Maximum Pit Research Articles

Characterisation of pitting corrosion for inner section of offshore wind foundation using laser scanning

Pitting corrosion is a complex mechanism and has been found in the inner sections of offshore wind structures where the standards at the time indicated that those sections were water tight and therefore free from corrosion. Pits propagate and grow in size and this can have serious implications for the structural integrity of the structure by reducing the fatigue life but also under some conditions changing to a crack whereby the damage can be accelerated. In this study, pitting corrosion is extracted from coupons exposed to the unique inner environment of offshore structures for a duration of 528–1049 days and modelled with time by extracting their geometries, such as minor length, major length and depth using laser scans. A maximum pit depth of 1.67 mm was observed. A series of analyses were run to understand the pitting mechanism and the effect of the stress concentration factor.

Localized corrosion: Passive film breakdown vs. Pit growth stability, Part VI: Pit dissolution kinetics of different alloys and a model for pitting and repassivation potentials

The pitting resistance of SS316L, SS304, SS430, and pure Fe was studied in chloride-containing solution. Among these alloys, SS316L exhibits the highest pit initiation rate, but also the highest pitting potential. To explain this phenomenon, the maximum pit dissolution current density (idiss,max) of the alloys in saturated pit solution was measured using one-dimensional artificial pit electrodes. A lower idiss,max was found to correlate with higher pitting and repassivation potentials. Based on a recently proposed pitting framework, a conceptual model for pitting and repassivation potentials was established, based on which the effect of idiss,max on pitting resistance was discussed.

Advanced intelligence frameworks for predicting maximum pitting corrosion depth in oil and gas pipelines

The main objective of this paper is to develop accurate novel frameworks for the estimation of the maximum pitting corrosion depth in oil and gas pipelines based on data-driven techniques. Thus, different advanced approaches using Artificial Intelligence (AI) models were applied, including Artificial Neural Network (ANN), M5 Tree (M5Tree), Multivariate Adaptive Regression Splines (MARS), Locally Weighted Polynomials (LWP), Kriging (KR), and Extreme Learning Machines (ELM). Additionally, a total of 259 measurement samples of maximum pitting corrosion depth for pipelines located in different environments were extracted from the literature and used for developing the AI-models in terms of training and testing.Furthermore, an investigation was carried out on the relationship between the maximum pitting depths and several combinations of probable factors that induce the pitting growth process such as the pipeline age, and the surrounding environmental properties. The results of the proposed AI-frameworks were compared using various criteria. Thus, statistical, uncertainty and external validation analyses were utilized to compare the efficiency and accuracy of the proposed AI-models and to investigate the main contributing factors for accurate predictions of the maximum pitting depth in the oil and gas pipeline.

Ultimate Pit Limit Optimization using Boykov-Kolmogorov Maximum Flow Algorithm

The ultimate pit limit optimization (UPLO) serves as an important step in the mine planning process. Various approaches of maximum flow algorithms such as pseudo-flow and push-relabel have been used for pit optimization, and have given good results. The Boykov-Kolmogorov (BK) maximum flow algorithm has been used in solving the computer vision problems and has given great practical results but it has never been applied in UPLO. In this work, we formulate and use the BK maximum flow algorithm and the push-relabel maximum flow algorithm in MATLAB Boost Graph Library within the MATLAB software in order to perform UPLO in two case studies. Comparing both case studies for the BK maximum flow algorithm and push-relabel maximum flow algorithm gives the same maximum pit values but the BK maximum flow algorithm reduces the time consumed by 12% in the first case and 16% in the second case. This successful application of the BK maximum flow algorithm shows that it can also be used in UPLO.

Influence of heat input on the pitting corrosion and tensile behavior of GTA welded martensitic stainless steel (AISI410 SS) joints

Two heat input combinations designated as low heat input and high heat input having values 2.418 kJ/mm and 3.615 kJ/mm respectively were used to weld the martensitic stainless steel (AISI 410 SS) base plates by gas tungsten arc welding process. Effect of heat input on the pitting corrosion and tensile performance of the joints in as welded condition and post weld heat treated condition was analyzed. On the basis of experimental results, it can be inferred that the weld joint made using low heat input combination (WJ 1) possessed the maximum pitting resistance (mass loss 0.6596 mg) and ultimate tensile strength (UTS) of 496 MPa in as received conditions. After the post weld heat treatment, a significant increment in UTS and pitting resistance was observed. Based on the optical microscopic results of the weld-metal, it was found that the secondary dendritic arm length and inter dendritic spacing increases with increase in the heat input. The grain coarsening effect was observed in the WJ 2 due to the slower cooling rate as compared to WJ 1. The variation in the pitting and tensile properties due to different thermal gradients was established across the weldment of both weld joints.

Quantitative assessment of environmental phenomena on maximum pit size predictions in marine environments

Maximum pit sizes were predicted for dilute and concentrated NaCl and MgCl2 solutions as well as sea-salt brine solutions corresponding to 40% relative humidity (RH) (MgCl2-rich) and 76% RH (NaCl-rich) at 25 °C. A quantitative method was developed to capture the effects of various cathode evolution phenomena including precipitation and dehydration reactions. Additionally, the sensitivity of the model to input parameters was explored. Despite one's intuition, the highest chloride concentration (roughly 10.3 M Cl−) did not produce the largest predicted pit size as the ohmic drop was more severe in concentrated MgCl2 solutions. Therefore, the largest predicted pits were calculated for saturated NaCl (roughly 5 M Cl−). Next, it was determined that pit size predictions are most sensitive to model input parameters for concentrated brines. However, when the effects of cathodic reactions on brine chemistry are considered, the sensitivity to input parameters is decreased. Although there was not one main input parameter that influenced pit size predictions, two main categories were identified. Under similar chloride concentrations (similar RH), the water layer thickness (WL), and pit stability product, (i·x)sf, are the most influential factors. When varying chloride concentrations (RH), changes in WL, the brine specific cathodic kinetics on the external surface (captured in the equivalent current density (ieq)), and conductivity (κo) are the most influential parameters. Finally, it was noted that dehydration reactions coupled with precipitation in the cathode will have the largest effect on predicted pit size, and cause the most significant inhibition of corrosion damage.

An Analysis of the Casting Polymer Mold Wear Manufactured Using PolyJet Method Based on the Measurement of the Surface Topography.

An important factor having an impact on the condition of machine parts is their surface topography. For instance, in the production of a molded element in casting or injection molding processes, the surface topography of the molding cavity has a significant impact on the surface condition of the product. An analysis of the wear of a mold made with the PolyJet technique was performed in this work, and we examined the surface topography using the stylus method after casting a wax model of the turbine blade. The surface topographies showed a gradual degradation of the mold cavity surface. After the manufacture of 40 castings, there was a significant deformation of the microstructure of the mold cavity. The maximum height value (Sz) parameter had the most dynamic change from 18.980 to 27.920 μm. Its growth dynamics are mainly influenced by maximum peak height (Sp) rather than the maximum pit height (Sv) parameter. In the case of the root mean square height (Sq) and arithmetic mean height (Sa), their gradual increases can be seen from 2.578 to 3.599 μm and from 2.038 to 2.746 μm. In the case of the value of the skewness (Ssk) parameter, a small positive skew was observed. As for the kurtosis (Sku) values, the distributions are clearly leptokurtic.

Electron transfer mediator PCN secreted by aerobic marine Pseudomonas aeruginosa accelerates microbiologically influenced corrosion of TC4 titanium alloy

Titanium alloys possess excellent corrosion resistance in marine environments, thus the possibility of their corrosion caused by marine microorganisms is neglected. In this work, microbiologically influenced corrosion (MIC) of TC4 titanium alloy caused by marine Pseudomonas aeruginosa was investigated through electrochemical and surface characterizations during a 14-day immersion test. Results revealed that the unstable surface caused by P. aeruginosa resulted in exposure of Ti2O3 and severe pitting corrosion with maximum pit depth of 5.7 μm after 14 days of incubation. Phenazine-1-carboxylate (PCN), secreted by P. aeruginosa, promoted extracellular electron transfer (EET) and accelerated corrosion. Deletion of the phzH gene, which codes for the enzyme that catalyzes PCN production, from the P. aeruginosa genome, resulted in significantly decreased rates of corrosion. These results demonstrate that TC4 titanium alloy is not immune to marine MIC, and EET contributes to the corrosion of TC4 titanium alloy caused by P. aeruginosa.

Finite Element Modeling of SS316 Pit Stability, with Respect to Geometry Parameters, Under Atmospheric Conditions

Additive manufacturing (AM) of metals have become a promising fabrication method, due to the decreased waste from conventional manufacturing and the ability to create complex geometries [1]. However, the surface roughness of powder based additively manufactured structures appears porous, with complicated geometries that are a concern for localized corrosion. Knowing which defects are more susceptible than others, from a geometry perspective, will greatly aid mitigation strategies either in terms of AM process parameters or through post-build surface treatments. This study will explore how surface defects created on AM stainless steel parts impact local corrosion stability under atmospheric conditions.The stochastic nature of the pits initiating and repassivating, combined with the complexities of the AM defects and those of thin water layers, make for a very large parameter space to explore. In effect, the most important aspect of localized corrosion under these conditions is the determination of whether a pit will repassivate or grow, and if it grows, how large can it become. Many different parameters affect the pit stability, including the geometry of the cathode size, the anode (pit) size, details of the environment (solution composition, electrochemical potential), and the water layer thickness.It is known that the potential at a pit mouth must be more positive than in order to grow stably [2]. The repassivation potential therefore serves as one way to measure pit stability, while other parameters in the system are held constant. An additional pit stability criteria is the pit stability product, (i ⋅ x), from Galvele’s seminal work [3]. The maximum pit model [4] uses these criteria, parameters that define the thin electrolyte, and the current-potential relationship for the cathodic reaction(s) on the external surface to define the largest hemispherical pit for which the Conservation of Charge is met.Finite element modeling is used here to determine what combinations of geometric parameters associated with surface defects due to AM processing of SS316 lead to the stabilization of a pit or not. Pits of different dimensions, including hemispherical, rectangle, and disk shaped, are assessed as isolated pits. The model’s geometric complexity is then increased to better represent an additively manufactured surface with many pits of different shapes and sizes based on cross-sectional data from actual surfaces. A range of atmospheric conditions are investigated, including a range of relative humidity and salt loading density. The boundary conditions within the model represent the solution kinetics of both scenarios. The water layer and loading densities were varied, according to the equation proposed by Chen et al. [5].SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2020-5408 A.[1] B. AlMangour and J. M. Yang, “Improving the surface quality and mechanical properties by shot-peening of 17-4 stainless steel fabricated by additive manufacturing,” Mater. Des., vol. 110, pp. 914–924, 2016.[2] J. Srinivasan, M. J. McGrath, and R. G. Kelly, “A High-Throughput Artificial Pit Technique to Measure Kinetic Parameters for Pitting Stability,” J. Electrochem. Soc., vol. 162, no. 14, pp. C725–C731, 2015.[3] J. R. Galvele, “Transport Processes and the Mechanism of Pitting of Metals,” J. Electrochem. Soc., vol. 123, no. 4, p. 464, 1976.[4] R. M. Katona, J. Carpenter, E. J. Schindelholz, and R. G. Kelly, “Prediction of Maximum Pit Sizes in Elevated Chloride Concentrations and Temperatures,” J. Electrochem. Soc., vol. 166, no. 11, pp. C3364–C3375, 2019.[5] Z. Y. Chen, F. Cui, and R. G. Kelly, “Calculations of the Cathodic Current Delivery Capacity and Stability of Crevice Corrosion under Atmospheric Environments,” J. Electrochem. Soc., pp. 360–368, 2008.

Determination of Key Marine Environment Effects on Bounding Pit Size Predictions

Stainless steels (SS) have been used extensively in coastal marine environments due to their enhanced corrosion resistance. One such example is the interim storage and the eventual transport of spent nuclear fuels (SNF) in SS casks. These SS casks may be subjected to corrosive exposure conditions, thus are susceptible to degradation through localized corrosion and subsequent stress corrosion cracking (SCC). Assessing the current damage state on the surface of these canisters would be ideal for informing future transport decisions, however, this is difficult due to confinement imposed by the concrete overpack. Due to the spatial limitation, prediction of the surface pitting corrosion damage is crucial to determining SCC susceptibility. Recent work in which the maximum attainable pit size can be calculated for given exposure conditions could form the foundation for predictions [1]–[3]. A review of relevant literature to SS’s in marine environments shows that potential surface conditions on the cask surface could be a thin electrolyte film containing high chloride concentration at elevated temperatures [4], [5]. Therefore, cathodic and anodic kinetics were evaluated in seawater and seawater simulated solutions (NaCl and MgCl2) at various temperatures. The reaction mechanisms for each solution and the impact on maximum pit size predictions will be discussed. Furthermore, certain bulk cations in seawater solutions (typically Mg2+ and Ca2+) have a strong thermodynamic driving force to form stable precipitates (such as hydroxides). Such precipitates have the propensity to decrease the cathodic current available and can decrease the maximum pit size. Calculations for max pit size predictions are carried out in order to account for environmental phenomena happening on the surface of a SS304L alloy. Overall, influences from precipitates and reaction mechanisms will lead to a decrease in the calculated bounding maximum pit size. Acknowledgements SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2020-5134 A.

Electrochemical Behavior of Salt Film and Its Role in Pit Growth

In a recently published series of papers for pitting corrosion,1-5 a new concept of maximum pit dissolution current density, i diss,max, was proposed to establish a unifying framework for pit growth stability. This framework provides an opportunity to revisit several key topics of this field and generates new insights to interpret the previous observations in a self-consistent way. In this work, the unifying framework is further expanded to establish a mathematical model describing the electrochemical behavior of salt film after it precipitates, i.e. the situation when i diss,max > i lim. It can be mathematically shown that the main function of a salt film during diffusion-controlled pit growth is to accommodate the extra potential of (E max - E sat) by regulating its thickness to adjust the actual potential at the pit surface to E sat, thus restricting the anodic dissolution current density at the diffusion-limited value.4 The salt film will respond to any changes of the applied potential, temperature, pit depth, and perforation radius of the pit cover. In addition, an analytical model is proposed for salt film growth based on ion transport, in which the film grows at the metal/film interface and dissolves at film/solution interface. Any disturbance causing a difference in growth and dissolution rates will trigger a self-regulating process that will, in turn, bring the pitting system back to steady state. Acknowledgments: This work was supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584.Reference G. S. Frankel, T. Li, and J. R. Scully, Journal of the Electrochemical Society, 164 (4), C180-C181 (2017).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (9), C484-C491 (2018).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (11), C762-C770 (2018).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (6), C115-C124 (2019).T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (11), C3341-C3354 (2019).

(Invited) Atmospheric Corrosion of Magnesium Alloys: Influence of Aluminium Content

Magnesium has gained considerable interest as a structural material for automotive and aerospace applications due to its low density and high specific strength. The use of magnesium alloys in engineering applications is, however, mainly limited by their unsatisfactory surface properties and their poor corrosion resistance. In recent years, significant improvements have been made in achieving a better corrosion resistance particularly by reducing the contents of impurities such as Fe, Cu, and Ni. Intermetallic phases, a result of the casting process, play an important role in the corrosion process. The role of these intermetallic phases has been addressed in a number of papers [1–3]. The role of aluminum in the atmospheric corrosion of magnesium alloys has less addressed in the literature [4]. Esmaily et al have shown recently that the rate of corrosion of magnesium alloys decreased when increasing the Al content. However these experiments were performed on commercial magnesium alloys produced high pressure die casting under constant RH exposure at 90% RH.In our work the corrosion behavior of binary Mg-Al alloys as well as that of commercial magnesium alloys with different aluminum contents have studied both under cyclic corrosion exposure in the laboratory and in field exposures in France and in Vietnam. Analyses of corrosion products have also been conducted. Additional in-situ measurements have been performed in order to better understand the atmospheric corrosion mechanisms of Mg alloys.An important decrease in the maximum pit depth can be observed after different laboratory exposures when increasing the aluminum content in the material. Similar results have been obtained after 9 months exposure in Field. Hence, from these results it is obvious that an increase of the aluminum concentration in Mg-Al alloys decreased the corrosion rate of the alloy. This lead in lower mass loss and less deep corrosion attacks in the magnesium grains. The analyses of corrosion products formed after the cyclic corrosion tests and field exposures revealed the presence of Magnesium carbonate and MgCO3(OH)4,4H20, respectively. In both cases magnesium hydroxide (Mg(OH)2 was also found in the corrosion products. The results will be discussed in relation with the microstructure of the cast materials. O. Lunder, J.E. Lein, S.M. Hesjevik, T.K. Aune, K. Nisancioglu, Werkstoffe und Korrosion 45 (6) (1994) 331–340. O. Lunder, J.H. Nordlien, K. Nisangliou, Corrosion Reviews 15 (3–4) (1997) 439–469.G. Song, A. Atrens, M. Dargusch, Corrosion Science 41 (1999) 249–273.M. Esmailly, D.B. Blucher, J.E. Svensson, M. Halvarson and LG Johansson, Scripta Materiala, 115 (2016), 91-96

In-Situ Raman Analysis of Precipitates Formed By Cathodic Polarization for Study of Atmospheric Corrosion in Marine Relevant Environments

Dry storage of spent nuclear fuel (SNF) in the United States exists across the country at independent fuel storage installations sites. At these sites the SNF is stored in stainless steel (SS) canisters equipped with a concrete overpack, where airflow through inlet and outlet vents allow for the passive cooling of the payload. While SS canisters are known for their enhanced corrosion resistance, when placed in a marine and near-marine environment they have shown to be suspectable to localized corrosion. In these environments, sea salt aerosols can adhere to the SS surface and, under certain temperature and relative humidity ranges, deliquescence can occur to form chloride rich brines. Under such exposure conditions, SS is known to undergo passive breakdown and pitting corrosion; thus, can be susceptible to subsequent stress corrosion cracking in the presence of residual stresses.In this study, we explore the relationship between the cathodic polarization and the surface brine present on 304-SS. Corrosion and pitting are a function of both the anodic current demand and the available cathodic current both of which have been shown to be dependent on the environmental exposure conditions. In concentrated salt solutions, certain bulk cations (Mg2+) have a strong thermodynamic driving force to form stable precipitates, such as hydroxides, driven by an increase in pH at the cathode from corrosion reactions, which can block cathodic reduction sites. Using in-situ Raman measurements during a cathodic polarization scan we attempted to identify under which conditions (e.g., potential, pH) precipitates form and what their overall composition is. In MgCl2 rich brines, we observed that the pH of precipitation and the identity of the precipitate were dependent upon the initial MgCl2 concentration, as predicted by thermodynamic modeling. The implications of these measurements demonstrate that the maximum pit size in MgCl2 brine surface environments may be limited as the cathodic reduction sites are blocked by precipitation, perhaps leading to the starvation of the pit and eventual brine dry out.Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Figure 1. In-situ Raman of SS in 0.189 M MgCl2 brine showing the formation of microcrystalline brucite. Figure 1

Statistical analysis of AA-1050 localized corrosion in anhydrous ethanol

Temperature-induced localized chemical corrosion of AA-1050 in anhydrous ethanol is examined experimentally at 105 °C and 110 °C and the generated data is analyzed based on statistical methods. Initiation times are described by a Weibull distribution whereas pit maxima are proven to be drawn from Gumbel parent distribution which is confirmed by modified Anderson-Darling test. Expected values and Gumbel parameters are correlated to reaction times in order to predict maximum pit sizes. Moreover, alcoholate corrosion reaction mechanism is postulated based on published literature and our observations. The statistical methodology can presumably be applied to other fuel-material combinations.

Pitting Morphologies and Characteristics of Low-Alloy Steel With and Without Plastic Deformation in Industrial and Non-industrial Marine Splash Zones

Pitting morphologies of E690 low-alloy steel in industrial and non-industrial marine splash zones are statistically analyzed, including the influence of plastic deformation. Results show that in a marine splash zone, E690 low-alloy steel experiences severe uniform corrosion and pitting corrosion, and the corrosion is more severe in the high-temperature non-industrial environment. The relationship between the pitting area changes and the depth can be well fitted to the Boltzmann cumulative distribution function to investigate the corrosion factors. In non-industrial marine splash zone, high content of chloride ions makes the metal surface have a high roughness and anodic dissolution is then promoted. The pitting depth is strongly promoted by anodic dissolution. In the marine splash zone, plastic deformation aggravates the maximum pitting depth, especially in the initial stage and in SO2-pollutant environments, although this effect gradually decreases. Pitting on low plastic deformation area in U bend samples may influenced by receiving electrons, which inhibits the protective FeOOH generation.

Nonlinear trending of corrosion of high nickel alloys in extended marine and atmospheric exposures

AbstractThe relatively limited data for the corrosion and pitting of high nickel alloys are reviewed herein and time-dependent trends developed for exposures in marine and atmospheric environments. Data sets for average or ‘uniform’ corrosion losses that are sufficiently extensive show topological consistency with the bimodal functional model previously observed for steels and various copper-nickel and aluminum alloys. Trends for localized corrosion (pit or crevice depth) plateau after earlier rapid growth over several years. The present observations add support to the concept that there is a change in corrosion behavior with extended temporal exposure and that this is generally consistent for many alloys. They also reinforce that shorter-term observations of maximum corrosion or pit depth usually is unsuited for extrapolation to, and prediction of, longer-term corrosion as typically important for practical infrastructure applications.

New insights from probabilistic modelling of corrosion in structural reliability analysis

Infrastructure intended to contain or exclude fluids or gasses, or reinforced with glass or other fibres may be subject to failure caused by pitting corrosion of the containment system or of the reinforcement. To assess the reliability of the infrastructure then requires probabilistic models for the deterioration processes involved. Typically the critical deterioration is through localized pitting and in particular the most extreme pit depth as this governs containment capability and also fibre strength. The ‘arch-typical’ distribution for representing maximum pit depth is the Gumbel extreme value distribution, for which complying data plot linearly on a so-called Gumbel plot. However, there is increasing evidence that large, homogeneous datasets show significant deviations from linearity. This is demonstrated for steel plates continuously immersed in seawater, for the interior corrosion of water injection pipelines and for crude oil production pipelines. Further examples are given for the maximum pit depth on stainless steel rollers in the papermaking industry and for localized corrosion of glass fibre reinforcement in concrete structures. In each case the non-linear trends obtained permit a re-interpretation of, and new insights for, the underlying physico-chemical-material mechanisms. The results are important for accurate representation of deterioration processes and for best-practice structural reliability analyses.

Synergistic effect of chloride ion and Shewanella algae accelerates the corrosion of Ti-6Al-4V alloy

The increasing utilization of titanium alloys in marine environments makes their microbiologically influenced corrosion study a timely matter. This work demonstrated that the corrosion of Ti-6Al-4 V alloy was accelerated by a marine bacterium Shewanella algae in 2216E medium with different Cl− level. Various electrochemical, pitting morphology and passive film analyses demonstrated that S. algae weakened the passive film, which made Cl− more aggressive. The synergy of those two factors caused considerable corrosion acceleration of the titanium alloy, leading to a maximum pit depth of 3.2 μm and corrosion current density of 26.5 nA cm−2 in 2216E medium with 3.50 % (w/w) Cl−.

Two years pitting corrosion of AA5005-H34 aluminium alloy immersed in natural seawater: data interpretation

ABSTRACT This paper reports pitting corrosion loss data of AA5005-H34 aluminium alloy immersed in natural seawater for up to 2 years. It is shown that the data for mass loss, maximum pit depth and the average value of 15 deepest pits as a function of exposure time are not closely consistent with the classical power-law function. Instead, the data show a greater affinity to the early part of a bi-modal trend. The uncertainty of the pit depth data was analysed using extreme value theory. The results are that scatter in the data sets increases with exposure time. This is considered to be the result of the pit depth data population being non-homogeneous, characterised by a mixture of deep pits with differing pitting morphologies. The results of this study suggest that longer-term data and homogeneous data population are likely to be more reliable for future corrosion loss prediction purposes.

Corrosion Behavior of 316L Stainless Steels Exposed to Salt Lake Atmosphere of Western China for 8 years

The evolution of corrosion behavior of 316L stainless steels exposed to salt lake atmosphere for 8 years was investigated. The results showed that the stainless steel in salt lake atmosphere had a greater corrosion rate during the initial exposure time and relatively lower corrosion rate during the subsequent exposure time. Dust depositions accumulated on the downward surface caused severe local corrosion of stainless steel. As exposure time prolonged, the relative amount of Croxide and Feoxide in the corrosion products gradually increased, which may directly affect the corrosion rate of stainless steels. Moreover, the maximum pit depth followed a power function with respect to exposure time.