API X70 Research Articles

Temperature effects on the resistance capacity of API X60 pipe elbow under bending moment using X-FEM method

Temperature effects on the resistance capacity of API X60 pipe elbow under bending moment using X-FEM method

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

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

Experimental investigation on the mechanical, microstructure XRD, SEM and corrosion analysis study of heat-treated API X70 steel

Experimental investigation on the mechanical, microstructure XRD, SEM and corrosion analysis study of heat-treated API X70 steel

Artificial neural network and YUKI algorithm for notch depth prediction in X70 steel specimens

The presence of notches directly influences the material's degree of resistance to fracture, as each notch is defined by its size and location in the structure. In this study, we present a methodology using an optimization technique that allows us to predict the notch depths based on one of the most important mechanical parameters, namely the maximum stress for each notch depth. This study starts with the experiments of standard pipe specimens, which have notches with different depths. A numerical model, using GTN parameters, is created based on the experimental model and its results are presented in form of stress and strain curves of API X70 steel specimens under uniaxial tensile tests. The high-performance numerical models used to simulate the experimental model consider a considerable number of different cases. The study is concluded by choosing the best optimization technique among different proposed algorithms, namely NN-YUKI, NN-JAYA, and NN-EJAYA. The validation of models and their accuracy is determined by comparing the outputs of NN-YUKI, NN-JAYA, and NN-EJAYA with experimental and numerical data. The obtained results using NN-YUKI determine the best optimization parameters and provide a good prediction of notch depth. This methodology gives an insight into the notch size under different loading conditions and is applicable to large structures like pipes under various loadings.

Non-destructive evaluation of aging in welded pipeline X60 and X65 by thermoelectric power means

In this investigation, the sensibility of the thermoelectric power (TEP) to the aging condition of API X60 and API X65 steel pipeline welded joints was evaluated. Specimens of both API welded joints were artificially aged at 300 °C for 3, 7, 9, 18, 30 and 45 h, the microstructural evolution was assessed via optical microscopy (OM) and scanning electron microscopy (SEM). Image analysis revealed no significant changes in the microstructure with respect to the aging time. Vickers micro-hardness evaluation showed that both welded joints reach a maximum hardness value after 3 h of artificial aging followed by a reduction in its value in the next aging conditions. TEP was measured using the hot tip technique applying different hot tip temperatures (55, 60, 65, 70 °C), where higher temperature values showed to increase the sensibility of the technique to detect microstructural changes that affect micro-hardness and where not possible to observe via OM and SEM. TEP and micro-hardness exhibit an opposite correlation, which was confirmed calculating the Pearson's correlation coefficient (r). The correlation coefficient decreases when higher hot tip temperatures where employed to measure TEP. The good correlation between TEP values and micro-hardness allows to use TEP measurement as a prediction tool of material micro-hardness.

Development and Application of a Thermal Microstructure Model of Laminar Cooling of an API X70 Microalloyed Steel

A thermal microstructure model of laminar cooling of X70 microalloyed steel skelp was developed to predict the effect of the laminar cooling temperature profile on the through thickness skelp microstructure. Plant trials using infrared video imaging were undertaken to establish the laminar cooling conditions prevalent in the industrial cooling system. The infrared video temperature measurements were used to develop a finite element thermal model of the skelp transiting the entire laminar cooling system. Dilatometer testing of the X70 steel with cooling rates ranging from 1 °C/s to 120 °C/s was undertaken to develop the CCT curve and to quantify austenite decomposition. The predicted thermal profile from the finite element model and the phase transformation behaviour were combined into a thermal microstructural model capable of predicting the phases that would develop through the skelp thickness as a function of the laminar cooling profile. The predicted through thickness microstructures were verified from electron backscattered diffraction (EBSD) phase analysis of industrially produced API X70 skelp.

Fracture-toughness estimation from small-punch test in hydrogen exhibiting ductile and ductile–brittle fracture modes

In this study, an energy-based fracture toughness estimation method based on a small-punch test in a hydrogen environment, exhibiting either ductile or combined ductile and brittle fracture modes is proposed. For the ductile fracture mode, the energy term due to gas pressure in the small-punch test in hydrogen environment is simply added to the existing energy-based fracture toughness estimation equation. For the combined ductile and fracture mode, modified equations for the plastic energy term are proposed to correct overestimation due to brittle cracking. The estimated fracture toughness values are shown to consistent with the published API X70 and X42 test data.

Investigation of erosion-corrosion failure of API X52 carbon steel pipeline

A failure analysis of API X52 steel pipeline was conducted. The investigation included complete material characterizations using tensile and hardness testing, optical microscope, SEM, and EDS. The main failure occurred in the downstream pipe located near the welded joint at the elbow outlet instead of elbow which was interesting. The main mechanism of failure was found to be erosion-corrosion mechanism that caused breakdown of the protective FeCO3 film, thinning of the downstream pipe, and finally failure. It is believed that the erosion-corrosion was induced by sand impingement due to turbulent flow that was promoted by sudden change in the flow cross section between the elbow inlet and upstream pipe and poor welding quality of joint at the elbow outlet.

Numerical investigation of the mechano-electro-chemical effect of X100 buried pipelines with pre-existing corrosion defects

This study investigates the corrosion kinetics and crack propagation in buried transmission pipelines made of high-strength low alloy steel API X100. Despite its cost-effectiveness and ability to withstand high operating conditions without increasing pipe wall thickness, the corrosion kinetics in near-neutral pH environments for this steel grade is not fully understood. To address this gap, two numerical models were developed. The first model, using COMSOL Multiphysics v5.6, showed higher electrolyte potential at the corrosion defect center due to stress-induced defect growth, increasing corrosion susceptibility. The second model, employing the XFEM approach, evaluated crack initiation, propagation, and von Mises stress distribution along the crack path. This research contributes to a better understanding of corrosion and crack behavior in corroded pipelines, aiding in their performance improvement in near-neutral pH soil environments.

Experimental and Numerical Fracture Toughness Evaluation of Spiral Seam Weld of API X65 Steel

In this research fracture toughness of spiral seam weld of API X65 is measured through the ASTM E1820 standard recommendations. According to thin-wall pipe of API X65 in this research, specimen sizes could not satisfy the plain strain condition of ASTM E399 therefore, indirect method is accomplished by evaluating the crack tip opening displacement. According to the nature of welding procedure and inhomogeneous probable defects in the different regions of seam weld, δ-R curve with multi-specimen technique of single-edge notched bend (SENB) specimens is applied for test procedure in this research. The measured CTOD and K1C are 0.23 mm and 265 MPam3/2 respectively. Furthermore, Three-dimensional finite element method numerical evaluation of crack propagation with GTN model has been performed. Good agreement with the other researches was observed for CTOD and fracture toughness of tested material. The difference was about 10 percent.

Anticorrosion Investigation of New Diazene-Based Schiff Base Derivatives as Safe Corrosion Inhibitors for API X65 Steel Pipelines in Acidic Oilfield Formation Water: Synthesis, Experimental, and Computational Studies.

The current study examines the evaluation of diazene-based Schiff base derivatives, namely, 4-((E)-(3-((E)-(hexylimino)methyl)-4-hydroxyphenyl)diazenyl)benzonitrile (S1) and 4-((E)-(3-((E)-(dodecylimino) methyl)-4-hydroxyphenyl)diazenyl)benzonitrile (S2). The structure elucidation of prepared the Schiff base compounds was performed by FTIR, 1H NMR, and 13C NMR. In addition, the corrosion inhibition capacity of these compounds was investigated for API X65 steel pipelines in 1 M HCl utilizing gravimetric and electrochemical methods. By conducting the experimental investigations at various doses, it was possible to assess the inhibition effectiveness and adsorption behavior of S1 and S2. With increasing concentration, both inhibitors became more effective at inhibiting corrosion. S1 and S2 suppressed both cathodic and anodic processes, as shown by the potentiodynamic polarization study. The charge transfer resistance (Rct) increased when S1 and S2 concentrations increased, according to the electrochemical impedance analysis (EIS) data. According to the Langmuir isotherm model, the adsorption of S1 and S2 inhibitors on carbon steel was discovered based on gravimetric measurements. The results were confirmed by theoretical data in addition to the experimental tests for the presence of S1 and S2 inhibitor films over the API X65 carbon steel surface.

Finite element simulation method for combined Ductile-Brittle fracture of small punch test in hydrogen

This paper presents a simulation method for combined ductile–brittle fracture of small punch (SP) test in hydrogen and application to test data of API X70 steel. For ductile fracture simulation, the multi-axial fracture strain damage model determined from un-embrittled material with the hydrogen-embrittlement constant determined from SP test in hydrogen is used. To simulate brittle fracture, the critical stress method is proposed, where the critical stress is determined using the V notch round bar tensile test in hydrogen. The determined models are applied to simulate the SP test in hydrogen showing combined ductile and brittle fracture mode. Simulation can well reproduce not only the load–displacement curve but also the circumferential ductile cracking, followed by radial brittle cracking, observed in the test.

Feasibility of orbital friction stir welding on clad pipes of API X65 steel and Inconel 625

Orbital friction stir welding (FSW) has been applied to clad pipes, which is certainly of interest to the oil and gas industry. In this context, an FSW system capable of performing sound joints in one pass with full tool penetration was developed. Orbital FSW was executed in 6 mm thick API X65 PSL2 steel clad pipes with 3 mm thick Inconel 625 using a polycrystalline cubic boron nitride (pcBN) tool. The metallurgical and mechanical properties of the joints were investigated. Sound joints with axial forces of 45–50 kN, tool rotational speeds of 400–500 rpm, and a welding speed of 2 mm/s were obtained, illustrating that the developed system can perform FSW joints without volumetric defects.

An evaluation of mechanical properties and estimation of environmental reduction factors in welded API X70 steel pipeline in natural seawater

Due to the detrimental effect of damage induced by seawater in pipeline structures, there is a need to investigate the effects of natural seawater and air environments on mechanical properties of representative pipeline materials, to obtain useful data for estimation of their service lives. Hence, in this work, a X70 steel pipeline plate was welded using submerged arc welding technique; and subjected to air and natural seawater environments. Test specimens were soaked in seawater for twelve months at 28 °C. The parent plates, weld regions and the heat affected zones were investigated by evaluating their mechanical properties and fracture surfaces. The experimental findings revealed that the tensile strengths of parent and weld were 634.00 MPa and 674.00 MPa respectively, while the compressive stresses were 750.10 MPa and 750.40 MPa respectively with highest hardness value of 239HV. The findings also revealed that weld area and heat affected zone depend on material thickness, heat input and possible effect of residual stresses in the weldment. The fracture surfaces of test specimens showed combination of brittle and ductile failure mechanisms. Comparison of the test results revealed that seawater had significant effect on the mechanical properties and surface morphology of the API X70 steel pipeline with respect to immersion time.

Synthesis of Ammonium-Based ILs with Different Lengths of Aliphatic Chains and Organic Halogen-Free Anions as Corrosion Inhibitors of API X52 Steel.

In the present work, synthesis and characterization of 15 ionic liquids (ILs) derived from quaternary ammonium and carboxylates were carried out in order to proceed to their evaluation as corrosion inhibitors (CIs) of API X52 steel in 0.5 M HCl. Potentiodynamic tests confirmed the inhibition efficiency (IE) as a function of the chemical configuration of the anion and cation. It was observed that the presence of two carboxylic groups in long linear aliphatic chains reduced the IE, whereas in shorter chains it was increased. Tafel-polarization results revealed the ILs as mixed-type CIs and that the IE was directly proportional to the CI concentration. The compounds with the best IE were 2-amine-benzoate of N,N,N-trimethyl-hexadecan-1-ammonium ([THDA+][-AA]), 3-carboxybut-3-enoate of N,N,N-trimethyl-hexadecan-1-ammonium ([THDA+][-AI]), and dodecanoate of N,N,N-trimethyl-hexadecan-1-ammonium ([THDA+][-AD]) within the 56-84% interval. Furthermore, it was found that the ILs obeyed the Langmuir adsorption isotherm model and inhibited the corrosion of steel through a physicochemical process. Finally, the surface analysis by scanning electron microscopy (SEM) confirmed less steel damage in the presence of CI due to the inhibitor-metal interaction.

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.

Impact of the correlation between random variables on the reliability assessment of the corroded pipelines

In the present work, an Algerian pipeline made of API X70 steel, used for transporting gas and subjected to corrosion attack for three decades, was investigated. Using an intelligent inspection tool, the sizes and orientations of the defects were determined to analyze and improve the accuracy of reliability and/or probability of failure estimates for the damaged pipelines. A probabilistic methodology has been developed to assess the reliability index and the sensitivity of each random variable, within the limit state function, of a gas-transporting steel pipeline that has been corroded for three decades. The reliability analysis utilizes the Second Order Reliability Method, which is based on the BFGS algorithm. In addition, the corrosion defect depth, pipe wall thickness, and corrosion defect length are the most dominant variables within the limit state function, followed by ultimate stress and operating pressure, respectively. Meanwhile, for a failure scenario, thus, it is essential to include a potential parameter such as the correlation coefficient between random variables within the objective function during reliability assessment. For instance, not taking into account the correlation between random variables can lead to an overestimation of the reliability index by 8.89% for a defect depth to wall thickness ratio d/t of 20%. This overestimation increases to 19.16% when the d/t ratio increases to 70%. If the correlation coefficient is significant, it can cause an increase of 8.86% in the error of reliability index assessment for a defect with a depth to wall thickness ratio of 20%, and an increase of 14.58% for a defect with a ratio of 50%. Besides, these avoid the conservative practice resulting from the negligence of the existing correlation between random variables within the limit state function. Hence, considering the correlation coefficients during reliability assessment contributes to setting optimal maintenance schedules for pipelines made of steel under localized corrosion attack.

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.

A synthesized pyrimidine derivative with highly efficient long-term corrosion protection for API X60 steel in CO2-saturated NACE brine ID196 under hydrodynamic condition

This research investigates the CO2 corrosion inhibition characteristics of a synthesized pyrimidine derivative whose molecular structure is embellished with nitrogen-based functional groups with the intention of achieving highly effective and stable film formation, at low doses, after prolonged corrosion period under turbulent hydrodynamics. For this purpose, 5-(4-(dimethylamino)phenyl)-2,7-dithioxo-2,3,5,6,7,8-hexahydropyrimido[4,5-d]pyrimidin-4(1H)-one (DPP) was synthesized using the one-pot method, and investigated as inhibitor against the corrosion of API X60 steel after instantaneous and prolonged (72 h) immersion in CO2-saturated NACE ID196 brine under 1000 rpm rotation speed. Results from potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements show that DPP is a mixed-type inhibitor which lowers the double layer capacitance and rate of charge transfer across the steel-solution interface with 97% efficiency. Its instantaneous adsorption blocks the steel surface from any noticeable microstructural damage, based on scanning electron microscopy (SEM) characterization. After prolonged exposure (72 h), the uninhibited steel experiences enhanced resistance, which inversely depreciated the DPP efficiency to > 73%. With DPP, however, the steel is significantly protected against surface microstructural degradation, based on SEM assessment. Computational modeling with density functional theory (DFT) and molecular dynamics simulation (MDS) provided molecular-level confirmation of the experimental results.

Comparison between a predicted and an experimentally measured residual stress field generated by side-punching of API X65 steel

A residual stress field was generated by a circular, flat-ended, rigid punch indenting a thick test specimen extracted from X65 grade-controlled-rolled pipeline steel. Laboratory X-ray diffraction was used to measure residual stress field the near-surface, whereas the contour method and neutron diffraction were used to quantify the through-thickness residual stress field. A numerical method was proposed to account for gauge volume variation which allowed a direct comparison of the Finite Element prediction with the experimental measurements. A good agreement between the measurements and prediction was observed, showing that the through-thickness compressive residual stress reaches the highest magnitude in the centre of the specimen. The validated results can be used with confidence for residual stress-crack interaction studies in single-edge notched bend SEN(B) and single-edge notched tension SEN(T) fracture specimens which are common in the oil and gas industry due to the inherited close level of constraint experienced in a pipe.