X80 Steel Research Articles

FGM concept used in damage analysis of heat-treated elbows under out-of-plane combined bending moment

The elbow is presented in pressurized tubular structures as a connecting element, generally subjected to bending moments either out-of-plane or in-plane, in closure or opening. Another mode of bending moment that can also occur in these tubular structures is the combined bending moment between out-of-plane and in-plane in closure, or out-of-plane and in-plane in opening. In this work, to better present the potential severity caused by this loading mode, an elbow structure attached by straight tubular sections made of X60 steel is analyzed and its damage under this combined bending moment with orientations between the plane and out-of-plane of the structure is discussed. A reinforcement proposal will be made in the second part of this work. Indeed, the structure is pretreated thermally at the elbow, resulting in a graded structure along the thickness with two different material constituents: the base metal and the thermally affected zone (HAZ). Based on the concept of Functionally Graded Materials (FGM), the gradation is by volume fraction between the base metal and the HAZ, following a power law function of a volume fraction index (n). This graded property is introduced along the thickness by finite element layers. The elastic-plastic behavior of the HAZ-base metal mixture is modeled using the Voce model and the Von Mises equivalent stress flow theory. Using the XFEM technique(extended finite element method), the damage of the pressurized and thermally treated structure under a combined out-of-plane bending moment shows that these parameters condition the response and the level of damage.

Probing the efficiency and mechanism of hydrogen permeation inhibition in pipeline steel by organic inhibitors

A hydrogen economy will require the use of steel pipelines to transport and store hydrogen. Methods and materials are urgently needed to prevent the embrittlement of steel pipelines in hydrogen service. In this work, we show that hydrogen permeation into pipeline steel can be mitigated by organic inhibitors, as demonstrated by a typical organic inhibitor benzotriazole (BTA) under simulated X65 steel pipeline cathodic protection conditions. Electrochemical and surface analytical techniques were used to probe the efficiency and mechanism of hydrogen permeation inhibition. In particular, a novel multi-electrode array method was designed to probe the inhibitor film by measuring local impedance and hydrogen charging currents. The ability and efficiency of BTA to inhibit hydrogen permeation were found to be closely associated with the formation and coverage of inhibitor films on steel surfaces. A model is proposed to illustrate the mechanism of hydrogen permeation inhibition by organic inhibitors.

Realizing the outstanding strength-toughness combination of API X65 steel by constructing lamellar grain structure

The development of pipeline steels with exceptional cryogenic toughness is deemed imperative for their applications in various engineering fields. In this work, API X65 steel with lamellar grain (LG) structure is constructed through warm deformation techniques. Comparative analysis with raw API X65 steel revealed notable enhancements in both yield strength (YS) and ultimate strength (UTS), exhibiting increments of 315 MPa and 164 MPa, respectively, while retaining substantial fracture toughness (KIc = 251.14 MPa m0.5). Remarkably, the LG steel exhibits a distinct absence of a ductile-brittle transition behavior over a wide temperature range, maintaining an exceptionally high impact energy from room temperature (RT) to liquid nitrogen temperature (LNT), and the Charpy impact energy exceeding 330 J at LNT, nearly 16 times higher than the raw API X65 steel. This performance can be primarily attributed to the superior plastic deformation capability, coupled with the delamination toughening mechanism. The resultant tortuous path of crack propagation effectively facilitates the absorption of substantial energy, decreases notch tip sensitivity depending on the temperature, stress triaxiality, and strain rate, thereby fostering excellent cryogenic toughness.

Shielding against erosion: Exploring the effectiveness of pre-erosion surface corrosion inhibitors

This study investigates the corrosion inhibition effect and adsorption process of two imidazoline corrosion inhibitors, HEIE and TDEI, on pre-eroded X65 steel surfaces. Analysis of weight loss and electrochemical measurements suggests that the irregular structure of pre-eroded surfaces may impede the uniform adsorption of corrosion inhibitors, resulting in reduced effectiveness pre-erosion. Particularly, at a 30° angle of pre-erosion, corrosion inhibition efficacy is observed to be at its lowest. The corrosion inhibition rates of HEIE and TDEI on X65 steel surfaces are found to be 11.9 % lower under pre-eroded conditions at a 30° angle compared to non-eroded surfaces at the same angle. Molecular dynamics (MD) simulations support these findings, indicating that TDEI exhibits lower energy bandgap values and more negative adsorption energies (Eads) compared to HEIE, aligning with experimental results. Moreover, TDEI demonstrates a smaller diffusion coefficient for corrosive agents than HEIE, suggesting stronger adsorption efficiency and a more pronounced protective effect. Study of the corrosion inhibition effect on pre-eroded surfaces provides new ideas and methods for improving protective measures.

Study on the mechanical properties of X80 pipeline steel under pre-charged high-pressure gaseous hydrogen

Hydrogen embrittlement (HE) is a significant challenge to the safe operation of hydrogen-blended natural gas pipelines. The mechanical properties of X80 steel were studied after H2 pre-charging followed by mechanical properties tests and fracture morphologies observation. Results indicated that the hydrogen saturation time of X80 steel was roughly 48 h. H2 pre-charging induced a decline in strength, plasticity, and fatigue properties, while hydrogen-assisted fatigue crack growth occurred during the early stage of fatigue crack growth rate tests. Additionally, the fracture morphologies transited from primary microvoid coalescence to a mixed mode characterized by ductile dimples and quasi-cleavage planes with increasing hydrogen. The HE susceptibility increased with increasing hydrogen partial pressure and decreasing loading frequency, but there existed a critical value (6 × 10−7 s−1) for the strain rate effect on the HE susceptibility. Under H2 pre-charging conditions, the predominant HE mechanism was the hydrogen-enhanced local plasticity (HELP) mediated hydrogen-enhanced decohesion (HEDE) mechanism.

Finite element analyses of buckling behavior in x60 steel pipelines under axial compression load

Finite element analyses of buckling behavior in x60 steel pipelines under axial compression load

Experimental and molecular dynamics study of the hydrogen embrittlement behavior of X52 steel: Analysis of abnormal hydrogen embrittlement susceptibility

The hydrogen embrittlement (HE) susceptibility of the X52 pipeline steels in simulated hydrogen-blended natural gas (HBNG) environments were investigated with a combination of in situ high-pressure gaseous hydrogen permeation tests, slow strain rate tensile (SSRT) tests and molecular dynamics simulation, the results were compared with the X80 steel. The HE susceptibility of the X52 steel was found higher than that of the X80 steel. The mechanism of the two steels showing different HE susceptibility was analyzed from a point of permeation parameters and molecular dynamics simulation. The results showed that the X52 steel contained more impurity elements and a larger grain size, leading to a higher hydrogen solubility and a microstructure with lower HE resistance. This study suggests that the steel microstructure and the hydrogen permeation property are crucial for the understanding and prediction of the HE susceptibility of the steels.

Study on the dynamic evolution of friction and wear of polyurethane material for pipeline inspection gauge

The dynamic evolution in friction and wear can lead to interface failure and induce vibrations in pipeline inspection gauge. The friction behavior between polyurethane and X70 steel was evaluated with annular face contact under 0.042 to 0.07 MPa. The temperature increase was recorded using infrared cameras. Dynamic simulations of frictional heat and stress-strain were conducted using Abaqus software. The results indicate that in the initial stages, abrasive wear, stress (1.5 MPa), and frictional temperature rise (65 °C) of PU were observed in the inner-ring region at 0.056 MPa. The surface roughness (3.394 μm) of the PU became comparable to that of the steel ring (3.768 μm) due to abrasive wear. In the later stages, a higher frictional temperature (80 °C) and increased stress (3.8 MPa) were observed in the outer ring. Concurrently, Schallamach waves and ridge-like stripes indicative of stick-slip behavior emerged in the outer ring. The viscoelastic hysteresis effect is the fundamental cause of the dynamic evolution of the friction coefficient and wear. Frictional heat exacerbates the evolution of stick-slip behavior and increases fluctuations in the friction coefficient. The findings of this research can be utilized to analyze the causes of interface failure and vibration in pipeline inspection gauge.

Microstructural, mechanical and nondestructive characterization of X60 grade steel pipes welded by different processes

Abstract In this paper, the welding quality of API 5L X60 steel pipes was investigated after the application of three different welding scenarios by applying submerged arc welding (SMAW), tungsten inert gas (TIG) and hybrid (TIG + SMAW) welding methods with an average heat input of ca. 1 kJ mm−1 for all passes. For this purpose, the ultrasonic and radiographic tests were done to detect possible discontinuities such as crack and porosity in the welding zones. In addition, the macro and microstructures of weld zones were made to examine different zones in terms of weld quality and phases. Moreover, the hardness, impact toughness and tensile tests were carried out to determine the mechanical properties of the weldments. The tensile strength of the pipe weldments was recorded to be ∼603, 610 and 625 MPa after the welding of pipes by SMAW, TIG + SMAW and TIG welding, respectively. In addition, the impact toughness of the welds was obtained to be 48, 76 and 66 J, for these welding methods, successively. According to the experimental findings, all three welding plans were successfully applied to the steel pipes and found to be suitable regarding the relevant international standards.

Effect of formic acid on aqueous corrosion mechanisms of mild steel

The effect of formic acid (HCOOH or shortly HFr) on corrosion mechanisms of X65 steel was systematically investigated in pH controlled, N2-sparged and CO2-sparged solutions using potentiodynamic polarization and linear polarization resistance (LPR) techniques. The results from the electrochemical experiments conducted in 1 wt.% NaCl solutions at 1 bar (total pressure) confirm that HFr is not significantly electroactive and therefore is not directly reduced on the steel surface under the conditions studied here. Experiments at various HFr concentration, temperature, pH, and flow rate also confirm that the main role of HFr on the corrosion of X65 steel is through the “buffering effect” mechanism. According to this mechanism, weak acids such as HFr increase the cathodic limiting current by providing hydrogen ions (H+) through their chemical dissociation similarly as is seen with acetic acid (CH3COOH or HAc).A comparison between HFr and HAc shows that these two organic acids have some differences in their behavior. First, HAc seems to retard the anodic reaction and decrease the corrosion rate, especially at lower temperatures and higher concentrations, while HFr does not. Second, the influence of these two acids on increasing the limiting current density seems to be similar at 30 °C, but at higher temperatures (50 °C, 80 °C), the cathodic limiting current density in the presence of HAc is greater than that with HFr at the same molar concentration. Under similar experimental conditions, HAc was observed to be less corrosive at lower temperature (30 °C), and more corrosive at higher temperatures (50 °C and 80 °C) compared to HFr at the same molar concentration.Experimental data collected in this study were used to validate a newly developed mechanistic model. According to our investigations this model shows an accurate fit to the experimental data at different HFr concentrations and pH at 30 °C. However, the model deviates from the experimental limiting current density value at higher temperatures (50 °C and 80 °C). It is speculated that this deviation results from a potential inaccuracy in the available temperature function for equilibrium constant of HFr dissociation reaction, which requires further investigations.

Damage analysis in welded steel pipe elbow under strong cyclic loading

According to cyclic loading modes, highly pressurized tubular elements, such as those in elbows, differ from other straight tubular structures in their modes of stress and damage. This work aims to perform a numerical prediction of a tubular structure. It consists of an X52 steel elbow welded to X65 grade ends by straight tubular sections. This pressurized structure is subjected to strong cyclic loading in bending moment applied until damage occurs. The bending moment is combined with different orientations between the closing or opening moment and the out-of-plane moment, presenting a possible but rarely analyzed situation. This cyclic loading mode is taken as an evaluative parameter in its various amplitudes, orientations, and patterns. The cyclic hardening of the elbow and straight tubular sections, including those of the welded joints, are all formulated by the combined isotropic and kinematic model introduced in the ABAQUS calculation code with parameters calibrated according to the Voce model and experimental results, using plasticity by the Von Mises equivalent stress flow theory. The appropriate XFEM (Extended Finite Element Method) technique is used in conjunction with the hardening model to overcome numerical calculation difficulties and predict damage in traction laws, separation by crack initiation and propagation. The results, in the form of hysteresis curves in cyclic bending moment and angular displacement, have shown a strong dependency that conditions the structure’s response as well as the level of its damage.

Preliminary Evaluation of the Influence of Hydrogen on the Fracture Toughness of an X65 Gas‐Transmission Pipeline Steel

Previous research has indicated that hydrogen decreases the fracture toughness of gas‐transmission pipeline steels. This study produced two values of fracture toughness for the X65 steel in the Dampier Bunbury natural gas‐transmission pipeline in air (JQ of 590 and 778 kJ m−2; equivalent to KQ of 369 and 487 MPa) and two essentially American Society for Testing of Materials–valid values of fracture toughness of KJ1C of 150 and 189 MPa for X65 subjected to in situ hydrogen charging thought to be equivalent to a hydrogen gas pressure of 200 bar. The fracture toughness for hydrogen‐charged specimens was lower than in air. The large spread of the fracture toughness in air was attributable to the fact that these JQ values were dependent on testing details. The spread of fracture toughness values in hydrogen was attributed to the variability of fracture toughness in hydrogen under these hydrogen‐charging conditions. There was considerable stable crack growth. The energy for stable crack growth increased with crack length. The fractography in the presence of hydrogen showed significant ductility, consistent with hydrogen‐assisted plastic fracture. The values of fracture toughness in air and with hydrogen were consistent with literature values.

Effect and mechanism of ionic liquid-polymer composite coating on enhancing hydrogen embrittlement resistance of X80 pipeline steel for hydrogen blended natural gas transportation

Blending hydrogen into existing natural gas pipelines is a cost-effective method for large-scale hydrogen transportation. However, high hydrogen ratios cause hydrogen embrittlement in pipeline steel, limiting transportation efficiency. Due to complex structures and harsh application conditions, existing coatings are difficult to apply on pipelines. To tackle such issues, we propose an ionic liquid-polymer composite coating using epoxy resin as coating substrate, based on the competitive adsorption of methane and hydrogen on pipeline steel. Ionic liquids with high methane selectivity were selected via quantum chemical calculation. The protective effect of coatings was characterized using hydrogen pre-charging constant strain tensile tests. Simulation and experimental results demonstrate that epoxy resin coatings reduce hydrogen embrittlement in X80 steel. Modified with selective CH4/H2 permeability ionic liquids, the epoxy resin coating enhances methane and hydrogen competitive adsorption on the steel surface, improving hydrogen embrittlement resistance. This novel coating offers a viable solution for achieving safe and high ratio hydrogen blended transportation in natural gas pipeline.

Effect of alternating current density on corrosion behaviour of X65 steel in weakly alkaline soil environment without cathodic protection

The corrosion behaviour of X65 steel in Shijiazhuang soil-simulated solution was investigated under different alternating current (AC) interference. Results show X65 pipeline steel presented weak passivation characteristics in this weakly alkaline solution, in which case AC interference could activate the anodic dissolution reaction and greatly accelerate uniform corrosion and pitting corrosion. AC interference could easily induce corrosion pits initiation and propagation in this weakly alkaline solution because of unstable passive film on steel surface and low pitting potential. Both the average corrosion rate and corrosion pits depth presented a power function with the increase of AC density.

Light-driven extracellular electron transfer accelerates microbiologically influenced corrosion by Rhodopseudomonas palustris TIE-1

This study investigates the microbiologically influenced corrosion (MIC) of X80 steel accelerated by the phototrophic bacterium Rhodopseudomonas palustris TIE-1. The photorespiration plays a key role in promoting extracellular electron transfer (EET)-induced MIC. In the early corrosion stage, unstable localized corrosion dominated in the dark, while intense diffusion-controlled corrosion occurs in light. Compared to the sterile anaerobic medium, R. palustris TIE-1 accelerated corrosion of X80 steel, with a significantly higher corrosion rate under light conditions, approximately three times that of dark conditions. Inhibition of photosynthetic electron transfer or cessation of photostimulation resulted in pronounced reduction in the corrosion rate.

Novel Proposal for Dissimilar Girth Welding of API 5 L X65 Steel Pipe with Internal Alloy 625 Cladding Using Both Low-Alloy Steel and Alloy 22 Combined Filler Metals

Novel Proposal for Dissimilar Girth Welding of API 5 L X65 Steel Pipe with Internal Alloy 625 Cladding Using Both Low-Alloy Steel and Alloy 22 Combined Filler Metals

Experimental study on strengthening the magneto-mechanical coupling effect of X80 steel by weak magnetic excitation

Abstract Current magnetic stress detection techniques are significantly impacted by external noise signals. The magnetic stress detection technology under excitation magnetic fields is proposed to weaken the external noise signals on the detection results. In this study, the uniaxial tensile magnetic signal testing system with the excitation magnetic field was built. The enhancement of the weak magnetic excitation on magnetic signals has been quantitatively analyzed and the concept of optimal weak excitation magnetic field has been proposed. The response law between triaxial magnetic induction intensity and stress under the excitation magnetic field is determined. The results indicate that the weak excitation magnetic field significantly enhances the magnetic induction signal intensity, more importantly, the linearity of the magnetic signal and stress response is also enhanced. Furthermore, the optimal excitation magnetic field under uniaxial stress states is 600 A/m, and the corresponding stress-magnetic change rate is 0.002 Oe/MPa. This study provides a theoretical basis for the long-distance detection of pipelines under weak magnetic excitation. The long-distance magnetic stress detection results of pipelines will become more accurate with the weak magnetic excitation which has a good engineering significance.

Stress-Corrosion-Cracking Sensitivity of the Sub-Zones in X80 Steel Welded Joints at Different Potentials.

X80 steel plays a pivotal role in the development of oil and gas pipelines; however, its welded joints, particularly the heat-affected zone (HAZ), are susceptible to stress corrosion cracking (SCC) due to their complex microstructures. This study investigates the SCC initiation mechanisms of X80 steel welded joints under practical pipeline conditions with varying levels of cathodic protection. The SCC behaviors were analyzed through electrochemical measurements, hydrogen permeation tests, and interrupted slow strain rate tensile tests (SSRTs) conducted in a near-neutral pH environment under different potential conditions (OCP, -1.1 VSCE, -1.2 VSCE). These behaviors were influenced by microstructure type, grain size, martensite/austenite (M/A) constituents, and dislocation density. The sub-zones of the weld exhibited differing SCC resistance, with the fine-grain (FG) HAZ, base metal (zone), welded metal (WM) zone, and coarse-grain (CG) HAZ in descending order. In particular, the presence of coarse grains, low dislocation density, and extensive M/A islands collectively increased corrosion susceptibility and SCC sensitivity in the CGHAZ compared to other sub-zones. The SCC initiation mechanisms of the sub-zones within the X80-steel welded joint were primarily anodic dissolution (AD) under open-circuit potential (OCP) condition, shifting to either hydrogen-enhanced local plasticity (HELP) or hydrogen embrittlement (HE) mechanisms at -1.1 VSCE or -1.2 VSCE, respectively.

Study on the effect of microstructure on toughness dispersion of X70 steel girth weld

The girth weld metal impact toughness would affect the safe operation of long transmission oil and gas pipeline. In order to further clarify toughness law of pipeline steel girth weld, the Charpy impact toughness of X70 steel girth weld at −10 °C was studied by standard impact method, and the impact energy range was determined to be 18–95 J. The impact energy range of girth welds varied significantly, and the toughness was discrete. The impact toughness of the different microstructures in the girth weld at −158 °C was studied by the small specimen impact test. The root weld metal mainly consisted of ferrite and a small amount of pearlite, and its impact toughness was low. The large effective grain size and dislocation density difference between large lath bainite (LB) and coarse granular bainite (GB) increased the strain heterogeneity during impact deformation. In fine GB, effective grain size reduction and uniform distribution of Martensite austenite (M–A) components reduced the local strain, resulting in more uniform deformation. Therefore, the sample with the fine GB had higher impact the toughness and ductile fracture mode. For the standard Charpy impact samples, the main reason for toughness dispersion was change of fine GB proportion. The fine GB proportions of P6-2, P3-3 and P3-2 were 46.7 %, 40.8 %, and 29.5 %, respectively. Simultaneously, the influence of position change on the impact energy was considered.

Hydrogen permeation and SCC susceptibility of X70 pipeline steel in CO2-saturated water environment containing acidic impurity

The effect of HNO3 and H2SO4 impurities on hydrogen permeation behavior and stress corrosion cracking (SCC) susceptibility of X70 steel in CO2-saturated water environment was investigated. Concurrently, a method for characterizing the contribution of corrosion-produced hydrogen to SCC was developed. HNO3 and H2SO4 boost the hydrogen permeation through promoting cathodic hydrogen evolution. The hydrogen embrittlement induced by corrosion-produced hydrogen, together with anodic dissolution, dominates the SCC process of X70 steel. The steel has much higher SCC susceptibility in H2SO4-containing environment than in HNO3-containing environment, which is closely related to the much stronger hydrogen embrittlement effect caused by H2SO4 than HNO3.