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.     

Influence of hydrogen pressure on fatigue properties of X80 pipeline steel

The low-cycle fatigue and fatigue crack growth (FCG) properties of X80 pipeline steel in hydrogen atmosphere were determined to investigate the variation of hydrogen pressure and its influence on fatigue life. The test environment was switched to a hydrogen atmosphere after 1000, 3000, or 5000 cycles of pre-fatigue testing in a nitrogen atmosphere. Notch tensile tests were conducted in nitrogen and hydrogen atmospheres after the specimens were pre-fatigued for 3000 or 5000 cycles. The results showed that the cycles to failure of X80 decreased exponentially with increasing hydrogen pressure. When the displacement amplitude (DA) values remained steady (below 3000 cycles), the X80 steels showed no noticeable deterioration in the fatigue properties with or without hydrogen. When the DA values increased (above 5000 cycles), cracks propagated slowly and fatigue properties were strongly reduced in the hydrogen atmosphere, but not in nitrogen. Hydrogen-accelerated crack growth dominates the reduction of fatigue life below 0.6 MPa of hydrogen pressure. Hydrogen-accelerated crack initiation plays a more important role than FCG in the reduction of fatigue life with increasing hydrogen pressure.     

Effect of microstructure inhomogeneity on hydrogen embrittlement susceptibility of X80 welding HAZ under pressurized gaseous hydrogen

Hydrogen embrittlement (HE) of high-grade pipeline welded joint is a threat to hydrogen gas transport. In this research, slow strain rate tension (SSRT) tests in high-pressure hydrogen gas, combined with hydrogen permeation tests and microstructure analysis were conducted on X80 steel, intercritical heated-affected zone (ICHAZ), fine-grained heat-affected zone (FGHAZ) and coarse-grained heat-affected zone (CGHAZ). The change of HE susceptibility from high to low was CGHAZ, FGHAZ, ICHAZ, and base metal. Microstructure was the important factor influencing hydrogen permeation and susceptibility to HE. Susceptibility to HE was increased in the order of “fine-grained massive ferrite (MF) and acicular ferrite (AF)”, “fine-grained granular bainite (GB) and MF”, “coarse-grained GB and bainite ferrite (BF) embedded with martensite-austenite (M-A) constitute”. The fine-grained MF and AF in base metal with lower hydrogen diffusivity can impede the embrittlement behaviour, while the coarse-grained GB and BF with higher hydrogen diffusivity in CGHAZ increased its susceptibility to HE.     

An integrated experimental and modeling approach to determine hydrogen diffusion and trapping in a high-strength steel

The hydrogen diffusion and trapping in AISI 4330 V high-strength steel is investigated by repetitive electrochemical hydrogen permeation tests, thermal desorption analysis, and hot and melt extraction. The analysis is coupled with a numerical model based on McNabb and Foster's kinetics with varying degrees of trap occupancy. The trapping parameters are obtained by fitting the numerical model to the experimental data, which permits to describe the diffusion and trapping processes for all tested conditions. In addition, the predictions calculated by the model are critically discussed and compared with those derived from usual approaches based on analytical solutions from Fick's laws and from Choo and Lee's method. An important difference is observed, indicating that the use of general analytical methods may not be adequate in the case of the studied steel. The use of more rigorous analysis provides a better understanding of trapping phenomenon and improved predictions of charging times and contents.     

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.     

Hydrogen trapping and hydrogen induced cracking of welded X100 pipeline steel in H2S environments

Hydrogen induced cracking (HIC) susceptibility of the welded X100 pipeline steel was evaluated in NACE “A” solution at room temperature according to the NACE TM0284-2011 standard. Both the kinetic parameters of the permeability $\left(J_{\infty }L\right)$, the apparent diffusivity (D_app) and the concentration of reversible and irreversible hydrogen in the base metal and welded joint of X100 pipeline steel were quantitatively investigated by hydrogen permeation test. The results showed that the welded joint with an inhomogeneous microstructure had a higher trap density and more susceptible to HIC due to two orders of magnitude larger in the concentration of irreversible hydrogen than that of base metal, though all presenting poor HIC resistance for both base metal and the welded joint. The HIC cracks initiated from the inclusions enriching in Al, Ca, Si, Mn. The cracks are primarily transgranular, accompanying with limited intergranular ones.     

The effect of hydrogen content and welding conditions on the hydrogen induced cracking of the API X70 steel weld

The self-restraint testing was used to investigate the influence of hydrogen content, preheating, and post-heating on the sensitivity of welding of API X70 pipeline steel to hydrogen induced cracking (HIC). The variation of hydrogen content was applied using a low hydrogen electrode E8018-G and a high hydrogen (cellulosic) electrode E8010-P1. Diffusible hydrogen of these electrodes was measured by mercury displacement method. The average diffusible hydrogen content of cellulosic electrode E8010-P1 and low hydrogen electrode E8018-G were 43.6 and 1.1 ml/100 g of weld metal, respectively. The results of visual inspection, penetrant test, and macroscopic examination showed that welding with cellulosic electrode leads to cracking unless both preheating and post-heating are applied. However, in the case of low hydrogen electrode, cracking occurs only if no preheating or post-heating is applied. The microstructure of the welded specimens in different conditions by optical and scanning electron microscopy (SEM) showed that the dominant phase in the weld zone of all specimens is bainite. The microhardness profile displayed that hardness limitation (350 HV) cannot predict the sensitivity to cold cracking; therefore, other parameters such as hydrogen content should also be considered.     

Hydrogen embrittlement behavior in the nugget zone of friction stir welded X100 pipeline steel

Hydrogen-induced damage is an inevitable challenge in pipeline safety applications, especially, the fusion welded joints owing to microstructure heterogeneity caused by welding process. In this work, X100 pipeline steel was subjected to friction stir welding (FSW) at rotation rates of 300–600 rpm under water cooling, and the relationship among the microstructure, hydrogen diffusivity, and hydrogen embrittlement (HE) behavior of the nugget zone (NZ) were studied. The NZ at 600 rpm had the highest effective hydrogen diffusion coefficient (D_eff) of 2.1 × 10^?10 m²/s because of the highest dislocation density and lowest ratio of effective grain boundary. The D_eff decreased with decreasing rotation rate due to the decrease of dislocation density and the increase of ratio of effective grain boundary, and the lowest D_eff of 1.32 × 10^?10 m²/s was obtained at 300 rpm. After hydrogen charging, the tensile strength of all specimens decreased slightly, while the elongation decreased significantly. As the rotation rate decreased, the elongation loss was obviously inhibited, and ultimately a lowest elongation loss of 31.8% was obtained at 300 rpm. The abovementioned excellent mechanical properties were attributed to the fine ferrite/martensite structure, low D_eff, and strong {111}//ND texture dramatically inhibiting hydrogen-induced cracking initiation and propagation.     

Effects of vanadium precipitates on hydrogen trapping efficiency and hydrogen induced cracking resistance in X80 pipeline steel

In this study, the number and size distribution of vanadium precipitates and their effects on hydrogen trapping efficiency and hydrogen-induced cracking (HIC) susceptibility were investigated in X80 pipeline steel. The results showed that as the vanadium content increased, the number of nanoscale vanadium precipitates clearly increased. Furthermore, the amount of hydrogen atoms trapped by vanadium precipitates gradually increased and the hydrogen diffusion coefficient decreased from 4.74 × 10^?6 cm² s^?1 in the vanadium-free V0 steel to 8.48 × 10^?7 cm² s^?1 in the V4 steel with 0.16% V, according to hydrogen permeation results. It also reduced the possibility of hydrogen atoms diffusing into the sites of harmful defects such as large-size oxides and elongated MnS inclusions, where cracks were caused more easily. In addition, the V3 steel with 0.12% V, containing the largest number of vanadium carbide particles of less than 60 nm, had the lowest HIC susceptibility.     

Hydrogen induced cracking susceptibility in different layers of a hot rolled X70 pipeline steel

Hydrogen induced cracking (HIC) behaviour was investigated in three layers of RD–ND plane. HIC test showed that all cracks initiated from the mid-thickness of the RD–ND plane and propagated in the rolling direction of the steel plate. Hydrogen permeation test results showed a lower permeability and diffusivity coefficient for the third layer resulting in the highest density of traps and consequently HIC susceptibility. Considering the HIC test and crystallographic texture measurements, cracks initiated from the grain boundaries associated with {100} grain orientation and arrested in regions with some strong texture components, such as {110}//ND, {112}//ND, and possibly {332}//ND. The role of HABs and CSLs boundaries was important in crack propagation.     

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.     

Hydrogen effect on a low carbon ferritic-bainitic pipeline steel

Hydrogen effect on an API 5L X65 low carbon ferritic-bainitic steel is investigated, by evaluating the fracture toughness parameters in air and in hydrogen environment. The hydrogen environment is manifested by in situ hydrogen charging of the X65 steel, using the electrolytic solution NS4, which simulates the electrolyte trapped between the pipeline steel and the coating in a buried pipeline. The fracture toughness results of the X65 are compared to two other pipeline steels with different microstructures, namely an X52 and an X70, possessing a banded ferritic-pearlitic and banded ferritic-mixed bainitic-pearlitic microstructure, respectively. The X65 steel exhibits significant reduction of fracture toughness parameter J₀ integral due to hydrogen charging and insignificant variation of fracture toughness parameter K_Q. Comparing the three steels, the lowest reduction of J₀ integral due to hydrogen charging, is met on the X52 and the highest in the X65.     

Effect of hydrogen on fracture toughness properties of a pipeline steel under simulated sour service conditions

The effect of hydrogen on the fracture toughness properties of an API X65 pipeline steel is studied under simulated H₂S in-service conditions. The fracture toughness properties are measured in LT and SL directions (perpendicular and parallel to the pipeline wall thickness, respectively), following ASTM E1820. Due to size restrictions of standard single edge notch bending (SEB) specimens at the direction parallel to the thickness of the pipeline wall, an experimental protocol (see the patent) was developed to carry out the fracture toughness tests, while complying with ASTM standard 1820. This approach is especially useful in situations where hydrogen induced cracking (HIC) and in a broader sense, stepwise cracking takes place, since these cracks initiate and grow primarily in planes parallel to the pipeline rolling plane. Such values of fracture toughness are often different from those commonly measured in planes perpendicular to the rolling plane. Hydrogen might not have the same effect on fracture toughness properties as measured in different directions, due to microstructural features which are inherent from steel manufacturing process. The steady state H₂S in-service conditions are simulated by electrolytically charging the specimen, for 48 h and then testing (ex-situ) the specimen for evaluating the fracture toughness properties. The steady state H₂S environment charging was obtained by measuring the hydrogen concentration in the bulk of the specimen through thermal desorption spectroscopy (TDS) at three levels of hydrogen concentration. It was observed that the K_Q was moderately decreased with increasing hydrogen concentration in the bulk of the steel, while CTOD₀ showed a significant reduction with increasing hydrogen concentration.     

Vapor-deposited iron sulfide films as a novel hydrogen permeation barrier for steel: Deposition condition,defect effect,and hydrogen diffusion mechanism

Hydrogen embrittlement is a serious problem in the oil/gas industry. In this work, various iron sulfide (FeS) films, including iron monosulfide (FeS), pyrite (FeS₂), and pyrrhotite (Fe₇S₈), were synthesized in X80 steel by chemical vapor deposition at 200 °C, 300 °C, 400 °C, and 500 °C. The corrosion resistance and hydrogen permeation properties of the FeS films were investigated through electrochemical methods. Results indicated that FeS films significantly improved the hydrogen barrier properties of the X80 steel, which was closely related to the crystal structure type and defects of FeS films. Defects like microcracks and pinholes during deposition can increase the porosity of the film, resulting in the film properties decreased. Moreover, FeS film (at 300 °C), which had the smallest apparent hydrogen diffusivity (D ? 2.64 × 10^?7 cm²/s) and apparent subsurface concentration (C_app ? 1.12 μmol/cm³), had the best hydrogen barrier properties. The corrosion resistance of FeS film (300 °C) was excellent.     

Recommendations on X80 steel for the design of hydrogen gas transmission pipelines

By limiting the pipes thickness necessary to sustain high pressure, high-strength steels could prove economically relevant for transmitting large gas quantities in pipelines on long distance. Up to now, the existing hydrogen pipelines have used lower-strength steels to avoid any hydrogen embrittlement. The CATHY-GDF project, funded by the French National Agency for Research, explored the ability of an industrial X80 grade for the transmission of pressurized hydrogen gas in large diameter pipelines. This project has developed experimental facilities to test the material under hydrogen gas pressure. Indeed, tensile, toughness, crack propagation and disc rupture tests have been performed. From these results, the effect of hydrogen pressure on the size of some critical defects has been analyzed allowing proposing some recommendations on the design of X80 pipe for hydrogen transport. Cost of Hydrogen transport could be several times higher than natural gas one for a given energy amount. Moreover, building hydrogen pipeline using high grade steels could induce a 10 to 40% cost benefit instead of using low grade steels, despite their lower hydrogen susceptibility.     

Effects of hydrogen-charging on the susceptibility of X100 pipeline steel to hydrogen-induced cracking

In this work, the hydrogen-induced cracking (HIC) behavior of X100 pipeline steel was investigated by a combination of tensile test, electrochemical hydrogen permeation measurement and surface characterization techniques. The effect of inclusions in the steel on the crack initiation was analyzed. Results demonstrated that the amount of hydrogen-charging into the X100 steel specimen increases with the charging time and charging current density. Hydrogen-charging will enhance the susceptibility of the steel to HIC. The cracks initiate primarily at inclusions, such as aluminum oxides, titanium oxides and ferric carbides, in the steel. The diffusivity of hydrogen at room temperature in X100 steel is determined to be 1.04 × 10⁻⁸ cm²/s.     

Hydrogen permeation under high pressure conditions and the destruction of exposed polyethylene-property of polymeric materials for high-pressure hydrogen devices (2)-

Aiming to elucidate physical property affecting to hydrogen gas permeability of polymer materials used for liner materials of storage tanks or hoses and sealants under high-pressure environment, as model materials with different free volume fraction, five types of polyethylene were evaluated using two methods. A convenient non-steady state measurement of thermal desorption analysis (TDA), and steady-state high-pressure hydrogen gas permeation test (HPHP) were used both under up to 90 MPa of practical pressure. The limit of TDA method of evaluation for the specimens suffering fracture during decompression process after hydrogen exposure was found. Permeability coefficient decreased with the decrease of diffusion coefficient under higher pressure condition. Specific volume and degree of crystallinity under hydrostatic environment were measured. The results showed that the shrinkage in free volume caused by hydrostatic effects of the applied hydrogen gas pressure decreases diffusion coefficient, resulting in the decrease of permeability coefficient with the pressure rise.     

GCr15钢在高应力状态下的氢脆及应力腐蚀断裂研究

本文通过分析研究GCr15钢高应力件由于其组织、应力和杂质的不均匀而在酸性、碱性及某些催化剂的作用下产生腐蚀电化学作用，直至产生氢脆及应力腐蚀断裂的原因和机理，提出了防止GCr15钢在高应力状态下的氢脆及应力腐蚀断裂的7项工艺措施。     

Investigation of the calcareous deposits formation controlled by interfacial pH and its effect on the hydrogen entry into AISI 4135 steel in seawater

The influence of interfacial pH between AISI 4135 steel and seawater under different polarization potentials on the formation of calcareous deposits has been studied. An interfacial pH of 9.61 at ?0.9 V vs. SCE using state of the art iridium oxide microelectrode was found to be the critical pH for the precipitation of magnesium hydroxide. Calcareous deposits with a double-layer structure comprising an inner-brucite layer and an outer-aragonite layer were found to form at potentials between ?1.0 V and ?1.2 V vs. SCE. Furthermore, the facilitation of hydrogen permeation into steel induced by the formation of calcareous deposits was verified using the Devanathan-Stachurski electrochemical test. The mechanism of calcareous deposits facilitates hydrogen permeation into steel is related to its inhibition on hydrogen recombination and escape processes.