Degree Of Pitting Research Articles

Finite element analysis of pitting corrosion on mechanical behavior of E690 steel panel

PurposeThe purpose of this study is to analysis the pitting corrosion on the mechanical behavior of E690 high-strength steel sandwich panel. The pitting corrosion depth and degree of pitting (DOP) damage were used to evaluate the mechanical behaviors such as peak load and specific energy absorption of E690 panel.Design/methodology/approachThe mechanical behavior of quasi-static compression, low-speed impact and three-point bending of E690 panel after pitting corrosion was simulated by ABAQUS nonlinear finite element method.FindingsThe quasi-static compression and low-speed impact mechanical properties can be greatly reduced by the pitting corrosion of the panel core, the pitting corrosion of the outer panel shows no obvious effect. The mechanical properties decrease with the increase of the pitting corrosion depth and DOP, and the influence of DOP is greater than that of pitting corrosion depth. The DOP of outer panel has less effect on mechanical properties of three-point bending compared with that of the core. Therefore, the pitting corrosion in the core of panel should be strictly controlled to prevent adverse effects on the mechanical properties of the structure.Originality/valueTo make up for the deficiency of the research on the corrosion behavior of high-strength steel sandwich panel structure, this paper chose E690 high-strength steel panel as the research object, and nonlinear finite element method was adopted to simulate the influence of pitting corrosion coverage area and pitting depth on its mechanical property degradation. The quasi-static compression, low-speed impact and three-point bending mechanical properties of panel with various DOPs and pitting depths were systematic studied.

Ultimate strength prediction of corroded plates with center-longitudinal crack using FEM and ANN

Corrosion and cracking are two main reasons for failure of plates in ships and offshore structures. In the current paper, the ultimate strength of plates with pitting corrosion and a longitudinal crack is investigated under uniform in-plane compression using non-linear finite element method (FEM). Ultimate strength of cracked-pitted plates are predicted using proper artificial neural network (ANN) under different aspect ratio, thickness of plate, number of pits, crack length, and pit depth over thickness of the plate. Based on the numerical results, in rectngular plates, ultimate strength for pitted plate and cracked-pitted plate are almost the same, while in square plates when degree of pitting is low, negligible effect of longitudinal crack on the ultimate strength is detected. For thin plates, less influence of pit corrosion on ultimate strength reduction is observed in comparison to thick plates. Also, it is found that the arrangements of pits in the cracked-pitted plates on ultimate strength reduction is more influential than number of the pits. Finally, an equation is suggested to predict the ultimate strength of corroded plated with longitudinal crack using ANN's weights and bias.

Experimental study on generalized constitutive model of hull structural plate with multi-parameter pitting corrosion

Pitting corrosion occurs on the surface of a steel hull structural plate may cause a significant degradation on structural performance. The influence of multiple pitting corrosion-related parameters on the properties of the commonly-used the NV-D36 hull structural plate is experimentally investigated through a uniaxial tension test in which the shape, diameter, depth and distribution form of pitting craters are taken into account. On the basis of the test results, the relations between the degree of pitting (DOP) damage and the properties, i.e. elasticity modulus, yield strength, ultimate strength and peak tensile strain, are studied. As the output of the test, a bilinear and a linear-exponential generalized constitutive models for the NV-D36 hull structural plates considering the multiple pitting corrosion-related parameters are proposed for the design and analytical purposes, respectively. The experimental investigation indicates that all the properties of the NV-D36 hull structural plate degrade linearly but at different rates as the degree of pitting damage increases. The efficient bilinear generalized constitutive model is proved to be acceptable for reserving a reasonable degree of margin. The linear-exponential generalized constitutive model can result in more accurate predictions about the uniaxial tensile response of the NV-D36 hull structural plate experiencing multi-parameter pitting corrosion.

Influence of Localized Pit Distribution and Bench-Shaped Pits on the Ultimate Compressive Strength of Steel Plating for Shipping

This work has developed numerical models simulating steel plate corrosion degradation and presents a series of novel finite element modeling to assess the influence of localized pit distribution and bench-shaped pits, which are often observed in long-term exposures. Four location patterns of one-sided corroded shipping steel plates have been considered, which include both geometric and material non-linearities. Validation of the modeling method is achieved by a thermoelastic stress analysis, which provides the principal stress distribution over the plate surface. The modeling results demonstrate that the frequently detected localized corrosion may reduce the ultimate strength by up to 20% compared to uniformly corroded plate. In addition, bench-shaped pits may further decrease the ultimate strength by up to 14% compared to the no-bench condition with the same degree of pitting.

Blast response of corroded steel plates

Numerical results for one- and both-sided corroded steel plates subjected to blast loading are presented. Finite element analysis, with ABAQUS software, is employed to determine the deformation and stress distributions. The results for the case of triangular pulse pres- sure on un-corroded plates are validated against literature-based data and then, detailed parametric studies are carried-out. The effects of influential parameters including, plate aspect ratio, degree of pit and different ratio of pit depth at each sides of the plate are investigated. The results show that position of pitted surface in respect to applied pressure is the most influential parameter on reduction of dynamic load carrying capacity of pitted plates. By increasing degree of pitting, reduction of dynamic load carrying capacity decrease more.

Deformation behaviour of corroded plates subjected to blast loading

Numerical results for simply supported rectangular steel plates subjected to blast loading are presented. The effects of geometric and material non-linearities are considered. Finite element analysis with ABAQUS software is used to determine the deformation of corroded plates subjected to blast loads. The results for the cases of triangular pulse pressure representative of gas explosion overpressure on unstiffened plates are validated using published data. Thorough parametric studies are performed to study the effects of influential parameters, including aspect ratio of plates, degree of pitting and corrosion patterns. The results show that a reduction in the dynamic load carrying capacity of 8% can occur due to corrosion in plates with 50% degree of pitting. Also it is shown that the mid-point deflection increases with an increase in the applied impulse, and degree of pitting, however, decreases with increasing plate aspect ratio. Corrosion pattern has significant effect on reduction of load carrying capacity. Maximum reduction occurs when pits are concentrated at the centre of plate. The region between core diameter and the edges of the plate is less dangerous.

Influence of pitting corrosion on strength of steel ships and offshore structures

The present paper deals with the influence of pitting corrosion on mechanical properties of mild and low alloy steels and strength of steel structures under static and quasi-static loads. Pitting corrosion is a very important phenomenon that influence local strength of ship hull members. The present paper is based mainly on Japanese publications. Analyzing the standard tensile diagrams one can see that that pitting corrosion reduces the load corresponding to yield stress (YS) and, even more markedly, tensile strength UTS, reduces almost to zero plastic flow strains at YS load level and dramatically reduces the total elongation to fracture. Nominal UTS load for uniformly corroded specimens is higher than that for pitted specimens at the same average thickness loss. The strength related to the true fracture surface area (i.e. reduced by pits, taking into account real path of the crack through the pits) is almost independent of the thickness loss and is almost the same as for uniform thickness loss. For wide specimens the tensile strength depends mainly on the local deformation ability, and the maximum loading ability for large members, predicted on the base of the total true fracture surface area, can be overestimated. Concept of equivalent thickness loss for plates under bending and compression and for more complex structural models as well as relation between the average and the equivalent thickness losses has been presented. Approach based on degree of pitting (ratio of pitted area to total plate surface area) has been shown as a real and more convenient than the approach based on the thickness loss.

Monitoring pitting‐crevice corrosion using the WBE‐noise signatures method

AbstractAn electrochemically integrated multi‐electrode array namely the wire beam electrode (WBE) and noise signatures analysis have been applied in novel combinations to study crevice corrosion behaviour in the presence of pits. Characteristic electrochemical noise signatures were found to correlate with characteristic changes in WBE current distribution maps, which indicate corrosion rates distributions, corrosion patterns and the degree of pitting and crevice corrosion. Specifically, two characteristic noise patterns were observed: (i) the characteristic noise pattern of quick potential changes towards more negative direction with no recovery (termed noise signature I) was found to correspond with the initiation and stabilization of the anode inside crevice; and (ii) the characteristic noise pattern of the cyclic potential oscillation at a constant frequency (termed noise signature II) was found to correspond with the stable anodic dissolution in the occluded cavity site in WBE current distribution maps. A new parameter namely the localization parameter (LP) has been proposed to describe the degree of localization. The LP for crevice corrosion was found to be low compared to that for pitting corrosion.

10408 船体構造部材の圧縮・せん断最終強度に及ぼす腐食ピットの影響(材料(2))

Corrosion pits with a conical shape have been observed in coated structural members of bulk carriers carrying coal and iron ore. In order to investigate the effect of pitting corrosion on ultimate compressive and shear strength of square plates, a series of FE-analyses has been conducted. It has been revealed that the ultimate strength is strongly affected by DOP (Degree of Pitting Intensity), pit diameter D and original thickness t_0. In some cases, corrosion pits are assumed to have a cylindrical shape in such analyses for simplicity. Square plates with corrosion pits having a cylindrical shape have been also analyzed. It has been also found that the ultimate strength is strongly affected by the shape of corrosion pits.

船体構造部材の静的強度に及ぼす腐食の影響 (第9報)

The aim of this research project is to establish a method of evaluating the effect of pitting corrosion with a circular cone shape on local strength of hold frames of bulk carriers. In the present study, an empirical formula for predicting ultimate strength of plates with pitting corrosion is proposed based on the results of FE analyses with pitted plates under uni-axial compression. In the formula, equivalent thickness for ultimate strength of pitted plates is expressed as a function of DOP (degree of pitting intensity), pit diameter and original thickness of pitted plates. Equivalent thickness predicted by the proposed formula has been compared with the results of FE analyses with pitted plates under various loading conditions and it has been revealed that the proposed formula could well predict the equivalent thickness for ultimate strength of pitted plates under uni-axial compression, shear, bi-axial compression, combined uni-axial compression and shear, combined bi-axial compression and shear, in-plane bend and combined in-plane bend and compression.

船体構造部材の静的強度に及ぼす腐食の影響 (第8報)

The purpose of this research project is to establish a method of evaluating the effect of pitting corrosion with a circular cone shape on local strength of hold frames of bulk carriers. In the present study, an empirical formula is proposed based on the tensile test results conducted in the previous study. In the formula, tensile strength reduction due to pitting corrosion is expressed as a function of DOP (degree of pitting intensity), pit diameter and original thickness of pitted plates. It has been shown that tensile strength of relatively small plates with pitting can be well predicted by the formula. In order to check the applicability of the formula to wide plates, a series of tensile test with wide specimens having artificial pits has been performed. It has been found that when diameter of all the pits is the same, prediction results of the tensile strength of wide specimens with artificial pits are conservative, and when pits with different diameter coexist, prediction of the tensile strength using average pit diameter give a little optimistic (non-conservative) results.

Some effects of weathering on joints in granitic rocks

Standard engineering weathering classifications, most of which are based on weathered granite, typically describe the appearance and condition of the weathered material (e.g. whether or not it is friable), the condition of individual minerals (e.g. degree of pitting and micro-cracking and changes in mineral composition), and the degree of staining on joint surfaces or the distance that staining extends into rock from the joints. These classifications do not address changes in frequency, length, and appearance of joints in the rock mass as weathering progresses. This account of work on vertical or steeply dipping joints in granitic rocks shows that not only are there statistically significant differences in mean joint spacings and mean trace lengths with increased weathering, but that the physical appearances of joints also changes as weathering progresses. Mean joint spacing is wide in fresh rock, becomes closer in moderately weathered rock, and then becomes progressively wider from moderately weathered rock through highly and completely weathered rock. Mean joint lengths follow a similar but inverse pattern. Mean trace lengths become shorter from fresh to slightly weathered rock, lengthen in moderately weathered rock, then progressively become shorter from moderately weathered rock through highly and completely weathered rock. Furthermore, joint appearance changes with increased weathering. Joints in fresh rock are sharp-edged and typically straight. The edges begin to round in moderately weathered rock, and in highly weathered rock, joint traces become sinuous and discontinuous around mineral grains. In completely weathered rock, the only visible joints are filled with minerals or marked with iron staining. It is proposed that this evolution in joint pattern and appearance results from increased cracking along grain boundaries and thermal expansion of individual mineral grains, and within-grain micro-cracking as weathering proceeds. These factors allow individual mineral grains to “move” into the spaces between joint surfaces, thus obscuring individual joints and making them appear shorter. These apparent changes in joint properties could lead to incorrect rock mass classification and thus, to inappropriate engineering design and costly errors during construction.

Characterization of corroding aluminium alloys with electrochemical noise and electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) and spontaneous voltage fluctuation measurements were made on three orthogonal faces of 7039-T64 and 2519 aluminium alloy specimens during 10 day exposure periods into aerated 3% NaCl solutions. The spontaneous voltage fluctuations generated by the specimens were analysed with two techniques designed to reveal the stochastic character of these signals and their fractal dimension to establish practical correlation between noise measurements and the degree of pitting of the corroding aluminium specimens. Attempts were made to correlate the results of these analyses with parameters measurable by microscopic examination of the specimens or calculated from EIS measurements. During this study it was found that the slope of the voltage fluctuations and the depression angle of EIS results were both good indicators of the pit density observable on the corroded aluminium specimens.

Reevaluation of Multiparameter Relative Dating Techniques and their Application to the Glacial Sequence Along the Eastern Escarpment of the Sierra Nevada, California

Four valleys, recently studied by other workers, were examined along the eastern Sierra Nevada to refine relative-dating techniques. A variety of weathering parameters and soil properties fail to delineate more than two major post-Sherwin Pleistocene glaciations. We correlate these two glaciations with the Tahoe and Tioga Glaciations. Type Mono Basin Till, usually considered to be pre-Tahoe, exhibits the following weathering similarities with Tahoe Till, if both are under sagebrush: (1) grusification of subsurface granitic boulders; (2) degree of pitting, mineral relief, and rind development on surface granitic boulders; and (3) very slight clay increase in the B horizon. Type Casa Diablo Till also has weathering characteristics similar to Tahoe Till, except a slightly more developed Bt horizon is present. Hence, dates on basalt of 0.126 ± 0.025 and 0.062 ± 0.013 my Casa Diablo Till also has weathering characteristics similar to Tahoe Till, except a slightly more developed Bt horizon is present. Hence, dates on basalt of 0.126 ± 0.025 and 0.062 ± 0.013 my (Bailey et al. 1976), which bracket type Casa Diablo, may provide age control on the Tahoe glaciation. In addition, we are unable to demonstrate that the Tenaya is a separate glaciation. In three of the four valleys studied our weathering data for Tenaya Till are equivalent with those for Tioga Till, but with those for Tahoe Till in the fourth valley. We were not satisfied with our ability to differentiate the Casa Diablo, Mono Basin, and Tenaya as separate glaciations even though data were collected in the type areas for two of these deposits. Reasons for suggesting a change back to a two-fold Tahoe-Tioga glacial sequence, rather than the present five-fold sequence, are that we have measured a greater number of parameters than has been done previously, soils were submitted to detailed laboratory analyses, and surface weathering features were studied under consistent present vegetation cover to avoid possible problems induced by ancient forest fires. Nevertheless our relative-dating scheme does not rule out the possibility of a more detailed glacial sequence.

Effect of calcium and boron on the incidence of tree and storage pit in apples of the cultivar Egremont Russet

SummaryThe influence of boron and calcium on tree pit and storage pit was examined in a two-year field trial on Egremont Russet apples in a commercial orchard in Herefordshire. Observations were also made on epidermal cracking of the fruit.Sprays of calcium nitrate reduced tree pit by 47% in the first season and by 57% in the second. In the second season the concentration of calcium in the sound fruits was 30% above control values following treatment with sprays of calcium nitrate, and 46% above control when the same treatment was combined with sprays of boron. Apples with tree pit had lower levels of calcium and magnesium than sound fruits.In the second season storage pit was reduced by 73%, and the degree of pitting by 76%, following sprays of calcium nitrate, and the cracking of fruit was entirely eliminated by sprays containing boron. Sprays of boron increased the content of boron, calcium, potassium and magnesium in sound fruit.