Stress Corrosion Cracking Of Type Research Articles

DFT Analysis of Ethanol Electro-Oxidation on Fe(110) and Fe3c(110) and Its Correlation with the Stress Corrosion Cracking of Carbon Steel

Stress Corrosion Cracking (SCC) of carbon steel in fuel-grade ethanol is typically intergranular in service, but it is nearly always transgranular, in short-term laboratory experiments. While this might be considered an inconvenience, it provides an important clue about the SCC mechanism. The important point is that the transgranular cracking occurs under much milder mechanical conditions than any known form of hydrogen embrittlement in ordinary carbon steel. For this and other reasons, hydrogen is not considered to be the cause of this form of SCC. Transgranular SCC of carbon steel occurs in a very particular set of environments. Anhydrous liquid ammonia, anhydrous ammonia-methanol and CO-CO2-H2O are the key systems to be considered, apart from alcohols. High-temperature water containing oxygen also causes transgranular SCC, but is a less severe environment, probably because a magnetite film imposes a compressive stress that partially opposes any embrittlement effect. In our view, the important factor connecting these examples is embrittlement by interstitials. Just as hydrogen can embrittle iron, so can nitrogen or carbon (or oxygen). The main distinction is the diffusivity of the interstitial in iron. Ammonia can be oxidized to N, and CO can be reduced to C (or, in the language of surface chemistry, this could be dissociative adsorption). Still, at ambient temperature, those interstitials can only diffuse a few nm in relevant times of seconds. But we know little about the effect of such near-surface embrittlement on the propagation of a crack, and research on such surface effects is very important. Striking mechanical and morphological similarities of the SCC of carbon steel in ethanolic media with those governed by a cleavage-like mechanism in CO-CO2 aqueous solutions prompted the investigation of the possibility of ethanol electrochemical oxidation into CO on ferrite (Fe) and cementite (Fe3C) surfaces. Density functional theory computations on (110) surfaces revealed that the catalytic activity of Fe and Fe3C through the α dehydrogenation pathway can significantly reduce the energy barrier of electro-oxidation of ethanol and production of CO to 0.575 and 0.480 eV, respectively. These first principle calculations indicate that at the anodic potentials applied during potentiostatic slow strain rate testing, ethanol electro-oxidation to CO is thermodynamically viable on carbon steel, giving further credit to the involvement of cleavage type SCC of carbon steel in ethanolic environments.

Irradiation-assisted stress corrosion cracking of Type 347 and Type 316 steels irradiated in commercial pressurized water reactors

Investigations of Type 347 and Type 316 austenitic stainless steel baffle-former bolt failures at 4-loop downflow pressurized water reactors (PWRs) in the US have identified significant amounts of transgranular cracking on the fracture surfaces along with intergranular cracking and ductile rupture. The expected failure mode for baffle-former bolts is irradiation-assisted stress corrosion cracking (IASCC), which typically results in an intergranular cracking mode. The presence of transgranular cracking raised the question of whether IASCC was responsible for the failures, or if a fatigue component was contributory. Detailed fractography and metallography of bolts with and without cracks confirmed that an environmentally-assisted cracking mechanism was responsible. Reviews of the literature identified numerous cases where stress corrosion cracks (including irradiation-assisted stress corrosion cracks) in austenitic stainless steels transitioned from intergranular to transgranular, typically as a more severe stress state developed. The potential cracking mechanisms are discussed. This allowed the conclusion that IASCC was responsible for the degradation observed in the baffle-former bolts, though a component of alternating loading cannot be excluded. The downflow plant configuration results in increased stress on neighboring intact bolts after bolt failure, resulting in the development of ‘clusters’ of failed bolts, which grew as additional bolts failed. This cluster growth contributed to the severe stress state imposed on the bolts.

DFT Analysis of Ethanol Electro-Oxidation on Fe(110) and Fe3C(110) and its Correlation with the Stress Corrosion Cracking of Carbon Steel

Striking mechanical and morphological similarities of the stress corrosion cracking (SCC) of carbon steel in ethanolic media with those governed by a cleavage-like mechanism in CO-CO2 aqueous solutions, prompted the investigation of the possibility of ethanol electrochemical oxidation into CO on ferrite (Fe) and cementite (Fe3C) surfaces. Density functional theory computations on (110) surfaces reveal that the catalytic activity of Fe and Fe3C through the α dehydrogenation pathway can significantly reduce the energy barrier of electro-oxidation of ethanol and production of CO to 0.575 and 0.480 eV, respectively. These first principle calculations indicate that at the anodic potentials applied during potentiostatic slow strain rate testing, ethanol electrooxidation to CO is thermodynamically viable on carbon steel, giving further credit to the involvement of cleavage type SCC of carbon steel in ethanolic environments.

Effect of Strain Hardened Inner Surface Layers on Stress Corrosion Cracking of Type 316 Stainless Steel in Simulated PWR Primary Water

In this study, the relationship between SCC growth rate and Vickers hardness for Type 316 stainless steel at various temperatures in simulated PWR primary water was investigated. In addition, IGSCC growth measurements were conducted using so-called functionally graded cold-rolled specimens made of Type 316 stainless steel, in simulated PWR primary water. Residual stress measurements were performed using the contour and slitting methods on the functionally graded cold-rolled specimens. The contour method measurements found highly tensile stress (350 MPa) toward the surface of the side with a larger thickness reduction and low-magnitude stress elsewhere. The purpose of these latter specimens was to evaluate the effect of heavily cold-worked layers on the inner surface of components made of Type 316 stainless steel on the possibility that IGSCC could penetrate through the wall thickness. The test data showed that the work-hardened inner surface does not always have a detrimental effect on SCC susceptibility. However, if any surface cracks exist within the work-hardened inner surface layer of any components, the stress at the crack tip becomes very large and SCC easily initiates. Nevertheless, even if IGSCC initiates from a heavily cold-worked layer at the inner surface, IGSCC growth rate in Type 316 stainless steel was found to eventually become negligibly small or arrests in the soft base material.

The beneficial effect of surface carbon coating on stress corrosion cracking of Type 304 austenitic stainless steels in high temperature water

A pronounced improvement in stress corrosion cracking initiation resistance resulting from the presence of a carbonaceous surface film was investigated for specimens strained dynamically in hydrogenated high temperature water. Microstructural characterisation of the post-test samples indicated that this improvement in SCC resistance was promoted by the formation of a more uniform and thick surface oxide layer that prevented localized oxidation.

Comparative Studies on microstructure, mechanical and corrosion behaviour of DMR 249A Steel and its welds

DMR249A Medium strength (low carbon) Low-alloy steels are used as structural components in naval applications due to its low cost and high availability. An attempt has been made to weld the DMR 249A steel plates of 8mm thickness using shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW). Welds were characterized for metallography to carry out the microstructural changes, mechanical properties were evaluated using vickers hardness tester and universal testing machine. Potentio-dynamic polarization tests were carried out to determine the pitting corrosion behaviour. Constant load type Stress corrosion cracking (SCC) testing was done to observe the cracking tendency of the joints in a 3.5%NaCl solution. Results of the present study established that SMA welds resulted in formation of relatively higher amount of martensite in ferrite matrix when compared to gas tungsten arc welding (GTAW). It is attributed to faster cooling rates achieved due to high thermal efficiency. Improved mechanical properties were observed for the SMA welds and are due to higher amount of martensite. Pitting corrosion and stress corrosion cracking resistance of SMA welds were poor when compared to GTA welds.

Effect of Pigging Damage on Sulfide Stress Corrosion Cracking of Type 316L Stainless Steel Cladding

Scouring pigging of oil and gas pipelines is used to maintain flow efficiency by abrading the inner surface to remove precipitates such as wax and scale. There has been uncertainty over whether pigging of corrosion resistant alloy pipelines used in sour service could adversely affect their resistance to localized corrosion and stress corrosion cracking (SCC). In this work, a novel environmental chamber was developed to enable scouring pigging to be simulated on pipeline steels while under tensile stress and exposed to deoxygenated brine. Using this configuration, representative pigging damage was reproduced on Type 316L stainless steel cladding with both ground and as-received finish prior to four-point bend testing in a range of environments. Under conditions in which the alloy is considered to be resistant to SCC, simulated pigging had no adverse effect on the resistance of the alloy to localized corrosion or cracking. Under more severe test conditions, in which the alloy is considered to be susceptible to SCC, specimens with an as-received surface experienced preferential pitting and cracking located at pigging scratches, whereas no such effect was observed for ground specimens. Electrochemical impedance spectroscopy measurements demonstrated that the abraded surface had a thinner passive film and a lower corrosion resistance than the as-received surface. However, this detrimental effect of surface abrasion, which is associated with the removal of the pickled and passivated surface, is taken into account by the conservatism of SCC test programs, in which ground specimens are typically included. These findings support the perspective that under normal operating conditions scouring pigging is not expected to increase the risk of pitting or SCC.

Stress corrosion cracking in Type.316 plates of a heat exchanger

In Jam petrochemical complex (JPC), Iran, the plates (ASTM A.240 Type.316) of some heat exchangers have been damaged due to the occurrence of cracks at the sitting place of gaskets. A comprehensive failure analysis including the chemical analysis, visual inspection, optical microscopy and scanning electron microscopy (SEM) of the cracks spread over the plates together with the energy dispersive X-ray spectroscopy (EDS) of the corrosion products and the measurement of chloride and sulfide ions content of the process water were employed for the examination of the failure mode and its causes. The obtained results indicate the building-up of the chloride and sulfide ions at the crevices between plates and gaskets at high temperature leads to stress cracking corrosion (SCC) of the plates. Moreover, the simultaneous presence of chloride and sulfide in the media hastens the SCC failure in the heat exchanger plates.

Using transmission Kikuchi diffraction to study intergranular stress corrosion cracking in type 316 stainless steels

Transmission Kikuchi diffraction (TKD), also known as transmission-electron backscatter diffraction (t-EBSD) is a novel method for orientation mapping of electron transparent transmission electron microscopy specimen in the scanning electron microscope and has been utilized for stress corrosion cracking characterization of type 316 stainless steels. The main advantage of TKD is a significantly higher spatial resolution compared to the conventional EBSD due to the smaller interaction volume of the incident beam with the specimen.Two 316 stainless steel specimen, tested for stress corrosion cracking in hydrogenated and oxygenated pressurized water reactor chemistry, were characterized via TKD. The results include inverse pole figure (IPFZ) maps, image quality maps and misorientation maps, all acquired in very short time (<60min) and with remarkable spatial resolution (up to 5nm step size possible). They have been used in order to determine the location of the open crack with respect to the grain boundary, deformation bands, twinning and slip. Furthermore, TKD has been used to measure the grain boundary misorientation and establish a gauge for quantifying plastic deformation at the crack tip and other regions in the surrounding matrix. Both grain boundary migration and slip transfer have been detected as well.

光ファイバAEセンサを用いた高温高圧水環境下で発生するSUS304鋼の応力腐食割れの発生・進展モニタリング

光ファイバAEセンサを用いた高温高圧水環境下で発生するSUS304鋼の応力腐食割れの発生・進展モニタリング

A multiscale constitutive model for intergranular stress corrosion cracking in type 304 austenitic stainless steel

Intergranular stress corrosion cracking (IGSCC) is a fracture mechanism in sensitised austenitic stainless steels exposed to critical environments where the intergranular cracks extends along the network of connected susceptible grain boundaries. A constitutive model is presented to estimate the maximum intergranular crack growth by taking into consideration the materials mechanical properties and microstructure characters distribution. This constitutive model is constructed based on the assumption that each grain is a two phase material comprising of grain interior and grain boundary zone. The inherent micro-mechanisms active in the grain interior during IGSCC is based on crystal plasticity theory, while the grain boundary zone has been modelled by proposing a phenomenological constitutive model motivated from cohesive zone modelling approach. Overall, response of the representative volume is calculated by volume averaging of individual grain behaviour. Model is assessed by performing rigorous parametric studies, followed by validation and verification of the proposed constitutive model using representative volume element based FE simulations reported in the literature. In the last section, model application is demonstrated using intergranular stress corrosion cracking experiments which shows a good agreement.

Effect of Welding Conditions on Residual Stress and Stress Corrosion Cracking Behavior at Butt-Welding Joints of Stainless Steel Pipes

Stress corrosion cracking (SCC) in Type 316 L low-carbon austenitic stainless steel recirculation pipes have been observed near butt-welding joints. These SCC in Type 316 L stainless steel grow near the welding zone mainly because of the high tensile residual stress caused by welding. Therefore, for SCC growth analysis, it is important to assess the residual stress caused by welding of stainless steel piping. In the present study, which is focused on the scatters of welding parameters such as heat input and welding speed, these values were measured experimentally by fabricating a series of butt-welded specimens of Type 316 pipes. The distribution and scatter of residual stress were also measured by stress relief and X-ray diffraction methods. The effects of welding parameters on residual stress distribution have been evaluated through welding simulations based on finite-element analysis using three-dimensional and axisymmetric models. Parametric analyses were also performed, while taking into account the variation of some welding parameters based on the experiments. SCC growth behavior was calculated using simulated residual stress distributions and applying a procedure in the fitness-for-service code. It was clearly shown that the uncertainties on welding heat input and speed have strong influences on SCC growth behavior because residual stress is also affected by the scatter of these welding parameters.

Stress corrosion cracking behavior of the wrought magnesium alloy AZ31 under controlled cathodic potentials

► We investigated stress corrosion cracking (SCC) behavior in Mg alloy. ► We examine SCC behavior dominated by anodic dissolution and hydrogen embrittlement separately. ► Threshold stress intensity factor is higher in hydrogen embrittlement type SCC. ► Crack propagation rates were accelerated by larger amount of charged hydrogen. Stress corrosion cracking (SCC) tests were performed using compact tension (CT) specimens in a NaCl solution under hydrogen-charged conditions to investigate the SCC behavior of the wrought magnesium alloy AZ31. The effect of NaCl concentration was estimated by conducting the SCC tests under a constant cathodic potential of −1.4 V, with NaCl concentrations of 0.5, 3.0 and 8.0%. The crack propagation rate (d a /d t ) became accelerated with increasing concentration due to the enhanced anodic dissolution by chloride ions. Subsequently, SCC tests were performed using a 3%NaCl solution with cathodic potentials at −1.4, −2.5 and −3.0 V to investigate the effect of cathodic potentials on SCC behavior. According to the Pourbaix diagram, the cathodic potential of −3.0 V corresponds to the immunity region, whereas −1.4 V is within the corrosion region and −2.5 V is the boundary between the two regions. In the immunity region, the SCC due to hydrogen embrittlement occurred when the K Iscc value was higher than that of the SCC dominated by anodic dissolution. The K Iscc value decreased and the crack propagation rate increased with decreasing cathodic potential in the immunity region at which SCC occurred due to hydrogen embrittlement. At the cathodic potential of −3.0 V, the d a /d t was insensitive to the stress intensity factor because highly charged hydrogen gave rise to brittle fracture.

Vacancy defects in a stress-corrosion-cracked Type 304 stainless steel investigated by positron annihilation spectroscopy

To reveal vacancy formation during the stress corrosion cracking (SCC), three factors influencing SCC in Type 304 stainless steels—sensitization heat treatment, corrosion treatment and tensile plastic deformation—were investigated by means of positron annihilation spectroscopy. Vacancy defects induced by the sensitization heat treatment and by tensile deformation were identified as monovacancies. These monovacancies were annealed within the same temperature range in which light water reactors are operated (280–320 °C). The above results allow us to conclude that such vacancy defects play an important role in high-temperature-water SCC crack propagation.

Hydrogen Embrittlement Type Stress Corrosion Cracking Behavior of Wrought Magnesium Alloy AZ31

Stress corrosion cracking (SCC) behavior of wrought magnesium alloy, AZ31, was investigated. SCC tests were performed using compact tension (CT) specimens in 3%NaCl solution under hydrogen charged conditions, where the cathodic potentials were -1.4, -2.5 and -3.0V. According to Pourbaix diagram, the cathodic potentials of -2.5 and -3.0V correspond to the immunity region. Under the immunity condition, hydrogen embrittlement (HE) type SCC occurred where the KIscc value was much higher than that of active path corrosion (APC) type SCC. The KIscc value decreased and the crack propagation rates, da/dt, increased with decreasing cathodic potential in the immunity region where HE type SCC occurred. At the cathodic potential of -3.0V, da/dt was insensitive to the stress intensity factor.

Preliminary Evaluation of Digital Image Correlation for In-situ Observation of Low Temperature Atmospheric-Induced Chloride Stress Corrosion Cracking in Austenitic Stainless Steels

Digital image correlation has been used to observe the growth of atmospheric-induced chloride stress corrosion cracking in type 304L stainless steel under controlled conditions of temperature, relative humidity and chloride-deposition density in a non-destructive manner. The technique is capable of detecting changes in crack dimensions that are difficult to discern via conventional optical microscopy, i.e. crack growth beneath salt layers and adherent corrosion product deposits, and measurement of crack opening displacements. Our results also demonstrate that suitable specimen design, combined with digital image correlation, will provide the means of comparing the growth behaviour of short atmospheric-induced chloride stress corrosion cracks with data obtained from conventional pre-cracked compact tension specimens as a function of mechanical "driving force".

Initial Stage of SCC of Type 316L Stainless Steel in High Temperature and High Pressure Aqueous Solution

Stress corrosion cracking (SCC) of Type316L stainless steel initiated by a slow strain rate test (SSRT) in a dilute sodium sulphate solution at 288{degree sign}C containing 8 ppm dissolved oxygen. Intergranular stress corrosion cracking (IGSCC) and Transgranular stress corrosion cracking (TGSCC) was observed from Surface of sample after SSRT. Orientation measurements of Type316L were performed by electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM) before SSRT. EBSD analysis was also performed after SSRT. An EBSD map was obtained even after SSRT. A relation between crystal orientation and crack initiation of IGSCC and TGSCC was characterized from EBSD data before SSRT. This demonstrates that the procedure proposed in this work can be of great use for obtaining crystallographic characteristics of crack initiation.

Evaluation of Stress Corrosion Cracking of Type 304L Stainless Steel in Low Concentration Sodium Hydroxide Solution with High Temperature

Stress corrosion cracking (SCC) of austenitic stainless steel serviced in aggressive environment often occurs in power, petrochemical industry, and leads to premature equipment failure and great economic loss. This paper focuses on the problem of the SCC on the 304L stainless steel nozzle of a hydrogenation reactor, which is caused due to on-line alkali cleaning. Susceptibility for SCC was evaluated by Slow Strain Rate Test (SSRT) for as-rolled and sensitized 304L stainless steel in low concentration sodium hydroxide solution with high temperature. The effects of different strain rates, different concentration of sodium hydroxide and different solution temperatures on SCC were investigated. On the basis of this, the contrast tests were also performed in high temperature pure water. After SSRT, fractograph of the fractured specimens was analyzed by using scanning electron microscopy (SEM).

Effect of Physical Property of Water on SCC Growth Rate of 316L Stainless Steels in High-Temperature Water

A number of mechanisms have been proposed to understand stress corrosion cracking (SCC) of metals, e.g. (1) slip dissolution and active pass corrosion based on anodic dissolution of metals, (2) tarnish rupture and internal oxidation based on oxidation ahead the crack tip followed by cracking of the oxides, and (3) hydrogen cracking, etc. If dissolution of metals takes the essential role in the stress corrosion cracking concerned, cracking susceptibility is expected to be significantly affected by dielectric constant of water. Because dielectric constant represents a character of water as a solvent, which determines solubility of metal oxides, and therefore corrosion rate of metals is strongly dependent on dielectric constant of water. K-constant type SCC growth rate tests have been done as a function of physical property (dielectric constant) of water by either manipulating temperature under iso-pressure condition (15MPa) or manipulating pressure under iso-thermal condition (330oC). Intergranular cracking was more enhanced and the crack growth was significantly accelerated under the condition of higher dielectric constant, indicating that dissolution of metal plays important role in the cracking mechanism of 316L stainless steels under the present testing conditions.

SCC behavior of solid-HIPed and irradiated type 316LN-IG stainless steel in oxygenated or hydrogenated water at 423–603 K

Effects of water temperature on the stress corrosion cracking (SCC) susceptibility were studied on a solid hot-isostatic pressed (solid-HIPed) type 316LN-ITER grade (316LN-IG) stainless steel in unirradiated or irradiated condition. Neutron irradiation was conducted at a nominal temperature of 473 K to a dose level of 1 dpa. Slow strain rate testing (SSRT) was performed over a temperature range from 423 to 603 K in oxygenated (DO = 10 ppm) or hydrogenated (DH = 1 ppm) water. In the unirradiated condition, intergranular (IG) type SCC occurred at 603 K in the oxygenated and in the hydrogenated water. In the irradiated condition, IASCC occurred above 573 K in oxygenated water. In the hydrogenated water, IASCC occurred at 513 K, but was suppressed at 573 K.