X80 Pipeline Steel Research Articles

Insight into sulfate-reducing bacteria corrosion behavior of X80 pipeline steel welded joint in a soil solution

The effect of sulfate-reducing bacteria (SRB) on the corrosion behavior of X80 steel welded joint in a soil solution was studied. The results indicated that SRB enhanced the corrosion of X80 steel welded joint. The corrosion behavior in the heat affected zone (HAZ) was quite different from those of in the weld metal (WM) and base metal (BM). The HAZ was an active region that could be preferentially and more quickly corroded. Macro-galvanic corrosion in the welded joint had a significant effect on the MIC behavior of the X80 steel welded joint, leading to the preferential corrosion of the HAZ.

Effects of CH4 and CO on hydrogen embrittlement susceptibility of X80 pipeline steel in hydrogen blended natural gas

The slow strain rate tensile experiments are carried out to investigate the tensile properties of X80 pipeline steel in hydrogen blended natural gas environments with different H2/CH4/CO contents. Mechanical properties and fracture morphologies are further analyzed. The results show that the hydrogen embrittlement susceptibility of X80 steel can be inhibited by the presence of CH4/CO, and the inhibition mechanisms are discussed. When the CH4 contents increase above 20 vol%, the inhibition on hydrogen embrittlement of X80 steel is stabilized. By comparison, the inhibitory effect of CO is more significant.

Microstructure and crystallographic texture of high frequency electric resistance welded X65 pipeline steel

Microstructure and crystallographic texture and their correlation with impact toughness of high-frequency electric resistance welded (HF-ERW) X65 Grade pipeline steel have been investigated. X65 base metal after HF-ERW has formed a typical hourglass-shaped weld joint with four different regions, including the thermomechanical-affected zone (TMAZ), fine-grained heat affected zone (FGHAZ), coarse-grained heat affected zone (CGHAZ), and bondline (Weld Zone). X65 base metal shows prominent (113) [110] and (112) [110] texture components due to thermomechanical-controlled processing. TMAZ depicted random texture with a minor intensity of Cube component (001)[110] due to the partial recrystallization during welding. In the FGHAZ and CGHAZ, near the bondline, the base metal texture has been converted to rotated Goss (110) [110], Goss (110) [001], and rotated cube (001) [110] due to the recrystallization of the austenite and the shear deformation in the austenite temperature range. A high density of {100} and {110} cleavage planes is observed in the CGHAZ, which is often found to be the fracture location for the impact toughness testing.

Generation mechanism of lack of fusion in X70 steel welded joint by fully automatic welding under steep slope conditions based on numerical simulation of flow field

X70 pipeline steel is butt welded by fully automatic welding at 25° slope, and the characteristic information of welding process is collected. A 3D transient heat and mass transfer model of weld pool is established. This model was verified by means of the shape of the weld pool and the two-dimensional shape of the weld, and then, the flow field of the fully automatic welding process under steep slope conditions was simulated to clarify the mechanism of the lack of fusion defect. The results show that the welding arc is deflected when it stays on both side walls of the groove. The slope makes the liquid metal tend to gather at the lower groove. When gravity plays a leading role in the flow of the molten pool, some liquid metal begins to flow out from the lower groove to the front end, resulting in an overflow phenomenon. The generation of overflow phenomenon and arc deflection cause the formation of a “void zone” at the structure mutation position in front of the groove. In the welding process, the liquid metal tends to flow to the side walls for heat transfer under various thermal effects, and forms a large range of eddy current at the side walls. This has a positive effect on sidewall melting. In addition, the effect of surface tension at the lower groove is more obvious than that at the upper groove, and the trend of upward flow along the side wall is stronger, so it is difficult for the high-temperature liquid metal in the arc center to flow to the “void area” located at the bottom of the side wall of the lower groove. Therefore, the bottom of the lower groove is more likely to cause lack of fusion defect.

Imidazoline behavior as corrosion inhibitor in the electrochemical characterization of SCC behavior of an API X70 steel exposed to brine solution

Abstract The effect of concentration of an organic imidazoline as inhibitor on internal stress corrosion cracking (SCC) behavior of an API X70 pipeline steel exposed to a brine solution was studied. The SCC process using simultaneously the slow strain rate stress test (SSRT) and electrochemical measurements was performed. Fracture surface analysis and secondary cracking were observed through a scanning electron microscopy (SEM). According to SEM fractography and SSRT results, the steel showed high SCC susceptibility with a brittle fracture and several secondary cracks without addition of inhibitor, whereas the addition of inhibitor to brine solution was effective to increase the SCC resistance of steel at concentrations of inhibitor of 50 and 100 ppm. A further addition of concentration of inhibitor had a negative effect on the mechanical properties of the steel. Electrochemical measurements results are in accordance with the SCC susceptibility, indicating that corrosion inhibitor film suppressed the anodic and cathodic reactions increasing the resistance to SCC until concentration of 100 ppm. Further addition of inhibitor aggravated the localized corrosion due to local desorption of inhibitor molecules. The Hilbert–Huang transform (HHT) analysis revealed the contribution of different corrosion process contained in the electrochemical current noise (ECN) signals at several inhibitor concentrations.

Inhibition Effect of Pseudomonas stutzeri on the Corrosion of X70 Pipeline Steel Caused by Sulfate-Reducing Bacteria.

Microbiologically influenced corrosion (MIC) is a common phenomenon in water treatment, shipping, construction, marine and other industries. Sulfate-reducing bacteria (SRB) often lead to MIC. In this paper, a strain of Pseudomonas stutzeri (P. stutzeri) with the ability to inhibit SRB corrosion is isolated from the soil through enrichment culture. P. stutzeri is a short, rod-shaped, white and transparent colony with denitrification ability. Our 16SrDNA sequencing results verify the properties of P. stutzeri strains. The growth conditions of P. stutzeri bacteria and SRB are similar, and the optimal culture conditions are about 30 °C, pH 7, and the stable stage is reached in about seven days. The bacteria can coexist in the same growth environment. Using the weight loss method, electrochemical experiments and composition analysis techniques we found that P. stutzeri can inhibit the corrosion of X70 steel by SRB at 20~40 °C, pH 6~8. Furthermore, long-term tests at 3, 6 and 9 months reveal that P. stutzeri can effectively inhibit the corrosion of X70 steel caused by SRB.

Piezomagnetic Behavior Corresponding to the Variations of the Toughness of X70 Steel Under Cyclic Loadings

The goal of this study is to investigate magnetic field characteristics corresponding to variations of the toughness of X70 pipeline steel under cyclic loading. After a series of stress-controlled cyclic loadings, the specimens were subjected to static tensile tests. Changes in the magnetic field were recorded simultaneously during the test. The results suggest that cyclic loadings will reduce the toughness of the material. The initial value and slope of the magnetic field-strain curve obtained in the static tensile test are related to the number of cyclic loadings. The evolutions of magnetic field and the stress-strain curve can reflect variations in the toughness of materials. Compared with the stress-strain curve, the magnetic field demonstrates the fatigue degradation process more markedly. The high sensitivity of the magnetic field to toughness may be used to estimate the degree of fatigue damage of steel.

Microstructure Characterization and Strengthening Mechanism Analysis of X100 Pipeline Steel

The strengthening mechanism of X100 high steel grade pipeline steel, including grain boundary strengthening, solution strengthening, precipitation strengthening, dislocation strengthening, and texture strengthening, was analyzed by the technics of scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), X-ray diffraction (XRD), physicochemical phase analysis, and so on. The results showed that the tested steel had a mixed structure of granular bainite and lath bainite, the average effective grain size was refined to about 1 μm by severe hot plastic deformation, the dislocation density was as high as 1.74 × 1015/m2, and the second phase precipitation was mainly (Ti, Nb)(C, N) in submicron scale and nanoscale NbC. Through orientation distribution function (ODF) orientation analysis, it was found that the tested steel had obvious anisotropy and had a strong rolling direction (RD) texture along the rolling direction compared with the 30° direction: {115}<110> and {113}<110>. After the quantitative analysis of strengthening mechanisms, it was found that the highest strengthening increment was caused by high-density dislocations in bainite of about 268 MPa, while the lowest strengthening increment was induced by precipitation particles of about 31 MPa.

Effect of Slow Strain Rates on the Hydrogen Migration and Different Crack Propagation Modes in Pipeline Steel

The slow‐strain‐rate test (SSRT) is the most commonly used method for evaluating pipeline steel in service environments. However, to accurately assess the sensitivity of steel to hydrogen, it is necessary to investigate the effect of different strain rates, taking into account microstructure‐influenced hydrogen migration. Herein, a hot‐rolled X70 pipeline steel sheet is investigated by a SSRT at different strain rates with and without synchronous hydrogen charging. The influence of the pearlite content and different strain rates on the hydrogen‐assisted crack propagation and hydrogen diffusion in pipeline steels is discussed. Using scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and hydrogen microprinting, the hydrogen atoms are observed to be easily segregated at the ferrite/pearlite (F/P) interface without external stress. Under loading, a higher strain rate results in lower hydrogen permeation content in steel, penetrating into pearlite and interacting with its internal vacancies, leading to transgranular fracture initiating from pearlite. At a low strain rate, the F/P interface is more vulnerable to hydrogen degradation, leading to intergranular crack mode along the interface and increased tendency to form secondary cracks. Therefore, strain rate–induced crack initiation and propagation characteristics should be considered during the SSRT.

Evaluation of Corrosion and Erosion-Corrosion Behavior of X65 Pipeline Steel in Flowing CO2-Saturated Electrolyte

In this study, the corrosion and erosion-corrosion behaviors of X65 pipeline steel in the flowing CO2-saturated electrolyte were electrochemically studied using a rotation disk system. The results showed that the accumulation of the Fe3C layer in the electrolyte without sand particles enhanced the cathodic reaction, increasing the corrosion rate. The increase in flow velocity facilitated the rapid accumulation of a thick Fe3C layer, which linearly increased the corrosion rate with increasing rotation speed. The sand impacts removed the corrosion product layer and broke the exposed Fe3C network, resulting in a negative synergy of erosion-enhanced corrosion. The erosion-corrosion negatively affected ferrites compared with the pearlites in an electrolyte containing sand due to the weaker erosion resistance.

Stress-based hydrogen damage model of X80 pipeline steel and its damage risk assessment under cathodic interference

In this paper, the crack propagation behaviors of X80 pipeline steel under different cathodic current conditions were investigated by constant displacement loading experiment of double cantilever beam (DCB) samples, and the subsurface hydrogen concentration rules were obtained by hydrogen permeation test. A hydrogen damage model based on the threshold stress intensity factor of hydrogen-induced cracking arrest was established for X80 pipeline steel. The hydrogen permeation data showed that in 0.5 mol/L H2SO4 + 0.2 g/L CH4N2S solution, the relationship between subsurface hydrogen concentration C0 and applied current density i satisfied the expression of C0/L∝ i when the current density was 1–10 mA/cm2. The relationship between the threshold stress intensity factor of hydrogen-induced cracking arrest KHSC and the subsurface hydrogen concentration C0 satisfied the expression of KHSC ∝ -lnC0. An analytical model of KHSC = -0.4648lnC0-1.5040 was proposed for the API X80 steel pipe used in the experimental. The KHSC value under cathodic interference was calculated according to the C0 value in the soil simulation solution, and the risk of crack growth was analyzed under service conditions.

Effect of Nb on microstructure and corrosion resistance of X80 pipeline steel

In this study, a series of χNb-X80 pipeline steels were obtained by adding different contents of Nb to X80 pipeline steel and after different cooling rates. The effects of Nb on the microstructure and corrosion resistance of X80 pipeline steel were studied by metallographic microscope, scanning electron microscope, differential scanning calorimeter, electrochemical corrosion, and salt spray corrosion. The results show that the high cooling rate will hinder the phase transformation, reduce the diffusion ability of Nb element at the grain boundary, inhibit the growth rate of ferrite grains, and refine the grains of the sample steel structure. The grain refinement effect is the best when the cooling rate is 40 °C/min. In addition, the reason why Nb improves the corrosion resistance of X80 pipeline steel is discussed from two aspects: the change of corrosion products and the effect of grain refinement. The analysis shows that Nb promotes the formation of a dense corrosion protective film, and this positive effect of the protective film overcomes the negative corrosion effect caused by the grain refinement caused by the precipitated Nb (CN), thereby enhancing the corrosion resistance of the substrate. The corrosion resistance is the best when the Nb content is 0.16 wt %.

In situ observation of deformation and failure behavior in the burn-through instability zone of in-service welding

Based on the in-situ high-temperature SEM and laser scanning confocal microscope (LSCM), the high-temperature plastic deformation and failure behavior of X65 pipeline steel at 1000℃ and 1200℃ were studied in this paper, and the strain evolution behavior in this process was analyzed by DIC technology. In this study, the precipitation and dissolution of carbide at the austenite grain boundary were observed during the in situ heating process. The external load showed a great effect on the growth of the grains, and the grains grew rapidly by swallowing each other. The grain size, material performance, and misorientation played an important role during the deformation and crack evolution. At high temperatures, cracks were mainly initiated and propagated in the position with a large plastic strain. The strain concentration showed a significant effect on crack initiation.

Microstructure and properties of X100 large-deformability pipeline steel based on heating on-line partitioning

It is often assumed that high strength and good plasticity cannot be obtained at the same time. However, a kind of X100 pipeline steel with a multiphase structure of bainite and fine M/A constituent has not only high strength and toughness but also excellent plasticity. In this paper, Heating on-line partitioning (HOP) was performed on a type of X100 pipeline steel to achieve the multiphase structure. Carbon atoms diffuse from bainite to austenite during the HOP process, improving the stability of austenite and increasing the volume fraction of retained austenite. Meanwhile, bainite laths widen and dislocation density drops, increasing the plasticity. On the other hand, carbides precipitation and the formation of martensite provide the steel with high strength.

High pH-SCC mechanism investigation of novel Nb/Ce-additional X100 pipeline steel

High pH-SCC introduces great risks to the service safety of X100 pipeline steel. The design of new Nb and RE composite regulated pipeline steel can help to reduce the high pH-SCC. By the addition of Nb and Ce elements into traditional pipeline steel, the toughness of the pipeline steel was enhanced while the sensitivity of high pH-SCC decreased under the action of cathode potential. Mechanism research indicated that the increase of Nb element inhibited the cathodic hydrogen evolution reaction and increased the number of irreversible hydrogen traps in the steel, thus improving the resistance of pipeline steel to high pH-SCC. The addition of Ce element inhibited the anodic dissolution and cathodic hydrogen evolution processes, and reduced the high pH-SCC sensitivity of pipeline steel by changing the solution and precipitation of Nb.

Hydrogen-Accelerated Fatigue of API X60 Pipeline Steel and Its Weld

In this work, the hydrogen fatigue of pipeline steel X60, its girth welds and weld defects were investigated through in situ fatigue testing. A novel in situ gaseous hydrogen charging fatigue set-up was developed, which involves a sample geometry that mimics a small-scale pipeline with high internal hydrogen gas pressure. The effect of hydrogen was investigated by measuring the crack initiation and growth, using a direct current potential drop (DCPD) set-up, which probes the outer surface of the specimen. The base and weld metal specimens both experienced a reduction in fatigue life in the presence of hydrogen. For the base metal, the reduction in fatigue life manifested solely in the crack growth phase; hydrogen accelerated the crack growth by a factor of 4. The crack growth rate for the weld metal accelerated by a factor of 8. However, in contrast to the base metal, the weld metal also experienced a reduction of 57% in resistance to crack initiation. Macropores (>500 µm in size) on the notch surface reduced the fatigue life by a factor of 11. Varying the pressure from 70 barg to 150 barg of hydrogen caused no difference in the hydrogen fatigue behavior of the weld metal. The fracture path of the base and weld metal transitioned from transgranular and ductile in nature to a mixed-mode transgranular and intergranular quasi-cleavage fracture. Hydrogen accelerated the crack growth by decreasing the roughness- and plasticity-induced crack closure. The worst case scenario for pipelines was found in the case of weld defects. This work therefore highlights the necessity to re-evaluate pipelines for existing defects before they can be reused for hydrogen transport.

The mechanism of inhibitive effect on hydrogen permeation of X70 steel by lanthanum microalloying: Enhanced kinetics of desorption

In this work, electrochemical hydrogen permeation tests were carried out to obtain the steady-state hydrogen permeation current of X70 pipeline steel in acid environment and alkaline electrolyte with applied cathodic overpotentials simulating the service conditions of pipelines. It is shown that La-microalloying can efficiently reduce the steady-state hydrogen permeation current density while maintaining the same mechanical performance. The experimental permeation data were fitted with Iyer-Pickering-Zamanzadeh (IPZ) and surface effect model to analyze the inhibitive mechanism on hydrogen permeation, and the results depicted that La element on the material surface greatly facilitates the desorption process of hydrogen atoms. In addition, the calculated hydrogen diffusion coefficient was found smaller after La microalloyed, which can be ascribed to the larger hydrogen trap density. It is suggested that La-microalloying can mitigate hydrogen damage of X70 pipeline steel in both acidic environment or under cathodic protection.

Residual strength prediction of X80 steel pipelines containing group corrosion defects

As subsea oil and gas pipelines are corroded by moisture, soil, and other external factors, their surfaces develop groups of corrosion defects, which are prone to stress concentration and affect the residual strength of the pipeline. To this end, a finite element (FE) model of an X80 pipeline containing group corrosion defects is established here using ABAQUS. Considering the influence of various defect sizes on the residual strength of the pipe, 46 sets of failure data for group corrosion pipes with different geometries and 364 sets of maximum von Mises stresses versus internal pressure for different operating conditions were obtained. The accuracy of the FE model was verified using burst tests. The residual strength prediction model of the pipes was obtained by 1stopt software. The results show that the key factor affecting the residual strength of pipes containing group corrosion defects is the depth of the deepest defect and the strength of the interaction between the group corrosion defects. Based on the DNVRP-F101 standard, a more accurate method for calculating the failure pressure of group corrosion pipes was obtained by introducing correction factors. The results of this study can provide theoretical support for the safe management of group corrosion X80 pipelines.

Corrosion behavior and mechanism of X80 pipeline steel welded joints under high shear flow fields

The internal-pipeline local corrosion in the welded joint region has been a widely concerning issue, particularly under the synergistic effect of high shear stress and electrochemical corrosion, which can easily result in pipeline rupture. Classical electrochemical testing techniques and wire beam microelectrode (WBE) are used to investigate the local corrosion behavior of X80 steel welded joints in a CO2-saturated NACE solution at different flow rates (velocities of 3 m/s, 5 m/s and 7 m/s), and the corrosion product composition and characteristics are analyzed via scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and three-dimensional (3D) measuring laser microscopy. The results show that different welded joint zones exhibit different corrosion degrees. The heat-affected zone (HAZ) shows the worst corrosion resistance, whereas the base metal (BM) and weld metal (WM) show similar corrosion resistances. The HAZ is an anode that corrodes unsatisfactorily at high flow rates, and the enhanced wall shear stresses peel off part of the dense corrosion product film, promoting the development of local corrosion. Therefore, the HAZ zone is a weak link in the X80 steel welded joints. This study provides scientific guidelines for the corrosion protection of long-distance oil & gas pipelines.

Research on Dynamic Alternating Current Corrosion Behavior of X65 Pipeline Steel Under Cathodic Protection

An indoor corrosion simulation experiment device was built to explore the influence of dynamic alternating current (AC) interference on the corrosion behavior of pipeline steel under different cathodic protection (CP) levels. When the interference time in each interference cycle is 350 s, the dynamic AC corrosion rate was comparable to the steady AC corrosion rate. For JAC of 30 A/m2, the corrosion rate of the specimen can be controlled below 0.0254 mm/y when the CP current density is higher than 0.06 A/m2. As JAC is greater than or equal to 100 A/m2, with the increase of the CP current density, the corrosion rate of the specimens decreased first, then increased and decreased again. In this paper, the real-time AC/DC potential on the surface of the specimen is monitored, combined with the Pourbaix diagram and the evolution of corrosion product film. The dynamic AC corrosion mechanism under different CP levels was explored.