Investigation of Hydrogen Embrittlement Susceptibility and Fracture Toughness Drop after in situ Hydrogen Cathodic Charging for an X65 Pipeline Steel

Helen P Kyriakopoulou; Panagiotis Karmiris-Obratański; Athanasios S Tazedakis; Nikoalos M Daniolos; Efthymios C Dourdounis; Dimitrios E Manolakos; Dimitrios Pantelis

doi:10.3390/mi11040430

Investigation of Hydrogen Embrittlement Susceptibility and Fracture Toughness Drop after in situ Hydrogen Cathodic Charging for an X65 Pipeline Steel

Micromachines (Basel). 2020 Apr 20;11(4):430. doi: 10.3390/mi11040430.

Authors

Helen P Kyriakopoulou¹, Panagiotis Karmiris-Obratański^{2

3}, Athanasios S Tazedakis⁴, Nikoalos M Daniolos⁴, Efthymios C Dourdounis⁴, Dimitrios E Manolakos³, Dimitrios Pantelis¹

Affiliations

¹ National Technical University of Athens, Shipbuilding Technology Laboratory, School of Naval Architecture and Marine Engineering, Athens 15780, Greece.
² AGH University of Science and Technology, School of Mechanical Engineering and Robotics, Mickiewicza 30, 30-059 Cracow, Poland.
³ National Technical University of Athens, School of Mechanical Engineering, Heroon Polytechniou 9, 15780 Athens, Greece.
⁴ Corinth Pipeworks S.A., Industrial Area of Voiotia, Thisvi, Domvraina 32010, Greece.

Abstract

The present research focuses on the investigation of an in situ hydrogen charging effect during Crack Tip Opening Displacement testing (CTOD) on the fracture toughness properties of X65 pipeline steel. This grade of steel belongs to the broader category of High Strength Low Alloy Steels (HSLA), and its microstructure consists of equiaxed ferritic and bainitic grains with a low volume fraction of degenerated pearlite islands. The studied X65 steel specimens were extracted from pipes with 19.15 mm wall thickness. The fracture toughness parameters were determined after imposing the fatigue pre-cracked specimens on air, on a specific electrolytic cell under a slow strain rate bending loading (according to ASTM G147-98, BS7448, and ISO12135 standards). Concerning the results of this study, in the first phase the hydrogen cations' penetration depth, the diffusion coefficient of molecular and atomic hydrogen, and the surficial density of blisters were determined. Next, the characteristic parameters related to fracture toughness (such as J, KQ, CTOD_el, CTOD_pl) were calculated by the aid of the Force-Crack Mouth Open Displacement curves and the relevant analytical equations.

Keywords: X65 pipeline steel; crack mouth open displacement (CMOD); crack tip opening displacement test (CTOD); fracture analysis; hydrogen embrittlement; in situ hydrogen cathodic charging.