Understanding REFRACTORY For API936 Personnel Certification Examination Reading 6 My Pre-exam Self Study Notes 2nd October 2015
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Iron Treatment Station in Basic Oxygen Furnace
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Iron Treatment Station in Basic Oxygen Furnace
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BOF Tapping
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BOF Tapping
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BODY OF KNOWLEDGE FOR API936 REFRACTORY PERSONNEL CERTIFICATION EXAMINATION API certified 936 refractory personnel must have knowledge of installation, inspection, testing and repair of refractory linings. The API 936 Personnel Certification Examination is designed to identify applicants possessing the required knowledge. The examination consists of 75 multiple-choice questions; and runs for 4 hours; no reference information is permitted on the exam. The examination focuses on the content of API STD 936 and other referenced publications.
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REFERENCE PUBLICATIONS: A. API Publications: API Standard 936; 3rd Edition, Nov 2008 - Refractory Installation Quality Control Guidelines - Inspection and Testing Monolithic Refractory Linings and Materials.
B. ACI (American Concrete Institute) Publications: 547R87 - State of the art report: Refractory Concrete 547.1R89 - State of the art report: Refractory plastic and Ramming Mixes
C. ASTM Publications: C113-02 - Standard Test Method for Reheat Change of Refractory Brick C133-97 - Standard Test Methods for Cold Crushing Strength and Modulus of Rupture of Refractories C181-09 - Standard Test Method for Workability Index of Fireclay and High Alumina Plastic Refractories C704-01 - Standard Test Method for Abrasion Resistance of Refractory Materials at Room Temperatures
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闭门练功
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闭门练功
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The Magical Book of Refractory
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Fion Zhang at Shanghai 2nd October 2015
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Reading VI Content: Reading 1 : Introduction to the Characteristics of Refractories and Refractory materials Reading 2 : Refractory manufacturing Refractory testing and Refractory properties Reading 3 : AP 42, Fifth Edition, Volume I Chapter 11: Mineral Products Industry Refractory Manufacturing Reading 4 : The Fundamentals of Refractory Inspection with Infrared Thermography
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Reading 1: Introduction to the Characteristics of Refractories and Refractory materials
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http://ispatguru.com/introduction-to-the-characteristics-of-refractories-and-refractory-materials/
Reading 1: Introduction to the Characteristics of Refractories and Refractory materials A suitable selection of the refractory lining material for a furnace can only be made with an accurate knowledge of the chemical (mineralogical) and physical properties of the refractories and refractory materials, and of the stresses of the materials during service. There are four types of stresses which refractories face during their period of service. These are given below: Thermal (effects) – The important properties for thermal stresses are pyrometric cone equivalent (PCE), refractoriness under load (RUL), Thermal expansion under load (creep), hot modulus of rupture, thermal expansion, reheat change (after-shrinkage and after-expansion) and thermal shock resistance. Thermo-technical – The important properties for thermo-technical stresses are thermal conductivity, specific heat, bulk density, melting point, thermal capacity and temperature conductivity. (physical properties?)
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Mechanical – The important properties for mechanical stresses are cold modulus of rupture and deformation modulus, crushing strength, abrasion resistance, porosity and density. (physical properties and forms) Chemical – The important properties for chemical stresses are chemical composition, mineralogical composition and crystal formation, pore size distribution and types of pores, gas permeability and resistance to slag, glass melts, gases and vapours.
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Some of the important physical and chemical properties are given below: 1. Melting point – Melting point (melting temperatures) specify the ability of materials to withstand high temperatures without chemical change and physical destruction. The melting points of major elements that constitute refractory composition in pure state vary from 1700 deg C to 3480 deg C. The melting point serves as a sufficient basis for considering the thermal stability of refractory mixtures and is an important characteristic indicating the maximum temperature of use. 2. Size and dimensional stability – The size and shape of the refractories is an important feature in design since it affects the stability of any structure. Dimensional accuracy and size is extremely important to enable proper fitting of the refractory shape and to minimize the thickness and joints in construction.
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3. Porosity – Porosity is a measure of the effective open pore space in the refractory and is expressed as the average percentage of open pore space in the overall refractory volume. The mechanical strength of a refractory material is largely determined by the true porosity which is composed of closed pores and open pores, the latter being either permeable or impermeable. For higher mechanical strength, low porosity of the refractory bricks is aimed. The important properties with respect to porosity is its behaviour during chemical attack by molten metal, slag, fluxes and vapour which can penetrate and thereby contribute to degradation of the refractory structure. High porosity materials tend to be highly insulating as a result of high volume of air they trap. The content of open pores of a brick is calculated from the water absorption. By using the water air displacement method, the open pores are classified either as permeable or effective or as impermeable pores.
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4. Bulk density – The bulk density (BD) is generally considered in conjunction with apparent porosity. It is a measure of the weight of a given volume including the pore space of the refractory. It is one of the important characteristic and provides a general indication of the product quality. An increase in bulk density increases the volume stability, the heat capacity, the resistance to abrasion and slag penetration. The bulk density is determined by means of a (1) hydrostatic scale, according to the (2) mercury displacement method or (3) by measurement.
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5. Cold crushing strength – It is a measure of the mechanical strength of the refractory brick. In furnaces, cold crushing strength (CCS) is of importance, because of bricks with high crushing strength is more resistant to impact from rods or during removal of slag than a brick with a low CCS. It is a useful indicator to the adequacy of firing and abrasion resistance in consonance with other properties such as bulk density and porosity. Comments: Typical CCS Values: Brick grade Silica Fire clay Corundum Magnesia Magnesia chromite Magnesia spinel Insulating Brick
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CCS (N /mm2) 15 -20 12 - 70 35 - 80 50 - 110 30 - 70 > 40 3 - 20
6. Pyrometric cone equivalent – It is the measurement of the refractoriness. Pyrometric cone eqquivalent (PCE) is the ability to withstand exposure to elevated temperature without undergoing appreciable deformation. Refractories due to their chemical complexity melt progressively over a range of temperature. This softening behaviour of the refractories is determined by PCE which consists of comparing ceramic specimen of known softening behaviour (seger or orton cones) with the cone of the refractory. Pyrometric cones are small triangular ceramic prisms that when set at a slight angle bend over in an arc so that the tip reaches the level of the base at a (1) particular temperature if heated (2) at a particular rate. The bending of the cones is caused by the formation of a viscous liquid within the cone body, so that the cone bends as a result of viscous flow.
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PCE is measured by making a cone of the refractory and firing it until it bends and comparing it with standard cone. PCE is useful for the quality control purpose to detect variations in batch chemistry that changes or errors in the raw material formulation. Refractoriness points to the resistance of the refractory to the extreme conditions of heat (> 1000 deg C) and corrosion when hot and molten materials are contained while being transported and/or processed. PCE cones before and after firing is shown at Fig. 1
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Fig 1 PCE cones before and after firing
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PCE cones after firing
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The Wiki: Pyrometric cones Equivalent Pyrometric cones are pyrometric devices that are used to gauge heatwork during the firing of ceramic materials. The cones, often used in sets of three as shown in the illustration, are positioned in a kiln with the wares to be fired and provide a visual indication of when the wares have reached a required state of maturity, a combination of time and temperature. Thus, pyrometric cones give a temperature equivalent; they are not simple temperaturemeasuring devices.
Definition The pyrometric cone is "A pyramid with a triangular base and of a defined shape and size; the "cone" is shaped from a carefully proportioned and uniformly mixed batch of ceramic materials so that when it is heated under stated conditions, it will bend due to softening, the tip of the cone becoming level with the base at a definitive temperature. Pyrometric cones are made in series, the temperature interval between the successive cones usually being 20 degrees Celsius. The best known series are Seger Cones (Germany), Orton Cones (USA) and Staffordshire Cones (UK).
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https://en.wikipedia.org/wiki/Pyrometric_cone
Self-supporting cones prior to firing (top) and after (bottom)
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https://en.wikipedia.org/wiki/Pyrometric_cone
Seger cones after use
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https://en.wikipedia.org/wiki/Pyrometric_cone
History In 1782, Josiah Wedgwood created accurately scaled pyrometric beads, which led him to be elected a fellow of the Royal Society. The modern form of the pyrometric cone was developed by Hermann Seger and first used to control the firing of porcelain wares at the Kรถnigliche Porzellanmanufaktur (Royal Porcelain Works) in Berlin, in 1886. Seger cones are to this day made by a small number of companies and the term is often used as a synonym for pyrometric cones. The Standard Pyrometric Cone Company was founded in Columbus, Ohio, by Edward J. Orton, Jr. in 1896 to manufacture pyrometric cones, and following his death a charitable trust was established to operate the company, now known as the Edward Orton Jr. Ceramic Foundation (also known as the Orton Ceramic Foundation or simply "Orton") in suburban Westerville, Ohio.
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https://en.wikipedia.org/wiki/Pyrometric_cone
Glaze cones were made by evaporating water from a liquid glaze until the resulting mass reached the consistency of a plastic clay. The plastic mixture was then formed into cones that were dried and set in a soft pad of clay in a kiln. When observed through the viewing port of a kiln, the potter could see when a glaze cone had reached its melting point. The rings were removed from the kiln through special loopholes in the kiln walls using metal rods and examined for signs of melting in the glaze.
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https://en.wikipedia.org/wiki/Pyrometric_cone
Usage For some products, such as porcelain and lead-free glazes, it can be advantageous to fire within a two-cone range. The three-cone system can be used to determine temperature uniformity and to check the performance of an electronic controller. The three-cone system consists of three consecutively numbered cones: ■ Guide cone – one cone number cooler than firing cone. ■ Firing cone – the cone recommended by manufacturer of glaze, slip, etc. ■ Guard cone – one cone number hotter than firing cone. Additionally, most kilns have temperature differences from top to bottom. The amount of difference depends on the design of the kiln, the age of the heating elements, the load distribution in the kiln, and the cone number to which the kiln is fired. Usually, kilns have a greater temperature difference at cooler cone numbers. Cones should be used on the lower, middle and top shelves to determine how much difference exists during firing. This will aid in the way the kiln is loaded and fired to reduce the difference. Downdraft venting will also even out temperatures variance.
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https://en.wikipedia.org/wiki/Pyrometric_cone
Both temperature and time and sometimes atmosphere affect the final bending position of a cone. Temperature is the predominant variable. The temperature is referred to as an equivalent temperature, since actual firing conditions may vary somewhat from those in which the cones were originally standardized. Observation of cone bending is used to determine when a kiln has reached a desired state. Additionally, small cones or bars can be arranged to mechanically trigger kiln controls when the temperature rises enough for them to deform. Precise, consistent placement of large and small cones must be followed to ensure the proper temperature equivalent is being reached. Every effort needs to be made to always have the cone inclined at 8째 from the vertical. Large cones must be mounted 2 inches above the plaque and small cones mounted 15/16 inches. With the cones having their own base, "self-supporting cones" eliminate errors with their mounting.
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https://en.wikipedia.org/wiki/Pyrometric_cone
Quoted: Additionally, small cones or bars can be arranged to mechanically trigger kiln controls when the temperature rises enough for them to deform.
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https://en.wikipedia.org/wiki/Pyrometric_cone
Control of variability Pyrometric cones are sensitive measuring devices and it is important to users that they should remain consistent in the way that they react to heating. Cone manufacturers follow procedures to control variability (within batches and between batches) to ensure that cones of a given grade remain consistent in their properties over long periods. A number of national standards and an ISO standard have been published regarding pyrometric cones. Even though cones from different manufacturers can have relatively similar numbering systems, they are not identical in their characteristics. If a change is made from one manufacturer to another, then allowances for the differences can sometimes be necessary.
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https://en.wikipedia.org/wiki/Pyrometric_cone
7. Refractoriness under load – Refractoriness under load (RUL) evaluates the softening behaviour of fired refractory bricks at rising temperature and constant load conditions. RUL gives an indication of the temperature at which the brick will collapse in service condition with similar load. However, under actual service conditions the bricks are heated only on one face and most of the load is carried by the relatively cooler rigid portion of the refractory bricks. Hence, the RUL test gives only an index of refractory quality, rather than a figure which can be used in a refractory design. Under service conditions, where the refractory used is heating from all sides such as checkers, partition walls etc. the RUL test data is quite significant. For RUL, samples in cylindrical shape of 50 mm height and 50 mm diameter are heated at a constant rate under a load of 0.2 N/mm2 (0.2Mpa) and the change in height includes the thermal expansion and also the expansion of test equipment. The test results are taken from the recording. The initial temperature is taken at 0.6 % compression while the final temperature is taken at 20 % compression or when the specimen has collapsed. RUL curves of different refractories are at Fig 2
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Fig 2 – RUL curves of different refractories
50 x Ф50 mm
0.2 N/mm2
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RUL Testing Set-up
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RUL
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8. Thermal expansion under load (Creep) – Thermal expansion under load (Creep) is a time dependent property which determines the deformation in a given time and at a given temperature by a refractory under stress. Refractory material must maintain dimensional stability under extreme temperatures (including repeated thermal cycling) and constant corrosion from hot liquid and gases. In the creep test, specimen of 50 mm diameter and 50 mm height with an internal bore for the measuring rod is heated at constant rate and under a given load (generally at 0.2 N/mm2). After the required temperature is reached, the samples is held for 10 -50 hours. The compression of the specimen, after maximum expansion has been attained, is given in relation to the test time as a measure of creep at a specified test temperature. Creep curves of refractories are at Fig 3
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Fig 3 Creep curves of refractories
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Creep curves of refractories
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Softening under load
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9. Volume stability, expansion and shrinkage at high temperature Permanent change in the dimension of a refractory due to contraction and expansion during service can take place due to: The changes in the allotropic forms which cause a change in specific gravity. A chemical reaction which produces a new material of altered specific gravity. The formation of a liquid phase Sintering reactions Due to fluxing by dust and slag or by the action of alkalis in case of fireclay refractories. After heating to high temperatures and subsequent cooling, a permanent change in dimensions often occurs. This can cause either loosening of bricks during service or the destruction of brickwork due to the pressure. Permanent linear change (PLC) on heating and cooling of the refractory bricks give an indication of volume stability of the brick as well as the adequacy of the processing parameters during manufacture. It is particularly significant as a measure of conversion achieved in the manufacture of silica refractories. Charlie Chong/ Fion Zhang
10. Reversible thermal expansion – Refractories like any other materials expands when heated and contracts when cooled. The reversible thermal expansion is a reflection on the phase transformation (?) that occurs during heating and cooling. The PLC and the reversible expansion are followed in the design of refractory lining for provision of expansion joints. As a rule, those with a lower thermal expansion co-efficient are less susceptible to spalling.
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Fig 4 Thermal expansion of different refractories
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11. Thermal conductivity – Thermal conductivity is defined as the quantity of heat that will flow through a unit area in direction normal to the surface area in a defined time with a known temperature gradient under steady state conditions. It indicates general heat flow characteristics of the refractory and depends upon the chemical and mineralogical composition as well as the application temperature. High thermal conductivity refractories are needed for some applications such as coke ovens, regenerators etc. On the other hand refractories with lower thermal conductivity are preferred in most application since they help in conserving heat energy. Porosity is an important factor in heat flow through refractories. The thermal conductivity of a refractory decreases on increasing its porosity. Although it is one of the least important properties as far as service performance is concerned, it evidently determines the thickness of the brickwork.
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12. Thermal shock resistance – It characterizes the behaviour of refractories to sudden temperature shocks. Temperature fluctuations can reduce the strength of the brick structure to a high degree and can lead to disintegrtaion or spalling in layers There are several methods of determining the thermal shock resistance each having its own advantages and disadvantages. 13. Specific heat – The specific heat is a material and temperature related energy factor and is determined with the help of calorimeters. The factor indicates the amount of energy (calories) needed to raise the temperature of one gram of material by 1 deg C. Compared to water, the specific heats of refractory materials are very low. These values are less than one fourth (Ÿ) of value of specific heat of water.
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14. Abrasion resistance – The mechanical stress of refractory bricks is not caused by pressure alone, but also the abrasive attack of the solid raw materials as it slowly pass over the brickwork and by the impingement of the fast moving gases with fine dust particles. Therefore the cold crushing strength is not alone sufficient to characterize the wear of the refractories. There is no approved method for testing abrasion resistance but there are some methods available to give reference values such as Bohme grinding machine method and sand blast method etc. Note: ASTM C704-01 Standard Test Method for Abrasion Resistance of Refractory Materials at Room Temperature
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15. Modulus of Rupture or Modulus of deformation – During thermal stress, generally combined with altered physical-chemical conditions because of infiltration, strain conditions occur in refractory brickwork which can lead to brick rupture or crack formation. In order to determine the magnitude of rupture stress, the resistance to deformation under bending stress (rupture strength) is measured. Determination of the modulus of deformation in the cold state is carried out, together with modulus of rupture, on a test bar resting on two bearing edges. In general, a high ductility is looked for in refractory bricks,i.e. a large deformation region without rupture, which means a high value of the ratio of modulus of rupture to modulus of deformation. The modulus of rupture is defined as the maximum stress of a rectangular test piece of specific dimensions which can withstand maximum load until it breaks, expressed in N/mm2. For hot modulus of rupture (HMOR) load is applied at a high temperature. The international standard test method is described in ISO 5013 with test piece dimensions of 150 mm x 25 mm x 25 mm. Note: ASTM C133-97 Standard Test Methods for Cold Crushing Strength and Modulus of Rupture of Refractories Charlie Chong/ Fion Zhang
16. Mineralogical composition and crystal formation – The behaviour of refractories of identical composition also depends on the type of raw materials used and on the reactions achieved during firing of the bricks. A glassy phase is more susceptible to attack by slag than a tightly interlocked crystal lattice structure. Two methods are used to identify mineralization composition. In the first method polarizing microscope or scanning electron microscope (SEM) is used. In the second method X-ray diffraction analysis is done.
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End of Reading 1. Charlie Chong/ Fion Zhang
Reading 2: Refractory manufacturing Refractory testing and Refractory properties
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http://ispatguru.com/introduction-to-the-characteristics-of-refractories-and-refractory-materials/
Refractory manufacturing Refractory testing and Refractory properties What is refractory ? Is it a material which should withstand high temperature only ? The right definition is that it should withstand high temperature,resistance to thermal and thermo chemical load, posses high volume stability, resistant to erosion and abrasion, be tough , and resistant to chemical corrosion etc. Or otherwise it should have high RUL, high PCE, low conductivity , high hot MOR, high creep resistance and optimum CCS etc. There is no refractory material which posses all the above properties 100 % Overall it is a compromise with all the above properties. Choice of refractories depend on the operating and mechanical conditions of the kiln.
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CCS testing machine
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Cold crushing equipment and CCS values Brick grade Silica Fire clay Corundum Magnesia Magnesia chromite Magnesia spinel Insulating Brick
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CCS ( N / mm2) 15 -20 12 - 70 35 - 80 50 - 110 30 - 70 > 40 3 - 20
PCE
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Creep test equipments
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Refractoriness under load RUL This is a measure of the resistance of a refractory body to the combined effects of heats of load.This test helps to study the behavior of a refractory product when subjected to a constant load under conditions of progressively rising temperature. The ground mass / matrix helps to bond the entire mass of a refractory brick strongly together. The amount and the strength of the glass is fixed by the alumina - silica ratio, fluxing oxide content and the temperature of firing. It is an important parameter to decide upon the safer limit of service temperature in a given situation. Contributing factors to the increased resistance to the pressure are: a) More thorough distribution of liquid throughout the brick b) The growth of crystals through the influence of heat c) Crystallization of a portion of the liquid during cooling.
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High temperature creep In a brick held at constant temperature and pressure, gradual solution of solid material up to the limits of its solubility in the liquid may cause some increase in the viscosity of the liquid. This increase is dependent on the nature of ground mass, glass content. Higher glass content will result higher deformation in this situation. This property of refractoriness is called high temperature creep. Lower deformation will ensure rigidity under the service condition. The creep is the measurement of deformation of a refractory product as a function of time when it is subjected to a constant load and heated at a specified temperature.
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Creep Curve
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Softening under load
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Linear expansion (Permanent linear change) High temperature reheat test may be used to reveal 1) if a brick has been fired long enough or at a high temperature 2) whether a brick has adequate refractoriness and volume stability It is expressed as a percentage , preferably by the ratio of the length of the test piece after heating and the original value of the length
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Equipments used to determine Thermal expansion
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Thermal expansion or refractory materials
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Equipments for thermal shock resistance test
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MOP- The resistance to bending stress of refractory products provide information on their deformation behavior at high temperature.
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HMOP
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Chemical composition By quantifying all the constituents present in refractory, it is possible to assess the chemical properties and melting behavior of a given refractory.As it is important to know the % Al2O3 in high alumina brick, % MgO in magnesite brick , and % SiO2 in silica brick etc.,the determination of minor constituents has also been recognized as controlling factors in the performance of many refractories. The chemical composition is of great importance with respect to attack by slag , glass melts , flue dusts and vapors. In general the principle applies that a brick is more resistant the lower the rate of chemical reaction gradient between the slag and brick is. Therefore, where the acid slag is expected , acid bricks are preferably used , and basic bricks where basic slag is expected.
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According to the behavior during contact reaction, the following groups of bricks can be differentiated. Acid group - fused (99% SiO2), Silicon carbide bricks, Zircon crystobalite . Zircon silicate Basic group - dolomite, magnesia, magnesia chrome, chrome magnesia ,forsterite Inert or neutral - carbon , high alumina chromite group
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Cup corrosion test Alkali test of a high alumina brick with K2CO3
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Alkali test of a sic containing high alumina brick with K2CO3
Mineralogical investigations by X-ray diffraction Determination of the mineral phases composition of material X-ray diffraction diagram of a used magnesia –spinel brick grade, salt infiltrated.
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Microscopically techniques ( micrologies) Light micoscopy ( transmitted light and reflected light microscopy Microprobe analysis ( WDS, EDS) Scanning electron microscopy Advantages of these micrlogies opposite other investigation methods Diagnosis of mineral phases composition in raw materials , refractory products etc and their configuration ( textural/ structural criterions, pore shape and size etc
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Mineralogical investigations- Reflected light microscopy Pictures of magnesia - spinel brick grades with different raw material composition
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Mineralogical investigations- Reflected light microscopy Pictures of magnesia - spinel brick grades with different raw material composition
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Mineralogical investigations- Reflected light microscopy Pictures of magnesia - spinel brick grades with different raw material composition
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Microprobe Analysis- Chemical – mineralogical composition in mm Boundary between slag and corundum brick Polished section image (reflected light microscope)
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Back scattered electron image (microprobe)
Mineralogical investigations- Scanning electron microscopy (SEM) Hydration of Magnesia . crack formation ,caused by formation of brucite(Mg(OH)2
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Minerological investigations
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End of Reading 2. Charlie Chong/ Fion Zhang
Reading 3: AP 42, Fifth Edition, Volume I Chapter 11: Mineral Products IndustryRefractory Manufacturing
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http://www3.epa.gov/ttn/chief/ap42/ch11/
AP42.VI-11.5 Refractory Manufacturing 11.5.1 Process Description Refractories are materials that provide linings for high-temperature furnaces and other processing units. Refractories must be able to withstand physical wear, high temperatures (above 538째C [1000째F]), and corrosion by chemical agents. There are two general classifications of refractories, clay and nonclay. The six-digit source classification code (SCC) for refractory manufacturing is 3-05-005. Clay refractories are produced from fireclay (hydrous silicates of aluminum) and alumina (57 to 87.5 percent). Other clay minerals used in the production of refractories include kaolin, bentonite, ball clay, and common clay. Nonclay refractories are produced from a composition of alumina (<87.5 percent), mullite, chromite, magnesite, silica, silicon carbide, zircon, and other nonclays.
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There are two general classifications of refractories: clay and nonclay. Clay refractories are produced from: fireclay (hydrous silicates of aluminum) and alumina (57 to 87.5%). kaolin, bentonite, ball clay, and common clay. Nonclay refractories are produced from a composition of: alumina (<87.5%), mullite, chromite, magnesite, silica, silicon carbide, zircon, and other nonclays. Charlie Chong/ Fion Zhang
Refractories are produced in two basic forms: 1. formed objects, and 2. unformed granulated or plastic compositions. The preformed products are called bricks and shapes. These products are used to form the walls, arches, and floor tiles of various high-temperature process equipment. The Unformed compositions include: 1. mortars, 2. gunning mixes, 3. castables (refractory concretes), 4. ramming mixes, and 5. plastics. These products are cured in place to form a monolithic, internal structure after application.
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Refractory manufacturing involves four processes: raw material processing, forming, firing, and final processing. Figure 11.5-1 illustrates the refractory manufacturing process. Raw material processing consists of crushing and grinding raw materials, followed if necessary by size classification and raw materials calcining and drying. The processed raw material then may be drymixed with other minerals and chemical compounds, packaged, and shipped as product. All of these processes are not required for some refractory products. Forming consists of mixing the raw materials and forming them into the desired shapes. This process frequently occurs under wet or moist conditions. Firing involves heating the refractory material to high temperatures in a periodic (batch) or continuous tunnel kiln to form the ceramic bond that gives the product its refractory properties. The final processing stage involves milling, grinding, and sandblasting of the finished product. This step keeps the product in correct shape and size after thermal expansion has occurred. For certain products, final processing may also include product impregnation with tar and pitch, and final packaging.
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1
TRANSPORTING 1
1
PM EMISSIONS
2
GASEOUS EMISSIONS
1
WEATHERING
STORAGE 1
(OPTIONAL) 1
2
CALCINING/ DRYING (SCC 3-05-005-02)
CRUSHING/ GRINDING (SCC 3-05-005-02)
(OPTIONAL)
1
SCREENING/ CLASSIFYING 1
1
1
DRY-MIXING/ BLENDING
STORAGE
PACKAGING
MIXING
FORMING 1
2
DRYING (SCC 3-05-005-01, -08) 2
1
FIRING
COOLING
(SCC 3-05-005-07, -09)
1
2
MILLING/ FINISHING
SHIPPING
Figure 11.5-1. Refractory manufacturing process flow diagram.1 (Source Classification Codes in parentheses.) 11.5-2
EMISSION FACTORS
1/95
Fused Products & Ceramic Fibers. Two other types of refractory processes also warrant discussion. ď Ž The first is production of fused products. This process involves using an electric arc furnace to melt the refractory raw materials, then pouring the melted materials into sand-forming molds. ď Ž Another type of refractory process is ceramic fiber production. In this process, calcined kaolin is melted in an electric arc furnace. The molten clay is either fiberized in a blowchamber with a centrifuge device or is dropped into an air jet and immediately blown into fine strands. After the blowchamber, the ceramic fiber may then be conveyed to an oven for curing, which adds structural rigidity to the fibers. During the curing process, oils are used to lubricate both the fibers and the machinery used to handle and form the fibers. The production of ceramic fiber for refractory material is very similar to the production of mineral wool.
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11.5.2 Emissions And Controls The primary pollutant of concern in refractory manufacturing is particulate matter (PM). Particulate matter emissions occur during the crushing, grinding, screening, calcining, and drying of the raw materials; the drying and firing of the unfired "green" refractory bricks, tar and pitch operations; and finishing of the refractories (grinding, milling, and sandblasting). Emissions from crushing and grinding operations generally are controlled with fabric filters. Product recovery cyclones followed by wet scrubbers are used on calciners and dryers to control PM emissions from these sources. The primary sources of PM emissions are the refractory firing kilns and electric arc furnaces. Particulate matter emissions from kilns generally are not controlled. However, at least one refractory manufacturer currently uses a multiple-stage scrubber to control kiln emissions. Particulate matter emissions from electric arc furnaces generally are controlled by a baghouse. Particulate removal of 87 percent and fluoride removal of greater than 99 percent have been reported at one facility that uses an ionizing wet scrubber.
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Pollutants emitted as a result of combustion in the calcining and kilning processes include sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), carbon dioxide (CO2), and volatile organic compounds (VOC). The emission of SOx is also a function of the sulfur content of certain clays and the plaster added to refractory materials to induce brick setting. Fluoride emissions occur during the kilning process because of fluorides in the raw materials. Emission factors for filterable PM, PM-10, SO2, NOx , and CO2 emissions from rotary dryers and calciners processing fire clay are presented in Tables 11.5-1 and 11.5-2. Particle size distributions for filterable particulate emissions from rotary dryers and calciners processing fire clay are presented in Table 11.5-3. Volatile organic compounds emitted from tar and pitch operations generally are controlled by incineration, when inorganic particulates are not significant. Based on the expected destruction of organic aerosols, a control efficiency in excess of 95 percent can be achieved using incinerators.
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Table 11.5-1 (Metric Units). EMISSION FACTORS FOR REFRACTORY MANUFACTURING: FIRE CLAY, EMISSION FACTOR RATING: D
a Factors represent uncontrolled emissions, unless noted. All emission factors in kg/Mg of raw material feed. SCC = Source Classification Code. ND = no data. b Filterable PM is that PM collected on or before the filter of an EPA Method 5 (or equivalent) sampling train. PM-10 values are based on cascade impaction particle size distribution. Charlie Chong/ Fion Zhang
Table 11.5-2 (English Units). EMISSION FACTORS FOR REFRACTORY MANUFACTURING: FIRE CLAY, EMISSION FACTOR RATING: D
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Table 11.5-3. PARTICLE SIZE DISTRIBUTIONS FOR REFRACTORY MANUFACTURING: FIRE CLAY, EMISSION FACTOR RATING: D
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Table 11.5-3. PARTICLE SIZE DISTRIBUTIONS FOR REFRACTORY MANUFACTURING: FIRE CLAY, EMISSION FACTOR RATING: D
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Chromium is used in several types of nonclay refractories, including chromemagnesite, (chromite-magnesite), magnesia-chrome, and chrome-alumina. Chromium compounds are emitted from the ore crushing, grinding, material drying and storage, and brick firing and finishing processes used in producing these types of refractories. Tables 11.5-4 and 11.5-5 present emission factors for emissions of filterable PM, filterable PM-10, hexavalent chromium, and total chromium from the drying and firing of chromite-magnesite ore. The emission factors are presented in units of kilograms of pollutant emitted per megagram of chromite ore processed (kg/Mg CrO3) (pounds per ton of chromite ore processed [lb/ton CrO3]). Particle size distributions for the drying and firing of chromitemagnesite ore are summarized in Table 11.5-6. A number of elements in trace concentrations including aluminum, beryllium, calcium, chromium, iron, lead, mercury, magnesium, manganese, nickel, titanium, vanadium, and zinc also are emitted in trace amounts by the drying, calcining, and firing operations of all types of refractory materials. However, data are inadequate to develop emission factors for these elements.
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Emissions of PM from electric arc furnaces producing fused cast refractory material are controlled with baghouses. The efficiency of the fabric filters often exceeds 99.5 percent. Emissions of PM from the ceramic fiber process also are controlled with fabric filters, at an efficiency similar to that found in the fused cast refractory process. To control blowchamber emissions, a fabric filter is used to remove small pieces of fine threads formed in the fiberization stage. The efficiency of fabric filters in similar control devices exceeds 99 percent. Small particles of ceramic fiber are broken off or separated during the handling and forming of the fiber blankets in the curing oven. An oil is used in this process, and higher molecular weight organics may be emitted. However, these emissions generally are controlled with a fabric filter followed by incineration, at an expected overall efficiency in excess of 95 percent.
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Table 11.5-4 (Metric Units). EMISSION FACTORS FOR REFRACTORY MANUFACTURING: CHROMITE-MAGNESITE ORE, EMISSION FACTOR RATING: D (except as noted)
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Table 11.5-5 (English Units). EMISSION FACTORS FOR REFRACTORY MANUFACTURING: CHROMITE-MAGNESITE ORE, EMISSION FACTOR RATING: D (except as noted)
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Table 11.5-6. PARTICLE SIZE DISTRIBUTIONS FOR REFRACTORY MANUFACTURING: CHROMITE-MAGNESITE ORE DRYING AND FIRING
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End of Reading 3. Charlie Chong/ Fion Zhang
Reading 4: The Fundamentals of Refractory Inspection with Infrared Thermography
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http://www.irinfo.org/articleofmonth/pdf/article_2_2006_james.pdf
The Fundamentals of Refractory Inspection with Infrared Thermography Abstract Thermography has been used to inspect the condition of refractory lined vessels and piping for many years now. It is a proven and accepted method for locating damaged and missing refractory material. Most companies however, do not fully understand the full benefits of performing refractory surveys. They mainly use thermography only before a plant turnaround to determine the extent of refractory damage in order to estimate the materials and labor needed for the repairs. This paper discusses the fundamentals of refractory inspection and how Thermal Diagnostics Limited has been using Infrared thermography in Trinidad and Tobago as an effective means of predicting areas of future refractory problems in addition to pre-turnaround surveys.
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http://www.tdlir.com/
Introduction First, let me introduce myself to those who do not know me. I am Sonny James, born and raised in Montreal, Canada but now living and working in beautiful Trinidad and Tobago. I have been doing thermography for the past thirteen years. My first thermographic inspection was helping my father with an electrical survey of a plastic injection factory. He strapped the camera on my shoulder and said, “find me some hot spots!” From that day on, I was fascinated by this remarkable technology. So, I am here today to talk about refractory inspections. Now, there may be some of you saying to yourselves, “what can a person from Trinidad and Tobago know about inspecting refractory?” And my answer would be this:
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The Island of Trinidad may well be considered the capital of refractory lined vessels. Trinidad is the largest producer and exporter of ammonia and methanol in the entire world. To date, we have 10 ammonia plants producing 5.7 million tons per year and 7 methanol plants producing 6.5 million tons per year. Trinidad and Tobago has the two largest methanol plants in the world; ATLAS Methanol that produces 1.7 million tons per year and M5000 that produces 1.8 million tons per year. We also have the largest direct reduced iron (DRI) steel plant in the world (1.4 million ton DRI MidrexTM Megamod) and much, much more. Most of these plants also surpass the technology that is currently found in North America and Europe as they are new, state-of-theart designs and much more efficient. The main reason Trinidad and Tobago is the world leader in ammonia and methanol production is due to its abundance of natural gas. In fact, the United States imports approximately 75% of its LNG directly from Trinidad and Tobago.
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What is just as amazing is that most of these plants are situated in an area only approximately 4 square miles called the Point Lisas Industrial Estate. In an average year, I inspect over 20 steam reformers, secondary reformers, boilers, transfer li ne piping, furnaces, and other refractory lined vessels. Because Trinidad has so many chemical plants situated so close to each other, it is imperative that high safety standards be put in place. One means of preventing a catastrophic failure is by regularly inspecting equipment with infrared thermography.
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Discussion Why Inspect for Refractory Problems? What many people are unaware of is that the repair cost of refractory lined equipment and the consequences that may occur due to refractory failure greatly exceeds that of rotating machinery and electrical failures. This is mainly because: 1. Repairing refractory lined equipment usually requires a total plant shutdown. This equipment is essential for the process and backups are not available, unlike a motor, pump or MCC breaker that can easily be switched over to a backup with minimal or no production loss. 2. The repair cost of refractory lined equipment is usually hefty, as it requires a lot more manpower labor, heavy equipment, materials and time to effectively carry out repairs. The main reason a vessel or piping is lined with internal refractory is because the internal temperature is so hot that it will destroy the actual steel shell of the vessel. So, refractory material is installed in order to minimize the heating of the external shell. Charlie Chong/ Fion Zhang
Internal Refractory Damage of Piping, Resulting in Critical Overheating of Steel
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Refractory also ensures that valuable energy is not being wasted and that vessel efficiency is kept at optimum levels. Refractory comes in various materials and application techniques such as brick, injectable, gunite, etc… Refractory is also exposed to tremendous stresses during a vessel’s operation. There is a great deal of expansion, contraction, heat, cyclic and convection (wind) stresses inside vessels such as reformers and boilers. There are even some refractory lined equipment that are under high pressures, such as transfer line piping. All of these stresses can cause refractory failure. When there is refractory failure, there is an inadequate insulating barrier between the extreme internal heat and the weak steel shell. This can lead to a vessel’s shell overheating and burn-through, resulting in dangerous gases, flames and heat exposure. Structural weakening can also occur, with the end result being a catastrophic failure. When you have a vessel or piping that is under high pressure, you have the dangers of a massive and potentially deadly explosion. It should be noted that when dealing with high-pressure equipment, the maximum allowable temperature of the metal is drastically reduced because of this added stress.
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Primary Reformer Wall Showing Multiple Refractory Problems
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The Inspection: When to Inspect? Refractory inspection is both an art and a science. Almost all thermographic inspections of refractory are performed while the vessel is operating under normal or full rates. This is because many thermographers and engineers are taught that IR should only be done when the equipment is under an adequate amount of load. This may be true for electrical and rotating equipment, but nothing can be further from the truth when it comes to refractory. The fact is that during the start-up cycle of a vessel, it goes through a series of changes in process and temperature that affect the refractoryâ&#x20AC;&#x2122;s behavior. When an IR inspection is conducted during the initial start-up period, you may notice several hot areas. This is usually due to cracks, gaps and voids in the refractory wall. These hot areas should be recorded for future reference, as these are the areas most prone to failure.
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With change of process, increased temperature and time during the start-up, you may notice these initial anomalies getting considerably hotter. Some areas may even reach close to critical temperature and even start to show visible signs of overheating on the external shell. These hot spots should also be recorded at this stage. The critical hot spots should also be closely monitored during the course of the start-up. When the vessel is close to or has reached full rates and temperature, you may notice that most of the hot spots observed during the stages of start-up have reduced in size and temperature. This is because the refractory has properly expanded and sealed off the cracks and gaps.
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You may also notice that some hot spots have remained. This is because there is some problem with the refractory at that area such as cracks, voids, failure, damage, etc. These problems should be recorded at this particular time, as these will be the majority of hot spots that will be observed during routine inspections while the vessel is under normal operation.
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36-Hour Timeline of Refractory Hot Spot During a Plant Start-Up
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By inspecting refractory during different start-up stages, you have recorded all current problems and you have also recorded potential areas that are susceptible to future problems or failure. You are now on your way to a successful predictive maintenance program for your refractory lined vessels by establishing your baseline data for future trending and monitoring.
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Houston, We Have a Problem! In refractory inspection, as with pretty much almost every other type of equipment inspected, there always comes the dreaded question of “How Hot Is Too Hot?” Now, when it comes to refractory, there is no one temperature or answer to your overheating problems. Many factors come into play when you’re dealing with a piece of equipment that usually results in total plant shutdown if repairs are to be done. Face it! Plants are in business to make money and the only way they make money is by production. So most of the time, shutting down a vessel for refractory repairs as a result of an excessive hot spot is usually not an option.
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Certain factors must be weighed first, such as: · Safety of plant personnel (I’d like to think that this is #1 on the list) · Affects on the equipment and end product · Business interruption costs · Current market price of the product being produced at the plant · And others… In most cases, overheating sections due to refractory problems can be temporarily overcome and controlled by certain methods. Remember that the main purpose of the refractory is to minimize the amount of heat exposed to the steel shell of the vessel. Therefore, if you no longer have this ability in a certain area due to internal refractory problems, you may be able to control and minimize the overheating on the external surface with the use of steam lances, hoses and spargers and in some cases with a constant flow of water.
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The process of external cooling will keep the shell of the vessel at that area from overheating and failure. The result: being able to keep the plant operational and making money. It is important to understand that although you now have a way of keeping the area cool via external means, you must still monitor this area on a frequent basis in order to verify that the cooling is effective and that the internal problem is not spreading or worsening. It should also be noted that this approach does not always apply to all critical refractory hot spots. There are some situations that you have no choice but to shut the vessel down to perform repairs. In some cases, you may be able to repair these overheating areas online with injectable refractory and other specialized online refractory repair techniques. You should also try to inspect and record all repairs in order to maintain a proper trend and database.
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Visible Example of Steam Cooling & Injectable Refractory Nipples
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Based on my years of experience inspecting refractory lined equipment, I have established a user defined Delta-T repair criteria that has proven to be quite efficient in prioritizing the severity of most refractory hot spots: # 1: 1°C - 35°C (2°F - 63°F): Indicates a possible minor problem & warrants periodic checks. # 2: 35°C - 70°C (63°F - 126°F): Indicates problem & warrants periodic monitoring. # 3: 70°C - 100°C (126°F - 180°F): Indicates concern & warrants frequent monitoring. # 4: >100°C (>180°F): Indicates high concern & warrants monitoring & corrective measures.
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This Delta-T repair criteria is very conservative and is only used as a guideline for plant engineers to determine what actions are warranted. Ultimately, the deciding factor as to exactly â&#x20AC;&#x153;How Hot is Too Hotâ&#x20AC;? is unique for every type of equipment. It is recommended that accurate Absolute temperatures be documented in order to reference with the maximum allowable shell temperature for that particular piece of equipment. It is only from these Absolute temperatures that an effective course of action can be taken.
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Identification of Refractory Problems When inspecting refractory lined piping such as a transfer line, locating and identifying problems due to refractory failure is fairly simple as there are usually no internal structures within the piping that may confuse the thermographer.
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Refractory Problems on a Typical Transfer Line Piping
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However, when inspecting vessels such as steam reformers, boilers, heaters, etc., it is important to know what the internal make-up of each vessel is. Internal supports and structures such as brackets, beams, trays, tubes and bolts that are attached to the shell of the vessel may actually be thermally visible during the inspection. This is because of heat conduction. So, knowing what is inside a vessel can help you in your analysis and diagnosis of your inspection.
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Top of Convection Box Showing Effects of Heat Conduction from Internal Anchors
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There are also certain areas within every vessel that are prone to refractory failure. Vessels are mainly designed by their functional or operational characteristics. Although the design of a vessel does accommodate refractory installation, there is no costeffective way to design a vessel to be fully refractory failure-proof. Some areas on vessels that are prone to refractory failure are: · · · · · · ·
Welded joint sections Corners and seams Man-way sections Top 180° of piping Roofs Opening areas such as sight-ways and ports Burner areas
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Although these are the most common places where refractory failure occurs, it is not uncommon to have problems and failures on the vertical wall sections and bottom flooring. It is important to inspect every accessible part of a vessel and piping in order to perform an effective refractory inspection. That is why it is important to take your time and inspect in a systematic way, making sure everything is inspected because the area you missed will quite often be the area that fails. It’s good practice to first perform a walkthrough of the entire vessel or piping system before turning on your imager. By doing this before your survey you benefit from: · Knowing how and where to start the inspection and what route to take · Identifying potentially unsafe and hazardous conditions · Identifying visibly noticeable problems and flagging them for your IR inspection
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Conclusion With the highly competitive markets out there, it is important to keep your production costs down as well as try to prevent equipment failures. By using Infrared Thermography actively and frequently on refractory lined equipment, you are in a better position to â&#x20AC;&#x153;predictâ&#x20AC;? problems, keep your equipment running during problem times and also properly schedule repairs and estimate the total materials needed for these repairs. The notions that refractory inspections should only be performed just before a scheduled plant turnaround in order to estimate repairs or be performed only when a visible problem is evident should be reviewed. Most refractory lined equipment is critical to your plantâ&#x20AC;&#x2122;s operation and should therefore be monitored on a regular basis.
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Point Lisas Industrial Estate Trinidad
Charlie Chong/ Fion Zhang
http://www.tdlir.com/
Point Lisas Industrial Estate Trinidad
Charlie Chong/ Fion Zhang
http://www.tdlir.com/
End of Reading 4. Charlie Chong/ Fion Zhang
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Good Luck!
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Good Luck!
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