Flexible risers are critical equipment for the production of oil and gas in offshore fields around the world. The annulus region may condense acidic water containing H2S exposing the tensile armour ...steel wires to a sour environment, which may promote sulphide stress cracking (SSC) and/or hydrogen-induced cracking (HIC). This work aims to evaluate through electrochemical and constant displacement tests the effectiveness of thermal spray aluminium (TSA) coating to mitigate SSC and HIC in high strength steel used to manufacture the tensile armour of a flexible riser. Electrochemical tests confirmed the anodic behaviour of the coating against the steel and estimated a service life of 2.5 years. The constant displacement test indicated that the non-coated samples failed by SSC although some cracks were also found in the samples mid-section due to HIC. For Al-coated samples, no signs of SSC and HIC were observed. The TSA coating showed a dual barrier effect, hindering either corrosion of steel or hydrogen up-taking, and neither SSC nor HIC was observed. Samples with a coating defect were cathodically protected and no HIC was observed.
•Non-coated steel failured by sulphide stress cracking (SSC) and showed cracks associated to hydrogen-induced cracking (HIC);•Thermal spray aluminium (TSA) coating suppressed SSC due the barrier effect and the cathodic protection;•TSA limited the hydrogen diffusion which hindered the HIC.
•Tests were conducted on H-shaped high-strength steel beams with perforated web.•Narrow and wide flange H-sections were subjected to three point and four point bending.•AISC, NAS, Eurocode, AS and CC ...are generally inappropriate for H-shaped high-•strength steel beams.•SDGS-2, DSM and CSM may be inapplicable to H-shaped high-strength steel beams.•with perforated web.
The study conducts an experiment on flexural behavior of H-shaped high-strength steel beams with perforated web subjected to both gradient and constant bending. A total of 12 specimens including narrow flange and wide flange H-section beams were tested, which were made of high-strength steel Q550D and TQ700MCD, respectively. The effects of the ratio of web depth to flange width (h/b), the ratio of flange width to thickness (b/tf), the ratio of web depth to thickness (h/tw), the ratio of hole diameter to web depth (d/h) and the number of holes in the web on the flexural behavior of H-shaped steel members with high strength were investigated. Test results consist of the failure mode, bending moment-midspan deflection curves as well as the strain distributions at the midspan and the perforated sections of H-shaped high-strength steel beams. It was found that the ultimate flexural strengths and the corresponding curvatures of the specimens under gradient bending are all greater than those of the specimens under constant bending. The flexural strengths of H-shaped high-strength steel members with or without holes in the web gained in the experiments were made the comparison with those determined from current designing guidelines of perforated or imperforated steel members. The comparison reveals that American National Standard (AISC 360-16) and North American Specification (NAS) are quite conservative; Eurocode 3 (EC3) is somewhat unconservative; Australian Standard (AS) and Chinese Coding (CC) are somewhat conservative. Furthermore, Direct Strength Method (DSM) is quite conservative, Steel Design Guide Series 2 and Continuous Strength Method (CSM) are somewhat conservative for the flexural behavior of H-shaped high-strength steel beams with perforated web.
Based on our completed experimental research, the fire resistance of Q550 high-strength steel (yield strength of fy = 550 N/mm2) hollow columns under axial compression is explored by a finite element ...numerical simulation and theoretical analysis. First, an accurate analysis model of high-strength steel columns under fire exposure is established using ABAQUS software, and a numerical simulation analysis is carried out. Based on verified finite element model, a parametric analysis of the fire resistance of high-strength steel columns is conducted. The effects of the section area A, section height-thickness ratio H/t, section height-width ratio H/B, overall bending defect amplitude e0, slenderness ratio λ and load ratio n on the fire resistance of high-strength steel columns are investigated. Finally, based on the parametric analysis results and different limit state judgement criteria, the calculation formulas for the critical temperature Tcr and maximum axial displacement umax of Q550 high-strength steel columns with rectangular sections under axial compression are proposed. The correctness of the formulas is verified by comparing the calculation results with the test results. The research of this paper provides a theoretical basis for improving the fire resistance design of high-strength steel columns at elevated temperatures, and greatly promote the healthy development and good application of high-strength steel in structural engineering applications.
•Tests on welded I-section two-span continuous beams for Q460 high strength steel.•The finite element model considering initial geometric imperfections and residual stresses was developed and ...verified against tests.•The extensive finite element parametric analyses were carried out for study on design method.•The overall buckling design method of two-span continuous beams for Q460 high strength steel in the relevant code was assessed and the corresponding suggestions were proposed.
To investigate the overall buckling behaviours of welded I-section two-span continuous beams for Q460 high strength steel and assess the reliability of the overall buckling design method for such beams stipulated in the Standard for design of high strength steel structures (JGJ/T483-2020) of China, a total of six two-span continuous beams were tested under concentrated loads, and the overall buckling modes and capacities were obtained. The finite element model (FEM) considering initial geometric imperfections and residual stresses was established and validated through comparing with the test results, and extensive parametric analyses were carried out through the validated FEM. Based on the formula of the elastic critical moment for simply supported beam given in Standard for design of steel structures (GB50017-2017) and the finite element analysis (FEA) results, the formula of the elastic critical moment for two-span continuous beam was proposed. The above proposed formula was substituted into the buckling factor formula in JGJ/T483-2020 to obtain the overall buckling design curves of two-span continuous beams for Q460 high strength steel. Furthermore, the obtained design curves were compared with the test and FEA results, which indicates that the design method in JGJ/T483-2020 is suitable for the overall buckling design of two-span continuous beam for Q460 high strength steel with non-dimensional slenderness value less than 1.5, and the design method in JGJ/T483-2020 is relatively conservative for the overall buckling design of two-span continuous beam for Q460 high strength steel with non-dimensional slenderness value greater than 1.5.
This paper presents the experimental investigation on the material properties and residual stress distributions of cold-formed high strength steel hollow sections. The nominal yield stresses (0.2% ...proof stresses) of the hollow sections were 700, 900 and 1100MPa. The sections were composed of 9 square hollow sections, 2 rectangular hollow sections and 6 circular hollow sections. 66 tensile coupons were tested to determine the modulus of elasticity, 0.2% tensile proof stress, ultimate tensile strength and elongation at fracture of the material. The results were also compared with the American, Australian and European standards. Based on the Ramberg–Osgood expression, a new constitutive model for high strength steel material is proposed. On three of the hollow sections, strength variation and cold-forming effect were studied by testing coupons extracted from different locations of the cross-sections. Residual stresses were also investigated both in longitudinal and transverse directions on three hollow sections using wire-cutting method. A total number of 82 longitudinal strips and 3 transverse rings were cut from the original sections.
•Cold-formed high strength steel hollow sections were examined.•Material characterizations were conducted through 66 tensile coupon tests.•Cold-forming effects were investigated on halves of the three hollow sections.•A new material model for high strength steel was proposed.•Residual stresses on three sections were measured and reported.
Martensitic steels have gained renewed interest recently for their use in automotive, aerospace, and defense applications due to their ultra-high yield strengths and reasonable ductility. A recently ...discovered low alloy martensitic steel, AF9628, has been shown to exhibit strengths greater than 1.5 GPa with more than 10% tensile ductility, due to the formation of ε-carbide phase. In an effort to produce high strength parts with a high degree of control over geometry, the work herein presents the effects of selective laser melting (SLM) parameters on the microstructure and mechanical properties of this new steel. An optimization framework to determine the process parameters for building porosity-free parts is introduced. This framework utilizes the computationally inexpensive Eagar-Tsai model, calibrated with single track experiments, to predict the melt pool geometry. A geometric criterion for determining maximum allowable hatch spacing is also developed in order to avoid lack of fusion induced porosity in the as-printed parts. Using this framework, fully dense samples were successfully fabricated over a wide range of process parameters, allowing the construction of an SLM processing map for AF9628. The as-printed samples displayed tensile strengths of up to 1.4 GPa, the highest reported to date for any 3D printed alloy, with up to 11% elongation. The demonstrated flexibility in process parameter selection, while maintaining full density, opens up the possibility of local microstructural refinement and parameter optimization for improved mechanical properties in as-printed parts. The process optimization framework introduced here is expected to allow successful printing of new materials in an accelerated fashion.
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Very high‐cycle fatigue life (VHCF) prediction of high‐strength steel based on machine learning (ML) was investigated in this paper. First, a total of 173 sets of experimental data on the VHCF of ...high‐strength steel were collected to train the ML model. The sensitivity coefficient analysis indicated that inclusion size and maximum stress were the strongest correlation parameters with fatigue life and selected as the input features for the final model training. The S–N curve predicted by the obtained ML model closely aligns with the actual S–N curve. Among the three algorithm models, namely, random forest, XG boost, and gradient boosting, the gradient boosting model exhibited superior performance and achieved the highest accuracy in predicting the VHCF life of high‐strength steel. A comparison between the Murakami model and the gradient boosting model was conducted. It is indicated that ML exhibits superior predictive performance with high efficiency and excellent accuracy.
Highlights
S–N curve predicted by machine learning model closely aligns with that by experiments.
Gradient boosting model exhibited superior performance in predicting the VHCF life.
Machine learning model outperforms the Murakami model in the terms of accuracy.
High-strength S135 drill pipe is an important component in the oil and gas exploration and development of deep and ultradeep wells under complicated environments. It is of great significance to the ...study on the corrosion fatigue fracture of high-strength steel S135 in complex environments. In this paper, two samples of smooth and unilateral notch were used to conduct fatigue in air, pre-corrosion fatigue and corrosion fatigue at different temperatures, respectively, to study the corrosion fatigue behavior of high-strength steel S135 under the complex environments of the notch, corrosion medium, temperature and alternating stress. The experimental results indicated that the influences of coupling multiple factors (notch, temperature, corrosion medium and alternating stress) on the corrosion fatigue of S135 steel were greater than that of single factor, and the more factors indicated the greater influence on fatigue. The influence of three kinds of coupling factors, such as the notch, corrosion medium and temperature, was the most significant (80.8%). In single factor, the impact of notch on fatigue was the largest (49.9%), followed by corrosion (41.6%) and temperature (34.4%). Obviously, the notch was the dominant factor of fatigue fracture, and the temperature had a significant influence on corrosion fatigue. It was found that the influence of coupling-factor on fatigue was less than of the superposition of single factor, so the relationship among multiple factors was not superposed but competitive and synergistic relationship. This can be attributed to the fact that the crack was always initiated from the corrosion pits at the notch root under coupling multi-factor in complex environments and the initiation was the combined action of stress concentration, anodic dissolution and temperature. The stress concentration at the notch was the main factor of crack initiation, and the electrochemical activity of at the notch root was the highest under the action of cyclic stress and this place gave priority to corrosive pitting, made the increase of local stress concentration and promoted the initiation of crack. And the temperature provided the energy to the corrosion electrochemical reaction and accelerated the evolution of the corrosion pits, so crack initiation was accelerated. Besides, article established the testing method of rotating bending fatigue in complex environments, revealed the relationship of fatigue fracture as well as the mechanisms of crack initiation and propagation of high-strength S135 steel under coupling multiple factors in complex environment.
To increase the usage of high-strength steel and aluminium alloy sheets for lightweight automobile body panels, the joinability of sheet combinations including a 780-MPa high-strength steel and an ...aluminium alloy A5052 sheets by mechanical clinching and self-pierce riveting was investigated for different tool shapes in an experiment. All the sheet combinations except for the two steel sheets by self-pierce riveting, i.e., the two steel sheets, the two aluminium alloy sheets, and the steel-aluminium alloy sheets, were successfully joined by both the joining methods without the gaps among the rivet and the sheets. Then, to show the durability of the joined sheets, the corrosion behaviour and the joint strength of the aged sheets by a salt spray test were measured. The corrosion and the load reduction of the clinched and the riveted two aluminium alloy sheets were little. The corrosion of the clinched two steel sheets without the galvanized layer progressed, and then the load after 1176 h decreased by 85%. In the clinched two galvanized steel sheets, the corrosion progress slowed down by 24%. In the clinched steel and aluminium alloy sheets, the thickness reduction occurred near the minimum thickness of the upper sheet and in the upper surface on the edge of the lower aluminium alloy sheet, whereas the top surface of the upper sheet and the upper surface of the lower sheet were mainly corroded in the riveted joint. The load reduction was caused by the two thickness reductions, i.e., the reduction in the minimum thickness of the upper sheet and the reduction in the flange of the aluminium alloy sheet. Although the load of the clinched steel without the galvanized coating layer and aluminium alloy sheets decreased by about 20%, the use of the galvanized steel sheet brought the decrease by about 11%. It was found that the use of the galvanized steel sheets is effective for the decrease of strength reduction due to corrosion.
Ternary zinc-aluminum-magnesium (ZnAlMg) alloy coatings are the focus of significant attention in the automotive and steel industries due to several advantages over traditional Zn-based coatings. ...Currently, the literature on this type of coating is limited and focuses mainly on their corrosion resistance and room temperature tensile properties. To assess the relevance of ZnAlMg coatings in current manufacturing processes such as hot stamping and welding of advanced high strength steels (AHSS), it is essential to understand their high-temperature performance, particularly their resistance to liquid metal embrittlement (LME) cracking. This study showed that the ZnAlMg coating had complete resistance to LME cracking at a temperature of about 900 °C, which is traditionally recognized as the temperature at which the highest levels of LME susceptibility are observed in the different families of AHSS. Elemental distribution analysis confirmed that due to an increase in the testing temperature, the lamellar eutectic microstructure of the coating dissolved into the Zn-matrix, with the constituent elements, Al and Mg, segregating towards the steel substrate and the coating surface, respectively. This led to the in-situ formation of a uniform α-Fe(Zn, Al) layer at the steel/coating interface which prevented the direct contact of liquid metal with the steel substrate, resulting in complete suppression of LME at high temperature. Numerical calculations of interdiffusion flux were used to investigate the diffusion behavior of the elements of interest at the interface which indicated that the α-Fe(Zn, Al) layer formed due to the high diffusion rate of Al towards the Fe substrate at 900 °C. The effectiveness of the α-Fe(Zn, Al) layer in mitigating LME was evaluated by calculating the work of adhesion, which showed that this layer preserved its integrity under an applied tensile load, successfully mitigating the initiation of LME. The findings of this study offer valuable insights into developing new avenues for advancing LME resistant coatings by utilizing ternary Zn-based alloy systems.
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