X80 Pipeline Steel Research Articles

Postweld Heat Treatment on Toughness of Electric- Resistance Welded X70 Steel

The effect of postweld heat treatment (PWHT) on Charpy V-notch impact toughness of a highfrequency electric-resistance welded (HF-ERW) grade X70 pipeline steel is investigated. PWHT thermal cycles are simulated using the Gleeble on the as-welded specimens. Microstructure, along with crystallographic texture and microhardness, is characterized in specimens that are impact tested at –5°C (23°F), –30°C (–22°F), and –45°C (–49°F). The impact toughness values show a wide scatter band and decrease with the increasing peak temperature of the PWHT. For higher peak temperatures, the microstructure of the heat-affected zone (HAZ) gradually changed from equiaxed ferrite to bainitic ferrite. Furthermore, the prior austenite grain size (PAGS) increases with the increasing peak temperature. The density of high-angle grain boundaries decreases, and the fraction of cleavage planes {100} parallel to the impact fracture plane increases for higher peak temperatures of the PWHT.

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.

Study of temperature effect on hydrogen embrittlement in X70 pipeline steel

The study investigates the temperature effect on hydrogen embrittlement (HE) in X70 steel using Devanathan-Stachurski and tensile tests under varying cathodic hydrogen-charging currents. The most severe HE temperature threshold is identified via scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) methods. The temperature thresholds for 10 mA/cm2 and 20 mA/cm2 are 293 K and 283 K, respectively, while no critical temperature at 30 mA/cm2. The underlying mechanism is studied, and a predictive model is established. Also, the primary hydrogen-induced fracture plane is identified as {110}, beneath where hydrogen enhances plastic deformation in {110}<111> and inhibits in {112}<111>.

In-situ pH monitoring of pre-notched X80 pipeline steel using an all-solid-state Pt/RuOx ultra-micro pH sensor

In the notch microenvironment caused by the stress corrosion of pipeline steel, the local pH value changes mediated by anodic-cathodic corrosion reactions played an important role in comprehending the local corrosion behavior. To address this issue, a radius 5 µm all-solid-state Pt/RuOx ultra-micro pH sensor was developed using cyclic voltammetry deposition method, which was combined with scanning electrochemical microscopy (SECM) to achieve in-situ monitoring the local pH distribution and evolution of the pre-notched X80 pipeline steel. The micro-sensor demonstrates a near Nernstian slope of −60.0 ± 3 mV/pH within the pH value range of 2.00–12.00, accompanied by an exceptionally rapid response time of 200 ms. Moreover, it exhibits high accuracy, strong long-term monitoring ability and remarkable resistance to the interference of common ions in seawater and ferrous ions generated by the corrosion of pipeline steel. Through monitoring the local pH distribution in simulated seawater solution at the notch of X80 pipeline steel, it was found that obvious pH alkalization occurs first on both the surface and inside of the notch, followed by gradual acidification, and this phenomenon is more obvious at the front of the notch. Combined with other characterization methods, a possible corrosion reaction mechanism at the notch of stress corrosion was proposed.

Effect of nutrient concentration on corrosion mechanism of X80 pipeline steel caused by sulfate-reducing bacteria

In this work, the effects of different nutrient contents in simulated soil solution containing sulfate-reducing bacteria (SRB) on the corrosion of X80 pipeline steel were studied. The highest amount of sessile SRB was found in the initial medium concentration of 1/3, followed by the concentration of 10%, and the lowest in the simulated soil solution without culture medium. However, the biofilm formed in the simulated soil solution without culture medium had the strongest adhesion and corrosiveness, with X80 steel having the highest corrosion rate, which was approximately 7.2 times of the initial medium concentration of 1/3. The research results have a positive role in promoting the development of SRB corrosion prevention technology for buried pipeline.

The Influence of Centerline Segregation on Impact Toughness in Welding Heat-Affected Zone of X70 Pipeline Steel

The influence of centerline segregation on the low-temperature impact toughness of the heat-affected zone (HAZ) of welded joints was studied by welding experiments on X70 steel plates rolled from continuous casting slabs with segregation grades of class 2 and class 3. The experimental results show that the impact toughness at HAZ from class 2 slab steel plate is more stable and has excellent low-temperature toughness than that of class 3 slab steel plate. The impact toughness of the HAZ of the class 3 slab steel plate is low to 100 J at −40 °C and has a severe fluctuation range (~150 J), and the delamination phenomenon is also observed in the fracture cross-section. The reason for this phenomenon is due to the enrichment of C and Mn elements in the centerline segregation zone. The formation of abnormal microstructure (martensite/bainite) in the segregation zone leads to stress concentration, which easily weakens the low-temperature toughness of the joint.

Influence of Xinjiang Saline Soil on Corrosion of X80 Pipeline Steel

A large-scale gas transmission pipeline project will pass through typical saline soil areas in Xinjiang, China, to find out the influence of the saline soil on the long-distance pipeline in this area, this paper investigates the corrosive behavior of X80 pipeline steel embedded in saline soil with multiple corrosion intensities. Firstly, NaCl, Na2SO4, NaHCO3, and deionized water were used to simulate the saline soil with different corrosion intensities, and then the corrosion test of X80 steel was carried out. A scanning electron microscope was used to observe the X80 steel before and after corrosion. Finally, the weight loss method was used to calculate the corrosion rate, and the corrosive behavior of X80 pipeline steel in Xinjiang saline soil environment was analyzed. The results show that: (1) X80 steel is susceptible to pitting corrosion in the saline soil environment; (2) the rate and level of corrosion were mainly related to the content of Cl− and SO4 2−. The greater the content, the stronger the pipeline is corroded; (3) the rate and level of corrosion were positively correlated with the corrosion intensities of saline soils.

To Investigate the Effect of Heat Treatment on API X70 Pipeline Steel

To Investigate the Effect of Heat Treatment on API X70 Pipeline Steel

Experimental investigation and phenomenological modeling of fatigue crack growth in X80 pipeline steel under random loading

Ocean structures are subjected to random environmental loads during their service life. Under the action of random loads, fatigue crack growth within pipeline steel exhibits transient behaviors such as retardation or acceleration. This poses significant challenges in predicting the fatigue life of ocean structures under random loadings. To establish a predictive model for fatigue crack growth in X80 pipeline steel under random loadings, this study first conducts fatigue crack growth experiments under constant amplitude and random loading conditions. Then, based on deep learning methods and the fracture yield zone theory, a phenomenological model is developed to predict fatigue crack growth in X80 pipeline steel under random loading conditions. The results show that under random loading conditions, the fatigue crack growth curve of X80 pipeline steel maintains a relatively clear logarithmic-linear feature during the stable crack growth stage. However, due to the continuous variation of stress ratio with loading sequence, the fatigue crack growth curve exhibits strong fluctuation characteristics; The phenomenological model established in this study for predicting fatigue crack growth under random loading conditions can relatively accurately reflect the overall trend of fatigue crack growth under random loadings, with a maximum prediction error of less than 10%.

Effect of yeast extract on microbiologically influenced corrosion of X70 pipeline steel by Desulfovibrio bizertensis SY-1

Microbiologically influenced corrosion (MIC) is a complicated process that happens ubiquitously and quietly in many fields. As a useful nutritional ingredient in microbial culture media, yeast extract (YE) is a routinely added in the MIC field. However, how the YE participated in MIC is not fully clarified. In the present work, the effect of YE on the growth of sulfate reducing prokaryotes (SRP) Desulfovibrio bizertensis SY-1 and corrosion behavior of X70 pipeline steel were studied. It was found that the weight loss of steel coupons in sterile media was doubled when YE was removed from culture media. However, in the SRP assays without YE the number of planktonic cells decreased, but the attachment of bacteria on steel surfaces was enhanced significantly. Besides, the corrosion rate of steel in SRP assays increased fourfold after removing YE from culture media. MIC was not determined for assays with planktonic SRP but only for biofilm assays. The results confirm the effect of YE on D. bizertensis SY-1 growth and also the inhibitory role of YE on MIC.

Mitigation of Desulfovibrio ferrophilus IS5 degradation of X80 carbon steel mechanical properties using a green biocide.

Most microbiologically influenced corrosion (MIC) studies focus on the threat of pinhole leaks caused by MIC pitting. However, microbes can also lead to structural failures. Tetrakis hydroxymethyl phosphonium sulfate (THPS) biocide mitigated the microbial degradation of mechanical properties of X80 steel pipeline by Desulfovibrio ferrophilus (IS5 strain), a very corrosive sulfate reducing bacterium. It was found that 100 ppm (w/w) THPS added to the enriched artificial seawater (EASW) culture medium before incubation resulted in 2.8-log reduction in sessile cell count after a 7-d incubation at 28 °C under anaerobic conditions, leading to 94% uniform corrosion rate reduction (from 1.3to 0.07mm/a), and 84% pitting corrosion rate reduction (from 0.70to 0.11mm/a). The X80 dogbone coupon incubated with 100 ppm THPS for 7 d suffered 3% loss in ultimate tensile strain and 0% loss in ultimate tensile strength compared with the abiotic control in EASW. In comparison, the no-treatment X80 dogbone coupon suffered losses of 13% in ultimate tensile strain and 6% in ultimate tensile stress, demonstrating very good THPS efficacy.

Electrochemical corrosion behavior of X80 pipeline steel welded joints fabricated by ultrasound-assisted submerged arc welding in CO2-saturated solution

In this study we investigated the electrochemical corrosion behaviors of X80 pipeline steel welded joints fabricated by ultrasound-assisted submerged arc welded (UASAW) joints in CO2-saturated solution. The microstructures of the UASAW joints were analyzed by using metallographic microscopy. Corrosion behavior of UASAW joints was investigated using immersion test, electrochemical polarization, and electrochemical impedance spectroscopy (EIS). The corrosion morphologies and products were characterized by scanning electron microscopy (SEM), energy dispersive spectroscope (EDS) and X-ray diffraction. Metallographic and the corrosion mechanism of UASAW was systematically studied. The investigation results showed that the microstructure of the UASAW weld zone is mainly composed of acicular ferrite and a little granular bainite. The minimum microhardness is obtained in fusion zone (FZ) because of many alloying elements dominated in the final precipitate distribution. Pitting corrosion resistance of the strong vibration region in FZ is attributed to the decline in active sites of the bainite, the UASAW had beneficial effect on the improvement of pitting corrosion resistance of X80 pipeline steel weldment.

Crack-Tip Opening Displacement of Girth Welds in a Lean X70 Pipeline Steel.

Crack-tip opening displacement (CTOD) tests were conducted on girth welds of two API 5L X70 pipeline steels (pipe A and pipe B) to investigate the influence of base metal composition on the fracture toughness of the joint. CTOD measurements across the weld showed that the weld fusion zone had the lowest CTOD values for both pipes, with pipe B having a higher CTOD value than pipe A. Detailed microstructure characterization of the multi-pass weld showed that the fusion zone in both pipes consisted of three distinct zones: the columnar zone, the coarse equiaxed zone, and the fine equiaxed zone. Both the columnar zone and coarse-grained equiaxed zone had acicular ferrite and grain boundary ferrite microstructures, whereas the fine-grained equiaxed zone had a finer ferrite microstructure compared to the other two zones. The main difference between the two pipes was the variation in ferrite grain sizes and the volume fractions of grain boundary ferrite and acicular ferrite. In comparison to pipe B, pipe A, with a higher concentration of Mo, Ni, and Cu in both the base metal and the weld fusion zones, consisted of a higher volume fraction of grain boundary ferrite and a lower volume fraction of acicular ferrite in the columnar and coarse-grained equiaxed zones. The lower concentration of Mo, Ni, and Cu in pipe B likely resulted in the formation of a predominantly acicular ferrite microstructure in the fusion zone, thereby improving the toughness of the weld joint in comparison to pipe A.

Effect of B. subtilis in simulated acid red soil on the corrosion behavior of X80 pipeline steel

The eastern section of China's West-east gas transmission project is laid in acidic red soil. NRB are widespread in soils and play an important role in metal corrosion. In this article, the corrosion failure behavior and mechanism of X80 pipeline steel under the action of NRB in simulated acidic soil were studied. It was found that the biofilm of B. subtilis had significant inhibitory on the overall corrosion of X80 steel. Electrochemical results prove that the corrosion rate of the sterile group after 14 days of immersion was about 4.5 times that of the bacterial group. However, the biofilm promotes the formation of local corrosion pits. Confocal laser scanning microscopy images indicate that that the corrosion pit depth of the bacterial group (46.1 μm) was three times that of the bacterial-free group (15.7 μm) after 14 days. The pH of the acidic environment was slightly improved by B. subtilis. XPS results proved that B. subtilis complicates the corrosion products of X80 steel through its nitrate reduction ability and metabolism.

Quantitative research on stress failure risk assessment for girth welds with unequal wall thickness of the X80 pipeline under lateral load

The cumulative length of the X80 steel pipeline extends to 17,000 km, with a predominant portion traversing mountainous terrains characterized by intricate geological formations. Recurrent geological hazards significantly impede the safe operation of oil and gas pipelines. Landslides can induce substantial axial forces on steel pipelines, significantly increasing the risk of pipeline failure. Moreover, as a result of sudden changes in mechanical structure, the pipeline's unequal wall thickness leads to local stress concentration, making it more vulnerable to external loads than the steel pipeline itself. Therefore, to analyze the mechanical response of steel pipelines under different working conditions, we establish a smooth particle hydrodynamics, finite element transverse landslide pipeline model for girth welds with unequal wall thickness and investigate a tearing accident caused by a lateral landslide in a section of the large-diameter natural gas pipeline. The landslide volume is found to be the main controlling factor for the failure of pipeline circumferential welds. According to the genetic algorithm backpropagation neural network, the von Mises stress of the most dangerous section of the pipeline is calculated based on pipeline and landslide parameters, and the error is 11.67 %. According to the API RP 581–2016 Risk-Based Inspection Methodology, a failure risk assessment matrix is established using the pipeline statute as an evaluation indicator to evaluate the landslide risk to pipelines in different regions. A variable-wall-thickness girth weld on the ZG pipeline was selected for application. This method has good applicability for evaluating the failure risk of circumferential welds with wall thicknesses of 12.8/15.3 mm under the action of small landslides.

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 Nb Content on the Microstructure and Impact Toughness of High-Strength Pipeline Steel

In this study, X80 pipeline steel is prepared with different Nb contents through the thermo-mechanically controlled rolling process. The effects of using two different Nb contents on the impact toughness and microstructure of the pipeline steel are examined using various experimental techniques. The results show that with the increase in Nb content, the transformation temperature Ar3 decreases, and the nucleation and growth of bainitic ferrite with lath features (LB) are promoted, while those of granular bainite (GB) are inhibited. In addition, the stability of the austenite phase increases with the increase in Nb content. Therefore, the volume fractions of LB and martensite–austenite (M/A) constituents increase, while the proportion of high-angle grain boundaries (HAGBs) decreases. The impact energy of pipeline steel at −45 °C is closely related to the Nb content. Specifically, the impact energy decreases from 217 J at 0.05 wt.% Nb to 88 J at 0.08 wt.% Nb. The cracks are preferentially formed near the M/A constituents, and the HAGBs significantly inhibit the crack propagation. The steel with 0.05 wt.% Nb has a lower content of M/A constituents and a higher proportion of HAGBs than the one with 0.08 wt.% Nb. In addition, as the Nb content increases, the crack initiation energy and the crack propagation energy decrease. Thus, the 0.05 wt.% Nb steel has a higher low-temperature impact energy.

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

Experimental study of decompression wave characteristics and steel pipe applicability of supercritical CO2 pipeline

High-strength pipeline steel is the optimal choice for continuously transporting large amounts of carbon dioxide (CO2) in the future Carbon capture, utilization and storage (CCUS) industrial chain, and supercritical CO2 (S–CO2) is the ideal phase state from an emitter to an onshore storage site. In CCUS projects, it is very indispensable to carry out the suitability of high steel-grade pipelines to ensure the safe operation of pipelines. It is considered a catastrophic incident for creatures and equipment once pipeline failure when fractures or propagation occurs. In this paper, the fracture propagation velocity of X70, X80, and X90 pipeline materials is calculated base on the high strength line pipe (HLP). Meanwhile, three sets of full-bore fracture (FBR) experiments of S–CO2 pipelines were conducted with similar initial status on an industrial-scale setup, and the decompression wave velocity was obtained with the data acquisition system. The result shows that the initial decompression wave velocity of S–CO2 is about 270 m/s, and the pressure plateau is between 6.8 and 7.3 MPa, corresponding to the decompression wave velocity, which is about in the range of 100–220 m/s. After that, the decompression wave velocity prediction model was established based on the homogeneous equilibrium method (HEM) and the equation of state (Eos), and the prediction results are more conservative than the experimental results. To ensure that the pipeline will not ductilely fracture in the event of a leakage or rupture, X70, X80 and X90 grade steel pipeline design wall thickness and minimum arrest toughness values are determined based on the two-curve method (TCM), respectively. Furthermore, a CO2 pipeline design model is developed based on the experimental data and decompression wave calculation method. The significant experimental data could be used for safety assessment and theoretical model validation in the CO2 transport pipeline and is useful in developing better fracture control models.