Showing papers on "Stress corrosion cracking published in 2004"

Corrosion in high-temperature and supercritical water and aqueous solutions: a review

Abstract: The aim of the present article is to review some of the common corrosion phenomena and describe the predominant corrosion mechanisms in high-temperature and supercritical water. Corrosion in aqueous systems up to supercritical temperatures is determined by several solution-dependent and material-dependent factors. Solution-depending factors are the density, the temperature, the pH value, and the electrochemical potential of the solution, and the aggressiveness of the attacking anions. Material-dependent parameters include alloy composition, surface condition, material purity, and heat treatment. Corrosion phenomena that are observed include intergranular corrosion, pitting, general corrosion, and stress corrosion cracking. The solubility and dissociation of both attacking species and corrosion products play the most important role for corrosion in high-temperature water. Both solubility and dissociation processes are strongly influenced by the density, or the ionic product, respectively, of the solvent. High values of both parameters favor ionic reactions, and thus, accelerate electrochemical forms of corrosion. At low densities, water behaves like a non-polar solvent, and thus, ions associate. In these cases, the concentation of e.g. aggressive H + drops down and thus, solutions containing species such as HCl become neutral and thus less aggressive. Further, corrosion products plug the surface and material loss stops. Materials parameters have influence especially on the initiation of corrosion. In the present article, these factors are linked with the physical and chemical properties of high-temperature and supercritical water. An outlook is also given for future research needs.

The effect of RRA on the strength and SCC resistance on AA7050 and AA7150 aluminium alloys

Abstract: The effect of retrogression and re-aging (RRA) on the strength and stress corrosion cracking (SCC) performance was evaluated in AA7050 and AA7150 aluminum alloys. Samples from extruded profiles, at their original condition (T77511 for AA7150 and T76511 for AA7050), were solution heat treated and aged at 120 °C for 1440 min (T6 condition). After that, retrogression was performed at 200 °C for times of 5, 10, 20 and 40 min, followed by a re-aging at 120 °C for 1440 min. Hardness and electrical conductivity measurements were used to characterize the samples after different retrogression times and during re-aging. Maximum hardness after re-aging was obtained in the samples retrogressed for 20 and 40 min. Tensile and SCC testing were performed on samples retrogressed for 20 and 40 min and re-aged, and the results were compared with the alloys at their original conditions. After RRA treatment it was observed an increase of 30% in the yield strength of the AA7050 alloy, while for the AA7150 alloy the mechanical properties were similar to the original condition. Both alloys, when submitted to RRA for 40 min retrogression, had a SCC performance similar to their original condition. However, retrogression time of 20 min decreased significantly the SCC performance.

Latest advances in the understanding of acid dewpoint corrosion: corrosion and stress corrosion cracking in combustion gas condensates

Abstract: Corrosion failures due to condensing flue gases containing H2O, SO3, NOx and HCl still occur more often than might be expected. The corrosion failures can be of several types: general corrosion, pitting attack and stress corrosion cracking (SCC). The chemistry of condensing gases is discussed, and some examples of corrosion in large‐scale installations are presented, including blast stoves for steel production, heat recovery steam generators, and waste incineration boilers. The use of thermal insulation inside boiler casings can result in nitrate SCC when the flue gas contains high concentrations of NOx. Nitric acid from flue gas can react with carbon steel and insulation material forming ammonium nitrate and calcium nitrate. Both materials have hygroscopic properties and are very corrosive, even above the water dewpoint of the gases.

Quantitative Assessment of Submodes of Stress Corrosion Cracking on the Secondary Side of Steam Generator Tubing in Pressurized Water Reactors: Part 3

Abstract: The work in this article is part of a project to develop a quantitative description of stress corrosion cracking (SCC) on the secondary side of pressurized water reactor (PWR) steam generator tubing based on existing information from operating plants and from laboratory experiments. This work is the second step in developing a predictive model for SCC on the secondary side. The first step involved developing a statistical framework into which dependencies of the various submodes of SCC can be inserted. The results of the present work will lead to quantitative descriptions of corrosion processes that, in turn, will be incorporated into the statistical framework. The chemistry of heat-transfer crevices will then be assessed to determine the proper inputs to the dependencies of the various submodes of SCC, and these will be connected to bulk environments. The modeling here is directed toward predicting the early occurrence of SCC that is too shallow to be detected by nondestructive examination (NDE)...

Stress Corrosion Cracking of Al-Mg and Mg-Al Alloys

Abstract: Al- and Mg-based alloys are being used for reducing the weight of automobiles. For structural applications, they must have adequate stress corrosion resistance, and yet, under some circumstances, stress corrosion cracking can occur in both alloy systems. Precipitation of the Mg-rich β-phase (Al3Mg2) at grain boundaries of Al-Mg alloys and the γ-phase (Mg17Al12) at grain boundaries of the Mg-Al alloys is a critical factor in their stress corrosion performance. In Mg-Al, the γ-phase is cathodic (noble) to the matrix, while in the Al-Mg case, the β-phase is anodic (active) to the matrix. These phases produce localized galvanic-induced corrosion that leads to intergranular stress corrosion cracking and crack growth rates of 350 and 1,800 times faster than the solution-treated condition, for Al-Mg and Mg-Al, respectively.

Quantitative Assessment of Submodes of Stress Corrosion Cracking on the Secondary Side of Steam Generator Tubing in Pressurized Water Reactors: Part 2

Abstract: The work in this article is part of a project to develop a quantitative description of stress corrosion cracking (SCC) on the secondary side of pressurized water reactor (PWR) steam genera...

Assessment of Tensile Residual Stress Mitigation in Alloy 22 Welds Due to Laser Peening

Abstract: This paper examines the effects of laser peening on Alloy 22 (UNS N06022), which is the proposed material for use as the outer layer on the spent-fuel nuclear waste canisters to be stored at Yucca Mountain. Stress corrosion cracking (SCC) is a primary concern in the design of these canisters because tensile residual stresses will be left behind by the closure weld. Alloy 22 is a nickel-based stainless steel that is particularly resistant to corrosion, however, there is a chance that stress corrosion cracking could develop given the right environmental conditions. Laser peening is an emerging surface treatment technology that has been identified as an effective tool for mitigating tensile redisual stresses in the storage canisters. The results of laser-peening experiments on Alloy 22 base material and a sample 33 mm thick double-V groove butt-weld made with gas tungsten arc welding (GTAW) are presented. Residual stress profiles were measured in Alloy 22 base material using the slitting method (also known as the crack-compliance method), and a full 2D map of longitudinal residual stress was measured in the sample welds using the contour method. Laser peening was found to produce compressive residual stress to a depth of 3.8 mm in 20 mm thick base material coupons. The depth of compressive residual stress was found to have a significant dependence on the number of peening layers and a slight dependence on the level of irradiance. Additionally, laser peening produced compressive residual stresses to a depth of 4.3 mm in the 33 mm thick weld at the center of the weld bead where high levels of tensile stress were initially present.@DOI: 10.1115/1.1789957#

Microstructure Dependence of Stress Corrosion Cracking Initiation in X-65 Pipeline Steel Exposed to a Near-Neutral pH Soil Environment

Abstract: A study was carried out to understand mechanisms of stress corrosion crack initiation in an X-65 pipeline steel exposed to a near-neutral pH soil environment under a mechanical loading condition typical of a pipeline operating in the field. Microcracks initiated on the polished surface of the X-65 pipeline steel after long-term exposure at open-circuit potential in a near-neutral pH synthetic soil solution. It was found that these microcracks were initiated mostly from pits at metallurgical discontinuities such as grain boundaries, pearlitic colonies, and banded phases in the steel. Strong preferential dissolution was observed along planes of the banded structures in the steel. Selective corrosion at these metallurgical discontinuities is attributed to the anodic nature of those areas relative to the neighboring steel surface. Consistent with previous observations, no increased susceptibility to crack initiation was found at physical discontinuities mechanically introduced into the surface of ste...

Environmental effects on cracking and delamination of dielectric films

Abstract: The effects of temperature and moisture on the adhesive and cohesive strength of dielectric materials and the interfaces that are composed of those materials commonly found in thin-film interconnect structures are reviewed. Debond growth rate versus debond driving energy curves (V-G curves) were collected over a range of environmental conditions for both dielectrics and dielectric/metal interfaces. Both are found to exhibit characteristics consistent with stress corrosion cracking mechanisms found in the bulk glass literature. The mechanisms identified in both systems are explained in terms of the salient chemical reactions occurring at the debond tip.

Effect of Line Pipe Steel Microstructure on Susceptibility to Sulfide Stress Cracking

Abstract: The purpose of this experiment was to evaluate the effect of microstructure on sulfide stress cracking (SSC) properties of line pipe steel. Different kinds of microstructures, with chemical compositions identical to one steel heat, were produced by various thermomechanically controlled processes (TMCP). Coarse ferrite-pearlite, fine ferrite-pearlite, ferrite-acicular ferrite, and ferrite-bainite microstructures were investigated with respect to corrosion properties, hydrogen diffusion, and SSC behavior. SSC was evaluated using a constant elongation rate test (CERT) in a NACE TM0177 solution (5% sodium chloride [NaCl] + 0.5% acetic acid [CH3COOH], saturated with hydrogen sulfide [H2S]). The corrosion properties of steels were evaluated by potentiodynamic and linear polarization methods. Hydrogen diffusion through steel matrix was measured by an electrochemical method using a Devanathan-Stachurski cell. The effect of microstructure on cracking behavior also was investigated with respect to crack nu...

Separation of Microstructural and Microchemical Effects in Irradiation Assisted Stress Corrosion Cracking using Post-irradiation Annealing

Abstract: Post-irradiation annealing (PIA) was conducted in order to clarify the role of microstructural and microchemical effects on irradiation assisted stress corrosion cracking (IASCC) susceptibility in simulated pressurized water reactor (PWR) primary water. Microstructures, hardening, radiation-induced segregation and IASCC susceptibility were examined in cold-worked SUS 316 stainless steels irradiated to 25 dpa in a PWR after annealing at 673–823 K for 1h. IASCC susceptibility, microstructures and hardening recovered as the annealing temperature increased whereas the grain boundary segregation of Cr and Ni remained almost unchanged. The results suggested that the change in IASCC susceptibility due to annealing is not attributed to the change in grain boundary segregation but to the change in micro-structures and hardening. The fact that a smaller recovery of radiation hardening caused a larger IASCC susceptibility suggested that a threshold hardening level exists for the occurrence of IASCC.

Stress Corrosion Cracking in Fuel Ethanol: A Newly Recognized Phenomenon

Abstract: An extensive multi-part program was organized and funded by the Subcommittee on Corrosion and Materials of the American Petroleum Institute (API) Committee on Refinery Equipment (CRE), with assistance from the Renewable Fuels Association (RFA), to examine stress corrosion cracking of steel equipment in fuel experience, in-situ monitoring of fule ethanol systems, and laboratory research studies. This article describes the studies and results.

IASCC Susceptibility and Slow Tensile Properties of Highly-irradiated 316 Stainless Steels

Abstract: Irradiation assisted stress corrosion cracking (IASCC) of cold-worked 316 stainless steels irradiated to doses up to 53 dpa was examined using slow strain rate tensile tests in 593 K simulated pressurized water reactor primary water while changing the content of dissolved hydrogen (DH) and dissolved oxygen (DO). A higher susceptibility was observed for higher doses and DH content, accompanied by increased corrosion product formation on the fracture surface and higher hydrogen accumulation near the fracture surface. At 53 dpa the susceptibility at both 0.02 and 8ppm DO was comparable to that at high DH content. The results indicated that IASCC was sensitive to DH content at doses less than 35 dpa but was less sensitive to both DH and DO content at 53 dpa. The subcrack formation and hydrogen accumulation in the hydrogenated condition suggested that processes associated with hydrogen would have an important role in IASCC in hydrogenated water. The same stainless steels were susceptible to intergranular type ...

Localized Dissolution of Millscale-Covered Pipeline Steel Surfaces

Abstract: Electrochemical impedance spectroscopy, corrosion potential measurements, and surface analysis by scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX) and Raman spectroscopy were used to investigate the localized dissolution of millscale-covered pipeline steel surfaces. The porous millscale originally present on the pipe surface exerts an influence on the corrosion of the pipeline and may contribute to the eventual onset of stress corrosion cracking (SCC). Three regions in the corrosion potential-time plot were observed after exposure to an aqueous environment, corresponding to the initial attempts at breakdown of the millscale, coupling of the dissolution of the underlying steel to reductive dissolution of the millscale, and active corrosion of the steel at the base of pores in the film supported by water reduction either on the metal or on the millscale surface. The corrosion rate increases as the dissolved carbon dioxide (CO2) concentration increases. Changes in the solu...

The corrosion behavior of nanocrystalline electrodeposits

Abstract: Nanocrystalline electrodeposits show tremendous improvements in many physical and mechanical properties compared to their conventional polycrystalline counterparts. Of particular concern for their applications as corrosion and wear resistant coatings is their intrinsic resistance to corrosive environments. This paper reviews recent advances in the understanding of the corrosion properties for several nanostructured pure metals (e.g., Ni and Co), alloys (e.g., Ni-P, Co-Ni-Fe) and composites (e.g., Ni-SiC). It will be shown that in many of these materials, grain size reduction to the nanometer range results in considerable improvement in their resistance to localized corrosion such as pitting, intergranular attack and intergranular stress corrosion cracking.

Development of a new tool to generate compressive residual stress within a machined surface

Abstract: Generally, critical machined parts such as aircraft parts require high fatigue strength and resistance to stress corrosion cracking. These machined parts almost all usually have tensile residual stress within the machined surface after milling. However, if the compressive residual stress within the machined surface can be obtained by a milling process alone, it is expected that fatigue strength and resistance to stress corrosion cracking of the machined components will be improved. The purpose of this study is to develop a new tool that can generate compressive residual stress within the machined surface concurrently with the milling process. This tool has cutting edges for material removal and a projection pin for a burnishing-like process. It was shown that the proposed cutter could generate effective compressive residual stress within the machined surface during the milling process. Residual stress levels were in the region of −100 to −200 MPa on the machined surface, and −300 to −400 MPa at 0.05 mm beneath the surface. These levels are almost comparable with those obtained by the shot peening process.

Role of temperature and strain rate on the hydrogen-induced intergranular rupture in alloy 600

Abstract: Tensile tests were conducted at various temperatures (77 to 550 K) and strain rates (10−5 to 10−1 s−1) in order to study the effects of hydrogen on the ductility loss and the intergranular fracture of hydrogen-charged (32 wt ppm) tensile specimens of alloy 600. The H-induced intergranular cracking was shown to require H segregation to grain boundaries (GBs) during plastic deformation. The concordance between the temperature/strain rate domains, where H-induced intergranular rupture of alloy 600 is observed and those of H transport by dislocations, is in favor of a major influence of this mechanism of H transport on the intergranular rupture of H-charged alloy 600 in the 180 to 500 K temperature range. The possible contribution of this mechanism to intergranular stress corrosion cracking (IGSCC) of alloy 600 in the pressurized water reactor (PWR) environment is discussed.