Microstructure effects on the fracture surface resistance of base metal in line pipe steels in high pressure H2 gas

Published

April 29, 2025

Author(s)

Andrew LeBoeuf, Santigopal Samanta, Joseph Ronevich, Christopher San Marchi, Zachary Buck, Matthew Connolly, Lawrence Cho, Kip Findley

Abstract

Cost-effective transportation of gaseous hydrogen requires the use of long-distance low-carbon steel pipeline networks. Employing higher strength (X65-X70) grades can allow for economic viability by enabling operation at higher pressures. While higher strength steel grades are expected to exhibit decreased fracture resistance due to exposure to hydrogen, recent data shows that fracture resistance can vary considerably for different pipeline steels within a similar strength range. The present work aims to understand microstructural effects in determining the fracture response of modern pipeline grades in hydrogen gas. ASTM E1820 fracture toughness tests were performed in 21 MPa of high purity hydrogen gas on CT and SENB samples extracted from modern thermomechanically processed (TMP) line pipe including an X70 (banded ferrite-pearlite), an X65 (fully ferritic with some dispersed pearlite colonies), an X65 (fully ferritic with a higher volume fraction of dispersed pearlite colonies), and an X70 (fully ferritic with some dispersed pearlite colonies). While the fracture resistance in hydrogen (KJQ-H) did not correlate strongly with yield strength, some correlation with the amount and morphology of secondary microconstituents was observed, primarily with the low KJQ-H of the banded ferrite-pearlite microstructure. A stronger correlation was observed between increasing KJQ-H values and increasing bainitic nature of the microstructures, as measured by histograms of grain boundary misorientation angle collected from electron backscatter diffraction (EBSD) scans. Spacing measurements between high-angle grain boundaries also revealed a correlation between smaller effective grain sizes and higher KJQ-H, particularly when using a cutoff angle of 5° between adjacent grains.

Proceedings Title

PVP2025-154718

Conference Dates

July 20-25, 2025

Conference Location

Montreal, Quebec, CA

Conference Title

ASME 2025 Pressure Vessels and Piping Conference

Pub Type

Conferences

Keywords

Pipeline Steels, Fracture, Hydrogen Embrittlement, Microstructure

Citation

LeBoeuf, A. , Samanta, S. , Ronevich, J. , San Marchi, C. , Buck, Z. , Connolly, M. , Cho, L. and Findley, K. (2025), Microstructure effects on the fracture surface resistance of base metal in line pipe steels in high pressure H2 gas, PVP2025-154718, Montreal, Quebec, CA (Accessed October 20, 2025)