Rate Stress Corrosion Cracking Research Articles

Failure Analysis of the Crack and Leakage of a Crude Oil Pipeline under CO2-Steam Flooding

This paper presents the failure analysis of the crack and leakage accident of a crude oil pipeline under CO2-steam flooding in the western oilfield of China. To analyze the failure behavior and cause, different testing, including nondestructive testing, chemical composition analysis, tensile property testing, metallographic analysis, and microanalysis of fracture and chloride stress corrosion cracking (SCC) testing, are applied in the present study. The obtained results showed that the pipeline under the insulation layer of high humidity, high oxygen content, and high Cl− environment occurred pit corrosion, and the stress concentration area at the bottom of the corrosion pit sprouted cracks. Besides, it is demonstrated that the cracks were much branched, mostly through the crystal, and the fracture showed brittle, which is consistent with the typical characteristics of chloride SCC. Meanwhile, the insufficient Ni content of the pipeline material promoted the process of chloride SCC, and the high-temperature working conditions also aggravated the rate of chloride SCC. In addition, efficient precautions were provided to avoid fracture.

Predicting Stress Corrosion Crack Tip Electrochemical Conditions and the Influence of Exposure Environment

Metallic structures are commonly exposed to marine atmospheric conditions in real world conditions, characterized by thin water layers (WL) allowing for corrosion to occur. For austenitic stainless steels in such atmospheric environments, pitting and stress corrosion cracking (SCC) are potential degradation mechanisms. The rate and extent of corrosion and SCC on the alloy surface is dictated by the combination of environmental, physicochemical, and geometric variables, which include relative humidity, temperature, electrolyte conductivity, electrolyte film thickness, in addition to the electrochemical kinetics on the alloy surface. Due to the large potential variation in environmental conditions, modeling can serve as an important tool to evaluate environmental effects on the corrosion and SCC of alloys and galvanic couples.In this study, Finite Element Modeling approaches are used to evaluate chemical and electrochemical conditions present in a crack exposed to marine, thin film environments. A full reactive transport model, incorporating metal hydrolysis and salt formation, is built to evaluate SCC crack tip conditions. The influence of WL thickness, stress intensity level, crack length, and specimen geometry are evaluated. Specifically, crack tip pH and equilibrium potential among other variables will be compared between the various atmospheric factors both spatially and temporally. The modeling results will be compared to atmospheric SCC experiments and help give insight into critical experimental and testing phenomena. Acknowledgements Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This document is SAND2021-5051 A.

Effect of Cold Working on the Driving Force of the Crack Growth and Crack Growth Rate of Welded Joints under One Overload

To understand the effect of cold working of welding heat-affected zone on the driving force of the crack growth and crack growth rate of stress corrosion cracking (SCC) near the welding fusion line, the finite element simulation method was used to analyze the effect of cold working on the tensile stress of the crack tip at different locations near the fusion line. On this basis, the strain rate of the crack tip in the Ford-Andresen model is replaced by the creep rate of the crack tip, and the creep rate of the crack tip is used as driving force for the crack growth of SCC. The effect of the cold working level at the heat-affected zone on the driving force of the crack growth and crack growth rate of SCC are analyzed, and driving force of the crack growth and crack growth rate of SCC after one overload was compared.

Comparative study of the stress corrosion behavior of a multiuse bainite steel in the simulated tropical marine atmosphere and seawater environments

Stress corrosion cracking (SCC) behavior of a multiuse high-strength low-alloy (HSLA) bainite steel was comparatively studied in the simulated seawater and marine atmosphere environments using electrochemical measurements, static load SCC and slow strain rate tensile (SSRT) tests. The difference in SCC behavior was characterized in detail by morphology observation via scanning electron microscopy (SEM) and corrosion product analysis via X-ray diffraction (XRD) and energy dispersion spectrum (EDS) techniques. The results indicate that the HSLA bainite steel is very sensitive to SCC in the simulated tropical marine atmosphere, mainly due to the thin and uneven electrolyte film, which is characterized by a fast oxygen transportation rate on the steel surface. The rust layer also plays an important role in determining SCC behavior in the simulated marine atmosphere, as it restrains the electrochemically anodic process and promotes the cathodic process, particularly the hydrogen evolution reaction, resulting in the nucleation and transgranular-mode propagation of SCC microcracks at the bottoms of pits. As a result, both localized anodic dissolution (AD) and hydrogen embrittlement (HE) effects are promoted, contributing to the significant increase in the susceptibility of HSLA bainite steel to SCC.

Influence of surface martensite layer on hydrogen embrittlement of Fe-Mn-C-Mo steels in wet H2S environment

This study investigated the effect of thermally induced surface martensite layer on hydrogen embrittlement of Fe-16Mn-0.4C-2Mo (wt.%) (16Mn) and Fe-25Mn-0.4C-2Mo (wt.%) (25Mn) steels through slow strain rate stress corrosion cracking testing and proof ring testing in wet H2S environment. The 16Mn steel had a surface layer of less than 150 μm in depth containing ε-martensite, α′-martensite and austenitic twins. The martensite layer is found to reduce the hydrogen embrittlement resistance of the steel. In comparison, the 25Mn steel developed a full α′-martensite surface layer, which exhibited practically nil effect on the hydrogen embrittlement resistance of the steel. The ε-martensite provides much larger interface areas with the mechanical twins of the austenite in the 16Mn steel than the α′-martensite/austenite interfaces in the 25Mn steel. These interfaces are hydrogen trapping sites and are prone to initiate surface cracks, as observed in the scanning electron microscope. The formation of the cracks is attributed to hydrogen concentration at the ε-martensite and austenitic twin interfaces, which accelerates material fracture.

A comprehensive analysis of the growth rate of stress corrosion cracks

This paper is a synthesis of earlier results supplemented by new results to define a comprehensive analysis of the growth rate of stress corrosion cracking (SCC). Two mechanisms, anodic dissolution (AD) and hydrogen embrittlement (HE), have been considered to calculate the SCC growth rate of AA 7050-T6 for a surface-breaking crack with blunt tip in an aqueous environment. The relative contributions of each mechanism and their mutual interactions have been quantitatively assessed. Results show that AD provides critical conditions for HE, which explains in part a stepwise propagation of the crack. Finally, the total crack growth rate due to the combined effects of AD and HE has been determined, and numerical results have been compared with experimental data, and a calculation of the crack growth rate for a practical configuration has been presented.

A quantitative prediction model of SCC rate for nuclear structure materials in high temperature water based on crack tip creep strain rate

The quantitative prediction of stress corrosion cracking (SCC) of structure materials is essential in safety assessment of nuclear power plants. A new quantitative prediction model is proposed by combining the Ford–Andresen model, a crack tip creep model and an elastic–plastic finite element method. The creep at the crack tip is considered to be the primary mechanical factor of protective film degradation, and the creep strain rate at the crack tip is suggested as primary mechanical factor in predicting the SCC rate. The SCC rates at secondary stage of creep are recommended when using the approach introduced in this study to predict the SCC rates of materials in high temperature water. The proposed approach can be used to understand the SCC crack growth in structural materials of light water reactors.

Effect of anions on stress corrosion cracking behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo

The effects of chloride, sulfate and carbonate anions on stress corrosion behaviors of ultra-high strength steel 23Co14Ni12Cr3Mo were studied by stress corrosion cracking (SCC) test method using double cantilever beam (DCB) specimens. The SCC morphology was observed by using scanning electron microscopy (SEM) and the composition of corrosion products was analyzed by using energy dispersive spectrometer (EDS). The results show that the crack propagates to bifurcation in NaCl and Na2SO4 solution, while the crack in Na2CO3 solution propagates along the load direction. The SCC rate in NaCl solution is the highest, while lower in Na2SO4 solution and little in Na2CO3 solution. From the SEM morphologies, quasi-cleavage fracture was observed in NaCl and Na2SO4 solutions, but intergranular features in Na2CO3 solution. The mechanism of anion effect on SCC of steel 23Co14Ni12Cr3Mo was studied by using full immersion test and electrochemical measurements.

Corrosion Behavior on Ni-base Alloys Applied with Nano-TiO2 in High Temperature Caustic Water

In Pressurized Water Reactor (PWR) power plants, Alloy 600, a Ni-Cr-Fe alloy, is used for steam generator tube materials. However, these tubes have experienced a lot of corrosion problems during their operation times. Several chemicals have been investigated for inhibitors of stress corrosion cracking (SCC) in the tube materials. Titanium dioxide (TiO2), which is sonochemically treated in water, was tested to evaluate the inhibition effect of SCC using a reverse U-bend specimen of alloy 600 under the condition of a 10% NaOH solution and a temperature of 315oC. The TiO2 particle size was reduced by ultrasonic power, and the morphology of the TiO2 powder was observed by a transmission electron microscope (TEM) based on the ultrasonic processing times. The particle size of TiO2 affects the SCC rate of the tube materials, and shows an improvement in resistance on SCC when decreasing the particle size of TiO2. When the nano-sized inhibitor is applied, the property of the oxide layer is changed to a more dense composition. The chemical composition in the oxide layer was analyzed using an X-ray photoelectron spectroscope (XPS) with a variation in the ultrasonic process times, and the difference in the Ti-compound structure between the oxide surface and inner layer of oxide was compared using XPS data. Keywords: Corrosion inhibitor, nanoparticle, sonochemistry, steam generator tube, stress corrosion cracking (SCC), titanium dioxide (TiO2).

The influence of different fluids on the static fatigue of a porous rock: Poro-mechanical coupling versus chemical effects

Characterization of time-dependent brittle deformation is important for estimating the long-term stability of rock structures in shallow environments such as underground mines which are exposed to water or in a water vapor environment. The poro-mechanical (pore pressure) and chemical (stress corrosion reactions) effects of fluids at crack tips are responsible for the subcritical propagation of microcracks. This brittle creep results in the weakening of porous rocks over time (i.e., static fatigue). The focus of this work was to characterize using very long duration uniaxial multi-step creep tests, both the fluids effects on subcritical stress corrosion cracking in a porous rock (oolithic iron ore). Different fluids with increasing levels of chemical influence (oil, ethanol and water) were tested and both acoustic and mechanical properties were investigated. The evolution of the cumulative number of AE (Acoustic Emission) events, which reproduces the shape of the creep curves very efficiently, and static elastic properties indicate that micro-cracking plays the main role in the creep process. The poro-mechanical effect, which is predominant under partially saturated (water or ethanol) conditions, decreases the rate of subcritical cracking through capillary attraction forces. These forces harden porous rocks by modifying the effective stress state, increasing the activation energy barrier of the stress corrosion process and the fracture toughness and decreasing the stress intensity factor. The chemical effect of fluids is related to minerals developing stress corrosion reactions at crack tips which enhance subcritical cracking. Immersion in water/ethanol annihilates capillary forces and decreases the activation energy of the chemical reactions, thus increasing dilatancy, the rate of stress corrosion cracking, AE activity and rock weakening. Under saturated conditions, the time-dependent strength and time to failure increase as the chemical influence of the interstitial fluid decreases but the cumulative number and energy of AE at failure do not seem to be influenced by the chemistry of fluids. The short-term strength and deformability are also influenced by the level of chemical influence of the interstitial fluid but to a less remarkable extent because of the slow rate of chemical reactions. Water is therefore the most effective chemical agent promoting stress corrosion of iron ore among the fluids tested in our study.

Identification of Inhomogeneous Material Strength near Weld Joint by Three-Dimensional Digital Image Correlation Technique

It has been shown that susceptibility and growth rate of stress corrosion cracking depend on the material strength such as yield strength. However, the material strength is not uniform near weld joint, where the stress corrosion cracking has been found in nuclear power plants. In this study, the digital image correlation (DIC) technique was applied for identifying the inhomogeneous material strength distribution near weld joint of a pipe. A specimen was taken from a butt welded joint and subjected to tensile test. The DIC technique enabled to measure the displacement field on the specimen surface during the tensile test. The local stress-strain curves were successfully measured and the inhomogeneous distribution of 0.2% proof strength was identified. It was confirmed that the stress triaxiality caused by inhomogeneous deformation had little influence on the identification of the proof strengths and local stress-strain curves. Furthermore, it was shown that the change in cross-sectional area of the specimen during the tensile test could be measured by the DIC technique, and then, the local stress (true stress) considering the change in the cross-sectional area was estimated.

OS1426 応力拡大係数変化率が疲労き裂進展挙動に与える影響

There is a possibility that the crack growth rate of stress corrosion cracking and fatigue crack depend on the value of ∂K/∂a (differential term of stress intensity factor) as well as stress intensity factor K. In this study, the effect of ∂K/∂a on crack growth rate was investigated during the fatigue test. Two types of specimens were prepared. One is CT specimen of which K increases under constant loading. The other is CDCB specimen of which K is constant. The effect of ∂K/∂a was clarified by comparing the CT specimen and CDCB specimen under same stress intensity factor. In addition, ΔK corrections considering ∂K/∂a were conducted for CT specimens. As a result, the crack growth rates in CT specimens were larger than CDCB specimens in the same ΔK. Corrected ΔK considering ∂K/∂a is mostly coincides with the value of the CDCB specimen. From those results, the crack growth rate varied due to the effect of ∂K/∂a in fatigue crack propagation was experimentally clarified. In addition, elimination of the influence of ∂K/∂a is possible by ΔK correction.

OS1424 軽水炉環境下でのSCCき裂進展速度の弾塑性破壊力学による評価

Applicability of elasto-plastic parameter for evaluating stress corrosion cracking (SCC) growth rate was examined. Currently linear fracture mechanical approach has been applied for crack evaluation; even though some SCC is found in plastic deformation zone near welding areas where linear elastic fracture mechanics no longer is applicable. Authors have proposed elastic-plastic approach "equivalent stress intensity factor K_j" for evaluating SCC growth rate based on J-integral value, which is valid in both elastic and plastic stress fields. In order to verify the applicability of evaluation by K_j, SCC propagation test in compact tension specimens with varying specimen size and stress conditions were conducted in boiling water reactor environment. As a specimen, sensitized type304 stainless steel was used. When a crack growth rate (CGR) of SCC was evaluated by stress intensity factor K, linear relationship between K and CGR does not exist in the high K value, where CT specimens are out of small scale yielding condition. CGR increases exponentially according to increasing stress intensity factor K to exceed linear relationship. On the other hand when CGR was evaluated by elasto-plastic parameter K_j, linear correlation between K_j and CGR was confirmed regardless specimen size and stress condition. This suggests that by applying elasto-plastic parameter K_j for SCC behavior, CGR at high K value could be estimated easily with using a smaller specimen.

Dependence of Stress Corrosion Cracking of Alloy 690 on Temperature, Cold Work, and Carbide Precipitation—Role of Diffusion of Vacancies at Crack Tips

Abstract The growth rate of stress corrosion cracking (SCC) was measured for cold-worked, thermally treated Alloy 690 (UNS N06690, CW TT 690) and cold-worked, solution-treated Alloy 690 (CW ST 690) in hydrogenated pressurized water reactor (PWR) primary water under static load condition. Three important patterns were observed. First, intergranular stress corrosion cracking (IGSCC) was observed in CW TT 690 in PWR primary water in the range between 320°C and 360°C; this rate of SCC growth was slower than in CW mill-annealed Alloy 600 (UNS N06600, CW MA 600). No significant IGSCC was observed in CW ST 690 after 5,109 h in hydrogenated PWR primary water at 360°C. This is opposite of the behavior reported in the literature for high-temperature caustic solutions. Second, to assess the role of creep, rates of creep crack growth were measured in air, argon, and hydrogen gas environments using 20% CW TT 690 and 20% CW MA 600 in the range between 360°C and 460°C; intergranular creep cracking (IG creep cracking) wa...

Effects of Environmental and Metallurgical Factors on the Stress Corrosion Cracking of Carbon Steel in Fuel-Grade Ethanol

Abstract This paper presents the results of a research program to study the effects of metallurgical variables, ethanol-gasoline blends, dissolved oxygen, and inhibitors on the stress corrosion cracking (SCC) of carbon steel in ethanol. The study utilized both slow strain rate (SSR) and fatigue precracked compact tension (CT) tests to characterize the effect of metallurgical and environmental variables on SCC. Metallurgical factors, including steel grade within a range of pipeline grades, welds, and heat-affected zone, do not appear to have a significant effect on the degree or rate of SCC. In terms of environmental factors, it is shown that SCC does not occur even in a fully aerated condition if the ethanol-gasoline blends contain less than approximately 15 vol% ethanol; SCC susceptibility and crack growth rate are higher in 50 vol% ethanol gasoline blend (E-50) than in either lower or higher ethanol concentration blends; oxygen scavenging can be an effective method to prevent SCC; water content above 4.5 wt% prevents SCC in ethanol; and fatigue precracked CT tests show similar trends in SCC susceptibility as SSR tests.

Fracture Behavior on SCC of API X52 Pipeline Steel Under Cathodic Protection

This paper analyzes the fracture behavior and mechanisms of stress corrosion cracking (SCC) of API X52 pipeline steel. Susceptibility and mechanism of SCC was investigated using slow strain rate tests (SSRT) performed at strain rate of 1 × 10−6 in/sec in a glass autoclave containing a soil solution with pH of 8.5 at room temperature. Cathodic polarization potentials of −100, −200 and −400 mV referred to Ecorr was applied in order to establish the effectiveness of cathodic protection in mitigating SCC of X52 pipeline steel. To study the effects of several over potential in SSRT were performed at different cathodic potentials. The results of reduction area ratio (RAR), time to failure ratio (TFR) and plastic elongation ratio (PER) indicate that X52 pipeline steel was susceptible to SCC. Scanning electron microscopy (SEM) observations of these specimens showed a brittle type of fracture with transgranular appearance. The failure and SCC mechanism of X52 steel in the soil solution was hydrogen based mechanism. This mechanism was confirmed through the internal cracks observed in these specimens. All cracking tests indicated that the SCC rate was enhanced by plastic deformation.

Application of Nano-Sized TiO<SUB>2</SUB> as an Inhibitor of Stress Corrosion Cracking in the Steam Generator Tube Materials

Several chemicals were studied to suppress the damage due to a stress corrosion cracking (SCC) of the steam generator (SG) tubes in nuclear power plants. SCC tests were carried out to investigate the performance of TiO2 on several types of SG tube materials. The SCC tests were conducted by using an m-RUB specimen in a 10% NaOH solution at a temperature of 315 degrees C. The test with the addition of TiO2 showed a decrease in the SCC rate for the SG tubing materials. In order to improve the inhibition property in a crevice of TiO2, a sonochemical technique was applied to reduce the size of the TiO2 particle. From the SCC tests with the RUB specimen, the SG tube materials showed an enhanced cracking resistance with the addition of nano-sized TiO2 and the surface property was also changed.

Stress corrosion cracking and selective corrosion of copper‐zinc alloys for the drinking water installation

AbstractDespite a generally good corrosion resistance to tap and industrial water, many brass taps and fittings have failed in the past by stress corrosion cracking (SCC) and selective corrosion (dezincification or preferred removal of a phase). The experimental investigations of the present study clarify the influence of the ammonia concentration on the two types of corrosion. Notched specimens made of the alloys CuZn39Pb3, CuZn40Pb2, CuZn37, CuZn36Pb2As and CuZn21Si3P are polarized anodically in pure tap water and tap water with realistic ammonia concentrations (15 and 30 ppm) under a simultaneous mechanical loading condition. The influence of stress and of the third alloying elements lead and arsenic are investigated and evaluated. The experiments show that the ammonia additions significantly increase the risk of dezincification of the α‐β‐brasses. The arsenic in the CuZn36Pb2As alloy avoids dezincification, but enhances the risk of SCC. The rate of selective corrosion and SCC consistently increases with increase in tensile stress.

Dependence of Stress Corrosion Cracking for Cold-Worked Stainless Steel on Temperature and Potential, and Role of Diffusion of Vacancies at Crack Tips

Abstract The growth rate of stress corrosion cracking (SCC) was measured for nonsensitized and sensitized, cold-worked Type 316 (UNS S31600, CW316) and Type 304 (UNS S30400, CW304) in hydrogenated ...

Cold Work and Temperature Dependence of Stress Corrosion Crack Growth of Austenitic Stainless Steels in Hydrogenated and Oxygenated High-Temperature Water

Abstract The rate of stress corrosion cracking (SCC) was measured for nonsensitized, cold-worked Type 316 (UNS S31600) and Type 304 (UNS S30400) in both hydrogenated pressurized water reactor (PWR)...