MBB4423 , CORROSION ENGINEERING

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UNTVERSITITEKNOLOGIP ETRONASCOURSEDATETIMEMBB4423 - CORROSION ENGINEERING2No SEPTEMBER 2012 (suNDAy)9.00 AM - 12.00 NOON (3 hours)INSTRUCTIONS TO CANDIDATES1.2.3.4.5.Answer ALL questions from the Question Booklet.Begin EACH answer on a new page in the Answer Booklet.Indicate clearly answers that are cancelled, if any.Where applicable, show clearly steps taken in arriving at the solutions andindicate ALL assumptions.Do not open this Question Booklet until instructed.There are sEVEN (7) pages in this Question Booklet including thecover page.FINAL EXAMINATIONMAY 2012 SEMESTERNote :Universit.i Teknologi pETRONASa-1.MBB 4423ln an electrochemical conosion experiment, an iron sample isimmersed in an aqueous de-aerated acid solution and held at apotential of {.3 V with respect to Standard Hydrogen Electrode(SHE) and pH 3. The Pourbaix diagram for lron- Water system at25oC is shown in FIGURE Q1a.Iû.50{.5ÞtFeO,FIGURE QIaEvaluate whether the ironaerated acid solution.sample will conode in this de-[5 rnarks]Analyse whether the iron sample will conode in alkalinesolution, pH = 9.[5 marks]t¡lToJõCú'oo-21.5-f.1.36pHllPourbaix Diagram for lron-Water System at 25tMBB 4423b. The reaction of iron corroding in an aerated acid at 25oC is given asFe+2HCl( aq) +l o, - FeCl,(aq)+Hro¿where:E1Fe2* l'Fe) = -0.440 V;E(H*lHz)=ov,F' = 96500 C/mol; and,R = 8.314 J/mol.K .i. Evaluate the thermodynamics of the corrosion if theconcentration of Fe2* is 1 and H* is 1.[6 marks]i¡. Determine the concentratÍon of Fe2* that no more corrosionis possible.3MBB 44232. The corrosion of iron in neutralwater (pH 7) in equilibríum with air involvestwo cathodic reactions of hydrogen evolution and oxygen reduction.Corrosion potential (E,oà in aerated water at pH 7 is measured as-0.45 V.The rates of both oxidation and reduction half-reactions are controlled byactivation polarization and the data are given in TABLE Q2.TABLE Q2lron HydrogenDensity 7.14 glcm"Atomic weight 65.37 g/moleReduction Potential E (Fe'*lFe)= -A.44V E(H*lHz)=0VExchange CurrentDensityio: 10- " A/cm' io = 10-'u Alcm'Tafel Slope É: +0.06 V/decade þ= -0.12 V/decadea. Determine anodic current density of the corrosion process.[6 marks]b. Analyse cathodic current density contributed by hydrogen evolutionand oxygen reduction.[10 marks]c. Evaluate the dominant cathodic current of the corrosion of iron inneutralwater.[4 marks]4ct.3.MBB 4423Corrosion monitoring is an important aspect of design andoperation in chemical process plant. There are numerous corrosionmonitoring methods and devices available such as linearpolarization resistance and corrosion coupon testing. The selectionof the methods and locations depends on many factors such asplant maintenance and operating philosophy of a particular plant.Propose and discuss TWO (2) objectives of corrosionmonitoring.[4 marks]resistance and[8 marks]ll Evaluate the application of linear polarizationweight loss coupons in corrosion monitoring.b. Onshore buried pipelines are exposed to both internal and externalcorrosion. The integrity of the pipelines depends on the accurateassessment of the condition of the pipelines. Propose possiblemethods for corrosion monitoring of typical onshore buriedpipelines. Justify.[8 marks]54.MBB 4423lnsulated above-ground storage tanks are susceptible to corrosionunder insulation (CUl) especially along the stiffener rings due towater ingression from damaged cladding and poor design of theinsulation jacket.Evaluate the type and mechanÍsm of the corrosion on theshell plates along the stiffener rings.[8 marks]ii. Propose TWO (2) design considerations to prevent theoccurrence of the corrosion under insulation of the storagetanks. Justify.[4 marks]One common corrosion prevention method is coating. However, thedegree of the prevention depends strongly on the quality of thecoating application and inspection. Formulate the requirements forsurface preparation, paint application and inspection of such work.[8 marks]b.þacl.5.MBB 4423CO2 corrosion is the main corrosion threat in upstream oil and gasproduction. There are many parameters influencing COz corrosionwhich pose challenges to an accurate prediction of the corrosion.Discuss the corrosion mechanism of carbon steel pipeline inthe COz environment.[6 marks]i¡. Evaluate the effect of temperature and CO2 partial pressurein the prediction of COz corrosion[8 marks]lnhibitors are commonly used as a corrosion prevention method inoil and gas industry. Propose TWO (2) possible mechanisms thatcontribute to their effectiveness. Justify.[6 marks]- END OF PAPER-b.