Gaseous inhibitors: A comprehensive overview on mitigating hydrogen embrittlement in pipeline steels

Keywords: Gaseous inhibitors; Hydrogen embrittlement; Pipeline steels

Overview

Hydrogen transport in pipelines is critical for renewable energy transition, but hydrogen embrittlement (HE) poses a major risk by weakening steels. Adding trace gases (inhibitors) like CO, O₂, and NH₃ can mitigate this effect.

Mechanisms of HE

• Adsorption → Dissociation → Absorption of H₂ on steel surfaces.
• Affected by microstructure, stress, and surface defects.
• Leads to cracking, reduced ductility, and fracture toughness.

Gaseous Inhibitors

Carbon Monoxide (CO)

• Competes with H₂ for adsorption sites, raising dissociation energy.
• Effectiveness depends on:
  • Concentration (better at higher ppm).
  • Loading frequency (lower frequency improves inhibition).
  • Gas pressure (higher pressure requires more CO).
  • Crosshead speed (too slow reduces effect).

Oxygen (O₂)

• More electronegative than H₂ → strong inhibitor via surface passivation.
• Inhibits crack growth, especially at ≥10 vppm.
• Efficiency influenced by strain rate and test frequency.

Ammonia (NH₃)

• Adsorbs effectively but decomposes to produce hydrogen.
• Works at certain conditions; less effective at low strain rates and high pressures.

Other Gases

• Effective: N₂O, SO₂ (moderate).
• Ineffective/Minimal: CO₂, CH₄, C₂H₂.
• Harmful: Sulfur-based gases (e.g., CH₃SH, H₂S).

Key Influencing Factors

• Higher inhibitor concentration → better mitigation.
• Lower loading frequency → more time for inhibitor adsorption.
• Higher H₂ pressure → requires more inhibitors.
• Lower crosshead speeds → reduce inhibitor efficiency.

Conclusions

• Gaseous inhibitors slow hydrogen adsorption but do not prevent equilibrium absorption.
• Continuous supply of inhibitors is essential.
• Techno-economic feasibility (compression costs, scaling) is a major barrier.
• More experimental research is needed across conditions (temperature, pressure, gas mix).

Funding

The research was supported by the Energy Transition Fund via the HyFit and HySource projects in collaboration with Fluxys. The work also received support from FWO (junior postdoctoral fellowship of the Research Foundation - Flanders via grant 1248122N).

Key Responsibilities as First Author

Literature Review & Knowledge Integration

Conducted an extensive review of hydrogen embrittlement mechanisms in pipeline steels, with a particular focus on gaseous inhibitors such as CO, O₂, and NH₃, synthesizing findings across surface science, materials engineering, and fracture mechanics.

Research Design & Methodology Development

Structured the study framework by combining theoretical models (e.g., Density Functional Theory insights, Sievert’s law) with experimental validation strategies to analyze inhibitor efficiency under varying loading, frequency, and pressure conditions.

Data Analysis & Critical Evaluation

Interpreted results from mechanical tests (fracture toughness, fatigue crack growth, J–∆a resistance curves) to assess the mitigation performance of different gaseous inhibitors. Identified key influencing factors such as gas concentration, crosshead speed, and hydrogen pressure.

Collaboration & Coordination

Coordinated with co-authors from Ghent University and Fluxys, integrating contributions across experimental work, computational modeling, and engineering applications. Ensured consistency in data interpretation and technical accuracy.

Manuscript Preparation & Scientific Writing

Led the drafting of the manuscript, including abstract, introduction, mechanisms, results, and conclusions. Translated complex surface chemistry and materials science findings into clear, comprehensive narratives suitable for publication in the International Journal of Hydrogen Energy.

Research Impact & Practical Implications

Highlighted techno-economic challenges of inhibitor use in large-scale hydrogen transport. Proposed future research directions involving varied conditions (temperature, hydrogen partial pressure, inhibitor mix) to optimize industrial applications.

Recommended citation: Jubica, L. Claeys, A. Laureys, W. De Waele, J. Schweicher, T. Depover, K. Verbeken, Gaseous inhibitors: A comprehensive overview on mitigating hydrogen embrittlement in pipeline steels, International Journal of Hydrogen Energy 136 (2025) 630-642. doi:10.1016/j.ijhydene.2024.08.018
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