Papers by Keyword: Stress Corrosion

Abstract: Welding is the process of permanently joining materials and tungsten inert gas (TIG) welding is widely used due to its precision, controlled heat input, and cost-effectiveness. This study investigates the stress corrosion behavior of TIG-welded 304L stainless steel in a saline environment, analyzing factors contributing to material degradation. The research involved tensile testing and fractographic analysis to characterize fracture modes and determine the key influences on mechanical strength. Additionally, a microstructural analysis of the heat-affected zone (HAZ) was conducted to assess changes induced by welding. The results indicate that exposure to a chloride-rich environment led to a reduction in mechanical properties, primarily due to the formation of corrosion-related compounds and material thinning. Fractographic analysis revealed a transition in fracture modes, highlighting the influence of corrosion on failure mechanisms. Furthermore, microstructural examination showed significant alterations in the HAZ, which affected the overall integrity of the welded joints. These findings contribute to a better understanding of corrosion-induced degradation in welded 304L stainless steel and provide insights for optimizing welding parameters to improve durability.

Abstract: The 7xxx series Al-Zn-Mg-Cu alloys are stronger than other age-hardenable aluminum alloys at their maximum aging state (T6). Despite having a wide range of applications currently, 7075 aluminum (AA7075) still has certain restrictions because of flaws such stress corrosion cracking (SCC) susceptibility. Here, AA 7075-T6 aluminum alloys underwent a salt spray corrosion test to study pitting corrosion. A shot-blasting procedure in a solution containing 3.5% sodium chloride was also used after heat treatment and aging for five days. Refined microstructure, residual stress, and other surface features were identified. Localized corrosion and the propagation of stress cracks were evaluated in relation to the surface properties, including the treated microstructure and residual stress. The aged sample's microstructure was better after heat treatment compared to the control sample after shot peening. The elongation was caused by the maximum strength's value dropping from 476 MPa to 375 MPa. Due to the dispersion of precipitates during curing, the heat treatment caused the depth of stress corrosion cracking for the double shot to decrease.

Abstract: The problems of stress corrosion or hydrogen blistering of gas pipelines are relevant and require careful study of the causes and factors that cause this type of corrosion-mechanical destruction of pipelines. The analysis of numerous publications on this problem revealed contradictions of information regarding the mechanism of stress corrosion and a lack of experimental materials on the substantiation of the nature and peculiarities of the nature of destruction on gas pipeline networks. Systematic experimental studies using different brands of pipe steels allowed to determine the brands of steels, which according to their characteristics are the most resistant to VBR in harsh operating conditions, including even in the most aggressive NACE environment with H₂S and CO₂ additives at a pressure of 10-15 atm. Moreover, the experimental studies were as close as possible to the operating conditions of pipelines of the gas transportation network. The obtained results of experimental studies can serve as a basis for developing methods of technical diagnostics and forecasting the actual state of pipelines, which will significantly prevent the occurrence of sudden destruction caused by stress corrosion. The influence of the service life of gas pipelines on the degree of flooding and microhardness of pipe steels was established, which made it possible to substantiate the embrittlement of the metal with the increase of service life. The values of impact toughness on samples with sharp and round notches and the amount of work of crack growth depending on the service life of the pipe steels were determined, which made it possible to choose steel grades characterized by the highest resistance to brittle fracture. It is shown that with the service life, the destruction occurs according to a brittle mechanism, which is confirmed by the increase in the share of the fibrous component in the fractured samples after impact tests. It was established that the lowest corrosion rate is possessed by new grades of improved steel grades 20А and 08 KhMChA.The PRFNV parameter proposed in the paper makes it possible to assess the susceptibility of pipe steels to stress corrosion cracking and provides an opportunity to regulate the corrosion crack resistance of pipelines by metallurgical methods.

Abstract: The inhibition performance of citrus x aurantiifolia extract (CXA) on the corrosion of mild steel in 1.5 M H₂SO₄, 2 M H₂SO₄, 3 M H₂SO₄, and 4 M H₂SO₄ solutions was evaluated by weight loss, potentiodynamic polarization techniques, and scanning electron spectroscopy equipped with energy-dispersive X-ray spectroscopy. CXA inhibited the mild steel corrosion in the sulphuric acid solutionswith optimal inhibition results of 96.06% in 1.5 M H₂SO₄ and 86.57% in 4 M H₂SO₄ from weight loss measurement. Weight loss, potentiodynamic polarization, and scanning electron microscopy tests confirm the inhibitive performance of this compound and the increase in inhibitor efficiency increases with inhibitor concentration. The polarization data showed that the inhibitor acts as a mixed-type inhibitor, and fits the Langmuir adsorption isotherm. The adsorption studies clarify the excellent adsorption of this compound on the mild steel surface. The inhibited steel in the acid solution displayed improved surface morphology due to the surface protection effect of CXA molecules. The citrus x aurantiifolia studied here easily mitigates the effect of stress corrosion cracking on mild steel in a sulphuric acid environment. Keywords: Mild steel, Stress corrosion, Adsorption, Corrosion inhibitor, Sulphuric acid, Citrus X Aurantiifolia

Abstract: Two states of aluminum alloy material 7B04 T651 and 7B04 T74 using C-ring specimen were selected to carry out stress corrosion simulation test with different stress levels, corrosion concentrations and time, and the fracture morphology of the crack was observed and analyzed by optical microscope and scanning electron microscope (SEM). The results showed that 7B04-T74 alloy was insensitive to stress corrosion and was not prone to stress corrosion cracking under constant tensile stress lower than 432MPa; The stress corrosion cracking time of 7B04 T651 alloy under three different concentrations has no significant difference, and the stress corrosion cracking occurs within 7 days under the stress of 180MPa-432MPa. The time of stress corrosion cracking increased with the decrease of stress. Stress corrosion cracking (SCC) was very sensitive to Cl element, and it was also easy to produce SCC when the concentration of corrosive medium was low, the threshold value of corrosion cracking was about 108 MPa. SEM and EDS analysis showed that the fracture surface was intergranular, mud-like corrosion products, and secondary cracks. At the same time, the matrix grain boundaries were weakened by Cl element.

Abstract: A crack is found on the surface of stainless steel casting support. The crack was analyzed by macro and micro observation of fracture surface, Energy Dispersive Spectrometer (EDS) analysis, chemical analysis, microstructure examination and hardness test. Moreover, the stress distribution was simulated by finite element analysis. The results show that the crack model of the support is stress corrosion. The stress at the crack location is the largest. Three main factors of stress corrosion were the crack of paint layer, marine atmospheric environment and the pretightening force for the support. Because the service environment cannot be changed, therefore, surface paint protective effect and reduction of preload can be improved to avoid stress corrosion cracking again on the support.

Abstract: There was an oil pipeline fracture found in the unlock process of Z well in western oilfield.The reason that made the oil tube fracturewassystematically studied usingmacroscopic analysis,physical and chemical property test,scanning electron microscope with an energy dispersive X-ray spectrometer and X-ray diffraction analysis.The results suggested that the requirement of relevant standard for C110 steel grade was satisfied with the chemical component and mechanical property of oil tube.The perforation of oil tube made H₂S in the fluid medium enter the oil set of connected rings. In addition, the high-pressure gas left by gas contained certain H₂S and O₂ so that the tubewould fracture and be invalid under the combined action of sulfide stress corrosion and oxygen corrosion.

Abstract: According to the demand of oil and gas field development with a small amount of hydrogen sulfide, CT80S sulfur resistance coiled tubing was developed through the raw materials and manufacturing technology. The microstructure, mechanical properties, fatigue life and corrosion resistance of the CT80S sulfur resistant coiled tubing were analyzed. The results showed that the microstructure of CT80S sulfur resistant coiled tubing was consisted of the ferrite and pearlite with the grain size of 12, banded structure of 1.0, and the inclusions was less than 1.0. The strength and hardness of the pipe meet the requirements of API Spec 5ST, and the hardness control was less than 18HRC. The pipe had excellent low cycle fatigue property, the mean fatigue life of Φ31.8 × 3.18mm tube was 1055 cycles when the internal pressure was 34.47MPa and the bending radius was 1219mm. According to NACE TM 0284 and NACE TM 0177 standard, the HIC and SCC performance tests were carried out in same solution. The results show that the developed tubing is insensitive to HIC and the resistance to sulfide stress corrosion is good, under 90%σs stress loading not break.

Abstract: Effect of heat treatments on the stress corrosion behavior of 7050 Al alloys in 3.5% NaCl solution has been investigated using slow strain rate tensile (SSRT) test. During the slow strain rate tensile process, electrochemical impedance spectroscopy (EIS) in real time was carried out to characterize the electrochemical behavior for different tempers 7050 Al alloys. The investigation shows that both the stress corrosion resistance of 7050 Al alloys is controlled by heat treatments due to the different precipitates state. The improvement of stress corrosion resistance is contributed to the tiny precipitates in matrix which are beneficial to corrosion potential and maintain passivation, and precipitates discontinuous distribution at grain boundary which obstruct intergranular crack connection. Moreover, base on the results, we find out retrogression and re-aging (RRA, i.e., T6 + 200 °C/ retrogression + water quench + T6) increases both tensile strength and stress corrosion resistance. The optimized of retrogression time is 30 minutes.

Abstract: The layered cylindrical shell is one of important structures of high pressure vessels. From 1977 to 2005 there were 8 urea synthesis reactors exploded. Seven of them were layered cylindrical shell structure. Therefore, there will be much more issues come out and waiting for us to study and explore. In this paper, we take the urea synthesis reactor exploded in 2005 in China as an example to study why and how a multi-layered exploded. Through the research work, we not only concluded why and how a multilayered vessel exploded but also established a method to analyze the serious explosion accident of complex vessels such as urea synthesis reactors.