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An examination surface morphology and in situ studies of metal
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An examination surface morphology and in situ studies of metal An examination surface morphology and in situ studies of metal Document Transcript

  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME84AN EXAMINATION SURFACE MORPHOLOGY AND IN SITUSTUDIES OF METAL DUSTING LEADS TO EXTERNAL PITS ONASTM A 516 GR 60 STEAM COIL OF WATER SEAL DRUM EXPOSEDTO FLARE GAS IN MTBE PLANT1A.C.Mariappan*, 2K.Krishnamoorthy & 3S.Mareeswaran1Asst. Professor, Department of Marine Engg., PSN College of Engineering & Technology2Research Scholar, Anna University, Chennai,3Research Scholar, Anna University, Chennai.A B S T R A C TMetal dusting or catastrophic carburization is venomous form of high temperaturecorrosion begins with carbon deposition on the metal surface followed by diffusion of surfacecarbon into the metal which eventually causes superficial deposition of carbon on the metaland kept prolonged for 720 hrs at temperatures in the range, 450oC -1100oC in carbon-supersaturated2(carbon activity > 1) environments having relatively low oxygen partialpressures. Experiments have been carried out in thermo gravimetric analysis evaluation. Ascreening process was conducted at two different materials with various alloy composition tochoose for further investigation. Two test coupons were taken for experimental analysisamong one of them ASTM A516 Gr60 carbon steel and another one is Chromium basedcarbon steel and both were exposed on the flare line testing locations found with metaldegradation varied in both cases. It was found that the poorer the alloy composition, thehigher the carbon formation rate. The presence of methanol increased the carbon formationrate significantly but the methanol content did not however seem to be decisive for the carbonformation rate. Field experiments were also carried out by the means of determining limitsfor carbon free operation.Key Words: MD, MTBE, CC, TGA, ASTM A516 Gr60, TML & Corrosion CouponLocations, SG, FG, HC, NG, SMRINTERNATIONAL JOURNAL OF ADVANCED RESEARCH INENGINEERING AND TECHNOLOGY (IJARET)ISSN 0976 - 6480 (Print)ISSN 0976 - 6499 (Online)Volume 4, Issue 4, May – June 2013, pp. 84-95© IAEME: www.iaeme.com/ijaret.aspJournal Impact Factor (2013): 5.8376 (Calculated by GISI)www.jifactor.comIJARET© I A E M E
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME85INTRODUCTIONMetal Dusting (MD) is one form of metal degradation due to the resulting ofcarburization resulting in accelerated localized pitting which occurs in carburizing gases andor process stream containing carbon and hydrogen. Pits usually form on the superficially andmay contain soot or graphite dust. Metal dusting or catastrophic carburization1(CC) isvenomous form of high temperature corrosion begins with carbon deposition on the metalsurface followed by diffusion of surface carbon into the metal which eventually causessuperficial deposition of carbon on the metal and kept prolonged for 360 hrs at temperaturesin the range, 450oC -1100oC in carbon-supersaturated2(carbon activity > 1) environmentshaving relatively low oxygen partial pressures. Experiments have been carried out in thermogravimetric analysis (TGA) equipment. A screening process was conducted of two differentmaterials with various alloy composition to choose for further investigation. Two testcoupons were taken for experimental analysis among one of them ASTM A516 Gr 60 carbonsteel and another one is Chromium based carbon steel and both were exposed on the flare linetesting locations (TML & Corrosion Coupon Locations) found with metal degradation variedin both cases. It was found that the poorer the alloy composition, the higher the carbonformation rate. The presence of methanol increased the carbon formation rate significantlybut the methanol content did not however seem to be decisive for the carbon formation rate.Field Experiments were also carried out by the means of determining limits for carbon freeoperation. Metal dusting(MD) or catastrophic carburization1engineering alloys arevulnerable to metal dusting when exposed to strongly carburizing environments at elevatedtemperatures, whereby the alloys corrode to produce metal, metal carbide, carbon, and oxideparticles. It has also been documented that metal dusting did happen at temperatures as highas 1100°C in heavily reducing environments. In petrochemical plants, for example, metaldusting has been experienced in steam reforming furnaces used to manufacture synthesisgases (e.g. H2, CO, and CO2). The graphite growth is caused by carbon atoms from the solidsolution attached to the graphite planes growing vertical to the alloy surface. This initiates alocalized degradation of the alloy and, as a result, metallic particles in the form of pitting arereleased and transfer into the coke layer.SYNTHESIS GAS MIXTURE: 25%CO+72%H2+3%H2OSynthesis Gas (SG) is nothing but the combination of Hydrogen and Carbon named asHydro Carbon (HC). SG is the production of methanol came from coal and also terms asFlare Gas (FG – Fig 1). Today, synthesis gas is most commonly produced from the methanecomponent in Natural Gas (NG), because natural gas contains hydrogen. Three processes arecommercially practiced. At moderate pressures of 4 MPa (40 atm) and high temperatures(around 850 °C), methane reacts with steam on a nickel catalyst to produce syngas accordingto the chemical equation:CH4 + H2O → CO + 3 H2This reaction, commonly called steam-methane reforming (SMR), is endothermic, andthe heat transfer limitations place limits on the size of and pressure in the catalytic reactorsused. Methane can also undergo partial oxidation with molecular oxygen (at atmosphericpressure) to produce syngas, as the following equation shows:2 CH4 + O2 → 2 CO + 4 H2
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME86As described above, several gas species, for example methane or higherhydrocarbons, are not expected or detected in significant concentrations due to slow kineticsand were rejected in the calculations. In order to calculate carbon activities higher than unityin the gas phase, all solid (and liquid) states of pure carbon were suspended in the TC-modeling. The carbon activity as a function of temperature and pressures for two possibleequilibrium based on the same input composition are shown bellow. If water vapor isexcluded from the equilibrium as shown in given example, the CO2 content increases from1.6% (in 23% CO + 2.5% H2O +73% H2) to 4.1% (in 20.4%CO +75.5%H2) at 650°C, butthe carbon activity will still be high.Fig – 1METHANOLMethanol, CH3OH, (i.e. methyl alcohol) is the simplest aliphatic alcohol, and is thefirst member of the homologous series. Methanol is a colorless liquid, completely misciblewith water and organic solvents and is very hydroscopic. Methanol has an agreeable odor anda burning taste. Methanol is a potent nerve poison.Methanol has the physical properties• Melting Point : -97oC• Boiling Point : 65oC• Relative Density : 0.8Methanol and it also called as wood spirits, is a chemical with the formula CH3OH (oftenabbreviated Me OH). Methanol acquired the name also known as methyl alcohol, woodalcohol and wood naphtha. "Wood alcohol" was once produced chiefly as a byproduct of thedestructive distillation of wood. Modern methanol is produced in a catalytic industrialprocess directly from carbon monoxide, carbon dioxide, and hydrogen.
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, IssueOther names of MethanolHydroxymethaneMethyl alcoholMethyl hydrateMethyl hydroxideMethylic alcoholMethylolWood alcoholMethanol can catalyze the production of methanol from carbonhigh selectivity (> 99.8%):CO + 2 H2 → CH3OHOne way of dealing with the excess hydrogen is to inject carbon dioxide into the methanolsynthesis reactor, where it, too, reacts to form methanol according to the equation:CO2 + 3 H2 → CH3OH + H2OSome chemists believe that the certain catalysts synthesize methanol using COintermediary, and consuming CO only indirectly.CO2 + 3 H2 → CH3OH + H2OWhere the H2O byproduct is recycled via the waterCO + H2O → CO2 + H2,This gives an overall reaction, which is the same as listed above.CO + 2 H2 → CH3OHStochiometric adjustmentStochiometric for methanol production requires the ratio of Hpartial oxidation process yields a ratio of 2, and the3. The H2 / CO ratio can be adjusted to some extent by the waterCO + H2O → CO2 + H2,It provides the appropriate stochiometric forToxicityMethanol has a high toxicity in humans.International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN6499(Online) Volume 4, Issue 4, May – June (2013)87Methanol can catalyze the production of methanol from carbon monoxide and hydrogen withOne way of dealing with the excess hydrogen is to inject carbon dioxide into the methanolsynthesis reactor, where it, too, reacts to form methanol according to the equation:Some chemists believe that the certain catalysts synthesize methanol using COintermediary, and consuming CO only indirectly.O byproduct is recycled via the water-gas shift reactionThis gives an overall reaction, which is the same as listed above.Stochiometric for methanol production requires the ratio of H2 / CO to equal 2. Theprocess yields a ratio of 2, and the steam reforming process yields a ratio of/ CO ratio can be adjusted to some extent by the water-gas shift reaction,the appropriate stochiometric for methanol synthesis.Methanol has a high toxicity in humans.International Journal of Advanced Research in Engineering and Technology (IJARET), ISSNJune (2013), © IAEMEmonoxide and hydrogen withOne way of dealing with the excess hydrogen is to inject carbon dioxide into the methanolsynthesis reactor, where it, too, reacts to form methanol according to the equation:Some chemists believe that the certain catalysts synthesize methanol using CO2 as an/ CO to equal 2. Theprocess yields a ratio ofgas shift reaction,
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME88Thermodynamic properties of MethanolPhase behaviorTriple point 175.5 K (−97.7 °C), PaCritical point 513 K (240 °C), 78.5 barStd enthalpy changeof fusion, ∆fusHo 3.1773 kJ/molStd entropy changeof fusion, ∆fusSo 18.1 J/(mol·K)Std enthalpy changeof vaporization, ∆vapHo +35.278 kJ/molStd entropy changeof vaporization, ∆vapSo 113 J/(mol·K)Gas propertiesStd enthalpy changeof formation, ∆fHogas-201.3 kJ/molStandard molarentropy,Sogas239.9 J/(mol K)Heat capacity, cp 52.29 J/(mol K) at 77°C61.43 J/(mol K) at 100-223°CHeat capacity ratio,γ = cp/Cv1.203 at 77°Cvan der Waalsconstantsa = 964.9 L2kPa/mol2b = 0.06702 liter per moleFLARE STACK / FLARE HEADERSThe released waste gases and liquids are routed through a large piping system placedvertically called as flare headers. The released gases are burned as they exit the flare stack’stip Fig - 3. The size, color and brightness of flame gives the resulting the flammablematerials flow rate in terms of joules per hour (or Btu per hour). Most industrial plant flareshave a vapor-liquid separator Fig – 2 (also known as a knockout drum) upstream of the flareto remove any large amounts of liquid that may accompany the relieved gases. Steam is veryoften injected into the flame to reduce the formation of black smoke. In order to keep theflare system functional, a small amount of gas is continuously burned, like a pilot light, sothat the system is always ready for its primary purpose as an over-pressure safety system.
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME89Fig - 2Some sources consider that flaring constitutes a hazard to human health and a contributor tothe worldwide anthropogenic emissions of carbon dioxide. For example, oil refinery flarestacks may emit methane and other volatile organic compounds as well as sulfur dioxide andother sulfur compounds, and toxics ... all of which are known to exacerbate asthma and otherrespiratory problems. As another example, flaring at oil and gas production sites may emitmethane, sulfur dioxide, aromatic hydrocarbons (benzene, toluene and xylenes), as well ascarcinogens such as benzapyrene.Fig - 3The adjacent flow diagram depicts the typical components of an overall industrial flarestack system:A knockout drums to remove any oil and/or water from the relieved gases.A water seal drum to prevent any flashback of the flame from the top of the flarestack.As alternative gas recovery system for use during partial plant startups and/orshutdowns as well as other times when required. The recovered gas is routed into the fuel gassystem of the overall industrial plant.A steam injection system to provide an external momentum force used for efficientmixing of air with the relieved gas, which promotes smokeless burning.
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME90A pilot flame (with its ignition system) that burns all the time so that it is available toignite relieved gases whenever needed.The flare stack, including a flashback prevention section at the upper part of the flarestack.ASTM A516 Gr 60A consistent description of metal dusting on ASTM A516 Gr 60 iron is proposed forthe field experiment and its related details are given in Table 1, 2 & 3:Chemical Composition of ASTM A516 Grade 60Composition Percentage % Composition Percentage %C 0.2 Cu 0.3Si 0.4 Ni 0.3Mn 0.5/1.40 Mo 0.08P 0.03 Nb 0.01S 0.03 Ti 0.03Al 0.02 V 0.02Cr 0.3Table 1 Typical Chemical Composition of ASTM A516 Grade 60 / ASME SA516 Grade 60Table 2 Typical Mechanical Values of ASTM A516 Grade 60 /ASME SA516 Grade 60Standard DescriptionASTM/ASME A/SA516 - Grade 60DIN Standard DIN 17155 HIIBritish Standard BS1501-161-430AEuropean Norm EN10028 P265GHTable 3 Equivalent Specifications and Standards of ASTM A516 Grade 60 /ASME SA516 Grade 60DUCTILE TO BRITTLE TRANSITIONNotched bar impact testing of a specimen over a temperature range will show achange from ductile fracture at higher temperatures to brittle fracture at lower temperaturesrevealed by a drop in impact energy. This testing raises the important issues concerning thefracture toughness of steel which can change dramatically over a relatively small temperaturerange. Consideration should therefore be taken when using steel in particular workingenvironments, especially ones where significant temperature variation is commonplace.Properties ValueTensile strength (N/mm2) 410/530Yield stress/ min (N/mm2) 265
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME91Sequential metal degradation was carried out in the following Oder:a) Cementite formation on the ferrite surface.b) Graphite formation on the Cementite layer.c) As the graphite layer grows thicker and tighter the carbon activity drops to unity and Cementitestarts to decompose, I .e. Type I mechanism.d) The eutectoid reaction may be fast enough to form an intermediate eutectoid layer;Cementite → Ferrite + Graphite.e) No more Cementite forms in contact with graphite in the coke, i.e. the steady state processhave started the Type II mechanism.
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME92CHROME MOLYBDENUM PIPE / PLATEChrome Molybdenum steel plate / Pipe (often referred to in the industry as Chrome Moly) isused for a wide variety of applications particularly in the oil and gas industry, the nuclearindustry and fossil fuel power stations. The molybdenum provides increased strength andhigher working temperatures whilst the chromium facilitates excellent corrosion resistanceand oxidation. Chrome Moly pipe has become a standard in the power generation industryand the petro-chemical industry, not only because of its tensile strength, corrosion resistanceand high-temperature strength, but also for its cost-effectiveness. Grades P-11 & P-22 areprevalent grades for the power industry, while P-5 & P-9 are the major refinery processinggrades utilized.Sizes:1/4” Nominal to 24”O.D. Seamless PipeWall Thickness – Schedule 40 through XXHChrome Moly Pipe Specifications & GradesSA335 & A335 – Grades P5, P9, P11,A691 1-1/4 Chrome through 9 Chrome (Welded Alternative to A335)
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME93Heat Treatment Requirements for Ni / Cr Metals:It was shown that the metal dusting process is characterized:(i) By a serrated appearance of the interface between graphite and the outer layer of thesubstrate, which is the instable carbide Fe3C in the case of iron and the metal phase in thecase of nickel,(ii) (ii) By the perpendicular orientation of the intrusions of graphite to the originalsurface of the substrate in the case of chromium. Hence, it can be supposed that the free endsof the growing graphite lattice planes act as active centers for disintegration.CONCLUSIONIn high Cr ferritic steels, the Cr diffusion rate is about one order of magnitude largerthan in austenitic steels. Ferritic Fe-20Cr steel is fully protected by a surface oxide film,while the austenitic 304 stainless steel undergoes metal dusting. The importance of rapid Crdiffusion is further discussed along with findings on the effects of surface finish.Due to development of advanced catalysts and efforts to increase the efficiency ofprocesses involving the production of syngas, metal dusting corrosion has become moreprevalent. Failures of iron-base alloys as well as nickel-base alloys which contain insufficientscale-forming elements have prompted equipment designers to seek materials that are moreresistant to metal dusting. Field and laboratory data confirm the desirability of addition ofElement P-5 P-9 P-11 P-22K41545 S50400 K11597 K21590Carbon 0.15 max 0.15 max 0.05 - 0.15 0.05 - 0.15Manganese 0.30 - 0.60 0.30 - 0.60 0.30 - 0.60 0.30 - 0.60Phosphorous,max0.025 0.025 0.025 0.025Sulfur, max 0.025 0.025 0.025 0.025Silicon 0.50 max 0.25 - 1.00 0.50 - 1.00 0.50 maxChromium 4.00 - 6.00 8.00 - 10.00 1.00 - 1.50 1.90 - 2.60Molybdenum 0.45 -0.65 0.90 - 1.10 0.44 - 0.65 0.87 - 1.13P-5 P-9 P-11 P-22Tensile Strength,min., psiksi 60 60 60 60MPa 415 415 415 415Yield Strength, min.,psiksi 30 30 30 30MPa 205 205 205 205
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME94certain scale-forming and carbide-forming elements in conjunction with a nickel-base alloymatrix to limit pit progression rates.All engineering alloys based on Fe, Ni, Co, even those alloyed with Cr, Al and Si, aremore or less susceptible to metal dusting, although the incubation time may differ. When ametal dusting pit starts to grow, the kinetics is catastrophic at least from an engineering pointof view. A solution to the metal dusting problem may be found in new alloy systems freefrom carbide formers, such as Fe and Cr, and free from graphite formers, such as Ni and Co.The best performer overall in the laboratory test was alloy 693, which possesses very highchromium and aluminum contents. In-situ field exposures in syngas environments haveconfirmed this alloys superior performance.Metal dusting prevention♣ Adjustment or careful selection of process parameters (T, P, C)♣ Development of new, metal dusting resistant, alloys♣ Application of coatings to protect the underlying metal/alloy matrix (Cr- surfaceoxide layer)♣ Mixing process gas with low concentration of sulfur compounds (H2S, CS2, (CH3)2S2,etc.)♣ Dense Cr-containing oxide is more protective Pre-polished samples treated in H2O/Arat the lowest temperature appear to have the best resistanceChromium based carbon steel and both were exposed on the flare line testinglocations found with metal degradation varied in both cases. It was found that the poorer thealloy composition, the higher the carbon formation rate. The presence of methanol increasedthe carbon formation rate significantly but the methanol content did not however seem to bedecisive for the carbon formation rate. Experiments were also carried out by the means ofdetermining limits for carbon free operation.REFERENCE[1]. Prange, F.A.: Corrosion 15 (12), 619t (1959).[2]. Eberle, F.; Wylie, R.D.: Corrosion 15, (12), 622t (1959).[3]. Hoyt, W.B.; Caughey, R.H.: Corrosion 15 (12), 627t. (1959)[4]. J. Pattinson,” On carbon and other deposits from the gases of blast furnaces inCleveland”, J. Iron Institute, No 1, London, pp. 85-100 (1876).
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 4, May – June (2013), © IAEME95[5]. E. Camp, C. Phillips, L. Gross, “Corrosion of 18-8 Alloy furnace tubes in hightemperature vapour Phase cracking service”, Corr., Vol. 1, p.149-160 (1945).[6]. H.J.Grabke, Metal dusting, Material and Corrosion, 2003, 54, pp. 736-746.[7]. “Handbook of Case Histories in Failure Analysis,” Esaklul, K. A., ed., ASM, 1992, pp351-353.[8]. Private Communications, Special Metals, December, 1997.[9]. S.Strauss and H.J.Grabke, Materials and Corrosion, 49, 1998, pp 321-327.[10]. D. B. Roach, “Carburization of Heat-Resistant Alloys”, Paper No 7, Corr., NACE(1976).[11]. Doi, T.; Kitamura, K.; Nishiyama, Y., et al.: Surf. Interface Anal. 40, 1374 (2008).[12]. Eberle, F.; Wylie, R.D.: Corrosion 15, (12), 622t (1959).[13]. Baker, B.A.; Smith, G.D.; Hartmann, V.W.; Shoemaker, L.E.: “Nickel-base materialsolutions to metal dusting problems”. CORROSION /2002 (Houston, TX, NACE,2002) (Paper No.2394).[14]. E. Pippel, J. Woltersdorf and R. Schneider, Materials and Corrosion, 49 309 (1998).[15]. C.M. Chun, J.D. Mumford and T.A. Ramanarayanan, J.Electrochem. Soc., 147 3680(2000).