Papers by Keyword: Stress Corrosion Cracking (SCC)

Abstract: The nature and mechanism of stress corrosion cracking have been studied and modeled in laboratory conditions. It was established that the destruction process develops in three stages: the formation of corrosion defects on the pipe surface, birth and subcritical growth of stress-corrosion cracks, and break. Release bands observed in focal fracture at subcritical crack growth stage indicate that fluctuating stresses are involved in the destruction development. Transcrystalline nature of the fracture at subcritical growth stage implies that SCC in pipelines develops in consonance with the hydrogen embrittlement mechanism.

Abstract: Indications were detected on dissimilar metal welds (DMW) of steam generators (SG) after 20 years of operation during NDT inspections. Indications started slowly growth every year. DMW on SGs had to be repaired. Paper describes experimental analysis and degradation mechanism of SG weld joints failures.

Abstract: A 7150 Al-Zn-Mg-Cu alloy is artificially aged at 120 ^oC for varying time. The peak hardness (T6 temper) is obtained at about 24 h at that temperature. Further, the T6 temper is subjected to retrogression and reageing (RRA) treatment. Slow strain rate test (SSRT) has been carried out on the T6 and RRA tempers. SSRT results indicated that the RRA temper have higher resistance to SCC compared to that of T6 temper. SCC behaviour of the alloy tempers have been explained with the help of microstructural features studied by transmission electron microscope (TEM). The large, discrete and discontinuous grain boundary precipitates observed in the microstructure of the RRA temper are believed to be the responsible factor for achieving higher SCC resistance. Further, SEM fractographs and crack morphology have also been analyzed to evaluate the SCC behaviour of the alloy tempers.

Abstract: This study deals with the effect of intermittent impact loading on the SCC growth behaviour of SUS304 austenitic stainless steel. To this end, the Split-Hopkinson pressure bar (SHPB) experiments on SUS304 were performed first to establish the dynamic tensile stress-strain response at strain rates up to 700s^-1. The analyses of dynamic stress intensity factors for wedge loading experiments on modified compact tension specimens, designated WLCT, were then performed by the finite element method. The SCC experiments with the intermittent impact loading for WLCT specimens of SUS304 by the use of the SHPB were mentioned and discussed as well.

Abstract: The impact of local concrete crack on the prestressed steel stress corrosion sensitivity is studied with the SSRT, SEM and other methods. The result shows that, the local concrete crack will increase the prestressed steel stress corrosion sensitivity. The formation of stress corrosion microcracks on the metal surface below the crevice is based on two mechanisms: one is the pitting corrosion nucleation mechanism caused due to Cl^-, and the other is the non-pitting corrosion nucleation mechanism caused due to the film rupture. Once the initial stress corrosion microcrack is formed on the metal surface in the crevice, the interior of microcrack will be in the anodic polarization state due to the effect of the electric field of anodic polarization in the crevice, the metal in the crack will continue to be corroded, and the crack will expand. Moreover, due to the anodic dissolution reaction in the crack, the Fe (OH)₃ and Fe₂O₃ films will be formed on the side wall of the crack, and if the nonmetallic slag inclusions and other defects exist on the side wall of the crack, the origin of secondary crack will be formed here, and the intergranular secondary stress corrosion microcrack will be produced.

Abstract: Temperature and operating pressure are important to stress corrosion cracking (SCC) of stainless steel. The SCC susceptibility of 18-8 type austenitic stainless steel, 06Cr18Ni11Ti (S32168), in an environment containing hydrogen chloride was assessed using the slow strain rate tensile (SSRT) test under different temperature and operating pressure. Results of the SSRT test indicated that the impact of operating pressure on the SCC susceptibility was different at different temperatures. The correlation degrees of temperature and operating pressure to SCC susceptibility were calculated using the grey relational theory. The correlation degree of temperature to the SCC susceptibility was greater than that of operating pressure to the SCC susceptibility.

Abstract: With Visual Basic (VB) language programming, on the basis of traditional SSRT testing, and by the superimposition of square wave load with certain frequency, the stress corrosion test of tensile fluctuating load can be realized. SCC sensitivity of specimen superimposed with square wave load is weaker and its fracture is flat. Results show that VB language programming can accurately and effectively simulate the fluctuating stress state of pipeline caused by pressure fluctuation of natural gas in the stress corrosion test of materials, and can better study the rule and mechanism of stress corrosion of materials, so as to find the economic and effective protection method.

Abstract: Based on the SSRT, by simulating different forms of applied loads, the paper conducts the research on the influence and mechanism of action from different waveforms upon the stress corrosion of pipeline steel. Results show that under the given F - SSRT testing condition, and when the fluctuation frequency and fluctuation amplitude are same, the sensitivity of the stress corrosion produced upon X70 pipeline steel is the weakest under the F-SSRT testing condition of superimposed square wave, and is the strongest under the F-SSRT testing condition of superimposed sine wave, which shows that the sensitivity degree of stress corrosion of materials under the F-SSRT with different load waveforms is obviously different.

Abstract: Slow strain rate tension tests were carried out in order to investigate effect on new corrosion inhibitor to stress corrosion cracking of prestressed steel wire in simulated concrete pore solution. Indeed, the results suggest that C₄H₁₃N₃ can form adsorption film on the metal surface, prevent chloride ion erosion. Meanwhile, MoO₄^2- may make the passive film become denser. The synergistic effect of C₄H₁₃N₃ with MoO₄^2-, can reduce the prestressed steel wire SWRH77B in 3.5%NaCl+ saturated Ca (OH)₂ solution stress corrosion sensitivity, prevent stress corrosion cracking effectively.

Abstract: The Kovar alloy leads broke from two integrated circuits (ICs) with TO (Tin Outline) package. Through the metallurgical microstructure analysis, energy dispersive spectrometer (EDS) analysis and fractography analysis, the failure mode of the leads was found to be stress-corrosion-cracking. After checking the whole plating process, it was found that the residual chloride ions resulted in stress-corrosion-cracking. The chloride ions were absorbed inside the residual organic containment below Ni-plating layer. And a corrective measure was proposed.