Pit Size Research Articles

Monte Carlo Simulation Method for Pit Erosion Process of Cable Wire Based on Bi-plane Cellular Automata

This paper proposed a new probabilistic Bi-plane cellular automaton (CA) model to simulate the localized pitting corrosion of stayed cables. The CA model introduced chloride ions and their evolution rules to take into account the local acidification catalysis is in microscopic scale. Besides, a Monte Carlo approach is adopted to analyze the statistical properties of corrosion pit size and their variation with respect to time. The proposed CA model is confirmed by several published experiments on pitting corrosion. It is capable to reproduce the experimental observations and enlarge the sample space for subsequent mechanical analysis.

Effect of Molybdenum on Pit Initiation Rate and Pit Growth Using Electrochemical Noise and Its Correlation with Confocal Laser Scanning Microscopic Studies

The effect of Mo concentration on pit initiation rate and pit growth in austenitic stainless steels (SS) were investigated by electrochemical noise (EN) and confocal laser scanning microscopy (CLSM) techniques for the first time. We used 304LN, 316LN and 317LN containing different concentrations of Mo (0.02, 2.53 and 3.58 wt.%) for our studies. Using EN technique, initiation of pits and growth of pits were analyzed using Weibull and Gumbel distribution function, respectively. Pit depth was obtained using CLSM and the correlation between pit aspect ratio and Mo concentration were studied. Weibull probability plots showed that the Mo present in the alloy reduces the pit generation rates and improves the passivity. The plot for the pit size distribution using Gumbel distribution function showed the lowest metastable pit in 317LN and the highest in 304LN, suggesting the improvement in the pitting corrosion resistance due to Mo addition. The CLSM imaging showed maximum pit depth for specimen 304LN and minimum for specimen 317LN SS. Specimen 316LN SS showed intermediate pit depth. The depth of the pits observed in 304LN, 316LN and 317LN ranged from 80-100 µm, 30-40 µm and 20-30 µm, respectively. Alloy 317LN containing highest Mo concentration (3.58 wt.%) showed the lowest pit aspect ratio values followed by alloy 316LN with 2.53 wt.% Mo. These results indicate that Mo present in the stainless steel helps in arresting the pit growth and improve the resistance to pitting corrosion.

Cause of Etch Pits during the High Speed Plasma Etching of Silicon Carbide and an Approach to Reduce their Size

To reduce the on-resistance in vertical power transistors, backside thinning is required after device processing. However, it is difficult to thin silicon carbide (SiC) wafers with a high removal rate by conventional mechanical processing because their hardness and brittleness cause cracks and chips during thinning. Therefore, the authors have attempted to thin SiC wafers using plasma chemical vaporization machining (PCVM), which is plasma etching using high-pressure plasma. PCVM has a high removal rate because of the high radical density in the high-pressure plasma, and it does not form a damaged layer on the processed surface because of the low ion energy. The authors have already achieved a very high removal rate of 15.6 μm/min by PCVM. However, many etch pits were generated on the wafer during PCVM in these high-speed machining conditions. Therefore, this study, using molten potassium hydroxide (KOH) etching, investigated the cause of such etch pits and found that they may stem from threading screw dislocation in the wafers. In addition, this research considered a process for reducing an etch pit size and succeeded in doing so by controlling wafer temperature.

Disadvantages of living in a populous neighborhood for sit‐and‐wait predators: Competition for space reduces pit‐trap size in antlion larvae

AbstractThe study of how trap design responds to biotic and abiotic conditions can help to understand the selective forces affecting the foraging of trap‐building organisms. We experimentally tested whether pit design can be modified by intraspecific competition for space in larvae of Myrmeleon crudelis, a common sit‐and‐wait predator that digs conical pit traps in the soil to capture walking arthropods. In a tropical forest in Costa Rica, we measured pit dimensions, larval body size, and the level of competition (i.e., density of neighboring traps) in 40 antlion larvae. These larvae were then taken to the laboratory and allowed to build new traps in individual containers. We measured within‐individual changes in the size of traps in the field and in the laboratory, and related these to the level of competition experienced in the field. Larvae with relatively high levels of competition in the field showed a greater increase in the size of their pits in the laboratory. This change was independent of larval size. Larvae with none or few neighbors in the field showed little change in their pit sizes, whereas those with higher competition levels increased their diameter and depth up to 1,400% and 1,000%, respectively. Our results demonstrate that, at least in high‐density aggregations, pit design is restricted by competition in addition to the constraints imposed by body size. This work suggests that biotic interactions can play a role in the design of extended phenotypes in sit‐and‐wait predators that live in dense aggregations.

Structural reliability assessment of offshore wind turbine support structures subjected to pitting corrosion‐fatigue: A damage tolerance modelling approach

AbstractThe structural integrity of offshore wind turbine (OWT) support structures is affected by one of the most severe damage mechanisms known as pitting corrosion‐fatigue. In this study, the structural reliability of such structures subjected to pitting corrosion‐fatigue is assessed using a damage tolerance modelling approach. A probabilistic model that ascertains the reliability of the structure is presented, incorporating the randomness in cyclic load and corrosive environment as well as uncertainties in shape factor, pit size and aspect ratio. A non‐intrusive formulation is proposed consisting of a sequence of steps. First, a stochastic parametric Finite Element Analysis (FEA) is performed using SMART© crack growth and Design Xplorer© facilities within the software package ANSYS. Secondly, the results obtained from the FEA are processed using an Artificial Neural Network (ANN) response surface modelling technique. Finally, the First Order Reliability Method (FORM) is used to calculate the reliability indices of components. The results reveal that for the inherent stochastic conditions, the structure becomes unsafe after the 18th year, before the attainment of the design life of 20 years. The FEA results are in very good agreement with results obtained from analysis steps outlined in design standard BS 7910 and other references designated as ‘theoretical analysis methods’ in this study. The results predict, for the case study, that the pit growth life is approximately 56% of the total pitting corrosion fatigue life. Sensitivity analysis results show that the aspect ratio of pits at critical size plays a significant role on the reliability of the structure.

On the Application of Bipolar Electrochemistry to Characterise the Localised Corrosion Behaviour of Type 420 Ferritic Stainless Steel

Bipolar electrochemistry has been applied to Type 420 ferritic stainless steel in order to determine the full spectrum of anodic-to-cathodic polarisation behaviour. The occurrence of crevice corrosion, pitting corrosion in combination with general corrosion, pitting corrosion only, general corrosion only, followed by a cathodic region has been observed. Instances of pitting corrosion initiated near chromium-rich carbides with Cr23C6, Cr3C2, and Cr7C3 identified as pit nucleation sites. The observed pit growth kinetics were independent of the electrochemical over-potential. Characterisation of the pit size distributions supports the presence of a critical dissolved volume for the transition of metastable to stable pit growth and pit coalescence.

On the dynamics of a lubricated roller contact

This study proposes a dynamic model of a lubricated roller contact, focusing on the excitation of surface pit/defect. The fluctuation of contact force caused by periodic surface topography variation is used to determine the dynamic displacements and velocities of contact bodies. These responses, in turn, affect the thickness and flow of lubrication film, impacting contact pressure, and consequently contact force that is required in the dynamic analysis. It is shown, as the pit size grows, the acceleration increment escalates, therefore, can be used as an effective indicator for pitting failure occurrence. Additionally, a comparison of contact pressure between dynamic simulation and its quasi-static counterpart points to the importance of dynamic responses in tribological behavior description.

Analysis and prediction of surface wear resistance of ball-end milling topography

Surface topography has an important effect on the wear resistance of contact surfaces. Non-smooth surfaces have stronger wear resistance than smooth surfaces. In this paper, the sliding wear characteristics of the surface of a quadrangular pit formed by ball-end milling were studied. Using the Archard wear model and the UMESHMOTION subroutine in ABAQUS software, the finite element simulation analysis of the sliding wear process was performed under dry friction conditions. Combined with finite element simulation data, the contact area, contact pressure, wear zones and the relative wear rate of the quadrangular pit topography with different sizes were analyzed, and the relationship between the quadrangular pit size and wear resistance was obtained. Based on Grey System Theory, the grey incidence between the relative wear rate of the topography surface and the areal surface roughness was obtained. Based on this, a zeroth order four variable grey model, GM(0, 4), for determining the wear resistance of the topography surface was established, and the model was verified experimentally. This research provides a new method for the judgment of the surface wear resistance of ball-end milling topography with the different sizes of quadrangular pits.

Synergistic effect of CeCl3 and benzotriazole on corrosion resistance of naturally aged and artificially aged AA2024 aluminium alloy

Abstract The corrosion behaviours of naturally aged and artificially aged AA2024 aluminium alloys in 0.5 mol/dm3 NaCl solution in the presence of environmentally friendly corrosion inhibitors of 10 mmol/dm3 CeCl3, 10 mmol/dm3 BTA and the inhibitor mixture (5 mmol/dm3 CeCl3 + 5 mmol/dm3 BTA) were analyzed. The goal of this work was to determine the level of the synergistic effect of the inhibitor mixture and to explain the nature of this effect. Corrosion properties of the inhibitor layer were studied using the electrochemical impedance spectroscopy (EIS), while the resistance to pit formation and pit growth was studied by applying potentiodynamic polarisation tests. The results of scanning electron microscopy (SEM/EDS) showed that the size of pits formed in naturally aged aluminium alloy was smaller than that formed in artificially aged alloy. The synergistic effect of the inhibitor mixture on corrosion properties of naturally aged alloy was observed throughout 96 h, and in later phases of testing of artificially aged alloy. The synergistic effect of the inhibitor mixture was not noticed on pit formation and pit growth.

AlGaN-based Schottky barrier deep ultraviolet photodetector grown on Si substrate.

This letter reports the influence of material quality and device processing on the performance of AlGaN-based Schottky barrier deep ultraviolet photodetectors grown on Si substrates. The thermal annealing can significantly improve Schottky barrier height and wet chemical etching can effectively remove etching damage. Meanwhile, the decrease of threading dislocation density and the pit size, especially the later, can substantially suppress reverse leakage. As a result, the reverse leakage current density of the as-fabricated deep UV photodetector was reduced down to 3×10-8 A/cm2. Furthermore, the responsivity of the deep UV photodetectors was greatly improved by reducing the point defect concentration.

Pitting corrosion modelling of X80 steel utilized in offshore petroleum pipelines

High strength steels such as X80 steels have recently been used more frequently in production of offshore structures. However, they may still be subject to degradation processes such as corrosion considering the conditions in marine environment. Pitting corrosion is a destructive form of corrosion which reduces the material resistance and may result in failure accidents with severe financial, human life and environmental consequences. The process of pitting corrosion is inconsistent and largely stochastic being influenced by a number of parameters with a high level of uncertainty. This makes it very difficult to predict corrosion in terms of its initiation time and spatial behavior. Therefore, it is vital to investigate pitting corrosion phenomena in offshore structures using a probabilistic approach for the assessment of structural reliability and operational safety. In this study, an in-situ experiment has been conducted on X80 steel in an NaCl solution in a laboratory environment to observe the generation and growth of corrosion pits. A probabilistic model based on Hierarchical Bayesian Approach (HBA) is developed for predicting the pitting corrosion growth rate using experimental results. In order to model the process more realistically, the proposed methodology considers the degradation process to be consisting of the time needed for pit initiation and propagation. The results indicate that the proposed methodology is capable of predicting the time required to reach a specific pit size. The methodology developed in this study can be applied to estimate the remaining useful life of subsea structures.

Comparative culm anatomy of metaxylem vessel pits in three different types of bamboo rhizome

AbstractNot only are vessel pits vital for the passage of sap into adjacent cells, but their anatomical morphology is also used as a tool to identify bamboo species. However, detailed studies comparing the pits’ structural parameters in culms of species with three rhizome types: sympodial bamboo, amphipodial bamboo, and monopodial bamboo, are lacking. Scanning electron microscopy (SEM) observations were conducted to obtain the qualitative and quantitative characteristics of vessel pits in sympodial, amphipodial and monopodial bamboos, from twelve bamboo species in eight genera. Sympodial bamboos possess small and ovoid bordered pits, whereas amphipodial bamboos contain an abundance of slit-like pits, with the greatest pit membrane length occurring in the vessel wall. Both minute and large pit sizes can be found in monopodial bamboos. This study identified the first compound pits ever to be found in a bamboo species and these were found to occur more frequently in amphipodial and monopodial bamboos than in sympodial bamboos. Using the distribution frequency of the pit chamber’s horizontal diameter, we were able to determine pit size as being either small, medium or large. The striking differences in the vessel pits’ qualitative and quantitative characteristics could be the result of different climate and environmental factors.

Pit and pit aperture dimensions in plantation-grown Douglas fir as affected by local growth conditions and height in stem

Abstract This study assessed whether allometric scaling applied to pit sizes in stems of Douglas fir. Pit and pit aperture diameters were measured in xylem from stems of four plantation-grown Douglas fir (Pseudotsuga menziesii) trees from each of two different sites in Denmark. One site had fertile soil, the other had poor soil fertility. Three different heights were accessed for each tree, and 40 pits were measured per height. Results showed that pit diameter varied between 17 and 24 μm and decreased significantly with increasing height above ground. Representing the position in the tree as a power function of distance from the top of the tree (L0.2) rather than the height above ground improved the model fit for pit diameter as expressed by the R2 value. However, the pit diameter relationship was found to be significantly affected by site, suggesting that anatomic dimensions relate not only to tree size but also to growth conditions. This would imply that even though pit size supposedly has a strong biophysical determination, some xylem plasticity may still be induced by environmental factors.

Obesity potentially protects against systemic bone loss in patients with rheumatoid arthritis treated with tumour necrosis factor inhibitors.

We aimed to investigate how systemic bone metabolism was affected after 1 year of treatment with tumour necrosis factor (TNF) inhibitors in rheumatoid arthritis (RA) patients. A total of 29 seropositive RA patients not treated for osteoporosis were enrolled and TNF inhibitors were administered for a year. Bone mineral density (BMD) at the lumbar spine, femur neck, and total hip was measured at baseline and 12 months after anti-TNF treatment. Blood samples were collected at baseline and 6 and 12 months after anti-TNF treatment and osteoclasts were cultured on bone slices. Weight was the strongest factor influencing systemic bone loss. Patients were categorised into two groups: obese (body mass index (BMI) ≥25 kg/m2) and non-obese (BMI <25 kg/m2). All patients showed decreased BMD at all sites. The obese group showed relatively little change in BMD, although the non-obese group showed significant decreases in BMD at all sites after 1 year of treatment with TNF inhibitors. Resorption pits created by osteoclasts decreased at 6 months and increased at 12 months in the non-obese group, while the obese group presented with steadily decreasing sizes of resorption pits at all-time points. Levels of receptor activator of nuclear factor kappa B ligand were significantly decreased at 12 months compared to baseline in the obese group, while they were increased in the non-obese group. One year of treatment with TNF inhibitors failed to halt systemic bone loss in RA patients, but obesity may have protective effects against bone loss.

The influence of manual and motor-manual pitting implements, pit size and quality on eucalypt performance, South Africa

Pitting is the preparation of a planting position. Various methods of pitting exist and range from manual pitting to fully-mechanised operations. Until recently, most pit preparation in South Africa was carried out manually using hand-held pitting implements (agricultural hoe, mattock, road pick) to create a 25 cm wide pit containing friable soil to a depth of 15–25 cm. However, there are several negative factors associated with manual pit preparation, such as poor ergonomics, intensive labour requirements, and inconsistent pit preparation. This has resulted in an increasing interest in semi- to fully-mechanised operations, where semi-mechanised motor-manual pitting methods are often considered more efficient and cost-effective than traditional manual operations. This study compared the performance of eucalypts planted into pits created by various pitting methods. Two trials were established with eucalypts on contrasting sites, one at Greenhill in the KwaZulu-Natal Midlands and one at Vroegeveld, Mpumalanga. Four manual implements (notch, agricultural hoe, mattock, road pick) and three different motor-manual heads (inverted A, Archimedes screw and Mondi-designed pitting head) were used to prepare and determine the effect of pit size/quality on tree survival, growth and uniformity. The notch pit implement created the smallest pit (1 L volume), whilst other implements created larger pits (4–6 L volumes). Pitting method did not have a significant effect on the success of re-establishment and subsequent tree performance on both sites (2.5 years after planting and thereafter). This indicates that for the soils tested, any possible negative tillage effects caused by any of the pitting implements did not affect the species planted. Factors such as operational costs, efficiency and ergonomics must therefore be considered to select relevant pitting methods, together with tree performance.

A data-driven probabilistic model for well integrity management: case study and model calibration for the Danish sector of North Sea

ABSTRACT The correct functioning of well completion in oil and gas facilities is eminently important to assure continuity of production operations together with an adequate safety level. To enhance the performance of production wells and reduce maintenance expenditures, a paradigm shift from corrective maintenance to proactive risk based maintenance is necessary. The feasibility of fully probabilistic risk-based inspection planning approach for oil wells has been investigated as pilot study carried out at Danish Hydrocarbon Research and Technology Centre (DHRTC). After establishing a baseline for the system taxonomy, failure modes and their dependencies on deterioration mechanisms, a data collection and analysis lead to the calibration of a corrosion probabilistic model, based on pit size measured from tubing inspections. This manuscript presents the results of the feasibility study, the calibration of a bespoke corrosion model for wells in the Danish sector of North Sea, the reliability analysis and the identification of a threshold value for the pit penetration to be compared with current oil & gas (O&G) regulations. The model is further used to compare expected maintenance costs for corrective maintenance and condition-based maintenance. Results show how the condition-based maintenance policy results in lower maintenance costs and potential extension of well lifetime.

Development mechanism of internal local corrosion of X80 pipeline steel

The occurrence and development mechanism of internal local corrosion has always been a controversial topic, and especially under flow conditions. In this paper, an improved high shear force loop was experimentally used, and local flow field is induced by simulating corrosion defects on the surface of X80 pipeline steel specimens. The characteristics of corrosion products deposited on the surface of specimens in CO2-saturated NACE solution were investigated by means of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). The 3D micromorphology of the corrosion test surface after remove the corrosion scale used to measure the size of localized corrosion pit. Under the influence of local defects, the wall shear stress (WSS) and turbulent kinetic energy of local flow fields enhanced significantly, and pressure fluctuations in local flow field were induced. The results showed that the characteristics of surface corrosion products varied with flow velocity. The corrosion scales formed in various regions of specimens with defects exhibited different surface micro-morphologies and chemical compositions. Overall, these data offer new perspectives for better understanding the mechanisms behind local corrosion.

Crystallinity Evaluation and Dislocation Observation for an Aluminum Nitride Single-Crystal Substrate on a Wafer Scale

The crystallinity of a 35-mm-diameter AlN single-crystal substrate grown by physical vapor transport was investigated using x-ray diffraction and Raman spectral mapping. Dislocations in the same sample were observed using an etch pit method, synchrotron x-ray topography, and transmission electron microscopy. The central area of a diameter of 25 mm was featured with high crystallinity and high uniformity, whereas the rim area showed degradation in crystallinity. An improvement in the radius of curvature was confirmed along the growth direction of [ $$ 000\bar{1} $$ ]. The dislocations were revealed as etch pits, and the position-dependent etch pit density was analyzed across the whole wafer. Transmission electron microscopy showed that under the current chemical etching condition, the size of the etch pits in the [ $$ 11\bar{2}0] $$ diagonal direction was approximately linearly proportional to the magnitude of the Burgers vectors, and therefore could be used to classify dislocations.

Brachypodium distachyon MAP20 functions in metaxylem pit development and contributes to drought recovery.

Pits are regions in the cell walls of plant tracheary elements that lack secondary walls. Each pit consists of a space within the secondary wall called a pit chamber, and a modified primary wall called the pit membrane. The pit membrane facilitates transport of solutions between vessel cells and restricts embolisms during drought. Here we analyzed the role of an angiosperm-specific TPX2-like microtubule protein MAP20 in pit formation using Brachypodium distachyon as a model system. Live cell imaging was used to analyze the interaction of MAP20 with microtubules and the impact of MAP20 on microtubule dynamics. MAP20-specific antibody was used to study expression and localization of MAP20 in different cell types during vascular bundle development. We used an artificial microRNAs (amiRNA) knockdown approach to determine the function of MAP20. MAP20 is expressed during the late stages of vascular bundle development and localizes around forming pits and under secondary cell wall thickenings in metaxylem cells. MAP20 suppresses microtubule depolymerization; however, unlike the animal TPX2 counterpart, MAP20 does not cooperate with the γ-tubulin ring complex in microtubule nucleation. Knockdown of MAP20 causes bigger pits, thinner pit membranes, perturbed vasculature development, lower reproductive potential and higher drought susceptibility. We conclude that MAP20 may contribute to drought adaptation by modulating pit size and pit membrane thickness in metaxylem.

Optimization of Initiation Sites of Tunnel Pits on Aluminum Foil Using Self-Ordered Concave Structures

The self-ordered concave structures fabricated on aluminum surface by aluminum anodic oxidation and oxide removal procedures were applied to control the pit initiation sites for tunnel etching of aluminum foil, where the tunnel pits would be correspondingly generated under the sites of self-ordered concave structures. The obtained sizes of the tunnel pits were 100–600 nm in width and 1.6 μm in length, which were mainly determined by the interpore distances of the concave structures and the tunnel etching conditions. Based on this process, the distribution of the tunnel pits on aluminum surface was improved observably, so that a high aspect ratio was successfully achieved.