Numerical analysis of microstructural characteristics on the hydrogen susceptibility of pipeline steels

Materials & Design, vol. 266, pp. 116164

Abstract

Hydrogen-induced degradation challenges the safe operation of pipeline steels. However, the quantitative influence of complex microstructural features on hydrogen transport and mechanical response is not well understood. This study presents a two-way coupled crystal plasticity–hydrogen diffusion framework for analyzing the hydrogen susceptibility of two API X70 pipeline steel grades with different microstructures: ferritic–pearlitic (=X70-T14) and predominantly bainitic (=X70-T19). Statistically representative three-dimensional microstructure models were generated using EBSD-based data enhanced by a Wasserstein generative adversarial network to capture realistic morphological and crystallographic distributions. The models were calibrated using macroscopic tensile tests and phase-specific macro-indentation data. The hydrogen transport, trapping, and degradation were evaluated under various stress states using a fracture indicator parameter that accounts for HELP (hydrogen-enhanced localized plasticity) and HEDE (hydrogen-enhanced decohesion) mechanisms. The results demonstrate that bainitic X70-T19 steel accumulates higher plastic strain, stress triaxiality, and hydrogen concentration. This leads to increased hydrogen susceptibility under uniaxial loading. In contrast, X70-T14 steel is more vulnerable under plane strain and biaxial tension. Additional parametric case studies reveal that non-metallic inclusions, voids, grain size, phase fraction, and banded pearlite-structures significantly influence hydrogen kinetics and local damage initiation. The proposed framework establishes a data-driven foundation for microstructure design toward hydrogen-resistant pipeline steels. • At low stress triaxiality, both X70 grades exhibit similar hydrogen resistance. • Ferritic-pearlitic X70 shows higher FIP values at elevated stress triaxialities. • Inclusions, voids and phase fraction control hydrogen localization. • HELP/HEDE coupling accelerates hydrogen-assisted damage evolution.

Authors 8

1. Berk Tekkaya corresponding Aachen Institute of Metal Forming

   RWTH Aachen University

   Affiliation as printed

   Institute of Metal Forming, Intzestraße 10, 52072, Aachen, Germany

2. Ioanna Papadioti

   Aristotle University of Thessaloniki

   Affiliation as printed

   Department of Civil Engineering, Aristotle University of Thessaloniki, 54124, Thessaloniki, Greece

3. Ilias Bellas

   University of Thessaly

   Affiliation as printed

   Department of Mechanical Engineering, University of Thessaly, 38334, Volos, Greece

4. S. Meenakshi Sundaram

   Aalto University

   Affiliation as printed

   Department of Mechanical Engineering, Aalto University, 02150, Espoo, Finland

5. Sophie Stebner Aachen Institute of Metal Forming

   RWTH Aachen University

   Affiliation as printed

   Institute of Metal Forming, Intzestraße 10, 52072, Aachen, Germany

6. Nikolaos Aravas

   Kyushu University · University of Thessaly

   Affiliation as printed

   Department of Mechanical Engineering, University of Thessaly, 38334, Volos, Greece

   International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Moto-oka Nishi-ku, Fukuoka, 819-0395, Japan

7. Junhe Lian Aachen Institute of Metal Forming

   RWTH Aachen University

   Affiliation as printed

   Institute of Metal Forming, Intzestraße 10, 52072, Aachen, Germany

8. Sebastian Münstermann Aachen Institute of Metal Forming

   RWTH Aachen University

   Affiliation as printed

   Institute of Metal Forming, Intzestraße 10, 52072, Aachen, Germany