X80 Pipeline Research Articles

Influence of hydrogen volume/specimen surface area ratio on hydrogen embrittlement sensitivity of X52 pipeline steel

In the transition towards green energy, long distance transportation of gaseous hydrogen by pipeline is considered to be an economically attractive solution. For safe transportation of hydrogen, it is important to conduct relevant mechanical tests in representative hydrogen environments and working conditions of pipelines to demonstrate acceptable hydrogen embrittlement resistance of the steel. One important issue is the testing condition for the ratio of gaseous hydrogen volume over specimen surface area required in mechanical testing since this has not been specified in any testing standards and codes or investigated. This study investigated this issue by performing slow strain rate tensile (SSRT) testing of an X52 pipeline steel in gaseous hydrogen with different ratios of hydrogen volume/specimen surface area, Rv/s, ml/mm2. It was found that, with increasing Rv/s ratio, the area reduction of the steel decreased and hydrogen embrittlement sensitivity increased in the range of the Rv/s ratios investigated. The saturating Rv/s ratio appeared to be ∼2.0 beyond which the effect of Rv/s ratio on hydrogen embrittlement sensitivity was relatively small. The macroscopic and microscopic observations on both the fracture and side surfaces of the SSRT tested specimens also found that the tendency to cleavage fracture increased with increasing Rv/s ratio. The results of the ab initio molecular dynamics (AIMD) simulations performed also predicted a dependence of hydrogen embrittlement on hydrogen volume when Rv/s ratio is relatively small.

Effect of Pseudomonas aeruginosa on Corrosion Behavior of X65 Carbon Steel.

X65 pipeline steel is widely used in the field of offshore oil and gas exploitation due to its excellent performance. However, due to the complex environment in the ocean, X65 pipeline steel is faced with a great risk of microbial corrosion failure. Therefore, it is of great significance to study the corrosion mechanism of X65 pipeline steel by microorganisms. In this paper, the corrosion effect of Pseudomonas aeruginosa (P. aeruginosa) secreting phenazine compounds on X65 pipeline steel was studied by the weight loss method, biofilm scanning electron microscopy analysis, surface corrosion morphology observation, electrochemical testing and medium pH test corrosion products. The results showed that the inoculation of P. aeruginosa accelerated the corrosion of X65 steel. After knocking out the phzM and phzS genes that regulate the synthesis of PYO, P. aeruginosa can still produce biofilms on the surface of X65 steel consistent with the morphology of wild-type P. aeruginosa, but the corrosion of X65 steel is significantly reduced. It is proved that PYO plays an important role in the corrosion process of P. aeruginosa on steel.

Impact of gravity on biofilm growth and corrosion of X65 pipeline steel by a sulfate reducing bacterium

Desulfovibrio ferrophilus (IS5) corrosion of X65 carbon steel was impacted by gravity. Six o’clock position (6P) had the highest sessile count due to gravity assisting planktonic cell settling in early biofilm formation, leading to most severe static corrosion followed by 9P and 12P. The 7-d weight loss at 6P was 49.6 ± 4.4 mg/cm2 (3.3 mm/a in uniform corrosion rate) followed by 9P with 35.7 ± 2.6 mg/cm2 (2.4 mm/a) and 12P with 20.5 ± 5.5 mg/cm2 (1.4 mm/a). The trend was supported by electrochemical measurements. The weight loss differences reduced considerably when there was agitation, supporting the gravity hypothesis.

Surface morphology of API 5L X65 pipeline steel processed by ultrasonic impact peening: An integrated experimental and computational study

Ultrasonic impact peening (UIP) is a highly effective surface engineering technique to improve material durability through peening-induced surface plastic deformation. These improvements are determined by not only the generation of surface compressive residual stresses but also the alteration of surface morphological features. In literature, researchers have focused primarily on the average roughness (Sa) to understand the morphology changes induced by UIP. From the surface engineering perspective, in addition to Sa, other surface morphological characteristics play key roles in determining material durability, particularly surface skewness (Ssk) and surface kurtosis (Sku), which describe the asymmetrical distribution of surface profiles and the sharpness of peak features, respectively. In this study, surface morphological characteristics of API 5L X65 pipeline steel processed by UIP are investigated with a focus on the effects of processing parameters on Sa, Ssk, and Sku. The results indicate that the optimized UIP conditions lead to the preparation of surfaces with valley structures as the dominant feature accompanied by blunt peaks, resulting in the elimination of stress concentration sites towards enhanced material durability. In addition, surface hardness, residual stresses, and peening-induced deformation depth are measured. Furthermore, to gain a comprehensive understanding of the material response and the underlying mechanisms driving surface morphological alterations by UIP, a finite element method (FEM)-based model is developed. By investigating the effect of process parameters (peening amplitude, peening cycles, and pin size) on the surface deformation depth and stress/strain distribution, a correlation between these process variables with surface characteristics is established.

Coupled slow strain rate and acoustic emission tests for gaseous hydrogen embrittlement assessment of API X65 pipeline steel

Hydrogen embrittlement (HE) sensitivity of API X65 pipeline steel was evaluated in this study through the simultaneous application of slow strain rate tests (SSRT) and acoustic emission (AE) monitoring on hollow dog-bone samples. Exposure to hydrogen gas decreased the elongation to fracture percentage with a significant rise in embrittlement index for the higher pressure of 10 MPa. SEM images of the fracture surfaces demonstrated that the fracture mechanism changed from ductile to ductile–brittle under 1 MPa pressure, and to predominantly brittle with quasi-cleavage characteristic when testing under 10 MPa hydrogen gas. Classification of the AE events based on waveform analysis revealed a mainly shear mode fracture for 10 MPa nitrogen sample, while a dominant tensile mode fracture was identified for the hydrogen charged samples.

Unraveling short-term O2 contamination on under deposit corrosion of X65 pipeline steel in CO2 saturated solution

The impact of short-term O2 contamination on the deposit-covered pipeline steel under a CO2-saturated solution was investigated using steel coupon and wire beam electrode. Results show that the brief exposure to O2 destroyed the FeCO3 film, and converted it into porous iron oxides, weakening its protection property. However, upon CO2 reinjection, the dense FeCO3 film regrew soon underneath the damaged FeCO3 layer on the bare steel, restoring its protective properties. Conversely, the localized corrosion beneath the deposits persisted and worsened, fueled by macro-cell current between the bare steel and the deposit-covered steel.

Hydrogen blistering and cracking of high-strength pipeline steel welds produced by electrochemical hydrogen charging

Pipeline steel system always faces a challenge of hydrogen embrittlement (HE) not only due to corrosion environments but also because of cathodic protection strategy. Especially in welded joint, heterogeneous microstructures lead to the difference in intrinsic HE resistance for different subzones. However, this aspect was often neglected when external loading was applied during evaluation of the HE. To eliminate the effect of external loading, the hydrogen damage behaviors of X100 pipeline steel weld were investigated only based on electrochemical hydrogen charging and the intrinsic HE resistance of each subzone was explored. The results showed that the HE resistance of the main regions in weld was decreased in order of weld metal, heat affected zone (HAZ) and base metal (BM), with different surface damage modes: the BM had predominantly hydrogen blistering; while others displayed mainly hydrogen cracking. The corresponding features for cross-sectional cracking were intergranular propagation along the pancaked grain boundaries in the BM and trangranular propagation in HAZ. For transgranular cracking propagation, the path first trended to initiate on the {100} cleavage plane, then grew on the {110} slip planes. The intergranular cracking was mainly attributed to the lamellar-structural prior grain boundaries that inherited numerous deformation dislocations during hot rolling of the base metal.

The Effects of Post Weld Heat Treatment on Microstructure and Mechanical Properties of API X70 Linepipe using Submerged Arc Welding

API X70 steel requires high strength and toughness for safety in extreme environments like high pressure and low temperature. Submerged Arc Welding (SAW ) is effective for manufacturing thick steel pipes. However, the welding heat input during SAW alters the microstructure and mechanical properties of the heat affected zone (HAZ). Therefore, investigating the correlation between microstructure and mechanical properties in welded X70 pipes is important to address potential degradation of HAZ and weld metal (WM). In this study, post weld heat treatment (PWHT) was performed to improve mechanical properties of HAZ and WM and to reduce residual stress caused by the welding process. We performed PWHT at 640°C for 15 hours and followed by air cooling. After heat treatment, we observed the microstructure through OM and SEM analysis, and investigated the mechanical properties through tensile test, hardness test, and Charpy impact test.

Corrosion behavior and mechanism of FeCoNi high-entropy alloy compared with X100 pipeline steel in a simulated alkaline soil environment

In this work, the corrosion behavior of FeCoNi HEA and X100 pipeline steel in a simulated Golmud soil environment was systematically studied utilizing electrochemical tests, surface analysis techniques and immersion measurement. The results indicate that FeCoNi HEA possesses superior anti-corrosion property than X100 steel by comparing the charge transfer resistance (Rct), passive current density (ip) and corrosion morphology. The microstructure and surface film are the principal factors causing the difference in corrosion resistance of the two alloys. More intact, uniform and dense passive film enhances the anti-corrosion performance of the HEA, while the nonprotective, loose and defective corrosion product film covering the surface of X100 steel is not conducive to inhibiting the corrosion of the steel substrate. The appearance of inclusions within the HEA can generate the micro-galvanic corrosion effect with the matrix, which promotes the substrate as an anode to induce pitting. Furthermore, multiple phases of X100 steel exhibits higher electrochemical activity compared to the HEA with a single Face Center Cubic (FCC) phase, which accelerates the corrosion of the steel. Moreover, the matrix of the HEA primarily experiences selected dissolution of Ni element.

Effect of immersion time on the corrosion behaviour of X70 and X80 line pipe steels in simulated concrete pore solution

Effect of immersion time on the corrosion behaviour of X70 and X80 line pipe steels in simulated concrete pore solution

Inhibition of corrosion on API 5L X52 pipeline steel in acid media by Tradescantia spathacea.

The concentration effect of Tradescantia spathacea (T. spathacea) as corrosion inhibitor of API 5L X52 steel in 0.5M of H2SO4 was studied here through electrochemical and gravimetric techniques. To achieve it, samples of the material were prepared to be submitted to each of the tests. Results from electrochemical impedance spectroscopy (EIS) showed that there was an optimum concentration of the inhibitor in which is reached the maximum inhibition efficiency, displaying the best inhibition characteristics for this system with a maximum inhibition of 89% by using 400ppm. However, the efficiency decreased until 40% when the temperature was increased to 60°C. Potentiodynamic polarization curves (PDP) revealed that some of the present compounds of T. spathacea may affect anodic and cathodic process, so it can be classified as a mix-type corrosion inhibitor for API 5L X52 in sulfuric acid. Also, this compound followed an adsorption mechanism; this can be described through a Frumkin isotherm with an adsorption standard free energy difference (ΔG°) of -56.59kJmol-1. Metal surface was studied through scanning electron microscope, results revealed that by adding inhibitor, the metal surface is protected; also, they evidenced low damages compared with the surface with no inhibitor. Finally, Tradescantia spathacea inhibited the corrosion process with 82% efficiency.

Distribution of hydrogen atoms at a notch on X52 steel under various loads and displacements studied by scanning Kelvin probe and finite element modeling

Abstract In this work, the distribution of hydrogen (H) atoms at a notch on an X52 pipeline steel under various applied loads or displacements were investigated by Volta potential measurements using a scanning Kelvin probe (SKP) and finite element modeling. The stress concentration at the notch is elastic under the test condition. The H atom diffusion and distribution is driven by stress, rather than strain, in the steel. However, when displacements are applied on the steel specimen, the strain dominates the H atom distribution. As the local stress or strain increases, the H atom concentration increases, as indicated by negative shifts of the Volta potential. By establishing the quantitative relationships among Volta potential, von Mises stress, and H atom distribution, this work attempts to provide a novel method for H atom detection in steels through the Volta potential measurement.

Assessing fracture toughness of vintage and modern X65 pipeline steels under in situ electrochemical hydrogen charging using advanced testing methodology

The susceptibility of pipeline steels to hydrogen embrittlement, which can significantly impair mechanical performance, especially fracture toughness, is a critical issue in infrastructure integrity. This study evaluates the fracture toughness of modern and vintage API X65 steels under cathodic polarization (CP) conditions, employing methods such as rising displacement testing, stepwise rising constant load testing, and constant load testing. Tearing crack growth was detected at crack tip opening displacements (CTODs) of 0.032 to 0.055 mm while subsequent crack arrest under constant force loading was observed with CTOD thresholds of 0.148 mm and 0.255 mm for modern and vintage X65, respectively. Electron channelling contrast imaging demonstrated that arrested cracks in both steels exhibited reduced plasticity and a higher propensity for crack branching compared to propagating cracks. These findings highlight the need for tailored strategies to mitigate the effects of hydrogen embrittlement in pipeline materials and underscore the differences in damage tolerance between steel generations.

Effect of post-weld heat treatment on corrosion resistance of X90 pipeline steel joints

Abstract In order to improve the corrosion resistance of welded joints, X90 pipeline steel joints were subjected to post-weld heat treatment at 610 °C, 640 °C, and 670 °C (holding time was 1 h). Through electrochemical corrosion and full immersion corrosion experiments, the corrosion resistance of welded joints under various conditions was tested, and the surface morphology and corrosion products of the corroded samples were analyzed by scanning electron microscopy and X-ray diffraction analysis. The experimental results show that the corrosion products of X90 pipeline steel welded joints in simulated soil solution mainly include Fe(OH)3, γ-FeOOH, α-Fe2O3, γ-Fe2O3, and a small amount of Fe3O4, FeCl3 and Fe. After heat treatment at 610 °C, the corrosion current density of the parent metal, heat-affected zone, and weld metal of the joint changes from 1.081, 2.889, 2.079 (×10−5 A cm−2) to 0.977, 2.211, 1.810 (×10−5 A cm−2), respectively, the corrosion resistance is improved.

Evaluation of Tribological Behavior of X65, X70, and X80 Pipeline Steels in the Presence of Hydrogen

Evaluation of Tribological Behavior of X65, X70, and X80 Pipeline Steels in the Presence of Hydrogen

Performance of two high-strength steels under electrochemical corrosive and stressed conditions

The corrosion behaviors of stressed API X-80 and API X-120 pipeline steels were investigated using electrochemical and slow strain rate tensile tests after being immersed in a saline solution containing 3.5% NaCl. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive x-ray spectroscopy (EDX) were used to create images of the flawed steel samples. Corrosion rates for API X-120 pipeline steel were found to be much lower than those of API X-80 pipeline steel in both stressed and saline environments. While different oxide layers were observed on the two steels, the result showed the oxide film was of iron carbonate. It was observed that the API X-120 steel surface was latently smooth in a saline solution environment which reduced the corrosion rate. As a result, the API X-120 pipeline steel was protected and had a delayed time-to-failure in comparison to the API X-80 pipeline steel when it was tested in steel under stress and in solution medium. This failure mechanism will not only be significant to the petroleum sector, but also to the industry that produces pipelines in terms of the choice of fitting material for pipe design. Specifically, this mechanism will have an impact on the design of fittings for pipes.

A Unified Fracture Model for X65 Pipeline Material Under Various Constraints Using the Extended Finite Element Method (XFEM)

Abstract It is generally accepted that the fracture strain is dependent on geometry/constraints in metals. However, the current available implementation of XFEM assumes a fixed fracture strain criterion independent of the constraints. The objective of this paper is to develop and implement a variable fracture strain criterion in XFEM that is capable of predicting a wide range of fracture conditions in X65 pipeline steels with various crack tip constraints. Various small-scale tests with different out of plane constraints obtained from the literature were simulated using the XFEM in ABAQUS software. For each test, the value of the maximum principal strain (Maxpe) as a fracture initiation criterion in the cohesive zone model (CZM) in XFEM framework was varied while keeping the fracture energy constant until the model was able to accurately replicate the reported experimental results. For each test, the crack tip constraints were characterized and the stress triaxialities and Lode angle parameters at the onset of fracture initiation were calculated from the models. The results allowed expressing the fracture strain as an explicit function of stress triaxiality which was then implemented in ABAQUS XFEM using UDMGINI subroutine. For the sake of comparison, the tests were simulated in finite element method (FEM) using a similar damage initiation model namely, the Johnson-Cook (J-C) model. A single model in XFEM was able to accurately replicate the experimental observations for all specimens and compared well to experiments in the way simulated by FEM damage model.

The inhibition effect of 1, 3-diazole glyoxaline on corrosion of API 5L X52 pipeline steel in oilfield produced water under sweet corrosive conditions

Corrosion induced by aqueous environments containing carbon dioxide (CO2) is a well-documented issue in the oil and gas industries, particularly affecting transportation via steel pipelines. Operational conditions during transportation, including temperature, flow rate, and solution chemistry, significantly influence the corrosion inhibition mechanism. In this study, the corrosion inhibition behavior of API 5L X52 steel in a 3.5 wt% NaCl brine solution saturated with carbon dioxide was investigated using 1, 3-diazole glyoxaline (DG) as an organic inhibitor. Both gravimetric and electrochemical methods were employed to assess corrosion rates and inhibitor efficiency across various temperatures, inhibitor concentrations, and rotational speeds. The outcomes showed that inhibition efficiency increased with inhibitor concentration and temperature. From weight loss measurements, the maximum inhibition efficiency was 98.58 % at 3 × 10−4 M of DG and 60 °C. The polarization investigations showed a reduction in the anodic and cathodic curves in the presence of the inhibitor. This suggested a mixed-type inhibition mechanism. The electrochemical impedance spectroscopy results showed an improvement in charge transfer resistance due to the formation of a protective layer on the metal surface. In addition, AFM, SEM, contact angle, hardness, and roughness measurements proved the enhancement in surface morphology due to the presence of DG.

Effect of Electrochemical Hydrogen Charging on Hydrogen Embrittlement and Mechanical Properties of Quenched Tempered X100 Pipeline Steel

Effect of Electrochemical Hydrogen Charging on Hydrogen Embrittlement and Mechanical Properties of Quenched Tempered X100 Pipeline Steel

Effect of Cathodic Polarization on SCC Behavior of a X52 Pipeline Steel in Service for 20 Years

Effect of Cathodic Polarization on SCC Behavior of a X52 Pipeline Steel in Service for 20 Years