Presence Of Crevices Research Articles

Hydromorphologically-driven variability of thermal and oxygen conditions at the block ramp hydraulic structure: The Porębianka River, Polish Carpathians

Growing anthropopressure in mountain streams aimed at limiting erosion and flood protection often caused adverse effects on the natural environment. In recent years, great attention has been paid to the restoration and conservation of natural habitats in mountain streams using environmentally friendly solutions such as the Block Ramp (BR) Hydraulic Structures. In this study we investigated the factors responsible for spatial variability in thermal and oxygen conditions at the single BR structure in the growing season, and the relation between water temperature and dissolved oxygen (DO) concentration. This has been done by measurements of hydraulic characteristics along with physicochemical properties of water, such as water temperature and DO concentration, at two different discharges. The redundancy analysis has been applied in order to describe the relationships among hydraulic parameters and physicochemical variables, and extract potential sources of water temperature and DO variability within the BR hydraulic structure. Results have shown that DO and water temperature distributions within the BR hydraulic structure depend on discharge conditions and are associated with the submergence of the block ramp. The highest heterogeneity in hydraulic, DO and water temperature conditions occurs at low flow and is associated with the presence of crevices between protruding cobbles at the block ramp. The lowest variability, in turn, occurs at high discharge, when the block ramp is completely submerged. The results indicated that thermal and oxygen conditions within the BR hydraulic structure are independent of hydraulic parameters at low flow. Moreover, the relation between DO concentration and water temperature is positive at low flow indicating potential impact of biological processes. On the contrary, at high discharge both, the DO concentrations and water temperature within the BR structure, depend on bed shear velocity and maximum Reynolds number.

Localized Corrosion of UNS A95052 Aluminum Alloy for Application in Multi-Effect Desalinator Plants

Aluminum alloy UNS A95052 (AA5052) is very attractive for desalination applications because of its good corrosion resistance in seawater at temperatures up to 125°C, low cost, good thermal conductivity, and non-toxicity of its corrosion products. The pitting corrosion potential, Epit, and the pit repassivation potential, Er,pit, of AA5052 were measured in deaerated 65,000 ppm sodium chloride (NaCl) solutions at 30°C, 60°C, and 85°C. Epit decreased with temperature, in accord with literature results. Er,pit was a function of anodic charge passed during pit growth stage. A complete evaluation of suitability of this alloy from a corrosion perspective requires also studies of crevice corrosion at different temperatures, considering that multi-plate designs of desalinators have metal plates in contact with rubber gaskets and seals. Cyclic potentiodynamic polarization was used to estimate crevice repassivation potentials, Er,crev, at 30°C, 60°C, and 85°C, in specimens with an attached rubber O-ring as a crevice former. This crevice former simulated the partially occluded geometry expected in desalination plants. Stable crevice corrosion potentials, Ecrev, were similar to Epit, and, when polarized to a similar anodic charge density, Er,crev were similar to Er,pit. Based on this result, from a corrosion perspective, the presence of crevices in the desalination plant is not expected to present an additional risk during operation of the plant. Electrochemical tests were also performed in saturated AlCl3 solutions to explain the results using Galvele’s localized acidification model.

Predicting the risk of pitting corrosion initiation of stainless steels using a Markov chain model

A probabilistic approach based on Markov chains for the assessment of pitting and crevice corrosion initiation is proposed. A Markov chain is a stochastic process that undergoes transitions from one state to another through a finite number of possible states, until a so‐called “absorbing state” from which the system has no tendency to evolve is attained. The proposed model calculates the probability to have pitting or to maintain a stable passive condition involving a large number of operating parameters related to both metal and environment: steel chemical composition (namely, the PREN index), chlorides content ([Cl−]), chloride critical threshold ([Cl−]cr), temperature, pH, fluid velocity, electrochemical steel potential, E, presence of crevices. Model and algorithms are mainly based on corrosion data collected from literature. Although the proposed model needs experimental confirmation, the simulations here presented seem acceptable, considering the engineering application of stainless steels.

Gas Gangrene: Case Presentation and Literature Data

Although a disease with a particularly historical, war-related implication, gas gangrene still retains its importance in pathology through its highly severe prognosis and rapid death in the absence of immediate treatment. The most common occurrences of the infection in times of peace are traffic accidents and natural disasters, but this can also occur in a non-traumatic context, in carcinomas and digestive tract ulcers or diabetes. The most commonly cited etiological agent is Clostridium perfringens, but other anaerobic germs as well as various aero-anaerobic associations may be responsible for the appearance of gangrene. The accumulation of gas bubbles through the action of etiological agents, highlighted by the presence of crevices or radiological examinations, is the hallmark of this condition. In this paper, the authors present the case of a 26-year-old man who died as a result of the gas gangrene with a rapid evolution (60 hours), which occurred in the progress of a soil telluric wound in the right thigh despite doctors’ efforts. The authors emphasize the importance of suspicion of the possibility of the occurrence of gangrene in wounds contaminated with vegetal remains or soil, on the one hand because the pathognomonic sign appears at an advanced stage of the infection and on the other hand because the prophylactic, surgical and medicinal treatment together with the resuscitation measures may be life-saving when applied in a timely manner.

Effects of chloride and crevice on corrosion resistance of stainless steels buried in soil within Seoul Metropolitan

Field and laboratory tests were conducted to find the factors affecting corrosion of stainless steels in soil. During one-year exposure, corrosion occurred within a joint and on the surface of type 304 pipe with the joint, which was buried at the site with a high chloride concentration of about 3680 ppm; however, corrosion was not observed at any of the other sites independent of the stainless steel grade and the presence of joints. At some sites, a seasonal fluctuation of corrosion potential was observed in the soil though corrosion did not occur. This observation may be due to the activity of sulfate reducing bacteria because a decrease of corrosion potential with the inoculated bacteria did not cause corrosion of stainless steels. These results indicate that both the level of chloride and the presence of crevices are the main factors affecting corrosion of stainless steels in soil but that the activity of bacteria is not. From measurements of pitting potential, a guideline for stainless steel use in soil is drawn as follows: Corrosion of stainless steels in soil occurs when the pitting potential of stainless steel under crevices in synthetic ground water that contains the same chloride concentration as the soil is less than the saddle potential. Finally, the guideline for stainless steels applications was provided in this paper according to this criterion.

Habitat Preferences of the Philippine Tarsier (Tarsius syrichta L.) in Loboc, Bohol, Philippines

A study was conducted to describle the habitat preference of the Philippines tarsier in Loboc, Bohol. Description of habitat preference was based on species composition and density of the different layers of the stand, mean height, mean diameter and basal area including physical attributes such as aspect, slope and elevation. Three habitat variants of the Philippine tarsier were observed in Loboc, Bohol. The first variant was a relatively open thicket with many small-diameter trees and shrubs and dense undergrowths. The second variant was a thicket of tall grasses, many small diameter trees and dense undergrowths growing under a mahogany plantation. The third variant was a thicket of many small diamater trees and shrubs with less evident woody vines and dense undergrowths with limited exposure to direct sunlight and strong wind being situated along gullies. Preferred habitat of the Phlippine Tarsier are small diameter trees as roosting sites and dense undergrowth as a source of insects and small vertebrates which are preferred food of the animal. The presence of crevices, which are unique to the limestone environment, serve as "hiding places" to protect the animals from predators.

Localized Corrosion and Phase Transformation of Simulated Archaeological Iron

The corrosion behaviors of simulated archaeological iron in solution (0.06 mol·L −1 NaCl+0.03 mol·L −1 Na 2SO 4+0.01 mol·L −1 NaHCO 3) simulating soil water composition was investigated by potentialdynamic polarization, constant potential polarization, and simulated occluded cell (O.C.) galvanostatic tests. X-ray diffraction (XRD), energy dispersive spectrometry (EDS), and scanning electron microscope (SEM) were used to study the corrosion morphology and the evolution of corrosion product. The objective was to discover the transformation process of archaeological iron, and determine the distribution of chlorinated corrosion products. The results showed that the presence of crevice, cavities, and channels facilitates the localized corrosion under rusts; the autocatalytic effect increases the concentration of Fe 2+, Cl −, and SO 4 2−, and promotes local acidification within the crevices and cavities. Meanwhile, the phase transformation of corrosion products is concluded to proceed by means of two ways. One is that the ferrous ions are transformed into different kinds of FeOOH via the intermediate Fe(II)-Fe(III) hydroxyl-salt ( i. e. Green Rusts); the other is that the Fe 2+ ions are transformed into FeCl 2, FeCl 3, and orange powders akaganeite at the crevices and cavities.

Maintenance of chitons on seawalls using crevices on sandstone blocks as habitat in Sydney Harbour, Australia

Intertidal seawalls support different assemblages and fewer species than do natural habitats. One explanation for these patterns may be the lack of some microhabitats on seawalls. Preliminary observations suggested that some features of sandstone seawalls, such as the presence of crevices among blocks, may provide chitons with an important habitat. To test the hypothesis that numbers of the chiton, Sypharochiton pelliserpentis, would be greater in crevices than on exposed surfaces of seawalls, sampling was done on sandstone seawalls in Sydney Harbour. S. pelliserpentis were more abundant in crevices among blocks than on exposed surfaces. Experimental manipulations transplanting chitons to exposed surfaces showed that they were found in greater numbers in crevices where those were available than on exposed surfaces. Chitons transplanted to blocks where crevices had been filled tended to move to non-filled crevices on other blocks. The design of seawalls could easily be improved to offer a better habitat for survival and maintenance of species such as chitons by incorporating crevices and similar features. In an increasingly urbanized world, understanding how to improve the value as habitat of man-made structures will be essential for conserving biodiversity.

Ovipositional Stimuli of Angoumois Grain Moth (Lepidoptera: Gelechiidae), a Primary Pest of Stored Grains

Ovipositional preferences of Sitotroga cerealella (Olivier) were measured in the laboratory to characterize the stimuli eliciting oviposition in this widespread pest of stored grains. Substrates used for oviposition included grains presenting both physical and chemical stimuli as well as surrogates presenting only physical stimuli. Chemical factors associated with grains stimulated oviposition, but physical stimuli, primarily the presence of crevices, were of much greater importance. Moths reared for approximately 15 generations in the laboratory were less sensitive to grain factors than were moths more recently collected from the field. Experiments with surrogrates presenting a precisely defined range of crevice sizes confirmed that ovipositional response increased as crevice size narrowed. The results suggest that factors influencing habitat selection are probably very important in this insect because of indiscriminate oviposition on substrates that present appropriate physical stimuli but are entirely unsuitable for larval consumption.

Spatial and temporal variability in the distribution of algae and invertebrates on rocky shores in the northwest Mediterranean

This study examines the distribution of algae and invertebrates on rocky shores in the northwest Mediterranean. The main objectives were to: (1) examine the consistency of vertical patterns of distribution in space and time; and (2) determine the relative importance of vertical position on the shore with respect to other sources of spatial and temporal heterogeneity. These patterns were investigated by repeatedly sampling two shores (about 70 km apart) in four different areas (10's to 100's of m apart) at each of three different heights. These areas were sampled eight times between April 1995 and August 1996. At each time, the percentage cover of sessile organisms and the density of molluscan grazers were estimated in three replicate plots (50×10 cm) in each area. The patterns of distribution and abundance of mobile animals were also examined in relation to season and topography of the substratum. At each level on each shore, sampling was done inside crevices in two areas randomly chosen among the four available, and outside crevices in the remaining two areas. This sampling was repeated in summer and in winter, at two randomly chosen dates in each season. There were large spatial and temporal fluctuations in patterns of abundance and distribution. There were inconsistencies in temporal changes from one shore to the other and among areas within levels for several of the organisms considered. Differences from one level on the shore to another were usually large but, in most cases, were not consistent from shore to shore or from time to time. The magnitude of these spatial and temporal effects was at least as large as that due to vertical position on the shore. Season and topography of the substratum were related to differences in the distribution and abundance of molluscan grazers but, again, these effects were variable in space and time. The results were, however, consistent with the hypothesis that limpets may benefit from the presence of crevices in proximity to their upper limit of distribution. Overall, results indicate that the structure of these assemblages cannot be predicted reliably on the basis of vertical position on the shore alone.

The importance of crevices to the intertidal snail Littoraria articulata (Philippi) in a tropical mangrove forest

The intertidal gastropod, Littoraria articulata (Philippi), is common on the trunks of mangroves at Coorooman Creek, Central Queensland. Individuals of shell length less than 3 mm were only found in empty tests of the barnacle Hexaminius popeiana (Foster). Larger snails were exposed on the trunk or occasionally in crevices such as knot holes. The relationship between shell length and shell strength differed between barnacle dwelling and larger L. articulata: in both cases it was linear, but the rate of increase of strength with increasing length was significantly greater for barnacle dwelling snails than for exposed ones. In contrast, there was an exponential relationship between shell strength and length for the weaker shelled Littoraria filosa (Sowerby), which occurs higher on the tree and does not inhabit barnacles. The survival of L. articulata was affected by the presence of crevices: significantly fewer disappeared from posts with artificial crivices than from those which lacked them, and some snails testhered to posts appeared to have been eaten by fish. The importance of crevices is discussed in relation to predation pressure, growth and habitat selection by larval L. articulata.

Decapod crustacean communities from calcareous seaweed andPosidonia oceanica(rhizome stratum) in shallow waters

Abstract Quantitative decapod studies carried out on calcareous seaweeds and Posidonia oceanica beds (mainly rhizome stratum), from shallow coastal waters of Almería (S, SE Spain), revealed that these biotopes represent part of the habitat of the same decapod crustacean community. A gradual transition from the decapod community in Posidonia to those in calcareous concretions is shown. This transition appears to depend on the relative developments of, and the interrelations between, both biotopes, as well as on the influence of a number of extrinsic factors such as the presence of crevices, photophilic seaweeds and sedimentation. However, when these two biotopes are well developed and independent they could be recognized by their differing quantitative species compositions, that is by the high dominance of a small number of and different species.

La celda Avesta: Un método para evitar problemas de corrosión por resquicios en los ensayos electroquímicos de corrosión por picaduras

A very common problem, that occurs during the electrochemical pitting corrosion tests of CRAs (corrosion resistant alloys) as stainless steels, is the simultaneous occurrence of crevice corrosion that difficults the evaluation of the electrochemical behaviour in presence of pitting corrosion mechanism only. Crevice corrosion appears as a consequence of the formation of crevices during the mountage of the specimen in the electrochemical cell. Several forms have been developed to avoid the presence of crevice during the electrochemical pitting corrosion test, but without satisfactory results. In the present study a relatively new and innovative method to eliminate the risk of crevice corrosion in the electrochemical tests is evaluated the Avesta cell. Anodic polarization electrochemical tests were carried out in a high alloy stainless steel in 3 % NaCl solution. The experimental results obtained using the Avesta cell were more reliable, reproducible and representative of the electrochemical behaviour of the material that those obtained using other methods of samples preparation to avoid the crevice formation.

Electrochemistry of galvanic couples between carbon and common metallic biomaterials in the presence of crevices

In vitro experiments were conducted upon some common metallic biomaterials and carbons, both isolated or forming galvanic couples, in a cell specially designed for crevice corrosion studies. The alloys examined were AISI 316L stainless steel, Ti6Al4V and Co-Cr-Mo. The types of carbon were glassy carbon and carbon fibre-reinforced carbon. The surface modifications were evaluated by SEM, AES and ESCA-XPS analyses. AISI 316L stainless steel suffered localized corrosion in open-circuit experiments whilst the other materials remained unattacked. Galvanic currents between metal-carbon couples were measured by zero resistance ammetry. The carbon-metal area ratio was 1:1. The results showed that 316L stainless steel and the Co-Cr-Mo alloy were prone to accelerated corrosion, whilst the Ti6AI4V alloy remained unattacked. The galvanic corrosion currents were also predicted using mixed potential theory from polarization curves obtained for each material. The experimental and theoretical values showed good agreement for the stainless steel and Co-Cr-Mo alloy. Long-term immersion tests with the same couples showed that the only metal not to suffer degradation was the Ti6Al4V alloy.

Stress Corrosion Cracking of Inconel Alloys and Weldments in High-Temperature Water — the Effect of Sulfuric Acid Addition

Abstract The stress corrosion cracking (SCC) susceptibilities of Alloys 600 and 690, AISI 316 NG stainless steel (SS), ASTM A508 carbon steel, and a number of compatible weld metals have been evaluated at 288 C in pure water and in pure water containing sulfuric acid additions. The sulfuric acid was added to simulate the effects of a resin release from the demineralizer system of a boiling water reactor (BWR). A combination of creviced and noncreviced slow strain rate, constant load, and crack growth rate tests were used in the evaluation. The results indicated that all of the alloys tested in the uncreviced condition were immune to cracking in the pure water environment. The presence of crevices in the pure water environment produced a susceptibility to SCC in Alloy 600, in Inconel I-82 and I-182 weld metals, and ASTM A508 steel, but not in Alloy 690. Cracking was enhanced by the addition of 1 ppm H2SO4 in slow strain rate tests (SSRTs) and constant load tests, but crack growth rates were not enhanced. All of the alloys tested in the resin intrusion environment were susceptible to cracking, except for the high chromium weld metals R-135 and Inconel I-72.

Field and laboratory experiences of Sulfide stress corrosion of a duplex stainless steel

AbstractTargets of this work have been: testing of duplex stainless steel in field (into a geothermal well) and in laboratory NACE environment in presence of crevices and sharp defects; development of testing based on fracture mechanics and comparsion with traditional testing approach.The following types of specimens have been used: smooth specimens for tensile tests at constant load with artificial crevices, U‐bend specimens and 1/2″ WOL‐modified fracture mechanics specimens.The results are only in partial accordance with available literature data and suggest to be very careful in extending laboratory results to real conditions, where, for instance, crevices and sharp defects always exist.

Corrosion Testing of INCONEL Alloy 690 for PWR steam generators

INCONEL alloy 690, an austenitic, highchromium modification of INCONEL alloy 600, was developed to resist stresscorrosion cracking and general corrosion in hightemperature aqueous environments associated with nuclear steam generators. Tests in nitric acid and nitrichydrofluoric acid show that the high chromium content provides alloy 690 with very good resistance to highly oxidizing environments. Extensive laboratory testing has shown the alloy to be very resistant to cracking in water over a wide range of high temperatures and oxygen concentrations, in the presence of crevices and lead or chloride contamination. Alloy 690 releases a negligible amount of material when exposed to highvelocity water at elevated temperatures. In constantextensionrate tests, alloy 690 resists crack propagation in a deaerated 10 pct solution of sodium hydroxide better than alloy 600. Longtime tests also suggest greater resistance of alloy 690 to intergranular attack in deaerated caustic solutions. Additionally, alloy 690 offers the necessary resistance to the highly oxidizing environments and hightemperature oxidation of radioactive waste disposal involving nitrichydrofluoric acid dissolution and vitrification.

Electrical-Potential Requirements for Cathodic Protection of Steel in Simulated Concrete Environments

Abstract Experiments have been conducted to establish the conditions of potential, pH, and chloride ion concentration under which steel will corrode and can be protected against corrosion in simulated concrete environments, and to determine the hydrogen evolution potentials of rebars in these environmental conditions. The results have shown the following: (1) No corrosion occurs on AISI Grade 1036 steel exposed in the freely washed condition in saturated Ca(OH)2 solutions containing 0.02, 1.0, 3.0, or 5.0M NaCl. In the presence of crevices (caused by limestone aggregate), however, corrosion will occur at chloride ion contents greater than 0.02M. Under these latter conditions, complete cathodic protection can be achieved by application of an electrical potential of −770 mVCuSO4. (2) Data obtained on specimens exposed in the freely washed condition to a 5.36M Cl− solution at differing pH indicate that the basic potential/pH diagram for Fe/Fe2O3/Fe3O4/H2O is correct in predicting the susceptibility of rebars...

A Review of the Application of Stainless Steels in Desalination Equipment

The corrosion performance of various types of stainless steels is discussed for the variety of environments associated with distillation‐type sea‐water desalination plants. Several factors related to the design and operation of desalination equipment can have important bearing on the corrosion performance of the stainless steels. The most important of these are flow rate, presence of crevices, deposit formation, temperature, and oxygen content. The performance of present‐day steels has been evaluated by full‐scale plant tests and also by specimen‐exposure tests. For the future, electrochemical procedures will help to explain the corrosion behavior of stainless steels in high‐temperature water and offer a means for evaluating new steel compositions with improved corrosion resistance.

Anodic polarization as a possible rapid method of deciding whether a given solution is corrosive or inhibitive

AbstractAnodic polarization curves have been obtained with twelve systems of mixed corrosive and inhibitive ions and it has been found that when the results are compared with total immersion tests, the corrosive or inhibitive nature of the solutions could be estimated from the nature of the polarization curves, with only one exception (NaNO2 + NaCl).In several cases corrosion occurred in the immersion tests when the polarization curves indicated that the solution was just inhibitive, but the borderline between corrosion and passivity is not clear cut and there are reasons for believing that with solutions in the borderline region this method has a slight bias towards passivity.The probability of corrosion increases with the size of the specimen and is affected by shape, i.e. by the presence of crevices where the inhibitor may become exhausted.When modified this method may form the basis of an accelerated test.