Papers by Keyword: Stress Corrosion

Abstract: A slow strain rate tensile (SSRT) test was used to investigate the effect of laser shock peening (LSP) on stress corrosion cracking (SCC) behavior of the 304 austenitic stainless steels (ASSs) in acid chloride solution. Mechanical properties and fracture morphology evolutions of the 304 ASSs were studied as a function of the pulse energies through slow speed tensile tester and scanning electron microscopy (SEM). The results showed that the percentage elongation after fracture increased significantly as the pulse energy rose. Fractographic examination revealed that all the samples appeared a tendency to SCC in the given conditions, but specimens treated by LSP had better resistance to stress corrosion.

Abstract: A slow strain rate tensile (SSRT) test was carried out to investigate the stress corrosion cracking (SCC) behavior of the sensitized 304L austenitic stainless steels (ASSs) in alkaline solution (0.5M NaOH). Mechanical properties and fracture morphology evolutions of the 304L ASSs were studied as a function of temperature through slow speed tensile tester and scanning electron microscopy (SEM). The results showed that the tensile strength and percentage elongation after fracture significantly reduced as the test temperature rose. Fractographic examination revealed both ductile and brittle fracture features for the specimens tested in different environments. However, the proportion of brittle fracture characteristics changed with the temperature.

Abstract: Leakage causes of branch pipe of unit thermal networks were discussed based on macroscopic observation, chemical composition analysis, metallurgical microstructure inspection, mechanical property tests, SEM and EDS analysis. The experimental results showed that frequent contact of outer pipe wall with corrosion media and thermal fatigue load led to early crack of the pipe. During compression test, the crack propagated under increased compression stress and burst finally. Suggestions were provided to prevent similar events happening.

Abstract: In this paper, metallographic examination, visual examination and scanning electron microscopy were used to analyze the perforation failure of the differential pressure transmitter impulse pipe. Macrostructure and microstructure of the hole, corrosion characteristics, and corrosion products were studied. Combined with the service conditions of natural gas pipe, relationship between the pipe material quality and the formation process of the perforation failure was determined utilizing fracture mechanics and corrosion analysis. The perforation failure may be caused by the defects and stress corrosion.

Abstract: An alloy chemical composition of a new ultra-high strength stainless has been successfully designed through strengthening mechanisms of carbide and intermetallic compounds. The forging round bar with diameter of 200 mm has been manufactured by means of ultra-high purity smelting and the whole process technologies of micro-unit refinement and phase change control. It was revealed that the developed steel assumes tensile strength of 1960MPa, elongation of 13.5%, fracture toughness K_IC greater than 90MPa·m^1/2, and K_ISCC greater 60MPa·m^1/2. Based on the microstructural observation and phase identification, it was found that the M₂C and the Laves phase were precipitated in the martensitic laths and a small amount of austenite phase was retained in between the Martensitic lath interfaces, which were related to the improved strength and toughness of the developed steel. Furthermore, it was indicated that the steel also presents high fatigue properties and good high-temperature mechanical properties. The corrosion resistance of the steel is equivalent to that of 15-5PH stainless steel but much better than that of the Aermet100 steel under the condition of the marine atmosphere and sea water immersion. This developed steel can be applied in marine corrosive environment without the surface protection and thus can save the expensive maintenance costs and avoid environmental pollution. Based on the promising properties, it was concluded that the developed steel has wide application prospects in the fields of aviation, aerospace, ships, advanced machinery, and advanced machinery manufacturing and other high-tech.

Abstract: Tests including the constant load tensile, three point bending and hydrogen induced cracking (HIC) are executed to evaluate the comprehensive properties of the 15CrMoR(H) with new smelting process in saturated hydrogen sulfide (H₂S) according to NACE and National Standard. By analyzing and fitting the results of constant load tensile test, the stress-life mathematical model of this material is given. Results show that the stress corrosion threshold of the constant load tensile is 0.7R_el (252MPa).The nominal stress of three point bending S_C is higher than 4.5 R_el (1620MPa). Results of HIC test show that the crack length rate CLR is 4.40%, the crack thickness rate CTR is 0.87% and the crack sensitive rate CSR is 0.04%. According to EFC standard, the safety margin is 3.4, 3.4 and 37.5 times respectively. All the experimental results show that the 15CrMoR(H) material has excellent H₂S stress corrosion cracking resistance properties.

Abstract: The steam generator is operated under the pressure of 15.5MPa and the temperature 327°C. Under this working condition the junction of the heat transfer tube and tube-sheet is accident-prone areas of the steam generator. By using ANSYS to carry out a thermal structure coupling analysis on the junction, it is found that a large tensile stress along axial and tangential directions occurs on outer surface of the heat transfer tube and is located at the region of 2.0 mm to 6.0 mm high over the tube-sheet. The stress attributes to the rapidly change of temperature on the tube outer surface and leads to the stress corrosions.

Abstract: The cracking for the faucet valve made from HPb59-1 brass was investigated by SEM and EDS, metallographic microscope, optical spectrum. The results show that it was a kind of stress corrosion cracking caused by machining stress and corrosive environment (such as sulfur, chlorine etc).

Abstract: The stress corrosion property of 07/09Cr2AlMoRE and its welding joint were investigated under different conditions. The results showed that the anti-SSC performance of welding joint was lower than that of the plate through the Sc experiment. The martensite and overheated structure appeared owing to the improper control during welding and heat treatment, which resulted in the lower anti-SSC property of welding joint. The temperature and Ph value had important effect on corrosion rate through analysis the data of comprehensive corrosion. The corrosion rate would rise 1 times when the temperature increased 30°C. The corrosion rate was improved nearly by one order of magnitude when the pH value decreased from 6 to 4. The corrosion surface was uniform and no any corrosion pit, which indicated that the microstructure and chemical component was nearly uniform.

Abstract: The aim of this study is to determine mechanical properties and stress-corrosion resistance of EN AW-AIZn5Mg1,5CuZr alloy from the aspect of microstructure changes depending on the applied heat treatment. Stress corrosion is caused by the effect of corrosion environment parallel to mechanical stress. It occurs when cracks appear in the metal which is exposed to a corrosion environment and static stretching stresses. The effect of the corrosion environment and stresses on the metal surface cause cracks which are placed perpendicularly to the direction of stretching stresses and may be intercrystalline, intracrystalline or mixed. Stress cracking observations show that distinct cracks are often preceded by the incubation phase. The intensity of microcracks in this phase can be determined by examining changes in mechanical properties caused by changes in alloy structures after various time intervals of the stress-corrosion experiment. This study outlines changes in mechanical properties and resistance of the aluminium alloy in question depending on the heat treatment parameters. Changes in mechanical and corrosion properties are reflected in the structural changes of EN AW-AIZn5Mg1,5CuZr alloy. In order to enhance stress-corrosion resistance and obtain good mechanical properties in Al-Zn-Mg alloys (Zn+Mg>5%), a special heat treatment with cooling with a stop is used. This publication shows suitable heat treatment parameters which guarantee good mechanical properties and high stress-corrosion resistance.