10 issues in the study of hydrogen embrittlement in hydrogen transmission pipelines. Do you know? ? ? ?
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***The 10 issues mentioned in Professor Cheng Yufeng, a member of the ***Royal Academy of Sciences and from the University of Calgary, in his report titled “Further Exploration of Hydrogen Embrittlement in Hydrogen Transport Pipelines” are as follows: Q1: Are enough H atoms generated in gas hydrogen pipelines to cause cracks? Can sufficient H atoms be produced in hydrogen-containing/hydrogen pipelines to lead to cracking? Q2: Is cathodic H-charging representative of gasous H-charging? Can cathodic electrochemical hydrogen charging represent gaseous hydrogen charging? Q3: Why are H atoms not charged (or at an appreciable amount) in the steels in gasous environments? Why is there no hydrogen incorporation in steels in gas-phase environments (or is the hydrogen content low)? Q4: What is a reliable gaseous H-charging method with convincing reproducibility? Which is the reliable gas-phase hydrogen charging method with good reproducibility? Q5: Although the controversial results regarding stress-strain behavior are evident, which one is correct and how does the H2 gas environment affect the deformation behavior of steels? Published research papers present clearly conflicting results regarding stress-strain behavior; which side is correct? How does a hydrogen environment affect the (plastic) deformation behavior of steel? Q6: Although the SSRT results are clearly controversial, does cyclic loading affect the uptake of hydrogen atoms and thus the fatigue behavior of steels? What is the interaction between hydrogen and fatigue? Some SSRT experiment results in the literature show opposite outcomes; does cyclic loading influence the uptake of hydrogen atoms, thereby affecting the fatigue behavior of steels? Q7: How is the amount of accumulated H atoms at pipeline defects quantified? More importantly, how are the modeling results verified for individual pipes? How can the amount of hydrogen atoms accumulated at pipe defects be quantified? More importantly, how can the results of modeling be verified within a pipeline? Q8: How is the pipe surface condition reproduced in the lab to obtain realistic H-charging results under controllable test conditions? How can the surface condition of pipes be replicated in the laboratory in order to achieve accurate hydrogen charging experiment results under controlled testing conditions? Q9: How does cyclic loading affect the entry and distribution of H atoms in steels? How does cyclic loading influence the incorporation of hydrogen atoms into steel and their diffusion within it? Q10: How does cyclic loading reduce the threshold H concentration to initiate cracks? How does repeated loading lower the hydrogen concentration threshold that leads to crack formation?
Q1: In a gas hydrogen tube, hydrogen atoms are usually in a gaseous state, rather than in an atomic form. Gaseous hydrogen is mainly composed of hydrogen molecules, namely hydrogen gas (H₂). In normal hydrogen tubes, the number of hydrogen atoms (individual hydrogen atoms, rather than parts of molecules) is very low, so they do not cause cracks to form. Q2: Cathodic electrochemical hydrogenation is a method of adsorbing hydrogen atoms or molecules onto a metal surface or injecting them into the metal. However, gas-phase hydrogenation usually refers to injecting hydrogen (H₂) into a material in a gaseous environment. Therefore, cathodic electrochemical hydrogenation does not represent gas-phase hydrogenation. Q3: In a gaseous environment, hydrogen atoms or molecules are more likely to react with other components in the gas (such as oxygen, nitrogen, etc.) rather than with elements in steel. Furthermore, an oxide layer usually forms on the surface of steel, which prevents further reactions between hydrogen atoms or molecules and the steel. Therefore, in a gaseous environment, the hydrogen content in steel is usually low. Q4: The current methods for hydrogenation in the gas phase mainly include cathodic electrochemical hydrogenation, high-temperature pyrolytic hydrogenation, and plasma-assisted hydrogenation. Among them, high-temperature pyrolytic hydrogenation and plasma-assisted hydrogenation are considered to be reliable and reproducible methods for gas-phase hydrogenation. Both methods can inject hydrogen into the material at high temperatures and pressures, and the reproducibility of the experimental results can be ensured by controlling the experimental conditions. Q5: There are disputes regarding the experimental results on stress-strain behavior, which may be due to differences in experimental conditions, material types, surface treatment, and other factors. Specifically, a hydrogen environment may affect the plastic deformation behavior of steel, such as reducing the yield strength and tensile strength of the material. However, further research and experimental verification are needed to determine which result is correct. Q6: Cyclical loading may affect the amount and distribution of hydrogen atoms in steel, thereby influencing the fatigue behavior of the steel. Specifically, cyclic loading can induce microcracks and defects in the material, and these areas can become sites for hydrogen atoms to accumulate, thereby accelerating the material’s fatigue failure. However, the mechanism of interaction between cyclic loading, hydrogen atom ingress, and fatigue behavior is not yet fully understood, and further research and experimental verification are required. Q7: The amount of accumulated hydrogen atoms can be quantified by placing measuring instruments at the pipeline defects or using non-destructive testing techniques. Furthermore, mathematical models can be developed to predict the diffusion and distribution of hydrogen atoms in pipes, and these models can be compared with experimental results to verify their accuracy and reliability. Q8: In the laboratory, the actual operating conditions of pipelines can be simulated by controlling experimental parameters such as temperature, pressure, and material surface treatment. For example, a high-temperature furnace can be used to simulate the high-temperature environment in pipes, and a gas generator can be used to simulate the gas flow within the pipes. More realistic hydrogen filling experiment results can be obtained through these methods. Q9: Cyclic loading may affect the diffusion and distribution of hydrogen atoms in steel. Specifically, cyclic loading can cause microcracks and defects in steel, and these areas may become sites for the accumulation of hydrogen atoms. Furthermore, cyclic loading may also affect the thickness and structure of the oxide film on the surface of the steel, thereby influencing the interaction between hydrogen atoms and the steel. Q10: Cyclical loading may lower the hydrogen concentration threshold, thereby inducing cracks, as it can cause microcracks and defects in the steel, areas that may serve as sites for hydrogen atoms to accumulate. Over time, the hydrogen concentration in these areas may increase to a level sufficient to induce cracks. Furthermore, cyclic loading may also affect the thickness and structure of the oxide film on the surface of the steel, thereby influencing the interaction between hydrogen atoms and the steel and reducing the hydrogen concentration threshold.
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