T-TYPE NAPHTHA PUMP STRAINER MESH FAILURE ANALYSIS

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Naptha pump failure 302It is clearly indicated in Figure 8 that type304 stainless steel is used for mild corrodents.Under the prevailing conditions of naphthacirculation, the presence of H 2S in wet conditiongreatly impairs the suitability of 304 stainlesssteel in the naphtha pumps.microstructure. The inferior corrosion andmechanical properties of the welded componentsin comparison with the base metal are due to thepreferential corrosion attack at the alloy depletedregion, segregated interfaces, dendritic cores andaustenite/delta-ferrite and other secondaryprecipitate interfaces in the weld metals. [5].Normally, SCC will not occur if theequipment/part is in compression. Failure istriggered by a tensile stress that must approachthe yield stress of the metal. The stresses may befrom faulty installation or represent residualstresses from welding, straightening, bending oraccidental denting of the component. Pits, whichact as stress concentration sites, will often initiatestress corrosion cracking.Figure 9. Yield Strength and corrodent action classify amultitude of stainless steels into 11 families [7].It is shown in Figure 9 that type 304 SS has loweryield strength than type 316 SS which contains2-3% molybdenum. Type 316 SS has highercorrosion resistance in reducing environments.Welding of austenitic stainless steel usuallyresults in weld metal with a dendritic andinhomogeneous microstructure having a smallamount of delta-ferrite, M 23C 6carbides, sigmaetc., and significant segregation of major alloyingelements at the phase interfaces. The presenceof delta-ferrite leads to preferential corrosionattack in the weld metal in certain environments.Pits have been shown to nucleate preferentially,depending on the alloy composition, either at theaustenite/delta-ferrite interfaces or inside thedendrite cores of austenite. The ageing of welddeposits, either during stress-relieving operationsor during exposure to high temperature in service,leads to the formation of complex precipitateIf austenitic steels are exposed to heattreatmentof less then 870° C, they can besensitized. For this reason, local stress relief ofunstabilized austenitic stainless steel is usuallyimpractical, since the runout areas immediatelyadjacent to the region being heat-treated will besensitized [6].Conclusions and RecommendationType 304 SS is susceptible to stresscorrosion cracking when used for naphthafeedstock. The choice of type 304 SS was notcorrect due to its susceptibility to SCC (StressCorrosion Cracking) and IGC (IntergranularCorrosion) due to sensitizing. Future failure canbe avoided by design modification, fabricationchanges, material changes and environmentalcontrol. The change of material was recommendedconsidering the present observations.Selection of 316 L (low carbon) stainless steelor carbon steel can reduce SCC & IGA problem.It is also suggested that regular cleaning ofstrainer after 20-25 days can improve theefficiency and reduce the chances of blockage orcontaminations.
303 Muhammad A. Butt et al.References1. A-lab Corporation. The American Association Forlaboratory accreditation 2005. Chemical testing.Dayton, OH.2. Philippe, M. 2002. Corrosion mechanism in theoryand practice. In: Stress Corrosion Mechanisms. Ed.Newman, R.C., pp. 402-406. Marcel Dekker. NewYork.3. Khan, I.H. 1989. Corrosion technology. Vol-2., pp.442. Institute of Chemical Engineering &Technology, Punjab University, Lahore.4. Roberge, P.R. 1999. Hand book of corrosionengineering, pp. 734-736. McGraw Hill Company,New York.5. Khatak, H.S. and Raj, B. 2002. Corrosion ofaustenitic stainless steels; mechanism, mitigationand monitoring. In: Sensitization and testing ofintergranular corrosion. Ed. Parvathavarthini, N.,pp. 123, 129-130. Narosa Publishing House NewDelhi.6. Philip, A.S. 2004. Encyclopedia of corrosiontechnology. 2 nd ed., pp. 569, 572. Marcel Dekker,New York.7. Kenneth J.M. 1980. Materials engineering-1,selecting materials for process equipment, chemicalengineering. McGraw-Hill Publications Co., NewYork, N.Y., pp. 15-19 and pp 36.
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T-TYPE NAPHTHA PUMP STRAINER MESH FAILURE ANALYSIS

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