X80 Pipeline Steel Research Articles

An enhanced Hosford–Coulomb fracture model for predicting ductile fracture under a wide range of stress states

In this study, an Enhanced Hosford–Coulomb (EHC) fracture model is proposed, which suits a wide range of stress states. The model is validated by quantitatively investigating the ductile fracture behaviors of Ti-6Al-3Nb-2Zr-1Mo titanium alloy through experiments and numerical simulations, and the fracture morphologies are characterized using scanning electron microscopy. The results show that the EHC model has higher accuracy in predicting ductile fracture strain for Ti-6Al-3Nb-2Zr-1Mo alloy compared to the original Hosford–Coulomb (HC) model. Finally, the accuracy and material applicability of the EHC model are further verified with X80 pipeline steel and AA2024-T351 aluminum alloy, demonstrating its advantages.

Accelerated stress corrosion cracking of X80 pipeline steel under the combined effects of sulfate-reducing bacteria and hydrostatic pressure

The microbially mediated metal stress corrosion cracking (SCC) mechanisms in deep-sea environments remain unclear, hindering the safe use of deep-sea equipment materials. Hydrostatic pressure facilitated microbiologically influenced corrosion resulting in the pitting depth increase. The stress concentration at the pit bottom induced anodic dissolution (AD), leading to ductile fracture. Hydrostatic pressure and iron sulfides both enhanced the hydrogen evolution reaction (HER). The sulfides produced by SRB metabolism inhibit hydrogen atom recombination, leading to a higher hydrogen permeation current and inducing hydrogen embrittlement (HE) fracture. The combined effect of AD and HE increases the SCC susceptibility of deep-sea pipeline steel.

Effect of temperature on the electrochemical corrosion behavior of X52 pipeline steel in NS4 simulated solution

In this study, the electrochemical corrosion performance of both the base material and welded joint of X52 pipeline steel was analyzed at various temperatures (room temperature-RT, 30 °C, 50 °C, and 80 °C) using microscopic characterization techniques and electrochemical methods in a simulated soil solution (NS4). Additionally, the influence of temperatures on the electrochemical corrosion behavior of the X52 pipeline steel base material and welded joint was examined. The findings indicate that the open circuit potential (Eocp) of the base material and welded joint shifts in the negative direction with increasing temperature. The corrosion current density increased from 30.7 to 110.2 μA∕cm2 and from 19.5 to 100.2 μA∕cm2, respectively, while the polarization resistance dropped from 637.3 to 272.6 Ω•cm2 and from 961.3 to 360.7 Ω•cm2. Notably, anodic dissolution controls the corrosion process of the base material and welded joint of X52 pipeline steel at room temperature. Furthermore, the charge transfer resistance (Rt) of the base material and welded joint gradually decreases with increasing temperature, and the corrosion process transforms into cathodic diffusion control. Additionally, the welded joint of X52 pipeline steel exhibits superior corrosion resistance to that of the base material at the same temperature.

Hydrogen Embrittlement Behavior of X42 Pipeline Steel in Gaseous Hydrogen with Different Pressures

Hydrogen Embrittlement Behavior of X42 Pipeline Steel in Gaseous Hydrogen with Different Pressures

Systematic quantification of hydrogen in pipeline steel by atom probe tomography after ambient charging and transfer

Atom probe tomography (APT) is a promising tool to measure the atomic-scale distribution of hydrogen in solid matter for the assessment of hydrogen embrittlement susceptibility of materials. However, the accuracy of such measurements resulting from ambient charging and transfer experiments needs to be established. In this work, APT quantification of hydrogen (H) and deuterium (D) in a typical X65 pipeline steel has been determined after ambient charging and transfer to ascertain the contribution of artifacts to the measured H/D signal. A series of experimental workflows related to sample preparation (electropolishing, focussed ion beam) and electrochemical charging conditions (different electrolytes and charging potentials) were explored for H/D measurement using APT. The results show that APT can be used to measure charged H/D with statistical confidence after ambient charging and transfer, that hydrogen ingress occurs during electropolishing, and using a more negative charging potential will introduce more H/D into the material.

Microstructural Evolution and Mechanical Properties of Reeled X65 Pipeline Steel during Cyclic Plastic Deformation and Natural Aging

The reel laying is recognized as a cost‐effective installation process for offshore pipelines. However, the mechanical properties are modified due to plastic deformation during the reel laying and lowering process of reeled pipelines and the subsequent natural aging in service. Cyclic plastic deformation (CPD) is conducted on X65 pipeline steel to simulate the strain experienced in the reel‐laying and lowering process, and then, the CPD specimen is aged at 250 °C to simulate natural aging in service. The dislocation configurations gradually evolve from dislocation lines and tangles into dislocation walls and cells due to the increase in strain level. After CPD and aging, the tensile strength increases by about 25 MPa, which is not significantly affected by the last introduced load direction and strain level. At the end of compressive loading, the yield strength and yield ratio decrease, but the uniform elongation increases significantly. In contrast, at the end of tensile loading, the yield strength and yield ratio increase, but the uniform elongation decreases slightly. The yield strength further increases as the strain level increases from 2 to 3%. Therefore, CPD and aging modify the mechanical properties of X65, considerably depending on the last introduced load direction and strain level.

The role of hydrogen gas in SRB-induced degradation of X80 pipeline steel in hydrogen-blending environments

The pipeline transportation of hydrogen poses higher challenges to the safety of pipes. In this study, the corrosion mechanisms of SRB in X80 pipeline steel under H₂ conditions were investigated. Thermodynamic analysis revealed that the introduction of hydrogen enhances SRB metabolic activity, facilitating the reduction of sulfate to sulfide and promoting hydrogen embrittlement. Additionally, hydrogen permeation tests confirmed that SRB significantly increase hydrogen diffusion in steel, accelerating corrosion. The enhanced hydrogen permeation under biotic conditions was linked to increased hydrogen uptake and sulfide formation, which further destabilized the steel microstructure. This study provides critical insights into the interplay between microbial activity, hydrogen permeation, and corrosion, offering a deeper understanding of the factors influencing hydrogen-assisted corrosion in steel pipelines. The findings contribute to the optimization of material performance and risk assessment in hydrogen-blended environments.

Mechanisms of pitting induced by containing Ce inclusions in X100 pipeline steel

Mechanisms of pitting induced by containing Ce inclusions in X100 pipeline steel

Combined acoustic emission and electrochemical methods for analyzing the uniform corrosion behavior of X90 high-grade steel pipelines

Long-distance, large-diameter, and high-pressure pipelines represent the future of oil and gas pipeline construction. X90 pipeline steel is expected to become the standard steel due to its high transmission efficiency and lower cost in the future, yet corrosion poses the most significant challenge to the development of high-strength pipelines. This study focuses on monitoring the uniform corrosion process of X90 steels using acoustic emission (AE) and electrochemical testing systems. The AE signals from corrosion were processed using wavelet de-noising, decomposition, and reconstruction to extract signal characteristics. Experimental results reveal that the corrosion process of X90 steel can be categorized into three stages: initial metal dissolution, corrosion product accumulation, and corrosion stabilization. Signal activity and strength follow normal distributions throughout these stages. During metal dissolution and corrosion stabilization, AE signals exhibit a frequency range of 100–200 kHz with relatively low amplitude. Conversely, during corrosion product accumulation, signals display a narrow frequency range with higher amplitudes, typically around 3 × 10-4V. Moreover, the appearance of a double-peak signal suggests the presence of two distinct AE sources.

Beneficial effect of heat input to improve microbial corrosion resistance of welded joint in X80 steel pipeline

In this paper, Desulfovibrio vulgaris corrosion of X80 steel welded joint with different heat inputs was carefully investigated. The results confirmed that in the sterile medium, general corrosion rate and localized corrosion susceptibility of heat affected zone (HAZ) were higher than those of weld zone (WZ) and base metal (BM). In the inoculated medium, the general corrosion rate of HAZ was still higher than that of WZ and BM. However, the number and depth of corrosion pits on WZ and BM surfaces, as well as the localized corrosion susceptibility, were much higher than those in HAZ, which was opposite to that in sterile environment, suggesting that the Desulfovibrio vulgaris corrosion of the welded joint was selective. With heat input increasing from 0.57 kJ/mm to 1.29 kJ/mm, general corrosion rate and localized corrosion susceptibility of HAZ and WZ simultaneously decreased in sterile or inoculated medium. In inoculated medium, localized corrosion of HAZ decreased more sharply than weld zone. Within the range of heat inputs tested, the study discerned a positive correlation: higher heat inputs correlated with an enhanced corrosion resistance of welded joint, irrespective of environmental conditions being sterile or inoculated. The findings provide a solid basis for the welding parameter determination to steel pipelines in oil and gas transportation.

Effect of hydrogen on low-cycle fatigue properties and the mechanism of hysteresis energy method lifetime prediction of X80 pipeline steel

Effect of hydrogen on low-cycle fatigue properties and the mechanism of hysteresis energy method lifetime prediction of X80 pipeline steel

Variations of the residual magnetic fields of X70 pipeline steels with double defects

The aim of this research is to correlate residual magnetic fields (RMFs) with double defects in ferromagnetic steels. Specimens of X70 pipeline steels were machined into smooth plates with two types of defect (single and double defects) for comparison. Tensile tests were carried out to detect the RMF signals on the surface of the defective specimens. The variation of the tangential component of the RMF signals was presented and magnetic parameters were defined to investigate the abnormal magnetic changes of the two types of defect. It was found that the peak value of the tangential component was not influenced by defect types and the valley value was capable of evaluating the interaction effect between defects. Correlation between the RMF signals and the location of double defects was also investigated. This research will promote the investigation of defect clusters in ferromagnetic steels based on the metal magnetic memory (MMM) technique.

Effect of Filler Wire Composition on Weld Metal Microstructure and Mechanical Properties in X80 Steel Laser Welds.

Laser welding was performed using different filler wires, ER70S steel, commercially pure iron, and pure nickel filler, in the context of welding X80 pipeline steel to assess the microstructure and mechanical properties of the weld metal. Introducing an ER70S wire promoted acicular ferrite formation in the fusion zone, compared to a bainitic microstructure in an autogenous laser weld. The use of pure iron wire was considered as a potential strategy for reducing hardenability, as it led to the dilution of alloying elements in the fusion zone, increasing ferrite content and reducing weld metal hardness to a level compliant with API pipeline standards. The addition of pure nickel wire was used to reveal the degree of weld metal mixing imposed by the laser (thus providing an unambiguous tracer element) when it is combined with filler material dilution in the fusion zone, revealing that the upper region contained 38% wire material and the lower region only 12%. This accounts for the differences observed between the upper versus lower portions of the weld metal when other wires are used, and the use of hardness mapping and micro-indentation demonstrates the correlation between the variations in mechanical properties and microstructural differences introduced by incomplete mixing of the filler wire elements.

Hydrogen permeation behavior of X80 pipeline steel under alternating wet-dry environment in the South China Sea

The riser sections of offshore pipelines are subject to cathodic potentials, alternating wet-dry (AWD) cycles and stresses in the service environment. The hydrogen permeation of X80 offshore pipeline with different cathodic potentials, dry/wet ratios, and constant tensile stress in AWD environment were investigated by the self made experimental equipment, which includes the three modules, i.e., the constant stress loading, the two-component cell hydrogen permeation, and AWD environment. Results showed that hydrogen permeation current fluctuates with the AWD, which is different from that in the bulk solution. In one AWD cycle, the permeation increases in the wetting stage and decreases in the dry stage. The smaller the dry/wet ratio, the longer the hydrogen permeation current keeps high level which is caused by the dense corrosion product layer. The hydrogen permeation currents in the elastic stress are greater than those in the plastic deformation, and unstressed conditions is the smallest.

Experimental Study on Hydrogen Embrittlement Behavior of X80 and X70 Pipeline Steels Evaluated by Hydrogen Permeation and Slow Strain Rate Tensile Tests

Experimental Study on Hydrogen Embrittlement Behavior of X80 and X70 Pipeline Steels Evaluated by Hydrogen Permeation and Slow Strain Rate Tensile Tests

Coupled effect of microstructure heterogeneity and hydrogen on local embrittlement of CGHAZ and IC-CGHAZ in X65 pipeline steel

The local embrittlement of the coarse-grained heat-affected zone (CGHAZ) and intercritically reheated CGHAZ (IC-CGHAZ) in X65 pipeline steel was investigated using an in situ crack-tip opening displacement test in air and H2S, combined with microstructure-based simulation. The IC-CGHAZ exhibited significantly lower cracking resistance, with the fracture toughness reduced by 50 % compared to CGHAZ in both environments (0.160 mm in air and 0.017 mm in H₂S for IC-CGHAZ, compared to 0.307 mm in air and 0.034 mm in H₂S for CGHAZ). The martensite/austenite (M/A) constituents showed exceptionally higher intrinsic hardness than the ferrite matrix. The continuous distribution of M/As along the prior austenite grain boundaries resulted in local hardening and the formation of heterogeneous hard zones in IC-CGHAZ. Such microstructure heterogeneity resulted in the unique partitioning of plastic strain localization and stress triaxiality that promotes premature fracture, particularly with the coupled effect of hydrogen. This study provides a novel perspective on the fracture mechanisms and the typical fracture morphology of IC-CGHAZs in pipeline steel under the coupled effect of microstructure heterogeneity and hydrogen.

Effects of hydrogen blending ratios and CO2 on hydrogen embrittlement of X65 steel in high-pressure offshore hydrogen-blended natural gas pipelines

In this study, the effects of hydrogen blending ratios and high CO2 content on hydrogen embrittlement (HE) of offshore natural gas X65 pipeline steel were investigated. In high-pressure hydrogen gas, the impact of hydrogen content on yield strength and tensile strength was minimal. However, the effect on elongation was more significant, with the area decreasing and the HE index increasing until the hydrogen-blended ratio approached 30%, at which point the HE index reached 8.94%. Introducing CO2 into high-pressure hydrogen-rich gas further increased the HE index with high CO2 content. At 40% CO2, the HE index was 2.42 times higher than in high-pressure hydrogen-blended mixtures (30% H2). Additionally, the local fracture morphology transitions from ductile to quasi-cleavage fracture with the addition of CO2 and H2.

Manipulating nano-WS2 aggregates in electroplated Ni coating to mitigate hydrogen embrittlement in X70 pipeline steel

WS2 is a two-dimensional nanomaterial with significant potential for hydrogen barrier applications. Herein, WS2/Ni composite coatings were fabricated on X70 pipeline steel substrates via electrodeposition. The properties of the composite coatings were systematically examined by electrochemical hydrogen permeation tests, hydrogen evolution kinetics tests, SSRT, SKPFM, and FEM. The results indicate that varying the deposition time leads to changes in coating microstructure, which correspondingly influence hydrogen permeation performance. Furthermore, the hydrogen barrier mechanism of the WS2/Ni composite coatings involves two key processes: the inhibition of hydrogen evolution reactions on the coating surface and hydrogen adsorption by WS2 within the coating interior.

Underlying mechanisms for the effect of Nb micro-alloying on the elemental distribution and precipitation behavior in the X70 weld metal

Niobium (Nb) is a widely recognized micro-alloying element due to its low cost and substantial impact on steel properties. While the effect of Nb in processed steels has been well investigated, studies on its elemental distribution and precipitation behavior in weld metal remain scarce. This study focuses on the weld metal of specially designed Nb-rich X70 pipeline steel by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) characterization, complemented with thermodynamic and kinetics modeling analysis. In the majority of the weld, Nb was essentially uniformly distributed. This suggests that Nb primarily exists in the solid solution form in the weld metal, which is also supported by precipitation kinetics modeling results. This is primarily due to the short thermal history associated with the welding process, which leads to insufficient time for the uniform precipitation of Nb. Two instances of Nb precipitates were observed at the weld centerline and reinforcement region. The low partition coefficient of Nb results in an elevated local concentration along the weld centerline. However, precipitation kinetics calculations suggest that this enhancement alone is not adequate to induce precipitate formation. The occurrence of MnS and the prior formation of Ti precipitates may provide heterogeneous nucleation sites for Nb, facilitating the nucleation of Nb precipitates in the weld centerline and reinforcement region.

Multi-objective prediction and optimization of X70 pipeline steel welding morphology in overhead laser-MAG hybrid welding based on RSM-NSGA-II

Multi-objective prediction and optimization of X70 pipeline steel welding morphology in overhead laser-MAG hybrid welding based on RSM-NSGA-II