Transmission, Distribution & Storage

Regularities of steel structure degradation of the “Novopskov-Aksay-Mozdok” gas main pipelines (Nevinnomysskaya CS) as well as the “Gorky-Center” pipelines (Gavrilovskaya CS) were studied. The revealed peculiarities of their degradation after long-term operation are suggested to be treated as a particular case of the damage accumulation classification (scheme) proposed by prof. H.M. Nykyforchyn. It is shown that the fracture surface consists of sections of ductile separation and localized zones of micro-spalling. The presence of the latter testifies to the hydrogen-induced embrittlement effect. However the steels under investigation possess sufficiently high levels of the mechanical properties required for their further safe exploitation both in terms of durability and cracking resistance.

A flake is a crack that is induced by trapped hydrogen within steel. To study its formation mechanism previous studies mostly focused on the formation process and magnitude of hydrogen pressure in hydrogen traps such as cavities and cracks. However according to recent studies the hydrogen leads to the decline of the mechanical properties of steel which is known as hydrogen embrittlement is another reason for flake formation. In addition the phenomenon of stress induced hydrogen uphill diffusion should not be neglected. All of the three behaviors are at work simultaneously. In order to further explore the formation mechanism of flakes in steel the process of flake initiation and growth were studied with the following three coupling factors: trap hydrogen pressure hydrogen embrittlement and stress induced hydrogen re-distribution. The analysis model was established using the finite element method and a crack whose radius is 0.5 mm was set in its center. The cohesive method and Bilinear Traction Separate Law (BTSL) were used to address the coupling effect. The results show that trap hydrogen pressure is the main driving force for flake formation. After the high hydrogen pressure was generated around the trap a stress field formed. In addition the trap is the center of stress concentration. Then hydrogen is concentrated in a distribution around this trap and most of the steel mechanical properties are reduced. The trap size is a key factor for defining the critical hydrogen content for flake formation and propagation. However when the trap size exceeds the specified value the critical hydrogen content does not change any more. As for the crack whose radius is 0.5 mm the critical hydrogen content of Cr5VMo steel is 2.2 ppm which is much closer to the maximum safe hydrogen concentration of 2.0 ppm used in China. The work presented in this article increases our understanding of flake formation and propagation mechanisms in steel.

It has been investigated the Ni-Co alloys (obtained from powder 0.1...0.3 mm under hot gaseous (in argon) isostatic pressure (up to 300 MPa) (Ni60Co15Cr8W8Al2Mo3) (Firth Rixon Metal Ltd Sheffield) and deformed (obtained by vacuum induced remealting) materials (Ni62Cr14Co10Mo5Nb3Al3Ti3) for gaseous turbine discs. Investigation has performed in the range of temperature 25…800°С and hydrogen pressure up to 70 MPa. By the 3D visualization of crack morphology it has been discovered the structure of fatigue crack surface and established the refer points on crack path including the boundary between the matrix and intermetallic particles (400×200 μm) crack opening structural elements distributions on the surface for selection of next local areas for more precision fracture surface and TEM examinations. Hydrogen influence on cyclic crack resistance parameters appears in the decreasing of loading cycles number (with amplitudes 15 MPa) in hydrogenated specimens of both alloys and increase with hydrogen concentration. At the highest hydrogen saturation regimes of Ni60Co15Cr8W8Al2Mo3 alloy (800°С 35 MPa Н2 36 hours С_Н = 32.7 ppm) number of cycles which necessary for crack initiation is 3 times less in comparison with specimen in initial state. At crack initiation step in hydrogenated Ni56Cr14Co15Mo5Al3Ti3 alloy it has been established that before intermetallic inclusion (400×200 μm) local stresses increased after its passing – has decreased. By fracture surface investigation it has been found the micro cracks up to 40 μm. Thin structure of heat resistant superalloys has characterises by disperse phase agglomeration with dimensions from 5 to 30 nm and crack propagation has a jumping character with no less then 50…70 nm steps.

Blending hydrogen into natural gas pipelines is a recent alternative adopted for hydrogen transportation as a mixture with natural gas. In this paper hydrogen embrittlement of steel pipelines originally designed for natural gas transportation is investigated. Solubility permeation and diffusion phenomena of hydrogen molecules into the crystalline lattice structure of the pipeline material are followed up based on transient evolution of internal pressure applied on the pipeline wall. The transient regime is created through changes of gas demand depending on daily consumptions. As a result the pressure may reach excessive values that lead to the acceleration of hydrogen solubility and its diffusion through the pipeline wall. Furthermore permeation is an important parameter to determine the diffusion amount of hydrogen inside the pipeline wall resulting in the embrittlement of the material. The numerical obtained results have shown that using pipelines designed for natural gas conduction to transport hydrogen is a risky choice. Actually added to overpressure and great fluctuations during transients that may cause fatigue and damage the structure also the latter pressure evolution is likely to induce the diffusion phenomena of hydrogen molecules into the lattice of the structure leading to brittle the pipe material. The numerical simulation reposes on solving partial differential equations describing transient gas flow in pipelines coupled with the diffusion equation for mass transfer. The model is built using the finite elements based software COMSOL Multiphysics considering different cases of pipe material; API X52 (base metal and nutrided) and API X80 steels. Obtained results allowed tracking the evolution with time of hydrogen concentration through the pipeline internal wall based on the pressure variation due to transient gas flow. Such observation permits to estimate the amount of hydrogen diffused in the metal to avoid leakage of this flammable gas. Thus precautions may be taken to prevent explosive risks due to hydrogen embrittlement of steel pipelines among other effects that can lead to alter safe conditions of gas conduction.

Pipeline failure caused by Hydrogen-Induced Cracking (HIC) also known as Hydrogen Embrittlement (HE) is a pressing issue for the oil and natural gas industry. Bursts in pipelines are devastating and extremely costly. The explosive force of a bursting pipe can inflict fatal injuries to workers while the combined loss of product and effort to repair are highly costly to producers. Further pipeline failures due to HIC have a long lasting impact on the surrounding environment. Safe use and operation of such pipelines depend on a good understanding of the underlying forces that cause HIC. Specifically a reliable way to predict the growth rate of hydrogen-induced cracks is needed to establish a safe duration of service for each length of pipeline. Pipes that have exceeded or are near the end of their service life can then be retired before the risk of HIC-related failures becomes too high. However little is known about the mechanisms that drive HIC. To date no model has been put forth that accurately predicts the growth rate of fractures due to HIC under extreme pressures such as in the context of natural gas and petroleum pipelines. Herein a mathematical model for the growth of fractures by HIC under extreme pressures is presented. This model is derived from first principles and the results are compared with other models. The implications of these findings are discussed and a description of future work based on these findings is presented.

Hydrogen embrittlement can cause catastrophic failure of high strength alloys yet determining localised hydrogen in the microstructure is analytically challenging. NanoSIMS is one of the few techniques that can map hydrogen and deuterium in metal samples at microstructurally relevant length scales. Therefore it is essential to understand the artefacts and determine the optimum methodology for its reliable detection. An experimental methodology/protocol for NanoSIMS analysis of deuterium (as a proxy for hydrogen) has been established uncovering unreported artefacts and a new approach is presented to minimise these artefacts in mapping hydrogen and deuterium in alloys. This method was used to map deuterium distributions in electrochemically charged austenitic stainless steel and precipitation hardened nickel-based alloys. Residual deuterium contamination was detected in the analysis chamber as a result of deuterium outgassing from the samples and the impact of this deuterium contamination was assessed by a series of NanoSIMS experiments. A new analysis protocol was developed that involves mapping deuterium in the passive oxide layer thus mitigating beam damage effects that may prevent the detection of localised deuterium signals when the surface is highly deuterated.

Hydrogen has been long known to provide a solution toward clean energy systems. With this notion many efforts have been made to find new ways of storing hydrogen. As a result decades of studies has led to a wide range of hydrides that can store hydrogen in a solid form. Applications of these solid-state hydrides are well-suited to stationary applications. However the main challenge arises in making the selection of the Metal Hydrides (MH) that are best suited to meet application requirements. Herein we discuss the current state-of-art in controlling the properties of room temperature (RT) hydrides suitable for stationary application and their long term behavior in addition to initial activation their limitations and emerging trends to design better storage materials. The hydrogen storage properties and synthesis methods to alter the properties of these MH are discussed including the emerging approach of high-entropy alloys. In addition the integration of intermetallic hydrides in vessels their operation with fuel cells and their use as thermal storage is reviewed.

The objective of this project is to take into account the mechanical constraints formed by diffusion of hydrogen or tritium in watertight palladium alloy cathode. To know the origin of these it was necessary to discriminating the damaging effects encountered. Effectively hydrogen and isotope induce deformation embrittlement stress corrosion cracking and cathodic corrosion in different regions of cathode. Palladium can be alloyed with silver or yttrium to favourably increase diffusion and reduce these constraints. Effects of electrochemical factors temperature cathode structure adsorbed transient complex of palladium and porous material support are given to estimate and to limit possible damage.

Recent research efforts to develop advanced–/ultrahigh–strength medium-Mn steels have led to the development of a variety of alloying concepts thermo-mechanical processing routes and microstructural variants for these steel grades. However certain grades of advanced–/ultrahigh–strength steels (A/UHSS) are known to be highly susceptible to hydrogen embrittlement due to their high strength levels. Hydrogen embrittlement characteristics of medium–Mn steels are less understood compared to other classes of A/UHSS such as high Mn twinning–induced plasticity steel because of the relatively short history of the development of this steel class and the complex nature of multiphase fine-grained microstructures that are present in medium–Mn steels. The motivation of this paper is to review the current understanding of the hydrogen embrittlement characteristics of medium or intermediate Mn (4 to 15 wt pct) multiphase steels and to address various alloying and processing strategies that are available to enhance the hydrogen-resistance of these steel grades.

In order to facilitate the application of hydrogen energy and ensure its safety the compressed hydrogen storage tank on board needs to be full of hydrogen gas within 3 minutes. Therefore to meet this requirement the effects of refueling parameters on the filling time need to be investigated urgently. For the purpose of solving this issue a novel analytical solution of filling time is obtained from a lumped parameter model in this paper. According to the equation of state for real gas and dimensionless numbers Nu and Re the function relationships between the filling time and the refueling parameters are presented. These parameters include initial temperature initial pressure inflow temperature final temperature and final pressure. These equations are used to fit the reference data the results of fitting show good agreement. Then the values of fitting parameters are further utilized so as to verify the validity of these formulas. We believe this study can contribute to control the hydrogen filling time and ensure the safety during fast filling process.