Nucleation Of Corrosion Cracks Research Articles

Corrosion Crack Nucleation Mechanism in the Welded Structures of X65 Steel in Natural Seawater

The nucleation mechanism of corrosion cracks in welded structures in natural seawater has been revealed through investigation on the corrosion behavior of X65‐welded structures in natural seawater. The evolution laws of surface corrosion morphology, residual stress, and areas of welded structures with the most serious corrosion damage were analyzed by microstructure observation, corrosion morphology observation, residual stress detection, and magnetic field detection. The results show that the main factors of determining surface corrosion morphology evolution law of welded structures are microstructures of the weld joint, heat‐affected zone (HAZ), and the fusion line. Due to the difference of corrosion rates between the weld joint, HAZ, and the coarse Widmänstatten structure in fusion line, the fusion line of welded structures receives the most serious damage while being corroded. Meanwhile, mutual reinforcement of residual stress and corrosion damage on the surface of welded structures further accelerate the nucleation of corrosion cracks. Under the influences of microstructure, residual stress, and corrosion, corrosion cracks that are parallel to weld joints generate first in the fusion line of welded structures. Therefore, it makes welded structures the source of marine steel structures’ corrosion failure.

Determination of the stress intensity factors due to corrosion cracking in ferroconcrete by digital image processing reflection photoelasticity

Nucleation of corrosion cracking can be detected and analyzed by digital image processing reflection photoelasticity by which the process mechanisms of crack extensions due to corrosion are quantitatively estimated. This study examines the distribution of expansion stress measured in initial cracking and partial cracking stages. Based on optical linear elastic fracture mechanics, the relation between the stress intensity factors and increment extensions are generated in different corrosion times. The accuracy of the method is demonstrated by comparisons of the predictions, the experimental predictions, and the numerical results.

In situ observation of intergranular crack nucleation in a grain boundary controlled austenitic stainless steel

Grain boundary engineering has been proposed to increase the lifetime performance of sensitized austenitic stainless steel in aggressive environments. Increased microstructure resistance is typically associated with higher fractions of twin (Sigma3) grain boundaries, but there is uncertainty about the properties and role of other boundaries. To develop predictive models for stress corrosion crack nucleation, more information is required about how grain boundary crystallography and the orientations of the grain boundary plane and its surrounding grains affect crack development. Digital image correlation combined with electron backscatter diffraction has been used to characterize the microstructure and to observe, in situ, the nucleation and propagation of short stress corrosion cracks in thermo-mechanically processed type 304 stainless steel. The crack path and its growth rate have been determined and are found to be influenced by the microstructure.

Three dimensional observations and modelling of intergranular stress corrosion cracking in austenitic stainless steel

Stress corrosion cracking is a life-limiting factor in many components of nuclear power plant in which failure of structural components presents a substantial hazard to both safety and economic performance. Uncertainties in the kinetics of short crack behaviour can have a strong influence on lifetime prediction, and arise due both to the complexity of the underlying mechanisms and to the difficulties of making experimental observations. This paper reports on an on-going research programme into the dynamics and morphology of intergranular stress corrosion cracking in austenitic stainless steels in simulated light water environments, which makes use of recent advances in high resolution X-ray microtomography. In particular in situ, three dimensional X-ray tomographic images of intergranular stress corrosion crack nucleation and growth in sensitised austenitic stainless steel provide evidence for the development of crack bridging ligaments, caused by the resistance of non-sensitised special grain boundaries. In parallel a simple grain bridging model, introduced to quantify the effect of crack bridging on crack development, has been assessed for thermo-mechanically processed microstructures via statically loaded room temperature simulant solution tests and as well as high temperature/pressure autoclave studies. Thermo-mechanical treatments have been used to modify the grain size, grain boundary character and triple junction distributions, with a consequent effect on crack behaviour. Preliminary three-dimensional finite element models of intergranular crack propagation have been developed, with the aim of investigating the development of crack bridging and its effects on crack propagation and crack coalescence.

Strain-induced passivity breakdown in corrosion crack initiation

Corrosion crack nucleation and growth are modelled as a moving boundary problem. The model incorporates three physical processes––dissolution, passivation and straining––into a continuum mechanical framework. The dissolution triggers surface advance; the passivation restrains the access of the environment to bare metal; the deformation causes for passivity breakdown. Plane cracks nucleating from surface pits in an elastic–plastic material body under fatigue load are considered. The problem is solved using a FEM program and a moving boundary tracking procedure. The model simulates how cracks form and grow in a single continuous course. The geometry of the developed cracks is found independent of the initial pit size. Plasticity is found to influence the curvature at the tip of the nucleated corrosion cracks. The most important evolution length parameter, the width of the corrosion crack, is found to depend on the size constraints of the tracking procedure. It is concluded that the model is deficient for determining all length scales observed in reality. Physical processes to be considered in an advanced model are proposed and discussed.

Mechanisms of crack propagation due to corrosion of reinforcement in concrete by AE-SiGMA and BEM

Nucleation of corrosion cracking is analyzed by acoustic emission-simplified Green's functions for moment tensor analysis, by which crack kinematics of locations, types and orientations are quantitatively determined. These kinematical outcomes are obtained as 3D locations and vectors, and thus visualized three-dimensionally by using virtual reality modeling language. The procedure is applied to corrosion cracking in reinforced concrete. To clarify the mechanisms of crack extension due to corrosion, numerical analysis is conducted by the boundary element method. A relation between the stress intensity factors and the increment of crack extension is studied on three crack patterns due to corrosion. The dimensionless stress intensity factors and the cracking modes are investigated. It is confirmed that cracking mechanisms due to corrosion of reinforcement are dominantly of the mode-I crack, along with mixed-mode and mode-II cracks.

The effect of sulfide inclusions on the susceptibility of steels to pitting, stress corrosion cracking and hydrogen embrittlement

AbstractRecent opinions on the effect of nonmetallic inclusions, especially sulfides, on the nucleation of pits, stress corrosion cracks, and hydrogen‐induced cracks are reviewed.The nonmetallic inclusions present in steels as impurities adversely affect the corrosion resistance of steels. This is true for both the general and local corrosion mechanisms, like pitting corrosion, stress corrosion cracking (SCC), and hydrogen embrittlement (HE).The effect of nonmetallic inclusions (in particular that of sulfides) on the pitting corrosion mechanism has been the subject of numerous investigations. A fairly aboundant information can be found in vast original literature and in many review articles [1–3]. The role of nonmetallic inclusions in SCC is relatively less covered in the pertinent literature. Since, however, the nucleation of corrosion cracks frequently starts from pits, and pits nucleate at sulfides, the presence of sulfides is likely to affect the SCC process.Another corrosion mechanism that leads to a local cracking of a metal is the hydrogen embrittlement. The presence of nonmetallic inclusions enhances susceptibility of steel to hydrogen‐induced cracking [4].This review will be concerned with the effect of nonmetallic inclusions on the local corrosion types mentioned.

The mechanism of the nucleation of corrosion cracks

X-ray diffraction analysis was used to study changes in the distribution of stresses of the first and the second kind in surface layers of stressed Cr18Ni10Ti steel specimens during the nucleation and growth of corrosion cracks. Based on the results obtained, a mechanism of nucleation of corrosion cracks in 18-8-type steels was postulated.