Stress Corrosion Cracking Of Metals Research Articles

Stress Corrosion Cracking of Metals and Alloys in Aggressive H2S–CO2–Cl– Environments

We have analyzed the data on stress corrosion cracking of steels of various grades in acidic H2S–CO2–Cl– solutions. For the active region of corrosion, we have obtained the dependence of the lifetime and the steady-state corrosion rate on external (concentration of solution components, temperature, and tensile stress) and internal parameters of corrosion (Cr, Ni, and Mo doping level and conditional yield stress for steel). The resultant dependences will make it possible to estimate the corrosion behavior and the possibility of using steel in an aggressive environment without resorting to durable and costly natural tests.

Effect of strain rate and sulfate reducing bacteria on stress corrosion cracking behaviour of X70 pipeline steel in simulated sea mud solution

In order to reduce the damage to the operation of oil and gas pipelines，the stress corrosion cracking (SCC) behavior of X70 pipeline steel in the South China Sea mud simulation solution under different strain rates and diverse growth days of sulfate-reducing bacteria (SRB) was investigated through slow strain rate test, scanning electron microscopy, and energy-dispersive spectroscopy. Results showed that the sensitivity of SCC initially increased and then decreased with the increase of strain rate when the number of SRB growth days was fixed. When the strain rates were 1 × 10−6 s−1 and 4 × 10−6 s−1, greater SRB growth days indicate more sensitivity of the SCC. When the strain rate increased to 7.5 × 10−6 s−1, the degree of the SCC in metals under the aseptic solution was small, and serious SCC would occur when SRB existed in the environment. The SCC sensitivity was maximum under the synergistic effect of strain rate of 4 × 10−6 s−1 and SRB number of 5.7 × 106 cells/ml.

Experimental Study of the Method for Resistance Heat Treatment of Tubes for Steam Generator

The main reason for appearance and development of corrosion damage of the nuclear power plant (NPP) steam generator heat exchanger pipes is the process of stress corrosion cracking of metal under the influence of the residual tensile stresses. The method for heat treatment and straightening of the heat exchanger pipes using distension is proposed. The approbation of the process in a production environment is carried out. The construction and operation of the experimental installation are described. The experimental results show that the proposed method provides mechanical properties, grain size and resistance to intergranular corrosion of metal pipes in accordance with the requirements of Standard Specification 14-3P-197-2001 (Seamless pipe of corrosion-resistant steels with improved surface condition). In pipes, heat-treated by the proposed method, the level of residual tensile stresses and the curvature are one order less than in the tubes, heat treated by the technology which is usually used.

The analysis of the stress corrosion effects for H atom in the symmetrical tilt Ni Σ 5 (012) grain boundary structure

We employ a first-principles total energy method based on density functional theory as implemented in the Vienna ab-initio simulation package (VASP) for a detailed analysis of the symmetrical tilt Ni Σ 5 (012) GB with H impurity atoms in the structure of Σ 5 (012) GB. The effects of H segregation at the Ni Σ 5 (012) GB are investigated in details. The main goal of this study is to perform the ab initio simulations for the Ni Σ 5 (012) GB including the various impurity atoms at GB level as well as pure grain boundary models of Ni Σ 5 (012) GB. The grains can either be pushed apart or pulled together depending on the size of the impurity and nature of the local relaxations. Fundamental understanding of stress-corrosion cracking in metals and alloys including various impurity atoms is important to develop a new-structural material. Our calculations are compatible with the other first principle calculations.

Upgrading the SPP-500-1 moisture separators-steam reheaters used in the Leningrad NPP turbine units

The specific features of existing designs of moisture separators-steam reheaters (MSRs) and experience gained with using them at nuclear power plants are considered. Main factors causing damage to and failures of MSRs are described: nonuniform distribution of wet steam flow among the separation modules, breakthrough of moisture through the separator (and sometimes also through the steam reheater), which may lead to the occurrence of additional thermal stresses and, hence, to thermal-fatigue damage to or stress corrosion cracking of metal. MSR failure results in a less efficient operation of the turbine unit as a whole and have an adverse effect on the reliability of the low-pressure cylinder’s last-stage blades. By the time the design service life of the SPP-500-1 MSRs had been exhausted in power units equipped with RBMK-1000 reactors, the number of damages inflicted to both the separation part and to the pipework and heating surface tubes was so large, that a considerable drop of MSR effectiveness and turbine unit efficiency as a whole occurred. The design of the upgraded separation part used in the SPP-500-1 MSR at the Leningrad NPP is described and its effectiveness is shown, which was confirmed by tests. First, efforts taken to achieve more uniform distribution of moisture content over the perimeter and height of steam space downstream of the separation modules and to bring it to values close to the design ones were met with success. Second, no noticeable effect of the individual specific features of separation modules on the moisture content was revealed. Recommendations on elaborating advanced designs of moisture separators-steam reheaters are given: an MSR arrangement in which the separator is placed under or on the side from the steam reheater; axial admission of wet steam for ensuring its uniform distribution among the separation modules; inlet chambers with an extended preliminary separation system and devices for uniformly distributing steam flows in the separator; separated layout of the of the separator and steam reheater; and use of transversely finned tube bundles for organizing cross flow of steam over the tubes.

A Review of Texture Related Corrosion of Thin Metallic Films

Most of electrochemical properties of thin materials are closely related with the microstructure of the thin films. In this paper, we review the preferred orientation dependency of metals in aqueous solutions. For example, aluminum foil etching in highly concentrated hydrochloric acid solution, etching of invar sheet for shadow masks, and texture related stress corrosion cracking of metals and alloys are discussed. All the phenomena were interpreted in terms of elastic properties of thin films and bulk materials. Keywords: Aluminum, corrosion, etching, invar, stress corrosion cracking, texture, thin film.

Avaliação da suscetibilidade à corrosão sob tensão da ZAC do aço inoxidável AISI 316L em ambiente de reator nuclear PWR

Aços carbono de baixa liga e aços inoxidáveis são amplamente utilizados nos circuitos primários de reatores nucleares do tipo PWR (Pressurized Water Reactor). Ligas de níquel são empregadas na soldagem destes materiais devido a características como elevadas resistências mecânica e à corrosão, coeficiente de expansão térmica adequado, etc. Nos últimos 30 anos, a corrosão sob tensão (CST) tem sido observada principalmente nas regiões das soldas entre materiais dissimilares existentes nestes reatores. Este trabalho teve como objetivo avaliar, por comparação, a suscetibilidade à corrosão sob tensão da zona afetada pelo calor (ZAC) do aço inoxidável austenítico AISI 316L quando submetida a um ambiente similar ao do circuito primário de um reator nuclear PWR nas temperaturas de 303ºC e 325ºC. Para esta avaliação empregou-se o ensaio de taxa de deformação lenta - SSRT (Slow Strain Rate Test). Os resultados indicaram que a CST é ativada termicamente e que a 325ºC pode-se observar a presença mais significativa de fratura frágil decorrente do processo de corrosão sob tensão.

Crack Detection Using Acoustic Emission Methods – Fundamentals and Applications

This paper addresses the fundamentals of the acoustic emission effect associated with fatigue and stress corrosion cracking in metals. It considers the microstructure of cracks and the magnitude of the different types of physical event that can occur at the crack tip during plastic deformation and stable crack growth. Expressions are given for the threshold plastic zone size ‘Dl’ at which local fracture instability occurs and the stress-wave displacement amplitude as a function of distance ‘ui(r)’ for the different wave types ‘i’ produced during crack extension. Dispersion of the stress-wave and its convolution into an electrical burst signal at the sensor is considered together with the choice of appropriate sensing frequency. A methodology is described for correcting the measured signal amplitude for attenuation in the structure and for determining the maximum sensor spacing for the detection and location of events of a specified magnitude ‘Mae’ similar to the Richter scale. Case studies are presented to illustrate the extensive database now available on acoustic emission from crack growth in metallic structures and the technical and commercial benefits to be gained from an acoustic emission based inspection strategy. The applications considered are: • Fatigue crack growth in the node joints of offshore structures, • Stress corrosion cracking in platform flow lines.

The Role of Texture in Stress-Corrosion Cracking of Metals and Alloys

The Role of Texture in Stress-Corrosion Cracking of Metals and Alloys

Chemical dissolution of iron in aqueous solutions

By anodic oxidation of hydrogen on the Pt ring of a metal-disk-Pt-ring rotating electrode in aqueous acid (pH 0.5–3) sulfate solutions, it is shown that during the polarization of the metal disk hydrogen coevolves by two parallel reactions. One is the well known electrochemical charge transfer process, while the other one is a direct chemical reaction of the metal, i.e. iron, with water molecules from the electrolyte. This process was proposed a long time ago by Kolotyrkin and co-workers, but their experimental results were subjected to serious criticism which is taken care of in the present paper. The chemical reaction is potential- and pH-independent and, depending on the actual conditions during the corrosion processes (actual potential, pH, etc.), can be of greater or smaller importance in the overall process. The consequences of the existence of this direct chemical reaction of metal with water molecules (i.e. H2O-induced corrosion or chemical corrosion) on pitting and stress corrosion cracking of metals is discussed.

1999 W.R. Whitney Award Lecture:Past, Present, and Future of Stress Corrosion Cracking

Abstract The systematic study of the problem of stress corrosion cracking of metals started in the middle of the 19th century. At the end of the 20th century, there is still no general agreement about the mechanisms involved in the process. In the present review, an analysis was made of the difficulties found in the study of this problem, the achievements in the field, and what should be expected for future decades.

NANOMETRIC VISUALIZATION OF LOCALIZED DAMAGE BY SCANNING PROBE MICROSCOPY

This paper demonstrates that the scanning probe microscopy (SPM; scanning tunneling microscopy (STM) and atomic force microscopy (AFM)) is capable of performing in situ nanoscopic observation of localized damage in an operating environment: initiation and growth processes of corrosion products, pitting corrosion and intergranular corrosion as well as stress corrosion cracking of metals. This technique is also applied to examine brittle fracture surfaces of various engineering materials including metals, ceramics and single crystal silicon, and the nanoscopic fracture features are discussed. We discuss the related issues in in situ SPM visualization, advantages and disadvantages of STM and AFM, and nanoscopic damage mechanisms based upon nanoscopic observation of damage process; we show that an AFM is more suitable for performing in situ, serial observation of corrosion processes.

Crack Tip Corrosion: Hydrogen Depolarization and Its Inhibition

Abstract Under laboratory conditions, electrode potential and pH values generated during crack tip dissolution are measured on stress corrosion cracks in metals in 3% NaCl solution. Metal dissolution in the crack tip is accompanied by hydrogen depolarization and hydrogen release. Hydrogen depolarization is the main depolarization reaction. An effort is made to reduce the crack growth by inhibiting hydrogen depolarization using CH3COONa salt.

Identifying local corrosion damage in constructional materials

A relationship is considered between a corrosion crack and a corrosion crevice as geometrical objects in which electrochemical processes occur. A model scheme is proposed for a corrosion crack or crevice, and it is shown that the geometrical factor represented by the characteristic width (opening) Δ* of a corrosion crack in the blind part, for which the corrosion rate is maximal, can be decisive in stress corrosion cracking in metals and alloys. A phenomenological criterion is proposed for the onset of corrosion cracking, which is used in a method of calculating the threshold stress intensity coefficient KIscc, which incorporates the corrosion-process parameters in the prefailure zone. Experimental and calculated data are compared, which confirms the approach.

The fractal dimension of stress corrosion cracks

We analyze pictures of experimental stress corrosion cracks in metals after digitalization and filtering and find that although they come from very different sources their fractal dimension is rather well defined to be d f = 1.38 ± 0.05.

A fracture analysis of cathodic delamination in rubber to metal bonds

The purpose of this paper is to provide a method of characterizing the resistance of various adhesives and surface preparations to cathodic delamination using a fracture mechanics approach. The approach is quite similar to that taken in the stress corrosion cracking of metals although no direct accouting is made of the diffusion processes that are involved. The main emphasis is on the large deformation analysis, including the nonlinear material behavior of the rubber, that is required for determining fracture parameters for correlation with debond growth rates.

Initiation of stress-corrosion cracking in metals

Two factors that have been found to have an important influence on stresscorrosion crack initiation, in certain cases, are the extent of environmental access and the presence of residual surface stresses. These are discussed, and examples from service are cited where such effects have played a major role. Restricted environmental access can be particularly significant in high-purity aqueous systems, such as exist in steam turbines, where the resulting stagnation can lead to the formation of aggressive environments and thus cause cracking. Residual stresses arising from machining operations can assist the initiation of cracks, while controlled shot-peening treatment has been found to be beneficial.

Applying critical potential data to avoid stress corrosion cracking of metals

Available data are assembled on the critical potentials for various metal-environment systems below which stress corrosion cracking (SCC) does not occur. Such data can be used practically to avoid SCC by use of cathodic polarization, inhibiting ions or by employing galvanic couples. The slow drift of the corrosion potential before coincidence with the critical potential explains in part the observed induction times for SCC. The relative positions of the two potentials with respect to each other explains the susceptibility or resistance to SCC of various metals in a variety of chemical media. Several models proposed to explain the SCC mechanism are reviewed in the light of the present evidence.

Effect of aqueous solutions of cuprammonium complexes on the machinability of brass

Thermodynamic analysis of the conditions under which the environment has a physicochemical effect on the mechanical properties of solids (the Rebinder effect) gives grounds for the view that fracture in solids may be facilitated by irreversible chemical reactions taking place on their surfaces [1, 2] as well as by the action of related (similar in molecular nature) liquid media. This permits examination from a common viewpoint of an extensive series of processes in which the environment affects the mechanical properties of solids: from purely physical adsorption to purely chemical reaction, for example, during the stresscorrosion cracking of metals and alloys. It is an essential condition for these processes that the energy of the solid-environmen t reaction should be commensurate with the surface energy [3], similar to the situation occurring when a solid is in contact with a related environment [4]. The purpose of our work was the experimental study of the effect of a chemically active environment on the mechanical properties of a solid material under conditions as favorable as possible for fracture to be facilitated as a result of surface reactions. Forced localized fracture (scratching with a diamond point) makes it possible to compare the results obtained with the facilitation of metal machining in the presence of metallic fusions previously studied in [5], a classic example of a reduction in strength resulting from a crop in surface energy; the system studied (brass solutions of ammonia and its derivatives) provides an opportunity for comparing the facilitation of fracture discovered with the patterns of stress corrosion. The investigation was carried out with a specially designed pendulum-type scratch sclerometer. The linear dimensions of the scratch (its width for the most part) were recorded at a constant level of dissipated energy (identical initial amplitude of pendulum swing), as was the speed of pendulum oscillation damping, which is proportional to the coefficient of friction (the linear reduction in amplitude with time characteristic of dry friction was established by preliminary experiments). The relative percentage increase in scratch width was taken as the measure of the effect of the environment on strength. During the experiments, the concentration of ammonia and of bivalent copper in the solution was varied over a wide range. The test agent was prepared by mixing solutions of ammonia and of copper salt of identical percentage concentrations in specified proportions. The liquid obtained was applied by pipette to the carefully polished surface of a brass plate on which a diamond cutting tool connected to the pendulum had made a scratch in about 100 consecutive passes; the cutting tool was pressed against the plate by a constant force. The test results showed that solutions of cuprammonium complexes in specified concentrations could greatly facilitate the fracture of alpha brass (Fig. 1). In these circumstances an increase in the coefficient of friction can be detected in this concentration region. Pure ammonia does not facilitate fracture; what is more, at high ammonia concentrations there is a considerable drop in friction and a reduction in the depth of the scratch as a result of tool slippage. It was necessary to study the connection between the data obtained by us and the composition of the solutions used in the experiments, because contradictory opinions are expressed in the literature on stress corrosion of alpha brass in cupramm0nium solutions as to precisely which ammonia complex is responsible for the fracture.

Role of surface charge in hydrogen charging, hydrogen embrittlement, and stress-corrosion cracking of metals

Role of surface charge in hydrogen charging, hydrogen embrittlement, and stress-corrosion cracking of metals