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

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l - M

illivo

lts

Appl

ied

Pote

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l - M

illiv

olts

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

illiv

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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

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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

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Appli

ed

Pote

ntia

l Vo

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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

-iSc:<Do

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

-1.4 >

-1.2 c-1-0 ,8

<D•+-JO

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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

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