Artificial Pit Research Articles

Metagenomics-based insights into the microbial community dynamics and flavor development potentiality of artificial and natural pit mud

Strong-flavor Baijiu (SFB) production has relied on pit mud (PM) as a starter culture. The maturation time of natural PM (NPM) is about 30 years, so artificial PM (APM) with a shorter maturation time has attracted widespread attention. This study reveals the microbial and functional dissimilarities of APM and NPM, and helps to elucidate the different metabolic roles of microbes during substrate degradation and flavor formation. Significant differences in the microbial community were observed between APM and NPM, manifesting as variations in the abundance of core microorganisms. Total of 187 high-quality metagenome-assembled genomes (MAGs) were obtained based on the metagenomic binning technology, mainly including Firmicutes (n = 106), Bacteroidota (n = 15) and Chloroflexota (n = 14). Furthermore, the relative concentration of flavor compounds in 4-year APM was similar to those in 30-year NPM, but different from those in 100-year NPMs. Methanosarcina, Methanobacterium, Methanoculleus, Anaerolineae bacterium and Aminobacterium were the key bacteria responsible for the flavor differences. From a functional perspective, amino acid and carbohydrate metabolism were key functions of PM microbial, and showed differences between APM and NPM. Finally, substrate degradation and flavor generation pathways were found to exist in multiple microorganisms. Combine the relative abundance of microorganisms with the absolute abundance of enzymes, Clostridium, Lactobacillus, Petrimonas, Methanoculleus, Prevotella, Methanobacterium, Methanosarcina, Methanothrix, Proteiniphilum, Bellilinea, Anaerolinea, Anaeromassilibacillus, Syntrophomonas and Brevefilum were identified as the key microorganisms in APM and NPM.

Influence of Artificial Pit on Corrosion Fatigue Behavior of 316LN SS and Its Weldment

AbstractThe effect of cyclic loading on smooth and pre-pitted type 316LN stainless steel and its weldment in acidified chloride environment is investigated in this study. The onset of fatigue cracks at the bottom of the pit is brought on by the maximum stress concentration effect in acidified chloride environment. Pre-pitted specimens exhibit a more pronounced fatigue life reduction compared to smooth specimens at lower stress amplitudes. The growth of a microscopic crack from an artificial pit, which is influenced by the combined effects of the pit electrolyte and stress concentration factor, is vital for maintaining structural integrity.

Neolithic burial of a dog on Olkhon Island (lake Baikal)

In 2022, archaeological activities were conducted to clarify the boundaries of the multilayer Unkhrug 1 site located on Olkhon Island (Lake Baikal). In the lowest layer of one of the test pits, a burial of an ancient dog in an artificial pit was found with the remains of a red deer. This find is very rare for the Neolithic of the Baikal region. A morphometric study of bone remains, a comparative analysis with other skeletal materials, and radiocarbon and isotope analyzes were conducted. The data obtained made it possible to establish the individual characteristics of the buried dog and its possible diet. An individual burial with a ritual meat part of a red deer carcass inside indicates the special significance of this individual for the Neolithic inhabitants of Olkhon Island.

Understanding the potentiodynamic critical pitting temperature

To better understand the potentiodynamic critical pitting temperature (CPT), the critical conditions of potential (E) and temperature (T) for repassivation of one-dimensional artificial pits at small depth (x) were investigated. Apart from repassivation resulting from excessive dilution of the pit solution, repassivation underneath the salt film was also observed. The critical conditions for repassivation in (E, T, x) space exhibit a complex functionality. The potentiodynamic-CPT should correspond to the lowest temperature of the critical (E, T) conditions for repassivation of metastable pits, and it represents a critical temperature below which salt precipitation at any potential leads to repassivation of metastable pits.

Optimizing Baijiu fermentation with high-yield ethyl caproate-producing Candida parapsilosis strain

Ethyl caproate is an important flavor substance of Baijiu. It is effective to increase the content of ethyl caproate to improve the quality of strong-flavor Baijiu. In this study, the high-yielding ethyl caproate Candida parapsilosis strain F-5 was isolated from pit mud. Under optimized fermentation conditions, F-5 achieved an ethyl caproate yield of 53.69 mg/L. A novel strategy was employed by adding caproic acid and F-5 directly to the fermented grain. The application of F-5 in the fermentation of Xiaoqu and strong-flavor Baijiu significantly increased the ethyl caproate content by 24.86% and 17.45%, respectively. Transcriptomic analysis showed that Lip2 and esterase genes in the lipase synthesis pathway, and Fas1, Fas2, Eht1, and Faa4 genes in the acyltransferase pathway were significantly upregulated. These findings suggest that strain F-5 has the potential to contribute to the development of artificial pit mud and improve the flavor quality of strong-flavor Baijiu.

Wear Failure Analysis of Ball Bearings with Artificial Pits for Gas Turbines

Wear Failure Analysis of Ball Bearings with Artificial Pits for Gas Turbines

Effect of structural heterogeneity on stable pit growth of Co-based metallic glasses

The artificial pit technique was employed to investigate the stable pit growth of Co68.15Fe4.35Si12.5B12Cr3 metallic glasses (MGs) exposed to 0.6 M NaCl solution. Critical parameters of pit growth stability were assessed to clarify the correlation between structural heterogeneity and stable pitting kinetics. Thermally induced degeneration of structural heterogeneity increases the repassivation potential and critical pit solution concentration required for pit survival, thus strongly inhibits the activation-controlled growth of salt-film-free pits. Nevertheless, the inhibitory effect on the diffusion-controlled growth of salt-film-covered pits is relatively weak, as revealed by the fact that the saturation concentration required for salt precipitation remains unaffected.

Oriented Bedrock Samples Drilled by the Perseverance Rover on Mars

AbstractA key objective of the Perseverance rover mission is to acquire samples of Martian rocks for future return to Earth. Eventual laboratory analyses of these samples would address key questions about the evolution of the Martian climate, interior, and habitability. Many such investigations would benefit greatly from samples of Martian bedrock that are oriented in absolute Martian geographic coordinates. However, the Mars 2020 mission was designed without a requirement for orienting the samples. Here we describe a methodology that we developed for orienting rover drill cores in the Martian geographic frame and its application to Perseverance's first 20 rock samples. To orient the cores, three angles were measured: the azimuth and hade of the core pointing vector (i.e., vector oriented along the core axis) and the core roll (i.e., the solid body angle of rotation around the pointing vector). We estimated the core pointing vector from the attitude of the rover's Coring Drill during drilling. To orient the core roll, we used oriented images of asymmetric markings on the bedrock surface acquired with the rover's Wide Angle Topographic Sensor for Operations and eNgineering (WATSON) camera. For most samples, these markings were in the form of natural features on the outcrop, while for four samples they were artificial ablation pits produced by the rover's SuperCam laser. These cores are the first geographically‐oriented (<2.7° 3σ total uncertainty) bedrock samples from another planetary body. This will enable a diversity of paleomagnetic, sedimentological, igneous, tectonic, and astrobiological studies on the returned samples.

Electron Acceptor Addition to Stimulate Anaerobic Methanotrophy in Oil Sands End Pit Lakes

A major question for the Alberta oilsands extraction industry is how to return tailings ponds to their original ecosystem functions at the end of their lifespan. This question is one of the most pressing in the oil industry, and while many potential solutions are being trialed, none are without issue. One solution is the creation of end pit lakes (EPLs), formed by filling a mine pit or tailings pond with fluid tailings and covering this with a freshwater cap. Over time, tailings settle to the bottom of the lake and become sequestered. As of 2018, there were 23 plans to pursue EPLs in Albertan oilsands mining operations (COSIA 2021), so research in oilsands reclamation via EPLs is essential. Alberta has only one full-scale EPL formed using tailings, Base Mine Lake (BML). It has been under reclamation since 2011. Although BML water quality is gradually improving over time, one persistent problem is the production of methane bubbles from the entrenched hydrocarbons. Ebullition of these bubbles carries contaminants into the water column. The potential to limit methane production biologically by stimulating methanotroph metabolism, is therefore of interest. Methanotrophs are microbes that consume methane. These methanotrophs can be aerobic, in the water column, or anaerobic below the sediment interface, where oxygen is depleted. Anaerobic oxidizers of methane, or AOM, are of particular interest due to methane only being produced in anaerobic conditions. However, AOM are not well-studied and there are many gaps in our knowledge about them. Base Mine Lake presents an important opportunity to document the presence of AOM in oilsands ecosystems, and identify if AOM can remove methane before it enters the water column. Methane is probably not the limiting factor for AOM in BML- instead, the electron acceptors used in the absence of oxygen are scarce. If microbiological methane removal were to increase after supplementing electron acceptors such as nitrate, sulfate, or iron, then this could be applied to the reclamation of artificial end pit lake systems. Our research aims to illustrate if AOM are present in BML, and if we can stimulate their metabolism via electron acceptor amendment. We performed amplicon and metagenomic sequencing across 5 sediment cores from BML. These cores penetrate over two meters below the water-sediment interface, up to 14 meters below the water’s surface. We designed anaerobic, 13C-isotope-spiked incubations for this sediment to track if any CH4 to CO2 conversion was underway. By tagging methane molecules with 13C, we are able to follow the biogeochemical transformations and demonstrate if any 13CH4 is converted to 13CO2, which would indicate methanotrophic activity. Additionally, microbes who take up 13C produce heavier DNA, possibly allowing us to identify the DNA of the players at work. Additionally, Illumina sequencing was done on all incubations to compare how electron acceptor addition prompted community shifts. In the incubation experiments, 13CO2 is being produced in several core samples incubated without O2. This finding indicates that methanotrophs are, in some capacity, active in anoxic conditions. When comparing different amendments of electron acceptors, there did appear to be a significant amount (p = 0.027) of 13CO2 produced in the sulfate-added 13CH4 treatment (Fig. 1). Other amendments had encouraging results, but were not statistically significant. Ongoing trials will provide more illuminating results via larger sample sizes, which will be completed by the end of the summer. Next we will characterize communities in the post-incubation sediment, using both amplicon sequencing and DNA stable isotope probing. This will suggest not only the identity of the organisms at play, but will also illuminate which electron acceptors were most beneficial to which groups. This analysis is complex and underway. Overall, the study of methanotrophy in artificial ecosystems with high emissions is an area of great interest, due to the high potential for amendment and improvement of the ecosystems using methanotrophs, as well as the ongoing discovery on AOM in artificial ecosystems. Oilsands end pit lakes are of interest, as an issue of cultural and political emphasis.

Succession of microbial community of the pit mud under the impact of Daqu of Nongxiang Baijiu

Complex microbiomes of pit mud play significant roles in imbuing flavors and qualities of Nongxiang Baijiu during fermentation. However, pit mud microbial enrichment and succession is a long process that is also accompanied by aging. Development of high-quality artificial pit mud becomes an urgent problem. In this study, a new medium based on space (TK) Daqu was used to effectively enrich the dominant microorganisms in pit mud. The results showed that Caproiciproducens was the most preponderance in the cultures unadded Daqu, whereas Clostridium sensu stricto 12 was the most preponderance, followed by Caproiciproducens in the enrichment cultures added TK Daqu. It is worth noting that TK Daqu balanced the relative abundance of Caproiciproducens and Clostridium sensu stricto 12 in 100-year PM culture (S100), which was more conducive to the increase of methanogens. PICRUSt2 prediction results showed that hydrogenotrophic methanogens could promote the synthesis of caproic acid by using the product H2 as the metabolic substrate and increased significantly in the pit mud enrichment cultures with TK Daqu. The increase of lactate dehydrogenase (EC 1.1.1.27) content in S100 contributed to the degradation of lactic acid and the increase of caproic acid. Adding TK Daqu enrichment cultures is more conducive to the enrichment and metabolic balance of pit mud microorganisms.

Influence of Excavation Pits on the Wave Hydrodynamics of Fringing Reefs under Regular Waves

Dredging materials from reef flats have become an important source of sand and aggregates for meeting the infrastructure needs of coral-lined shores in subtropical and tropical regions, especially for low-lying atoll islands. Dredging at the reef flats can generate artificial excavation pits, which not only have profound influences on coral ecological stability but also deeply affect the hydrodynamic characteristics of coral reefs. To deepen the understanding of the influence of excavation on the wave hydrodynamics of fringing reefs, the wave propagation, wave transformation, wave setup, and wave runup processes of regular waves on fringing reefs with artificial pits have been systematically analyzed using a non-hydrostatic numerical wave solver (NHWAVE). The effects of some significant factors have been carefully investigated. According to the study findings, the existence of artificial pits can result in a slight decrease in the wave height around the artificial pit. The time-mean maximum of wave runup height at the backreef slope can be reduced to some extent when the artificial pit is present. When placed close to the reef edge, the artificial pit can have noticeable effects on the hydrodynamic characteristics of fringing reefs, particularly the wave setup along the reef flat. It is hoped that the study findings can provide further reference for evaluation of the influences of artificial pits on the wave hydrodynamics of fringing reefs.

Genome Analysis and Optimization of Caproic Acid Production of Clostridium butyricum GD1-1 Isolated from the Pit Mud of Nongxiangxing Baijiu.

Caproic acid is a precursor substance for the synthesis of ethyl caproate, the main flavor substance of nongxiangxing baijiu liquor. In this study, Clostridium butyricum GD1-1, a strain with high caproic acid concentration (3.86 g/l), was isolated from the storage pit mud of nongxiangxing baijiu for sequencing and analysis. The strain's genome was 3,840,048 bp in length with 4,050 open reading frames. In addition, virulence factor annotation analysis showed C. butyricum GD1-1 to be safe at the genetic level. However, the annotation results using the Kyoto Encyclopedia of Genes and Genomes Automatic Annotation Server predicted a deficiency in the strain's synthesis of alanine, methionine, and biotin. These results were confirmed by essential nutrient factor validation experiments. Furthermore, the optimized medium conditions for caproic acid concentration by strain GD1-1 were (g/l): glucose 30, NaCl 5, yeast extract 10, peptone 10, beef paste 10, sodium acetate 11, L-cysteine 0.6, biotin 0.004, starch 2, and 2.0% ethanol. The optimized fermentation conditions for caproic acid production by C. butyricum GD1-1 on a single-factor basis were: 5% inoculum volume, 35°C, pH 7, and 90% loading volume. Under optimal conditions, the caproic acid concentration of strain GD1-1 reached 5.42 g/l, which was 1.40 times higher than the initial concentration. C. butyricum GD1-1 could be further used in caproic acid production, NXXB pit mud strengthening and maintenance, and artificial pit mud preparation.

Numerical investigation of effects of artificial excavation pit on transformation and runup processes of tsunami-like wave over fringing reef

In recent years, excavating materials from the reef flat gradually becomes the main source of sand and aggregate for the coral-lined coasts in tropical and subtropical regions, especially the low-laying atoll islands. These artificial excavation pits are bound to have significant impacts on the wave hydrodynamics over the fringing reefs. However, effects of the excavation pit on the hydrodynamic characteristics of tsunami-like wave over the fringing reef are few studied. To fill the knowledge gap of previous research, effects of artificial excavation pit on the transformation and runup processes of tsunami-like wave over the fringing reef have been systematically investigated in this study based on a high-resolution two-phase flow model. Effects of several main factors are carefully discussed. Research results indicate that the presence of excavation pit can have noticeable influences on the wave transformation and runup processes of tsunami-like wave over the fringing reef. Complex interactions between the breaking surge bore and the water body in the excavation pit can be observed. The complicated flow field in the pit can dissipate more wave energy and result in a lower maximum wave runup height. However, the local wave height near the pit in most situations can be amplified. It is hoped that the research findings can broaden the understandings on the wave hydrodynamics over the fringing reef with the artificial excavation pit.

Dependence of Pit Growth Rate on Applied Potential and Chloride Concentration under Conditions with and without Fluid Flow

Pitting corrosion on stainless steel is one of the most serious problems caused by seawater intrusion into power plants because it possibly perforates boundary structures, such as piping or containers, and leads to solution leakage. Although the evaluation of the pit growth rate in accordance with the corrosion condition is required to secure the plant’s safety, the dependence of the pit growth rate on various corrosion conditions is not fully understood. In this study, the effects of applied potential and chloride concentration on the pit growth rate on Type 304L stainless steel were assessed with and without fluid flow by performing the pit penetration test with in situ observations of pit initiation and penetration. An artificial one-dimensional pit experiment was performed to obtain a fundamental understanding of pit growth with and without fluid flow. In addition, three-dimensional pit growth behavior was further analyzed by measuring a dissolution current of a single three-dimensional pit. In the pit penetration test, the effects of applied potential and chloride concentration on the pit growth rate differed depending on the fluid flow condition; the pit growth rate is almost independent of the applied potential and chloride concentration without fluid flow, whereas the growth rate was decreased by decreasing the potential and chloride concentration with fluid flow. For the results of the artificial one-dimensional pit experiment, regardless of the fluid flow condition, stable pit growth in the depth direction was suggested to be diffusion-controlled. Measuring the time variation of the dissolution current of a single three-dimensional pit indicated that the three-dimensional pit growth involves temporary passivation and reactivation, which depend on the fluid flow condition and applied potential. This suggested pit growth in the pit penetration test proceeded discontinuously depending on the corrosion conditions, resulting in a dependence of the pit growth rate on the corrosion conditions.

Assessing the influence of calcium on X65 carbon steel pitting using an artificial pit

AbstractCorrosion products that form on carbon steel in sweet (CO2) environments can protect the steel by retarding interactions between the substrate steel and a corrosive electrolyte. Such protective films could become damaged at local sites leading to potential differences and the emergence of galvanic currents with the consequence of pitting in certain envfironments. The large protected surface (with a higher positive potential) becomes a cathode while the tiny exposed surface (with a lower positive potential) becomes the anode. Films formed in a Ca2+‐rich environment often comprise mixed calcium and iron carbonates in the form, CaxFe(1−x)CO3. This work utilized an artificial pit to investigate pitting under CaxFe(1−x)CO3 film conditions. Mixed carbonate films were grown on cathode discs (25‐mm diameter) for 96 h at pH 7.5, 50°C. Freshly polished anode pins were screwed onto the cathode disc and the galvanic currents were measured for 24 h. The anode/cathode area ratios were varied by using pins of 1, 2, and 3 mm diameter. Scanning electron microscope, X‐ray powder diffraction, and energy‐dispersive X‐ray were employed to examine the electrode surfaces after the test while surface profilometry was conducted to obtain pit profiles on the anode pins. Galvanic current increased with the addition of 682 ppm Ca2+ to the solution while pseudopassivation occurred under mixed calcium–iron carbonate films. The galvanic current was observed to drop as corrosion products formed on the anode electrode. Profilometry revealed the emergence of pits on the anode electrode. The pitting threshold was commensurate with the magnitude of the galvanic current density recorded.

Quantitative evaluation of surface cleanliness of weathering steel treated by continuous wave laser

A 3 kW continuous-wave (CW) laser was used for the laser cleaning of weathering steel with artificial corrosion pits. Specimens with different degrees of corrosion were obtained by NaCl deposition in artificial pits of 10 mg/m2, 100 mg/m2 and 1000 mg/m2 through constant dew point dry and wet cycles for one year. To develop quantitative evaluation methods that can be applied on-site, the cleanliness of the laser-cleaned surface was evaluated through visual observation, turning time, and photographic analysis. The results reveal that the photometric analysis based on the CIE L*a*b* color space can be used to evaluate the surface cleanliness of surfaces treated with a CW laser, which is consistent with the results of the turning time test. The color difference of the surface before and after the laser treatment can be used as a quantitative index to evaluate cleanliness. The proposed laser surface treatment procedures can provide a reference for cleaning corroded weathering steel structures and achieve cleanliness of more than 80 % and a longer turning time.

Fungal Diversity Profiles in Pit Mud Samples from Chinese Strong-Flavour Liquor Pit.

Pit mud, a specific fermented soil, is an essential material for the fermentation of Chinese strong-flavour liquor. However, few studies to date have sought to characterize the spatial profiles of pit mud fungal communities in fermentation cellars from Chinese strong-flavour liquor distilleries. In this analysis, differences in fungal community structures and physicochemical properties in pit mud samples from different spatial positions within fermentation cellars were analyzed, revealing unique characteristic multidimensional pit mud fungal community profiles. Penicillium roqueforti, Pichia kudriavzevii, Aotearoamyces nothofagi, Penicillium robsamsonii, Alternaria arborescens, Trichosporon insectorum, Seltsamia ulmi, Trichosporon coremiiforme, Malassezia restricta were dominant in the pit mud samples form the upper cellar wall, whereas Metarhizium frigidum, Calonectria pseudoreteaudii, Penicillium clavigerum, Fusarium equiseti, Simplicillium chinense, Aspergillus intermedius, Trichosporon coremiiforme, Fusarium circinatum, Alternaria radicina, Aspergillus heterocaryoticus were predominant in the middle cellar wall. Alternaria radicina, Cladosporium chasmanthicola, Alternaria helianthiinficiens, Penicillium argentinense, Antarctomyces psychrotrophicus, and Trichosporon inkin are majorly present in the down cellar wall layer. Bipolaris axonopicola, Ramgea ozimecii, Penicillium argentinense, Calonectria queenslandica, Metarhizium robertsii, and Penicillium roqueforti were identified as the dominant fungi in pit mud samples from the cellar bottom. Additionally, Alternaria destruens and Alternaria doliconidium are present at notably high levels in all layers of pit mud samples. Moisture, pH, PO43-, acetic acid, humus, K+, Mg2+, Ca2+, butyric acid, and caproic acid levels in these different pit mud positions exhibited a rising incremental pattern from the upper wall layer to the bottom layer, whereas lactic acid levels were significantly lower in the bottom pit mud layer relative to these other layers. Moisture, pH, and NH4+-N were identified as the three most significant factors associated with fungal community composition through a redundancy analysis. Overall, these findings may offer a theoretical foundation for future efforts to improve or standardize artificial pit mud.

A comparison study of crevice corrosion on typical stainless steels under biofouling and artificial configurations

In this work, the crevice corrosion behavior and biofouling coverage of 316L stainless steel (316L SS), 2205 duplex stainless steel (2205 DSS), and 2507 super duplex stainless steel (2507 SDSS) in natural seawater were investigated through long-term field exposure tests. The results revealed that both artificial crevice corrosion and biofouling-induced crevice corrosion occurred on the surface of three stainless steels. The corrosion rate was ranked as 316L SS » 2205 DSS＞2507 SDSS. The deepest area of the artificial corrosion pit was at the edge of the crevice, which was related to the IR drop and acidification of the localized solution. The highest biofouling coverage and the most severe biofouling-induced corrosion occurred on the surface of 316L SS. The attachment of large organisms to the metal surface formed a fouling barrier layer, further blocking the flow of material over the crevices, and the artificial crevice corrosion was accelerated. The initiation of barnacle-induced corrosion was due to the formation of a crevice between the barnacle and the substrate, resulting in the entry of seawater. The acidification of the solution caused by catalytic-occluded cells was responsible for the continuous development of barnacle-induced corrosion, which was similar to the propagation of the artificial crevice corrosion.

Critical Crevice Temperature – an Electrolyte Modeling Perspective

Critical pitting and crevice temperatures have been measured for many alloys using open-circuit potential tests in standard electrolytes, such as the 10 % FeCl3 or mixtures of NaCl with FeCl3 and CuCl2 for many years. Although these measurements are primarily used for alloy ranking purposes, there is interest in using them for applications with different solution chemistries. On the other hand, critical pitting temperature has been modeled in terms of the threshold condition for the formation of metal-chloride salt film or the maintenance of a critical metal-chloride concentration in the pit environment, using artificial pit electrodes and relatively simple solutions, such as NaCl. This paper addresses a modeling approach to bridge the gap between the immersion tests, electrochemical measurements, and theory. An irreversible thermodynamics model is combined with concentrated electrolyte speciation model to predict the critical crevice temperature of several Ni-Fe-Cr-Mo-W alloys. The model computes the repassivation and corrosion potentials of alloys as functions of solution composition and temperature. The superposition of these parameters provide a conservative estimate of the critical crevice corrosion temperature. The predicted values are validated against critical crevice temperature data reported in the literature. The effect of aqueous electrolyte composition on critical crevice temperature is calculated and compared to field experience. The model is further extended to mixed solvent systems, where the solvent is a non-aqueous environment. The implications of the model are discussed.

Effect of Melt Pool Boundaries on Repassivation of Selective Laser Melted Stainless Steel

Recent studies have shown that melt pool boundaries (MPBs) in selective laser melted (SLM) stainless steels (SS) can serve as preferential sites for pit initiation and corrosion propagation. In this study, we utilize electrochemical polarization experiments combined with detailed microstructural analysis to elucidate the role played by MPBs on localized corrosion in chloride media. Potentiodynamic polarization of artificial 1-D pits constructed from SLM SS316L grown to sufficient depth showed a sudden current drop below the salt-film dissolution potential on the downward scan, which was followed by an active Tafel-like behavior until the zero-current potential (ZCP) was reached. The observed current drop marks a critical potential for pit stability and characterizes the partial repassivation of the pit, as the current density value after the drop was significantly greater than the reported current density at complete repassivation. When the same 1-D pit was polarized upwards from a potential below the ZCP, it showed characteristic re-activation before salt film formation. This behavior was unique to SLM SS316L and was not found in conventional wrought SS316L. Moreover, 1-D artificial pit study on SLM SS316L using a modified ASTM G192 sequence showed a similar partial repassivation behavior. Scanning electron microscopy of SLM SS316L pit bottom morphology after long-term potentiostatic polarization at a potential between the partial repassivation potential and the ZCP showed selective, crystallographic attack along MPBs. The morphology also revealed melt pool fall-out due to the continued attack of the MPBs. Scanning transmission electron microscopy characterization of the SLM 316L material revealed Cr and Mo depletion at the MPBs. The observation of passivating element depletion at MPBs is in line with calculations of solute partitioning during melt pool solidification for the material under study. Based on our results, we conclude that localized corrosion under conditions at the edge of passivity can lead to selective attack of Cr- and Mo-depleted MPBs. The implications of inter-melt-pool corrosion on component structural integrity and protective repassivation potentials will be discussed. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2022-4016 A