Showing papers on "Stress corrosion cracking published in 2001"

Role of Mg in the stress corrosion cracking of an Al-Mg alloy

Abstract: The corrosion and stress corrosion cracking (SCC) susceptibility of an Al-Mg alloy, AA5083, has been shown to depend on the precipitation of the Mg-rich β phase, (Al3Mg2), but not the enrichment of elemental Mg at grain boundaries to an enrichment ratio of 1.4. These results were determined by measuring the progress of Mg enrichment at grain boundaries, for increasing thermal-treatment times, using auger electron spectroscopy (AES) of grain boundaries exposed by fracture within the spectrometer and by analytical electron microscopy (AEM) of thin foils. The progress of the β phase precipitation was followed by AEM and scanning electron microscopy (SEM), for the same thermal-treatment times. The lack of a Mg-segregation effect on SCC was demonstrated by results obtained with X-ray photoelectron spectroscopy (XPS) analysis of Mg-implanted Al following in-situ electrochemical tests and SCC tests, while the dominance of β phase precipitation was demonstrated by electrochemical analysis and SCC testing. Crack-growth tests of alloy AA5083 demonstrated faster cracking at potentials anodic to the open circuit potential (OCP) with no increase at potentials cathodic to the OCP.

2001 W.R. Whitney Award Lecture: Understanding the Corrosion of Stainless Steel

Abstract: In order to predict corrosion damage on passive metals, it is essential to use statistical methods and semi-empirical models, but at the same time we must maintain active inquiry into the fundamental deterministic processes that occur during localized corrosion. If it were the case that atomistic events occurring within the intact passive film were responsible for, say, the beneficial effect of alloyed molybdenum, then we would have a gigantic job to do. Luckily, it appears that the quality of the passive film mainly affects the nucleation frequency of pits and has little or no bearing on the effects of environmental or metallurgical variables: T, Cl−, Br−, H2S; Mo, N, σ …. We find that the anodic kinetics of the metal in the already-developed microenvironment of a pit can account for the effects of a large number of variables in pitting corrosion. Specifically, above the critical pitting temperature (CPT), the potential required to precipitate an anodic salt film in a cavity of relevant size is ...

Combined effect of special grain boundaries and grain boundary carbides on IGSCC of Ni–16Cr–9Fe–xC alloys

Abstract: Susceptibility to intergranular stress corrosion cracking in Ni–16Cr–9Fe– x C alloys in 360°C primary water is reduced with increasing fraction of special grain boundaries, i.e. coincident site lattice boundaries (CSLB) and low angle boundaries, and grain boundary carbides. Intergranular stress corrosion cracking (IGSCC) was investigated using interrupted constant extension rate tensile tests in a primary water environment at 360°C. Thermal–mechanical treatments were used to increase the fraction of special boundaries from approximately 20–25% to between 30 and 40%. In a carbon-doped heat, further heat treating was used to precipitate grain boundary carbides preferentially on high-angle boundaries (HAB). Orientation imaging microscopy was used to determine the relative grain misorientations and scanning electron microscopy (SEM) was used to identify specific grain boundaries after each interruption. After each strain increment, the same regions in each sample were examined for cracking. Results showed that irrespective of the microstructure condition, CSLBs always cracked less than HABs. Results also showed that IGSCC is reduced with increasing solution carbon content, and for the same amount of carbon in solution, the addition of grain boundary carbides reduced IGSCC still further. The best microstructure was the one consisting of an enhanced CSLB fraction and chromium carbides precipitated preferentially on high-angle boundaries.

The effects of an Fe–Zn intermetallic-containing coating on the stress corrosion cracking behavior of a hot-dip galvanized steel

Abstract: This study deals with the mechanical behavior of galvanized, interstitial free (IF) steel in air and sodium chloride water. Tensile tests conducted in air at different strain rates lead in general to a ductile behavior. It can become brittle when tested in a NaCl solution at particular strain rate values. Fractographic analysis shows a brittle fracture similar to hydrogen embrittlement (HE). A detailed analysis taking into account both the individual mechanical strength of the phases on the coating as well as the electrochemical reaction between Zn and water allow the explanation of this embrittlement. Hydrogen can be produced and can penetrate the cracks formed inside the intermetallic phases of the coating during loading, thus, reaching the steel substrate. The HE of the IF steel, assisted by zinc dissolution and galvanized coating low toughness, appears to be the cause of the loss of ductility observed in the presence of specific environmental conditions, strain rates and morphologies of the coating.

Environment-Assisted Cracking of Corrosion-Resistant Alloys in Oil and Gas Production Environments: A Review

Abstract: The environment-assisted cracking (EAC) susceptibility of corrosion-resistant alloys (CRA) used in oil and gas production is reviewed. The alloy categories are limited to martensitic stain...

Effects of surface preparation on pitting resistance, residual stress, and stress corrosion cracking in austenitic stainless steels

Abstract: Surface finishing treatments such as shot blasting and wire brushing can be beneficial in improving the integrity of machined surfaces of austenitic stainless steels. These operations optimize in-service properties such as resistance to pitting corrosion and stress corrosion cracking (SCC). In this study, ground steel surfaces were subjected to a series of sand blasting and wire brushing treatments. The surfaces were then characterized by their hardness, surface residual stress state, and resistance to stress corrosion and pitting corrosion. Some samples were selected for depth profiling of residual stress. It is found that surface hardening and the generation of near-surface compressive residual stress are the benefits that can be introduced by sand blasting and brushing operations.

High‐resolution analytical electron microscopy characterization of corrosion and cracking at buried interfaces

Abstract: Recent results are presented demonstrating the application of cross-sectional analytical transmission electron microscopy (ATEM) to corrosion and cracking in high-temperature water environments. Microstructural, chemical and crystallographic characterization of buried interfaces at near-atomic resolutions is shown to reveal evidence for unexpected local environments, corrosion reactions and material transformations. Information obtained by a wide variety of high-resolution imaging and analysis methods indicates the processes occurring during crack advance and provides insights into the mechanisms controlling environmental degradation. Examples of intergranular attack and cracking in type 316 austenitic stainless steel and Ni-based alloy 600 are presented to illustrate the potential for this approach. The presence of deeply attacked grain boundaries off the main cracks, revealed by TEM, is believed to indicate a major role of active corrosion in the stress corrosion cracking (SCC) process. Corroded boundaries were filled with oxides to the leading edges of attack. Analyses of the oxide films and impurities in the narrow intergranular penetrations and crack tips with widths of 10 nm or less indicate influences of the grain boundary characteristics and water chemistry. Boundary and precipitate corrosion structures can be used to identify the local electrochemistry promoting degradation in complex service environments. Solution impurities such as lead are found in high concentrations at nanometer-wide reaction zones in samples from secondary water environments, indicating water access at leading edges of the attack and the influence of these impurities on the corrosion processes. Results for specific samples are used to demonstrate the ability of cross-sectional ATEM to reveal new details of buried corrosion structures that cannot be detected by other methods.

Mechanisms of High-pH and Near-Neutral-pH SCC of Underground Pipelines

Abstract: This paper provides an overview of mechanisms for high-pH and near-neutral-pH stress corrosion cracking of underground pipelines. Characteristics and historical information on both forms of cracking are discussed. This information is then used to support proposed mechanisms for crack initiation and growth.Copyright © 1996 by ASME

Effects of Cooling Time and Alloying Elements on the Microstructure of the Gleeble-Simulated Heat- Affected Zone of 22% Cr Duplex Stainless Steels

Abstract: The effects of austenite stabilizers, such as nitrogen, nickel, and manganese, and cooling time on the microstructure of the Gleeble simulated heat-affected zone (HAZ) of 22% Cr duplex stainless steels were investigated The submerged are welding was performed for comparison purposes Optical microscopy (OM) and transmission electron microscopy (TEM) were used for microscopic studies The amount of Cr2N precipitates in the simulated HAZ was determined using the potentiostatic electrolysis method The experimental results indicate that an increase in the nitrogen and nickel contents raised the δ to transformation temperature and also markedly increased the amount of austenite in the HAZ The lengthened cooling time promotes the reformation of austenite An increase in the austenite content reduces the supersaturation of nitrogen in ferrite matrix as well as the precipitation tendency of Cr2N The optimum cooling time from 800 to 500 °C (Δt8/5) obtained from the Gleeble simulation is between 30 and 60 s, which ensures the austenite content in HAZ not falling below 25% and superior pitting and stress corrosion cracking resistance for the steels The effect of manganese on the formation of austenite can be negligible

Modeling of the chemistry and electrochemistry in cracks : A review

Abstract: The state of the art in crack chemistry modeling is assessed. An overview of conceptual understanding of the processes occurring in a crack is given, and the foundations for establishing m...

Effect of Retained Austenite on Corrosion Performance for Modified 13% Cr Steel Pipe

Abstract: Effect of retained austenite on the corrosion performance of modified 13% Cr martensitic stainless steel (0.025%C-13%Cr-[4% to 6%]Ni-[1% to 2%]Mo) seamless pipe is investigated. Retained a...

Cracking and fracture of suspension bridge wire

Abstract: When water enters a suspension bridge cable, the wires that make up the cable start to deteriorate. The protective zinc coating is the first element that is damaged, followed by corrosion of the steel itself. The wires are subjected to high axial tensile stresses from the bridge loading, bending stresses caused by straightening the curved wires inside the cable, and residual stresses introduced in their manufacture. These stresses, along with the corrosive environment, can lead to stress corrosion cracking or hydrogen-assisted cracking, two processes that lead to eventual failure of the wires. A fracture analysis indicates that the wires in the cable may be subjected to slightly different forces than a wire tested in the laboratory, but that the results of laboratory tests will give conservative values of cable strength.

The influence of a corrosive wood-cutting environment on the mechanical properties of hardmetal tools

Abstract: The influence of a corrosive wood-cutting environment on the strength of hardmetals and on their behaviour under static loading conditions has been investigated. Two commercial hardmetals were tested, which differed in hard phase composition. The results show exposure to this environment to have a highly detrimental influence on the strength of both hardmetals investigated, due to localised corrosive attack which results in the formation of stress raisers. The relative loss in strength as a function of corrosion time is the same for both hardmetals. However, the performance of the two grades differ significantly when a static load is applied in this corrosive environment: the strength of the WC-Co grade remains unaffected by the applied load, while the grade containing a mixed carbide phase exhibits stress corrosion cracking which results in a further reduction in strength.

Effects of alloying elements on the mechanical properties and corrosion behaviors of 2205 duplex stainless steels

Abstract: The effects of alloying elements on the microstructure, mechanical properties, and corrosion behaviors of duplex stainless steels (DSSs) have been investigated in this study. Experimental alloys were prepared by varying the concentrations of the constituent elements in DSSs. Hot ductility test, tensile test, charpy impact test, and corrosion test were performed to evaluate the properties of the experimental alloys. The results showed that the extent of edge cracking of DSSs increased with the increasing value of the crack sensitivity index (CSI). The higher the hot ductility index (HDI) was, the better the hot ductility of DSSs achieved. Austenite (γ) stabilizer generally caused a decrease in the strength and an increase in the charpy impact absorbed energy of the stainless steel. On the contrary, ferrite (α) former exerted its beneficial effect on the strength but became detrimental to the toughness of DSSs. The presences of sulfur and boron also caused a decrease in the impact energy, but nitrogen and carbon hardly affected the toughness within the concentration range tested in this study. The value of pitting nucleation potential (E np ) of different nitrogen contents in 3.5 wt.% NaCl solution at room temperature was almost the same, but the value of pitting protection potential (E pp ) among these alloys was increased with increasing the content of nitrogen. The susceptibility to stress corrosion cracking (SCC) of DSSs was high when tested in boiling 45 wt.% MgCl2 solution. On the other hand, the time to failure of the experimental steels in 40 wt.% CaCl2 solution at 100 °C was longer than that in MgCl2 solution. Nitrogen could affect the SCC behavior of DSSs in CaCl2 solution through the combinative effects by varying the pitting resistance and the slip step dissolution. An optimum nitrogen (N) content of 0.15 wt.% was found where the highest SCC resistance could be obtained. Although γ phase exhibited better resistance to SCC, cracks were found to penetrate through α and γ grains or to propagate along the α/γ interface. As a result, a mixed transgranular plus intergranular mode of fracture surface was observed.

Application of catalytic nanoparticles to high temperature water systems to reduce stress corrosion cracking

Abstract: A method and system for reducing stress corrosion cracking in a hot water system, such as a nuclear reactor, by reducing the electrochemical corrosion potential of components exposed to high temperature water within the structure. The method comprises the steps of: providing a reducing species to the high temperature water; and providing a plurality of noble metal nanoparticles having a mean particle size of up to about 100 nm to the high temperature water during operation of the hot water system. The catalytic nanoparticles, which may comprise at least one noble metal, form a colloidal suspension in the high temperature water and provide a catalytic surface on which a reducing species reacts with least one oxidizing species present in the high temperature water. The concentration of the oxidizing species is reduced by reaction with the reducing species on the catalytic surface, thereby reducing the electrochemical corrosion potential of the component.

Stress corrosion cracking susceptibility of ultra-fine grain copper produced by equal-channel angular pressing

Abstract: The stress-corrosion cracking (SCC) of ultra-fine grain (UFG) severely pre-deformed copper immersed into 1 M NaNO2 aqueous solution is investigated in terms of transient anodic current and fracture morphology. It is found that UFG copper possesses notably better resistance to SCC when compared to its coarse-grain counterpart. In contrast to the coarse grain copper, which fractures transgranularly in a cleavage manner, SCC in UFG specimens occurs intergranularly. The primary role of grain boundaries in SCC of UFG materials is argued from both mechanical and electrochemical aspects. The relatively high resistance to stress-corrosion damage in the UFG state and the intergranular type of SCC are connected with microstructural features of ECA-processed materials. Phenomenology of SCC is discussed from the standpoint of the film rupture and slip dissolution model specified for the severely pre-deformed materials.

Effects of alloy chemistry, cold work, and water chemistry on corrosion fatigue and stress corrosion cracking of nickel alloys and welds.

Abstract: Reactor vessel internal components made of nickel-base alloys are susceptible to environmentally assisted cracking (EAC). A better understanding of the causes and mechanisms of this cracking may permit less conservative estimates of damage accumulation and requirements on inspection intervals. The objective of this work is to evaluate and compare the resistance of Alloys 600 and 690 and their welds, such as Alloys 82, 182, 52, and 152, to EAC in simulated light water reactor environments. The existing crack growth rate (CGR) data for these alloys under cyclic and constant loads have been evaluated to establish the effects of alloy chemistry, cold work, and water chemistry. The experimental fatigue CGRs are compared with CGRs that would be expected in air under the same mechanical loading conditions to obtain a qualitative understanding of the degree and range of conditions for significant environmental enhancement in growth rates. The existing stress corrosion cracking (SCC) data on Alloys 600 and 690 and Alloy 82, 182, and 52 welds have been compiled and analyzed to determine the influence of key parameters on growth rates in simulated PWR and BWR environments. The SCC data for these alloys have been evaluated with correlations developed by Scott and by Ford and Andresen.

Effects Of Hydrogen Peroxide On Intergranular Stress Corrosion Cracking Of Stainless Steel in High Temperature Water, (IV): Effects of Oxide Film on Electrochemical Corrosion Potential

Abstract: In order to determine the effects of hydrogen peroxide on electrochemical corrosion potential (ECP) of type 304 stainless steel (SUS304), ECPs were measured using a high temperature, high pressure ...