The development of green and low-carbon energy is imminent at present, and the hydrogen has been widely concerned as a low-carbon energy. At the present, it is the most economical and effective way to use the natural gas pipeline steel in service for long-distance hydrogen transport, but the pipeline steel is susceptible to hydrogen permeation, and hydrogen damage may invariably be caused by hydrogen permeation in the hydrogen-containing environment, which seriously affects the safe operation of the pipeline. Therefore, it is of great significance to study the hydrogen permeation behavior of pipeline steel used for transporting hydrogen-doped natural gas. The research methods of hydrogen permeation behavior of pipeline steel mainly include electrochemical hydrogen permeation and gaseous hydrogen permeation now. Herein, the similarities and differences in the hydrogen permeation processes and the factors affecting the hydrogen permeation behavior of pipeline steels caused by different hydrogen permeation methods are briefly described. The models and methods for calculating hydrogen permeation parameters are also introduced.

Hydrogen embrittlement is one of the problems when the high strength Al-alloy is applied in hydrogen related service environments. This paper first summarizes the sources of hydrogen and its role in high-strength Al-alloys, along with the main mechanisms of hydrogen embrittlement: hydrogen enhanced localized plasticity (HELP), hydrogen enhanced decohesion (HEDE), and adsorption induced dislocation emission (AIDE). The effects of microstructure (such as second phase, dislocation, and grain boundary) and environmental factors (including temperature, humidity, and strain rate) on the hydrogen embrittlement sensitivity of high-strength Al-alloy are analyzed and discussed. It is highlighted that the synergistic interactions of hydrogen and second phase with cracks during the hydrogen embrittlement process, as well as the coupling effects of various environmental factors on the hydrogen embrittlement sensitivity of high-strength aluminum alloys, are urgent issues that need to be addressed. Finally, it is worthy to point out that regulating the structure and number of irreversible hydrogen traps is one of the effective strategies to mitigate hydrogen embrittlement.

The key of understanding hydrogen embrittlement mechanism of metals is to fully elucidate the interaction between hydrogen and dislocation. This paper introduces the history, content and development of the theory of hydrogen enhanced localized plasticity (HELP) and reviews it critically. The unsettling questions regard HELP mechanism are emphasized and addressed. In order to answer the unsettling questions, a new research methodology to reveal the interaction between hydrogen and dislocation is presented and prospected.

To transfer the blend natural gas with hydrogen through the existing natural gas pipelines is currently one of the most economical and effective ways for hydrogen energy transportation. However, when pipelines in contact with hydrogen-enriched atmospheres, hydrogen atoms can permeate into the pipeline steels inducing hydrogen damages, which can severely threaten the safety of pipelines. Factors such as high-pressure, stress, and corrosive media during service may be involved to the damage of pipelines. Based on these issues, this paper summarizes the compatibility of pipeline steels with hydrogen, analyzes the adsorption and diffusion of hydrogen within the steels from the perspectives of hydrogen permeation behavior and testing methods. Additionally, it summarizes the forms and mechanisms of hydrogen damage in pipeline steels and welds of transportation of hydrogen-blended natural gas, in terms of the relevant influencing factors. The findings may provide a theoretical basis for the selection, design, and safe service of transporting hydrogen-blended natural gas pipelines, promoting the safe development of the hydrogen economy.

Hydrogen-natural gas blending is an important way to achieve long-distance, low-cost, and large-scale transportation of hydrogen energy. However, hydrogen-induced fatigue damage of pipelines may occur due to the simultaneous presence of fatigue loading and hydrogen, hence, seriously threatening the service safety of hydrogen-blended natural gas pipelines. Therefore, studying the role of hydrogen in pipeline steel and clarifying the mechanisms and influencing factors of hydrogen-assisted fatigue crack growth (HA-FCG) of pipeline steel can provide a basis for optimizing the performance and conducting risk assessment of HA-FCG of pipeline steel. In this paper, research progress on HA-FCG of pipeline steels in hydrogen-blended natural gas environment was summarized. Firstly, the mechanisms and models of HA-FCG were introduced. Secondly, the effect of microstructure, welding, load and service environment on HA-FCG of pipeline steels in hydrogen-blended natural gas environment was reviewed. Finally, the research directions of this field in future were discussed.

Zr-2.5Nb alloy pressure tubes are important structural components in heavy-water reactor. During operation of a heavy-water reactor, a large amount of hydrogen isotopes is produced by the corrosion reaction between the pressure tubes and the heavy-water coolant. Some of the hydrogen isotopes can be absorbed into the pressure tube. When the concentration of hydrogen atoms exceeds the solid solubility of hydrogen in Zr-2.5Nb alloy, hydrides are precipitated. The precipitation of hydrides will lead to deterioration of mechanical properties of Zr-2.5Nb alloy, and then leads to the expansion of microcracks inside the pressure tubes. The phenomenon is called Delayed hydrides cracking (DHC) which is one of the most important potential risks during the service of pressure tubes. Therefore, it is of great significance to study the DHC behavior of pressure tube. In this paper, the research progress on the testing methods for DHC behavior, the relevant mechanisms and models as well as the influencing factors of DHC behavior are reviewed, and the shortcomings of current researches and the future development trends are pointed out.

Hydrogen energy, as a clean energy source, has attracted much attention and is now a major focus in the energy field. Transporting hydrogen to user terminals via the existing urban gas polyethylene pipelines is a key approach for promoting the large-scale utilization of hydrogen energy. However, prolonged exposure of polyethylene pipes to hydrogen environments may cause irreversible changes to their mechanical properties, potentially compromising the transportation safety. At present, research on the mechanical properties of polyethylene pipes in hydrogen environments is still in its early stages in China. This article reviews the recent progress in understanding the influence of hydrogen environments on the mechanical properties of polyethylene pipes. By systematically analyzing the results of tensile, creep, fracture, and fatigue tests of polyethylene pipes in environments with or without hydrogen respectively, the impact of hydrogen on the mechanical properties of polyethylene pipes is summarized and discussed. The findings indicate that lower hydrogen pressures presented negligible effect on mechanical properties of polyethylene pipes is, while significant changes occurred in high-pressure hydrogen environments, i.e. the mechanical properties of polyethylene pipes will undergo significant changes. However, it remains unclear whether these changes are driven by hydrogen itself or environmental pressure. This review provides valuable insights for advancing hydrogen transportation technologies using urban polyethylene pipelines.

Hydrogen energy, known as an efficient and clean energy source, has significant potential when it is blended with natural gas and transported by the existing pipeline for long distance. This integration not only boosts the utilization of green hydrogen in the energy sector, but also accelerates the country's transition to new energy sources. However, the participation of hydrogen alters the conventional failure patterns of natural gas pipelines, increasing the risks of hydrogen-embrittlement and -corrosion. This paper systematically reviews the latest advancements in composite protection technologies designed to mitigate hydrogen-embrittlement and -corrosion of pipelines. The composite protection technologies for hydrogen-embrittlement and -corrosion of pipelines were summarized, including those related with Ni-containing coatings, Mo-containing coatings, graphene oxide coatings, and metal or metal oxide-organic composite coatings etc., so as the characteristics and development status of every tech. Compared to inorganic coatings, organic composite coatings offer greater versatility, broader applicability, and enhanced dual protection against both hydrogen-permeation and -corrosion. Currently, the electrochemical liquid-phase hydrogen permeation is adopted as the main testing method for hydrogen embrittlement sensitivity of coatings, however which can not faithfully reproduce the high-pressure gaseous hydrogen environments of hydrogen-blended natural gas pipelines. In the future a new hydrogen embrittlement sensitivity test method for coatings may be expected, which should be conducted under conditions of hydrogen permeation induced by combine the coexistence of gas- and liquid-phase hydrogen charging while companied with corrosion. Finally, this review may provide valuable insights for the development of hydrogen permeation-resistant and anti-corrosion composite coating technologies for hydrogen-blended natural gas pipelines.

Four model Ni-Cr alloys with varying chromium content were pre-charged with hydrogen. Then their oxidation behavior was assessed in a high-temperature, high-pressure water (290 ^oC/9 MPa) for 720 h via scanning electron microscopy (SEM), Raman spectroscopy, and transmission electron microscopy (TEM). The results revealed that Cr-rich oxide scales of different structures were formed on both the hydrogen-charged and uncharged alloys. Notably, the thickness of oxide scales on the hydrogen charged alloys increased significantly compared to that on the uncharged ones, indicating that pre-hydrogen charging could accelerate the oxidation rate of the alloy in high-temperature high-pressure water. Moreover, as the Cr content increased, a denser Cr-rich oxide scale could form for the uncharged alloys, enhancing its protectiveness. However, under the influence of hydrogen pre-charging, selective dissolution of Ni-containing oxides occurred in the inner portion, leading to substantial voids beneath oxide scale and diminishing the protective capability of the oxidation scale.

Underground hydrogen storage (UHS) has emerged as the optimal solution for large-scale hydrogen storage. In such case, however there is a risk of hydrogen leakage, which, in combination with factors like microorganisms and stress loads present in the underground environment, poses a threat to hydrogen-exposed metallic materials. Hence, the corrosion behavior of J55 steel in a simulated environment of hydrogen leakage in storage facilities with trace hydrogen (0.01%-1%) coupled with sulfate-reducing bacteria (SRB) and the presence stress was assessed via four-point bending method. The results indicate that SRB accelerates the anodic reaction and the corrosion of J55 steel, leading to significant pitting on the steel surface. Moreover, the presence of stress causes stress concentration on the surface of J55 steel, enhancing the localized corrosion induced by SRB, and promoting the development and growth of cracks associated with pit accumulation. When stress, SRB, and hydrogen coexist, an increase in hydrogen concentration in the system (0%, 0.22%, 0.44%) leads to a significant increase in the maximum pitting depth of J55 steel, exacerbating its corrosion. SRB can utilize electrons provided by H₂ to produce corrosive byproducts such as H₂S. The presence of hydrogen further facilitates crack propagation and pit formation.

Deep understanding on the interaction of hydrogen atoms with pipeline steel is crucial for the matter of the integrity and safety in-service of hydrogen pipeline infrastructure, especially for the case when the existing pipelines with corrosion defects were adopted as hydrogen transportation pipeline. Herein, a finite element (FE) model was developed by coupling mechanical- and diffusion-fields in COMSOL Multiphysics, so that the effect of internal pressure, defect location, defect length and depth on the hydrogen diffusion and distribution was assessed. Results demonstrated that internal pressure may induce local stress concentration and non-uniform hydrogen distribution at defect. Hydrogen concentration at defect increases with the internal pressure, but the threshold of hydrogen concentration at internal corrosion defects is lower than that at external corrosion defects, and the corresponding positions of the maximum hydrogen concentration are different for the two defects. Moreover, the defect length and depth also affect the hydrogen concentration threshold and where the hydrogen concentration maximum emerges, but such effects vary depending on whether the corrosion in question is internal or external.

The effect of small injected amount of O₂ and CO on the hydrogen embrittlement susceptibility of X52 pipeline steel in pure gaseous hydrogen was investigated by slow strain rate tensile tests, while the fracture of the tested steel was characterized by scanning electron microscope. Results reveal that the hydrogen embrittlement susceptibility of X52 pipeline steel decreases with the increase of the injected amount of O₂ and CO in the gaseous hydrogen. For the gaseous hydrogen with either 0.01% (volume fraction) O₂ or 0.02% (volume fraction) CO, the acquired hydrogen embrittlement index of X52 pipeline steel is 0.83% and 8.11%, which correspond to 3.96% and 38.66% those in pure gaseous hydrogen, respectively. It follows that the competitive adsorption of O₂ and CO with the presence of H₂ leads to the reduction of hydrogen embrittlement sensitivity of the pipeline steel.

The material properties of pressure tube will gradually deteriorate under high temperature, high pressure and high irradiation operating conditions of heavy water reactor (HWR), especially when the Zr-alloy absorbs deuterium/hydrogen from the coolant, it will become susceptive to the delayed hydride cracking (DHC), thus threatening the boundary integrity of the pressure tube. According to the Canadian Standard CSA N285.8, the threshold stress intensity factor (K_IH) for DHC needs to be evaluated. In response to this demand, the K_IH measurement method of pressure tube materials was studied. The K_IH was determined using compact tensile specimens, which were pre-charged with hydrogen by electrochemical method for about 180 mg/kg before tensile tests, and their K_IH values were measured at 250, 180, 150 and 120 ^oC respectively. The test results showed that the K_IH value of pressure tube Zr-2.5NbZr-alloy can be determined more accurately by using the K-reduction method at temperatures between 150 and 250 ^oC, and the measured values have no obvious dependence on the test temperatures.

The hydrogen permeation behavior of X80 pipeline steel with different thicknesses was studied by means of electrochemical hydrogen permeation test, and the influence of hydrogen pre-charging time on the mechanical properties of X80 pipeline steel was also assessed via slow strain rate tensile test. Meanwhile, finite element analysis was used to simulate hydrogen concentration within the steels, which were hydrogen pre-charged for different times. The results indicate that as the thickness increases, the steady-state current density and steady-state hydrogen permeation flux of X80 pipeline steel decrease. Moreover, the penetration time and lag time of hydrogen diffusion increase, suggesting that the increase in steel thickness enhances both the quantity of hydrogen traps and the pathways for hydrogen diffusion of the steel. Additionally, pre-charging time significantly impacts the susceptibility to hydrogen embrittlement of the steel, resulting in a slight increase in yield strength and a notable decrease in elongation with the increasing pre-charging time. Macroscopic and microscopic fracture surface analyses reveal that steels subjected to in-situ hydrogen charging exhibit distinct brittle fracture characteristics. As the pre-charging time increases, the ductile fracture features diminishing, while the number of secondary cracks increased gradually, which may be attributed to the increased concentration of hydrogen atoms within the steel. The fitting results show that the internal hydrogen concentration is negatively correlated with the elongation and positively correlated with hydrogen embrittlement sensitivity.

Herein, the effect of the 10 MPa natural gas blended with 0%, 5%, 10%, 15%, 20% and 100% (volume fraction) hydrogen respectively on the hydrogen embrittlement (HE) susceptibility of typical home-made medium- and low-strength seamless tube steels L245、X42 and X52 by means of slow strain rate tensile test (SSRT), aiming in understanding the environmental adaptability of the relevant steel tubes. The results show that low-strength steels L245 and X42 maintain good ductility at low hydrogen-blending ratio (≤ 10%), showing minimal influence of hydrogen. However, at higher hydrogen-blending ratios (≥ 20%), the elongation at break decreases significantly, and the HE susceptibility rises. The HE susceptibility of medium strength steel X52 is relatively high at 5% hydrogen and increases linearly by higher hydrogen-blending rations. The fracture morphology aligns with SSRT results, where steels L245 and X42 exhibit good plasticity and toughness at lower hydrogen-blending ratio (≤ 10%), while X52 steel shows partial brittleness. HE is mainly driven by the hydrogen enhanced localized plasticity (HELP) mechanism, accompanied by hydrogen enhanced strain-induced vacancies (HESIV) mechanism. At high hydrogen-blending ratios (≥ 20%), the three steels all show brittle fracture characteristics, driven by a mechanism of mixed HELP and hydrogen enhanced decohesion (HEDE). Overall, a hydrogen-blending ratio below 10% is considered as a safe operating limit for these seamless steel pipes.

Herein, the effect of different hydrogen doping ratio on the hydrogen embrittlement and corrosion behavior of X80 pipeline steel in 4 MPa hydrogen-doped natural gas was investigated by means of insitu hydrogen permeation measurement and stress-strain curve measurement, as well as electrochemical corrosion methods and corrosion morphology characterization etc. The results indicate that in hydrogen-doped natural gas environment, hydrogen permeation follows a "stable-rise-decline" pattern. As the hydrogen doping ratio increases, the penetration time and the time to reach the peak current of the hydrogen permeation were shortened. The mechanical properties of the hydrogen-charged steels showed a decline compared to the blank ones. Besides, with the increasing hydrogen doping ratios, the corrosion current density of X80 pipeline steel increases, the impedance modulus decreases, and the corrosion tendency intensifies. Based on the above research, a failure mode of hydrogen-doped natural gas transmission pipeline steel under the coupled effect of hydrogen embrittlement and corrosion was established.

The hydrogen embrittlement sensitivity of different welded structures of DH36 marine engineering steel was comparatively studied via hydrogen diffusion measurement and slow strain rate tests (SSRT). The results show that the hydrogen diffusion coefficient is the highest for the heat-affected zone, followed by the weld zone, and the base metal zone is the lowest. The hydrogen embrittlement coefficient is the highest for the heat-affected zone, and obvious hydrogen embrittlement can be observed in the heat-affected zone by an applied polarization potential of -950 mV, while the base metal and weld zone exhibit hydrogen embrittlement characteristics only when the cathodic protection potential of -1050 mV was applied. The results indicate that the heat-affected zone has higher hydrogen embrittlement sensitivity than the weld zone, however, the weld zone has higher sensitivity than the base metal zone.

With the rapid development of hydrogen energy industry and the urgent need for safe storage and transportation of hydrogen, it has become a major trend to utilize the existing long-distance natural gas pipelines for hydrogen transportation. However, blending hydrogen into natural gas pipelines can adversely impact pipeline steel, posing new problems and challenges for the safe transportation. Herein, the mechanical behavior of X80 pipeline steel in atmospheres of hydrogen blended methane was assessed via in-situ slow-rate tensile test, gas-phase hydrogen permeation test and hydrogen content measurements. The main concern lies in that the effect of different hydrogen-blending ratios on the mechanical properties, hydrogen permeation behavior and the hydrogen content of X80 steel at a temperature of 298 K, along with the impact of temperature on the kinetic parameters of gas-phase hydrogen permeation by the hydrogen-blending ratio of 10%. Results indicated that as the hydrogen-blending ratio increases, the yield and tensile strength of X80 pipeline steel decreased slightly, while the elongation at break decreased gradually, and both the hydrogen embrittlement sensitivity index and the hydrogen permeability coefficient and diffusion coefficient increased. The hydrogen permeability and diffusion coefficients increase with the increase of temperature under the condition of 10% hydrogen doping ratio. At temperatures between 298 K and 373 K, the hydrogen diffusion activation energy and permeation activation energy of X80 pipeline steel were 1.56 and 11.25 kJ/mol, respectively.

The effect of cathodically hydrogen charging on the crevice corrosion behavior of 2205 duplex stainless steel in 3.5%NaCl solution was investigated by means of measurements of potentiodynamic polarization, Mott-Schottky, and potentiostatic polarization, as well as scanning electron microscopy (SEM) and confocal laser microscopy (CLSM). The results show that the defect density of the passive film on the surface of 2205 duplex stainless steel increases, and the pitting potential decreases significantly with the increased hydrogen charging time. This results in the decrease of the critical crevice corrosion potential and the increased crevice corrosion susceptibility. The pitting corrosion and the striped corrosion inside the crevice is observed for the specimen without hydrogen charging. However, for the specimen with hydrogen charging, the grooved corrosion at the crevice mouth is observed at the high polarized potential, and the pitting corrosion inside crevice founded at the low polarized potential.

The effect of different annealing processes on microstructure evolution and hydrogen embrittlement sensitivity of 304 austenitic stainless steel was studied. The results show that after being subjected to annealing within the reverse phase of martensite transformation, the content of martensite as a rapid diffusion channel of hydrogen decreases continuously, correspondingly, the hydrogen content decreases, as a result, the hydrogen embrittlement sensitivity of the steel decreases. After annealing within the recovery and recrystallization stage, the dislocation density decreases, the fine equiaxed grains appear, the hydrogen content decreases, and thus the hydrogen embrittlement sensitivity of the steel also decreases. However, after annealing within the grain growth stage, the hydrogen content per unit area of grain boundaries increases, and the hydrogen embrittlement sensitivity of the steel increases. As a whole, after annealing treatment within the recovery and recrystallization stage, the 304 austenitic stainless steel present better comprehensive properties.

According to the acquired environmental factors of polluted Marine atmosphere at Qingdao coastal area, an environment spectrum composed of varying ultraviolet irradiation and weekly soaking was designed for laboratory accelerated test. Thereafter, the corrosion behavior of three stainless steels, 430, 316L and 2205 was studied in parallel via lab testing with the proposed spectrum, and further, the correlation of the acquired data was evaluated with the outdoor exposure test results at selected sites in polluted Marine atmospheric environment of Qingdao area. The tested steels were characterized by means of weightlessness method, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), corrosion electrochemistry etc. The results show that after 480 h test of UV irradiation + weekly shocking, 430 stainless steel underwent obvious corrosion, 316L stainless steel showed obvious pitting corrosion, and 2205 stainless steel experienced no obvious corrosion. However, the gray correlation analysis reveals that the laboratory corrosion data for the three stainless steels 430, 316L and 2205 and showed relatively good correlation with those of outdoor exposure test. Accordingly, the following three formulas may be proposed: T₄₃₀ = 50.0114t ^0.134351, T_316L = 66.32242t ^0.52341 and T₂₂₀₅ = 620.8745t ^0.112522, as the corrosion-life prediction model for the corrosion of three stainless steels 430, 316L and 2205 in Qingdao polluted Marine atmospheric environment respectively.

Marine corrosion has always been a major challenge constraining the effective development and utilization of marine resources, among which microbiologically influenced corrosion (MIC) occupies an extremely important position. As an emerging alloy material, high entropy alloys (HEAs) show significant potential in inhibiting MIC due to their unique high mixed entropy properties. Herein, a HEA FeNiCoCrW_0.2Al_0.1 was designed and prepared, and then its corrosion behavior in sulfate-reducing bacteria (SRB) containing solutions was assessed with particular attention to the process of passivation film formation. The results showed that the HEA formed a double-layered passivation film in SRB solution, and the main component of the outer layer was Cr₂O₃, which had strong protective properties. However, the corrosion resistance of the HEA in the SRB solution was reduced compared with that in the sterile medium. This phenomenon may be related to the biological activities of SRB and the direct effect of their metabolites, which promote biofilm formation and weaken the original passivation film, resulting in the impaired corrosion resistance of the alloy. Based on the theory of cathodic depolarization, a mechanism for the passivation film formation of HEAs in SRB solution was proposed, and the influence of biofilm on the protective efficacy of the passivation film on the alloy was further analyzed.

The initial corrosion behavior of three pure irons of different purity 3N2, 4N2 and 5N2, carbon steel Q235B, weathering steel SPA-H and stainless steel 304L in 3.5%NaCl solution was comparatively investigated by means of immersion test, electrochemical measurements, scanning electron microscopy, 3D profiling microscope and laser confocal Raman microscope. Results showed that according to the electrochemical impedance value, the corrosion rate of the six test materials from low to high is as following: 304L < 5N2 < 4N2 < 3N2 < SPA-H < Q235B. The scanning electron microscopy observation and 3D profiling microscope measurement revealed that the three pure irons 3N2, 4N2 and 5N2 exhibited localized corrosion; while the 3N2 presented the deepest corrosion pits. The corrosion products mainly consisted of Fe₃O₄, γ-FeOOH and α-FeOOH for all the six test materials.

Welding joints are not only weak areas of conventional corrosion, but also preferred locations for microbiologically influenced corrosion (MIC). In this article, MIC behavior of different regions of the Cu-bearing steel welded joint, including the base metal (BM), heat affected zone (HAZ), and weld metal (WM), was studied by immersion test in SRB containing solution with electrochemical measurement.Results showed that a uniform and dense bacterial biofilm was formed and covered on the BM specimen, while a loose porous one on WM and HAZ specimens. The electrochemical results indicated that the (R_ct + R_f) value of BM specimen increased steadily with the prolonging immersion time, while that of WM and HAZ specimens fluctuated. As a result, a few of shallow pits were observed on the surface of BM specimen, but many small and deep pits distributed in clusters appeared on the surface of WM and HAZ specimens. Analysis suggested that the microstructure inhomogeneity of WM and HAZ specimens provides sites for bacterial selective adhesion, resulting in biofilm with microscopically heterogeneous surface morphology, which promote local corrosion. Thus, the MIC resistance of WM and HAZ specimens is lower than that of BM specimen.

With the development of urban construction, it is inevitable that high voltage direct current transmission projects and buried oil and gas pipelines often share the proximity of public space corridors. Therefore, the potential danger of corrosion and damage to the adjacent buried oil and gas pipelines due to current leakage of transmission lines is becoming more and more prominent. In this paper, the stress corrosion sensitivity of X70 steel in a simulated solution of near-neutral soil under direct current (DC) was studied by means of electrochemical polarization curve, electrochemical impedance spectroscopy and slow strain rate tensile method. The results showed that the anode polarization of X70 steel increased with the increase in DC density. When the DC density was less than 0.5 mA/cm², the corrosion rate decreased with the increase in DC density. When the DC density increased to 1 mA/cm², the corrosion product film could not prevent the anodic dissolution and the corrosion rate increased sharply. In the absence of DC, the cracking mechanism of X70 steel was hydrogen induced cracking. Under the synergistic effect of DC and stress, DC led to continuous anodic dissolution at the crack tip. With the increase in DC density, the cracking mechanism of X70 steel in the simulated solution of near-neutral pH changed from hydrogen induced cracking to anodic dissolution.

The Zr-Sn-Fe-Cr-Ni alloy, due to its insensitivity to dissolved oxygen in high-temperature water corrosion environment, is suitable for reactors with high dissolved oxygen content such as Small Modular Reactors and Advanced Boiling Water Reactors. To develop high-performance Zr-Sn-Fe-Cr-Ni alloys, the Sn content was reduced, and the content of Fe, Cr, and Ni was appropriately increased based on the Zircaloys. Then the influence of heat treatments on the microstructural variations of the new Zr-1.35Sn-0.22Fe-0.13Cr-0.05Ni alloy was characterized. Meanwhile, the corrosion behavior of the Zr-1.35Sn-0.22Fe-0.13Cr-0.05Ni alloys, being subjected to two different heat treatments, was studied in high-temperature and high-pressure water at 360 ^oC/18.6 MPa for 330 d by taking Zircaloy-4 as comparison. Results show that the two different heat treated Zr-1.35Sn-0.22Fe-0.13Cr-0.05Ni alloys exhibited more or less the same corrosion behavior with typical approximate parabolic kinetics in the initial corrosion stage. After 220 d and 250 d of exposure, corrosion transitions occurred respectively. Compared to Zircaloy-4, the corrosion transition time was significantly delayed. This suggests that reducing the Sn content is advantageous in delaying the time for the occurrence of the corrosion transition during the initial corrosion period, which may be conductive to the improvement of long-term corrosion resistance of the Zr-Sn-Fe-Cr-Ni alloys. This may be ascribed to that by increasing the intermediate annealing temperature or extending the holding time by α-phase region for Zr-1.35Sn-0.22Fe-0.13Cr-0.05Ni alloy may be facilitate the increase of the average size of second phase particles, thus make the atomic ratio Fe/Cr closer to 1, which may be conductive to effectively delay the occurrence of the first corrosion transition of the Zr-Sn-Fe-Cr-Ni alloys during the initial corrosion period.

The corrosion behavior of Cu-alloys used for marine propeller, including Mg-Al bronze (MAB), Ni-Al bronze (NAB) and Mn brass (MB) in 3.5%NaCl solutions with different pH values (2, 4, 6.8, 10, 12) was assessed via long-term mass change measurement, electrochemical test, and corrosion morphology observation. The results show that the corrosion rate of the three Cu-alloys is the highest when the solution pH = 2, this may be due to the severe dissolution of κ phase and preferential corrosion of β/β′ phases. When the solution pH = 4, 6.8 and 10, the corrosion mass loss rate of the three Cu-alloys is close, and for the solution pH = 12, the three Cu-alloys exhibit passive behavior with the least mass loss. MAB presents the highest corrosion rate and the worst corrosion resistance in any test solution. The mass loss rate of NAB in the solution of pH = 12 is close to that of MB, while the mass loss rate in other solutions is the lowest. After long-term immersion in the solution of pH = 6 and 8 respectively, the corrosion products film formed on the NAB surface exhibits the best protectiveness. In the solution of pH = 12, passive films may form on the surfaces of the three Cu-alloys, and their impedance increases rapidly with extended immersion time. The ranking order of the protectiveness of passive films is as: MB, NAB and MAB from high to low, which consistent with the mass change measurement results.

Corrosion behavior of 5383 Al-alloy and its welded joints was investigated in a nature seawater by applied different loads (50%R_el, 80%R_el, 100%R_el). Its stress corrosion behavior was assessed via a four-point bending device by applied constant load and electrochemical measurement. The results showed that the bare 5383 Al-alloy exhibited obvious passivation phenomenon, while no passivation for the welded joints. When the applied load was lower than the yield strength, the charge transfer resistance (R_ct) of the welded joints decreased by an order of magnitude compared to that without applied load. When the applied load was equal to the yield strength, R_ct decreased by two orders of magnitude. This is because when the load is increased up to the level of yield strength, not only the microstructure and stress state of the alloy are changed, but the surface passivation film is also difficult to form. Therefore, due to losing the protective effect of the passivation film, the corrosion may gradually propagate inward to the interior, resulting in an increase in the corrosion rate of welded joints of 5383 Al-alloy.

Accurate prediction of the corrosion rate of oil and gas pipelines is crucial for maintaining pipeline safety, and the diversity and difficulty of choosing corrosion rate prediction models have brought challenges to practical applications. Herein, to improve the traditional linear integration strategy, firstly the global error and local error are synthesized and a comprehensive error evaluation index is postulated, then a novel linear integration strategy is established accordingly, its wide applicability and superiority are confirmed by rigorous testing with five standard test functions. By applying this strategy to the prediction of pipeline corrosion rate, an efficient integrated prediction model was successfully constructed via combining the FLA-optimized BP neural network, Kriging and ELM model. The results show that the new strategy performs better in terms of prediction accuracy and stability compared with the single model and the traditional integrated model, while the integrated model reaches the best performance when the local error adjustment factor is set to 0.5; In case the combination of the three models is adopted for prediction, it can produce better results rather than any single model, therefore the prediction effect is significantly improved. This study has important engineering application value for the reliability assessment and maintenance decision of pipeline systems.