Development Of Stress Corrosion Cracking Research Articles

Mitigation effects of over-aging (T73) induced intergranular corrosion on stress corrosion cracking of AA7075 aluminum alloy and behaviors of η phase grain boundary precipitates during the intergranular corrosion formation

The stress corrosion cracking (SCC) behaviors of over-aged and peak-aged AA7075 aluminum alloys in a 5 wt% NaCl solution were compared. Even though the over-aging process induced intergranular corrosion (IGC), it decreased the SCC susceptibility of the material. Grain boundaries (GBs) with misorientation angles less than 30° and the grain matrix were considered factors that reduced the IGC propagation rate, thereby preventing the development of SCC in the over-aged material. η phase grain boundary precipitates (GBPs) underwent de-alloying, forming Cu-enriched particles during the IGC formation. However, the cathodic properties of these particles are not the key factors determining whether the IGC will occur or not.

Experimental tests and numerical simulations of ultimate strength on acid etching tempered glass under four-point bending

Acid etching tempered glass (AETG) is a new building material formed by chemical etching of the surface of tempered glass (TG). It is considered that the bending strength of the specimen will show great dispersion due to the comprehensive influence of surface defect distribution. This paper studies the influence of three key factors, including the etching process, age, and loading rate, on bending strength by a four-point bending test. Two-parameter Weibull function is used to analyze the test results so that the characteristic values of the bending strength of specimens in each group can be obtained. The XFEM model of AETG was established based on the experimental results. The results show that the acid etching process changes the surface roughness and surface residual surface stress of TG. The bending strength is improved obviously but can be stabilized gradually after six months. The established XFEM model can better simulate the development of stress corrosion cracking and is close to the characteristics of failure fragments in the experiment.

Influence of Surface Machining on Development of Stress Corrosion Cracking of Distribution Wheels of Main Circulation Pump in Nuclear Power Plants

The present work deals with the causes of the damage to the distribution wheel of the main circulation pump of the nuclear power plant. During the solution of the problem, a significant influence of the final machining on the formation of cracks was found. Coarse surface machining can cause strain-induced martensite on the distribution wheel surface. Small pitting, which was observed on the surface of the distribution wheel, can be caused by the presence of martensite with less corrosion resistance. Thermal stress and residual stress after coarse final surface machining caused the growth of the cracks which initiated from the pitting.

METHODICAL APPROACH TO THE STUDY OF STRESS CORROSION CRACKING MECHANISM OF PIPELINE STEEL AT CATHODIC PROTECTION BY LINEAR SWEEP VOLTAMETRY

A methodological approach to the rapid assessment by linear sweep voltammetry method stress corrosion cracking (SCC) mechanism of pipeline steels of various grades under cathodic protection has been developed. The proposed approach serves as the basis for the electrochemical study of the mechanism of stress corrosion cracking of pipeline steel at various protective potentials for laboratory conditions. The ratio of polarization currents at fast () and slow () scanning potential rate was determined, its analysis was carried out depending on the polarization potential for steels of various grades. It was established that polarization potentials at which the difference between corrosion rate of the crack’s tip and the other surface is the maximum (maximum value of ) and the rapid development of stress corrosion cracks begin, which is differ for steels of various grades and equal near -0.75 V for X70 steel, -0.85 V for 09G2S steel and -0.8 V for 17G1S steel. The boundaries of the polarization potentials are established, beyond which the SCC mechanism of the investigated steels in the model soil environment NS4 changes, namely: from -0.75 V to -1.05 V for X70; -0.85 V to -1.0 V for 09G2S; from -0.8 V to -0.98 V for 17G1S. This indicates the possibility of SCC development with different rates and patterns, all other things being equal. The results of the work can be useful both for a theoretical understanding of the SCC mechanism and for an express assessment of the SCC mechanism in a soil environment and, in particular, in underfilm electrolyte under a disbanded coating.

Soil cryogenesis as a natural risk factor for gas pipelines in the permafrost zone during modern warming

The paper summarizes the experience of studying the effect of modern warming on the thawing depth of sandy and loamy soils in the permafrost zone. The definition of soil cryogenesis as a natural process and facies as the end result of soil cryogenesis as a process is given. The effect of soil cryogenesis facies on stress corrosion cracking of gas pipes of the Gazprom system in cold and warm seasons has been studied. It was found that the facies of soil cryogenesis are interconnected by the process of energy and mass exchange. It is shown that in the annual cycle, each facies formed by soil cryogenesis is the basis for the development of stress corrosion cracking of gas pipelines.

Intergranular SCC mechanism of ultrasonic nanocrystalline surface modified AISI 304 SS in H2SO4 solution containing chloride

In this work, the stress corrosion cracking (SCC) susceptibility of AISI 304 stainless steel processed using ultrasonic nanocrystalline surface modification (UNSM) treatment, was studied in 1 M H2SO4 containing 5 wt.% NaCl by means of combined slow strain rate test with electrochemical methods. The mechanical properties are improved by the UNSM, however the time to failure decreases due to the higher anodic dissolution kinetics of the UNSM sample, which remain in the order of mA/cm2 compared to µA/cm2 of the as-received (AR) sample. Adsorption of chloride ions has been identified by the presence of an inductive loop in the Nyquist plot, indicating a more reactive surface of the UNSM sample, which promotes dealloying of the metal. The development of several transgranular SCC (TG‒SCC) areas in the UNSM sample, compared to the AR, plus the nucleation of intergranular SCC (IG‒SCC) in the UNSM region is studied by scanning electron microscopy (SEM), X-ray micro-computed tomography (micro-CT), and electron back scattered diffraction (EBSD).

Intergranular stress corrosion cracking of steel gas pipelines in weak alkaline soil electrolytes

Abstract The paper presents an overview of the main types of stress corrosion cracking (SCC) of pipeline steels under operating conditions of high-pressure buried gas pipelines. Up to the present time, there have been cases of transgranular cracking in gas pipelines in near-neutral pH soil electrolytes in Russian territory. The present work studies fragments of pipes containing cracks as well as soil samples at the excavation sites of gas pipelines running through the territory of the Astrakhan region. It was found that the cracks formed as a result of SCC of pipe metal and are of intergranular character of propagation. It is also established that the chemical composition of the soil along the gas pipeline differs from the previously studied compositions of corrosive environments that encourage the development of intergranular SCC of pipeline steels.

Corrosion of the Second Contour of Power-Generating Units of Nuclear Power Plants with WWÉR-1000 Reactors

We present a survey of experimental investigations of the mechanisms of erosion-corrosion damage to the heat-exchange equipment of power-generating units with WWER-1000 (water-cooled, watermoderated) reactors. By using metallographic methods, we study the in-service defects of different regions. It is shown that the nature of defects in thick-walled structures made of pearlitic steel of the 10GN2MFA type is initially explained by the pitting corrosion caused by the electrochemical interaction of the metal with particles of the sludge, i.e., products of the corrosion-erosion wear of the equipment made of copper alloys. We make a conclusion that the complex interdependent processes of corrosionerosion wear of the equipment are running under the conditions of the second circuit. In their final stage, we observe the development of stress-corrosion cracking. Hence, for the prevention of in-service defects of equipment of the second circuit, it is necessary to remove copper-containing structures.

Ex situ characterization of metallurgical inclusions in X100 pipeline steel before and after immersion in a neutral pH bicarbonate solution

The initiation of corrosion pits in pipeline steels plays an important role in the development of stress corrosion cracking. In order to reveal the effect of inclusions on corrosion initiation sites and also to clarify contradictory results from previous literature, we proposed an ex situ characterization method that is allowed to characterize exactly the same inclusion or location of the surface of steel before and after corrosion tests. The time-dependent corrosion behaviour of the inclusions and the surrounding X100 steel matrix at the same area before and after early stage immersion in a near-neutral pH bicarbonate solution was investigated by ex situ scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and localized electrochemical impedance spectroscopy (LEIS). The sizes of most inclusions in X100 steel are below 3 μm. The results challenge the long-held opinion of previous work that corrosion pit initiations are related with the inclusions. It has been found that most of the inclusions remain stable (intact) during the whole testing time although severe corrosion occurs on the matrix of the steel. The chemical composition of the inclusion greatly affects the chemical stability of the inclusion. SiO2 inclusions and complex inclusions with a high SiO2 content remain intact although obvious general corrosion occurs on the steel matrix under the investigated immersion period. Inclusions with little Si, such as Al–Mg–Ca–O enriched inclusions, totally disappear after certain immersion time. During the immersion, the corrosion product tends to deposit at the interstice between the inclusion and steel matrix.

2015 Frank Newman Speller Award: Stress Corrosion Cracking and Nuclear Power

In order to provide background for a review of stress corrosion cracking (SCC) in nuclear power plants, a review is first presented of the history of occurrence of SCC in fossil fired power plants and a few related applications. The historical development of SCC in nuclear power plants is then described. The many materials and components that have been affected by SCC over the years are identified, as are the material, stress, and environmental factors involved. A particular focus of this monograph is the question of how it happened that materials with significant susceptibility to SCC were used for so many important structural applications in nuclear power plants. To address this question, the historical development of both pressurized water reactor designs and boiling water reactor designs is reviewed. The review covers factors such as the material types selected for test and use, the operating temperatures used as the designs evolved, and the qualification tests and prior operating experience that were relied upon for selection of materials. Some conclusions as to the factors involved in the choice of materials that turned out to be susceptible to SCC are presented, together with some suggestions for how to minimize such problems in the future.

Geochemistry of a paleosol horizon at the base of the Sausar Group, central India: Implications on atmospheric conditions at the Archean–Paleoproterozoic boundary

A paleosol horizon is described from the contact of the Sausar Group (∼2400 Ma) and its basement (Tirodi Gneiss; >2500 Ma) in Central India. Physical evidence of pedogenesis is marked by the development of stress corrosion cracks, soil peds, corestone weathering and nodular rocks. XRD and SEM-EDX data indicate the presence of siderite, ankerite, uraninite, chlorite, alumino-silicate minerals, ilmenite, rutile and magnetite, in addition to quartz, feldspar and mica. The chemical index of alteration, the plagioclase index of alteration, and the chemical index of weathering show an increasing trend from parent rock to the paleosol and indicate a moderate trend of weathering. The A-CN-K plot indicates loss of feldspars, enrichment in Al2O3 and formation of illite. Different major element ratios indicate baseloss through hydrolysis, clay formation, leaching of some elements, and more precipitation with good surface drainage. The paleosol is depleted in HREE in comparison to the parent rock indicating high fluid-rock interaction during weathering. The paleosol samples show flat Ce and Eu anomalies, low ΣREE, and high (La/Yb)N, indicative of a reducing environment of formation. Reducing condition can also be inferred from the concentration of elements such as V, Co, Cu, Pb, and Zn in the paleosol profile. Although enriched in Fe and Mg, the overall geochemical patterns of the paleosol indicate oxygen deficient conditions in the atmosphere and development by weathering and leaching processes associated with high precipitation and good surface drainage at the time of development of this paleosol during the Archean–Paleoproterozoic transition.

Modification of Bbituminous Coatings to Prevent Stress Corrosion Cracking of Carbon Steel

Stress corrosion cracking (SCC) is the most dangerous kind of pipelines corrosion. The SCC appears on the stressed metal due to contact with aggressive media through the rupture of polymer coating. Inhibition of the SCC is one of the urgent tasks of corrosion protection of underground pipelines. The research reports the method of inhibiting the SCC of pipe steels by modification of polymer protective coatings. With help of slow strain rate test (SSRT) the effect of general corrosion inhibitors and surfactants on the propensity X70 pipe steel to the SCC in aggressive electrolytes has been investigated. The vinyl-containing silane (VS) is shown to be an effective inhibitor of SCC of steel. The VS has been proposed as a modifying additive to a bitumen coating (DEKOM-GAZ type). Modification of coating should provide both satisfactory adhesion and exit of the SCC inhibiting compounds to electrolyte under film and their adsorption onto the metal surface in the case of mechanical damage or loss of adhesion. Peel shear test at an angle 90° away from steel plate has been used for evaluation of adhesive properties of modified coating. It has been shown that the additive of the VS does not impair the adhesion of the protective coating. Using FTIR microscopy output of the inhibitor molecules from the polymer matrix to solution and their adsorption onto the metal surface was evaluated. The aqueous extract obtained by exposure of the polymer coating with the addition of the VS in contact with water for 30 days has been investigated. IR-spectra analysis showed that predominantly the VS goes from the coating into solution and adsorbs on the metal surface. Thus the modified polymer coating, the use of which will prevent the development of SCC of carbon steel, has been developed.

Influence of milling on the development of stress corrosion cracks in austenitic stainless steel

We have examined the influence of mechanical surface finishing on the development of residual stresses, and on the subsequent formation of stress corrosion cracks, in 316Ti austenitic stainless steel after exposure to boiling magnesium chloride. The surface residual stresses of as-received plate, prior to machining, were found to be biaxial and compressive. However, abrasive grinding produced significant compressive stresses in the machining direction but much lower perpendicular stresses. On the other hand, milling produced high biaxial tensile stresses (approaching the ultimate tensile strength, UTS, of the material), which were found to be relatively insensitive to cut depth but to vary as a function of feed rate. On the milled surfaces a distinctive pattern of stress corrosion cracking was evident with longer primary cracks nucleating along the milling direction and secondary, shorter, cracks nucleating perpendicularly. As the surface tensile stress was lower perpendicular to the milling direction, we postulate that the nucleation of primary cracks parallel to machining must be driven by the surface profile after machining (and associated micro-stresses) as much as by the macroscopic residual stresses.

Corrosion pitting and environmentally assisted small crack growth

In many applications, corrosion pits act as precursors to cracking, but qualitative and quantitative prediction of damage evolution has been hampered by lack of insights into the process by which a crack develops from a pit. An overview is given of recent breakthroughs in characterization and understanding of the pit-to-crack transition using advanced three-dimensional imaging techniques such as X-ray computed tomography and focused ion beam machining with scanning electron microscopy. These techniques provided novel insights with respect to the location of crack development from a pit, supported by finite-element analysis. This inspired a new concept for the role of pitting in stress corrosion cracking based on the growing pit inducing local dynamic plastic strain, a critical factor in the development of stress corrosion cracks. Challenges in quantifying the subsequent growth rate of the emerging small cracks are then outlined with the potential drop technique being the most viable. A comparison is made with the growth rate for short cracks (through-thickness crack in fracture mechanics specimen) and long cracks and an electrochemical crack size effect invoked to rationalize the data.

Peculiarities of the development of stress-corrosion cracking on a pipeline section from the results of repeated in-tube nondestructive testing

The results of the repeated in-tube nondestructive testing (INDT) of a gas pipeline section were analyzed. It was established that the process of stress corrosion cracking (SCC) develops at an increasing rate. The instability of the stressed state due to large-scale repair works was experimentally established to be one of the possible causes for the accelerated development of SCC processes.

Electrochemical impedance spectroscopy analysis of X70 pipeline steel stress corrosion cracking in high pH carbonate solution

In this study, electrochemical impedance spectroscopy (EIS) technique was used to investigate the development of stress corrosion cracking (SCC) in X70 pipeline steels. Slow strain rate testing (SSRT) was performed on steel samples in high pH bicarbonate solution. Potentiostatic EIS tests were also conducted regularly to determine the changes associated with the SCC. The Bode modulus and phase diagrams for cracks were calculated. Furthermore, the suitable frequency window for detection of the cracks by EIS was determined. Finally, a circuit model proposed for the cracking.

Analysis of the development of stress corrosion cracking in pipelines of compressor stations

The problem of corrosion cracking in underground gas pipelines has been a focus of attention of gas-transporting enterprises for more than 15 years, but so far there is neither an unambiguous assessment of the main causes of this phenomenon nor acceptable methods for reducing it (except detection of stress corrosion cracking (SCC) flaws by means of in-tube flaw detection and the subsequent elimination of these flaws). One important feature of the manifestation of the problem of SCC in main gas pipelines is the selectivity of cracking (SCC is identified in a small fraction of pipes), the causes of which are unknown. It is still not clear whether this feature is due to the time delay of SCC or this effect has another origin and is associated with the resistance of the greater part of pipes to stress corrosion damageability. This issue is directly related to forecasting of the further development of stress corrosion damageability both for gas pipelines in which SCC has already been detected and for segments in which SCC problems have not yet arisen. An especially pressing task is assessing the possibility of the development of SCC in process pipelines of compressor stations situated in regions where the presence of the SCC process on linear segments has been identified, because equipment operation and the presence of maintenance staff on the station territory involve increased risk.

Structural features of crack formation during corrosion cracking

Stress corrosion cracking (SCC) causes damage to main gas pipelines due to formation and development of cracks on the outer surface of a tube. Prevention of SCC crack development and fracture of a gas pipeline is an important problem of diagnostics that can be solved in various ways. The most effective approach involves systematic use of in-tube nondestructive testing and local testing in shafts, owing to which the position of a flaw and its linear size are determined. The hazard of the flaw (residual life of a tube with cracks) is found and a decision is made about the necessity and methods of flaw repair, such as cutting out the tube, grinding the flaw, and reinsulating the tube surface, and the date of repeated nondestructive testing is set. These measures ensure timely discovery of potentially hazardous flaws and make it possible to take the necessary steps for preventing development of SCC.

Use of rayleigh waves in testing stress-corrosion breaks in pipelines by the acoustic emission method

Four models describing emission of Rayleigh waves by cracks with normal breaking have been suggested for testing various stages of development of stress-corrosion cracking in pipelines by the acoustic emission (AE) method. Parameters of AE pulses for identifying stages of stress-corrosion breaking of pipelines have been determined in the process of investigation.

Study of the influence of welding parameters on the stress corrosion resistance of AISI 304 steel

Austenitic stainless steel has been welded to coat pressure vessels in petrochemical plants. The material is highly susceptible to stress corrosion in chloride environments, which can damage the weld and lead to the rupture of the component. In this work we did the evaluation of the influence of welding parameters on the stress corrosion resistance of AISI 304 steel exposed to a magnesium chloride solution. AISI 304 sheets were manually welded using three different coated electrodes (AWS E309-16, E308L-16, E316L-16) and two heat inputs (5.0 and 9.0 kJ/cm). The welded samples were analysed by tensile strength tests, optical microscopy and corrosion tests carried out according to ASTM G36-73 guidelines. The results showed that the AWS E309-16 electrodes produced the best results due to the microstructure of the resulting weld metal. The presence of a network of ferrite particles in an austenitic matrix acts as a barrier to crack propagation, thus enhancing the resistance to stress corrosion of the material. This effect is associated to the morphology and distribution of the phase rather than its contents. Welding in a direction parallel to the stress axis using a relatively high heat input improved the stress corrosion of the material even further. The HAZ (Heat Affected Zone) of AISI 304 steel was highly susceptible to stress corrosion in chloride solution. The presence of carbide precipitates in the austenite grain boundary deteriorated the corrosion resistance of the steel, as they promoted anodic dissolution and the development of stress corrosion cracks.