VLA Electronics Memo No. 226
National Radio Astronomy Observatory Cathodic Protection of the VLA 60 mm Waveguide
Rudy Latasa October 1995
A corrosion survey of the underground waveguide at the VLA was conducted in May of 1980 and completed in March of 1981. At that time a recommendation was made by Pacific Corrosion Research, Inc. that a cathodic protection system be installed. Due to the high current demand and the cost, it was unfeasible to consider the sacrificial anode so the impressed current system was installed.
Common criteria for protection of the steel from corrosion required a minimum of -300 millivolts and an ideal of -800 millivolt potential relative to natural potential. The waveguide- to-soil natural potential ranged from -400 mv to -600 mv on the north and east arm. The west arm natural potential from A0 to A7 was in the range of -400 mv to -500 mv while the potential reading from W8 to W38 was in the range of -100 mv to -200 mv.
The consultant calculated that the total current required to give us minimum protection would be 228 amperes. This calculations was done on seventy-two observing stations, ~60km of 60mm underground waveguide and the track rail. The cathodic protection system consists of 11 air cooled rectifiers, 186 each 4" x 40" graphite anodes, 3 5 each 4" x 4" x 56 magnesium anodes. The magnesium anodes were used in several areas, such as road crossings, and some underground tanks. The underground tanks have since been removed.
The first set of graphs show the 1980 natural potential versus the 1984 applied potential and the 1980 natural potential versus the 1990 applied potential. The second set show the 1990 applied potential versus the 1993 and 1995 applied potential. All of the graphs show the minimum protection and the ideal protection. It was not until 1990 that we started to get into the ideal protection area. This was due to prevention maintenance and upgrading of the anode bed watering system. You'll also see that at each rectifier the potential goes high then tends to drop off with distance, and this is due to the high current that has to be applied to get the protection required at the end of each arm.
1
2
Applied Versus Natural PotentialEast Arm 1980 Natural and 1984 Applied
4siO
■+S<1)•+-jOQ.s
•+-J<0
Min. Protected Potential Ideal Protected Potential
Min. Nat Potential
2 3 4 5 6 7 8 9 10 11 Manhofes(Rectifiers 3=5.5 & 8=8)
&o'<u-C:c:<D- i- jOa.'O,0a
NATURAL East NP
East AP
Manhole NP
Manhole AP
West NP
West AP APPLIED
Applied Versus Natural PotentialEast Arm 1980 Natural and 1984 Applied
aO
c:-t-~.oCL. 0. 2 0 . £ °- cc ^ ^ 0.
2.8-.6-.4-.2-1 -
.86H42H0
Min. Protected PotentialI.-300 MV
I13 14
Ideal Protected Potential
■18 19 20 21 22 23 24
Manholes(Rectifiers 15= 11 AMPS)
2 h 1.8
1.6 1.4 1.2 1
b0.80.60.4
b0.20
£o
c:<Do
a .'C.a>c la<c
Min. Nat. Potential
Applied Versus Natural PotentialEast Arm 1980 Natural and 1984 Applied
&*0/o<DOCL~cd•+-JCD
Ideal Protected Potential
25 26 27 28 29 30 31 32 33 34 35 Manholes(Rectifier 25=30 amps)
Min. Protected Potential
.-300 MV
Min. Nat. Potential
Applied Versus Natural PotentialEast Arm 1980 Natural and 1990 Applied
£o
.03c:<1> H—io
CL
23S—iCD
Natural
2 3 4 5 6 7 8 9 10 11 Manholes (Rectifier 8 = 12.75) Min Nat. Potential
West NP
West AP
Manhole NP
Manhole AP
East NP
East AP Applied4
Nat
ural
Pot
entia
l V
olts
Applied versus iNamrai roienuaisEast Arm 1980 Natural and 1990 Applied
Min. Protected Potential
.300 MV
Ideal Protected Potential
13 14 15 16 17 18 19 20 21 22 23 24 Manholes(Rectifier 15 = 1 lamps 24 = 18amps)
Min. Nat. Potential
West NP
West AP
Manhole NP
Manhole AP
East NP
East AP. appliednatural
Applied Versus Natural PotentialsEast Arm 1980 Natural and 1990 Applied
O
.<tsc0
CL
251
natural
Min Protected Potential Ideal Protected Potential
West NP
West AP
28 29 30 Manholes
Manhole NP
Manhole AP
Min. Nat. Potential
East NP
East AP
o03c;a>“K iOa.■o.oaa
applied5
Appl
ied
Pote
ntia
l - M
illivo
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Appl
ied
Pote
ntia
l - M
illiv
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Applied PotentialsEast Arm 1990 and 1993 Applied
0 1 2 3 4 5 6 7 8 9 10 11 Manholes(Rectifiers 3=8.2 8=12Amps)
South NP South AP
Manhole NP Manhole AP
North NP North AP
Applied PotentialsEast Arm 1990 and 1993 Applied
13 14 15 16 17 18 19 20 21 22 23 24 25 Manholes Rectifiers 15=10.5 & 25=19amps
South NP South AP
Manhole NP Manhole AP
North NP North AP
6
Appl
ied
Pote
ntia
l - M
illivo
lts
Appl
ied
Pote
ntia
l -
Mill
ivol
ts
Applied PotentialsEast Arm 1990 and 1993 Applied
a=o
.TOc£oCL"Oa
" Minimal Protection Protected------------------------------------------------------
28 29 30 31 32 33 34 35 36 37 Manholes(Rectifiers 26=18 Amps)
South NP South AP
Manhole NP Manhole AP
I North NP North AP
Applied PotentialEast Arm 1993 and 1995
oc.
1.8-1.6-
i i 1.4-.TOc
1.2-1-
0.8-0.6-
Oa•9? 0.4-8: 0.2-
o-\0 1 2 3 4 5 6 7 8 9 10 11 12
Rectifeier 3=1 lamps and 8=17amps 1995
East ■ ■ Manhole m ^ Westi l i l East Manhole HH wesf
7
Appl
ied
Pote
ntia
l - M
illiv
olts
Appl
ied
Pote
ntia
l -M
illivo
lts
Appl
ied
Pote
ntia
l -M
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Applied PotentialEast Arm 1993 and 1995
13 14 15 16 17 18 19 20 21 22 23 24 25 Rectifeier 15=15amps and 25=20amps 1995
Applied PotentialEast Arm 1993 and 1995
26 27 28 29 30 31 32 33 34 35 36 37 Rectifeier 15=15amps and 25=20amps 1995
EastEast
ManholeManhole
WestWest
8
Appl
ied
Pote
ntia
l -M
illivo
lts
Appl
ied
Pote
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l -M
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Applied Versus Natural PotentialNorth Arm 1980 Natural and Applied 1984
O
c:<DO
CL
53■i-o(0
Min. Protected Potential Ideal Protected Potential
1 2 3 4 5 6 7 8 9 10 11 Manholes(Rectifier 1=7.5 & 7=7 Ampsl
Co-+-J.O
.TO■isc0)oCL~0.0)aQ.
Min. Nat. Potential
Natural South NP
South AP
Manhole NP
Manhole AP
North NP
North AP ------------------ Applied
Applied Versus Natural PotentialNorth Arm 1980 Natural and Applied 1984
O
T̂Oc:<DOCL~CD■+-jTO5:
Min. Protected Potential Ideal Protected Potential
13 14 15 16 17 18 19 20 21 22 23 24Manhofes(Rectifier 13 & 24ea. = 9.5 Amps
21.81.61.41.210.80.60.40.20
o
■isc0)oCL~o.0)a
Min. Nat. Potential
South NP
South AP
Manhole NP
Manhole AP
North NP
North AP AppliedJ
Applied Versus Natural PotentialNorth Arm 1980 Natural and Applied 1984
O
-CnC■Kioa.'cB
oo
2 t .z = : _____________________ _
1.8H Min. Protected Potential1.
1 .
1
0.0.2- 0
Ideal Protecred Potential
MV or better
29 30 31 Manholes
Min. Nat. Potential
o
/D*£3cCDOQ..<DQ.a
Natural |g South NP
H South AP
Manhole NP
Manhole AP
North NP
North AP Applied
Applied Versus Natural PotentialNorth .Arm 1980 and 1990 Applied
aO
c:<D •+—> o CL 0. £ 0.
0.03^ 0.
Min. Protected Potential Ideal Potected Potential
2 3 4 5 6 7 8 9 10 11 12 Manhole(Rectifier 7=22 amps,
r 2-1.8 *kj-1.6 O-1.4 *c5-1.2 •4̂
H <1>I o
-0.8 CL
-0.6 -o0)
-0.4 Q-0.2 a
t-o
Min. Nat Potential
itural South NP
South APManhole NP
Manhole APNorth NP
North AP appliedTer
Applied Versus Natural PotentialNorth Arm 1980 and 1990 Applied
*4-oO
cd)•+-JoCL
5TO
Min. Protected PotentialI Ideal Protected Potentialj-2-1.8 £-1.6 o>-1.4 TO-1.2 *£2c-1-0.8
0)o
CL
-0.6 ~o<D-0.4 Q.-0.2 Q.
13 14 15 16 17 18 19 20 21 22 23 24 Manhofe(Rectifier 13=8.75 & 24 = 13 amps)
Min. Nat. Potential
NATURAL - South NP
South AP
Manhole NP
Manhole AP
North NP
North AP. APPLIED
£o
c:<DO
CLTO
£
Applied Versus Natural PotentialNorth Arm 1980 and 1990 Applied
Min. Protected Potential Ideal Protected Potential
25 26 27 28 29 30 31 32 33 34 35 Manhofe(Rectifier 13=8.75 & 24 = 13 amps)
r2-1.8 £-1.6 o-1.4 TO-1.2 C-1-0.8
<DoCL
-OR “Od>-0.4 Q.-0.2 a
4-0
Min. Nat. Potential
Natural South NP
South AP
jfgm Manhole NP
Manhole AP
North NP
North AP Appliedli
Appl
ied
Pote
ntia
l Vo
lts
Appl
ied
Pote
ntia
l Vo
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Applied PotentialNorth Arm 1990 and 1993 Applied
-2- 1.8- 1.6-1.4- 1.2-1- 0.80.60.40.20
Applied PotentialNorth Arm 1990 and 1993 Applied
0 1 2 3 4 5 6 7 8 9 10 11 12 Manhole(Rectifier 7=11.5 Amps)
SouthSouth
ManholeManhole
NorthNorth
Minimal Protection Protected
13 v14 15 16 17 18 19 20 21 22 23 24 25 Manhole (13=20.5 & 24=12 Amps)
SouthSouth
ManholeManhole
NorthNorth
12
Appl
ied
Pote
ntia
l Vo
lts
Appli
ed
Pote
ntia
l Vo
lts
Appli
ed
Pote
ntia
l Vo
lts
Applied PotentialNorth Arm 1990 and 1993 Applied
26 27 28 29 30 31 32 33 34 35
SouthSouth
ManholeManhole
NorthNorth
Applied PotentialNorth Arm 1993 1995
Rectifer 7(1993=1 lamps 1995=9.5amps)13
Appl
ied
Pote
ntia
l Vo
lts
Appli
ed
Pote
ntia
l Vo
lts
Iss45c:a0 a.01
Applied PotentialNorth Arm 1993 1995
c:0 Q,31
13 14 15 16 17 18 19 20 21 22 23 24 25 Rectifier(13=20amps 24=12.25 amps1995)
Applied PotentialNorth Arm 1993 1995
a275c:oCL
*0.0)Q.£
sTO45c:0 a.■cCD
1
26 27 28 29 30 31 32 33 34 35
14
Applied Versus Natural PotentialWest Arm 1880 natural and 1984 Applied
2 3 4 5 6 7 8 9 10 11 Manhofes(Rectifier 6= 1 lamps) Min. Nat. Potential
Natural ___________ ^ South NP — Manhole NP ^ North NP
South AP Manhole AP ^ Applied
Applied Versus Natural PotentialWest Arm 1980 natural and 1984 Applied
O
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CL
5
514 15 16 17 18 19 20 21 22 23
Manhofes(Rectifier 14=9 amps)
t 2
-1.8 £-1.6 o-1.4 '<c-1.2 c :
-1-0.8
0)-UoOa.
-0.6 '0<D
-0.4 a-0.2-0
Min. Nat. Potential
Natural ggjggjj South NP m Manhole NP
South AP Manhole AP
North NP
North AP Applied15
Nat
ural
Pot
entia
l V
olts
Applied Versus Natural PotentialWest Arm 1980 natural and 1984 Applied
o
.32 cQ>0
^ O .i
1 * | j 0.-
Min. Protected Potential Ideal Protected Potential 00 CD
C\J ^
1-----------------------------------------------------------------------------------------------------------------------------------------1----------1_
&"o
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-1.2 c-1-0 ,8
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-0 .6O
-0.4 aQ
-0 .2■q;
25 26 27 28 29 30 31 32 33 34 35 36 37 38 Manholes(Rectifier 2 6 - 12amps) Min. Nat. Potential
Natural South NP m Manhole NP ^ |§ North NP
m H South AP Manhole AP § fg North A P ^ q_̂ ---------------- Applied
Applied Versus Natural PotentialWest Arm 1980 and 1990 Applied
Natural
Min.Protected Potential Ideal Protected PotentialT 2-1.8 a-1.6 o>-1.4 to-1.2 c-1-0.8
£oCL-0.6 73<D-0.4 a-0.2 *
4-02 3 4 5 6 7 8 9 10 11
Manhole (Rectifier 6=10 Amps)
Min. Nat Potential
SOUTH NP
SOUTH APMANHOLE NP
MANHOLE AP
NORTH NP
NORTH AP^ Applied16
Applied Versus Natural PotentialWest Arm 1980 and 1990 Applied
“4-0"o
42C<D*4-0OCL
•4̂ 1TO
1.111.-1.:
o. £0 o.
2 8 6H 4 2 1 8 6H
0.4 0.2H 0
:k e t
Min.Protected Potential
.-300 MV
Ideal Protected Potential
swim liiiriiFiiii an13 14 15 16 17 18 19 20 21 22 23 24
Manhole (Rectifier 14 = 10.5 amps)
21.81.61.41.2
M- 0.8- 0.6-0.4- 0.2-0
o/DCa>o
CL“Oa
Min. Nat Potential
Natural — ►UUU
SOUTH NP
SOUTH AP
MANHOLE NP
MANHOLE AP
NORTH NP
NORTH AP^ Applied
Applied Versus Natural PotentialWest Arm 1980 and 1990 Applied
O
TO-4̂3c:<D•4-0OCL
TO
2 8H 6 4H 2 1H
0.8 .6 4 2 0
0.0.
Natural
Min. Protected Potential
.-300 MV
Ideal Protected Potential
f t
25 26 27 28 29 30 31 32 33 34 35 36 37 Manhole (Rectifier 26= 17.5 amps)
21.8
- 1.6-1.4
1.210.8
h0.60.40.2
1-0
o
TO•£2c:0)-*~joCL73.0)
Min. Nat Potential
SOUTH NP
SOUTH AP
MANHOLE NP
MANHOLE AP
NORTH NP
NORTH AP^ Applied17
Appl
ied
Pote
ntia
l Vo
lts
Appl
ied
Pote
ntia
l Vo
lts
Applied PotentialsWest Arm 1990 and 1993
Rectifier 6=20amps1993 22amps1995
Applied PotentialsWest Arm 1990 and 1993
Minimal Protection Protected
13 14 15 16 17 18 19 20 21 22 23 24 25Rectifier 14=10amps 1993 and 1995
SouthSouth
ManholeManhole
NorthNorth
18
Appl
ied
Pote
ntia
l Vo
lts
Appl
ied
Pote
ntia
l Vo
lts
Appli
ed
Pote
ntia
l -M
illivo
lts
Appl
ied
Pote
ntia
l Vo
lts
Applied PotentialsWest Arm 1990 and 1993
26 27 28 29 30 31 32 33 34 35 36 37 Rectifier 26=17amps 1993 & 15amps 1995
Applied PotentialWest Arm 1993 and 1995
1 2 3 4 5 6 7 8 9 10 11 Rectifier 6 = 21 amps 1993 and 1995
South
SouthManhole
Manhole
North
North
19
Appli
ed
Pote
ntia
l -M
illivo
lts
Appli
ed
Pote
ntia
l Vo
lts
Appli
ed
Pote
ntia
l -M
illivo
lts
Appl
ied
Pote
ntia
l -M
illiv
olts
Applied PotentialWest Arm 1993 and 1995
Minimal Protection Protected
13 14 15 16 17 18 19 20 21 22 23 24 25 Rectifier 14 =10amps 1993 21amps 1995
Applied PotentialWest Arm 1993 and 1995
25 26 27 28 29 30 31 32'33'34 35 36 37 Rectifier 25=17amps 1993 and 21amps1995
Protected
SouthSouth
ManholeManhole
NorthNorth
?0
Appli
ed
Pote
ntia
l -M
illivo
lts
Appli
ed
Pote
ntia
l -M
illiv
olts