Occurrence Of Stress Corrosion Cracking Research Articles

Mitigation of Helium Leakage Risks Within the Cryostat of ITER Including Diagnosing the Occurrence of Stress Corrosion Cracking Within the Thermal Shield Cryogenic Helium Pipes

Mitigation of Helium Leakage Risks Within the Cryostat of ITER Including Diagnosing the Occurrence of Stress Corrosion Cracking Within the Thermal Shield Cryogenic Helium Pipes

Simulation of wave propagation in austenitic stainless steel welds with solidification structure predicted by Cellular Automaton method

Austenitic stainless steel is widely used in nuclear power plants (NPPs) and a variety of occurrences of stress corrosion cracking (SCC) near its weld have been reported among NPPs. Ultrasonic testing is a critical technique for the detection and depth sizing of SCCs. However, such welds' anisotropic and heterogeneous properties cause difficulties in ultrasonic testing when ultrasonic waves propagate through welds. Deeply understanding the characteristics of ultrasonic waves with wave propagation simulation is effective to improve the accuracy of ultrasonic testing. To this end, it is necessary to take crystal orientation and grain boundary into account simultaneously in the numerical model. In this study, a model was developed so that the Cellular Automaton (CA) method can simulate the solidification structure from multilayer and multipass welding process, then the solidification structure of a 7-layer and 7-pass weld of austenitic stainless steel was predicted based on welding conditions. Finally, the finite element method was used to compute wave propagation in austenitic stainless steel weld with the solidification structure predicted. Numerical results of wave propagation in austenitic stainless steel weld were compared to those obtained by experiment.

An Overview High Performance of Stress Corrosion Cracking Behavior for Aeronautic Applications

Tensile stress combined with exposure to a corrosive environment result in a cracking process known as stress corrosion cracking (SCC). It falls in the threshold of the material's fatigue limit and dry cracking. Tensile stress can be applied directly or exist as residual stress within the material. SCC results from specific combinations of composition, environment, and stress. Processes like cold forming, welding, heat treating, machining, and grinding introduce residual stresses. Stress erosion cracking (SCC) occurs when cracks form under static tensile stress and the environment around us . It develops by the result of the interaction between mechanical stress and corrosion/oxidation reactions. The occurrence and progression of SCC depend on the materials, applied loads, and environmental conditions. Some Contributing Factors to SCC In summary, two main features of SCC are emphasized: localization and acceleration of oxidative reactions.

Effect of Laser Peening on the Corrosion Properties of 304L Stainless Steel.

Dry canisters used in nuclear power plants can be subject to localized corrosion, including stress corrosion cracking. External and residual tensile stress can facilitate the occurrence of stress corrosion cracking. Residual stress can arise from welding and plastic deformation. Mitigation methods of residual stress depend upon the energy used and include laser peening, ultrasonic peening, ultrasonic nanocrystal surface modification, shot peening, or water jet peening. Among these, laser peening technology irradiates a continuous laser beam on the surface of metals and alloys at short intervals to add compressive residual stress as a shock wave is caused. This research studied the effect of laser peening with/without a thin aluminum layer on the corrosion properties of welded 304L stainless steel. The intergranular corrosion rate of the laser-peened specimen was a little faster than the rate of the non-peened specimen. However, laser peening enhanced the polarization properties of the cross-section of 304L stainless steel, while the properties of the surface were reduced by laser peening. This behavior was discussed on the basis of the microstructure and residual stress.

Effect of Testing Conditions, Gauge, and Temper on Stress Corrosion Cracking of AA7xxx Aluminum Aerospace Plate Alloys

The European Aviation Safety Agency’s recent safety information bulletin (SIB 2018-04R2) describes a brittle intergranular cracking phenomenon in 7xxx aluminum alloys and recommends testing conditions. These testing conditions are severe compared with expectations regarding, temperature, humidity, and stress in aerostructures. In this study, strong increases in time to failure of smooth specimens tested in humid air were observed when reducing either temperature or stress to levels closer to what is representative of in-service conditions. The cracking morphologies after testing in hot, humid air were identical to those described in the literature for in-service occurrences of stress corrosion cracking (SCC), including the observation of crack arrest markings consistent with a mechanism of alternate local corrosion and crack propagation by hydrogen embrittlement. The differences between such fracture surfaces and those observed in the industry standard SCC screening test, which uses a chloride-containing solution to accelerate initiation and propagation, can be attributed to the pitting of the crack surface in a chloride-containing solution in the wake of the propagating crack. The performances of 7xxx-T7 aluminum plates SCC testing in either hot, humid air or a chloride-containing aqueous solution have been compared as a function of thickness, over-aging treatment, and composition. There is a strong effect of plate thickness in both tests, with substantial decreases in initiation time and lifetime for thinner plates. The effect of plate gauge is such that “legacy” materials (such as 7010-T7651, 7050-T7651, and 7050-T7451) passing the SIB 2018-04R2 test at high thicknesses, fail at lower gauges, yet have been flying for nearly 50 y. An increase in SCC performance with increased overaging is observed in both tests. As a consequence, comparisons of SCC performance of alloy compositions should be made wherever possible at identical plate thickness and for aging treatments that result in comparable strengths. When this is done, high Zn concentration 7449-T76++ (7449-T7651 with additional aging) shows a slightly worse strength-SCC balance than 7010-T7651 and 7050-T7651. The observed trends in SCC performance in the two tests are consistent, suggesting that similar repeated initiation and propagation mechanisms are responsible for cracking in humid air and in aqueous NaCl environments.

Stress corrosion cracking of cable bolts in tunnels: An in-situ testing approach

Premature failure of cable bolts in underground tunnels is a major concern for the mining and civil industries. The unexpected failure of cable bolts in tunnels can threaten the safety of excavation operations and cause subnational economic losses. In this study, an in-situ testing method was developed to identify the cause of failure in the environment where the cable bolts are installed. The testing was conducted in two underground mine tunnels in Australia. The coupon made from non-galvanised and galvanised cable bolt wires with multiple stressed sections were installed in the tunnel roof, allowing direct exposure of coupons to different rock strata environments. The coupons were retrieved from the tunnels after almost ten months and analysed for corrosion. Results from both tunnels showed the occurrence of stress corrosion cracking (SCC) in both non-galvanised and galvanised coupons. The cracking predominantly occurred in the sections exposed to claystone layers. The framework developed in this study can be applied to different regions of any underground spaces to assess the propensity of the environment to cause premature reinforcement failure.

Identification of the root causes of accidents at hazardous production facilities of the fuel and energy complex

The article presents the results of the analysis of statistical data on accidents at the facilities of the main pipeline gas transportation for the period from 2008 to 2018. It has been established that the dynamics of accident rates has a cyclical wave-like character. In the course of analyzing information on accidents that occurred during the study period, groups of the main causes of accidents in the main pipeline gas transportation were identified. In addition, in the course of the study, the nature of the occurrence of stress corrosion cracking was studied in detail, and the root factors that led to the occurrence of accidents for this reason were identified. With the help of regression analysis, a functional relationship was established between the number of accidents due to corrosion destruction and hidden defects, which included defects of the pipe manufacturer and defects in construction and installation works.

Stress corrosion cracking of rockbolts: An in-situ testing approach

Premature failure of rockbolts due to stress corrosion cracking (SCC) is an unresolved global issue in underground structures, particularly underground mines. To date, SCC of rockbolts has been produced in laboratory-based studies under laboratory conditions, however no attempt to produce SCC in-situ in actual underground coal mine conditions has previously been made. In this study, an innovative testing methodology was used in which a rockbolt coupon was developed with multiple stressed sections. The test coupon could be placed in-situ within a borehole in an underground mine, exposing it to the borehole environment, the surrounding rock strata and the groundwater. In-situ coupons were made from both 1355 and HSAC840 grade rockbolt steels and installed within a typical rockbolted horizon where known SCC failure of rockbolts had occurred. SCC occurred in the 1355 grade in-situ coupons, but not in the HSAC840 grade ones despite service failures of HSAC840 rockbolts having occurred in the same underground mine. The difference in behaviour of the HSAC840 coupons and in-service rockbolts is most likely due to different stress regimes acting on the coupons and the rockbolts. Localised corrosion was observed on both steels although analysis of the groundwater indicated that it had low corrosivity. Microbiological analysis showed that a range of bacteria known to be involved in corrosion were present on the rockbolt coupons and in the underground environment. This suggested that the occurrence of localised corrosion and SCC in low corrosivity groundwater could be due to the presence of microbial organisms, in particular, sulphate reducing bacteria. The results of this study provide detailed insights into the SCC of rockbolts in the underground environment. The method developed here can be used to study other reinforcement elements and stressed settings for stress corrosion cracking.

Study of Al-Zn-Cu-Sm Efficiency for Low-Voltage Sacrificial Anode Candidate

Sacrificial anode is one of the most effective methods for preventing corrosion in seawater environment. Aluminum (Al) anode works very well in seawater environment with high electrochemical capacity and high driving voltage. Commonly used aluminum alloy sacrificial anodes have the possibilities to trigger the occurrence of Stress Corrosion Cracking and Hydrogen Embrittlement due to overprotection on high-strength steel. The low voltage sacrificial anode was developed to overcome this problem. Electrochemical behavior of Al-5Zn-0.5Cu alloy with varied samarium (Sm) addition of 0.02 wt% and 0.1 wt% was investigated in this study. The commonly used Al-5Zn-0.02In alloy is also tested as a comparison. Anode efficiency test with weight loss method according to DNVGL-RP-B401 standard was conducted to determine the performance of Al-5Zn-0.5Cu-xSm alloy. The addition of 0.1 wt% Samarium shows the best anode performance with electrochemical capacity 2809.80 Ah/kg and 98% efficiency. Al-5Zn-0.5Cu-0.1Sm alloy is the most potential alloy to be developed as a low potential sacrificial anode to replace commonly used aluminum sacrificial anode with indium addition.

An experimental study on stress corrosion behavior of A131/A and A131/AH32 low carbon steels in simulated seawater

Stress corrosion behavior of ASTM A131/A and A131/AH32 steels were investigated in simulated seawater (SSW) through slow strain rate test (SSRT), static load test in combination with fracture observation, and also electrochemical assessments. According to the results, both steel showed susceptibility to stress corrosion cracking (SCC) in SSW but the SCC susceptibility was higher in steel grade A131/AH32. Scanning electron microscopy (SEM) observation of fractured surfaces exhibited SCC occurrence on both steel. The application of tensile stresses in the elastic range caused an increase in corrosion rate of the two steel in marine environments, however, the corrosion potential presented no changes. In the tensile stress of 70% of yield stress, the A131/AH32 steel demonstrated a higher increase in the corrosion rate than that of the grade A131/A steel. It was found that the general corrosion rate of steel grade A131/A was higher than that of grade A131/AH32 steel in the marine environment, and the reason was attributed to the differences on the steels' alloying elements in particular on carbon content.

Mineralogically influenced stress corrosion cracking of rockbolts and cable bolts in underground mines

Stress corrosion cracking (SCC) of rockbolts and cable bolts in underground mines has been identified as a serious international problem over the past two decades. The frequent occurrence of rockbolt and cable bolt SCC in strata containing clay and groundwater suggests the presence of certain mineral types may be an influencing factor. To identify the environmental factors leading to SCC and evaluate the effects of mineralogically influenced corrosion, a laboratory testing program capable of recreating the underground bolting environments was designed and conducted. A static load was applied to specimens of rockbolts and cable bolts placed in “corrosion cells” containing groundwater, clay, coal or a combination of those materials for about 300 days. Results from these tests revealed that the mineralogical materials indirectly affected the rate of corrosion by significantly altering the local water chemistry. The mechanical load applied to the specimens was found to accelerate the rate of corrosion, and corrosion pits were observed to have formed on the steel surfaces. The generation of corrosion pits would likely result in local stress concentration and contribute to SCC. The results of this study provide further insights into the environmental factors leading to SCC and the proposed methodologies can be used for investigating this type of failure through in-situ experiments.

Investigation of cable bolts for stress corrosion cracking failure

Premature failure of cable bolts due to stress corrosion cracking (SCC) in mining and civil industries is a worldwide problem with limited cost-effective solutions. A load frame capable of applying tensile loads was designed and constructed to simulate and examine SCC of full-size cable bolts (up to 2.4 m in length) under simulated in-situ conditions. The tension loading apparatus was used to conduct periodically increasing strain rate (PISR) tests on cable bolts in simulated underground environments. The PISR test was appropriate and reliable for examining SCC susceptibility of TG and Superstrand cable bolts including the effects of wire arrangement, galvanisation and indentation. Overall, TG cable bolts were more susceptible to SCC than Superstrand cable bolts. In each type of cable bolt, the one with plain wires was approximately 30% more resilient to SCC in terms of time to failure than the one with indented wires. Galvanising was not able to prevent SCC, however it considerably delayed SCC occurrence. The results of this study provided detailed insight into SCC of different types of cable bolts and can be further used for setting up optimal support regimes in different geological and environmental conditions.

Occurrence of Near-Neutral pH Stress Corrosion Cracking in X80 and X100 Pipe Steels Under Various Cathodic Protection Conditions

In this work, proof ring tests with a duration of 220 d were performed to investigate the effect of cathodic protection (CP) on the occurrence of stress corrosion cracking (SCC) of X80 and X100 pipe steels in near-neutral pH environment. Various CP conditions were used in the study to mimic the possible CP circumstances occurring in the field, i.e., under-protection, standard-protection, and over-protection. Also, the delayed CP conditions, i.e., 110-d without CP followed by 110-d with CP, were applied to simulate the interruptions of CP in the real world. The results showed that a sufficient continuous CP could prevent the occurrence of SCC cracks. Under a given condition X100 steel tended to form deeper cracks than X80 steel. The cracks formed in both X80 and X100 steels exhibited normal/quasi-normal depth distributions. Only a small fraction of cracks would propagate deep into the steel. For X80 steel, with CP no higher than −776 mV, CP exhibited an inhibiting effect on both SCC crack initiation and propagation, and the inhibiting effect increased with CP level. For X100 steel, it was indicated that hydrogen effect played a more significant role in crack initiation compared to that in X80 steel. The application of CP would retard the crack growth in X100 steel, but promote more cracks to form. Under the delayed CP conditions, the growth of cracks developed in X80 steel could be effectively controlled by the delayed CP of −776 mV; for the deeper cracks formed in X100 steel, a CP level higher than −776 mV was needed to achieve an effective control on the growth. For both materials, the delayed CP of −1,126 mV would enhance crack initiation.

Measurement of chlorine concentration on steel surfaces via fiber-optic laser-induced breakdown spectroscopy in double-pulse configuration

The corrosive environment provided by chlorine ions on the welds of stainless steel dry cask storage canisters for used nuclear fuel may contribute to the occurrence of stress corrosion cracking. We demonstrate the use of fiber-optic laser-induced breakdown spectroscopy (FOLIBS) in the double-pulse (DP) configuration for high-sensitivity, remote measurement of the surface concentrations of chlorine compatible in constrained space and challenging environment characteristic for dry cask storage systems. Chlorine surface concentrations as low as 5mg/m2 have been detected and quantified by use of a laboratory-based and a fieldable DP FOLIBS setup with the calibration curve approach. The compact final optics assembly in the fieldable setup is interfaced via two 25-m long optical fibers for high-power laser pulse delivery and plasma emission collection and can be readily integrated into a multi-sensor robotic delivery system for in-situ inspection of dry cask storage systems.

Effects of environmental factors on stress corrosion cracking of cold-drawn high-carbon steel wires

Premature failure of cable bolts due to stress corrosion cracking (SCC) is a phenomenon that has reported to occur in underground environments. This paper presents an experimental study to determine the impacts of environmental factors on SCC in high-carbon steel cable bolts used in ground support system. The service life of the wire strands was measured under a range of accelerated SCC conditions using three- and four-point loading jigs. Fractographic analyses of the fracture surfaces of the failed wires displayed typical features indicating that hydrogen embrittlement was involved in SCC in these tests. It was shown that the presence of hydrogen sulphide is more critical than its concentration in SCC. The pH and level of applied stress were determined to have a direct impact on the occurrence of SCC. The deflection angle of the crack path was observed to be an inverse polynomial function of the applied stress level in the wire. This demonstrated the significance of the stress level on the fracture mechanism of cable bolts. Furthermore, the use of a protective galvanised coating on cable bolts was found to be a promising countermeasure against SCC. The results of this study provide detailed insight into the environmental factors involved in SCC of high-carbon steel wires and can be further used for setting guidelines for assessment of environments which cause susceptibility to SCC.

Temperature factors effect on occurrence of stress corrosion cracking of main gas pipeline

The purpose of the article is to analyze and compare the data in order to contribute to the formation of an objective opinion on the issue of the growth of stress corrosion defects of the main gas pipeline. According to available data, a histogram of the dependence of defects due to stress corrosion on the distance from the compressor station was constructed, and graphs of the dependence of the accident density due to stress corrosion in the winter and summer were also plotted. Data on activation energy were collected and analyzed in which occurrence of stress corrosion is most likely constructed, a plot of activation energy versus temperature is plotted, and the process of occurrence of stress corrosion by the example of two different grades of steels under the action of different temperatures was analyzed.

Laser Shock Peening for Suppression of Hydrogen-Induced Martensitic Transformation in Stress Corrosion Cracking

The combination of a susceptible material, tensile stress, and corrosive environment results in stress corrosion cracking (SCC). Laser shock peening (LSP) has previously been shown to prevent the occurrence of SCC on stainless steel. Compressive residual stresses from LSP are often attributed to the improvement, but this simple explanation does not explain the electrochemical nature of SCC by capturing the effects of microstructural changes from LSP processing and its interaction with the hydrogen atoms on the microscale. As the hydrogen concentration of the material increases, a phase transformation from austenite to martensite occurs. This transformation is a precursor to SCC failure, and its prevention would thus help explain the mitigation capabilities of LSP. In this paper, the role of LSP-induced dislocations counteracting the driving force of the martensitic transformation is explored. Stainless steel samples are LSP processed with a range of incident laser intensities and overlapping. Cathodic charging is then applied to accelerate the rate of hydrogen absorption. Using XRD, martensitic peaks are found after 24 h in samples that have not been LSP treated. But martensite formation does not occur after 24 h in LSP-treated samples. Transmission electron microscopy (TEM) analysis is also used for providing a description of how LSP provides mitigation against hydrogen enhanced localized plasticity (HELP), by causing tangling and prevention of dislocation movement. The formation of dislocation cells is attributed with further mitigation benefits. A finite element model predicting the dislocation density and cell formation is also developed to aid in the description.

Influence factors on stress corrosion cracking of P110 tubing steel under CO2 injection well annulus environment

Stress corrosion cracking (SCC) behavior of P110 tubing steel in simulated CO2 injection well annulus environments was investigated through three-point bent tests, potentiodynamic polarization and EIS measurements. The results demonstrate that SCC of P110 tubing steel could occur in acidulous simulated environment, and the sensitivity of SCC increases with the decrease of pH, as well as increase of sulfide concentration and total environmental pressure. Both anodic dissolution and hydrogen embrittlement make contributions to the SCC. Adequate concentration of corrosion inhibitor can inhibit the occurrence of SCC on account of the inhibition of localized anodic dissolution and cathodic hydrogen evolution.

Investigation into recurring military helicopter landing gear failure

Abstract The skid landing gear of a military helicopter failed while the helicopter was moored on the ground at the airport. The rear cross tube of the landing gear assembly was found fractured into two separated pieces. The fracture occurred in the right flange of the rear cross tube, where a connection with the spring tube is established using a clamp. The initial visual inspection of the fracture zone revealed a presence of heavy corrosion and significant damage of the anti-corrosion protective layer on the outer surface of the flange of the rear cross tube. Fractographic analysis highlighted corrosion as the main cause of the failure. Evidence was found to show that the fracture was initiated from corrosion pits located on the exterior, underside of the cylindrical part of the flange. Metallographic examination discovered corrosion pits with micro cracks and multiple branched secondary cracks in the crack origin area, indicating the occurrence of stress corrosion cracking. Chemical analysis of the corrosion deposits showed the presence of sodium, chlorine, calcium and sulfur. The stress analysis of the helicopter landing gear assembly, carried out by means of finite element method, confirmed that the crack origin was located at the area with the maximum tensile stress in the flange.

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.