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By Thomas M. Barczak

Purchasing a new set of longwall shields requires a substantial investment. A poor shield design can lead to economic hardships, safety concerns for the mine workers, and closure of the mine. This paper addresses several key points that should be considered in the procurement process: (1) understanding your goals and the logic in selecting a higher capacity shield, (2) the importance of completing performance testing before production shield fabrication begins, (3) making sure performance testing is properly done, (4) measuring load(stress) development during performance testing, (5) testing a shield to failure, and (6) the value of buying extra shields. In addition, several challenges are proposed for consideration in future shield designs. These include (1) 100,000 life-cycle expectancy, (2) improved hydraulic diagnostic capability, (3) smart load control by optimizing setting pressures, (4) lubricated link joint design concepts, (5) composite material applications to reduce shield weight, (6) incorporating periodic weighting predictive algorithms into the data-processing software, (7) advanced component load measurement on two to three specially instrumented shields to detect loading in the structural components, and (8) constant set leg cylinder design.

Jan 10, 2000

By H. W. Graham

AS these annual occasions in honor of Henry Marion Howe continue through the years, there is progressively less likelihood that the lecturer will have had personal knowledge of Dr. Howe. The present speaker is one of those who unfortunately had no opportunity to come under the inspiring presence of this great metallurgist. A review of Howe's work shows it to cover a comprehensive range of interests and to evidence an impressive richness of detail. Not only was Howe at home in the laboratory, but he was familiar with the processes of iron and steel making and had a real understanding of them writings include much that is descriptive of processes with a wealth of material that is becoming of increasing historical value. He recorded his studies of the theoretical aspects of processes and published at least two process classifications, one in 1890 that was lengthy and somewhat theoretical, and a second in 1906 that was more of a practical listing. Wide as Howe's field of interest was, it is significant of the circumstances of his time that he gave little consideration to raw materials or to their effect on iron and steel making processes. In 1933, Waterhouse, Howe lecturer for that year, presented a descriptive summary of the major steelmaking processes, and in 1946 Joseph discussed the blast furnace process. Otherwise Howe lectures have not dealt with processes as major subjects. In today's lecture, with no effort to describe the mechanical arrangements of iron and steel making facilities, it is proposed to examine the essential technological elements of the processes, to explore the inter-relation of these elements, and particularly to seek recognition and understanding of those factors which determine why certain processes are or are not used. The discussion of this lecture will deal with the major well-known large tonnage processes, with only such attention to processes of minor tonnage and special character as may be warranted for explanation by contrast. Subject to the errors of generalization and the short- comings of condensation involved in presentation limited to a single hour, it is proposed to examine broadly but intensively those operations which convert raw materials into steel. It is an innovation for a Howe lecturer to discuss the raw materials of the iron and steel industry, but the changing circumstances of passing years intensify the influence of raw materials on processes and require the metallurgist to be alert for the process adjustments that may become advisable or mandatory. For a half century the metallurgical processing of iron and steel has followed a surprisingly straight path, but this does not necessarily mean that there are no curves in the road ahead. Ages ago primitive man came to know iron in its metallic form, not only by the

Jan 1, 1947

By D. J. Barrett, M. A. Sochocky

INTRODUCTION Summary of Factors Influencing Comminution Circuit Design The selection of an appropriate comminution circuit for a specific ore is one of the most important decisions in the design of a processing plant. The importance is related to the fact that the capital and operating costs for crushing and grinding plant generally represent, as is well known, the major portion of the plant costs. This chapter will, therefore, identify as many as possible of the factors which influence the selection of a comminution circuit. The number of factors which will have to be considered for any comminution project will depend, among other things, on the type of project. If, for example, the project is an entirely new mining development, then most, if not all, the factors identified will have to be analyzed. If the project is an expansion of a developed mining operation or if the new orebody is adjacent to a viable operation, then the existing operation will influence the choice of factors or design constraints which need to be considered. The existing infrastructure or supporting systems may be quite adequate to accommodate the requirements of any expansion or new development. Hence, those factors may not have to be considered. To cover, however, the widest spectrum of projects, the factors which have been identified in this chapter are those which will have to be considered for the most complex of projects, that of developing an entirely new mining operation. The range of factors is as broad as the range of different ore types. Thus, each development must be treated with individualized care. The most important step in the development is the analysis and understanding of the ore characteristics. The hardness of the ore, its abrasiveness, friability, moisture content, grade, mineralization including gangue mineralization, liberation size, chemistry, and other characteristics should be the first to be analyzed in the investigation. The next should be the determination of factors such as plant size, throughput, location, climate, accessibility, and availability of water. The selection of samples for initial bench scale work and bulk sampling (when needed) for further

Jan 1, 1982

By K. K. Wu

In some cases, coal barrier pillars must be relied on to withstand high hydrostatic pressures in order to prevent inundation of active mine workings. Such barriers are particularly important in areas, such as parts of West Virginia, where much of the future mining is down dip of mines which have been abandoned, or are currently being worked. Also, where multiple seam mining is conducted, a barrier pillar in one mine may be critical to safety in a mine in a lower seam. MSHA's Coal Mine Safety and Health district offices and the Mine Waste and Geotechnical Engineering Branch of the Pittsburgh Technical Support Center, have recently been involved in the study of barrier pillars in Kentucky, Virginia, West Virginia, Ohio and Oklahoma. In this paper, the factors involved in determining the required width of pillar are discussed, past practices for sizing barriers are reviewed, and related current Federal regulations are examined. In addition, the results of laboratory testing of bottom rock are presented.

Jan 1, 1980

By Raymond Mancha

THE number of installations of propeller mine fans completed during the years of 1936 and 1937 is evidence of the increasing popularity of the propeller fan with the American mining industry. During the period from 1931 to 1936, there were several different low-pressure, low-efficiency propeller fans available, which filled a definite need in replacing inefficient centrifugal fans operated at comparatively low pressure by means of purchased power. Since 1936, however, the trend toward the propeller fan has greatly increased, as propeller fans are now available practically without pressure limitations and capable of efficiencies high enough to warrant replacement of efficient centrifugal fans in many instances. Few manufacturers of propeller mine fans base their fan-operating characteristics upon similar test methods, primarily because of inadequate facilities for testing in the factory and the need of a test code incorporating a calibrated duct or nozzle that makes possible the testing of large propeller fans quickly, accurately and without prohibitive expense and space requirements. As a result, fan manufacturers have resorted to various methods for testing large propeller fans in the factory, and different yardsticks have produced uncomparable and often inaccurate performance data. It is the purpose of this paper to describe and discuss in detail the test procedure of the Jeffrey Manufacturing Co., which has been proved both accurate and practical. Fig. 1 shows a plan, a side elevation and two end elevations of the test duct with a propeller fan of the exhaust type in place. Testing propeller fans exhausting permits greater accuracy than testing these fans blowing, because in the former uniform flow conditions are more easily established at Pitot tube stations where fan pressure and air-volume measurements are desired. Any residual rotation remaining in the air discharged from a propeller fan blowing into a test duct must be removed before an attempt is made to obtain accurate pressure and volume readings. Although various devices for straightening the air may be placed between the blowing fan and the volume-measuring station without resulting complications, uniform flow so obtained at the pressure-measuring station necessitates corrective calculations to compensate for duct resistance

Jan 1, 1939

This chapter defines light as a type of energy, and tells how different features of light are measured. It 1s important to understand the units of light measurement because they are used throughout the rest of the book. But more Important, this will help you to understand the "regs" and how to get the best out of the lighting you have available! By the time you complete this chapter, you should know what candle-power, foot-candle, and foot-lambert refer to, and you will also be able to tell why the helmet that the new miner wears appears orange to human eyes. Light that you "see" is really radiant energy that hits the retina of the eye. Radiant energy moves out from a light source much like a series of bullets from a number of machine guns being fired at the same time in all directions.

Jan 1, 1976

By Fred N. Kissell

In This Chapter [The explosibility of methane gas mixtures Effect of pressure and temperature on explosibility Less common sources of methane ignitions The amount of methane stored in coal Forecasting the methane emission rate Layering of methane at the mine roof When the recirculation of mine air is hazardous The importance of higher air velocity in preventing methane explosions and Mine explosions, barometric pressure, and the seasonal trend in explosions] Dealing with methane in mines and tunnels requires knowledge of the circumstances under which dangerous accumulations of methane are likely to occur. This knowledge involves the properties of the gas itself, an awareness of where these accumulations are likely to occur, and facts on how methane mixes safely into the mine air. The other chapters in this handbook address the handling of methane under a variety of specific circumstances, such as at continuous miner faces or coal storage silos. This chapter addresses some broad concepts that serve as a foundation for the suggestions provided in other chapters. THE EXPLOSIBILITY OF METHANE GAS MIXTURES Methane entering a mine or tunnel often enters as a localized source at high concentration. Figure 1–1 depicts a cloud of methane being diluted into a moving air stream. In this illustration, methane enters the mine from a crack in the roof. As the methane emerges from the crack, it progressively mixes with the ventilation air and is diluted. In the event that this progressive dilution reduces the concentration from 100% to 1%,2 as shown in Figure 1–1, the methane passes through a concentration range of 15% to 5%, known as the explosive range. In the explosive range, the mixture may be ignited. Above 15%, called the upper explosive limit (UEL), methane-air mixtures are not explosive, but will become explosive when mixed with more air.

Jan 6, 2006

By George Hunt

THE first practical treatment of wood to prevent decay was devised early in the 19th century. At that time the oaken navy of England, when . the nation was fighting for its very existence, seemed doomed to annihilation by the swift ravages of decay. The acute situation inspired a desperate search for preventive measures and resulted in the development of the Burnett, Bethel and Kyan processes for impregnating wood with zinc chloride, coal-tar creosote and mercuric chloride, respectively. In the century that has elapsed, their use has spread throughout the world and the three original preservatives are used today in enormous quantities. Meanwhile, improved processes have been developed, new preservatives discovered, and the practice of impregnating wood to make it last longer has attained a position of major importance in the field of structural materials. USE OF PRESERVATIVES BY- THE RAILROADS In the application of wood preservatives in the United States the railroads have been the leaders for the past 50 years or more.. Having found, that decay is the chief cause of the early destruction of wood and that preservative treatment is the remedy, they have treated their ties and timber in increasing amounts(1) ?-in 1925 about 220,000,000 cubic feet. By preservative treatment the Santa Fe Railroad saves annually 1,500,000 ties in its 18,000 miles of track, and many other railroads effect similar savings. (2) In like manner the life of wooden bridges and trestles,(3) poles, marine piling, water tanks and other wooden railroad structures has been greatly increased, reducing the amount of timber required annually to maintain them.(5),(7)

Jan 2, 1927

By George Hunt

THE first practical treatment of wood to prevent decay was devised early in the 19th century. At that time the oaken navy of England, when the nation was fighting for its very existence, seemed doomed to annihilation by the swift ravages of decay. The acute situation inspired a desperate search for preventive measures and resulted in the development of the Burnett, Bethel and Kyan processes for impregnating wood with zinc chloride, coal-tar creosote and mercuric chloride, respectively. In the century that has elapsed, their use has spread throughout the world and the three original preservatives are used today in enormous quantities. Meanwhile, improved processes have been developed, new preservatives discovered, and the practice of impregnating wood to make it last longer has attained a position of major importance in the field of structural materials. USE OF PRESERVATIVES BY THE RAILROADS In the application of wood preservatives in the United States the railroads have been the leaders for the past 50 years or more. Having found that decay is the chief cause of the early destruction of wood and that preservative treatment is the remedy, they have treated their ties and timber in increasing amounts(1)?-in 1925 about 220;000,000 cubic feet. By preservative treatment the Santa Fe Railroad saves annually 1,500,000 ties in its 18,000 miles of track, and many other railroads effect similar savings. (2) In like manner the life of wooden bridges and trestles,(3) poles, marine piling, water tanks and other wooden railroad structures has been greatly increased, reducing the amount of timber required annually to maintain them.(5),(7)

Jan 1, 1927

By J. S., Douglas

IN 1880, the late James Douglas, LL.D., was superintendent of the Chemical Copper Co., operating the Hunt & Douglas process for the treatment of the siliceous copper ores of the Jones mine at Phoenixville, Pa. In conjunction with this a refining furnace was operated. After correspondence with Ben Williams, of Bisbee Ariz., who was commencing the mining and smelting of the Copper Queen ore. Dr. Douglas decided-to make his first journey to Arizona. While making plans for the trip lie visited a friend in Philadelphia, a .Mr. Logan, a prominent lawyer. He, through Professor Treadwell, brother of the discoverer of the great Treadwell gold mine of Douglas Island, Alaska, had an option with his min¬ing partner, Mr. Lenig, on the Eureka and Wade Hampton claims near the headwaters of the Verde River in Yavapai County, Arizona. These two claims, later the source of practically all of the wealth of the Jerome district, were then owned by C. P. Head and Co. Prescott merchants. Hugo Richards, banker, and formerly sutler at Camp Apache; Rod and John McKinnon prospectors and Nova Scotians; and perhaps one or two 'other owners of minor interests. Mr. Logan, hearing of Dr. Douglas intended trip to Bisbee, asked him to go first to see the two mining prospects, and this, Douglas, in need of the $500 fee, agreed to do as the time on the option on the claims was running short.

Jan 1, 1935

By William H. Love

ATLAS shaft was sunk to explore at depth a portion of the eastern end of the dry belt, or silver belt, of the Coeur d’Alene mining district. The Atlas mine is a mile east of Mullan and is on the south side of the Osburn fault. Equal partners in the venture are Hecla Mining Co., Newmont Mining Co., New Jersey Zinc Co. and Atlas Mining Co., the financing being equally shared by Hecla, Newmont, and New Jersey Zinc. As outlined the project had as its goal deep exploration of prominent structures developed in the Atlas in upper levels. Plans called for deepening the shaft from the 800 level to the 2400 level with subsequent drifting, crosscutting, and diamond drilling on the 2400.

Jan 11, 1954

By AIME AIME

THE following is the discussion of a paper, with the same title, by N. L. Alison, which appeared in our February issue: E. F. Tillson commented that while the fundamentals are well presented it would have been of interest to him to have had the author add some of his own experiences with fan installations. A. W. Hesse remarked concerning the use of the forward curved blade fan on the surface at a metal mine which has, ordinarily, but few airways, that the farther they are driven, the higher the resistance rises, and less air will be delivered, as the water gage will remain constant with a consequent loss in quantity. D. Harrington added that the metal mines do not or¬dinarily install fans until the mine is well developed, so changes are relatively slower after fan installation than at a coal mine.

Jan 1, 1930

By F. W. Brackebusch, R. O. Sack

"A method for determining the fineness of Au in electrum from the composition of fahlore coexisting with pyrite and chalcopyrite is presented. This method is based on previously published experimental brackets and activitycomposition models for electrum and fahlore, and it is potentially useful for defining temperatures of hydrothermal mineralization and retrograde evolution of precious metals deposits. The authors demonstrate that it successfully predicts compositions of electrum reported for this assemblage in the literature and illustrate its application for three gold-quartz vein deposits from the Coeur d’Alene mining district, Idaho, that are prospects of the New Jersey Mining Company, the Coleman vein, High-Grade prospect, and Silver Strand mine. Temperatures calculated from average electrum compositions estimated from gravity concentrates (molar Au/(Au+Ag) = 0.76-0.39) and from microprobe analyses of the fahlores (molar Ag/(Ag+Cu) = 0.039 ± 0.004, Zn/(Zn+Fe) = 0.57 ± 0.03, As/(As+Sb) = 0.23 ± 0.02) from the Coleman vein indicate that the electrums underwent retrograde re-equilibration to temperatures between about 80°C and 240°C, roughly 80°C below the temperature of hydrothermal mineralization and 10°C to 40°C above the temperature inferred for retrograde equilibration of Fe and Zn between sphalerite and fahlore. Fahlores from the High-Grade prospect [molar Ag/(Ag+Cu) = 0.009 ± 0.004, Zn/(Zn+Fe) = 0.55 ± 0.11, and As/(As+Sb) = 0.04 ± 0.03] and Silver Strand mineralized zone [molar Ag/(Ag+Cu) = 0.10 ± 0.04, Zn/(Zn+Fe) = 0.63 ± 0.02, and As/(As+Sb) = 0.06 ± 0.02] exhibit strong core to rim depletions in Ag due to retrograde operation of the reaction1/10Cu10Fe2Sb4S13 + Ag + FeS2 =Cu-fahlore electrum pyriteCuFeS2 + 1/10Ag10Fe2Sb4S13chalcopyrite Ag-fahlorewhich proceeds to the left with decreasing temperature. Electrum inclusions in arsenopyrite from the High-Grade prospect [molar Au/(Au+Ag) = 0.90 ± 0.02] define a minimum bound on the temperature of hydrothermal mineralization of 273°C, and the temperatureelectrum composition curve constructed for the most Ag-rich fahlore in the Silver Strand mine indicates that the fineness of its electrum is significantly less than in the other deposits."

Jan 1, 2004

Assure fail-safe stopping of a mining vehicle immediately following a loss of electric power. Approach A separate emergency brake system which actuates when electrical power is interrupted, was installed on several mining vehicles and tested in a long-term underground mining demonstration. How It Works Separate, spring-actuated brakes, which press against brake discs, are used to stop the vehicle following power failure. To allow norm al movement of the vehicle, hydraulic oil under pres? sure from the vehicle's hydraulic system is directed to a spring? loaded piston in each emergency brake housing. That pressure causes the piston to compress the spring and relieves the spring pressure against the puck, thereby allowing the brake disc to turn freely. See Figure 1 A. If the electrical power fails or if the machine is turned off, a valve in the hydraulic line to the emergency brakes opens. That valve, shown as ?Solenoid Valve (automatic)" in Figure 1, which is normally held closed by its electrical solenoid while the vehicle is electrically powered, is opened by the spring in the valve assembly. The pressure in the hydraulic line which is connected to the emergency brakes then drops to

Jan 1, 1978

By M. R. Swaan, G. J. Stewart

"ABSTRACTThe application of failsafe techniques to ask the ""What if"" questions about any process has been well established in the chemical industry for many years. The unusual number of fatalities that occurred in Ontario during 1986-87, prompted Inco management to look at the Fail Safe techniques as a method of improving safety performance.INTRODUCTIONOne of the major areas at any time for potentially disastrous accidents is the shaft, where all men and materials must travel. In April 1987, Inco's Thompson Mine's first Fail Safe Team was established to look at its shaft operations. The initial group of eight people was made up of hourly equipment operators, mine foremen, engineering, maintenance and the superintendent. This group took the name of Shaft Risk Analysis Team or SRAT.The many tasks or jobs that are performed in a shaft prompted the team to divide the work under six major headings; slinging, moving men, skipping, dewatering, shaft inspections and moving materials. Each of these areas contained many different tasks which are interrelated. The only way to understand this interrelationship was to flow chart the steps that actually occur in getting any job done.The flow charting is done by the foreman and operators using existing standard manuals and their experience of what actually takes place. In many cases, it soon became apparent that they had been ""working around"" many problems created by their standards. Fine tuning of these flow charts takes place at the weekly meetings, where input from all involved leads to a better understanding of the actual job being analyzed and its potential hazards. Two major points need to be emphasized in getting good flow charting at a mine:I. It must never be blame oriented or you will never discover how the jobs are actually done and hence you won't know what to improve.2 . All team members must have equal voting rights in deciding how to put the charts together so that they have ownership of the finished product. It is far too easy to end up with amanagement view of the way it should be. Many different techniques or methods are being employed to improve the tasks and reduce the risks associated with any job once the basic flow chart is established. The ones found to be the most useful are highlighted."

Jan 1, 1989

By Anup Kumar Mandal, Sanjoy Chowdhury, Biswajit Das

"Tailing pond of an iron ore mine necessitated raising the height of its embankment to create additional storage capacity. The tailing pond is located in eastern India and raising the height of embankment was going on during the month of January, 2014. Upstream method of construction was adopted since there was no space available at the downstream side. During the construction, about 200 m stretch of the north east embankment of height about 5.5 m failed forming a classical slip circle on the upstream side involving about half the top width of the embankment. To find out the root cause of the slope failure, detail geotechnical investigation work was carried out within the embankment as well as in the adjacent areas within the pond. About 7.5m thick very soft tailings were detected below the constructed embankment. Shear strength of the soft tailing was very low and was inadequate to sustain imposed embankment load. This resulted in the failure of the embankment. Analysis of the tailing deposit revealed that even after failure, settlement was continuing due to imposed embankment load. Under normal onedimensional consolidation, the tailing deposit would have taken about 5.7 years for 90% of primary consolidation. However, in order to mitigate the scarcity of storage space, mining plan required raising the height of the embankment within next six to eight months. Therefore, despite the fact that there was a failure, it was necessary to continue the construction on the underlying weak stratum. The system was redesigned with installation of prefabricated vertical drains (PVDs) to accelerate the consolidation process thereby gaining the in-situ strength. Strength was additionally enhanced by installing geogrids in multiple layers. It stabilized the existing embankment and also ensured construction of additional height over and above the existing embankment.INTRODUCTIONBeneficiation plant in the Iron mines enhances the mineral content by separation of contaminants and fines. The residue (waste material) is called tailings/tailings depending upon the grain sizes. These tailings in a slurry form are generally disposed in a pond called as tailing pond/tailing pond. Height of embankment of such ponds is increased either by upstream or by downstream or by centrally raising methods in different phases as quantum of deposition in the pond increases with time."

Jan 1, 2015

By T. M. Ahmed

Sherritt International Corporation experienced corrosion failures with the 316L stainless steel tubing in a high-pressure still condenser employed for ammonia recovery. A detailed failure analysis was conducted on the condenser tubing to determine the mode and the root cause of the failure. The analysis included both optical and scanning electron microscopy (SEM) of the inner and outer surfaces of the tube as well as characterization of the corrosion products using energy-dispersive X-ray spectroscopy (EDX). Results revealed that the corrosion attack was confined to the first ?100 mm of the tubing at the inlet where the tube was connected to the top tubesheet. The tube suffered both external stress-corrosion cracking (SCC) and crevice corrosion from the shell side (water side), and wall thinning of the inner surface (the tube side) due to erosion corrosion. It was evident that failure of one of the tubes occurred due to SCC that penetrated the whole wall thickness and resulted in a leak failure. Some prevention measures are proposed to avoid this type of corrosion attack in the future.

Jan 1, 2005

By Andrelio Marcos Ribeiro, Lucio Ribeiro Camisao, Antonio Carlos Ataíde, Alan de Sousa Pereira, Renato Siqueira Campos

The annealing and pickling line n. 1, responsible for the production of stainless steel 3xx, 4xx and 430a in thicknesses from 4 to 0.4 mm, has two vertical strip accumulators. These are intended not to let the material exceed the determined time in the furnace and in the pickling, and consequently do not cause defects like burning and excessive pickling. Strip accumulator n. 1 avoids the line from stopping during welding execution of the coils in the welding machine. In sequence, the strip accumulator n. 2 avoids the line from stopping at the end cutting of the tips, and in the coils removal from the pickling. The strip accumulators have a roller table that during the strip accumulation moves vertically downwards while its counterweight moves vertically upwards, and do the inverse movement when the material is released. On December 12th 2018, the failure occurred in the strip accumulator n. 1, where it was verified that the shaft of one of the pulleys had been fractured by high-cycle mechanical fatigue, which was characterized by alternating bending. With the fracture of the shaft, occurred the unevenness of the counterweight that damaged the guides. Failure analysis of this occurrence was based on the PDCA methodology, when was verified a weld between the shaft and the pulley. The analysis of the microstructure transformation in the molten zone, in the heat affected zone and in the base metal was carried out in an optical microscope, and no abnormality was observed. It was also carried out the end test by penetrating liquid, finding an inadequate weld in its geometry, as well as longitudinal trunks along the center of the weld bead. However, after a huge investigation of the causes, it was found that the failure was triggered by an inadequate design of the pulley shaft. It was also verified that the shaft had an open measure, inadequate for the operational context. After the analysis, action plans were drawn up based on the FMEA methodology to inhibit the failure recurrence.

Oct 7, 2019

By N. Parnian

"Carryover of caustic soda (NaOH) in the steam path caused catastrophic failure of superheater 304H stainless steel tubes in a steam generator and led to an unexpected shutdown after just five months of continuous service of petrochemical following the start of production. The cause of the failure was studied, with a focus on the formation of sigma phase in the weld joint and effect of caustic embrittlement on stress corrosion cracking (SCC). The cracks were examined at the seam weld, heat affected zone (HAZ), and Ubend areas. Hardness was measured for the base metal, HAZ, and weld metal, and microstructures were examined using optical microscopy and scanning electron microscopy (SEM). Crack initiation is attributed to gouging on the precipitated carbide at the HAZ and also the formation of sigma phase in the weld metal, as shown by energy dispersive X-ray (EDX) analysis. In addition, cracking was propagated by caustic embrittlement because of residual stresses and hammering. Finally, the characteristic feature of fracture was illustrated by SEM fractography, and consists mostly of intergranular SCC and some quasicleavage transgranular. INTRODUCTIONThree key factors are needed for the initiation and propagation of intergranular stress corrosion cracking (IGSCC): a susceptible material, a corrosive environment, and sufficient stress. Although austenitic stainless steels are susceptible to sensitization and IGSCC, they are widely used in boiler and superheater tubes because of their high corrosion resistance, high oxidation resistance, acceptable mechanical characteristics at elevated temperatures, and low cost.Sodium hydroxide is injected to neutralize acidic constituents in the steam path, but caustic can concentrate in boiler tubes and attack the surface metal (known as gouging) even traces of caustic in the steam can deposit on surfaces and cause local concentrations of several percent (ASM handbook, 1992). Not only sensitized grains but also sigma phase formed in the weld metal can initiate caustic cracking. In this research, the cause of the failure of 304H stainless steel superheater tubes in a methanol petrochemical plant in Iran was studied with a focus on the effects of caustic embrittlement on IGSCC."

Jan 1, 2012

By Cleber Caetano Thomazi

Rotary kilns are continuous process equipment used on calcining of nickel ore. The chemical and physical reactions are created by means of heat up the material to predetermined temperatures. Tertiary air fans are attached to the kiln shell to maintain oxidizing/reduction conditions. Special ducts orientate the air flow inside the kiln. In the present work, two types of failure on distinct tertiary ducts mounted on the same kiln are reported. Chemical analysis, hardness test, metallographic and fractographic examinations were carried out. Fabrication related problems and creep were identified as the root causes of damages.

Oct 30, 2017