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The influence of hydrogen on the fracture of X65 was studied. The fracture toughness in air was 369 MPa√m. The ASTM-valid fracture toughness with cathodic hydrogen charging was lower but was similar for these charging conditions 189 MPa√m and 181 MPa√m at 9 mA/cm2; 192 MPa√m and 179 MPa√m at 16 mA/cm2; and 177 MPa√m at 25 mA/cm2; even though the fractography changed from (i) ductile fracture by microvoid coalescence in air and at 9 mA/cm2 to (ii) more brittle fracture for hydrogen charging at 16 mA/cm2 and 25 mA/cm2, with flat facets and secondary cracks, which increased with increasing current density. • The influence of hydrogen on the fracture of X65 was studied. • The fracture toughness in air was 369 MPa√m. • The ASTM-valid fracture toughness with cathodic hydrogen charging was lower. • The fracture toughness with hydrogen was 152–186 MPa√m. • The fractography changed from ductile fracture to more brittle fracture with increasing hydrogen. [ABSTRACT FROM AUTHOR]

This study investigates the corrosion behavior of dissimilar gas tungsten arc (GTA) welded joints between super duplex stainless steel (sDSS 2507) and pipeline steel (X-70) using electrochemical and immersion corrosion tests. The GTA welds were fabricated using ER2594 and ER309L filler metals. The study examined the electrochemical characteristics and continuous corrosion behavior of samples extracted from various zones of the weldments in a 3.5 wt.% NaCl solution, employing electrochemical impedance spectroscopy, potentiodynamic polarization methods, and an immersion corrosion test. EIS and immersion investigations revealed pitting corrosion in the X-70 base metal/X-70 heat-affected zone, indicating inferior overall corrosion resistance due to galvanic coupling. The corrosion byproducts identified in complete immersion comprised α-FeOOH, γ-FeOOH, Fe3O4, and Fe2O3, whereas γ-FeOOH and Fe3O4 were predominant in dry/wet cyclic conditions. Corrosion escalated with dry/wet cycle conditions while maintaining a lower level in complete immersion. The corrosion mechanism involves three wet surface stages in dry/wet cycles and typical oxygen absorption during complete immersion. Proposed corrosion models highlight the influence of Cl−, O2, and rust layers. [ABSTRACT FROM AUTHOR]

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. • The efficiency and mechanism of an organic hydrogen permeation inhibitor is investigated. • A multi-electrode array was used to probe the inhibitor film formation and coverage. • The capability of hydrogen permeation inhibition is related to inhibitor film formation. • The efficiency of hydrogen permeation inhibition is affected by inhibitor film coverage. • A model is proposed to explain the mechanism of hydrogen permeation inhibition. [ABSTRACT FROM AUTHOR]

The impact of Flavin adenine dinucleotide (FAD) on sulfate-reducing bacteria (SRB) corrosion of a pipeline welded joint (WJ) was investigated under anaerobic condition in this paper. The results showed that the thickness of the corrosion product on heat affected zone (HAZ) was lower than that on base metal (BM) and welded zone (WZ), and the FAD addition enhanced the development of the protruding microbial tubercles on the WJ. The local corrosion degrees of the BM and WZ coupons were significantly higher than that of the HAZ coupon. Besides, the FAD addition simultaneously promoted local corrosion of all three zones of the WJ in the SRB inoculated environment, and the promotion role was much more pronounced on the WZ coupons. The selective promotion effect of FAD on SRB corrosion in the WJ was attributed to the special structure of the WZ, the selected SRB attachment and the FAD/FADH2 redox feedback cycle. [ABSTRACT FROM AUTHOR]

The present work investigates the effect of microstructure, pH as well as the role of aggressive chloride ions on the corrosion behavior of American Petroleum Institute (API) X70 and X80 steel grades. The corrosion behavior was studied using single-run cyclic polarization in different solutions followed by microstructural analysis of the corroded samples to determine the mode and extent of corrosion damage. The solutions consist of a near-neutral aqueous sodium chloride solution, mildly alkaline carbonate-bicarbonate solution (pH-8.8), and highly alkaline carbonate-bicarbonate solution (pH-12) with and without the presence of chlorides. Ferrite phase in both the steel was found to dissolve preferentially in the different solutions leading to pitting as a result of microgalvanic coupling with the cementite and/or bainite phase. Interestingly, the corrosion resistance of the X70 grade was found to be greater than X80 at near-neutral as well as low alkaline carbonate-bicarbonate solutions, whereas the X80 performed better in higher pH solutions. Such contrasting corrosion behavior is attributed to the compactness, thickness, and electronic resistance of the passive oxide/hydroxide films formed during polarization in both the steel. [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of a 0.1 T static horizontal magnetic field on the corrosion of X70 pipeline steel in 0–0.05 mol/L sodium bicarbonate solutions. The weight loss data indicate that the magnetic field reduces the average corrosion rate during immersion within 48 h in all the test solutions. The magnetic field tends to increase the average corrosion rates for the immersion time of 72 h and 96 h. The magnetic field increases the proportion of magnetite in corrosion products formed on the specimen of immersion in 0.05 mol/L sodium bicarbonate solution for 168 h. The open-circuit potentials (OCP) are in the active zone of the E-pH diagram within 48 h immersion with 0 T and 0.1 T magnetic field. A 0.1 T magnetic field delays the process for the electrode to enter the passive zone of the E-pH diagram. The linear polarisation resistance (LPR) data shows that the resistance of the active zone with 0.1 T magnetic field is larger than that with 0 T. The electrochemical impedance results also indicate that the electrode is in an active state when the potential is below −700 mVSCE and in a passive state when the potential is above −200 mVSCE.

Here, X100 pipeline steel was subjected to FSW by controlling the peak temperature in the ferrite phase region, and preheating was used to tailor microstructure characteristics and enhance the strength-plasticity combination of the NZ. The conventional NZ contained ultrafine ferrite recrystallized grains (0.6 μm), and nanometer-sized (Ti, Nb)C and NbC precipitates were dispersed in the ferrite matrix. After preheating, fine ferrite grains (1.3 μm) were obtained in the preheating NZ, and the amount of precipitates decreased. The high yield strength (YS) of 1049 MPa was achieved in the conventional NZ, but the uniform elongation (UE) of 3.6% decreased markedly, only reaching ∼61% of UE of the base metal (BM). After preheating, a perfect YS of 852 MPa and UE of 9.1% were obtained in the preheating NZ, reaching 105% and 154% of that of the BM. The abovementioned excellent mechanical properties were attributed to the formation of fine ferrite recrystallized grains and precipitates, which provided a consistently high strain hardening rate.

This study describes how microstructural constituents affected the hydrogen embrittlement resistance of high-strength pipeline steels. The American Petroleum Institute (API) X60, X70, and X80 pipeline steels demonstrated complicated microstructure comprising polygonal ferrite (PF), acicular ferrite, granular bainite (GB), bainitic ferrite (BF), and secondary phases, e.g., the martensite-austenite (MA) constituent, and the volume fraction of the microstructures was dependent on alloying elements and processing conditions. To evaluate the hydrogen embrittlement resistance, a slow strain rate test (SSRT) was performed after electrochemical hydrogen charging. The SSRT results indicated that the X80 steel with the highest volume fraction of the MA constituent demonstrated relatively high yield strength but exhibited the lowest hydrogen embrittlement resistance because the MA constituent acted as a reversible hydrogen trap site.

Naphthenic acid corrosion is a well-recognized factor contributing to corrosion in the construction of offshore industry pipelines. To mitigate the corrosive effects, minor quantities of alloying elements are introduced into the steel. This research specifically explores the corrosion effects arising from immersing low-carbon steel, specifically A333 Grade 6, in a naphthenic acid solution. Various weight percentages of niobium were incorporated, and the resulting properties were observed. It was noted that the addition of 2% niobium in low-carbon steel exhibited the least mass loss and a lower corrosion rate after a 12 h immersion in naphthenic acid. Microstructural analysis using scanning electron microscopy (SEM) revealed small white particles, indicating the presence of oil sediment residue, along with corrosion pits. Following the addition of 2% niobium, the occurrence of corrosion pits markedly decreased, and only minor voids were observed. Additionally, the chemical composition analysis using energy-dispersive X-Ray analysis (EDX) showed that the black spot exhibited the highest percentage of carbon, resembling high corrosion attack. Meanwhile, the whitish regions with low carbon content indicated the lowest corrosion attack. The results demonstrated that the addition of 2% niobium yielded optimal properties for justifying corrosion effects. Therefore, low-carbon steel with a 2% niobium addition can be regarded as a superior corrosion-resistant material for offshore platform pipeline applications. [ABSTRACT FROM AUTHOR]

This study investigates the structure–property relationship in a dissimilar joint between super duplex stainless steel (sDSS 2507) and pipeline steel (X-70) using gas tungsten arc welding and ER2594 filler. Tubing and risers used to transport hydrocarbons are regularly joined using these dissimilar metals. The microstructures of lower heat input (LHI-0.7 kJ/mm) and higher heat input (HHI-1.4 kJ/mm) weldments were examined to understand the influence of heat input on the structure–property relationship. The weldments' mechanical characteristics were tested via hardness, impact, and tensile tests. Base metal and weld zone/interface characterization were studied utilizing optical and scanning electron microscopes with energy-dispersive spectroscopy (EDS). Elemental variation was confirmed by EDS spectra, elemental line mapping, and electron probe microanalysis with wavelength-dispersive spectrometer along the weld interface and weld zone. Significant microstructure variation was observed in X-70 BM at the LHI and HHI weld interfaces. Type II boundary and macro-segregation forms like peninsulas and islands were present in both weldments. In LHI and HHI weldment, duplex microstructure dominates the weld zone cap and filler pass. In the backing pass, duplex microstructure replaces skeletal ferrite, which predominates in the root pass of the HHI weld zone. LHI weldment has an average microhardness of 275 ± 7 HV0.5, while HHI had 285 ± 5 HV0.5. Both weldment's tensile tests revealed that the sample fractured on the weaker X70 BM side. LHI and HHI weldments had 600 MPa and 610 MPa ultimate tensile strengths and 22% and 18% elongation percentages, respectively. LHI weldments (200 ± 7 J, 210 ± 4 J) and HHI weldments (210 ± 5 J, 220 ± 8 J) have lower average impact toughness in cap and root pass than the sDSS 2507 BM (320 ± 3 J) and X-70 BM (300 ± 6 J), respectively. The increase in heat input led to a minimal 2% difference in tensile strength, a notable 10% increase in hardness, and a slight 5% variation in impact toughness between LHI and HHI weldments. Marine and offshore applications may benefit from investigating the sDSS 2507/X-70 DWJ's process parameter selection, thermodynamic analysis, and structure–property relationship. [ABSTRACT FROM AUTHOR]

This study explores the microstructural characterization of pearlite phase transformation in high-strength low-alloy API X60 steel, which is used in pipelines. Understanding the formation, phase percentages, and morphology of the pearlitic phase is crucial since it affects the mechanical properties of the considered steel. In this research, a phase-field model, particularly the Cahn-Hilliard approach, was used in order to simulate the formation and morphology of the pearlite phase in response to different heat treatments. Both double- and triple-well potentials were considered for comprehensively studying pearlite's morphology in the simulations. The simulation results were then compared with experimental outcomes obtained by metallography and field-emission scanning electron microscopy analyses. Considering the doublewell potential can help simulate only two phases, ferrite and cementite, which is less compatible with the experiment results than the triple-well potential, which gives the possibility of simulating a three-phase microstructure, ferrite, cementite, and austenite, and a better match with experimental data. The study revealed that as the cooling rate increases, the interlamellar spacing and layer thickness decrease. Additionally, the difference between experimental and simulation results using triple-well potential was approximately ~10%. Therefore, triple-well potential formulation predictions have better agreements with experimental results for the development circumstance of pearlitic structures. [ABSTRACT FROM AUTHOR]

Microstructure is an important factor affecting hydrogen diffusion in pipeline steels. Due to the different stress and heat conditions, the surface and internal microstructure of the rolled pipeline steels is different. The ferrite grain size in surface layer of X42 pipeline steel is smaller than other locations, while the surface layer of X52 pipeline steel has continuous banded ferrite/pearlite structure and grains with uneven size. Hydrogen permeation behavior is investigated at different positions in the normal direction of X42 and X52 pipeline steels using the electrochemical hydrogen permeation technique. The results show that the values of the effective diffusion coefficient of surface layer in X42 and X52 pipeline steels are the smallest, while the values of the subsurface hydrogen concentration at steady state are the largest. Hydrogen microprint experiment results indicate hydrogen atoms mainly escape at pearlite, ferrite grain boundaries and near inclusions in X42 and X52 pipeline steels. • The surface and interior microstructure of rolled pipeline steel is inconsistent. • Hydrogen diffusion is hindered by grain boundaries. • The continuous banded ferrite/pearlite structure impedes hydrogen diffusion. • Hydrogen atoms mainly escape at pearlite and ferrite grain boundaries. [ABSTRACT FROM AUTHOR]

In the current investigation, X70 pipeline steel plate was welded using submerged-arc welding. Thereafter, a (Fe0.5Ni0.2)61Cr9Co6Si1.5B17.5Nb5 amorphous alloy coating with a thickness of 400 ± 30 μm was successfully deposited on the surface of welded X70 pipeline steel by high velocity oxy-fuel (HVOF). The corrosion resistance of the substrate and coating in acidic environments was discussed, and the corrosion mechanisms were analyzed. The results show that the coating is completely amorphous with a dense microstructure, showing a typical thermal spray laminar flow-like structure. The corrosion potential (Ecorr) and self-corrosion current density (Icorr) are − 396 mV and 2.061 × 10−6 A/cm2, respectively. The Ecorr of all coatings is better than that of substrate. The coating A, where the BM zone is located, has the largest capacitance resistance arc radius and the smallest Icorr (1.427 × 10−7 A/cm2), which provides the best corrosion resistance. The maximum Icorr of the coating (Icorr = 2.320 × 10−7 A/cm2) is one order of magnitude lower than the minimum Icorr of the substrate (Icorr = 2.061 × 10−6 A/cm2), which indicates that the coating has better corrosion resistance than the substrate. The corrosion mechanism of the coating in H2SO4 solution is active dissolution of metal elements in the coating (initial stage) and passivation film protection coating (later stage). This work provides a very valuable idea to solve the problem of corrosion failure of X70 pipeline steel. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

[Objective] One of the most efficient and economical approaches for storing and transporting hydrogen energy is to blend hydrogen at a certain ratio into the existing natural gas pipeline network for large-scale long-distance transmission. However, the exposure of pipeline steel to hydrogen environments can lead to hydrogen embrittlement, which undermines its mechanical properties and poses potential risks to pipeline safety. Consequently, it is crucial to evaluate the mechanical properties of pipeline steel used for hydrogen-enriched compressed natural gas(HCNG) transmission and understand the influence rules of hydrogen blending ratios on the steel's susceptibility to hydrogen embrittlement. [Methods] Slow strain rate tensile experiments were conducted with in-situ hydrogen charging under high-pressure gas-phase conditions using a self-designed experimental system adhering to the requirements of Standard Test Method for Determination of Susceptibility of Metals to Embrittlement in Hydrogen Containing Environments at High Pressure, High Temperature, or Both(ASTM G142-2016). Additionally, quasi-static fracture toughness experiments with in-situ hydrogen charging under high-pressure gas-phase conditions were performed using an Instron 8801 servo hydraulic fatigue test system. These experiments investigated the hydrogen embrittlement behavior of X65 pipeline steel, considering varying hydrogen pressure conditions. Moreover, the influence of different hydrogen blending ratios on the mechanical properties of the pipeline steel was analyzed, taking into account fracture morphology characteristics. [Results] The X65 pipeline steel exhibited a decrease in total percentage elongation after fracture by up to 11.5% when hydrogen was charged at 3%,5%, and 10% under a total pressure of 9 MPa, compared to hydrogen-free environments. The fracture toughness decreased by 23.5% and 43.1%, respectively, when hydrogen was charged at 3% and 10%. The severity of hydrogen embrittlement increased with higher hydrogen ratios. Concerning fracture morphology, specimens with hydrogen ratios below 10% displayed ductile fractures without typical brittle fracture morphology. [Conclusion] To ensure the safe operation of X65 pipelines, particularly those that have been in service for several years, it is recommended to conduct evaluations and analyses of the mechanical properties, focusing on the steel's susceptibility to hydrogen embrittlement before introducing HCNG transmission.

The addition of small amounts of certain gases, such as O 2 , CO, and SO 2 , may mitigate hydrogen embrittlement in high-pressure gas transmission pipelines that transport hydrogen. To practically implement such inhibition in gas transmission pipelines, a comprehensive understanding and quantification of this effect are essential. This review examines the impact of various added gases to hydrogen, including typical odorants, on gaseous hydrogen embrittlement of steels and evaluates their inhibition effectiveness. O 2 , CO, and SO 2 were found to be effective inhibitors of hydrogen embrittlement. Yet, the results in the literature have not always been consistent, partly because of the diverse range of mechanical tests and their parameters. The absence of systematic studies hinders the evaluation of the feasibility of using gas phase inhibitors for controlling gaseous hydrogen embrittlement. A method to quantify the effectiveness of gas phase inhibition is proposed using gas phase permeation studies. • Concise review of hydrogen embrittlement and control strategies in hydrogen pipelines. • Comprehensive literature review of gas phase inhibition of hydrogen embrittlement. • Inhibition effectiveness based on mechanical testing was evaluated and tabulated. • O 2 , CO or SO 2 are strong candidates for gas phase inhibition. • Typical gas odorants have no significant inhibition effect on hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

In this study, we systematically investigate electrochemical hydrogen charging conditions equivalent to hydrogen gas pressures relevant for hydrogen transportation in X65 pipeline steel. By performing hydrogen gas permeation, a relationship for Sieverts' law was established, which was used in combination with electrochemical hydrogen permeation to determine the equivalent hydrogen pressure. The results revealed that cathodic protection simulated condition at –1050 mVAg/AgCl was equivalent to a hydrogen pressure of 12.3 bar. The addition of thiourea, a hydrogen recombination poison, and changing the applied potential in the cathodic direction increased the equivalent hydrogen pressure. In this way, an electrochemical charging condition equivalent to a potential hydrogen gas pressure for hydrogen transportation (200 bar) was determined. [ABSTRACT FROM AUTHOR]

This study explores the microstructural characterization of pearlite phase transformation in high-strength low-alloy API X60 steel, which is used in pipelines. Understanding the formation, phase percentages, and morphology of the pearlitic phase is crucial since it affects the mechanical properties of the considered steel. In this research, a phase-field model, particularly the Cahn–Hilliard approach, was used in order to simulate the formation and morphology of the pearlite phase in response to different heat treatments. Both double- and triple-well potentials were considered for comprehensively studying pearlite’s morphology in the simulations. The simulation results were then compared with experimental outcomes obtained by metallography and field-emission scanning electron microscopy analyses. Considering the double-well potential can help simulate only two phases, ferrite and cementite, which is less compatible with the experiment results than the triple-well potential, which gives the possibility of simulating a three-phase microstructure, ferrite, cementite, and austenite, and a better match with experimental data. The study revealed that as the cooling rate increases, the interlamellar spacing and layer thickness decrease. Additionally, the difference between experimental and simulation results using triple-well potential was approximately ∼10%. Therefore, triple-well potential formulation predictions have better agreements with experimental results for the development circumstance of pearlitic structures.

In this research, the efficacy of specific heat treatment procedures in mitigating hydrogen embrittlement in X100 pipeline steels is discussed. The studied steels underwent a one-step austenitization process at temperatures of 780 °C (HT1), 830 °(HT2), and 880 °C (HT3) for 90 min, followed by oil quenching, tempering at 600 °C, and air cooling. The susceptibility of both the heat-treated and as-received (REF) specimens to HIC was assessed using an electrochemical hydrogen charging, tensile testing, micro-hardness testing, and electron backscatter diffraction (EBSD) techniques. The results showed that an increase in annealing temperature from 780 to 880 °C considerably decreases hydrogen embrittlement susceptibility. The hardness value at the centerline of the as-received (REF) specimen was found to be higher than that of the heat-treated specimens. Additionally, calculations of the hydrogen embrittlement (HE) index for all specimens were conducted. The results show that the REF specimen, which demonstrated the highest hardness and HE index values, has greater susceptibility to HIC. Conversely, the HT3 specimen, which was annealed at 880 °C and displayed the lowest hardness and HE index values, showed commendable resistance to HIC. The EBSD analysis revealed a decrease in Kernel average misorientation (KAM) values in heat-treated specimens, with the lowest values found in HT3. Dominant textures in all studied steels, {011} and {111}, were considered HIC-resistant and recrystallization mapping indicated a peak area of recrystallized grains in the REF specimen. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Hydrolyzed polyacrylamide (HPAM), a viscosity booster in the enhanced oil recovery process, has been found to be prone to microbial degradation. The effect of HPAM degradation on the electrochemical properties and corrosion behavior of C20 steel was examined in oilfield injection water containing sulfate-reducing bacteria (SRB). Microscopic and spectroscopic analyses showed that HPAM promoted SRB growth, which resulted in the precipitation of higher amount of ferrous sulfide in the test medium. Electrochemical investigations revealed that the HPAM biodegradation enhanced the corrosion rate and localized perforation of steel. These were possible because the HPAM degradation furnished the test medium with nutrients like acetate and ammonium ions, which sustained microbial activities, thus boosting the anodic dissolution of steel. [ABSTRACT FROM AUTHOR]

The corrosion behavior of C20 pipeline steel was studied under Fe oxide and sand deposits in oilfield produced water containing sulfate‐reducing bacteria (SRB) via electrochemical techniques and surface analyses. A galvanic current of about 2 μAcm−2 was detected when the Fe oxide deposited sample and the bare steel were coupled in zero resistance ammeter (ZRA) mode, with the former being the anodic member of the couple. The Fe oxide deposited steel recorded severe localized corrosion after 14 days of testing in the SRB inoculated oilfield produced water. Corrosion severity decreased on the sand‐deposited steel, with general corrosion as the dominant morphology of surface attack. The development of product film was a vital factor in steel corrosion under the Fe oxide deposit. [ABSTRACT FROM AUTHOR]

In this research, the correlation between the defect depth and the tangential piezomagnetic field of X70 steel was investigated. Tensile tests were carried out to measure the piezomagnetic fields on the surface of X70 specimens with different defect depths. The variations of piezomagnetic fields were compared to the simulation results of a theoretical model. The influences of loads and defect depths on magnetic parameters were discussed. This research demonstrates the potential possibility of evaluating the defect depth of ferromagnetic steels using piezomagnetic fields. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Pipelines provide an efficient and economical method for hydrogen transportation with a high capacity over wide ranges and long distances, contributing to accelerated realization of a full-scale hydrogen economy. However, steel pipelines are prone to hydrogen embrittlement in high-pressure gaseous environments once the generated hydrogen (H) atoms enter the steels. Dislocations are one of the most common defects contained in steels. The H atom generation and adsorption at dislocation emergences on pipeline steels have not been fully understood. This work investigated and determined the stable hydrogen adsorption configurations at the emergence of an edge dislocation on iron (Fe) (100) crystalline plane by density functional theory. The partition function was used to study the thermodynamics of dissociative adsorption of hydrogen, as well as the effects of dissociated impurity gases (i.e., oxygen, methane and water vapor) existing in the carried fluid, under pipeline operating conditions. Results demonstrate that the dislocation core is the stable site for hydrogen adsorption, followed by the sites with a tensile strain at the dislocation, although the dissociative adsorption of hydrogen can also occur at the compressive strain sites. An elevated hydrogen gas pressure and low temperature favor the hydrogen adsorption. The three impurity gases can have dissociative adsorption occur at the edge dislocation. Moreover, their adsorptions are more thermodynamically favorable than hydrogen. Oxygen has the most stable adsorption configuration, followed by water vapor and then methane. Pre-adsorbed O-containing gases (i.e., oxygen and water vapor) compete with the hydrogen adsorption and decrease the stability of the hydrogen adsorption configuration. The competing effect of the impurity gases with hydrogen adsorption occurs only when they adsorb at the compressive sites of the dislocation. When the impurity gases pre-adsorb at the tensile strain sites of the dislocation, they have little influence on hydrogen adsorption. [Display omitted] • Determined stable hydrogen adsorption configurations at an edge dislocation emergence on Fe (100) plane. • Explained the mechanism of hydrogen atom distribution at the edge dislocation. • Studied the effects of dissociated impurity gas molecules on adsorption of hydrogen on Fe (100) plane with edge dislocation. [ABSTRACT FROM AUTHOR]

The paper presents the research results on assessment of in-service degradation of the 0.17 C-Mn-Si steel of gas transit pipeline operated for 36 years. High degradation degree of the operated steel was manifested in a significant decrease in plasticity characteristics, impact toughness and resistance to stress corrosion cracking and hydrogen embrittlement compared to the as-delivered steel. The tests carried out using the low stress method revealed significant changes in elastic hysteresis, elasticity modulus and relative residual deformation of the steel depending on its state (as-delivered and post-operated ones), demonstrated to be highly sensitive to assess in-service degradation degree of pipeline steels. [ABSTRACT FROM AUTHOR]

Hydrogen-induced mechanical degradation was evaluated in different environmental conditions on two X70 pipeline steels having the same composition but different thermomechanical processing parameters, and a further correlation between microstructural features and hydrogen embrittlement (HE) susceptibility was established. HE susceptibility was determined by performing the Slow Strain Rate Tensile Test (SSRT) in air, ex-situ hydrogen-charged, in corrosive media, in-situ hydrogen-charged and Charpy impact tests before and after hydrogen charging in a wide range of temperatures. The SSRT results indicated that the synergistic action of stress and hydrogen in in-situ charged sample leads to maximum HE susceptibility in both X70 steels. Charpy results demonstrated that ductile-to-brittle transition temperature (DBTT) increases after hydrogen charging. The texture analysis revealed that X70-2 with a higher volume fraction ratio of Ƴ-fiber/{100}<011> demonstrated improved HE resistance, whereas X70-1 with higher fractions of {113}<110> and {100} || ND demonstrated a higher DBTT than before and after hydrogen charged X70-2. • Hydrogen embrittlement susceptibility was studied in various testing environments. • Synergy of stress and H enhances hydrogen embrittlement susceptibility significantly. • Ductile-to-brittle transition temperature increases after hydrogen charging. • Lower fraction of Ƴ fiber/{100}<011> enhanced sensitivity to hydrogen embrittlement. • Failure behavior depends on the H environmental conditions. [ABSTRACT FROM AUTHOR]

Existing guidance from ASTM standards on extracting mechanical properties from uniaxial tension test data is not suitable for high-volume applications because it lacks automation. The Pacific Gas and Electric Company (PG&E) has performed over 450 uniaxial tension tests on samples extracted from dozens of distinct natural gas pipeline features in support of materials verification efforts; 144 of these tests recorded the entire deformation response up to fracture and were subsequently analyzed herein. Algorithms were developed to enable automatic, batch post-processing of the tensile data. Among the mechanical properties that this software extracts from the tensile data are the power-law hardening exponent and strength coefficient. A novel algorithm was developed to calculate these power-law parameters while accommodating the range of yielding and hardening behaviors present among the low carbon pipeline steels tested in this effort. The algorithm, presented in this brief technical note, first identifies the lower limit of the hardening region by calculating the tangent modulus of the stress–strain curve, which reaches its maximum value at the onset of strain hardening. The end of uniaxial hardening coincides with the ultimate tensile stress and the end of uniform deformation. From there the algorithm computes the power-law hardening parameters using conventional linear regression. Analysis of the data shows that this approach is more accurate than two other approaches: (1) regressing from 0.2% plastic strain to the limit load, and (2) iteratively regressing to identify the region that minimizes the regression error. The advantage of this approach, over existing methods, is observed for materials that exhibit a yield plateau. To further demonstrate the utility of the strain hardening information collected during this effort, the relationship between strain hardening exponent and ratio of yield strength to ultimate tensile strength from this data was compared to those reported in previous literature pertaining to remaining life assessments of steel line pipe. Overall, the strain hardening data obtained in this algorithm indicates greater hardening in pipeline steels than some previously published results. This algorithm has been made available as part of this paper's supplementary materials. [ABSTRACT FROM AUTHOR]

The inability to produce raw materials in sufficient quantities, such as fruits, plants, pigments and resins, to manufacture green inhibitors is considered one of the biggest reasons that hinder the commercial use of these eco-friendly inhibitors. In Asia and Africa, date fruit is produced in large quantities. This fruit contains polysaccharides (primarily galacturonic acid) that can be used as a green inhibitor. The inhibition effect of Ghars date extract (GDE) on the corrosion of API 5L X70 pipeline steel in 0.5 M HCl solution was studied for the first time using electrochemical impedance spectroscopy, potentiodynamic polarization curves, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results show that GDE is an excellent inhibitor. The inhibition efficiency was 94 % at 2 g/L GDE. The GDE follows the Langmuir adsorption isotherm and involves physical adsorption. The GDE acts as a mixed-type inhibitor. [ABSTRACT FROM AUTHOR]

Understanding the causes of hydrogen embrittlement and its detrimental effects is essential for ensuring the integrity of pipeline steel. Various testing methods, including slow strain rate and fatigue life testing, are commonly employed to evaluate the susceptibility of metals to embrittlement. Pipeline steel materials often exhibit reduced toughness, accelerated crack propagation, and other hydrogen-related damage during slow strain rate tests conducted at hydrogen pressures below 5 MPa or in environments with a hydrogen volume fraction of 10% in blended natural gas. To simulate the conditions of steel serving in a hydrogen-rich environment,experiments incorporate methods of gas-phase hydrogenation and electrochemical hydrogenation. The former simulates the effects of different gas-phases on hydrogen embrittlement, while the latter replicates long-term hydrogen permeation. This paper provides an overview of the process and mechanisms of hydrogen embrittlement and analyzes three technologies for prevention and control:(1) modification of pipeline steel materials and processing techniques to optimize microstructure, enhance diffusion rates,and mitigate hydrogen atom aggregation;(2) introduction of gas inhibitors to slow hydrogen molecule adsorption on material surfaces through competitive adsorption; and(3) utilization of coatings on the inner pipeline wall to provide a barrier between hydrogen and the steel. Based on these insights, the paper offers suggestions for further optimizing pipeline hydrogen embrittlement control technology.

Naphthenic acid corrosion is a well-recognized factor contributing to corrosion in the construction of offshore industry pipelines. To mitigate the corrosive effects, minor quantities of alloying elements are introduced into the steel. This research specifically explores the corrosion effects arising from immersing low-carbon steel, specifically A333 Grade 6, in a naphthenic acid solution. Various weight percentages of niobium were incorporated, and the resulting properties were observed. It was noted that the addition of 2% niobium in low-carbon steel exhibited the least mass loss and a lower corrosion rate after a 12 h immersion in naphthenic acid. Microstructural analysis using scanning electron microscopy (SEM) revealed small white particles, indicating the presence of oil sediment residue, along with corrosion pits. Following the addition of 2% niobium, the occurrence of corrosion pits markedly decreased, and only minor voids were observed. Additionally, the chemical composition analysis using energy-dispersive X-Ray analysis (EDX) showed that the black spot exhibited the highest percentage of carbon, resembling high corrosion attack. Meanwhile, the whitish regions with low carbon content indicated the lowest corrosion attack. The results demonstrated that the addition of 2% niobium yielded optimal properties for justifying corrosion effects. Therefore, low-carbon steel with a 2% niobium addition can be regarded as a superior corrosion-resistant material for offshore platform pipeline applications.

Pipeline transportation is the most economical means of transporting oil, natural gas, and other energy sources over a long distance. With the increasingly harsh service environment of pipeline transportation, the requirements of pipeline steel in terms of strength, hydrogen-induced fracture resistance, and corrosion resistance have increased. In areas such as plateaus or deep seas, excellent low-temperature toughness is important to ensure the safe transportation of pipeline steel. Drop weight tear testing is one of the most effective methods for measuring the low-temperature toughness of pipeline steel. The test involves large specimens with full wall thickness. Through the characterization of the ductile–brittle shear area and ligament width of the sample, the toughness and tear resistance of pipeline steel can be better reflected. However, the drop weight tear test is difficult, time-consuming, and laborious, and it consumes a large amount of experimental resources. In this work, a machine learning-based model for predicting the drop weight tear test-derived shear area was established according to production line datasets provided by steel mills and pipeline steel datasets collected from the literature. Different machine learning algorithms were tested using the two datasets. The best models were random forest models. Strategy I included only production line datasets, and the Pearson correlation coefficient (PCC), which is the performance index, predicted by the machine learning model was 0.64. Strategy II involved literature data and production line data, and the PCC predicted by the machine learning model was 0.92. The consideration of literature data effectively improved the prediction accuracy of the drop weight tear test shear area. Moreover, in strategy II, to avoid the overfitting of the machine learning model, a feature screening technique was adopted. Finally, a genetic programming-based symbolic regression approach was developed to establish a formula describing the relationship between the selected features and the target shear area data. The PCC of the precision of this formula was 0.83, which indicates that the formula can be used to estimate the drop weight tear test-derived parameters of pipeline steel. The machine learning technology provides a new method for optimizing and predicting the drop weight tear test-derived shear area of pipeline steel. Moreover, the combination of production line data and literature data remarkably improved the accuracy of the machine learning model, which also allows for the prediction of other material production line data via machine learning techniques.

With the increasingly imperious demands for energy transformation and development of hydrogen energy utilization in China,X80 high-strength pipeline steel will face the risks of operating in a hydrogen environment. As the in-service pipeline is subjected to both static load and cyclic load, and the interaction between cyclic load and hydrogen is more complex, the evaluation of properties of pipeline steel in the hydrogen environment must consider both the tensile and fatigue properties. Specifically, the effect of hydrogen on the tensile and fatigue properties of X80 steel was analyzed through the tensile test and the fatigue crack growth test in a high-pressure hydrogen environment. Thus, a fatigue crack growth model of X80 pipeline steel was established to quantify the hydrogen pressure. The results show that hydrogen has no significant effect on the tensile property of X80 pipeline steel. Whereas, a higher hydrogen pressure will lead to a greater fatigue crack growth rate, and the fatigue crack growth rate at the hydrogen pressure of 3 MPa is 10 times that in a nitrogen environment. This indicates that hydrogen has a significant impact on the fatigue crack growth of X80 pipeline steel. In addition, the fatigue property of X80 pipeline steel will become a key factor for the safety design and integrity evaluation of the pipeline in the hydrogen environment.

The escalating global demand for energy resources, particularly oil and natural gas, underlines the critical need for enhancing the performance of pipeline infrastructure. This necessity is particularly pronounced in extreme environments such as remote permafrost zones and polar regions, where pipeline steels are exposed to exceptionally low temperatures. In this review, the effects of alloying elements and thermomechanical processing on the low-temperature toughness of pipeline steels are comprehensively examined. It particularly focuses on the influence of alloy elements niobium (Nb), molybdenum (Mo), chromium (Cr), boron (B), and vanadium (V), and process factors like cooling rate, finish cooling temperature, and rolling reduction. The discussion also emphasizes the significance and prospects of augmenting the low-temperature toughness of pipeline steels, as a measure to manufacture high-grade pipeline steels. These insights are valuable for engineers, researchers, and policymakers engaged in the field of pipeline construction and energy development.

Multiple flow erosion-corrosion under high pressure environment is a key problem for safe operation of oil gas gathering and transporting pipelines. For the high pressure erosion-corrosion failure problem of the gathering and transporting pipeline in CO2 environment, the high pressure erosion-corrosion apparatuses of gathering and transportation pipeline in CO2 environment were elaborated, mainly including high pressure jet impingement system, high pressure rotor rotating system and high pressure loop test system. The mechanism of high pressure erosion-corrosion was reviewed, and it was pointed out that erosion-corrosion was controlled by electrochemical corrosion and erosion wear. Besides, the effects of factors such as flow rate, velocity of solid particles, size of solid particles, temperature, pH value, and CO2 partial pressure on high pressure erosion-corrosion were summarized. Finally, the development direction of high pressure erosion-corrosion study of the gathering and transporting pipeline in CO2 environment were prospected.

Pipeline welding is an integral part of oil and gas exploration industries. Often the welded joint failures were due to lack of weld quality, improper heat treatment and even poor workmanship. Further, the use of new material in pipeline industry puts focus on a better understanding of qualifying requirements of welding for reducing the failures in future. This necessitates the need for development and design of suitable welding fluxes for joining these materials. In this paper an attempt is made to study the effects of submerged arc welding fluxes on weldability as well as structural integrity issues in pipeline steels. Physicochemical and thermophysical properties of submerged arc fluxes widely affects the mechanical behaviour of pipeline steels. This paper presents an overview of the role of welding parameters, flux composition, cooling rate, slag behaviour and physicochemical properties of slag on final welded joint properties such as tensile strength, impact toughness etc. during submerged arc welding.

Acicular ferrite has appeared in various low carbon microalloyed steel welds (e.g., laser-arc hybrid welds) due to its high grain boundary density and toughness. However, the transformation kinetics and crystallographic structure characteristics of acicular ferrite in laser-arc hybrid welds are still unclear. In this paper, the nucleation and growth kinetics of acicular ferrite in laser-metal active gas hybrid welds with different cooling rates (1–150 K/s) were investigated and their crystallographic characteristics were revealed from the perspective of variant. The result showed that acicular ferrite can nucleate at all the test cooling rates in weld metal, and the microstructure coexisting with acicular ferrite changes from polygonal ferrite and granular bainite with a low cooling rate to lath martensite with a high cooling rate. As the cooling rate increases, the phase transformation temperature of acicular ferrite decreased, and the phase transformation mode changed from partitioning local equilibrium to negligible partitioning local equilibrium. The variety of the phase transformation mode and the higher phase transformation driving force led to an increase in the growth rate of acicular ferrite. Compared with the bainite and martensite in the base metal, the acicular ferrite had the characteristics of light variant selection, uniformly distributed operating factor and small variant size, which resulted in high-density effective grain boundaries. To obtain more acicular ferrite, the cooling rate should be increased as much as possible on the premise that the phase transformation termination temperature was higher than the Ms. [ABSTRACT FROM AUTHOR]

In this paper, hydrogen diffusion behavior in pipeline steel is thoroughly investigated. The effect of various microstructural factors affecting hydrogen diffusion are discussed using literature review. The results of this survey show that the hydrogen diffusion in pipeline steels depends strongly on the microstructure of steel, crystallographic texture, dislocation density, grain size, presence of different elements, precipitates and inclusions. Based on the results, the interfaces between the retained austenite and martensitic layer are considered as the possible hydrogen trap sites. Moreover, the apparent diffusivity decrease due to hydrogen trapping by dislocations is well documented without need for cyclic loading. The grain size and nature of grain boundaries plays an important role in the hydrogen diffusion and trapping. There is an optimum grain size in which the hydrogen diffusion reaches its maximum value. Various elements, inclusions and precipitates which are present in the microstructure of pipeline steel have a considerable role in hydrogen diffusion. Based on the hydrogen microprint technique results, the increase in the grain size decreases the hydrogen trapping by triple junctions and grain boundaries.

Taking X100 and X80 pipeline steels as research objects，their stress-strain curves in air and under different applied potentials were obtained through the slow strain rate tensile test (SSRT).The stress corrosion sensitivity analysis showed that the applied potential had a significant effect on the SCC sensitivity and corrosion cracking mechanism of X100 and X80 pipeline steels in 3.5%NaCl neutral solution.Under the same stress corrosion conditions，the SCC sensitivity of X100 pipeline steel was lower than that of X80 pipeline steel.The characteristics and differences of the corrosion resistance of X100 and X80 pipeline steels were analyzed by combing the observation of fracture morphology and fast/slow scan tests of polarization curves，the stress corrosion mechanism type of X100 and X80 pipeline steel materials under different applied potential conditions could be obtained，when the applied potential was higher than -395 mV，the metal was in the state of activation dissolution；when the applied potential was -395～-462 mV(X80 steel) or -395～-504 mV(X100 steel)，the mechanisms were membrane crackinganodic dissolution(AD) and hydrogen induced crack.If the applied potential further decreased，the mechanism was hydrogen induced crack.

Hydrogen can degrade the mechanical properties of steel components, which is commonly referred to as "hydrogen embrittlement" (HE). Quantifying the effect of HE on the structural integrity of components and structures remains challenging. The authors investigated an X70 pipeline steel through uncharged and hydrogen-charged (notched) tensile tests. This paper presents a combination of experimental results and numerical simulations using a micro-mechanics-inspired damage model. Four specimen geometries and three hydrogen concentrations (including uncharged) were targeted, which allowed for the construction of a fracture locus that depended on the stress triaxiality and hydrogen concentration. The multi-physical finite element model includes hydrogen diffusion and damage on the basis of the complete Gurson model. Hydrogen-Assisted degradation was implemented through an acceleration of the void nucleation process, as supported by experimental observations. The damage parameters were determined through inverse analysis, and the numerical results were in good agreement with the experimental data. The presented model couples micro-mechanical with macro-mechanical results and makes it possible to evaluate the damage evolution during hydrogen-charged mechanical tests. In particular, the well-known ductility loss due to hydrogen was captured well in the form of embrittlement indices for the different geometries and hydrogen concentrations. The limitations of the damage model regarding the stress state are discussed in this paper. [ABSTRACT FROM AUTHOR]

Pipeline transportation is one of the most economical ways to transport crude oil and natural gas over long distances. High toughness is one of the important qualities of pipeline steel to ensure safe transportation, wherein a key factor characterizing toughness is Charpy impact toughness (CIT). In this work, according to the production line data provided by a steel mill and the experimental data collected in literature, two machine learning model construction strategies were proposed. One was based solely on the production line dataset, and the other was based on the production line dataset together with the literature dataset. In these two strategies, the random forest model displayed the best prediction results, the accuracy of strategy I was 0.58, and the accuracy of strategy II was 0.90, wherein literature data effectively improved the CIT prediction accuracy. Finally, an optimized CIT model based on machine learning algorithms was established. The proposed strategy of literature data-assisted production line data provides a new perspective for optimizing and predicting the performance of traditional structural materials. [ABSTRACT FROM AUTHOR]