ORGANIC COATINGS FOR CORROSION PROTECTION OF TRANSFORMERS IN UNDERGROUND CHAMBERS (Nace 2012 paper 1338))

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Underground electrical transformers are frequently submitted to a very aggressive environment because of the stagnated water of underground chambers which is heated and contaminated. In Brazil, carbon steel structures of underground transformers are usually protected with coal tar epoxy paints in order to ensure their reliability. However, the use of this type of paints is being strongly restricted because coal tar contains complex mixtures of polycyclic aromatic hydrocarbons which contain many toxic and potentially carcinogenic substances. Aiming at replacing coal tar based paints by an environmentally friendly one; several paints were selected in the local market and submitted to performance tests in order to compare them with coal tar based paint. In addition, anodes were evaluated to study the application of galvanic cathodic protection in areas of metal exposure due to coating flaws. This paper presents and discusses the obtained results.

Os transformadores elétricos subterrâneos estão frequentemente expostos à corrosão intensa decorrente da estagnação de água aquecida e contaminada das câmaras subterrâneas. No Brasil, as estruturas de aço-carbono do transformador subterrâneo são usualmente protegidas com pintura de epóxi alcatrão de hulha que contém substâncias tóxicas e potencialmente cancerígenas. Com o objetivo de substituir as tintas à base de alcatrão de hulha por tintas ecologicamente corretas, tintas disponíveis no mercado nacional foram selecionadas e submetidas a ensaios de desempenho para a sua comparação com a tinta de alcatrão de hulha. Além disso, anodos foram avaliados para o estudo da aplicação de proteção catódica galvânica do metal exposto em áreas de falhas do revestimento. Este artigo apresenta e discute os resultados obtidos.

ARAUJO, A.; PANOSSIAN, Z; ALMEIDA, N.L; MARTINS, M.C.; JUNIOR, S.D.A. Organic coatings for corrosion protection of transformers in underground chambers. In: NACE INTERNATIONAL CONFERENCE & EXPO, 2012, Salt Lake City, Proceedings... Salt Lake City: NACE 2012.

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ORGANIC COATINGS FOR CORROSION PROTECTION OF TRANSFORMERS IN UNDERGROUND CHAMBERS (Nace 2012 paper 1338))

  1. 1. Organic Coatings for Corrosion Protection ofTransformers in Underground ChambersIPT – Institute for Technological Research - Corrosion and ProtectionLaboratorySão Paulo/BrazilMarch/2012IPTAdriana de AraujoZehbour PanossianNeusvaldo L. de AlmeidaAlberto S. JuniorAES Eletropaulo - São PauloMetropolitan ElectricityClay M. Martins1
  2. 2. Outline2• Introduction• Objectives• Methodology• Results• Conclusions• Future activities (field tests)
  3. 3. 3UNDERGROUND CHAMBER (VAULT)water level markTransformerIn the city of São Paulo, there are about 4000 UC. TheIn the city of São Paulo, there are about 4000 UC. Thetransformers installed there and other electric facilitiestransformers installed there and other electric facilitiesare submitted to an aggressive environment.are submitted to an aggressive environment.
  4. 4. 4TRANSFORMER TANKNET WORK PROTECTORPEOPLE ACCESSSidewalkConcrete wallsEQUIPMENT ACCESSCross section view
  5. 5. AGRESSIVE INVIRONMENT IN THE CHAMBERSHeated water (< 60 ºC).Heated water (< 60 ºC).Contaminated water (Contaminated water (Solid material,distinctive color and odour).Work temperature (< 70 oC)High temperature (< 120 oC)rain + urban debris, groundwaterrain + urban debris, groundwaterinfiltration and sewer leakageinfiltration and sewer leakageStagnated water with periodic floodingthermometer
  6. 6. 6SteamSteamBecause of the steam in theBecause of the steam in thechambers, the emerged partchambers, the emerged partof the transformers areof the transformers areconstantly exposed to a highconstantly exposed to a highhumidity atmosphere andhumidity atmosphere andwater dropletswater droplets
  7. 7. 7BlisterRust and flakingRust and flakingRust and debris depositionRust and debris depositionAs a result of theAs a result of theaggressive environment,aggressive environment,in few years the coatingin few years the coatingis quite damaged.is quite damaged.
  8. 8. 8RustRustFlakingFlakingSUPERFICIALPROCTECTION FAILURE
  9. 9. 9• most of them: 500 kVA;• Some are retrofittedand repainted in lessthan 5 years• The repaint is doneby the companystaff.• coal tar paint overcoal tar paint overshelf primer (ironshelf primer (ironoxide)oxide)Complex mixture of PAHsComplex mixture of PAHsHigh VOCHigh VOC
  10. 10. 10ObjectivesSelect new protective coatingEnvironment-friendly and high performanceEnvironment-friendly and high performanceSelect galvanic anode for the cathodic protectionof the transformers
  11. 11. 11Methodology -select a new coating
  12. 12. 12PaintThicknessapplied(μm)ResinVOC(g/L)Highdry filmporcoat(µm)Primer paint OthersAA 450 Epoxypolyamide377 140Epoxy zincphosphate _BB 400 176 400 _ _C 300300Epoxymodified143 1000 _ STST/CDCD/ERERD 300300 255 500 _ STST/CDCD/DTDTE 300300 150 150 _ STST/CDCD/ERER/DTDTSTST - accepts mechanical surface treatment or flash rust.DTDT - accepts high relative humidity or slightly moisturesurface.ERER - improve edge protection.CDCD - suitable for use with cathodic protection systems.Paint FeaturesData establishedTable 1: Main features of the studied paints
  13. 13. 13Specimens for performance tests• small carbon steel sheets (10 cm x 15 cm x 3 mm):grounded (remove the sharp edges), cleaned (removecontaminations), blasted (steel grit, Sa 2½, ISO 8501-1):roughness of about 50 µm, painted (according to their datasheets), scribed some specimens (2 mm)• select those specimens most appropriate: accordingto the following criteria: damages: ASTM D 5162 (holiday detector); thickness (defined in Table 1): ASTM B 499; Adherence: ASTM D 4541 (> 15 MPa)
  14. 14. 14Performance laboratory tests for coating selectionEIS: immersion 5 % NaCl solution for 24 h.Scanned frequency range was from 105Hzto 10-3Hz and the amplitude ofperturbation was 20 mV.Salt spraySalt spray: ASTM B 117, exposure time was3000 h, with weekly visual inspections. InInthe end, measurement of thethe end, measurement of the creepagecreepagecorrosioncorrosion andand EISEIS (Bode diagrams).(Bode diagrams).
  15. 15. 15Cathodic disbondingCathodic disbonding: ASTM G 8ASTM G 8 (method B: impressedcurrent, 30 days, hole Ø 6.35 mm);Anode3 specimens
  16. 16. 16Water from 20 UC was collected in field. The were chemically analyzed anda representative one was selected for a immersion test.Water: pH 7.8; low conductivity 54 µS/cm; clpH 7.8; low conductivity 54 µS/cm; cl--22mg/L; SOmg/L; SO442-2-6 mg/L.6 mg/L.The specimens were exposed to immersion inheated and contaminated water and to a highhumidity atmosphere. The test was conductedby 3600 h, with weekly visual inspection.Vapor spaceVapor spaceImmersed partHeating plateHeating plate(~ 70(~ 70 ooC)C)Immersion testImmersion test
  17. 17. 17Methodology -select anode for cathodicprotection
  18. 18. 18One reactor was developed especially for the evaluation ofanodes for the galvanic protection of the undergroundtransformers. Tested anodes : aluminum, zinc and magnesium.1 anode ~ Ø 18 mm x 25 mm inheight.5 carbon steel coupons: 1 ~ Ø 60 mm4 ~ Ø 30 mm.Water 1: pH 7.8; conductivity 54 µS/cmpH 7.8; conductivity 54 µS/cm;;clcl--2 mg/L; SO2 mg/L; SO442-2-6 mg/L.6 mg/L.Water 2: pH 4.5,;conductivity 73 µS/cmpH 4.5,;conductivity 73 µS/cm;clcl--22 mg/L; SO22 mg/L; SO442-2-5 mg/L.5 mg/L.Electrode potential and current flowestablished was monitored. In the end,the corrosion rate was calculated.
  19. 19. 19Results
  20. 20. 20CoatingSalt sprayVisualinspectionCreepagecorrosion(mm)Log of the Impedance modulus date(│Z│, ohm/cm2 at 0.01 Hz)Blank specmens After 3000 hThicknessAAUnchangedUnchanged 4.84.8 8,0218,021 8,0668,066455455 541541 484484BBUnchangedUnchanged 6.36.3 7,887,88 7,8867,886410410 359359 371371CCUnchangedUnchanged 4.04.0 7,8897,889 8,8698,869289289 287287 342342DDUnchangedUnchanged 6.26.2 8,318,31 8,5038,503290290 301301 323323EUnchangedUnchanged 6.86.8 7,8377,837 8,3598,359284284 268268 285285
  21. 21. CoatingCathodicdisbondingImmersion test in contaminated waterAverageequivalent circlediameter- ECD(mm)Visual inspectionEmerged area Immersed areaAA15.015.0 Unchanged Blister after 240 hBB11.811.8 Unchanged Blister after 240 hCC17.717.7 Unchanged Unchanged after 3600 hUnchanged after 3600 hDD19.1 Unchanged Blister after 864 hBlister after 864 hE34.2 Unchanged Blister after 672 h
  22. 22. Coated test specimens after3600 h of immersion in acontaminated waterCoating CBlistersBlistersBlistersBlisters
  23. 23. Sacrificial anode selection test results – TEST 1 (pH 4.5)MetallicmaterialTestduration(h)Electrode potential(mV, Ag/AgCl)Current(mA)Corrosionrate (µm/y)Aluminumanode912 -936 0.615 941Zinc anode 912 -610 mV-610 mV 0.021 15Magnesiumanode912-933 0.694 53< 850 mV (Ag / AgCl)equilibrium potential of thereaction Fe2++ 2e ⇔ Fe
  24. 24. Sacrificial anode selection test results – TEST 2 (pH 7.8)MetallicmaterialTestduration (h)Electrode potential(mV, Ag/AgCl)Current(mA)Corrosionrate (µm/y)Aluminumanode936 -1106 3.146 1224Zinc anode 936 -922 0.183 12Magnesiumanode336 h -1115 6.626 2750Stopped galvaniccurrent flow
  25. 25. ConclusionsThe adopted methodology for the coating selectionwas considered adequate. The exposition in watercollected in the field was the most important test.Coating C showed the best performance, followed byD, both a modified epoxy paint. The replacement willbe done after the confirmation of the effectiveness ofC in field tests.Aluminum alloy anode was considered the mostappropriate for transformers protection at theunderground chambers.25
  26. 26. 26Ongoing activitiesIn the laboratory, all coatings are being evaluated by immersedtest in the solution of sodium chloride for 4 months.Periodically, impedance curves were plotted.
  27. 27. 27In the field, all coatings are being evaluated associatedwith galvanic cathodic protection. The cathodic protectionwas also applied at five transformers.
  28. 28. Thank youfor your attention!28Question?complex question or details, please ask me by e-mail:aaraujo@ipt.br

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