Corrosion Cracking Research Articles

Impact of PVA-coated aggregate on concrete impermeability and creep characteristics under hydraulic pressure and development of a creep model

In marine engineering projects such as sea dikes, concrete must exhibit both exceptional impermeability and plastic deformation to prevent cracking and subsequent internal corrosion due to synergistic deformation with the foundation. This study enhances the interface transition zone (ITZ) and plastic deformation of concrete by applying a PVA film to the aggregate surface. We use nuclear magnetic resonance to investigate the internal pore distribution and conduct permeability tests to assess its impermeability. Utilizing a self-developed triaxial hydraulic creep apparatus, we tests the concrete's creep performance under hydraulic pressure. Compared with conventional waterproof concrete, the findings reveal that the PVA film on the aggregate surface significantly increases the water penetration pressure of the concrete and markedly enhances the momentary deformation and creep deformation under hydraulic pressure, significantly extending the time to creep. Furthermore, the study proposes a creep model incorporating a fractional derivative-based dashpot model, combined with the Burgers model. This research offers a novel approach and theoretical support for developing impermeable and plastic concrete suitable for marine engineering applications.

A Study on a New Method for Simultaneous Internal Curing and hydrophobic in Concrete

The high hydrophilicity and permeability of concrete caused by many pores and hydroxyl groups produced by cement hydration are the main factors leading to dry shrinkage, cracking, and poor corrosion resistance of concrete. Giving concrete internal curing and hydrophobicity is an effective measure to solve the above problems. In this paper, a new idea and preparation method for an organic combination of hydrophilic and hydrophobic materials are proposed to improve the service life of concrete structures. Furthermore, the combined effects of hydrophilic and hydrophobic amphoteric materials (HAM) on the mechanical properties, internal curing properties, and hydrophobic properties of concrete were comprehensively investigated. In addition, the physical and chemical action mechanisms were analyzed in conjunction with microscopic tests. The results indicated that HAM rapidly released water within 3-7 days before concrete curing, and then slowly released water accompanied by the release of hydrophobic materials, gradually from hydrophilic to hydrophobic properties; The addition of HAM did not reduce the mechanical properties of concrete, which solved the problem of low compressive strength of integral hydrophobic concrete; The addition of HAM reduced the drying shrinkage of concrete by 154.12%, increased the contact angle to 96°, and decreased the water absorption rate by 36%, allowing the concrete to achieve better internal curing and a hydrophobic effect. The preparation of this material can open up a new way to solve the hydrophilic and hydrophobic properties required by concrete at the same time, and fill the gap that concrete can not balance hydrophilic and hydrophobic properties.

Degradation law of bond strength of reinforced concrete with corrosion-induced cracks and machine learning prediction model

During long term operation service, reinforced concrete (RC) structures are subjected to corrosive media such as chloride salts, which results in the degradation of interface bond performance, subsequently reducing the load bearing capacity and service life of the structures. To accurately assess the durability of RC structures in environments such as oceans and salt lakes, this study combines experimental methods with machine learning (ML) techniques to explore the degradation patterns and predictive models of bond performance under chloride salt corrosion. Accordingly, a series of central pull-out tests were conducted based on an electrochemical accelerated-dry-wet cycle corrosion regime to investigate the degradation patterns of bond performance between corroded steel bars and concrete under different corrosion degree and corrosion-induced crack widths. By comparatively analyzing the evolution patterns of cracks and the morphology of the steel bars in reinforced concrete specimens and their failure modes, and integrating the mechanical degradation mechanism with chemical and microscopic corrosion mechanisms, an in-depth analysis of the corrosion-induced degradation patterns at the bond interface was performed. The internal relationships between corrosion degree, corrosion-induced crack width and bond strength were discussed, and the variation patterns of bond strength with corrosion-induced crack width and corrosion degree were explored. Moreover, the bond strength patterns were analyzed from an energy perspective. The results indicate that bond strength and bond energy decrease with an increase in the corrosion-induced crack width of the concrete. Additionally, based on the experimental data from this study, ML predictive models for bond strength were established using corrosion-induced crack width as the control variable. The results show that the ML-based bond strength predictive models fit well with the experimental data, offering higher accuracy and reliability compared to traditional bond strength models. The research findings provide significant theoretical basis and practical guidance for safety assessment, maintenance, reinforcement, and full-life design of corroded RC structures.

Bayesian updating of relationships between crack width and corrosion level in reinforced concrete based on a large set of experimental data

AbstractThe evaluation of rebar corrosion in reinforced concrete (RC) structures presents a significant challenge for structural engineers, with on‐site visual inspections and crack width measurements playing a key role in the preliminary assessment. A general approach is to use corrosion models to predict the corrosion level of existing structures, and subsequently update these predictions by means of on‐site data. In this process, empirical models are often applied that relate the observed damage, such as corrosion‐induced cracks, to the corrosion level. However, these models have large uncertainties and are often not applicable to conditions that deviate from the test setups used to derive the empirical relations. This research aims to expand the applicability of these practical, existing empirical models for on‐site corrosion assessment through Bayesian updating techniques. To this aim, a Bayesian framework is developed to update crack width–corrosion models. The Bayesian updating methodology is illustrated for a simple regression model, and for a more complex relation that accounts for additional variables. A novel online database (KUL‐edCCRC) is used that is published accompanying this paper. The obtained results illustrate that the updated models have better agreement with the experimental results, and it is found that the confidence intervals of the regression parameters decrease for an increasing number of observations, even for a small number of additional datapoints. The results hence prove the efficiency of the approach to integrate information from new observations with prior information to adjust the crack width–corrosion model for specific conditions or cases, resulting in a more relevant model as more information becomes available.

A new sight on the fracture behavior of GH4169 produced by NaCl-induced corrosion in a humid environment of 600 °C

A novel fracture mechanism of GH4169 alloy, produced by active corrosion, was proposed via a slow-strain rate test in a NaCl deposition contained 600 °C humid environment. Circular active corrosion accelerates form of Fe, Cr-depletion and Ni-rich region. The region has elevated stacking fault energy and reduced shear modulus, inhibiting the planner slip yet promoting dislocation tangles ahead of the internal corrosion zone. Localized Stress concentration occurs, facilitating crack propagation. The synergistic interplay between cracking and active corrosion processes accelerates the rupture of GH4169 alloy, leading to reduced ductility and tensile strength of GH4169 alloy in the environments.

The corrosion expansion force and cracking separation between corroded section steel arch frame and shotcrete in tunnel primary support

High chloride content in the subsea tunnel environment leads to inevitable corrosion of I-shaped steel in primary support. Corrosion generates expansive force between I-shaped steel and concrete, eventually cracking the concrete protective layer, and weakening the bond strength, severely impacting the tunnel support system’s durability. The main purpose of this article is to obtain the corrosion expansion force generated at the interface between corroded I-shaped steel and concrete, as well as the mechanical response characteristics of concrete under the action of corrosion expansion force. Firstly, nine I-shaped steel concrete components were fabricated for electro-accelerated corrosion test, obtaining the variation curve of corrosion expansion force with corrosion rate and protective layer thickness. The experimental results indicated that the development of corrosion expansion force can be divided into three stages: initial free corrosion stage (corrosion rate ρ = 0.5 % – 0.7 %), stage with a noticeable increase in corrosion expansion force (corrosion rate ρ = 0.7 % – 12 %), and expansion-induced cracking (corrosion rate ρ > 12 %). Meanwhile, a three-stage corrosion expansion force model for concrete and corroded I-shaped steel was proposed, which was correlated to the experimental curve well. Finally, the mechanical characteristics of the surrounding concrete during the development process of different corrosion expansion forces were explored through ANSYS software. The numerical results indicated that these cracks due to corrosion expansion force primarily occurring in the contact region between the concrete and the I-shaped steel flange, specifically in three areas: the central part of the flange and its two corners; The tensile stress in the concrete surrounding the web plate is less than that at the flange, leading to the initial longitudinal cracking observed on the outer surface of the flange.

Analysis, Assessment, and Mitigation of Stress Corrosion Cracking in Austenitic Stainless Steels in the Oil and Gas Sector: A Review

This comprehensive review examines the phenomena of stress corrosion cracking (SCC) and chloride-induced stress corrosion cracking (Cl-SCC) in materials commonly used in the oil and gas industry, with a focus on austenitic stainless steels. The study reveals that SCC initiation can occur at temperatures as low as 20 °C, while Cl-SCC propagation rates significantly increase above 60 °C, reaching up to 0.1 mm/day in environments with high chloride concentrations. Experimental methods such as Slow Strain Rate Tests (SSRTs), Small Punch Tests (SPTs), and Constant-Load Tests (CLTs) were employed to quantify the impacts of temperature, chloride concentration, and pH on SCC susceptibility. The results highlight the critical role of these factors in determining the susceptibility of materials to SCC. The review emphasizes the importance of implementing various mitigation strategies to prevent SCC, including the use of corrosion-resistant alloys, protective coatings, cathodic protection, and corrosion inhibitors. Additionally, regular monitoring using advanced sensor technologies capable of detecting early signs of SCC is crucial for preventing the onset of SCC. The study concludes with practical recommendations for enhancing infrastructure resilience through meticulous material selection, comprehensive environmental monitoring, and proactive maintenance strategies, aimed at safeguarding operational integrity and ensuring environmental compliance. The review underscores the significance of considering the interplay between mechanical stresses and corrosive environments in the selection and application of materials in the oil and gas industry. Low pH levels and high temperatures facilitate the rapid progression of SCC, with experimental results indicating that stainless steel forms passive films with more defects under these conditions, reducing corrosion resistance. This interplay highlights the need for a comprehensive understanding of the complex interactions between materials, environments, and mechanical stresses to ensure the long-term integrity of critical infrastructure.

The Effects of Internal Curing and Shrinkage Cracking Avoidance on the Corrosion of Reinforced Concrete Walls with Superabsorbent Polymers

The pursuit of durable and sustainable construction has driven interest in innovative materials, with superabsorbent polymers (SAPs) emerging as a promising solution, especially for the concrete industry. SAPs offer significant benefits to the durability of concrete structures, including mitigation of autogenous shrinkage, enhanced freeze–thaw resistance, crack sealing, and stimulation of autogenous healing. This study focuses on the impact of internal curing with SAPs on crack formation and corrosion initiation in large-scale reinforced concrete walls (14 m × 2.75 m × 0.8 m). Both commercial SAPs based on acrylic acid chemistry and in-house-developed SAPs based on alginates were evaluated. Key findings reveal that the reference wall exhibited visible cracking just five days after casting, while the SAP-treated wall remained crack-free throughout a 24-month monitoring period. Moreover, the reference wall showed corrosion initiation at two locations near the cracks within six months, whereas the SAP-treated wall exhibited no signs of corrosion potential. Laboratory tests further demonstrated a slight reduction in chloride penetration and carbonation in SAP-treated specimens compared to the reference. These results highlight the efficacy of SAPs in enhancing the durability and longevity of reinforced concrete structures.

Study on seismic behavior of corroded reinforced concrete walls in flexural-shear failure

In this study, artificial climate-accelerated corrosion tests and pseudostatic loading tests were conducted on six reinforced concrete (RC) shear walls subjected to flexural-shear failure. The effects of the corrosion degree and axial compression ratio parameters on the seismic performance of RC shear walls were investigated. The corrosion conditions (corrosive cracks and corroded steel bars), failure process, bearing ability, deformation capacity and energy consumption capacity were compared. The test results showed that chlorine salt erosion induced severe deterioration of the properties of the RC shear wall. The internal reinforcement of the specimen was severely corroded near the protective layer. The failure mode of the severely corroded specimens changed from the original flexural-shear failure mode to the bending failure mode. Rebar corrosion markedly decreased the bearing ability, deformability and energy dissipation capability of the specimens. Based on the limited test data in this study, the existing equations for calculating the parameters of the characteristic points were modified, and equations for calculating the parameters of the skeleton curve of the corroded RC shear wall were proposed. The cyclic corrosion degradation index was utilized to define the degradation of various mechanical properties of the specimen (yield load, hardening stiffness, reloading stiffness, peak load, unloading stiffness, etc.). With cyclic loading, and considering the pinching characteristics, a restoring force model of a corroded RC shear wall was established based on the Ibarra-Medina-Krawinkler (IMK) model. The comparison illustrated that the built restoring force model was in good agreement with the skeleton curve and hysteresis rules and could accurately reflect the hysteresis performance of corroded RC shear walls to a certain extent.

Research and application of surface spray anti-corrosion technology for coiled tubing in pressurized environment

In this study, the corrosion risk of coiled tubing under high pressure, high temperature and high sulfur conditions was investigated, and the protection solution was put forward. In this paper, spray paint is used to prevent corrosion of tubing, and the effects of high temperature desulfurization and nano super absorbent spraying agent are compared. The pressure jet spraying device is designed for uniform spraying during operation to improve corrosion resistance. Determine the best spraying position and monitoring point. The results show that nano-coating agent can prevent cracking and serious corrosion, and its application effect in oil wells meets the requirements. These findings support that anti-corrosion spraying technology on coiled tubing surface can effectively prevent tubing corrosion in high temperature, high pressure and corrosive environment.

Seismic Performance of Corroded ECC-GFRP Spiral-Confined Reinforced-Concrete Column.

Preventing corrosion in the steel reinforcement of concrete structures is crucial for maintaining structural integrity and load-bearing capacity as it directly impacts the safety and lifespan of concrete structures. By preventing rebar corrosion, the durability and seismic performance of the structures can be significantly enhanced. This study investigates the hysteresis behavior of both corroded and non-corroded engineered cementitious composite (ECC)-glass-fiber-reinforced polymer (GFRP) spiral-confined reinforced-concrete (RC) columns. Employing experimental methods and finite element analysis, this research explores key seismic parameters such as crack patterns, failure modes, hysteretic responses, load-bearing capacities, ductility, stiffness degradation, and energy dissipation. The results demonstrate that ECC-GFRP spiral-confined RC columns, compared to traditional RC columns, show reduced corrosion rates, smaller crack widths, and fewer corrosion products, indicating superior crack control and corrosion resistance. Hysteresis tests revealed that ECC-GFRP columns, at a 20% target corrosion rate, exhibit an enhanced load-bearing capacity, ductility, and energy dissipation, suggesting improved durability and seismic resilience. Parametric and sensitivity analyses confirm the finite element model's accuracy and highlight the significant influence of concrete compressive strength on load-bearing capacity. The findings suggest that ECC-GFRP spiral-confined RC columns offer promising applications in coastal and seismic-prone regions, enhancing corrosion resistance and mechanical properties, thus potentially reducing formwork costs and improving construction quality and efficiency.

Improving intergranular cracking and stress corrosion cracking resistance of highly sensitized AA5083 Al-Mg alloy via reversion heat treatment

This study systematically examines the impact of reversion heat treatments (220–280 ℃ for 1 h) on the microstructure evolution, electrochemical corrosion, intergranular cracking (IGC) and stress corrosion cracking (SCC) of a severely sensitized (175 ℃/100 h) AA5083 alloy. Increasing the reversion temperature gradually enhances the corrosion resistance by dissolving the β′-Al3Mg2 phase, with the optimal treatment identified as 280 ℃/1 h. The βˊ phase maintains its planar film shape and continuously covers the grain boundaries after reversion treatment below 240 °C, but spheroidizes at the triple junctions at 260 °C. The morphology of the βˊ phase is dictated by grain boundary diffusion and interface diffusion. Reversion treatments improve SCC resistance by dissolving the β′ phase and reducing yield strength, attributed to anodic dissolution and hydrogen embrittlement mechanisms. This research offers valuable insights into the practical benefits of reversion treatments for Al-Mg alloy marine applications, addressing safety concerns related to sensitization.

INVESTIGATION OF STRUCTURAL AND MECHANICAL PROPERTIES OF TUBING STEELS

The study of the structural and mechanical properties of tubing steels used in wells at oil and gas condensate fields is of particular interest due to the resource intensity of these systems and the high cost of their repair and restoration. Tubing is operated under conditions of increased loads under the influence of its own weight, internal pressure and constant contact with highly aggressive media. As a result of simultaneous exposure to corrosive media and operational loads, tubing is the most consumable downhole material. The destruction and, as a result, the breakage of the tubing suspension occurs as a result of mechanical abrasion and cracking of the pipe body, the development of fatigue cracks in the thread, etc. Contact with aggressive agents of the extracted fluid and reservoir waters leads to various types of corrosion damage: ulcerative, pitting, corrosion fatigue, corrosion cracking, meza corrosion, biocorrosion, etc. Corrosion foci are localized on the inner and outer surfaces of pipes. The problem is complicated by the increased content of carbon dioxide (CO2), hydrogen sulfide (H2S), as well as the presence of various bacteria in oil and gas fields.This article is devoted to the study of the mechanical characteristics and microstructure of tubing steels that were in operation under conditions of complicating factors and highly aggressive corrosive environment. Tubing pipes Ø73x5.5 of strength group E. were tested. The following research methods were carried out: visual inspection; determination of the chemical composition of steel; determination of hardness; uniaxial tensile test; optical microscopy.As a result of the tests, quantitative characteristics of the mechanical properties of the steels were obtained. A significant decrease in the hardness, tensile strength and yield strength of steel has been established under prolonged exposure to complicated operating conditions. Metallographic studies have established the contamination of steels with silicates of various shapes, amounting to 3 and 2 points according to GOST 1778. Microstructural studies have been carried out. The fine-grained ferrite-carbide structure of steels has been revealed. This structure corresponds to the heat treatment mode: quenching followed by tempering.

Study on electrochemical corrosion dynamics of cathode dic shield in concrete crack

Abstract Corrosion of steel reinforcement is a primary factor that negatively impacts the service life and safety of bridges made of concrete. Cathodic protection techniques are widely used to protect reinforcing bars in concrete against corrosion. However, it is inevitable that corrosion cracks will develop in the concrete during long-term operation, which will significantly shorten the cathodic current protection distance and increase the degree of corrosion of the rebar within the cracks. Therefore, electrochemical experiments and characterization of corrosion forms were carried out based on the company’s design of a rectangular connection device, we studied HRB500 steel in 3 wt.% corrosion behavior in rectangular joints under different CP current densities in NaCl solution. The results showed that with increasing experimental time, the corrosion in the crevice transitioned from activation corrosion to oxygen concentration corrosion, with the open-pore potential of the HRB500 steel inside the crevice appearing as a positive shift and the open-pore potential outside the crevice shifting from positive to negative. When implementing cathodic protection, the corrosion of HRB500 steel within the crevice is activated, while the corrosion outside the crevice changes from anodic to mixed controlled corrosion and from full to pitting corrosion. With the increase of CP current density, the corrosion process of HRB500 steel outside the gap is mainly dominated by cathode control, then gradually weakens, and the corrosion form changes from pitting to comprehensive corrosion.

A new analytical model for bond strength between corroded steel strand and concrete

Degradation of bond strength due to corrosion of steel strands is of great importance for serviceability of prestressed concrete structures. An analytical model is proposed to demonstrate the effect of corrosion of steel strand on reduction of bond strength. Corrosion expansion force generated by steel strand corrosion before and after corrosion cracking is firstly estimated. Then, the reduced gripping effect of the concrete, change of friction coefficient between the corroded strand and reduction force on the bearing face are considered in calculating the pre-rib extrusion force. Finally, the enhancement of bond strength due to transverse confinement of stirrups is considered and the ultimate bond strength of corroded steel strand is calculated. Comparison of results between the prediction and experimental result shows the proposed model can be used to reasonably evaluate the bond strength. The prediction result of the bond strength model is affected by the degree of strand corrosion, but almost not by the drawing method.

Effects of ZrW2O8 Content on the Microstructures and Properties of Composite Coatings Produced by Laser Cladding

Addressing the issue of cracking in laser-cladding Ni-based composite coatings with WC particles, this study explored an approach to fabricating a crack-free coating by incorporating ZrW2O8 powder. The influence of varying ZrW2O8 contents on the crack susceptibility, microstructure, microhardness, wear resistance, and corrosion resistance of Ni60/WC composite coatings was systematically examined. The findings indicate that the ZrW2O8 content significantly impacts the microstructure and functional properties of the coating. Furthermore, it is suggested that the main contributors to preventing crack formation and diffusion are believed to be the pressure interaction caused by the negative expansion effect of ZrW2O8, as well as the in situ phase transition and diffusion toughening of ZrO2 during its decomposition process. The feasibility of achieving crack selfhealing through the addition of specific amounts of ZrW2O8 powder has been conclusively demonstrated.

Deterioration and imperfection of the ship structural components and its effects on the structural integrity: A review

Abstract The design of ship structural safety is crucial to ensure the ship’s survivability during the operation. Extensive research has been conducted on ship structural components, including box girders, stiffened panels, and plates, beyond the ideal conditions by considering the implication of manufacturing processes, vessel usage, and aging in the form of defects like cracks, corrosion, and imperfections, both locally and globally. Previous research has also explored various methodologies, conditions, and parameters to understand the impact of damages and imperfections on ship structure and strength. However, there is a significant need to bridge the gap in prior research to advance technology and ship structural strength analysis. A comprehensive benchmark study specifically focused on improving ship structural component needs, identifying differences and gaps among existing studies as challenging. This article thoroughly reviews ship structural components, such as box girders, stiffened panels, and plates, while examining the effects of structural defects like corrosion, cracks, and imperfections on ship structural integrity. It synthesizes the influence of various defect parameters, including crack length, angle, position, corrosion severity, pit corrosion, pit diameter, and pit models, using finite element modeling and experimental investigations, particularly emphasizing ship structural components. The comparative analysis of methods and parameters presented in this review will serve as a valuable reference for future investigations and studies related to ship structural strength and design. The article’s contribution is expected to enhance the understanding of ship structural strength, contributing to the sustainability and effectiveness of vessel design in the global maritime industry.

Wide temperature range corrosion mechanism of M50 bearing steel in deteriorated oil-water mixture

Bearing corrosion is one of the important causes of engine failures in shipborne aircraft, and solving the problem of bearing corrosion failure is urgent. This article uses chromatography, image analysis, and finite element simulation to study the high-temperature deterioration behavior of Mobil Jet Oil Ⅱ aviation lubricating oil, as well as the corrosion mechanism of M50 bearing steel in oil–water mixture under a wide temperature range. The results indicate that deteriorated lubricating oil without salt water doping does not have corrosiveness. Mobil Jet Oil Ⅱ aviation lubricating oil at 200 °C has obvious deterioration within 48 h, where consumption and decomposition of additives cause acidity changing from pH 8.1 to pH 2 and surface tension decreasing by 11.3 %. The crack corrosion caused by acid and the galvanic corrosion of secondary cementite accelerate the pitting corrosion process. The corrosion enhancement effect of temperature on oil–water mixture shows a parabolic trend. Corrosion can be effectively reduced by lowering the temperature of lubricating oil and quickly removing moisture.

Experimental research of the influence of irrigation and duration of exploitation on crack resistance and corrosion destruction resistance of pipe steel

For the first time in the work, systematic and comprehensive experimental studies of the influence of the service life of pipelines on the absorption of hydrogen by pipe steels, which is known to cause embrittlement of the metal, were carried out. In this regard, the microhardness of the structure increases sharply, and the crack resistance parameters of pipe steels also deteriorate. As an additional criterion for hydrogen exposure, the stress intensity factor K1C can be used, which characterizes the potential ability of a metal to resist brittle fracture. The curves of the temperature dependence of the K1C coefficient illustrate the change in the viscosity of steel caused by structural transformations during heat treatment and the subsequent effect of dissolved hydrogen on the metal structure during long-term operation of pipelines in corrosive and aggressive environments, in particular those used in water supply and drainage systems. It is known that the K1C coefficient is very sensitive to changes in the structure, that is, it is a local parameter of crack resistance that must be taken into account when designing and calculating pipeline structures. Additional studies established the dependence of the destruction of pipe steels of the 06G2BA brand, taking into account the preliminary stresses from 0.3σТ to 0.9σТ. Unstressed pipe steels are characterized by the highest resistance to destruction, that is, previous stresses of steel samples weaken the crack resistance of the metal. Additional studies of sulphide corrosion destruction according to the NACE methodology provided an opportunity to determine the susceptibility of pipe steels to corrosion destruction. Steels 06 G2BA and 08HMChА are characterized by the highest corrosion resistance.

Effect of the triangular prism dent on stress corrosion cracking behavior of alloy 690TT heat transfer tube in a lead-containing alkaline solution

In this paper, the microstructural changes and mechanical characteristics of alloy 690TT heat transfer tube with a triangular prism dent are investigated by combining experimental and simulation methods, and subsequently examines their influence on stress corrosion cracking (SCC) behavior. The results indicate that the deformation mechanism caused by impact dent is slip and twinning. The structural transformation of high-density dislocations, as well as Copper and Brass deformation textures, are formed at dent bottom, resulting in stress concentration through work hardening, which greatly increases SCC sensitivity. Oxidation preferentially occurs along grain boundaries and dislocations, and the corrosion products are formed, which exhibit a semi-coherent orientation relationship with the matrix. Oxidation is essentially a de-alloying process in which oxygen diffuses inward and Cr migrates towards the oxidation zone. The wedge force generated by corrosion products provides another driving force for initiation and propagation of SCC cracks, in addition to external loads and residual stress. SCC cracks propagate in the form of intergranular stress corrosion cracking and transgranular stress corrosion cracking in a high temperature lead-containing alkaline solution.