NDT of Fracture Toughness for Pipeline Steels

Overview

Main Objective

The primary objective of the Phase I project is to demonstrate sensitivity of the nonlinear guided wave system to the Fracture Appearance Transition Temperature (FATT) of API 5L pipe steels in a laboratory environment and to show how the FATT is connected to the fracture toughness.

Public Abstract

Ultrasound-based technology to nondestructively determine fracture toughness of pipeline steels will be developed. Fracture toughness is the material parameter that, along with applied loading and flaw geometry, dictates the critical crack size, and therefore controls the flaw size that must be detected during inspections. A major challenge facing pipeline operators is that many pipelines are old, making their structural integrity uncertain, and that material pedigree of the pipeline steel is unknown. Therefore, operations must be based on minimum values of the material parameters. The probability that actual fracture toughness is higher than the minimum is reasonably high, which means that pipelines are operating below capacity. Nondestructive determination of fracture toughness by ball indentation has not sufficiently solved the problem. Nonlinear features of ultrasonic wave propagation are sensitive to material nonlinearities, associated with microstructure (based on composition and processing), that dictate fracture toughness. Prior results indicate that ultrasonic nonlinearity is related to fracture appearance transition temperature, which in turn is related to fracture toughness. Herein, wave interaction of two circumferential guided waves will be used to generate nonlinear features (in a completely nondestructive way) that will be related to the fracture appearance transition temperature obtained from Charpy V-notch impact tests.

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