Showing papers on "Stress corrosion cracking published in 1998"

Corrosion of metal orthopaedic implants.

Abstract: In situ degradation of metal-alloy implants is undesirable for two reasons: the degradation process may decrease the structural integrity of the implant, and the release of degradation products may elicit an adverse biological reaction in the host Degradation may result from electrochemical dissolution phenomena, wear, or a synergistic combination of the two Electrochemical processes may include generalized corrosion, uniformly affecting the entire surface of the implant, and localized corrosion, affecting either regions of the device that are shielded from the tissue fluids (crevice corrosion) or seemingly random sites on the surface (pitting corrosion) Electrochemical and mechanical processes (for example, stress corrosion cracking, corrosion fatigue, and fretting corrosion) may interact, causing premature structural failure and accelerated release of metal particles and ions The clinical importance of degradation of metal implants is evidenced by particulate corrosion and wear products in tissue surrounding the implant, which may ultimately result in a cascade of events leading to periprosthetic bone loss Furthermore, many authors have reported increased concentrations of local and systemic trace metal in association with metal implants1,4,5,9-11,14,18,25,26,28,29,47,49-55,58,71,72,75-77,87,90,108-110 There also is a low but finite prevalence of corrosion-related fracture of the implant This review focuses on electrochemical corrosion phenomena in alloys used for orthopaedic implants A summary of basic electrochemistry is followed by a discussion of retrieval studies of the response of the implant to the host environment and the response of local tissue to implant corrosion products The systemic implications of the release of metal particles also are presented Finally, future directions in biomaterials research and development …

Hydrogen-Facilitated Anodic Dissolution of Austenitic Stainless Steels

Abstract: Effects of hydrogen in alloys on their anodic polarization curves and the dissolution behavior of types 304 and 310 (UNS 30400 and UNS 31000) stainless steels (SS) in 0.5 M sulfuric acid (...

Corrosion of alloy 625 in aqueous solutions containing chloride and oxygen

Abstract: Alloy 625 (UNS N06625) is used frequently as a reactor material for the oxidation of hazardous organic wastes in supercritical water (supercritical water oxidation [SCWO]). In the presence of chloride (Cl−) and oxygen (O2), all Ni-based alloys corrode fast in high-temperature, subcritical water. High-pressure, high-temperature-resistant tube reactors made of alloy 625 were used as specimens. Coupons were exposed simultaneously inside the test tubes. Experimental conditions included temperatures up to 500°C and pressures up to 38 MPa. Pitting corrosion was observed at temperatures above ≈ 130°C to 215°C. At higher temperatures (up to the critical temperature of water), transpassive dissolution dominated. Under certain conditions, transgranular stress corrosion cracking (TGSCC) appeared in the transition zone between the passive and transpassive regions leading to premature failure of the test reactors. Parts of the corrosion products were insoluble in supercritical water and formed thick layers in...

Mechanics and thermodynamics on the stress and hydrogen interaction in crack tip stress corrosion: experiment and theory

Abstract: The hydrogen distribution around a crack tip subject to stress corrosion for pipeline steels was measured by secondary ion mass spectrometry (SIMS) and modelled by finite element analysis. The results show that hydrogen will be generated and accumulated around the SCC crack tip. From thermodynamics analysis, it has been found that the interaction between the stress and hydrogen at the crack tip will increase the activation energy for anodic dissolution. Hydrogen plays an important role in the process of SCC for pipeline steels by promoting stress corrosion cracking of anodic dissolution type.

Mitigating intergranular attack and growth in lead-acid battery electrodes for extended cycle and operating life

Abstract: Deterioration in the performance of lead acid batteries is primarily governed by weight loss and growth of the positive electrodes, arising from creep and intergranular corrosion/cracking. The present investigation examines the impact of increasing the frequency of grain boundaries having low-Σ misorientations (Σ≤29), described by the Coincident Site Lattice (CSL) model, which are known to be resistant to these intergranular degradation phenomena. Electrode microstructures of various PbCaSn alloys processed to contain frequencies of special boundaries (in excess of 50 pct) exhibited reductions in weight loss of between 26 and 46 pct accompanied by declines in grid growth of between 41 and 72 pct. Moreover, the distribution of intergranular attack/cracking in the microstructure of these alloys can be predicted on the basis of the frequency of low-Σ special boundaries and grain size. In general, improvements in corrosion and creep/cracking occur without compromising tensile properties such as yield strength, ultimate tensile strength (UTS), and ductility. Modifying the crystallographic structure of grain boundaries in Pb alloy battery electrodes, thus, provides an opportunity for minimizing grid thicknesses (weight) and, hence, material costs in battery production, or for maximizing energy densities (Wh/kg) and cycle life performance.

Roles of H2S in the Behavior of Engineering Alloys: A Review of Literature and Experience

Abstract: Hydrogen sulfide (H{sub 2}S) has long been associated with the cause of corrosion damage and sulfide stress cracking (SSC) in high strength steels and high hardness weldments used in oil and gas production, petroleum refining, and petrochemical/chemical processing. Other applications where sulfide species have produced environmental cracking include heavy water production, electric power, marine applications and many others where sulfate reducing bacteria can flourish and oftentimes produce substantial amounts of H{sub 2}S. H{sub 2}S has also been associated with internal blistering, hydrogen induced cracking (HIC) and stress oriented hydrogen induced cracking (SOHIC) of carbon steels used in refinery vessels in wet H{sub 2}S service and pipelines containing sour (H{sub 2}S-containing) fluids. In recent years, new stainless alloys have been implemented in lieu of conventional steels in many applications where H{sub 2}S corrosion is particularly severe. These materials have been used along with chemical inhibitors to mitigate corrosion. These alloys, however, may in some cases also be susceptible to SSC, localized corrosion and anodic stress corrosion cracking (SCC) in sour environments. In this review, the behavior of carbon and low-alloy steels, stainless steels, and nickel alloys in sour environments is discussed. Emphasis is placed on the identification of the various typesmore » of H{sub 2}S-related corrosion and environmental cracking that can occur, the origin and mechanisms, and the methods of control.« less

Stress corrosion crack propagation in AerMet 100

Abstract: Fracture mechanics tests were carried out for AerMet 100 in distilled water and NaCl (3.5 and 35 gl−1). The initiation period at higher values of the stress intensity factor indicated that load application in the stress corrosion cracking (SCC) environment is a necessary but not sufficient factor for SCC and that time is needed for some other factor (e.g., the local hydrogen concentration) to reach an appropriate value. The threshold stress intensity factor, KISSC, was found to increase with decreasing NaCl concentration. The plateau stress corrosion crack velocity was 2 × 10−8 m s−1 for NaCl (3.5 and 35 gl−1). The fracture mode was transgranular with small areas of an intergranular nature.

Hydrogen Evolution and Enrichment Around Stress Corrosion Crack Tips of Pipeline Steels in Dilute Bicarbonate Solution

Abstract: Hydrogen involvement in the process of stress corrosion cracking (SCC) of pipelines in a dilute bicarbonate solution was studied. Hydrogen distributions in the steels were determined using...

Role of Carbides in Stress Corrosion Cracking Resistance of Alloy 600 and Controlled-Purity Ni-16% Cr-9% Fe in Primary Water at 360°C

Abstract: Intergranular stress corrosion cracking (IGSCC) of two commercial alloy 600 (UNS N06600) conditions (heat-treated at low temperature [600LT] and at high temperature [600HT]) and two controlled-purity Ni-16% Cr-9% Fe alloys (carbondoped mill-annealed [CDMA] and carbon-doped thermally treated [CDTT]) were investigated using constant extension rate tensile (CERT) tests in primary water (0.001 M lithium hydroxide [LiOH] + 0.01 M boric acid [H3BO3]) with 1 bar (100 kPa) hydrogen overpressure at 360°C and 320°C. Heat treatments produced two types of microstructures in the commercial and controlled-purity alloys: one dominated by grain-boundary carbides (600HT and CDTT) and one dominated by intragranular carbides (600LT and CDMA). CERT tests were conducted over a range of strain rates and at two temperatures with interruptions at specific strains to determine the crack depth distributions. Results showed IGSCC was the dominant failure mode in all samples. For the commercial alloy and controlled-purity a...

Residual stress effects in stress-corrosion cracking

Abstract: This paper describes a wide variety of residual stress effects in stress-corrosion cracking (SCC) of metallic materials on the basis of previous research of the author on high-strength steel in the form of hot-rolled bars and cold-drawn wires for prestressed concrete. It is seen that internal residual stress fields in the material play a very important—if not decisive—role in the SCC behavior of any engineering material, especially residual stresses generated near the free surface or in the vicinity of a crack tip.

ESEM observations of SCC initiation for 4340 high strength steel in distilled water

Abstract: The stress corrosion cracking (SCC) initiation process for 4340 high strength steel in distilled water at room temperature was studied using a new kind of instrument: an environmental scanning electron microscope (ESEM). It was found that the applied stress accelerated oxide film formation which has an important influence on the subsequent SCC initiation. SCC was observed to initiate in the following circumstances: (1) cracking of a thick oxide film leading to SCC initiation along metal grain boundaries, (2) the initiation of pits initiating SCC in the metal and (3) SCC initiating from the edge of the specimen. All these three SCC initiation circumstances are consistent with the following model which couples SCC initiation with cracking of a surface protective oxide. There is a dynamic interaction between oxide formation, the applied stress, oxide cracking, pitting and the initiation of SCC. An aspect of the dynamic interaction is cracks forming in a protective surface oxide because of the applied stress, exposing to the water bare metal at the oxide crack tip, and oxidation of the bare metal causing crack healing. Oxide crack healing would be competing with the initiation of intergranular SCC if an oxide crack meets the metal surface at a grain boundary. If the intergranular SCC penetration is sufficiently fast along the metal grain boundary, then the crack yaws open preventing healing of the oxide crack. If intergranular SCC penetration is not sufficiently fast, then the oxidation process could produce sufficient oxide to fill both the stress corrosion crack and the oxide crack; in this case there would be initiation of SCC but only limited propagation of SCC. Stress-induced cracks in very thin oxide can induce pits which initiate SCC, and under some conditions such stress induced cracks in a thin oxide can directly initiate SCC.

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (I), Effects of Hydrogen Peroxide on Electrochemical Corrosion Potential of Stainless Steel

Abstract: In order to determine effects of hydrogen peroxide on stress corrosion cracking of structural materials in the primary cooling systems of boiling water reactors, a high temperature high pressure water loop with controlled hydrogen peroxide concentrations and lower possible oxygen concentrations has been fabricated. Test specimens are installed in a stainless steel autoclave which has poly tetra-fluoro-ethylene (PTFE) inner liner to prevent decomposition of hydrogen peroxide on the autoclave surfaces. Hydrogen peroxide is injected into the autoclave inlet through the injection line which also has PTFE inner liner. The concentration of hydrogen peroxide is measured at the autoclave outlet by sampling water via the PTFE-lined sampling line. More than 65% of the injected hydrogen peroxide remains at the autoclave outlet at elevated temperature (288°C). Electrochemical corrosion potential (ECP) of stainless steel is then measured in the autoclave while changing hydrogen peroxide and oxygen concentrations. From these measurements it is concluded that, at the same oxidant concentration: (1) ECP of stainless steel exposed to hydrogen peroxide is higher than that exposed to oxygen; (2) ECP is much affected by specimen surfaces; and (3) ECP shows a hysteresis pattern for on its concentration dependence. ECP of stainless steel with an oxidized surface formed under high hydrogen peroxide concentration is much higher than that with a mechanically polished surface and it is less affected by oxidant species and their concentrations.

Linearly-increasing-stress testing of carbon steel in 4 N NaNO3 and in Bayer liquor

Abstract: This paper reports the application of linearly increasing stress testing (LIST) to the study of stress corrosion cracking (SCC) of carbon steel in 4 N NaNO3 and in Bayer liquor. LIST is similar to the constant extension-rate testing (CERT) methodology with the essential difference that the LIST is load controlled whereas the CERT is displacement controlled. The main conclusion is that LIST is suitable for the study of the SCC of carbon steels in 4 N NaNO3 and in Bayer liquor. The low crack velocity in Bayer liquor and a measured maximum stress close to that of the reference specimen in air both indicate that a low applied stress rate is required to study SCC in this system. (C) 1998 Chapman & Hall.

Correlation Between Acoustic Emission Signals and Hydrogen Permeation in High Strength, Low Alloy Steel Cracking in Wet H 2 S

Abstract: Plates of high strength, low alloy (HSLA) steel (JIS-G-3115 SPV-50Q) were found to be susceptible to sulfide stress cracking and hydrogen-induced cracking (HIC) in wet H{sub 2}S. The diffusion coefficient for the hydrogen atom in the SPV-50Q steel was determined at 25--60 C and the activation energy for diffusion was 24.7 kJ/mol. The HSLA tensile specimens were immersed in the H{sub 2}S-saturated NACE solution (0.5% acetic acid + 5% NaCl) at ambient temperature and their tensile properties were examined after hydrogen charging. The results suggest that the failure behavior is controlled by the barrier effect of the dense iron sulfide film on the steel surface and is not caused by the diffusion of hydrogen atoms in the steel. This suggestion is supported by the results of hydrogen permeation measurements, scanning electron microscopy examination, and acoustic emission (AE) tests. Results of potentiodynamic scans and hydrogen permeation tests indicate that the AE signals observed in the H{sub 2}S environment may come from the formation or rupture of an iron sulfide film on the metal surface. The energy of AE signals in the H{sub 2}S environment is much higher than that under cathodic charging. When HIC occurs in H{sub 2}S-saturated NACE solution, AEmore » energy values are often higher than 500 dB {times} {mu}s.« less

Stress corrosion cracking of steam turbine rotors

Abstract: In the wake of the catastrophic failure of a low-pressure (LP) turbine disk at the Hinkley Point Nuclear Station in 1969, considerable research and development has been devoted to the prob...