Study Of Microstructure Degradation Of Boiler Tubes Due To .
Kavita Sankhala et al Int. Journal of Engineering Research and ApplicationsISSN : 2248-9622, Vol. 4, Issue 7( Version 2), July 2014, pp.93-99RESEARCH ARTICLEwww.ijera.comOPEN ACCESSStudy of Microstructure Degradation of Boiler Tubes Due ToCreep for Remaining Life AnalysisKavita Sankhala*, Zeeshan Gauri**, Pradeep Sharma***, Dharmendra KumarJainDepartment of Mechanical Engineering, Career Point University, KotaGuide, Department of Mechanical Engineering, Govt. Polytechnic college KotaABSTRACTIn the current scenario of power shortage in India, the main objective is to ensure availability of power plantand increasing its reliability. During assessment ,testing and inspection a simple question has to be asked againand again‖ How long the particular power plants can be operated safely and cost-effectively with satisfyingincreased requirements and operational availability with reduced pollutant emissions, even after their designedlife. So to answer this important question regarding the operational capability of the existing plant the remaininglife analysis (RLA) has to be done. The condition of the plant equipments can be assessed only by way of aRLA methodology. On the basis of RLA proper decision can be made about the plants safety and availability.There are many methods to carry out the RLA of the critical components out of which ―microstructure study‖ isa method. In this paper we have tried to outline the RLA procedures and review the various damage mechanismsbased on microstructure study. It is also presents the microstructure changes and properties of 106720 servicehour exposed boiler tube in a 120 MW boiler of a thermal power plant.Keywords - service exposed boiler tubes, microstructure, remaining life analysis, creep.I.INTRODUCTIONIn recent years, from oil refinery topetrochemical and power generation industries, moreand more plants throughout the world are facing acommon issue—aging equipments like turbines,boiler tubes usually over 15 to 30 years old.Questions bearing in managers’ minds are what is themachine condition and whether they can becontinually operated (if yes, how long). The answeris important not only for safety concerns but also forcost reduction, especially with today’s limitedbudgets, and is more critical with the equipmentsworking at elevated temperature. Therefore, there isan increasingly strong desire for the engineeringaftermarket service to perform ―Remaining LifeAssessment‖ of the equipments which are working athigher temperatures like boiler tubes.Remaining life assessment is to use metallurgicaland fracture mechanics Methodologies to predict theremaining life of structures and components that havebeen in service for an extended period of time usuallyclose to or beyond the designed life. Traditionally, ifparts are found with material degradations ordamages during an overhaul, they might be scrappedand replaced for risk-free consideration; even thoughthey might have some useful life. Remaining lifeassessment offers a possible tool to estimate theuseful remaining lifetime and avoid prematurescrapping of the parts. So remaining life assessmentis considered to be attractive method / process forcost reduction and reduction downtime.www.ijera.comRemaining life assessment has often been improperlyreferred to as ―life extension.‖ Actually this analysiscannot extend the lifetime of the components. It canonly assess the useful remaining lifetime, based onthe metallurgical examinations and ssessments indicate the need for extensivereplacements and refurbishments, life extension maynot prove to be a viable option. Above and beyondthis objective, remaining life assessment technologyserves many other purposes. It helps in setting upproper inspection schedules, maintenance procedures,and operating procedures. It should, therefore berecognized at the outset that development oftechniques for remaining life assessment is moreenduring in value and broader in purpose than simplythe extension of plant life. For instance, it has beenpossible to extend the inspections, on the basis ofassessments based on fracture mechanics, resulting inconsiderable savings.In implementing remaining life assessmentprocedures, appropriate failure definition applicableto a given situation be determined at the outset, andthe purpose for which the assessment is being carriedout must be kept in mind. While the feasibility ofextended plant life may be one objective, a morecommon objective is the setting of appropriateintervals for inspection, repair, and maintenance. Inthis context, remaining life assessment procedures areused only to ascertain that failures will not occurbetween such intervals. It should never be assumed93 P a g e
Kavita Sankhala et al Int. Journal of Engineering Research and ApplicationsISSN : 2248-9622, Vol. 4, Issue 7( Version 2), July 2014, pp.93-99that having performed a remaining life assessmentstudy for a 20 life extension, one could then wait for20 years without monitoring. Periodic checks toensure the validity of the initial approach areessential. In this sense, remaining life assessmentshould be viewed as an ongoing task, rather than aone-time activity.A phased approach, in which the initial levelincludes no incursive techniques followed by otherlevels of actual plant monitoring, then followed bynondestructive inspections and destructive testswould be the most logical and cost-effectiveapproach. In Level I, assessments are performedusing plant records, design stresses and temperatures,and minimum values material properties from theoriginal equipment manufacturer (OEM). Level IIinvolves actual measurements of dimensionstemperatures, simplified stress calculations, andcoupled with the use of minimum material propertiesfrom the OEM. Level III involves in-depthinspection, stress levels, monitoring, and generationof actual material data from removed from thecomponent (destructive testing). The degree of thedetail and accuracy of the results increases fromLevel I Level III, but at the same time, the cost of theassessment also increases. Depending on the extentof the information available and the results obtained,the analysis may stop at any level or proceed to thenext level as necessary.In evaluating the failure criteria or remaininglife, one needs to understand the various failuremechanisms that can occur. In boiler machinerycomponents which are working on elevatedtemperature, the failure criteria can be governed byone or a combination of the following failuremechanisms: Fatigue—high cycle or low cycle Corrosion/corrosion fatigue Stress corrosion cracking (SCC) Erosion—solid particle or liquid Erosion corrosion Creep rupture/creep fatigue High temperature corrosion/ Mechanical (foreign objective) damageHowever, in remaining life assessment, usuallyonly those mechanisms depending on temperatureand time are taken in to account. For example, forboiler tubes engineers usually focus on thermal stressinduced low cycle fatigue, creep rupture andtempering embitterment cracking. These failuresusually are slow processes; therefore, they can beassessed and forecasted by examining the warningevidences in the material.Countless works have been done to study thebehaviors of fatigue crack initiation/ propagation andcreep or rupture in steels and alloys. Scientist andengineers have reached such a level that, by knowingthe flow size or microstructure deterioration /www.ijera.comwww.ijera.comdamage. One can theoretically calculate and predictthe remaining life time of the parts, based on theknowledge of the material properties andunderstanding of the stress distribution.II.CREEP LIFE ASSESSMENTMETHODOLOGYCreep is high temperature damage mechanismwhich includes time dependent deformation and hightemperature creep cracking. In other words creepdamage is the result of permanent plastic deformationat elevated temperatures and at stresses much lessthan the high temperature yield stresses.Microstructure damages detected by the presence ofcreep voids at the grain boundaries which havetendency to coalescence during the time and form acracks these cracks generally propagates in an intercrystalline manner in components that fail over anextended time. So the Life assessment methodologybased on creep failure analysis can broadly beclassified into three levels[1]. Level 1 methodology isgenerally employed when service life of thecomponents is less than 80% of their design lives. Inlevel 1, assessments are performed using plantrecords, design stress and temperatures, andminimum values of material properties fromliterature. When service life exceeds 80% of thedesign life, Level 2 methodology is employed. Itinvolves actual measurements of dimensions andtemperatures, stress calculations and inspectionscoupled with the use of the minimum materialproperties from literature. However when lifeextension begins after attaining design life, Level 3methodology is employed. It involves in-depthinspection, stress analysis, plant monitoring andgeneration of actual material data from samplesremoved from the component. The details andaccuracy of the results increase from level 1 to level3 but at the same time the cost of life assessmentincreases. Depending on the extent of informationavailable and the results obtained, the analysis maystop at any level or proceed to the next level asnecessary.One of the crucial parameters in estimation ofcreep life is the operating temperature. Althoughsteam temperatures are occasionally measured in aboiler, local metal temperatures are rarely measured.Due to load fluctuations and steam side oxide-scalegrowth during operation, it is also unlikely that aconstant metal temperature is maintained duringservice. It is therefore more convenient to estimatemean metal temperature in service by examination ofsuch parameters as hardness, microstructure, andthickness of the steam-side oxide scale for tubes.Because the changes in these parameters arefunctions of time and temperature, their currentvalues may be used to estimate mean metaltemperature for a given operating time. The estimated94 P a g e
Kavita Sankhala et al Int. Journal of Engineering Research and ApplicationsISSN : 2248-9622, Vol. 4, Issue 7( Version 2), July 2014, pp.93-99www.ijera.comtemperature can then be used in conjunction withstandard creep rupture data to estimate the remaininglife. Several methods for estimation of metaltemperature have been reviewed elsewhere .(2.a) Hardness based approachChanges in strength of low-alloy steel withservice exposure depend on time and temperature.Thus change in hardness during service may be usedto estimate mean operating temperature for thecomponent.This approach is particularly suitable whenstrength changes in service occur primarily as a resultof carbide coarsening neglecting stress inducedsoftening. The database on changes in hardness dueto long-term service is employed to assess remaininglife[2].(2.b) Microstructure based approachToft and Marsden demonstrated that there arebasically six stages of spheroidization of carbides inferrite steels. Using Sherby-Dorn Parameter, theyestablished a reasonable correlation of microstructurewith mean service temperature [3].Similar semiquantitative and qualitative approaches involvingdatabase on changes in microstructure as a functionof service history have been widely used [4].Oxidescale thickness based approach. Extensive data fromliterature indicate that in relatively pure steam, thegrowth of oxide scales is a function of temperatureand time of exposure. Several expressions have beenproposed in the literature to describe oxide scalegrowth kinetics [5,6].III.CREEP RUPTURE AND STRESSRUPTUREEvidence of creep damage in the hightemperature regions of boiler tubes has been observedin some instances [7]. The stresses and metaltemperature at these locations are assessed against thecreep rupture data for that particular grade of steel/ormaterial. Traditionally one has used a Larson-Miller(LM) plot of the type shown in Figure (1).The degree of safety margin depends on the userand what lower bound design curve is applied. Sincethese curves are based upon the chemistry, variationin chemistry for a particular grade can Have an effecton the Larson-Miller curve.In assessing remaining life of the componentsdue to creep, such as at boiler tubes, crack initiationis used as the criterion. However, with the emergenceof cleaner steel and fracture mechanics and anincreasing need to extend the life of a component,application of crack growth techniques have becomecommon in the past decade. For crack initiation asthe fracture criterion, history-based calculationmethods are often used to estimate life.www.ijera.comFig.(1) Larson Miller Curve For AlloySteel(ASTM A470 Class 8)(3.a) Methods for Crack Initiation Due to CreepFor the analytical method, one must haveaccurate operating history of the components, whichmay consist of temperature, applied loads, changes inoperation, such as shut downs or variation in speed orpressure. A simplistic estimation of the creep lifeexpended can be made by assessing the relaxed longterm bore stresses and rim stresses against thestandard rupture data using the life fraction rule.(3.b) Metallographic examinationMetallographic techniques have been developedthat can correlate changes in the microstructure andthe onset of incipient creep damage, such as triplepoint cavitations at the grain boundaries. For thistechnique, measurements by replication technique aretaken on crack sensitive areas that are subjected tothe higher temperatures and stresses. These areas aregenerally indicated by experienced analysis ofprevious damages. The Creep damage measured byreplication is classify into four damage stages Isolated cavities (A) Oriented cavities(B) Macro-cracks (linking of cavities) (C) Formation of macro-cracks (D)Fig(2) shows the location of the four stages onthe creep strain /exposure time curve [12]95 P a g e
Kavita Sankhala et al Int. Journal of Engineering Research and ApplicationsISSN : 2248-9622, Vol. 4, Issue 7( Version 2), July 2014, pp.93-99 Vickers hardness tests need to be performed indifferent regions of the cross section of eachsampleFrom the readings of the geometrical data, theoperating conditions and time, the remaining lifeof the tubes operating under creep conditionscould be estimated. There is a well-establishedmethodology for that. [10]V.Fig.(2) Replicas For Remaining Life AssessmentIV.STUDY METHODOLOGYThe methodology used to evaluate the microstructural degradation in boiler tubes due to creep hasbeen determined from the experience gained fromprevious studies of boiler tubes degraded in field andin laboratory[8] Figure(3).Fig(3) Methodology applied to evaluate the microstructural degradation www.ijera.comRESULTS OF METALLOGRAPHYEXAMINATION OF METALAfter first 15–20 thousand hours operation ofpipe-lines made of steel BS 3059/622/50 SE at thetemperature of 545 C and pressure 14 MPa theconsiderable changes of structures occur. Thechanges of ferrite chemical composition, coagulationof carbide in ferrite, and also increase of sizes ofcarbides along the grain boundaries was observed.(Table 1)Time, hours030000 70000 90000The quantity of Crin Cr carbides, %18.620.321.629.3The quantity of Moin Mo carbides, %45.346.848.748.9The quantity of Vin V carbides, %666767.869.2The quantity ofcarbide phases, %1.24.6213.320.3Table [1] Changes of chemical composition ofcarbide phasesThe microstructure of metal of a steam line ispresented on photographs (Fig. 4, 5, 6 and 7). Theyshow that microstructure of specimens consists offerrite, pearlite (Table 1). The microstructure of metalof a steam line is presented on photographs (Fig. 4, 5,6 and 7).They show that microstructure ofspecimens consists of ferrite, pearlite and nonmetallic inclusions [11].Microscopy techniques have to be used tocompare the microstructures of the samples.Optical microscopy has to be performed for apreliminary evaluation and possible correlationwith the Toft and Marsden criterion [9].Analysis of the microstructure has to beperformed by scanning electron microscopy. Bymeans of extraction replicas of each of thesamples.Room temperature tensile tests with flatspecimens should obtain from the samples.www.ijera.com96 P a g e
Kavita Sankhala et al Int. Journal of Engineering Research and ApplicationsISSN : 2248-9622, Vol. 4, Issue 7( Version 2), July 2014, pp.93-99www.ijera.comFig.(4) Microstructure of not operated steel BS3059/622/50 SEThe microstructure of not operated steel (Fig. 4a, b) consists of pearlite (black phase), ferrite (whitephase) and non-metallic inclusions. The photographs(Fig. 5 a, b) show the microstructure of 30000 hoursoperated steel.Fig.(6) Microstructure steel BS 3059/622/50 SEafter 70000 hoursThe microstructure of steel corresponds tonumber 6 – 7 of a scale of standards. Themicrostructure consists of ferrite, pearlite and nonmetallic inclusions. In comparison with amicrostructure of 29572 hours of operated steel, anamount of carbides and their coagulation in ferriteincreases (Fig. 6 b). On the photographs (Fig. 7 a, b)the microstructure of 94942 hours operated steel arepresented.Fig.(5) Microstructure steel BS 3059/622/50 SEafter 30000 hoursThe microstructure of steel corresponds tonumber 6 of a scale of standards. Changes of themicrostructure are visible on the photographs. Themicrostructure consists of ferrite, pearlite and nonmetallic inclusions. On the boundaries of ferritegrains line-ups of carbides are visible (Fig. 5 b).Onthe photographs (Fig. 6 a, b) the microstructure of70229 hours operated steel are presented.www.ijera.com97 P a g e
Kavita Sankhala et al Int. Journal of Engineering Research and ApplicationsISSN : 2248-9622, Vol. 4, Issue 7( Version 2), July 2014, pp.93-99[2][3][4]Fig.(7) Microstructure steel BS 3059/622/50 SEafter 90000 hoursThe microstructure of steel corresponds tonumber 7 of a scale of standards. The microstructureconsists of ferrite, carbides and small amount ofpearlite. In the body of grains of ferrite it is possibleto see the small particles of carbides, but the majorpart of carbides are between the boundaries of grains(Fig. 7 b). Observed changes of the steel structuredetermine changes of mechanical and physicalcharacteristics of the metal of pipelines.VI.[5][6]CONCLUSIONSContinuous time high temperature operation mayleads to changes of steel structure. There will be achange of constituents of ferrite and pearlite of steel.The grains of ferrite grow and their coagulationoccurs, pearlite is diminished. The alloyingelements,(chrome, molybdenum and vanadium)during a high temperature long-term operation fromferrite solid solution to transforms into a carbidephases. During a long-term operation at hightemperature the amount of carbides increases andcoagulation of carbides occurs, therefore freedom ofdislocations mobility increases, and it increases acreep of material and defines change of othermechanical characteristics. On evaluating a furtheropportunity of operation of a steam line the basiclimiting parameter of the long time operated heatresistant steels is disparity of carbides. All mentionedproperties have non-linear changes. Long-termoperation at working temperature of 545 C lead tochange of ultimate tensile strength and yield strength,elongation and reduction of area, impact strength andhardness.[7][8][9][10][11][12]REFERENCES[1]R Viswanathan and R.B. Dooley, Creep LifeAssessment Techniques for Fossil PowerPlant Boiler Pressure Parts, InternationalConference on Creep. JSME, 1. Mech. E.,ASME, and ASTM, Tokyo, Apr 14-18,1986, 349-359.www.ijera.com[13]www.ijera.comR. Viswanathan, J.R. Foulds, and D.A.Roberts, Methods for Estimating theTemperature of Reheater and SuperheaterTubes in Fossil Boilers, in Proceedings ofthe International Conference on LifeExtension and Assessment, The Hague, June1988.L.H. Toft and R.A. Mardsen, The Structureand Properties of 1% Cr-0.5%Mo Stee
based on microstructure study. It is also presents the microstructure changes and properties of 106720 service hour exposed boiler tube in a 120 MW boiler of a thermal power plant. Keywords-service exposed boiler tubes, microstructure, remaining life analysis, creep. I. INTRODUCTION In recent years, from oil refinery to
degradation kinetics in manure and soil under laboratory aerobic conditions was investigated. OTC degradation kinetics was found to be described well by the previously developed availability-adjusted first-order model at all moistures and low temperatures (e25 C). OTC degradation increased with increasing moisture from 60 to 100%.
Nov 01, 2016 · degradation products. The FDA and ICH guidance mandate the requirement of forced degradation to recognize how the quality of a drug substance and drug product varies with time and different environmental factors [5,6]. The developed and validated analytical method permits the analysis of each degradation products. Unfortunately, there
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Costs of Land Degradation due to LUCC The estimates show that the annual cost of land degradation in the region due to land use/cover change is about 6 bln USD, most which due to rangeland degradation (4.6 bln USD), followed by desertification (0.8 bln USD), deforestation (0.3 bln USD) and abandonment of croplands (0.1 bln USD). 10
In this study, the relationship between microstructure, aging and mechanical behavior was studied for Sn-3.4Ag-4.8Bi and Sn-3.4Ag-1.0Cu-3.3Bi and compared to SAC305. The alloys were prepared in bulk form by rapidly quenching from 260 C resulting in an as-solidified microstructure similar to that observed in solder joints.
Microstructure: Embossed surface and Expansion of graphite Swelling Degradation of material Evaporation of material Microstrucure: No apparent change in microstructure Chemical Analysis: Amount of O and Si keeps constant before and after the study Chemical Analysis: Higher amount of O and Si Presence of pollution probably
mechanical behavior to the microstructure of these systems. For highly concentrated colloids, however, our knowledge on the relations between structural and mechanical properties is rather limited. This is partly due to the considerable difficulties involved in experimentally characterizing the microstructure of highly concentrated systems.
BAB 2 LANDASAN TEORI 2.1 Program Pensiun 2.1.1 Definisi Program Pensiun Berdasarkan Undang-Undang Republik Indonesia Nomor 11 tahun 1992 tentang Dana Pensiun didefinisikan bahwa program pensiun adalah setiap program yang mengupayakan manfaat pensiun bagi peserta. Manfaat pensiun itu berupa pembayaran berkala yang diberikan setelah peserta mencapai usia pensiun. Definisi tentang Dana Pensiun .
