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.

1. Organic Coatings for Corrosion Protection of
Transformers in Underground Chambers
IPT – Institute for Technological Research - Corrosion and Protection
Laboratory
São Paulo/Brazil
March/2012
IPT
Adriana de Araujo
Zehbour Panossian
Neusvaldo L. de Almeida
Alberto S. Junior
AES Eletropaulo - São Paulo
Metropolitan Electricity
Clay M. Martins
1

2. Outline
2
• Introduction
• Objectives
• Methodology
• Results
• Conclusions
• Future activities (field tests)

3. 3
UNDERGROUND CHAMBER (VAULT)
water level mark
Transformer
In the city of São Paulo, there are about 4000 UC. TheIn the city of São Paulo, there are about 4000 UC. The
transformers installed there and other electric facilitiestransformers installed there and other electric facilities
are submitted to an aggressive environment.are submitted to an aggressive environment.

4. 4
TRANSFORMER TANKNET WORK PROTECTOR
PEOPLE ACCESS
Sidewalk
Concrete walls
EQUIPMENT ACCESS
Cross section view

5. AGRESSIVE INVIRONMENT IN THE CHAMBERS
Heated water (< 60 ºC).Heated water (< 60 ºC).
Contaminated water (Contaminated water (Solid material,
distinctive color and odour).
Work temperature (< 70 o
C)
High temperature (< 120 o
C)
rain + urban debris, groundwaterrain + urban debris, groundwater
infiltration and sewer leakageinfiltration and sewer leakage
Stagnated water with periodic flooding
thermometer

6. 6
Steam
Steam
Because of the steam in theBecause of the steam in the
chambers, the emerged partchambers, the emerged part
of the transformers areof the transformers are
constantly exposed to a highconstantly exposed to a high
humidity atmosphere andhumidity atmosphere and
water dropletswater droplets

7. 7
Blister
Rust and flakingRust and flaking
Rust and debris depositionRust and debris deposition
As a result of theAs a result of the
aggressive environment,aggressive environment,
in few years the coatingin few years the coating
is quite damaged.is quite damaged.

8. 8
RustRust
FlakingFlaking
SUPERFICIAL
PROCTECTION FAILURE

9. 9
• most of them: 500 kVA;
• Some are retrofitted
and repainted in less
than 5 years
• The repaint is done
by the company
staff.
• coal tar paint overcoal tar paint over
shelf primer (ironshelf primer (iron
oxide)oxide)
Complex mixture of PAHsComplex mixture of PAHs
High VOCHigh VOC

10. 10
Objectives
Select new protective coating
Environment-friendly and high performanceEnvironment-friendly and high performance
Select galvanic anode for the cathodic protection
of the transformers

11. 11
Methodology -
select a new coating

12. 12
Paint
Thickness
applied
(μm)
Resin
VOC
(g/L)
High
dry film
por
coat
(µm)
Primer paint Others
AA 450 Epoxy
polyamide
377 140
Epoxy zinc
phosphate _
BB 400 176 400 _ _
C 300300
Epoxy
modified
143 1000 _ STST/CDCD/ERER
D 300300 255 500 _ STST/CDCD/DTDT
E 300300 150 150 _ STST/CDCD/ERER/DTDT
STST - accepts mechanical surface treatment or flash rust.
DTDT - accepts high relative humidity or slightly moisture
surface.
ERER - improve edge protection.
CDCD - suitable for use with cathodic protection systems.
Paint FeaturesData established
Table 1: Main features of the studied paints

13. 13
Specimens for performance tests
• small carbon steel sheets (10 cm x 15 cm x 3 mm):
grounded (remove the sharp edges), cleaned (remove
contaminations), blasted (steel grit, Sa 2½, ISO 8501-1):
roughness of about 50 µm, painted (according to their data
sheets), scribed some specimens (2 mm)
• select those specimens most appropriate: according
to 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
Performance laboratory tests for coating selection
EIS: immersion 5 % NaCl solution for 24 h.
Scanned frequency range was from 105
Hz
to 10-3
Hz and the amplitude of
perturbation was 20 mV.
Salt spraySalt spray: ASTM B 117, exposure time was
3000 h, with weekly visual inspections. InIn
the end, measurement of thethe end, measurement of the creepagecreepage
corrosioncorrosion andand EISEIS (Bode diagrams).(Bode diagrams).

15. 15
Cathodic disbondingCathodic disbonding: ASTM G 8ASTM G 8 (method B: impressed
current, 30 days, hole Ø 6.35 mm);
Anode
3 specimens

16. 16
Water from 20 UC was collected in field. The were chemically analyzed and
a 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--
22
mg/L; SOmg/L; SO44
2-2-
6 mg/L.6 mg/L.
The specimens were exposed to immersion in
heated and contaminated water and to a high
humidity atmosphere. The test was conducted
by 3600 h, with weekly visual inspection.
Vapor spaceVapor space
Immersed part
Heating plateHeating plate
(~ 70(~ 70 oo
C)C)
Immersion testImmersion test

17. 17
Methodology -
select anode for cathodic
protection

18. 18
One reactor was developed especially for the evaluation of
anodes for the galvanic protection of the underground
transformers. Tested anodes : aluminum, zinc and magnesium.
1 anode ~ Ø 18 mm x 25 mm in
height.
5 carbon steel coupons: 1 ~ Ø 60 mm
4 ~ 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; SO44
2-2-
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; SO44
2-2-
5 mg/L.5 mg/L.
Electrode potential and current flow
established was monitored. In the end,
the corrosion rate was calculated.

19. 19
Results

20. 20
Coating
Salt spray
Visual
inspection
Creepage
corrosion
(mm)
Log of the Impedance modulus date
(│Z│, ohm/cm2 at 0.01 Hz)
Blank specmens After 3000 h
Thickness
AA
UnchangedUnchanged 4.84.8 8,0218,021 8,0668,066
455455 541541 484484
BB
UnchangedUnchanged 6.36.3 7,887,88 7,8867,886
410410 359359 371371
CC
UnchangedUnchanged 4.04.0 7,8897,889 8,8698,869
289289 287287 342342
DD
UnchangedUnchanged 6.26.2 8,318,31 8,5038,503
290290 301301 323323
E
UnchangedUnchanged 6.86.8 7,8377,837 8,3598,359
284284 268268 285285

21. Coating
Cathodic
disbonding
Immersion test in contaminated water
Average
equivalent circle
diameter- ECD
(mm)
Visual inspection
Emerged area Immersed area
AA
15.015.0 Unchanged Blister after 240 h
BB
11.811.8 Unchanged Blister after 240 h
CC
17.717.7 Unchanged Unchanged after 3600 hUnchanged after 3600 h
DD
19.1 Unchanged Blister after 864 hBlister after 864 h
E
34.2 Unchanged Blister after 672 h

22. Coated test specimens after
3600 h of immersion in a
contaminated water
Coating C
Blisters
Blisters
Blisters
Blisters

23. Sacrificial anode selection test results – TEST 1 (pH 4.5)
Metallic
material
Test
duration
(h)
Electrode potential
(mV, Ag/AgCl)
Current
(mA)
Corrosion
rate (µm/y)
Aluminum
anode
912 -936 0.615 941
Zinc anode 912 -610 mV-610 mV 0.021 15
Magnesium
anode
912
-933 0.694 53
< 850 mV (Ag / AgCl)
equilibrium potential of the
reaction Fe2+
+ 2e ⇔ Fe

24. Sacrificial anode selection test results – TEST 2 (pH 7.8)
Metallic
material
Test
duration (h)
Electrode potential
(mV, Ag/AgCl)
Current
(mA)
Corrosion
rate (µm/y)
Aluminum
anode
936 -1106 3.146 1224
Zinc anode 936 -922 0.183 12
Magnesium
anode
336 h -1115 6.626 2750
Stopped galvanic
current flow

25. Conclusions
The adopted methodology for the coating selection
was considered adequate. The exposition in water
collected in the field was the most important test.
Coating C showed the best performance, followed by
D, both a modified epoxy paint. The replacement will
be done after the confirmation of the effectiveness of
C in field tests.
Aluminum alloy anode was considered the most
appropriate for transformers protection at the
underground chambers.
25

26. 26
Ongoing activities
In the laboratory, all coatings are being evaluated by immersed
test in the solution of sodium chloride for 4 months.
Periodically, impedance curves were plotted.

27. 27
In the field, all coatings are being evaluated associated
with galvanic cathodic protection. The cathodic protection
was also applied at five transformers.

28. Thank you
for your attention!
28
Question?
complex question or details, please ask me by e-mail:
aaraujo@ipt.br