energy values was done. SE(B) specimens were machined and tested according to ASTM E339. Standard Charpy specimens were machined and tested according to ASTM E23. The notch remained within the evaluation zone to obtain KIC and Charpy specimens at the HAZ and WB. The KIC and CVN values are higher for the BM, followed by the HAZ and the WB. These KIC and CVN values are similar to those reported by other authors in API 5L pipelines. The decrease in KIC and CVN values is due to the microstructure present in the temperature transformations. For BM, the ferrite matrix with pearlite colonies could be presented, while for the WB zone, martensite and finer bainite are detected. In some regions of the HAZ temperatures are reached that promote the transformation of the ferritic/pearlitic structure of the BM into austenite. KIC-CVN correlation equations values should be used only to estimate KIC values when KIC data cannot be obtained from standard specimens.