Showing papers on "Stress corrosion cracking published in 1991"

The postulated mechanisms for stress corrosion cracking of aluminum alloys: a review of the literature 1980-1989

Abstract: The stress corrosion cracking (SCC) of aluminum alloys is a well-documented phenomenon, but there is considerable disagreement in the scientific literature as to what mechanism causes it. This paper reviews the past 10 years of publications and describes the experimental methods and the proposed SCC mechanisms of about 90 selected papers. Different SCC mechanisms have been proposed for the different aluminum alloy systems: for example, anodic dissolution is generally favored in the 2xxx series aluminum alloys, while hydrogen-induced cracking is favored in the 7xxx series. However, considering the conflicting reports in the literature, it is still possible that other mechanisms are operational.

Fundamental aspects of corrosion films in corrosion science

Abstract: 1. Thermodynamics of Corrosion.- 2. Kinetics of Corrosion.- 3. Properties of Corrosive Films.- 4. Corrosion Inhibition and the Role of Films.- 5. Films and Pitting Corrosion.- 6. Role of Films in Stress Corrosion Cracking and Hydrogen Embrittlement.- 7. Role of Films in Erosion-Corrosion.

A theory of transgranular stress-corrosion cracking

Abstract: A model is proposed to explain transgranular stress-corrosion cracking (T-SCC) in f.c.c. materials, wherein selective dissolution at the crack tip has the effect of lowering the KIc for cleavage. Crack propagation is shown to be anisotropic, with {110} 〈001〉 growth being discontinuous due to crack arrest by dislocation blunting. Renucleation involves active dissolution of slip planes at the crack tip which changes the stress state at critical Lomer-Cottrell locks causing them to fail by cleavage. Crack growth in directions away from {110} 〈001〉 is continuous. When the crack is propagating, its instantaneous velocity is essentially independent of growth direction. The system studied was Cu-25% Au in 0.6 M NaCl solution at potentials between 300 and 430 mV (s.c.e.), which precludes hydrogen embrittlement.

Brittle fracture of an Au/Ag alloy induced by a surface film

Abstract: The film-induced cleavage model of stress-corrosion cracking (SCC) has been tested using an Ag-20 at. pct Au alloy in 1 M HClO4 solution. Brittle cracks, both intergranular (IG) and transgranular (TG) in nature, were formed by high-speed loading of a thin foil covered with a dealloyed (nanoporous gold) layer. These cracks were found to propagate through the dealloyed layer and into the uncorroded bulk face-centered cubic (fcc) material for a distance of many microns. Hydrogen embrittlement (HE) can be excluded on thermodynamic grounds; thus, only film-induced cleavage can explain the observed decoupling of stress and corrosion in the fracture process.

The applicability of duplex stainless steels in sour environments

Abstract: Very low tolerable partial pressures of H2S (pH2S) have been reported for duplex stainless steels in sour environments. However, such steels resist stress corrosion cracking (SCC) in sour ...

Effect of Palladium Coatings on the Corrosion Potential of Stainless Steel in High-Temperature Water Containing Dissolved Hydrogen and Oxygen

Abstract: The electrochemical behavior of untreated 316 (UNS S31600) stainless steel and similar samples with thin coatings of palladium are compared in high-temperature water containing varying concentrations of hydrogen and oxygen. The differences in potentials are consistent with the hypothesis that the electrochemical recombination of hydrogen and oxygen on the surface controls the corrosion potential (mixed potential) of the sample. Palladium coatings as thin as 0.03 µm result in marked improvement in the response to hydrogen water chemistry (HWC) in lowering the corrosion potential below the critical value for protection against stress corrosion cracking (SCC) even at relatively low hydrogen injection rates and high residual oxygen concentrations. Because the diffusion coefficient of hydrogen is greater than that of oxygen, the protection potential can be achieved with hydrogen: oxygen ratios in the bulk water below the stoichiometric ratio of 2.0 required to form water. Constant extension rate tests...

A mechanistic study of transgranular stress corrosion cracking of type 304 stainless steel

Abstract: Transmission electron microscopy (TEM) was utilized to characterize the deformation substructure of 304 stainless steel tested for transgranular stress corrosion cracking (TGSCC) in 45 wt pet MgCl2 at 155 °C. The TEM characterization was conducted in thin foils prepared from the fracture surface and from a series of known depths below the fracture surface. The results indicate that the stacking fault energy (SFE) of the material immediately ahead of the crack tip is lowered, with the deformation mode at small distances (a few microns) in front of the growing crack front being entirely coplanar while at larger distances homogeneous. The reduction in the SFE is attributed to absorbed hydrogen formed during the cathodic reaction. Based on this and previous observations of transgranular stress corrosion characteristics of aus-tenitic stainless steels in chloride environments, a “hydrogen-induced cleavage” model is proposed. This model is essentially a modification of a model based on enhanced structural reactivity associated with Lomer-Cottrell locks proposed by Robertson and Tetelmann in 1962.27

Proton-induced grain boundary segregation in stainless steel

Abstract: A technique is developed which addresses the problem of irradiation assisted stress corrosion cracking of stainless steels in light water reactors using high energy protons to induce grain boundary segregation. These results represent the first grain boundary segregation measurements in bulk produced by proton irradiation of stainless steel. The technique allows the study of grain boundary composition with negligible sample activation, short irradiation time, rapid sample turnaround and at minimal cost. Scanning Auger electron microscopy is used to obtain grain boundary composition measurements of irradiated and unirradiated samples of ultra high purity (UHP) type 304L stainless steel and UHP type 304L steels with the additions of phosphorus (UHP + P) and sulphur (UHP + S). Results show that irradiation of all three alloys causes significant Ni segregation to the grain boundary and Cr and Fe away from it. Irradiation of the UHP + P alloy also results in segregation of P at the grain boundary from...

Stress corrosion cracking of [110] and [100] tilt boundaries of α-Cu-Al alloy

Abstract: Intergranular stress corrosion cracking (SCC) of Cu–9 at.% Al alloy bicrystals with symmetrical [110] and [100] tilt boundaries has been investigated under constant applied stresses in an ammoniacal solution at 303 ± 2 K. The susceptibility, defined by the inverse of time spent for initiation and propagation of the brittle crack along the boundary, was found to be strongly dependent upon the misorientation. Susceptibility minima were found at misorientations where interfacial energy cusps have been often observed in copper and aluminium in the literature. The grain-boundary energy is considered to be one of the crucial factors which determine the susceptibility. It is suggested that the susceptibiliy is affected by the dislocation behaviour at a grain boundary. A stress field generated as a result of interaction between lattice dislocations and a grain boundary may reduce the resistance to intergranular SCC. The susceptibility rapidly decreases, most probably owing to the increase in dislocations...

Fracture mechanics data and modeling of environmental cracking of nickel-base alloys in high temperature water

Abstract: Environmental cracking of ductile nickel-base alloys has occurred both in pressurized water reactors (e.g., steam-generator tubing) and boiling water reactor components such as pressure-vessel safe ends, weld butters, and filler metals for joining nickel-base alloys or dissimilar metals, and attachment welding pads on pressure vessels. Accurate assessment of the interrelated effects of material, environment, and mechanics on environmentally assisted crack growth rates is required for life prediction of nuclear power reactor components. The objective of this study is to understand and predict the environmental cracking behavior of ductile nickel-base alloys in 288° C water. Experiments were performed on 1T CT specimens of Alloy 600 base metal, and Alloy 182 and Alloy 82 weld metals to evaluate the effects of water chemistry, heat treatment, and stress intensity on crack growth rate. Fracture mechanics, crack growth data on ductile nickel-base alloys were also thoroughly surveyed to provide an over...

Evaluation of stress corrosion crack initiation using acoustic emission

Abstract: Acoustic emission response has been used to detect the development of short intergranular stress corrosion cracks in laboratory samples of sensitized type 304 (UNS S30400) stainless steel (SS). Tests were conducted at 25°C in water containing either 15 ppm of Na2S2O3 or 100 ppm of NaCl. Cylindrical samples with piezoelectric detectors mounted on both ends and the corrosion cell confined to the gauge section were used. The dual detectors allowed discrimination between signals generated within the sample from those generated from the surroundings. It was found that intergranular stress corrosion cracks of 200 to 300 µm length by 100 to 200 µm depth could be reliably detected with this technique. Shallow 10-µm-deep longitudinal flaws were also detected in tests conducted in the 100 ppm NaCl environment.

Effect of microstructure on stress corrosion cracking behaviour of austenitic stainless steel weld metals

Abstract: Austenitic stainless steel welds with different ferrite contents were produced using the submerged arc welding (SAW) strip-cladding process. The clads were removed and remelted using the gas tungsten arc welding (GTAW) process. They were post-weld heat treated at 600, 800 and 1000 °C for 1, 10 and 100 h. Stress corrosion cracking (SCC) tests were conducted on notched tensile samples in a 5N H2SO4 + 0.5N NaCl solution at room temperature. The results showed that when the ferrite network was discontinuous or globularized due to heat treatment, the SCC resistance was better than when the network was continuous. Welds deposited by the low heat input (GTAW) process showed better SCC resistance than their SAW counterparts because they had a finer ferrite network. The overall cracking was due to SCC in austenite and anodic dissolution of ferrite.

Intergranular Cracking of Ni-16Cr-9Fe Alloys in High Temperature Water

Abstract: The objective of this work is to provide a better understanding of the role of microstructure in intergranular stress corrosion cracking (SCC) of controlled-purity, Inconel 600-type alloys...

Room temperature stress corrosion cracking of stainless steels in indoor swimming pool atmospheres

Abstract: Work undertaken to elucidate failures of standard austenitic stainless steels in indoor swimming pool atmospheres which have occurred in recent years in Europe and North America is described. The unusual feature of these failures is that they occurred by a stress corrosion cracking (SCC) mechanism at ambient temperature. Conditions which have given rise to room temperature SCC in laboratory tests are described and mechanisms which may give rise to such conditions in practice are postulated. The work described also involved a survey of conditions in indoor swimming pools as well as experimental work on a range of stainless steels in various environments.

On stress corrosion cracking in aluminum-lithium alloys

Abstract: The stress corrosion cracking (SCC) susceptibility of two aluminum-lithium alloys, a binary AlLi and a ternary AlLiCu alloy, in 0.5 M NaCl solution was investigated using the constant elongation rate technique (CERT). Susceptibility increased with decreasing strain rate and with aging. The alloys were susceptible under both anodic and cathodic applied potentials. The susceptibility dependence of the alloys as a function of applied potential correlates well with published hydrogen permeability data. The susceptibility increased dramatically when hydrogen was charged into the specimen using a hydrogen re-combination “poison” during CERT testing. These experiments suggest that hydrogen plays a major role in the SCC of these alloys. A brittle hydride having the composition LiAlH4 forms in the AlLi system under conditions of severe SCC susceptibility. The brittleness of the hydride is explained. The formation of the hydride is a sufficient condition for SCC of AlLi alloys. A process of SCC in AlLi alloys is proposed wherein hydrogen causes damage by the formation of a hydride.

Effect of Benzotriazole on the Stress Corrosion Cracking and the Electrochemical Polarization of 70/30 Brass in Fluoride Solutions

Abstract: The slow strain rate testing (SSRT) technique was used to study the susceptibility of stress corrosion cracking (SCC) of 70/30 brass in fluoride solution at 20°C. The inhibiting effect of 1,2,3‐benzotriazole (BTA) on the susceptibility of SCC was assessed from experimentally obtained quantitative expressions in terms of maximum stress and reduction of area in these solutions. Electrochemistry of the brass/fluoride/BTA system is presented, and correlation between SCC inhibition and the electrochemical behavior was established. Results are summarized as follows: (i) SCC of 70/30 brass can occur in the fluoride solution, and the critical fluoride concentration is 10 ppm or less, above which SCC will occur. (ii) The effective BTA concentration is 300 ppm or more in 1000 ppm F−, above which SCC can be inhibited. The cathodic reaction on brass is significantly polarized by the presence of BTA. (iii) Anodic potentials promote the SCC of 70/30 brass in fluoride environment, while cathodic potentials inhibit it.

Hydrogen Embrittlement of Pearlitic Steels: Phenomenological Study on Notched and Precracked Specimens

Abstract: In this paper a broad phenomenological study of the hydrogen embrittlement of high strength pearlitic steels is presented. The experimental study includes fracture tests under aggressive e...

Effect of Partial Pressure of Hydrogen on IGSCC of Alloy 600 in PWR Primary Water

Abstract: The frequently reported effect of the partial pressure of hydrogen on the alloy 600 susceptibility to intergranular stress corrosion cracking (IGSCC) in high-temperature water is explained...

A critical-evaluation of the stress-corrosion cracking mechanism in high-strength aluminum-alloys

Abstract: Attempts have been made to elucidate the mechanism of stress-corrosion cracking (SCC) in high-strength Al-Zn-Mg and Al-Li-Zr alloys exposed to aqueous environments by considering the temperature dependence of SCC susceptibility based upon the anodic dissolution and hydrogen embrittlement models. A quantitative correlation which involves the change of threshold stress intensity,KISCC, with temperature on the basis of anodic dissolution has been developed with the aid of linear elastic fracture mechanics. From the derived correlation, it is concluded that the threshold stress intensity decreases as the test temperature increases. This suggestion is inconsistent with that predicted on the basis of hydrogen embrittlement. It is experimentally observed from the Al-Zn-Mg and Al-Li-Zr alloys that the threshold stress intensity,K,ISCC, decreases and the crack propagation rate,da/dt, over the stress intensity increases with increasing test temperature. From considering the change in SCC susceptibility with temperature, it is suggested that a gradual transition in the mechanism for the stress-corrosion crack propagation occurs from anodic dissolution in stage I, where the crack propagation rate increases sharply with stress intensity, to hydrogen embrittlement in stage II, where the crack propagation rate is independent of stress intensity.

Corrosion resistant high chromium stainless steel alloy

Abstract: A high-chromium stainless steel alloy having improved resistance to stress corrosion cracking in high temperature water is comprised of, in weight percent; about 22 to 32 percent chromium, about 16 to 40 percent nickel, up to about 10 percent manganese, up to about 0.06 percent carbon, and the balance substantially iron. A preferred high-chromium alloy is further comprised of about 2 to 9 weight percent of a metal from the group consisting of titanium, niobium, tantalum, and mixtures thereof. Another preferred high-chromium alloy is further comprised of a platinum group metal in an effective amount to reduce the corrosion potential of the alloy in high-temperature water provided with hydrogen.

Fracture control guidelines for stress corrosion cracking of high strength alloys

Abstract: This document provides guidelines for obtaining and using stress corrosion cracking (SCC) test data for high strength alloys, which are used typically in aerospace structures. Both fracture mechanics and non-fracture mechanics tests are considered, but the emphasis is on using fracture mechanics as part of an overall strategy - a fracture control plan - to prevent or control SCC in service. In fact, the control of SCC in aerospace structures is not feasible, and SCC fracture control planning for high strength alloys in aerospace structures must be directed to preventing SCC in service.

Versatile Corrosion Resistance of INCONEL Alloy 625 in Various Aqueous and Chemical Processing Environments

Abstract: INCONEL@ alloy 625 is a nickel-chromium-molybdenum alloy that is used for its high strength, excellent fabricability and weldability, and outstanding corrosion resistance. The outstanding and versatile corrosion resistance of INCONEL alloy 625 under a wide range of temperatures and corrosive environments is the primary reason for its wide acceptance in chemical processing and other applications. This paper will present laboratory and field data related to the resistance of alloy 625 to various aqueous media causing localized corrosion, stress corrosion cracking and other forms of attack. Also the versatility of the alloy for use in oxidizing, carburizing, chlorinated solvents and simulated waste incinerator type environments containing halide species, will be demonstrated. @INCONEL is a trade mark of the Into family of companies. Superalloys 718,625 and Various Derivatives Edited by Edward A. Lmia The Minerals, Metals & Materials Society, 1991

Intergranular stress corrosion cracking of alloy 600 and x-750 in high-temperature deaerated water/steam

Abstract: Intergranular stress corrosion cracking (IGSCC) has been studied in two similar nickel-base alloys, alloys 600 and X-750, in deaerated steam at elevated temperatures (380 °C) In both cases, IGSCC occurs through the nucleation, growth, and linkup of grain boundary voids rather than by grain boundary dissolution The rate of IGSCC is much faster in both alloys when they are heat-treated so that carbon is kept in solution instead of precipitating as grain boundary carbides This higher carbon content allows the formation of a higher methane pressure in grain boundary voids Slip impingement on the grain boundary plays a central role in nucleating a set of voids with a spacing of about 02 μm A second set of more closely spaced bubbles develops between these through the action of stress-assisted diffusion of material from the first set of bubbles

Sulfide Stress Cracking Failures of 12Cr and 17-4PH Stainless Steel Wellhead Equipment

Abstract: Sulfide stress cracking case histories of 12Cr and 17-4PH stainless steel tubing hangers are presented along with the results of NACE Standard TM0177 laboratory tests performed on the fail...

IGSCC crack growth of alloy 600 and X-750 in steam

Abstract: The crack growth rate for IGSCC has been measured in two nickel base alloys, Alloy 600 and X-750, in deaerated, superheated steam between 300 and 400° C. Measurements were made using MWOL ...