Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Loading Dependence of Mitigation Effect of CO on Hydrogen Embrittlement of Pure Iron and Low
Carbon Steel
Ryosuke Komoda1, 2, Masanobu Kubota2, Aleksandar Staykov2, Patrick Ginet3,Jader Furtado4, Laurent Prost5, Akihide Nagao2, 5
1Fukuoka University, Fukuoka, Japan.
2International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka Japan.
3Air Liquide France Industrie, Saint Priest, France.
4Materials, Design & Manufacturing Group, Air Liquide Research & Development, Jouy-en-Josas Cedex, France.
5Air Liquide Laboratories, Kanagawa, Japan.

also conducted to elucidate the mechanism whereby the loading rate
and fatigue loading frequency affect the mitigation effect of the CO on
the HE.

ABSTRACTThe mitigation effect of carbon monoxide (CO) on hydrogen
embrittlement (HE) was studied in terms of the loading rate dependenceby fracture toughness tests, fatigue crack growth tests, and density
functional theory (DFT) simulations. The experimental results
demonstrated that the mitigation effect is reduced with a decreasing
loading rate in the lower crack growth rate region. The DFT
simulations revealed that this is caused by the incomplete coverage ofthe iron surface by CO. Oppositely, the mitigation effect increased withthe decreasing loading rate in the higher crack growth rate region due toa lack of CO adsorption on the iron surface.

EXPERIMENTAL PROCEDURE
Material
The materials used were an ASTM A333 grade 6 low carbon pipe steel
and laboratory-made pure iron. The pure iron was used to identify themechanism by which the loading rate affects the mitigation of HE
under the simplified conditions than the case of a low carbon steel. The
chemical compositions and mechanical properties of the materials areshown in Tables 1 and 2, respectively.

KEY WORDS: Hydrogen embrittlement; iron and low carbon steel;carbon monoxide; loading rate; fracture toughness; fatigue crack
growth; DFT simulation.

Table 1. Chemical compositions of materials used (mass %).
MaterialCSiMnPSCr Ni
A333
0.11
0.25 1.21 0.010 0.002 0.03 0.05
Pure iron 0.0048 <0.003 <0.003 0.002 0.0003 -INTRODUCTION
The first process of hydrogen embrittlement (HE) in gaseous hydrogen(H2) is hydrogen uptake from the gaseous hydrogen into the material.
The dissociation of the dihydrogen molecule into hydrogen atoms is aheterogeneous catalysis process of hydrogen uptake that requires iron(Fe) surface catalytic sites [Lennard-Jones, 1932]. When a specific gas
impurity that has a stronger interaction with the Fe surface than the H2molecule, such as oxygen (O2) and carbon monoxide (CO), is containedin the environmental H2 gas, the gas impurity results in deactivation ofthe catalytic Fe surface following preferential adsorption of theimpurity on the Fe surface [Staykov, Yamabe, and Somerday, 2014]. Asa consequence, hydrogen uptake in iron or steel is suppressed, whichleads to mitigation of the HE [Holbrook, Cialone, Collings, Drauglis,Scott, and Mayfield, 2012; Somerday, Sofronis, Nibur, San March, andKirchheim, 2013].
In this study, CO was mixed with H2 gas as an impurity to investigateits mitigation effect on the HE in fracture toughness and fatigue crack
growth tests in conjunction with the effects of the loading rate andfatigue loading frequency, respectively. Density functional theory(DFT) simulations of the CO and H2 approaching the Fe surface wereFe
Bal.
Bal.

Table 2. Mechanical properties of materials used.
UltimateYieldReduction Vickers
tensile Elongation
Material
strengthin area
hardness
strength
(%)
(MPa)
(%)
HV
(MPa)
A333
355
481
4481136
Pure iron
198
265
5487
121

Fracture toughness and fatigue crack growth testsThe fracture toughness and fatigue crack growth tests were conductedin accordance with the ASTM E1820 and ASTM E647 standards,respectively. The configurations of the compact tension (CT)specimens used in these two types of tests are shown in Fig. 1. Bothtypes of CT specimens have side grooves with a depth of 1.0 mm witha notch root radius of 0.3 mm in order to avoid crack tunneling.
The test environments were H2, nitrogen (N2), and CO added H2 gases.
The purity in the bottle of these gases were ≥99.9999%. Especially, the3038