Stress corrosion cracking

A study of the effect of allium cepa extract as an inhibitor on mild steel corrosion in 0.5M HCl was made at ambient temperature. The experiments were performed with the weight loss/corrosion rate and potentiostatic polarization measurement techniques. Polarization measurement was performed using a potentiostat (Autolab PGSTAT 30 ECO CHIMIE) interfaced with a computer for data acquisition and analysis. Effective corrosion inhibition of the extract on the steel test specimens in the different concentrations of HCl used was achieved as indicated with the results obtained. There was increasing inhibition performance with increasing concentration of the extract inhibitor. The best inhibition performances were achieved at the lower exposure times for all the extract concentrations used in the 0.5 M HCl. A good correlation of results was obtained for the gravimetric and polarization experiments. A mixed type inhibitor is indicated with the results of ba and bc.

The initiation of stress corrosion cracking in fcc Fe-Cr-Ni ternary alloys was studied by means of quantum chemical molecular dynamics at 288°C. This study showed that the iron and chromium atoms segregate faster than nickel atoms at the surfaces. The atomic model showed that nickel enrichment occurred at the inner oxide layer. The binding energy helps reduce the mobility of the nickel atoms. The surface morphology showed that Fe, Cr, and O accumulate on the very top surface while Fe, Cr, Ni, and O bonding takes place beneath this revealing the formation of an outer and inner oxide film. The diffusion of oxygen and hydrogen into the surface increases when it is under strain. The deeply diffused hydrogen becomes negatively charged by taking electron from metal atoms. Consequently, the process weakens the metallic bonds following with the result that oxygen can diffuse easily into the surface. It seems that hydrogen effectively functions as an oxygen carrier. This kind of reaction process can take place in the molecular domain of a crack tip and thus play a vital role in initiating the SCC process.

This paper is a review of the texture development in zirconium alloys (in the form of thick walled tube reduced extrusion or TREX, thin-walled tubing and sheets) of importance to light and heavy water nuclear reactor technology along with the resultant anisotropic mechanical properties. Quantitative characterization of texture and mechanical anisotropy are emphasized leading to procedures useful to fabricators in optimizing textures for good formability as well as for acceptable in-service performance. A brief history of the development of zirconium alloys is presented followed by texture development and characterization. Mechanical anisotropy is discussed in terms of transverse contractile strain ratios from which the formability (B parameter) is derived. Results on the effect of annealing temperature as well as test temperature on anisotropy parameters are presented. The review concludes with a brief summary of texture effects on creep, stress corrosion cracking and hydride formation. Recent advances in fuel cladding bring out the challenges in characterizing the texture and anisotropy due to Nb additions and microstructural gradients in the new Zircaloyse , 1 such as Zirloe , 2 , Duplexe , 3 and Triclad e , 4 .

This research reports the consequences of mass loss estimations by utilizing of oxygen scavengers in boilers to limit the consumption rate of carbon steel tubes. The consumption rate information was chosen from the literature as function of temperature, pressure, and inhibitors level. Consumption rate increased with increasing in temperature and pressure, and diminished with inhibitor level. Hydroquinone, ascorbic acid, and ethanolamine were utilized as consumption inhibitors. The present work is focused on deciding the artificial neural network (ANN) and mathematical formulas so as to increase great expectation properties. Five scientific models and five ANN display structures were recommended. Computer aided program was utilized for building up these models. The outcomes demonstrate that the polynomial mathematical model and multi-layer discernment can precisely anticipate the deliberate information with high relationship coefficients. Multi-Layer Perceptions (MLP) 3:3-4-1:1 was the best model over than the others with higher correlation coefficient.

A new type of intergranular stress corrosion cracking (IGSCC) has been observed in low carbon martensitic stainless steel at heat affected zone (HAZ). Nano level microstructural analysis was carried out to investigate IGSCC factors. It was found that cracks propagate along prior austenite grain boundaries where a row of carbides had been formed. Cr-depleted zones at the grain boundaries were characterized by a STEM-EDX analysis and that morphology was obtained by deconvoluting this results. It is concluded that Cr-depleted zones only a few nanometers in width are enough to cause IGSCC at HAZ in this steel under certain circumstances.

Titanium resists seawater and brine at temperatures as high as 260 C, and is also resistant to corrosion by sulphur dioxide; hydrogen sulphide; and aqueous solutions of those gases. Titanium is fully resistant to corrosion and stress corrosion cracking in the standard NACE test solution containing 3000 ppm dissolved H 2 S, 5% NaCl, and 0.5% acetic acid (pH 3.5).

Standard test methods such as the Electrochemical Potentiokinetic Reactivation Test (EPR–ASTM G108) and the Double-Loop EPR test (DL-EPR–ISO12732) are commonly used to characterise sensitisation behaviour in austenitic stainless steels. These tests provide a quantitative assessment of microstructure susceptibility. Factors such as different grain size may be accounted for, but additional information on the network of sensitised boundaries is neglected. This paper reports a new approach to characterise the development of sensitisation, applied to a Type 304 austenitic stainless steel subjected to thermo-mechanical processing. DL-EPR testing is augmented by large area Image Analysis (IA) assessments of optical images to measure the dimensions and connectivity of the attacked grain boundary network. Comparison is made with the standard assessment methods, and a new method is proposed, based on normalisation by a cluster parameter to describe the network of susceptible grain boundaries....

The paper presents results of the experimental investigation of the role of strain rate and temperature on stress corrosion cracking (SCC) of mild steel at elevated temperatures. For investigation of SCC-susceptibility, slow strain rate tests were carried out at various strain rates (in the range of 0.12 £ 10 26-0.55 £ 10 26 s 21) in an industrial caustic solution and an inert environment (liquid paraffin) at 90 and 150 8C. The mode of the SCC crack propagation and the fractographic details of the specimens tested in the two environments have been compared. The investigation suggests susceptibility of the mild steel to SCC in the given caustic solution at 150 8C only when the tests were carried out at a strain rate , 0.25 £ 10 26 s-1 , and no susceptibility at 90 8C.

Susceptibility to stress corrosion cracking (SCC) of two candidate alloys for the inner container of the multi-barrier nuclear waste package was evaluated by using wedge-loaded precracked double-cantilever-beam (DCB) specimens in deaerated acidic brine (pH Ϸ 2.70) at 90ЊC. Materials tested included Alloy C-22 and Ti Grade-12. Duplicate samples of each material were loaded at different initial stress intensity factor (K I ) values ranging between 22 and 43 MPa √ m. Both metallography and the compliance methods were used to determine the final crack length. The final stress intensity for SCC (K f ) was computed from the measured final wedge load and the average crack length. The results indicate that, in general, the final crack lengths measured by metallography and compliance agreed well with one another, thus, providing very similar K f values. The alloy C-22 showed higher susceptibility to SCC than Ti Grade-12 in terms of the average crack growth. Fractographic evaluation by scanning electron microscopy (SEM) of broken DCB specimens revealed three distinct regions showing the characteristics of fatigue precrack, SCC, and fast fracture. ᭧

The development of an intergranular stress corrosion crack initiation site in thermally sensitized type 304 austenitic stainless steel has been observed in situ in high temperature oxygenated water using digital image correlation of time-resolved optical observations.  The grain boundary normal stresses were calculated using the Schmid-Modified Grain Boundary Stress (SMGBS) model of Was et al, applying three-dimensional data for the grain boundary planes and grain orientations.  The initiation site coincided with the most highly stressed sensitised boundary, demonstrating the importance of the combined contributions to crack initiation of grain boundary structure and plastic strain incompatibility.

The influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in simulated Pressurized Water Reactor (PWR) primary water has been investigated. A-286 microstructure was characterized by transmission electron microscopy for ageing heat treatments at 670°C and 720°C for durations ranging from 5 h to 100 h. Spherical c 0 phase with mean diameters ranging from 4.6 to 9.6 nm and densities ranging from 8.5 · 10 22 m À3 to 2 · 10 23 m À3 were measured. Results suggest that both the c 0 phase mean diameter and density quickly saturate with time for ageing heat treatment at 720°C while the c 0 mean diameter increases significantly up to 100 h for ageing heat treatment at 670°C. Grain boundary g phase precipitates were systematically observed for ageing heat treatment at 720°C even for short ageing periods. In contrast, no grain boundary g phase precipitates were observed for ageing heat treatments at 670°C except after 100 h. Hardening by c 0 precipitation was well described by the dispersed barrier hardening model with a c 0 barrier strength of 0.23. Stress corrosion cracking behaviour of A-286 was investigated by means of constant elongation rate tensile tests at 1.5 · 10 À7 s À1 in simulated PWR primary water at 320°C and 360°C. In all cases, initiation was transgranular while propagation was intergranular. Grain boundary g phase precipitates were found to have no significant effect on stress corrosion cracking. In contrast, yield strength and to a lesser extent temperature were found to have significant influences on A-286 susceptibility to stress corrosion cracking.

were examined for microscopic defects in order to evaluate their role in causing brittle fracture. The rods evaluated utilized different types of glass fibers and resin systems. Niemeyer's generalized approach to Partial Discharge (PD) modeling was used to investigate the development of electrical discharges inside the rods. The results indicated that the PD inception voltage was well above the highest system voltage used presently. Thus, it was concluded that the reactive species required for the formation of acids could not be developed inside the rod. The results also suggest that chemical reactions other than acid production can promote stress corrosion cracking of the rod and these may play a significant role in the failure process.

Incidents of failure due to corrosion/stress corrosion cracking of high-pressure gas pipelines in Pakistan have been observed to occur after about 15-20 years of service. The present paper constitutes the failure analysis of an 18-inch diameter electric resistance-welded gas pipeline. The failure was characterized, on the basis of all the available evidence and the metallurgical examination carried out on the ruptured pipe, as a stress corrosion failure that had initiated at a longitudinal 'stress raiser'. This stress raiser, which was essentially a manufacturing defect, constituted a longitudinal 'step' on the pipe surface that had resulted from the faulty trimming/shaving of the weld flash. The findings of this study, thus, emphasize the need for the care that must be taken during the shaving-off of the weld flash.

Characteristics of tempered martensite embrittlement (TME), hydrogen embrittlement (HE), and stress corrosion cracking (SCC) in high-strength steels are reviewed. Often, it is important to determine unambiguously by which of these mechanisms failure occurred, in order to suggest the right actions to prevent failure recurrence. To this aim, samples made of high-strength AISI 4340 alloy steel were embrittled by controlled processes that might take place, for example, during the fabrication and service of aircraft landing gears. The samples were then fractured and characterized using light and scanning electron microscopy, microhardness tests, and X-ray diraction. Fractography was found to be the most useful tool in determining which of these mechanisms is responsible for a failure, under similar conditions, of structures made of AISI 4340 alloy steel. #

The root cause of repeated water leaks due to cracking in a circumferential weld of the heating jacket of a petrochemical reactor was traced to cyclic steam pressure, not accounted for in the design. Fractographic and metallographic analyses of the jacket base and weld materials revealed widely open cracks, initiation and propagation being due to larger than allowable cyclic stresses. There were no indications of environment induced cracking, neither creep nor stress corrosion cracking. Appendix 2 of API RP 579 was used to verify alternative designs for the substitution of the heating jacket. Due to time restraints, the substituted part had to be built with a lower strength steel. Reconstruction was successfully done using an austenitic SA 316L stainless steel.

The structural response of post-tensioned beams with bonded wires has been studied experimentally, and a numerical model is proposed. The tests simulated the effect of stress corrosion failure and development of anchorage of the wires on each side of the fracture. The residual structural performance for loading up to failure was also measured. The nonlinear finite element model with interface elements reproduces the different phases of prestressing wire breaking with rebonding and loading of the beam, taking into account local and global parameters. The distribution of damage caused by wire breaking has been assumed to occur in different locations and different failure modes were studied. Conclusions are drawn for the performance of deteriorating prestressed structures.

Room temperature cathodic hydrogen embrittlement in alloy 718 was investigated by means of slow strain rate tensile tests conducted on specimens charged either prior to or during deformation. Tensile tests performed on precharged specimens at strain rates of 5 ×10 − 7 , 5×10 − 5 and 5×10 − 3 s − 1 suggest that hydrogen embrittlement is correlated with hydrogen segregation to moving dislocation and transport by these dislocations. Observations of 1 mm planar cleavage microfacets on fracture surfaces of specimens charged either prior to or during deformation support the idea that embrittlement occurs by strong hydrogen-deformation interactions. In light of these results, the role of the cathodic hydrogen produced by the corrosion process inside a crack during stress corrosion cracking is discussed in conjunction with the corrosion enhanced plasticity model, proposed some years ago by one of the authors. It is suggested that hydrogen transport by dislocations and localisation along active slip planes may be the controlling stage of the cracking process.

The present article describes the failure of a primary reformer tube in an ammonia plant. The failure took place at the stub end of the reformer tube where a SS 321 flange was joined to a HK 40 catalyst tube by welding. Detailed metallurgical examinations indicated that the failure was due to stress corrosion cracking. Both longitudinal and transverse cracks were observed at the region of fracture. The cracks originated at the interface of the weld and HAZ at the inner surface and progressed to the outside of the tube in the transverse (thickness) direction. Microstructural study revealed chromium carbides precipitation at the grain boundaries in the heat affected zones on either sides of the weld. The results clearly indicated that the steel had undergone sensitisation which subsequently led to failure of the reformer tube by stress corrosion cracking. #

This paper presents an updated review of the external corrosion and failure mechanisms of buried natural gas and oil pipelines. Various forms of external corrosion and failure mechanisms such as hydrogen-induced cracking (HIC), hydrogen embrittlement (HE), corrosion fatigue (CF), stress corrosion cracking (SCC) and microbiologically influenced corrosion (MIC) for oil and gas pipelines are thoroughly reviewed. The factors influencing external corrosion and possible forms of environment-assisted cracking (EAC) of pipeline steels in the soil are also reviewed and analyzed in depth. In addition, the existing monitoring tools for the external corrosion assessment and the models for corrosion prevention and prediction, failure occurrence, and remaining life of oil and gas pipelines, are analyzed. Moreover, the articles on external corrosion management, reliability-based models, risk-based models, and integrity assessment including machine learning and fuzzy logic approaches, are also reviewed. The conclusions and recommendations for future research in the prevention and prediction of external corrosion are presented at the end.

Stress corrosion cracking and hydrogen cracking are two important forms of environmental cracking which can cause serious failures in the oil and gas, pipeline, process and many other industries. Both forms of cracking result in normally ductile metals failing in a brittle manner. In many if not most cases, analysis clearly shows which of these failure modes has occurred. However, there can be situations where the two can be confused. This paper reviews the differences and similarities between the two modes, concentrating on the metals and environments, especially steels in sulphide environments, where confusion can arise. It looks at the various forms of cracking, the nature of cracking, its causes and how it is prevented. Sulphide stress cracking can be especially troublesome as, unlike other forms of hydrogen damage, the cracking initiates at the surface. A review of the mechanism of sulphide stress cracking is given, along with its relationship to stepwise cracking. There can also be confusion between these two forms of damage, as a case study from the literature shows.

Until a few years ago there had been no record of stress corrosion cracking (SCC) as a main cause of failures in Argentine pipelines, but as the pipeline system became of a certain age this mechanism started to have an important impact on reliability. This study analyzes three blowouts attributed to high pH SCC in different oil and natural gas transmission pipelines, which occurred by the sudden propagation of longitudinal cracks at the outer surface of the pipes. #

Corrosion is an unavoidable but a controllable process. Due to the issues of toxicity of substances like chromate inhibitors, there is an increasing interest in exploration and utilization of eco-friendly inhibitors, which are also known as green inhibitors. This review briefly discusses some of the interesting features of the green inhibitors reported during the last decade.

Hydrogen evolution and permeation occur during electroplating, corrosion, and cathodic protection. Hydrogen accumulates in areas of high stress and may reach a critical concentration, potentially causing fractures and catastrophic damage. This chapter describes hydrogen permeation and hydrogen-induced damage in metals and alloys. It also discusses hydrogen evolution kinetics, theoretical diffusion solutions, and basic hydrogen permeation models. Models are used as a diagnostic tool to determine the effectiveness of various metals and alloys as hydrogen permeation inhibitors. It then explains experimental atomic hydrogen permeation transient determination and hydrogen absorption rate constants and diffusivity evaluation into metals using case studies. Hydrogen embrittlement, hydrogen-induced cracking, hydrogen blistering, and hydrogen stress cracking are also discussed to show the relationship to hydrogen permeation and hydrogen-induced cracking mechanisms. Finally, various techniques used to prevent and control hydrogen damage of metals and alloys are described.

The new generation of highly alloyed super duplex stainless steels such as Zeron 100 are preferable materials for industrial applications demanding high strength, toughness and superior corrosion resistance, especially against stress corrosion cracking (SCC). SCC is an environmentally assisted failure mechanism that occurs due to exposure to an aggressive environment while under a tensile stress. The mechanism by which SCC of duplex stainless steel is expected to suffer depends on the combination of electrochemical and the mechanical interaction between austenite and ferrite in the duplex alloys. The main aims of this work are to study the suitability of digital image correlation (DIC) to monitor the initiation and propagation of SCC and to understand how the microstructure of duplex stainless steel influences the kinetics of crack initiation and growth. The combined analysis of DIC, SEM and EBSD was used to study the relative crack propagation and the effect of interphase boundarie...

Many efforts have been made to understand the effects of hydrogen on steels, resulting in an abundance of theoretical models and papers. However, a fully developed and practically applicable predictive physical model still does not exist industrially for predicting and preventing hydrogen damage. In practice, it is observed that different types of damages to industrial boiler components have been associated with the presence and localization of hydrogen in metals. In this paper, a damaged boiler tube made of grade 20 – St.20 (or 20G, equivalent to AISI 1020) was investigated. The experimental research was conducted in two distinctive phases: failure analysis of the boiler evaporator tube sample and subsequent postmortem analysis of the viable hydrogen embrittlement mechanisms (HE) in St.20 steel. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hydrogen attack (HTHA) during service, as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, tube wall thickness measurement, tensile testing, hardness measurement, impact strength testing (on in-strumented Charpy machine), analysis of the chemical composition of corrosion products – deposit and the microstructural characterization by optical and scanning electron microscopy – SEM/EDX. The HTHA damage mechanism is a primary cause of boiler tube fracture. Based on the multi-scale special model, applied in subsequent postmortem investigations, the results indicate a simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. The model is based on the correlation of mechanical properties to the SEM fractography analysis of fracture surfaces.

Titanium alloys can suffer from halide-associated stress corrosion cracking at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide promote the cracking of water vapour in the gas stream, depositing embrittling species at the crack tip. Here we report, using isotopically-labelled experiments, that crack tips in an industrial Ti-6Al-2Sn-4Zr-6Mo alloy are strongly enriched (> 5 at.%) in oxygen from the water vapour, far greater than the amounts (0.25 at.%) required to embrittle the material. Surprisingly, relatively little hydrogen (deuterium) is measured, despite careful preparation and analysis. Therefore, we suggest that a combined effect of O and H leads to cracking, with O playing a vital role, since it is well-known to cause embrittlement of the alloy. In contrast it appears that in α + β Ti alloys, it may be that H may drain away into the bulk owing to its high solubility in β-Ti, rather than being retained in the stress field of the crack tip. Therefore, whilst hydrides may form on the fracture surface, hydrogen ingress might not be the only plausible mechanism of embrittlement of the underlying matrix. This possibility challenges decades of understanding of stress-corrosion cracking as being related solely to the hydrogen enhanced localised plasticity (HELP) mechanism, which explains why H-doped Ti alloys are embrittled. This would change the perspective on stress corrosion embrittlement away from a focus purely on hydrogen to also consider the ingress of O originating from the water vapour, insights critical for designing corrosion resistant materials.

Hydrogen embrittlement of a precipitation-hardened Fe-26Mn-11Al-1.2C (wt.%) austenitic steel was examined by tensile testing under hydrogen charging and thermal desorption analysis. While the high strength of the alloy (>1 GPa) was not affected, hydrogen charging reduced the engineering tensile elongation from 44 to only 5%. Hydrogen-assisted cracking mechanisms were studied via the joint use of electron backscatter diffraction analysis and orientation-optimized electron channeling contrast imaging. The observed embrittlement was mainly due to two mechanisms, namely, grain boundary triple junction cracking and slip-localization-induced intergranular cracking along micro-voids formed on grain boundaries. Grain boundary triple junction cracking occurs preferentially, while the microscopically ductile slip-localization-induced intergranular cracking assists crack growth during plastic deformation resulting in macroscopic brittle fracture appearance.

Component failures due to the hydrogen embrittlement (HE) were observed in different industrial systems, including high-pressure hydrogen storage tanks, aircraft components, high-strength alloy components, and high-strength steel fasteners [1,2]. The contemporary approach in studying the effects of hydrogen on the mechanical properties of steels at different scales is based on the implementation of various multiscale (macro, micro-meso, and nano-atomic) modeling approaches and the applications of advanced multiscale experimental methods, Fig. 1 [3]. Simultaneous action in a cooperative manner of the hydrogen-enhanced localized plasticity (HELP) and the hydrogen-enhanced decohesion (HEDE) mechanism of HE, according to the HELP + HEDE model [4] of HE, were confirmed to be active, depending on the local concentration of hydrogen in steel [2-5], Table 1 [2]. Further investigations of the mechanical properties of steels at different length scales exposed to hydrogen damage should open a new window in the research related to the simultaneous action of HE mechanisms. It will also provide improved maintenance and the accurate service life prediction of various industrial components exposed to multiple active HE mechanisms [5,6].

Austenitic stainless steels with their good weldability, superior corrosion resistance and excellent performances in higher temperatures are an important material for engineering applications in industrial plants. Intergranular stress corrosion cracking (IGSCC) in austenitic stainless steels is a critical failure mechanism where cracking can result from sensitisation of certain grain boundaries after heat treatment (e.g. post-weld stress relief) or fast neutron irradiation in nuclear plant. Sensitisation is a decrease in the local resistance to stress corrosion, to a degree that depends on the grain boundary structure. Developments of predictive models for stress corrosion crack nucleation require more information about the effect of several external parameters (e.g. stress and time) on the likely extent of crack growth. Understanding is also required about how the grain boundary crystallography and the orientations of grain boundary plane and its surrounding grains affect crack propagation.
In this PhD thesis, the effects of time, applied stress and microstructure on populations of short crack nuclei have been investigated in sensitised type 304 austenitic stainless steel, tested under static load in an acidified potassium tetrathionate (K2S4O6) environment. Statistical evaluation, using the Gumbel extreme value distributions enables analysis of the growth rate of the population of short crack nuclei. This methodology has been developed, in order to quantitatively evaluate the influence of grain boundary control on crack development. These investigations showed an increase in the expected crack length with increasing time and grain size. Although the crack length tends to increase with stress, the effect is not strong. The grain boundary controlled microstructures exhibited significantly higher resistance to intergranular crack propagation. Direct observations of intergranular crack initiation and propagation, using digital image correlation (DIC) along with electron back scatter diffraction (EBSD), in various microstructures has been used to study the crack nucleation sites and crack interactions with grain boundaries of different characteristics. The effect of microstructural modification on crack growth kinetics has also been investigated. A significantly longer incubation period for crack initiation and lower crack growth rate were observed in thermo-mechanically treated microstructure.
New methods have been developed to assess the clustering characteristics of grain boundaries of particular properties. The network properties of boundaries classified by EBSD data have been compared with the network of corroded grain boundaries in electro-chemically tested samples. Image analyses (IA) was employed to evaluate the geometrical properties of susceptible boundaries clusters in a range of microstructures produced by sequential thermo-mechanical processing (TMP).
DL-EPR testing method of sensitisation assessment has been augmented by large area image analysis (IA) assessments of optical images to measure the dimensions and connectivity of the attacked grain boundary network. This approach determines the degree of sensitisation of the susceptible grain boundaries in the microstructure, and is used to explain IGSCC behaviour. A new method of degree of sensitisation determination is proposed, based on normalisation by a cluster parameter for the network of susceptible grain boundaries.

Effect of residual stress generated during tube fabrication, roll expansion and machining of stainless steel on the stress corrosion cracking (SCC) susceptibility was studied by testing fabricated tubes, tube-tube sheet joint and heavily machined plate of austenitic stainless steel (SS) in boiling MgCl 2 . U bend samples of machined plate were exposed to acidified SO 4 + Cl À environment at room temperature to study its ambient temperature SCC behavior. The results correlate the SCC behavior of the SS tubes and roll expanded joints to the nature and magnitude of residual stresses present. The study also highlights the distinct difference in ambient temperature SCC behavior of machined vs. nonmachined surfaces.

Resumen. El número y la severidad de los defectos superficiales del acero de pretensado son variables aleatorias que deben ser caracterizadas probabilísticamente para valorar su efecto sobre la resistencia del acero a la fatiga y a la corrosión bajo tensión, ya que ambos procesos de fisuración comienzan en defectos superficiales. Las medidas realizadas en esta investigación con un rugosímetro de contacto confirman el resultado obtenido por observación directa de que la profundidad de defecto dominante en áreas de tamaño fijo se ajusta a la distribución de Gumbel. Asimismo se ha comprobado que el número y la profundidad de los defectos siguen respectivamente distribuciones de tipo Poisson y de tipo exponencial, y se ha establecido la relación existente entre sus valores medios, los parámetros de escala y de localización de la distribución de Gumbel y el área de medida del defecto dominante.

Concrete is a homogenous mixture and cracks in concrete are inevitable so there is a need for repair which affects the economic life of any structure. To overcome this problem an inherent biomaterial is developed, a self-repairing material which can remediate the cracks in concrete. Bacterial concrete is a technique which is highly desirable because the calcium precipitation is induced as a result of microbial activities. This helps in increasing the strength and durability of concrete. As per the results, it is clearly observed that there is increase in compressive strength, tensile strength and durability in bacterial concrete as compared with normal concrete. This is the main objective of the bacterial concrete for which it was introduced. Various tests which are carried out to study these properties of concrete are compressive strength test, Split tensile test. Scanning Electron Microscope (S.E.M) is used to study the growth of bacteria in the concrete. It is observed that for bacterial proportion 10 5 cells (24 ml of bacteria in 1000ml), there is significant increase in compressive strength of the bacterial concrete i.e. around 25% increase in strength as compared with normal concrete. For this purpose bacteria used is Bacillus Subtilis.

This paper considers our recent research on rock bolt stress corrosion cracking (SCC) which studied the influence of metallurgy using a range of (1) existing rock bolt steels and (2) commercial steels. The chemical composition, mechanical properties and microstructures of these steels varied considerably. The aim is to understand this failure mechanism and in particular to apply the knowledge gained from the study of SCC and hydrogen embrittlement (HE) of steels. The resistance of 1008, X65, X70 and 4145H to SCC/HE was similar, an effect which could be hardly expected as these steels have different strengths, microstructures and H-trap distributions. Different steel microstructures (pearlitic-ferritic and tempered martensite) had similar resistance to SCC and HE in the most aggressive conditions (pH 2.1 and À1500 mV SCE ) and had the same dimple rupture fracture surface.

Sherritt International Corporation experienced corrosion failures with the 316L stainless steel tubing of the high pressure still condenser employed for ammonia recovery. A detailed failure analysis was conducted on the condenser tubing to determine the mode and the root cause of failure. The analysis included both optical and scanning electron microscopy (SEM) of the inner and outer surfaces of the tube and also, characterization of the corrosion products using Energy-Dispersive X-ray spectroscopy (EDX). Results revealed that corrosion attack was confined to the first ~ 100 mm of the tubing at the inlet where the tube is connected to the top tubesheet. The tube suffered both external stress corrosion cracking (SCC) and crevice corrosion from the shell side (water side), and wall thinning of inner surface (the tube side) due to erosion corrosion. It was evident that failure of one of the tubes occurred due to SCC that penetrated the whole wall thickness and resulted in a leak failure. Some prevention measures are proposed to avoid this type of corrosion attack in the future.

Since serious corrosion problems that have plagued the light water reactor (LWR) industry for decades. The complex corrosion mechanisms involved and the development of practical engineering solutions for their mitigation will discussed. After a brief discussion of the basic designs of the boiling water reactor (BWR) and pressurized water reactor (PWR), emphasis will be placed on the general corrosion of LWR containments, flow-accelerated corrosion of carbon steel components, intergranular stress corrosion cracking (IGSCC) in BWRs, primary water stress corrosion cracking (PWSCC) in PWRs and irradiation assisted stress corrosion cracking (IASCC) in both systems. Finally, the corrosion future of both plants will be discussed as plants extend their period of operation for an additional 20 to 40 years.

Chemical composition and heat treatments of spray-deposited AlCuMgAg-base alloys for use at ambient and moderately elevated temperatures have been optimized for high strength and high fracture toughness. This alloy development has led in particular to two new age hardenable aluminium alloys (N213 and N232) with excellent property combinations.

Many scientists have through time developed interests in undertaking researches related either directly or indirectly to corrosion, which could be attributed to increasing cases of material breakdown as a result of corrosion. There are therefore several published works focused on studies of the corrosion behavior and mechanism of various metals in several different environments or media. In this review paper, we explored and analyzed the various recent research works on corrosion kinetics using weight loss method, and to a certain extent about corrosion inhibition.

Stress corrosion crack growth in mild steel was investigated by using the finite element simulation method. A model simulating crack growth considered an edge crack located on the metal surface, under tensile remote stress acting on a sample. Numerical analysis was performed using the Code _Aster software to simulate crack growth. Three related variables were evaluated. K, dK/da and maximum stress. Values of these variables were recorded every 2 mm of the crack growth. Results showed an increase in the values of K and maximum stress, while there was a decrease in the values of dK/da, as the crack length increased. There was a good agreement between the results obtained analytically in the literature and numerically obtained here by using finite elements. The results obtained here are consistent with what has been obtained in most of the studies that have been conducted in this regard.

There were three consecutive occurrences of bellows failure in a particular pressure safety valve (PSV) of a petroleum refinery within a time span of one week. The bellows were made of 316L grade austenitic stainless steel, and the PSV was mounted on one of the vessels of vacuum gas oil service in a hydrocracker unit. Metallurgical analysis of the failed bellows revealed that the failure had occurred by stress corrosion cracking (SCC). It was found that the SCC was promoted in the bellows due to the presence of high amount of chloride ions in the operating environment. Studies confirmed that SCC had initiated from the outer surface of the bellows and propagated inwards, resulting in leakage of hydrocarbon from the PSV. The source of chlorine in the environment was identified. It was discovered that SCC in
the bellows was caused due to a previous failure in the heavy polynuclear aromatics (HPNA) absorption bed located upstream the process flow line. This failure was due to the presence of high concentrations of chlorine in the granulated activated carbon that was used in the HPNA absorption bed. During the repair of the HPNA bed, there was deposition of carbon soot on the body of the PSV. This carbon soot was the source of chloride ions for SCC to occur in the bellows. Generally, in chloride SCC, crack propagation in 316L SS takes place by
transgranular mode. In the present case, however, the crack propagation was predominantly by intergranular mode. The metallurgical factors responsible for this change in micro-mechanism of crack propagation during SCC have been discussed.


A tensile apparatus with constant strain rate, suitable for corrosion tests in molten salts has been used to determine the mechanical characteristics of 304L stainless steel in molten NaCI-CaCls at 570°C from a = f [(Al)/(10) ~o] curves for different strain rates. Potentiometric measurements, executed simultaneously, have determined the electrochemical conditions during mechanical testing. Results show a strain rate field in which the stress corrosion cracking occurs.

This paper presents the failure analysis of AISI-304 stainless steel tank that was fabricated by welding and used for the storage of styrene monomers. After about 13 years of satisfactory operation, significant cracking was observed adjacent to the weld joints and in base plate near tank foundation. Weld repair was by shielded gas arc welding using AISI 308 stainless steel filler

Treatment for compound and/or comminuted fractures is frequently accomplished via external fixation. To achieve stability, the compositions of external fixators generally include aluminum alloy components due to their high strength-to-weight ratios. These alloys are particularly susceptible to corrosion in chloride environments. There have been several clinical cases of fixator failure in which corrosion was cited as a potential mechanism. The aim of this study was to evaluate the effects of physiological environments on the corrosion susceptibility of aluminum 7075-T6, since it is used in orthopedic external fixation devices. Electrochemical corrosion curves and alternate immersion stress corrosion cracking tests indicated aluminum 7075-T6 is susceptible to corrosive attack when placed in physiological environments. Pit initiated stress corrosion cracking was the primary form of alloy corrosion, and subsequent fracture, in this study. Anodization of the alloy provided a protective layer, but also caused a decrease in passivity ranges. These data suggest that once the anodization layer is disrupted, accelerated corrosion processes occur. '

Posing a major integrity threat, the phenomenon of Stress Corrosion Cracking (SCC) has been investigated and discussed intensively since the 1970's. On the basis of a deeper understanding of this threat today, integrity management programs have been developed further in the recent past.

The aircraft aluminium alloys generally present low weldability by traditional fusion welding process. The development of the friction stir welding has provided an alternative improved way of satisfactorily producing aluminium joints, in a faster and reliable manner. In this present work, the influence of process and tool parameters on tensile strength properties of AA7075-T 6 joints produced by friction stir welding was analysed. Square butt joints were fabricated by varying process parameters and tool parameters. Strength properties of the joints were evaluated and correlated with the microstructure, microhardness of weld nugget. From this investigation it is found that the joint fabricated at a tool rotational speed of 1400 rpm, welding speed of 60 mm/min, axial force of 8 kN, using the tool with 15 mm shoulder diameter, 5 mm pin diameter, 45 HRc tool hardness yielded higher strength properties compared to other joints.