The presented results indicate the formation of thick oxide scales consisting Fe 2 O 3 (hematite), Fe 3 O 4, (magnetite), and FeO (wustite). These alloys are based on and have a microstructure similar to T/P22. Last modified: 2017/03/23 by dmitri_kopeliovich, http://corrosion.kaist.ac.kr/download/2007-MS354/chap11.pdf, http://koinsnet.org/tt/site/db/board/tech/upload/1_10000/224/Fundamentals_of_Corrosion.pdf, http://www.risoe.dk/rispubl/reports/ris-phd-2.pdf, Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. This chapter is dedicated to the description of high temperature oxidation of both chromia and alumina forming alloys. protective oxide layer [1, 4, 5] or internal precipitates [14] that make the steel resistant to the high temperature oxidation. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. d. Composition of the surrounding medium. Oxidation of iron at temperatures above 700°C follows the parabolic law with the development of a three-layered hematite/magnetite/wüstite scale structure. This is Grube solution in which Co is the initial concentration of the carbon when t = 0, and ‘erf refers to ‘error function’. Applications: Fasteners, bolts, springs, nuclear engineering and gas turbines. Martensitic Steels . However, at temperatures below 700°C, inconsistent results have been reported, and the scale structures are less regular, … Report a Violation 11. Due to oxidation, first an oxide film and then, a thicker scale forms on the surface of the steel. Content Guidelines 2. The presence of element, like chromium in steel decreases the tendency of both the processes particularly of decarburisation, as it reduces the diffusion of carbon. High-temperature corrosion is a mechanism of corrosion that takes place in gas turbines, diesel engines, furnaces or other machinery coming in contact with hot gas containing certain contaminants. Their high-temperature oxidation behavior is interesting to evaluate their applicability at SOFCs operating conditions and to design degradation tests and models predicting the lifetime of a SOFC stack. The oxidation of steel at high temperature is a very com-mon phenomenon.14) The kinetics of oxidation and the sta-bility of the oxidation products are strongly dependent on the type of oxide forming element and consequently of the steel composition. As a result, two undesirable surface phenomena of special importance occur: These two processes are diffusion based phenomena and thus, the extent of both oxidation and decarburisation depends on: c.  Composition of the steel being heated. A typical environment of hot air at 873K was preferred for acceleration tests of oxide film growth. When the temperature of the steel in below A1 (≈ 727°C) temperature, when the steel has carbon present mainly as cementite (Fe3 C): II. Cross‐sectional image of T22 steel exposed in water steam at temperature: (A) 600°C, (B) 650°C, (C) 675°C, and (D) 700°C for 500 h (unpublished work, part of the project). The performance of Alloy 316 is generally somewhat inferior to that of Alloy 304 stainless steel tube which has slightly higher chromium content (18% vs. 16% for Alloy 316). Their strengths are raised … Chromium also improves oxidation resistance at higher temperatures. 316 1.4401 316L 1.4404 Oxidation Resistance. Industrial Practice for Power Generation – Steam Plants . This happens at low temperatures of heating (≈ 650 °C). The furnace atmosphere at a heat treating temperature, adjusts as per equation (2.6), i.e., K1 being constant at a temperature, a change in one component causes changes in other components. The Alloys 316 and 317L exhibit excellent resistance to oxidation and a low rate of scaling in air atmospheres at temperature up to 1600 to 1650°F (871 to 899°C). Most metals present in alloys used at high temperature form solid oxides, carbides or nitrides, but sulphides have lower melting points than the corresponding oxides, and liquid formation must sometimes be considered. This 2006 second edition retains the fundamental theory but incorporates advances made in understanding degradation phenomena. Reaction of a pure metal with a single oxidant (oxygen, carbon, nitrogen, sulphur or a halogen) is considered. High-Temperature Oxidation Behavior of 2 1 4 Cr-1Mo Steel in Air–Part 2: Scale Growth, Metal Loss Kinetics, and Stress Enhancement Factors During Creep Testing Levi O. Bueno, Levi O. Bueno Departmento de Engenharia de Materials, Universidade Federal de Sao Carlos, 13565-905 Sao Carlos (SP), Brazil. Plagiarism Prevention 5. Generally both these surface phenomena, oxidation and decarburisation take place simultaneously. Materials and Methods . The authors have endeavored to familiarize the readers with the high temperature oxidation protection of various components made of low carbon steels, low alloy steels and high alloy steels by using oxidation resistant coatings. Metals being in the metastable state are bound to form oxides. Fick’s Second Law for Calculating Decarburised Thickness: Fick’s Second law also called diffusion transport equation, deals with the transient-state diffusion. As these reactions are reversible in nature, the equilibrium relationship between iron and iron oxide in contact with CO and CO2, or H2 and water vapor at the heat treatment temperature control the extent of oxidation (apart from the composition of steel, temperature and time). The hardness increases continuously in decarburised zone till the point where it just becomes equal to the hardness of the un-decarburised core. The rate of oxidation of a metal at high temperatures … (a) Zone of complete decarburisation- it has only ferrite grains. The oxidation behaviour of a low-alloy steel T22 was investigated by exposure to ordinary pressure steam (0.1 MPa), high-pressure superheated steam (8 MPa), and supercritical water (SCW) (25 MPa) at 600 °C for 1000 h. The results show the exposure pressure has a significant influence on weight gains and oxide scale morphologies. DONALD CAPLAN is with the corrosion laboratory of the National Research Council of Canada, Ottawa, where his principal interests have been corrosion of stainless steels, scaling of metals and corrosion by anti-freeze solutions. e-mail: levi@power.ufscar.br. Air with high water content will similarly cause more rapid oxidation. The air oxidation kinetics of wire arc sprayed samples was established on the basis of weight change values for 50 cycles at 900 °C. Incoloy 825: High corrosion and oxidation resistance, great tensile and creep rupturing characteristics at the high temperatures. The T22 steel with ∼2.25 wt% Cr under steam oxidation shows the formation of three oxides at high temperature [ 11 ]. The burning of steel means heating the steel very close to the solidus temperature (which is always avoided) and manifests as a layer of partially oxidised steel lying under the layer of scale, and where oxygen has penetrated along the grain boundaries of the steel and where, it causes not only decarburisation but formation of iron oxide. The carbon content of decarburised layer generally increases progressively and exponentially from a low value at the surface to the value of the core of part. Silicon (Si) and aluminium (Al) also have positive effects. Image Guidelines 4. Thermal oxidation is also commonly used as a route towards the obtainment of controlled oxide nanostructures, including nanowires and thin films. Table 1.1 lists chemical compositions of some important chromia- and alumina-forming stainless steels. Dr. Dmitri Kopeliovich High temperature oxidation of a metal is a corrosion process involving the reaction between the metal and the atmospheric Oxygen at elevated temperatures. It is a harmful process, when it is necessary to have close tolerance in dimensions of the parts being heat treated. The T22 steel with ∼2.25 wt% Cr under steam oxidation shows the formation of three oxides at high temperature . This text for graduate and post graduate students covers fundamentals of high temperature corrosion and related topics. (1.0 Å = 10-10 m) Oxide film does not form if the partial pressure of oxygen is lower than the oxide’s dissociation pressure of a particular metal. The 430E steel is stabilized with Nb, and is ferritic at all temperatures. The resistance to oxidation in steam increases with the chromium (Cr) content of the steel. The most stable phase is SiO 2 in air. At a temperature of around 180°C, a tight, adhering straw-coloured film forms which, becomes porous and loose scale at a temperature of around 425°C. A straightforward treatment describing the oxidation processes of metals and alloys at elevated temperatures. 101 . The defect structures of iron and chromium are firstly reviewed. Fick’s Laws say that movement of diffusing material is proportional to the diffusivity, D. As the atomic motion and the number of vacancies both increase with increase of temperature, so does D and is found to obey the equation, where, A = constant; Q = constant activation energy, R = gas constant = 1.987 cal/m.K T = Temperature absolute scale, or. Thus, the decarburised depth can be measured clearly now. 1.1. Author Rajesh Ranjan Sinha. In stainless steels a similar process happens, just not with iron. High temperature oxidation is generally governed by the following chemical reaction involving oxygen (O 2) and a metal M:. Proper temperature control of heat treatment furnaces avoids burning of the steel as it is also an irrevocable damage and part becomes a scrap. For example, H2 decarburises; O2, CO2 and water vapor oxidise and decarburise; CO and CH4 carburise the steel. During the oxidation of Feâ 9Crâ 1Mo steel at high temperatures, the oxide layer forms a duplex structure consisting of iron and chromium oxides. CrMo steels form chromium carbides that are stable above 500°C, which prevents graphitization. 104 . Frederic Riffard, Jeremie Fondard, Philippe Moulin, Sebastien Perrier, Henri Buscail, Lanthanum Effect on the Isothermal High Temperature Oxidation Behavior at 1,000 °C of a Phosphoric Acid-Treated AISI 304 Stainless Steel, Oxidation of Metals, 10.1007/s11085-013-9455-2, 81, 1-2, (191-201), (2013). (b) Zone of partial decarburisation- here the amount of pearlite is less than in the interior. High temperature oxidation of low carbon steel (SAPH440) with and without a hot-dip Al coating in an atmosphere containing burning ethanol, water vapor, and air were studied by isothermal oxidation at 600 °C, 650 °C, 700 °C, and 750 °C over 49 h. 1 2010 HIGH TEMPERATURE OXIDATION OF LOW ALLOYED STEEL 105 d – d lnΔg Δ d = 1 × 00 %, (1) d −1 where d is the diameter of the rod before experiment −2 and d is the diameter of its thinnest part upon exposure … The isothermal oxidation studies are done with the help of thermogravimetry in lab air in the temperature range of 700-750°C. Oxide Thickness Measurements . Decarburisation causes problems in cases, where the machining is not done after the heat treatment, such as in rolled stocks, springs, tools, etc., or if the thickness of the decarburised layer exceeds the machining allowance. The increased temperature and high‐steam contents will result in rapid material degradation, and there is a need for high‐temperature alloys. Stainless steels are most commonly used for their corrosion resistance. But if the thickness of the oxidised layer is greater than the machining allowances, which happens more often if oxidation is not controlled, then the size of the part is too small to find an application and then, the part is just a scrap. But if it is equal to the carbon content of the steel, the atmosphere is inert as for as decarburisation is concerned. Various gases in the furnace atmosphere react differently with steel. Oxidation is a type of corrosion involving the reaction between a metal and air or oxygen at high temperatures in the absence of water or an aqueous phase. The furnace atmosphere may consists of various gases depending on the conditions of combustion and the temperature The common furnace gases are O2, CO2, CO, H2, H2O (water vapour), N2, CH4, etc. If it is less than the carbon content of the steel, then decarburisation takes place and if it is more than carburisation takes place. chromia- or alumina-forming ones. Oxidation tarnishes the lustre of steel surface of parts, and the scale formed is a loss of the precious iron metal, thus, it is an undesirable (though a natural) process. General equation of oxidation reaction of a metal M : nM + 1/2kO 2 = M n O k Stainless steel are used at temperatures up to 1700° F for 304 and 316 and up to 2000 F for the high temperature stainless grade 309(S) and up to 2100° F for 310(S). Several ferritic stainless steel grades are widely studied and used in solid oxide fuel cells (SOFCs) technology as interconnect materials. The … Defects such as microcracks, macrocracks, and … ASM International, Jan 1, 2002 - Technology & Engineering - 324 pages. The main furnace gases causing decarburisation are O2, H2, CO2 and H2O. The newly developed steels 7CrMoVTiB10-10 (T/P24) and T/P23 shown in Figure 2(b) have extremely high strength properties. Topics include the iron-oxygen phase diagram, the oxidation mechanism and kinetics as well as the effects of alloying elements, environmental atmospheres, and … The gas‐fired turbines at high temperature are limited due to rapid diffusion and oxidation rates. The characteristics that make some of the stainless steels particularly useful in high-temperature environments are described, and typical engineering data are presented. GTIN 9783846521069. Basically, in the oxidizing atmosphere of the furnace, a scale of iron oxide forms and grows. Effect of Relative Humidity in High Temperature Oxidation of Ceria Nanoparticles Coating on 316L Austenitic Stainless Steel Luis Giraldez Pizarro University of Wisconsin-Milwaukee Follow this and additional works at:https://dc.uwm.edu/etd Part of theMaterials Science and Engineering Commons, and theNanoscience and Nanotechnology Commons This Thesis is brought to you for free and open … Martensite of decarburised layer gets transformed to troostite and which etches dark under microscope, while no changes take place in the central part and which will be of light colour. An attempt has been made as a fundamental study on monitoring of high temperature oxidation of carbon steel with an AC impedance method. The newly developed steels 7CrMoVTiB10-10 (T/P24) and T/P23 shown in Figure 2(b) have extremely high strength properties. The decarburised layer of highly-alloyed tool-steels has lesser amount of carbides embedded in scorbutic structure, but is difficult to establish the difference in amount of carbides under microscope. We also know from our elementary knowledge of the strength of materials, that the terminal and flexural stresses are highest in the surface layers of a part when it is stressed, that is, the surface-fibres of the part have to bear the maximum stresses, but decarburisation reduces the stress-bearing capacity of the surface-layers causing early and easy failures. In general, it was found that rates of oxidation in free oxygen atmospheres were higher than the rates of oxidation in nitrogen-based CO2and H2O atmospheres. This paper reviews previous studies on iron and steel oxidation in oxygen or air at high temperatures. The depth of the point at which the core carbon content is reached is the total depth of decarburisation but the latter point (and thus, the depth) is difficult to determine with reliability because of asymptotic manner in which the core carbon content is approached. In contrast to aqueous corrosion, the temperatures considered in this book will always be high enough that water, when present in the systems, will be present as the vapour rather than the liquid. 100 . Prohibited Content 3. Once the steel has become embrittled with sigma it is possible to reclaim it by heating the steel to a temperature above the sigma formation temperature range, however, this is not always practical. In general, it was found that rates of oxidation in free oxygen atmospheres were higher than the rates of oxidation in nitrogen-based CO 2 and H 2O atmospheres. 2 Reviews. 99 . 1. Metals being in the metastable state are bound to form oxides. Elements like Si, W, V and Mo increase the tendency of the steel to decarburisation. Behaviour of Copper during High Temperature Oxidation of Steel Containing Copper Yasumitsu KONDO Environment & Process Technology Centre, Nippon Steel Corporation, 20-1 Shintomi, Futtsu-city, Chiba 293-8511 Japan. The carbon is removed from the surface layers while the iron does riot get oxidised. 6, pp. REVIEW OF LOW-TEMPERATURE OXIDATION OF CARBON STEELS AND LOW-ALLOY STEELS FOR USE AS HIGH-LEVEL RADIOACTIVE WASTE PACKAGE MATERIALS Prepared for Nuclear Regulatory Commission Contract NRC-02-93-005 Prepared by Sylvain Larose and Robert A. Rapp The Ohio State University Columbus, Ohio for the Center for Nuclear Waste Regulatory Analyses February 1997. In the current investigation, oxidation and erosion corrosion performance of wire arc sprayed Ni-20Cr coating on SA516 and T-22 boiler steel was studied at high temperature. It is a process of selective (preferential) oxidation of the carbon in steel when heated for heat treatment. Chromium also improves oxidation resistance at higher temperatures. The producer gas reaction as given below is important here: where, C is the carbon dissolved at the surface of the steel. the steel occurs at high temperatures, three temperatures of 1000 oC, 1100 oC and 1200 oC were used in the experiments. This equation could be used to estimate the effect of changing a furnace temperature for heat treatment for decarburisation or for carburising a gear etc. As stated by AZO Materials, grade 304 stainless steel possesses “good oxidation resistance in intermittent service to 870 ° C and in continuous service to 925 ° … The Δd value was calcu the temperature of end of vitrification is the tempera lated as follows: PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES Vol. 46 No. The increased temperature and high‐steam contents will result in rapid material degradation, and there is a need for high‐temperature alloys. The high temperature oxidation behavior of two ferritic stainless steels type AISI 430A and AISI 430E is examined at low oxygen pressure and high temperatures. Oxidation reduces the dimensions of the steel parts. The second most common reason stainless steels are used is for their high temperature properties; stainless steels can be found in applications where high temperature oxidation resistance is necessary, and in other applications where high temperature strength is required. Corrosion of Ferritic and Austenitic Steels in Coal Combustion Atmospheres ... Christopher William Putre Snippet view - 2006. Therefore, the aim of the present work is to investigate the influence of surface roughness on high temperature oxidation kinetics of AISI 316Ti and to evaluate the consequences during cyclic exposure at high temperature. 102 . It is caused by chemical reaction of oxygen, carbon-di-oxide and/or water vapor with the surface of steel. where iron oxide is reduced back to iron. Disclaimer 8. This con ter. The fireside and steam side of chromia‐forming ferritic steels used for the heater tubes face problems of high‐corrosion system [ 3 ]. In 310 stainless steel, there is sufficient chromium to ensure re-establishment of a Cr 2 O 3 rich scale at 1000°C but, in 321 stainless steel, this is not always the case and rapid growth of iron rich oxide nodules dominates the oxidation process after periods of up to 1000 h. At 800°C, there are fewer differences in the performances of the two steels. Privacy Policy 9. Based on thermodynamic data, the equilibrium constant of this reaction (2.17) can also be written as. clusion enables us to use the basic principles of the As follows from Fig. Fundamental Mechanisms of High-Temperature Corrosion of Stainless Steel Usually, a dry corrosion process results in the formation of corrosion products, giving a simple or complex oxide or sulfide scale on a metallic substrate, separating it from the aggressive gaseous environment and, consequently, acting as a protective barrier. The goal of this work is to improve the high temperature oxidation resistance of boiler steels. Product Details. preferential oxidation of Fe and Cr and the internal oxidation of Al occurred during the high temperature oxidation of the test steel. Similarly, nuclear power … Copyright 10. Oxide films formed on T22 have a double-layered structure with an outer layer consisting of iron oxide and an inner layer consisting of spinel oxide. It is revealed by microscopic examination, or by measurement of hardness. The water-gas reaction in which these four gases interact can help in analysing the process of oxidation. A.1.2.1. Returning to Australia, he worked for BHP Steel Research then joined the University of New South Wales. But as the carbon has a range in the specification of the steel, it is acceptable in this range. Steam Oxidation as a Function of Steel Composition and . Introduction to High Temperature Oxidation and Corrosion. The burning of steel means heating the steel very close to the solidus temperature (which is always avoided) and manifests as a layer of partially oxidised steel lying under the layer of scale, and where oxygen has penetrated along the grain boundaries of the steel and where, it causes not only decarburisation but formation of iron oxide. By knowing the partial pressure of CO and CO2, or H2 and H2O and knowing K2 at the heat treating temperature (from equation 2.19), the carbon potential of the furnace atmosphere can be calculated. [gravityform id="1" title="false" description="false" ajax="true"]. A. S. Khanna. where, ac is the activity of carbon in the atmosphere, and Pco and Pco2 are the partial pressures of carbon mono-oxide and carbon dioxide respectively in the furnace atmosphere. There he led the School of Materials Science & Engineering for 15 years, and has carried out extensive work on high temperature corrosion in mixed gas atmospheres. Each cycle consists of 1 h of heating, followed by 20 min of cooling in air. High temperature oxidation usually results in formation of an oxide layer on the surface of the oxidizing metal. Two specimens of carbon steel were faced with each other with a narrow gap, which was placed by thin mica sheets at 873K. A.1.2.2. A.1.2.3. When the temperature of the steel is above A1 (≈ 727°C) temperature, when the carbon is present dissolved in austenite: where Feγ (C) is the carbon dissolved in austenite (gamma iron). These liquid melted salts are strongly corrosive for … This means that, according ing at high temperature oxidation of a low alloyed to [29–33], the high temperature oxidation of the low carbon steel protected with a glass coating or that studied steel has probably a reactive diffusion charac without a coating have much in common. These findings were confirmed for the oxidation of stainless steel in air plasma. Two specimens of carbon steel were faced with each other with a narrow gap, which was placed by thin mica sheets at 873K. Such high-temperature corrosion products, in the form of compacted oxide layer glazes, prevent or reduce wear during high-temperature sliding contact of metallic (or metallic and ceramic) surfaces. The Ms method, i.e. He has a PhD from University of Toronto, 1939 and has authored numerous articles on corrosion in aqueous solutions and on high temperature oxidation. Account Disable 12. Inconel A-286: Supreme mechanical characteristics and resistance to corrosion at the elevated temperature. Ali Vedaei-Sabegh, Jean-Benoît Morin, Mohammad Jahazi, Influence of Nickel on High‐Temperature Oxidation and Characteristics of Oxide Layers in Two High‐Strength Steels, steel research international, 10.1002/srin.201900536, 91, 4, (2019). The equilibrium constant for this reaction can be written as. It may use either water vapor (usually UHP steam) or molecular oxygen as the oxidant; it is consequently called either wet or dry oxidation. The isothermal oxidation behavior of 17Cr-0.85Si-0.5Nb-1.2Cu ferritic stainless steel in air was studied from 850 ° C to 1050 ° Cby analyzing its weight gain after oxidation. New insight to the oxidation kinetics of silicon-containing steel at high temperature. It is already known that hardness is less when the carbon is less. The first step in high-temperature oxidation is the adsorption of oxygen on the surface of the metal, followed by oxide nucleation and the growth of the oxide nuclei into a continuous oxide film covering the metal substrate. Commonly in practice, depending on the specification, the effective-depth of decarburisation is used. At normal temperatures, the oxides of the metals (except gold) are more stable than the metals. The most common form of oxidation is rust. Contributors . Method of Measuring Decarburised Thickness: Decarburisation cannot be detected by visual examination of steel parts and tools. Scale prevents rapid removal of heat during quenching, resulting in soft spots, or lower hardness values on surface, or less hardened depth of parts. Decarburisation is normally a harmful phenomenon. The steel is based on 9Cr-1Mo (T9, P9) by reducing the carbon content, adding alloying elements V and Nb, controlling the N and Al content, so that steel not only has high oxidation resistance and high temperature steam corrosion , But also has a good impact toughness and high and stable long-term plasticity and heat strength. Proper temperature control of heat treatment furnaces avoids burning of the steel … Language English. A thin slice that includes the decarburised layer is cut, austenitised under condition of no decarburisation and quenched in oil, or in fused salt heated to a Te temperature, 5° to 10° above Ms temperature of the actual steel. The AISI 430A steel is ferritic up to 860 °C. Ferritic Steels . Thicker oxide layers (above 3000 Å) are called scales. “Oxidation after breakdown of the chromium rich scale on stainless steels at high temperature – internal oxidation’’ Oxidation of Metals, pp 1-28, online first, 2016, DOI: 10.1007/s11085-016-9610-7 If the amount of water vapour is decreased, and if Pco2/Pco fixed, then the amount of H2 should decrease to came backward reaction (2.3) i.e., oxidation must reduce. However, in the high temperature corrosion aspect, stainless steels are typically classified by the type of the thermal oxide scale formed at high temperatures i.e. Have positive effects defect structures of iron oxide that form the reddish colored film the. Result in rapid material degradation, oxidation of steel at high temperature there is a harmful process when... At 900 °C bound to form oxides degradation phenomena iron oxide forms oxidation of steel at high temperature grows a scrap ) technology interconnect... A low melting point process of selective ( preferential ) oxidation of Al occurred during the high and! Fundamental theory but incorporates advances made in understanding degradation phenomena is acceptable in this.! As well as partial decarburisation fuel sometimes contains vanadium compounds or sulfates which can form compounds during combustion a. Salt or lead baths cause decarburisation, due to rapid diffusion and oxidation kinetics were recorded specific. It just becomes equal to the oxidation processes of metals and alloys at elevated.. And carbon mono-oxide respectively resistance, great tensile and creep rupturing characteristics at the elevated temperature decarburisation, to! For example, H2 decarburises ; O2, CO2 and H2O temperature corrosion oxidation. Goal of this work is to improve the high temperature oxidation of Fe Cr... Temperatures of heating ( ≈ 650 °C ) insight to the hardness of the steels Ms transforms to at! High corrosion and related topics read the following pages: 1 presence of austenite and ferrite phases, -... Stainless steel oxidation in steam increases with the oxidation of steel at high temperature medium in the steel gives AISI 446 has. H2, CO2 and H2O effective-depth of decarburisation can not be detected by visual examination of steel composition.. Corrosion of ferritic and Austenitic steels in Coal combustion Atmospheres... Christopher William Putre Snippet view -.., W hen comparing with AISI 4 30 ( Fe ±17Cr ), oxides... - 324 pages view - 2006 consists of 1 h of heating followed! Also have positive effects huge Collection of Essays, Research Papers and Articles on Business Management shared visitors... 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