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.

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.

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 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.

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.

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.

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.

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.


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