Research and demonstration on hydrogen compatibility of pipelines: a review of current status and challenges

Hydrogen transportation by pipelines gradually becomes a critical engineering route in the worldwide adaptation of hydrogen as a form of clean energy. However, due to the hydrogen embrittlement effect, the compatibility of linepipe steels and associated welds with hydrogen is a major concern when designing hydrogen-carrying pipelines. When hydrogen enters the steels, their ductility, fracture resistance, and fatigue properties can be adversely altered. This paper reviews the status of several demonstration projects for natural gas-hydrogen blending and pure hydrogen transportation, the pipeline materials used and their operating parameters. This paper also compares the current standards of materials specifications for hydrogen pipeline systems from different parts of the world. The hydrogen compatibility and tolerance of varying grades of linepipe steels and the relevant testing methods for assessing the compatibility are then discussed, and the conservatism or the inadequacies of the test conditions of the current standards are pointed out for future improvement.     

Hydrogen effects on X80 pipeline steel in high-pressure natural gas/hydrogen mixtures

Blending hydrogen into existing natural gas pipelines has been proposed as a means of increasing the output of renewable energy systems such as large wind farms. X80 pipeline steel is commonly used for transporting natural gas and such steel is subjected to concurrent hydrogen invasion with mechanical loading while being exposed to hydrogen containing environments directly, resulting in hydrogen embrittlement (HE). In accordance with American Society for Testing and Materials (ASTM) standards, the mechanical properties of X80 pipeline steel have been tested in natural gas/hydrogen mixtures with 0, 5.0, 10.0, 20.0 and 50.0vol% hydrogen at the pressure of 12 MPa. Results indicate that X80 pipeline steel is susceptible to hydrogen-induced embrittlement in natural gas/hydrogen mixtures and the HE susceptibility increases with the hydrogen partial pressure. Additionally, the HE susceptibility depends on the textured microstructure caused by hot rolling, especially for the notch specimen. The design calculation by the measured fatigue data reveals that the fatigue life of the X80 steel pipeline is dramatically degraded by the added hydrogen.     

From the perspective of new technology of blending hydrogen into natural gas pipelines transmission: Mechanism,experimental study,and suggestions for further work of hydrogen embrittlement in high-strength pipeline steels

Blending hydrogen into high-strength pipeline steels for high-pressure transmission may cause materials' hydrogen embrittlement (HE) failure. Although the hydrogen-induced failure of metallic materials has been studied for a long time, the process of hydrogen into the materials, hydrogen-induced delayed failure, and dynamic mechanisms of high-strength pipeline steels under high pressure have not been fully understood. This paper aims to provide a detailed review of the latest research on the hydrogen-induced failure of high-strength pipeline steels in hydrogen-blended natural gas transmission. First, introduced the typical hydrogen blending natural gas pipeline transmission projects and their associated research conclusions. Then, described the physical process of the HE in high-strength pipeline steels and the principle, development, and latest research progress of typical hydrogen embrittlement mechanisms in detail. Third, reviewed the research methods and progress of experimental and theoretical simulations for the HE in steels, including hydrogen permeation (HP) experiments, hydrogen content measurements, hydrogen distribution detection, mechanical property tests, and molecular dynamics simulations. The shortcomings of existing experimental and theoretical simulation methods in the hydrogen-induced analysis of high-strength natural gas pipeline steels under high pressure are discussed. Finally, the future research directions and challenges of this problem are proposed from three aspects: the multimechanism synergy mechanism, the improvement of experimental methods, and the establishment of a new interatomic multiscale model.     

The experiment study to assess the impact of hydrogen blended natural gas on the tensile properties and damage mechanism of X80 pipeline steel

Environmental hydrogen embrittlement has become a non-negligible problem in the hydrogen blended natural gas transportation. To qualitatively study the degradation mechanism of X80 steel used in the natural gas pipelines, the slow strain tensile experiments are carried out in this work. The nitrogen and hydrogen are adopted to simulate the hydrogen blended natural gas to explore the tensile properties of X80 steel. According to the volume proportion of hydrogen, the test atmospheres are divided into the reference atmosphere and the hydrogen-contained atmospheres of 1%, 2.2% and 5%. The tensile experiments of the smooth and notched specimens are conducted in the above gas atmospheres. Mechanical properties and fracture morphologies after stretching are further analyzed. The results show that the hydrogen blended natural gas has little effect on the tensile and yield strengths. Distinguished from the hydrogen volume proportion of 1% and 2.2%, with the increase of hydrogen proportion, the effect of hydrogen on mechanical properties of specimens increases significantly. Moreover, the deteriorated mechanical properties of notched specimens are more seriously than those of smooth specimens. This work provides the basis for safe hydrogen proportion for X80 pipeline steel when transporting hydrogen blended natural gas.     

Feasibility analysis of blending hydrogen into natural gas networks

Hydrogen fuel has the potential to mitigate the negative effects of greenhouse gases and climate change by neutralizing carbon emissions. Transporting large volume of hydrogen through pipelines needs hydrogen-specific infrastructure such as hydrogen pipelines and compressors, which can become an economic barrier. Thus, the idea of blending hydrogen into existing natural gas pipelines arises as a potential alternative for transporting hydrogen economically by using existing natural gas grids. However, there are several potential issues that must be considered when blending hydrogen into natural gas pipelines. Hydrogen has different physical and chemical properties from natural gas, including a smaller size and lighter weight, which require higher operating pressures to deliver the same amount of energy as natural gas. Additionally, hydrogen's small molecular size and lower ignition energy make it more likely to permeate through pipeline materials and seals, leading to degradation, and its wider flammability limits make it a safety hazard when leaks occur. In this study, we investigate these potential issues through simulation and technical surveys. We develop a gas hydraulic model to simulate the physical characteristics of a transmission and a distribution pipeline. This model is used throughout the study to visualize the potential impacts of switching from natural gas to hydrogen, and to investigate potential problems and solutions. Furthermore, we develop a Real-Time Transient Model (RTTM) to address the compatibility of current computational pipeline monitoring (CPM) based leak detection methods with blended hydrogen. Finally, we suggest the optimal hydrogen concentration for this model, and investigate the amount of carbon reduction that could be achieved, while considering the energy needs of the system.     

Evaluation of the safe separation distances of hydrogen-blended natural gas pipelines in a jet fire scenario

The desire for sustainable development in various countries has increased the use of hydrogen energy. Considering cost and time savings, the introduction of hydrogen into existing natural gas pipelines is an excellent option, and the failure consequences of hydrogen blending in natural gas pipelines should be considered. In this study, a solid flame model is used to calculate the thermal radiation intensity of a hydrogen-blended natural gas jet fire. A method is proposed to modify the calculation of the view factor in the near field, and parameters such as the specific heat capacity and calorific value of pure gas are replaced by the parameters of the mixed gas. The data of the Thornton and modified models are compared with the experimental results, and the modified model result is found to be more accurate. Using the modified model, the variations in different hydrogen blending ratios, internal pressures, and pipe diameters with the safe separation distance of the thermal radiation intensity in a pipeline accident are investigated, and the relationships between them are analyzed.     

Dynamic modeling and characteristic analysis of natural gas network with hydrogen injections

With the transformation of energy structure, the proportion of renewable energy in the power grid continues to increase. However, the power grid's capacity to absorb renewable is limited. In view of this, converting the excess renewable energy into hydrogen and injecting it into natural gas network for transportation can not only increase the absorption capacity of renewable energy but also reduce the transportation cost of hydrogen. While this can lead to the problem that hydrogen injection will make the dynamic characteristics of the pipeline more complicated, and hydrogen embrittlement of pipeline may occur. It is of great significance to simulate the dynamic characteristics of gas pipeline with hydrogen injection, especially the hydrogen mixture ratio. In this paper, the cell segmentation method is used to solve each natural gas pipeline model, the gas components are recalculated in each cell and the parameters of partial differential equation are updated. Additionally, the dynamic simulation model of natural gas network with hydrogen injections is established. Simulation results show that for a single pipeline, when the inlet hydrogen ratio changes, whether or not hydrogen injection has little influence on the pressure and flow. The propagation speed of hydrogen concentration is far less than that of the pressure and flow rate, and it takes about 1.2 × 10⁵ s for the 100 km pipeline hydrogen ratio to reach the steady state again.     

Hydrogen related degradation in pipeline steel: A review

To support our increasing energy demand, steel pipelines are deployed in transporting oil and natural gas resources for long distances. However, numerous steel structures experience catastrophic failures due to the evolution of hydrogen from their service environments initiated by corrosion reactions and/or cathodic protection. This process results in deleterious effect on the mechanical strength of these ferrous steel structures and their principal components. The major sources of hydrogen in offshore/subsea pipeline installations are moisture as well as molecular water reduction resulting from cathodic protection. Hydrogen induced cracking comes into effect as a synergy of hydrogen concentration and stress level on susceptible steel materials, leading to severe hydrogen embrittlement (HE) scenarios. This usually manifests in the form of induced-crack episodes, e.g., hydrogen induced cracking (HIC), stress-oriented hydrogen induced cracking (SOHIC) and sulfide stress corrosion cracking (SSCC). In this work, we have outlined sources of hydrogen attack as well as their induced failure mechanisms. Several past and recent studies supporting them have also been highlighted in line with understanding of the effect of hydrogen on pipeline steel failure. Different experimental techniques such as Devanathan–Stachurski method, thermal desorption spectrometry, hydrogen microprint technique, electrochemical impedance spectroscopy and electrochemical noise have proven to be useful in investigating hydrogen damage in pipeline steels. This has also necessitated our coverage of relatively comprehensive assessments of the effect of hydrogen on contemporary high-strength pipeline steel processed by thermomechanical controlled rolling. The effect of HE on cleavage planes and/or grain boundaries has prompted in depth crystallographic texture analysis within this work as a very important parameter influencing the corrosion behavior of pipeline steels. More information regarding microstructure and grain boundary interaction effects have been presented as well as the mechanisms of crack interaction with microstructure. Since hydrogen degradation is accompanied by other corrosion-related causes, this review also addresses key corrosion causes affecting offshore pipeline structures fabricated from steel. We have enlisted and extensively discussed several recent corrosion mitigation trials and performance tests in various media at different thermal and pressure conditions.     

Options of natural gas pipeline reassignment for hydrogen: Cost assessment for a Germany case study

The uncertain role of the natural gas infrastructure in the decarbonized energy system and the limitations of hydrogen blending raise the question of whether natural gas pipelines can be economically utilized for the transport of hydrogen. To investigate this question, this study derives cost functions for the selected pipeline reassignment methods. By applying geospatial hydrogen supply chain modeling, the technical and economic potential of natural gas pipeline reassignment during a hydrogen market introduction is assessed.The results of this study show a technically viable potential of more than 80% of the analyzed representative German pipeline network. By comparing the derived pipeline cost functions, it could be derived that pipeline reassignment can reduce the hydrogen transmission costs by more than 60%. Finally, a countrywide analysis of pipeline availability constraints for the year 2030 shows a cost reduction of the transmission system by 30% in comparison to a newly built hydrogen pipeline system.     

Effect of hydrogen addition on the route preference in natural gas flow in regular,horizontal T-junctions

During the transport of natural gas through pipelines small amounts of condensate can be formed due to temperature and pressure changes. If this natural gas/condensate flow arrives at a regular, sharp-edged T-junction in the pipeline system an interesting phenomenon may be observed i.e. unequal phase splitting of gas and condensate. In this paper its has been shown that the addition of hydrogen into a natural gas stream results in a different splitting behaviour in comparison with the natural gas flow without hydrogen addition.     

Thermodynamics of spontaneous dissociation and dissociative adsorption of hydrogen molecules and hydrogen atom adsorption and absorption on steel under pipelining conditions

While hydrogen pipelines have attracted increased attention, safety of the pipelines has been a concern in terms of hydrogen embrittlement (HE) occurring upon hydrogen atom (H) generation and permeation in the steels. In this work, thermodynamic analyses regarding H generation and adsorption on pipeline steels by two potential mechanisms, i.e., spontaneous dissociation and dissociative adsorption, were conducted through theoretical calculations based on Gibbs free energy change of the H generation reactions. Moreover, H adsorption free energy and configurations were determined based on density functional theory (DFT) calculations. Effects of H adsorption site, H coverage and hydrostatic stress on H adsorption and absorption were discussed. Spontaneous dissociation of hydrogen gas molecules to generate hydrogen atoms is thermodynamically impossible. Dissociative adsorption is thermodynamically feasible at wide temperature and pressure ranges. Particularly, an increased hydrogen gas partial pressure and elevated temperature favor the dissociative adsorption of hydrogen. Hydrogen atoms generated by dissociative adsorption mechanism can adsorb stably at On-Top (OT) and 2-fold (2F) Cross-Bridge sites of Fe (100), while hydrogen adsorption at 2F site is more stable due to a higher electron density and a stronger electronic hybridization between Fe and H. The influence of H atom coverage on dissociative adsorption occurs at low coverages only, i.e., 0.25–1.00 ML as determined in this work. External stresses make dissociative adsorption more difficult to occur compared with a fully relaxed steel. Both tetrahedral sites (TS) and octahedral sites (OS) can potentially host absorbed H atoms at subsurface of the steel. Absorbed H atoms will be predominantly trapped at TS due to a low energy path and exothermic feature. Diffusion of H atoms from steel surface to the subsurface is more difficult compared with the dissociative adsorption.     

Dynamic behaviour of non-isothermal compressible natural gases mixed with hydrogen in pipelines

This paper focuses on non-isothermal transient flow in mixed hydrogen–natural gas pipelines. The effect of hydrogen injection into natural gas pipelines has been investigated in particular the pressure and temperature conditions, Joule–Thomson effect, linepack and energy consumption of the compressor station. The gas flow is described by a set of partial differential equations resulting from the conservation of mass, momentum and energy. Real gas effects are determined by the predictive Soave–Redlich–Kwong group contribution method. The Yamal-Europe gas pipeline on Polish territory has been selected as case study.     

An MILP model for the reformation of natural gas pipeline networks with hydrogen injection

A mixed integer linear programming (MILP) model is proposed for the reformation of natural gas pipelines. The model is based on the topology of existing pipelines, the load and pressure at each node and the design factors of the region and minimizes the annual substitution depreciation cost of pipelines, the annual construction depreciation cost of compressor stations and the operating cost of existing compressor stations. Considering the nonlinear pressure drop equations, the model is linearized by a piecewise method and solved by the Gurobi optimizer. Two cases of natural gas pipeline networks with hydrogen injection are presented. Several adjustments are applied to the original natural gas pipeline network to ensure that our design scheme can satisfy the safety and economic requirements of gas transportation. Thus, this work is likely to serve as a decision-support tool for the reformation of pipeline networks with hydrogen injection.     

氢气管输技术研究进展

利用现有“全国一张网”的天然气管道设施,将氢气掺入天然气管道输送,可有效解决中国氢气规模化输送难题。该文综述目前关于氢气管道输送的研究成果,总结氢气管道建设现状;分析输氢工艺安全性,阐述管线泄漏的危害性及防护措施,分别讨论高压输送管道、中低压配送管道和管道焊缝的相容性;归纳目前的燃气互换性方法及设备适应性。指出了目前氢气管输面临的问题：掺氢比例等参数对氢气渗透、聚集、泄漏、喷射火灾等安全问题的影响尚不明确;氢气与典型管材的相容性研究不足;缺少纯氢和掺氢管道输送技术相关标准规范体系。     

A review of technical and regulatory limits for hydrogen blending in natural gas pipelines

There is rising interest globally in the use of hydrogen for the provision of electricity or heat to industry, transport, and other applications in low-carbon energy systems. While there is attention to build out dedicated hydrogen infrastructure in the long-term, blending hydrogen into the existing natural gas pipeline network is also thought to be a promising strategy for incorporating hydrogen in the near-term. However, hydrogen injection into the existing gas grid poses additional challenges and considerations related to the ability of current gas infrastructure to operate with blended hydrogen levels. This review paper focuses on analyzing the current understanding of how much hydrogen can be integrated into the gas grid from an operational perspective and identifies areas where more research is needed. The review discusses the technical limits in hydrogen blending for both transmission and distribution networks; facilities in both systems are analyzed with respect to critical operational parameters, such as decrease in energy density, increased flow speed and pressure losses. Safety related challenges such as, embrittlement, leakage and combustion are also discussed. The review also summarizes current regulatory limits to hydrogen blending in different countries, including ongoing or proposed pilot hydrogen blending projects.     

Failure pressure analysis of hydrogen storage pipeline under low temperature and high pressure

Low temperature and high pressure line pipes are widely used in hydrogen storage, air separation plant, liquefied natural gas (LNG) transportation etc. The material properties of pipes at low temperature are different from those at room temperature. If the medium in the pipe is corrosive, it will cause the pipe wall thickness to decrease. However, the failure pressure of the corroded hydrogen storage pipeline at extremely low temperature is lacking of adequate understanding. In this paper, we provided a novel failure pressure equation of the mild steel line pipe with corrosion defects at extremely low temperature. Firstly, a mechanical model of the line pipe with corrosion defects is established. And then, an analytical solution of the mechanical model is obtained based on elastic theory. Next, a failure pressure equation of the corroded hydrogen storage pipeline at extremely low temperature is developed. In the end, the accuracy of the failure pressure equation is verified by comparing with finite element method (FEM). The results suggest that the calculated value of the failure pressure equation is consistent with that of FEM. This paper provides a theoretical basis for the safety assessment of low temperature hydrogen storage pipeline. The new equation presented in this paper can provide useful guidance for the design of low temperature and high pressure pipelines.     

Study on the stratification of the blended gas in the pipeline with hydrogen into natural gas

When blending hydrogen into existing natural gas pipelines, the non-uniform concentration distribution caused by the density difference between hydrogen and natural gas will result in the fluctuations of local hydrogen partial pressure, which may exceed the set one, leading to pipeline failure, leakage, measurement error, and terminal appliance. To solve the problem, the H₂–CH₄ stratification in the horizontal and undulated pipe was investigated experimentally and with numerical simulations. The results show that in the gas stagnant situation, hydrogen-methane blending process will cause an obvious stratification phenomenon. The relations between the elevation, pressure, hydrogen fraction, etc., and the gas stratification are figured out. Moreover, even when the blended gas flows at a low rate, the hydrogen-caused stratification should also be considered. Thereafter, the blended gas should be controlled into a situation with low pressure and high speed, which could help to set the pressure, speed, the fraction of H₂.     

Analysis of electrochemical hydrogen permeation through X-65 pipeline steel and its implications on pipeline stress corrosion cracking

Electrochemical hydrogen permeation tests were performed to measure the hydrogen permeation current through the X-65 pipeline steel in the electrolytes simulating the soil conditions to initiate near-neutral pH stress corrosion cracking (SCC) in pipelines. The hydrogen permeation current was analyzed following the constant concentration model. It is shown that, AQDS, simulating the organic compound in the soil, inhibits hydrogen permeation by decreasing the sub-surface hydrogen concentration, while sulfide promotes hydrogen permeation by inhibiting the hydrogen recombination and thus increasing the sub-surface hydrogen concentration. The steel specimen is more susceptible to stress corrosion cracking in the soil solution with a higher sub-surface hydrogen concentration, indicating that hydrogen is involved in near-neutral pH SCC in pipelines. It is suggested that hydrogen promotes the cracking of the steel, accompanying with the anodic dissolution on the crack sides and at the crack tip.     

Effects of internal hydrogen and surface-absorbed hydrogen on the hydrogen embrittlement of X80 pipeline steel

Effects of internal hydrogen and surface-absorbed hydrogen on hydrogen embrittlement (HE) of X80 pipeline steel were investigated by using different strain rate tensile test, annealing and hydrogen permeation tests. HE of X80 pipeline steel is affected by internal hydrogen and surface-absorbed hydrogen, and the latter plays a major role due to its higher effective hydrogen concentration. The HE susceptibility decreases with increasing the strain rate because it is more difficult for hydrogen to be captured by dislocations at the high strain rate. Annealing at 200 °C can weakened HE caused by internal hydrogen, while it has little effect on HE caused by surface-absorbed hydrogen. HE of X80 pipeline steel is mainly determined by the behavior of dislocation trapping hydrogen, which can be attributed to the interaction between hydrogen and dislocation.     

Failure analysis of corroded high-strength pipeline subject to hydrogen damage based on FEM and GA-BP neural network

The pipeline is a major approach to achieving large-scale hydrogen transportation. Hydrogen damage can deteriorate the material performance of the pipe steel, like ductility and plasticity reduction. Corrosion is dominating damage that impairs a pipeline's bearing capacity and structural reliability. However, previous research barely investigated the effect of hydrogen damage on failure behaviors, residual strength and interacting effect between adjacent corrosions of corroded high-strength pipelines transporting hydrogen. Besides, hardly any burst pressure model considers hydrogen damage. In this paper, several approaches, including the finite element method (FEM), regression analysis, the orthogonal test method, and the artificial neural network method, are applied to fill the gap. First, a series of finite element models with different geometric features and hydrogen damage is established to investigate the effects of hydrogen damage and corrosion on failure behaviors and residual strength. The results show that hydrogen damage can change the corroded pipeline's failure behaviors and reduce the residual strength. Second, based on the simulation results and regression analysis, a new burst model is developed to consider the hydrogen damage and improve the estimation accuracy. Third, based on the genetic algorithm (GA), a GA-BP neural network is established and trained for accurate and efficient residual strength estimation considering hydrogen damage. Furthermore, an orthogonal test is designed and performed to investigate the effects of critical parameters on the burst pressure of the corroded pipeline after hydrogen damage. The results indicate that hydrogen damage and corrosion length have similar contributions to the residual strength. Finally, the simulation results of pipelines with multiple corrosions show that hydrogen damage has a significant impact on the interacting effect between adjacent corrosions. The results obtained are valuable for further integrity management of steel pipelines carrying hydrogen.