NS4 Solution Research Articles

Resilience analysis of stress corrosion cracking in AISI 4340 steel under varying industrial electrochemical conditions

Stress Corrosion Cracking (SCC) presents a substantial challenge within industries where materials confront both mechanical stresses and corrosive environments. This work comprehensively examines SCC, incorporating the collection and analysis of a diverse dataset. The dataset encompasses pivotal parameters, including time to failure, corrosion rates, and electrochemical data. These parameters are meticulously garnered through Slow Strain Rate Testing on carefully prepared smooth, round tension specimens. The experiments are vigilantly overseen through a condition-based data acquisition and logging system, employing various Potentiostatic loads to mirror real-world electrochemical conditions. This research elucidates the intricate interplay between mechanical stresses, electrochemical processes, and corrosive conditions, rendering crucial insights for industries dependent on material integrity amidst formidable environmental challenges. Findings show that AISI 4340 Steel specimens exposed to a +400mV potential in NS4 solution exhibit an extended time to failure of approximately 7.4 days. Conversely, a −1200mV potential in NS4 accelerates the failure to around 5.24 days. In a 3.5wt% NaCl solution at 0mV, the time to failure is approximately 5.76 days. On the other hand, an applied potential of +400mV increases the failure time to approximately 6.16 days. And an applied potential of −1200mV accelerates the failure time to approximately 4.77 days. Specifically, the study reflects on structures submerged in water and those buried underground, represented by NS4 (Near Neutral Soil Simulating Solution) and 3.5w.t.% NaCl solutions, simulating real-world corrosive conditions. Through a deeper comprehension of SCC, industries can better anticipate and mitigate the risks associated with material failure in harsh environmental conditions, advancing the safeguarding of critical infrastructures.

Effect of Temperature on the Corrosion Behavior of a Al2Cr5Cu5Fe53Ni35 Multi-Principal Element Alloy (MPEA) in Simulated Soil Environments

The effect of varying temperatures (15, 35, and 45 °C) on the corrosion behavior of a new single-phase distorted face-centered cubic (fcc) Al2Cr5Cu5Fe53Ni35 multi-principal element alloy (MPEA) was studied in simulated soil environments (NS4 solution). X-ray diffraction and electron backscattered diffraction were used to confirm the presence of a single phase throughout the microstructure. Electrochemical tests such as electrochemical impedance spectroscopy and linear polarization resistance were performed to evaluate the interfacial behavior and corrosion rate at various test conditions. Additionally, cyclic potentiodynamic polarization (CPP) tests were also carried out at the selected temperatures to study the pitting behavior of the MPEA. Surface characterization techniques such as X-ray photoelectron spectroscopy and scanning electron microscopy were used to identify the nature of the passive film formed in such complex materials as well as study the pitting characteristics after CPP testing. A stable passive film was found to be present all tested temperatures with the absence of preferential sites for pitting due to homogenous element distribution.

Modeling 3D finite element analysis of a semi-elliptical crack on stress corrosion cracking of API X52 pipeline

In this study, an external semi-elliptical crack was modeled in a 3D API 5 L X52 pipeline with stress corrosion cracking (SCC). To make the crack, the finite element method (FEM) was used to obtain the failure pressure (Pf) and its mechanical behavior. The longitudinal crack had a constant length (2c) and varied with depth (a). The properties of X52 steel subjected to SCC using the slow strain rate technique (SSRT) were considered. True stress-strain curves were obtained in air and in an NS4 solution with pHs of 3.5 and 9.5 at temperatures of 25 and 50 °C. According to the SCC index calculated from the mechanical properties of the SSRT, the X52 steel is susceptible to SCC at pH 3.5 and 50 °C. The mechanical properties of the tensile test using the stress-strain curves decreased as the pH and temperature changed, compared to those carried out at room temperature. This was due to the corrosion and hydrogen embrittlement produced by the solution on the X52 steel. The failure pressure is sensitive to the stress-strain curve; if the stress-strain curve decreases, the failure pressure also decreases. Corrosion defects, such as longitudinal cracks in X52 steel, which could be susceptible to SCC in an NS4 solution, decrease the failure pressure (Pf) and its capacity to withstand pressures of up to 75 % in pipe-grade steel that transports hydrocarbons.

Synergistic effect of microorganisms and a direct current electric field on X70 steel corrosion in a near-neutral solution

In this paper, the corrosion behavior of X70 steel in the near-neutral simulated soil solution (NS4 solution) under the synergistic effect of sulfate reducing bacteria (SRB) and a direct current electric field (DCEF) were explored. The corrosion rate was determined with the electrochemical technique and the corrosion morphology and corrosion products were respectively characterized by SEM and XPS. In the sterile solution, corrosion morphology of X70 steel was pitting and the corrosion rate increased with the increase in DCEF intensity and exposure time. When DCEF was absent, the corrosion rate of X70 steel in bacterial NS4 solution was faster than that in the sterile solution and the corrosion morphology was general corrosion. The acceleration effect of DCEF on corrosion was more significant than that of SRB. Under the synergistic effect of SRB and DCEF, when DCEF intensity increased below 500 V/m, the metabolic activity of SRB was gradually enhanced and the corrosion rate of X70 steel decreased. The protective effect of biofilm weakened the acceleration effect of DCEF on corrosion and the corrosion behavior was controlled by SRB corrosion. When DCEF intensity increased above 1000 V/m, SRB cells were inactivated and the corrosion rate of X70 steel increased. The corrosion behavior of X70 steel was controlled by DCEF. Based on the above research results, preventative actions were proposed.

Full‐scale testing of near‐neutral pH stress corrosion cracking growth behavior of a vintage X52 oil pipe

AbstractThis study presents an experimental investigation conducted on a 40‐year‐old vintage X52 oil pipe segment to assess the growth behavior of near‐neutral pH stress corrosion cracking (SCC). Six cracks were introduced on the pipe specimen, each of which was associated with a unique combination of metallurgical and environmental condition. SCC growth was evident in two base metal cracks respectively exposed to C2 and NS4. Stress intensity factors at the two cracks were evaluated using extended finite element method. Near‐neutral pH environment effects were observed to have a more pronounced effect on the stress intensity factor threshold for growth than on the growth rate. Higher stress levels and aging likely contribute to the difference in growth rates of different cracks. Electrochemical analysis suggests the corrosion‐crack propagation interplay, with a faster corrosion in the NS4 solution than that in the C2 solution consistent with the observed slower crack growth in NS4.

Stress corrosion cracking under extreme near-neutral GCC conditions, parametric and comparative study using phase field modeling

Stress Corrosion Cracking (SCC) is a failure mechanism that occurs when certain materials are subjected to both external or residual stresses and corrosion. This combined effect leads to the development of cracks in the susceptible materials. Submerged steel pipelines in the petroleum sector are built of low-alloy steels having a ferrite-cementite composition, including API 5L X70. Such materials are sensitive to SCC damage in aqueous systems. The film rupture dissolution repassivation (FRDR) process is used in this study to evaluate the cracks and pits growth in oil and gas pipelines in the Gulf area under diverse SCC environmental conditions. The SCC crack propagation and pit growth under near-neutral environmental conditions were analyzed using phase field modelling. X70 steel under NS4 the solution was used for the analysis to represent the anodic dissolution film rupture mechanism. A parametric study was done to study the impact of different electrochemistry and phase field parameters on crack growth behaviour. The study assess the susceptibility to SCC caused by an pit by employing diverse settings to evaluate the impact of corrosion parameters and the interaction among the FRDR mechanism. The corrosion rates are influenced by the interface kinetics coefficient (L), which exhibits an accelerated effect as L increases. This transition from fracture-controlled to dissolution-controlled SCC growth occurs until the system reaches the diffusion limit, beyond which further increases in L do not significantly impact corrosion rates. Moreover, higher values of the kinetic coefficient (k) advance the creation of SCC cracks at the crack front, resulting from corrosion originating from pitting at the crack mouth. This process leads to the refinement of the pit and its transformation into a crack. A comparison analysis was utilized to validate our simulation under a near-neutral NS4 solution for X70 steel by correlating the findings with other numerical methods for crack growth utilizing the same material and environmental parameters. The results show decent agreement with the comparative study.

Corrosion resistance and mechanism of X100 pipeline steel laser-metal active gas hybrid welds with Cr containing welding wire in NS4 solution

The corrosion mechanism of pipeline steel laser-metal active gas (MAG) hybrid welds have been widely concerned with its applied in pipeline welding. The corrosion mechanism of X100 pipeline steel laser-MAG hybrid welds with Cr containing welding wire in NS4 solution was investigated. The corrosion products of weld metal (WM) had a double-layer structure, of which the outer and the inner layer were composed of FeOOH and Cr(OH)3, respectively. Compared with the base metal (BM), WM had higher Cr content and more homogeneous microstructure, so it can form dense corrosion layer, making its corrosion resistance reach the level of the BM.

Effects of cathodic protection potential on microbiologically induced corrosion behavior of X70 steel in a near-neutral pH solution

Sulfate reducing bacteria (SRB) are considered as one of the main causes for the failures of buried metal pipes. Although many researchers reported that more negative cathodic protection potential was required in environments containing SRB, SRB would increase the concentration of hydrogen adsorbed on steel surface and thus lead to hydrogen embrittlement. In the study, the optimum cathodic protection (CP) potentials of X70 steel in bacterial and sterile media were evaluated with electrochemical impedance spectroscopy. The morphology and composition of corrosion products were characterized by a scanning electron microscope (SEM), an energy dispersion x-ray spectrometer (EDS), and an x-ray photoelectron spectrometer (XPS). The corrosion morphology of X70 steel in NS4 medium was pits and the corrosion in the bacterial medium was more serious than that in the sterile medium. The corrosion products of X70 steel were FeOOH and Fe2O3 in the sterile medium, whereas its corrosion products in the bacterial medium were FeOOH and FeS. When CP potential was −775 mV, SRB growth was promoted and the optimal protection effect on X70 steel was achieved in the bacterial NS4 medium. Pits were still observed under the biofilm and the corresponding corrosion mechanism was extracellular electron transfer (EET). When CP potential was −875 mV, X70 steel realized the optimal protection in the sterile NS4 solution. However, CO2 hydrolysis and SRB metabolism in the bacterial medium resulted in hydrogen-induced pits. When CP potential was −1025 mV, the growth of SRB was inhibited and severe hydrogen evolution corrosion occurred on X70 steel in bacterial and sterile NS4 media. The optimal CP potential for pipeline steel in the sterile medium may lead to hydrogen corrosion in the bacterial medium when H+ concentration was high.

Ispitivanje zavarenih spojeva kontrolisanog valjanog čelika X70 za gasovod dugog radnog veka

The complex properties (mechanical, microstructure, and electrochemical) of controllable rolling X70 steel pipes of the main gas pipeline with a diameter of 1420 mm after an operation for 20 years and emergency reserve pipe after a similar period of storage were studied. Taking into account specified heterogeneity caused by the technological effect on X70 steel of controllable rolling, it is difficult to draw unequivocal conclusions about the effect of operational work on changes in the condition of welded joints of investigated pipes. It was established that operating loads did not significantly affect the characteristics of base metal and welded joints. Electrochemical properties (corrosion potential, hydrogen recovery potential, anodic curves slopes) of long-term operated pipes of different manufacturers (Ukraine, France) and stock pipes in NS4 solution are similar. Due to the high reserve of impact viscosity at standard temperature conditions, investigated pipes are characterized by satisfactory resistance against breaking.

Corrosion mechanism and damage characteristic of Q235B steel under the effect of stray current in NS4 simulated soil solution

Dynamic direct current (DC) may cause severe electrochemical corrosion on buried steel pipelines near urban rail transits. In this paper, the corrosion behavior of Q235B steel under dynamic DC interference was carried out in NS4 simulated soil solution (NS4 solution) including potassium chloride (KCl), sodium bicarbonate (NaHCO3), calcium chloride (CaCl2), Magnesium sulfate heptahydrate (MgSO4.7 H2O) and deionized water. The electrochemical corrosion behaviors of Q235B steel in NS4 solution were studied by means of potentiodynamic polarization (Tafel curve) and electrochemical impedance spectroscopy (EIS) techniques. Dynamic DC was simulated by four types of applied current according to the leakage current rule of rail trains arriving at and departing from the platform. The results of Tafel curves showed that Q235B steel exhibits a decrease in corrosion resistance with increasing applied current density, and anodic reaction exhibited active dissolution controlled by charge transfer. EIS results indicated that Nyquist plots of samples included double capacitive arcs and exhibited Warburg impedance characteristics caused by the concentration gradient. Weightlessness measurement showed that the average corrosion rates of four types of samples were 1.0, 1.4, 2.0, and 2.5 g.cm−2. d−1, respectively. In addition, the corrosion morphology indicated that samples featured in pitting corrosion, which was correlated to applied dynamic DC values and counts, and corrosion products were Fe3O4 and Fe (OH)3. Finally, the study shows that corrosion of buried steel pipelines is related to rail train arriving types and counts.

Evaluation of the green inhibitor effect on the corrosion of pipeline steel in NS4 medium

Prospects for the use of ascorbic acid as a green corrosion inhibitor of low-alloy steels (17H1S steel) in the model environment NS4 was studied. The influence of ascorbic acid concentration on the potential vs time dependence was investigated. The inhibition effect of ascorbic acid in concentration range 0.1–1.5 g/l was also examined using weight loss and electrochemical methods. The optimal concentration of ascorbic acid for protection of the low-alloy 17H1S steel in the NS4 solution against corrosion was defined.

Corrosion Study and Control of an A-36 Steel Immersed in Chloride Solutions Using a Laboratory Developed Prototype

The corrosion of ASTM A-36 steel was studied in three electrolytes, NaCl, seawater, and NS4 solution, using the Linear Polarization Resistance and Electrochemical Impedance Spectroscopy technique for twenty days. At the same time, variations in the pH of the solution were recorded daily. To control corrosion of the steel an electronic prototype for an impressed current cathodic protection system (ICCPS) was developed in the laboratory taking into account current demand measurement. The prototype was developed with an Arduino UNO board and its modules. In the present work, the operation of the prototype controlling corrosion of A-36 steel immersed in NS4 solution is reported during 15 days of continuous exposure.

Experimental and quantum chemical studies of some derivative of decahydroacridinedione-1,8 as corrosion inhibitor of steel 17 gs in ns4 solution

The use of inhibitors remains one of the most effective and economically sound methods of corrosion protection in various aggressive environments. Since universal inhibitors do not exist, effective inhibitors or compositions should be developed for each individual case. The inhibitory properties of N – phenyl – decahydroacridindiones – 1,8 in groundwater imitats were investigated in this research. Inhibitory properties has been studied by the use of the electrochemical and gravimetric methods.

Effect of Acicular Ferrite and Bainite in API X70 Steel Obtained After Applying a Heat Treatment on Corrosion and Cracking Behaviour

The effect of acicular ferrite (AF) and bainite (B) obtained by heat treatment (HT) applied to an API X70 steel on corrosion resistance and stress corrosion cracking (SCC) susceptibility was evaluated through polarization curves and slow strain rate tests respectively, in NS4 solution and congenital water (CW). The HT was carried out at 1050 °C for 15 and 30 min followed by water quenching. Change of ferrite–perlite to AF and B was observed as result of heat treatment applied to X70 steel. Effect of HT time in terms of microstructure obtained was analysed. The mechanical properties obtained by the HT are higher than X100 steel. HT-30 min improve the corrosion resistance of X70 steel exposed to both solutions, which are related to coarse and homogeneous microstructure of AF and B. Localized corrosion was observed in the steel exposed to both solutions. HT-15 min improve mechanical properties and higher content of fine AF, but decreases SCC resistance. Steel with higher content of fine AF microstructure is more susceptible to SCC. SCC indexes revealed that the heat-treated steel could be susceptible to SCC in CW confirmed by the secondary cracks observed. The SCC mechanism was hydrogen embrittlement. Meanwhile, steel HT by 15 min exposed to NS4 solution could be susceptible to SCC. Crack growth rate was higher in steel HT by 15 min, which are related to more fine and brittle AF microstructure.

The influence of external and internal factors on stress corrosion cracking of low-alloyed pipe steel

The article presents investigation results of the regularities of stress corrosion cracking (SCC) of controllable rolling X70 pipeline steel under the influence of various factors: corrosion-active environment, potential, pre-accumulated stresses, periodic wetting, etc. Factors, acting in the conditions of the gas pipe mains operation, were simulated in the laboratory conditions and their influence on the SCC susceptibility of X70 pipe steel was investigated. It was found that in NS4 solution, potential shifting to the cathode area promotes the increasing of the SCC susceptibility of X70 steel. Under cathodic protection at potential equal to -1.0 V, the fracture characteristics change, a brittle component appears in the fracture, and the coefficient KS increases compared to the breaking of samples without cathodic potential. Under such a potential there may appear some differences in the SCC susceptibility of X70 steel, which have a minor structural features: steel with less contamination of non-metallic inclusions is less susceptible to brittle cracking. Accumulated cyclic stresses, periodic wetting, the presence of coatings with different transient resistance and the stress concentrator promote the increase of the degree of SCC susceptibility of X70 pipeline steel at a potential of -1.0 V.

Relationship between cathodic protection current and limit diffusion current as an additional criteria of cathodic protection

The influence of the temperature and oxygen concentration in NS4 solution on the electrochemical characteristics of X70 steel for pipelines and the relationship of cathodic protection current density to limiting diffusion current density, in the normalized DSTU 4219 range of protective polarization potentials from -0.75 V to -1.05 V (сh.s.е.) were investigated. It has been established that with increasing of the temperature from 20 to 80 °C, the corrosion activity of X70 steel increases, which is confirmed by more negative values of corrosion potential and an increasing of the corrosion rate, and indicates on the prevailing effect of temperature on the corrosion process compared to the effect of oxygen concentration. In the temperature range considered, the limiting diffusion current has a maximum value at 40 °C and decreases with increasing of temperature, correlating with a decreasing of the oxygen concentration. Under conditions of free oxygen access to the NS4 solution in the normalized DSTU 4219 range of protective polarization potentials, the ratio of cathodic protection to limiting diffusion current varies from 0.4 to 1.3 at temperatures (20-40) oС, at temperatures (60-80) oC the ratio is less than 1. Under conditions of limited oxygen access, the ratio increases from 1.1 to 4.7. Using calculated and experimental results, it was shown that, at various values of relationship , conditions for excessive hydrogen evolution can be created, which represents a threat to the safe operation of the pipeline over time. Data on the ratio values should be taken into account when analyzing the protection state of pipelines.

Evaluation of Corrosion of a Fe-40Al-2RE Intermetallic Alloy in NS4 Solution

The corrosion study of Fe-40Al+2% Rare Earths (RE) intermetallic alloy in NS4 solution at room temperature was carried out. The intermetallic alloy was previously produced by melting in an induction furnace. The alloy microstructure is constituted by a minority phase of Fe3Al, homogeneously dispersed in the majority phase of FeAl. The effect of pH condition was presented in the corrosion mode, at pH 5 the sample showed uniform corrosion, while at pH 3 and 7 some pitting sites were observed, however the metallic samples showed uniform corrosion on the exposed areas. The anodic dissolution mechanism occurred preferentially in the FeAl phase observed at pH 3, which corresponds to the majority phase or alloy microstructure. Electrochemical results were complemented with the microstructure and chemical characterization by scanning electron microscopy, energy dispersion spectroscopy and X-ray diffraction analysis.

Effect of non-conventional heat treatment of API X60 pipeline steel on corrosion resistance and stress corrosion cracking susceptibility

PurposeThe purpose of this paper is to study the effect of heat treatment (HT) applied to an API X60 steel in corrosion resistance and stress corrosion cracking (SCC) susceptibility through slow strain rate tests (SSRT) in NS4 solution and congenital water (CW) to assess external and internal SCC, respectively.Design/methodology/approachAPI X60 steel was heat treated at a temperature of 1,200°C for 30 min followed by water quenching. Specimens from this steel were machined according to NACE TM 198. SSRT were performed in a constant extension rate tests (CERT) machine at room temperature at a strain rate of 1 × 10–6s–1. For this purpose, a glass cell was used. Corrosion behavior was evaluated through polarization curves (PCs).FindingsThe SCC index obtained from SSRT indicates that the steel heat treated could be susceptible to SCC in CW and NS4 solution; the mechanism of SCC was hydrogen embrittlement. Thus, CW may promote the SCC phenomenon in pipelines. HT improves the steel corrosion resistance. Higher corrosion rate (CR) was observed when the steel is exposed to CW. The corrosion process in X60 steel shows that the oxidation reaction in the anodic branch corresponds to an activation process, and the cathode branches reveal a diffusion process.Originality/valueThe purpose of the heat treatment applied to X60 steel was to generate a microstructure of acicular ferrite to improve the corrosion resistance and SCC behavior.

Stress corrosion cracking behavior of X90 pipeline steel and its weld joint at different applied potentials in near-neutral solutions

X90 pipeline steel is a new generation of pipeline steel developed after X80 and X100 pipeline steels, and it is now a new research hotspot at home. In order to thoroughly study the effect of applied potential on the soil stress corrosion cracking (SCC) behavior of X90 pipeline steel, we investigated the SCC behaviors of base metal and weld joint samples in the straight-weld pipe of X90 pipeline steel at different applied potentials in near-neutral solution using electrochemical measurements methods and slow strain rate testing (SSRT). Besides, the fracture surfaces were observed through scanning electron microscope (SEM) and the mechanisms of the corrosion cracking behaviors were analyzed. And the following research results were obtained. First, the polarization curves of the base metal and weld joint samples in the NS4 solution present the typical characteristics of anodic dissolution but no activation–passivation phenomenon happens. Second, in the NS4 solution, the base metal and weld joint samples present SCC sensitivity. The SCC sensitivity indicator which is expressed by yield loss percentage elongation and yield loss percentage elongation area decreases firstly and then increases with the negative increase of the applied potential, and the SCC sensitivity of weld joint is higher than that of base metal. Third, there are three mechanisms on the SCC behaviors of base metal and weld joint samples, i.e., anodic dissolution mechanism when the applied potential is open circuit potential (EOCP), anodic dissolution and hydrogen embrittlement mechanism when the applied potential is −850 mV, and hydrogen embrittlement mechanism when the applied potential is −1000 mV and −1200 mV. It is concluded that the research results can provide a technical support and theoretical basis for the large-scale application of X90 pipeline steel.

Feature of stress corrosion cracking of degraded gas pipeline steels

Stress corrosion cracking (SCC) of steels can reduce the structural integrity of gas pipelines. To simulate in-service degradation of pipeline steels in laboratory the method of accelerated degradation consisted in subjecting specimens to electrolytic hydrogenation, to loading up the certain plastic deformation and heating of specimen at 250°C was recently developed. The purpose of this paper was to analyse mechanical and SCC behaviour of in-service and in-laboratory degraded gas pipeline steels and to reveal some fractographic features of SCC. Three pipeline steels of the different strength (17H1S, which is equivalent of API X52, API X60 and API X70) were investigated. The characteristics of the as-received pipeline steels with different strength were compared with the properties of pipeline steels after in-service and in-laboratory degradation. An influence of the NS4 solution on SCC resistance of 17H1S and API X60 steels in the as-received state and after the accelerated degradation, using slow strain rate tension method, was analysed. The noticeable decrease of plasticity for 17H1S and API X60 steels after long-term operation was shown. Deep microdelaminations revealed in the central part of fracture surfaces for the operated steels can be considered as the signs of dissipated damaging in the metal caused by texture and hydrogen absorbed by metal. Comparison of the SCC tests results showed that the characteristics of both steels in the as-received state were insignificantly changed under the influence of the environment. At the same time, the degraded steels were characterized by a high sensitivity to SCC. It was shown fractographically that it associated with cracking along interfaces of ferrite and pearlite grains with secondary deep intergranular cracks formation and also by delamination between ferrite and cementite inside pearlite grains. The similar fracture mechanism at SCC tests was revealed for near the outer surface of the specimens and in the central part of the fracture surfaces of in-laboratory degraded specimens. These results demonstrated the key role of hydrogen during SCC and in-bulk cracking as well.