Showing papers on "Stress corrosion cracking published in 2005"

A Critical Review of the Stress Corrosion Cracking (SCC) of Magnesium Alloys

Abstract: This review aims to provide a foundation for the safe and effective use of magnesium (Mg) alloys, including practical guidelines for the service use of Mg alloys in the atmosphere and/or in contact with aqueous solutions. This is to provide support for the rapidly increasing use of Mg in industrial applications, particularly in the automobile industry. These guidelines should be firmly based on a critical analysis of our knowledge of SCC based on (1) service experience, (2) laboratory testing and (3) understanding of the mechanism of SCC, as well as based on an understanding of the Mg corrosion mechanism.

Microstructural Characterization of SCC Crack Tip and Oxide Film for SUS 316 Stainless Steel in Simulated PWR Primary Water at 320°C

Abstract: Recent studies on stress corrosion cracking (SCC) behaviors of austenitic stainless steels in hydrogenated high-temperature water show that low potential SCC (LPSCC) can occur on cold-worked SUS 316 stainless steel (hereinafter, 316SS). In this study, oxide films and crack tips on cold-worked 316SS exposed to hydrogenated high-temperature water were characterized using analytical transmission electron microscopy (ATEM), grazing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES) in order to study the corrosion and SCC behaviors of these films and crack tips. A double layer structure was identified for the oxide film after a constant extension rate tensile (CERT) test. The outer layer was composed of large particles (0.2–3 μm) of Fe3O4 and the inner layer consisted mainly of fine particles (~10 nm) of FeCr2O4. In addition, nickel enrichment was identified at the metal/oxide interface. Particles of Fe3O4 were also identified on the crack walls. These results indicate that the same elec...

A study on stress corrosion cracking and hydrogen embrittlement of AZ31 magnesium alloy

Abstract: The stress corrosion cracking (SCC) behavior and pre-exposure embrittlement of AZ31 magnesium alloy have been studied by slow strain rate tensile (SSRT) tests in this paper. It is showed that AZ31 sheet material is susceptible to SCC in distilled water, ASTM D1.387 solution, 0.01 M NaCl and 0.1 M NaCl solution. The AZ31 magnesium alloy also becomes embrittled if pre-exposed to 0.01 M NaCl solution prior to tensile testing. The degree of embrittlement increased with increasing the pre-exposure time, It is proposed that both the pre-exposure embrittlement and SCC were due to hydrogen which reduces the cohesive strength. i,e,. hydrogen embrittlement, (c) 2005 Elsevier B.V. All rights reserved.

Stress corrosion cracking susceptibility of friction stir welded AA7075–AA6056 dissimilar joint

Abstract: Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow strain rate tensile (SSRT) tests in air have shown that the weld nugget is marginally overmatched in the weldment, and the fracture occurred in the relatively weaker thermo-mechanically affected zone/heat affected zone (TMAZ/HAZ) of the AA6056 alloy. SSRT tests in 3.5% NaCl solution at a nominal strain rate of 10−6 s−1 have shown that this dissimilar weldment is not susceptible to stress corrosion cracking (SCC) under these test conditions. Also in this case fracture was observed in the TMAZ/HAZ of the AA6056 alloy, with a behaviour very similar to that observed in the tests in air. However, at a still lower nominal strain rate, 10−7 s−1, the TMAZ/HAZ region of AA7075 alloy was found to be susceptible to SCC, exhibiting intergranular fracture. As a whole it is concluded that though the weld nugget is resistant to SCC, the TMAZ/HAZ region of AA7075 in the weldment is prone to SCC in 3.5% chloride solutions at nominal strain rate levels in the order of 10−7 s−1.

Influence of metallurgical variables on sensitisation kinetics in austenitic stainless steels

Abstract: Austenitic stainless steels are the most favoured construction materials for various components required in chemical, petrochemical, fertiliser and nuclear industries. However, these steels are prone to sensitisation. In the sensitised condition, the steels are quite susceptible to intergranular corrosion and intergranular stress corrosion cracking in chloride and caustic environments resulting in the premature failure of the fabricated components during precommissioning and service periods. The topic of sensitisation has been of interest in studies worldwide. The studies included mechanism of sensitisation, test methods, data generation, and influence of several variables and protection methods. This article covers a review of important contributions to this topic with special emphasis on the influence of metallurgical variables. The present state of understanding is discussed in the following areas: mechanisms, test methods, sensitisation diagrams, influence of chemical composition, cold work and grain size, low temperature sensitisation, modelling and laser surface treatment. The need for further investigation in certain areas is highlighted.

Mechanical and corrosion properties of rheocast and low-pressure cast A356-T6 alloy

Abstract: In this study, the mechanical and corrosion behavior of rheocast and low-pressure cast A356-T6 alloy were examined and compared with each other. Tensile, impact and high-cycle fatigue tests were conducted to characterizing the mechanical behavior. For the study of general corrosion and stress corrosion cracking behavior of A356-T6 alloy, polarization, potentiostatic and in situ slow strain rate tests were performed on both products of A356-T6 alloy in a 3.5% NaCl solution. It was found that the mechanical and corrosion behaviors, as well as the microstructural features, of A356-T6 alloy were substantially affected by different processing routes. The tensile elongation and the impact energy values of A356-T6 were, e.g., greatly improved with rheocasting process. The resistance to general corrosion and stress corrosion cracking was also improved with rheocasting process. This study strongly suggests that the microstructural features, including the volume fraction and the shape of eutectic Si particles, are largely responsible for the variation in the mechanical and corrosion properties of A356-T6 alloy with different processing routes.

A Review of Corrosion of Titanium Grade 7 and Other Titanium Alloys in Nuclear Waste Repository Environments

Abstract: Titanium alloy degradation modes are reviewed in relation to their performance in repository environments. General corrosion, localized corrosion, stress corrosion cracking, hydrogen-induced cracking, microbiologically influenced corrosion, and radiation-assisted corrosion of Ti alloys are considered. With respect to the Ti Grade 7 drip shields selected for emplacement in the repository at Yucca Mountain, general corrosion, hydrogen-induced cracking, and radiation-assisted corrosion either do not initiate or propagate sufficiently fast over a 10,000-year time frame in likely repository environments to cause penetration of the drip shield. Stress corrosion cracking (in the absence of disruptive events) is of no consequence to barrier performance; and localized corrosion and microbiologically influenced corrosion are not expected to occur. To facilitate the discussion, Ti Grades 2, 5, 7, 9, 11, 12, 16, 17, 18, and 24 are included in this review.

Slow strain rate corrosion and fracture characteristics of X-52 and X-70 pipeline steels

Abstract: The susceptibility to stress corrosion cracking (SCC) in a NACE solution saturated with H2S, of the X-52 and X-70 steels was studied using slow strain rate tests (SSRT) and electrochemical evaluations. SCC tests were performed in samples which include the longitudinal weld bead of the pipeline steels and were carried out in the NACE solution at both room temperature and 50 °C. After failure, the fracture surfaces were observed in a scanning electron microscope (SEM) and the chemical analysis were obtained using X-rays energy dispersive (EDXs) techniques. The specimens tested in air, exhibited a ductile type of failure, and whereas, those tested in the corrosive solution showed a brittle fracture. Specimens tested in the NACE solution saturated with H2S presented high susceptibility to SCC. Corrosion was found to be an important factor in the initiation of some cracks. In addition, the effect of the temperature on the corrosion attack was explored. The susceptibility to SCC was manifested as a decrease in the mechanical properties. Potentiodynamic polarization curves and hydrogen permeation measurements were made. The diffusion of atomic hydrogen was related to this fracture forms. The hydrogen permeation flux increased with the increasing of temperature.

Role of irradiated microstructure and microchemistry in irradiation-assisted stress corrosion cracking

Abstract: Irradiation has a profound effect on the stress corrosion cracking propensity of austenitic alloys in high-temperature water. Irradiation-assisted stress corrosion cracking (IASCC) has been well documented both in the laboratory and in service over the past two decades. Numerous studies have shown that the degree of intergranular stress corrosion cracking increases with dose. However, the microstructure is simultaneously changing in several ways (dislocation loops, voids, segregation and hardening) and, not surprisingly, they all correlate with increased cracking susceptibility. As a consequence of their simultaneous development, the attribution of IASCC to one or more of these features has been difficult to establish. Mechanisms based on each of the principal effects of irradiation in the alloy are considered. Arguments can be made in support of any one of these features as the cause of IASCC, but substantial evidence exists to refute a first order correlation. The mechanism of IASCC is more likely due t...

Resistance to brittle fracture of glass reinforced polymer composites used in composite (nonceramic) insulators

Abstract: In this paper, the most important results are presented and discussed from a multiyear interdisciplinary study directed toward the identification of the most suitable glass/polymer composite systems with the highest resistance to brittle fracture for high voltage composite insulator applications. Several unidirectional glass/polymer composite systems, commonly used in composite insulators, based either on E-glass or ECR-glass fibers embedded in either polyester, epoxy, or vinyl ester resins have been investigated for their resistance to stress corrosion cracking in nitric acid. The most important factors (fiber and resin types, surface fiber exposure, polymer fracture toughness, moisture absorption, interfacial properties, sandblasting) affecting the resistance of the composites to brittle fracture have been identified and thoroughly analyzed. It has been shown that the brittle fracture process of composite (nonceramic) insulators can be successfully eliminated, or at least dramatically reduced, by the proper chemical optimization of composite rod materials for their resistance to stress corrosion cracking.

Case Reviews on the Effect of Microstructure on the Corrosion Behavior of Austenitic Alloys for Processing and Storage of Nuclear Waste

Abstract: This article describes the corrosion behavior of special austenitic alloys for waste management applications. The special stainless steels have controlled levels of alloying and impurity elements and inclusion levels. It is shown that “active” inclusions and segregation of chromium along flow lines accelerated IGC of nonsensitized stainless steels. Concentration of Cr+6 ions in the grooves of dissolved inclusions increased the potential to the transpassive region of the material, leading to accelerated attack. It is shown that a combination of cold working and controlled solution annealing resulted in a microstructure that resisted corrosion even after a sensitization heat treatment. This imparted extra resistance to corrosion by increasing the fraction of “random” grain boundaries above a threshold value. Randomization of grain boundaries made the stainless steels resistant to sensitization, IGC, and intergranular stress corrosion cracking (IGSCC) in even hot chloride environments. The increased corrosion resistance has been attributed to connectivity of random grain boundaries. The reaction mechanism between the molten glass and the material for process pot, alloy 690, during the vitrification process has been shown to result in depletion of chromium from the reacting surfaces. A comparison is drawn between the electrochemical behavior of alloys 33 and 22 in 1 M HCl at 65 °C. It is shown that a secondary phase formed during welding of alloy 33 impaired corrosion properties in the HCl environment.

Stress corrosion cracking of type 321 stainless steels in simulated petrochemical process environments containing hydrogen sulfide and chloride

Abstract: The susceptibility to stress corrosion cracking (SCC) of type 321 stainless steel (type 321s) in a simulated petrochemical process environment containing hydrogen sulfide and chloride (20 wt.% NaCl + 0.01 M Na2S2O3, pH 2) was assessed using the slow strain rate tensile (SSRT) test and static load (U-bend) tests at the free corrosion potentials. In the SSRT, effects of environmental factors, such as chloride (Cl−) plus thiosulfate (S2O32−), Cl− concentration, solution pH, and temperature, on the susceptibility to SCC of type 321s were critically examined. In addition, factorial design experiments using Yates's algorithm quantitatively estimated the individual and interactive effects of temperature, Cl− concentration, and solution pH on the SCC susceptibility of type 321s. In the U-bend tests, specimens were immersed in an autoclave containing deaerated 20 wt.% NaCl + 0.01 M Na2S2O3 aqueous solution (pH 2) for 1400 h at either 80 or 300 °C. Results of the SSRT tests indicated that the effects of environmental factors on the SCC susceptibility of type 321s decreased in the following order: temperature effect ≫ solution pH effect > Cl− concentration effect. The mechanism of SCC induced by corrosion pits or TiC particles (5–10 μm) is discussed. In addition, results of the U-bend tests show that the susceptibility of type 321s to SCC decreases with increasing temperature, which is related to the more compact surface film containing chromic oxide (Cr2O3) and magnetite (Fe3O4) that forms at the higher temperatures.

Fracture toughness of polycrystalline silicon carbide thin films

Abstract: Thin film polycrystalline silicon carbide (poly-SiC) doubly clamped microtensile specimens were fabricated using standard micromachining processes, and precracked using microindentation. The poly-SiC had been deposited on Si wafers by atmospheric pressure chemical vapor deposition, a process which leads to residual tensile stresses in the poly-SiC thin films; we measured the residual stress adjacent each specimen via a micromachined strain gauge. The stress intensity factor, KI, at the crack tip in each specimen depends on the magnitude of these residual stresses and the precrack length. Upon release, those precracks whose stress intensity exceeded a critical value, KIc, propagated to failure, whereas no crack growth was observed in those precracks with K

Circumferential notched tensile (CNT) testing of cast iron for determination of threshold (KISCC) for caustic crack propagation

Abstract: The paper discusses the use of circumferential notch tensile (CNT) specimens for determination of stress intensity factor ( K I ), and novel extension of CNT technique to determination of threshold stress intensity for propagation of stress corrosion cracking ( K ISCC ). Using CNT testing, K ISCC data have been generated for a cast iron in hot caustic solutions. The features of intergranular propagation of caustic cracks have been established using scanning electron microscopy.

Corrosion Fatigue and Near-Neutral pH Stress Corrosion Cracking of Pipeline Steel and the Effect of Hydrogen Sulfide

Abstract: Crack advance has been studied in an X-70 pipeline steel, using the compliance technique. The electrolyte used in the study was a very dilute brine bubbled with 10% carbon dioxide (CO2). C...