AlllOt, 17A7b 4

NBSIR 78-1486 (DOE)

A 1 1 1 0-1 7-ittSJl''-3 Development of In-Situ

Techniques for the Detection

and Measurement of Corrosion

of Copper Concentric Neutrals

in Underground Environments

J. Kruger, U. Bertocci, E. Escalante, and J. L. Mullen

Corrosion and Electrodeposition Section

Chemical Stability and Corrosion Division

National Measurement Laboratory

National Bureau of Standards

Washington, D.C. 20234

June 1978

Annual Report

Prepared for Department of Energy

Washington, D.C. 20545

. 1)56

73-1486

National Burgac eZ Standards MAY 1 4 1979

^

nm- i\cc-(tvr

NBSIR 78-1486 (DOE)

« */ DEVELOPMENT OF IN-SITU

TECHNIQUES FOR THE DETECTION

AND MEASUREMENT OF CORROSION

OF COPPER CONCENTRIC NEUTRALS

IN UNDERGROUND ENVIRONMENTS

J. Kruger, U. Bertocci, E. Escalante, and J. L. Mullen

Corrosion and Electrodeposition Section

Chemical Stability and Corrosion Division

National Measurement Laboratory

National Bureau of Standards

Washington, D.C. 20234

June 1978

Annual Report

DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

Prepared for Department of Energy

Washington, D.C. 20545

Ut- -

[ U.S. DEPARTMENT OF COMMERCE. Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Executive Sunmary

In the second year of a three year project aimed at developing techniques

and instrumentation for detecting and measuring corrosion on copper concentric

neutral (CCN) wires, the following points were accomplished:

1) Current-potential and ac impedance measurements on a number of

specimens have been performed in the laboratory under different

environmental conditions, and the data analyzed.

2) The development of equipment and techniques for the employment

of electrochemical noise as a diagnostic tool has continued. A

special potentiostat has been built and tested.

3) Potential and polarization measurements on buried cables in the

field have been carried out. A number of sources of interference

have been found, and techniques for minimizing their effect on

the measurements have been developed.

4) Examination of portions of the buried cables, and modification of

the soil in order to accelerate corrosion have been carried out.

In the coming year it is planned to correlate polarization measurements of corrosion with visual inspection, test various laboratory developed

techniques in the field, carry out measurements in larger cable systems and

on an actual operating cable.

1. Introduction

This is the second annual report of a three year project whose

objective is to develop techniques for detecting and measuring corrosion

on copper concentric neutral (CCN) wires buried in the soil.

During the first year, efforts in the laboratory were directed

at finding the conditions that produce rapid localized corrosion as

observed in the field. This was accomplished as reported in our

annual technical report of January 1977. Also, during the first year

specimens were prepared and buried at the outdoor NBS site, and preliminary measurements were made on these specimens. In the year

covered by this report, 1977, our immediate objective was to bring

the findings in the laboratory to bear on the measurements at the

outdoor test site.

The laboratory work consisted in testing polarization and

impedance measurements on CCN wires in electrolytic cells under

various conditions, and in developing and testing instrumentation

for the measurement of electrochemical noise, a technique that

shows promise of eventual application in the field.

A major part of the work in the past year has been directed

to the development of field measurement techniques on actual CCN

cables buried underground, both in the presence and in the absence

of a superimposed ac signal. Some experiments on the effect of

modifying the composition of the soil on electrochemical measurements has also been carried out,

2. Laboratory Studies

2.1 Polarization measurements

In order to provide useful data for assessing the significance

of polarization measurements on buried cables, tinned CCN wire
electrodes immersed in neutral solution gelled with agar,

with and without the addition of NaCl , have been tested, taking

current-potential readings at long time intervals. The results have

been analyzed using the curve-fitting method developed by Mansfeld (1).

For this purpose a program to be used on a desk calculator was

developed. The parameters derived from the analysis of the polarization curves are summarized in Tables I and II. In the tables

the open circuit potential (O.C.P.) versus the normal hydrogen

electrode (NHE) as well as the corrosion current density I are corr

reported. The constant B, whose meaning is explained in equation

(1), and the anodic and cathodic Tafel slopes b and b are also

a c given, as they are obtained from the curve-fitting program. The

quality of the fit is also indicated. Where no fit was possible,

the corrosion current was estimated with the linear polarization

method.

The fitting of the experimental values to the fundamental

equation of electrode kinetics was found to depend quite strongly

on the value chosen for the open circuit potential, which particularly

affected the value of the Tafel slope constants. For these reasons,

some of the values listed in the tables are considered of doubtful

reliability.

In spite of the scatter caused by the difficulty in chosing

the optimum fitting conditions, a number of general conclusions can

be drawn:

a) Corrosion currents tend to decrease with time, indicating

that corrosion products have some protective value at least if no

removal is possible as it is in agar gelled solutions.

- 2

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b) The presence of chlorides tends to increase the corrosion

current

.

c) The value of the constant B, necessary for the evaluation

of the corrosion current I corr from simple linear polarization

measurements according to the equation

i corr

Ai , 1 1 AE B RpB 0 )

lies between 20 and 30 mV.

d) Concerning the cathodic Tafel slope b

c

, it was expected to

find a value of infinity in every case, since the cathodic process is

supposed to be the diffusion controlled reduction of oxygen. Very

large values of b

c were actually found in many cases: however, values

between 100 and 200 were also frequently calculated by the curvefitting program. A tentative explanation is that some of the oxidation

products of the CCN wire (either copper or tinning alloy) were being

reduced during cathodic polarization. This would be in agreement

with the results of the potentiodynamic scans, described in the previous

annual report, where cathodic peaks were found on tinned wire and

on pure copper in chloride containing solutions. Reduction of

corrosion products should be made more likely in these experiments

where, as in the soil, even soluble corrosion products cannot be

removed by convection. These results, therefore, can be signficant

for the interpretation of the field measurements,

e) No easily detectable differences were found between specimens

exposed to an ac signal and those not so treated. Since visual

observation of the specimens has not been performed yet, it is not

known whether pitting has occurred at a different rate on the two

- 3

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types of specimens. However, it should be stressed that the polarization measurements were always performed while the a c signal

was disconnected. The failure to detect a significant difference

in polarization resistance between specimens with and without ac

once this signal is removed, indicates the need to carry out these

measurements when the ac signal is being applied.

2.2 Impedance measurements

Impedance measurements, which have been extensively used in

electrode kinetics research (2), are being applied to corrosion

studies (3). These measurements are very attractive, because

if the electrode system under investigation can be considered as

consisting of a resistor R

$

in series with a parallel combination

of a resistor and a capacitor C^, a plot of the imaginary impedance

Z" versus the real impedance V will give R

s as the limit of V

when the frequency approaches infinity and (R£ _ R

S

) as the limit

of Z' when the frequency approaches zero. The physical interpretation

of R

s is the resistance in the electrolyte that causes the ohmic

drop error, and R

$

is the electrode or polarization resistance, in

the absence of complicating kinetic factors at the electrode.

Additional information can be obtained by a careful analysis of the

curves, but obtaining polarization resistance and ohmic drop would

be sufficient for estimating corrosion rates.

During this year impedance measurements have been made on a

number of cells where the electrode was a piece of tinned CCN wire

in solutions gelled with agar and under various environmental conditions.

The results obtained are summarized in Tables III, IV, V and VI,

and some of them are presented in graphic form in fig. 1 and 2.

- 4

-
Examination of the results shows that the high frequency limit

of V is at the most a few ohms, indicating a negligible and

therefore a very small ohmic drop error. On the low frequency side

the readings were limited to 5 Hz by our equipment, and all the curves

show that this frequency is still too high to allow a measurement of

the reaction resistance. Differences due to the experimental conditions can be derived from the tabulated values, but a large scatter

in the data taken at various times since the tests began obscures

the significance of other factors and makes interpretation difficult.

The impedance is larger (at the same frequency) in solutions without

chlorides and in the presence of oxygen. This might indicate that

a more protective film forms in the absence of chlorides, but since

the frequency range is limited, it is impossible to draw reliable

estimates of the reaction resistance. The impedance seems to be

larger for samples to which no a,c, signal has been applied, and

perhaps there is a trend to larger values with time. The scatter

of the results, however, makes these conclusions highly speculative.

A peculiar shape in the Z'-Z" curves for specimens in N 0

had been observed and mentioned in a previous quarterly report.

This was a semicircle at the high frequency end of the plot, suggesting a complex electrode reaction. Curves showing this feature

are shown in fig. 2. Unfortunately subsequent careful measurements

were never able to show this feature again. The new curves obtained

are also shown in fig. 2.

We have also tried to extend the frequency range of the impedance

measurements more than two orders of magnitude. These measurements are

very time-consuming and therefore only a few attempts have been made.

Fig. 3 and 4 show results for a wire in nitrogen and one in oxygen.

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Both figures show that it would be necessary to extend the low frequency

well beyond 10 mHz, which is our limit at the present time. The results

are therefore inconclusive: in the case of Na^SO^ in Np (fig. 3)

Z" is still rising at 0.02 Hz. Although the plot would not be incon2

sistent with a reaction resistance of the order of 150kfi-cm , and there2 fore with a corrosion current of a few tenths of a yA/cm , as obtained

from polarization measurements on the same cell (see table I), it

could be argued that the impedance is due to diffusion processes. Fig.

4, obtained in an oxygen atmosphere is also inconclusive. If is possible

that the plot shows the existence of two electrode reactions with two

time constants, but since no maximum in Z" could be observed no firm

conclusions can be drawn.

Impedance measurements therefore do not show much promise to

become a useful diagnostic tool for the purposes of this project

for two reasons: a) a large scatter in the results obscures their

significance, and this is likely to occur also in measurements in

the field, b) the frequency range required seems to extend to

extremely low frequencies, with attendant complications as to the

instrumentation necessary, not to mention the long time involved in

obtaining the data.

2.3 Noise measurements

The major accomplishment has been the successful development at

NBS of a special low noise potentiostat . This instrument has shown

much better characteri sties than commercial potentiostats whose noise

level, as shown in fig. 5, is such that in many cases it can obscure

the information sought.

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The NBS potentiostat has a special amplifier for the detection

of the a.c. current that runs through the test cell. The useful

frequency range is from 10 mHz to 1 kHz. The noise current I n generated

by the potentiostat can be considered as the sum of I caused by the

control voltage, and I. generated inside the a.c. amplifier

By means of the circuit shown in fig. 6, the instrument can be

calibrated, measuring the noise spectrum for various values of the

resistor simulating the working electrode. Results are shown in

fig. 7. The noise current is inversely proportional to the value of

the resistor employed since it is

I cv

= V /R

cv

(3)

where V cvis the noise voltage in the control voltage generator. V

can be measured directly, with the circuit in fig. 6, by turning the

switch up and measuring directly the noise voltage across the resistor.

The results are shown in fig. 8. The upper solid trace is V cv which

appears with the spectra shown in fig. 7. V cv

is of the order of

5-10 ^V//Hz~ but increases up to 100 nV//Hz at very low frequency

where flicker noise is predominant. The dotted line on fig. 8

indicates that a certain degradation in the quality of the signal

occurs when a current near to maximum output of the potentiostat

is drawn. The two peaks at 60 and 180 Hz are due to incomplete

shielding from the a.c. power. They, however, can be reduced by

better electromagnetic shielding, and are not very troublesome

since they can easily be recognized as spurious signals.

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-
Fig. 8 shows also the spectral amplitude when the potentiostat

is disconnected. The noise found here is due to the amplifying and

measuring circuits and represents the minimum detection level of the

equipment in the present configuration. The potentiostat adds to that

a noise which is only five times larger.

When the resistor simulating the working electrode is larger

than a few Kft the noise current does not increase anymore. As shown

by equations (2) and (3), in these conditons the value of 1^, the

noise generated by the a.c. amplifier is predominant. This is of the

order of 3. 10~^A/»4fz.

In order to form an idea of the capabilities of the noise measurement system, some electrode systems have been investigated. As an

example of a low noise electrode the deposition and dissolution of

copper in copper sulfate has been tested. Results are shown in fig. 9.

The noise levels are consistent with a reaction resistance of the

2 order 20ftcm , which can be calculated by combining equations (2) and

(3): o

V 5-10 0 cv

R

= = TT- (4)

V'a V3

' 10

' 11

Such a resistance is equivalent to an exchange current density of about

2

1 mA/cm , close to that found in the literature. Higher noise, that

is lower reaction resistance, is found when current is passing. These

results are in agreement with the i nterpretation that the noise measurements in this case are equivalent to a wideband impedance measurement,

from which one can derive the value of the reaction resistance.

A corroding system, aluminum in boric:borate solution, in

the absence and in the presence of a small amount of NaCl , has also been

- 8-
tested. Results are shown in fig. 10 and 11. The noise spectra of

fig. 10 in the absence of NaCl show only minor changes by anodic

polarization. The current is small, and changes are limited to an increase in noise at low frequencies and to a shift in the peak at

about 600 Hz, probably due to a decrease of the electrode resistance.

Only by strong cathodic polarization, when hydrogen evolution sets in

(i = -1 mA/cm ), is the noise level drastically increased at all

frequencies, as shown by the solid line in fig. 10. We have too little

experience for the interpretation of this result; it is possible

that the high noise is associated to the discrete nature of hydrogen

bubble formation.

Fig. 11 shows the dramatic effect of the addition of 0.01 M

NaCl, which is known to cause pitting. While the zero current spectrum

is not affected, anodic polarization causes a steady increase in

current, often in bursts, and an increase in noise levels of more than

two orders of magnitude. The spectrum exhibits rather well developed

peaks, as shown in fig. 12, but whether these features occur in a

systematic way is not yet known.

2.4 Summary of the laboratory work

The objectives achieved in the past year can be summarized as

follows

:

a) Current-potential measurements on CCN wires have been

carried out, showing the influence of the various environmental

condi tions

.

b) Kinetic parameters, useful for the interpretation of the field

polarization measurements, have been obtained from the analysis of

the current-potential data.

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c) Impedance measurements on CCN wires have been tested as

to their suitability as a diagnostic tool in the field. The results

have been negative.

d) The development of instrumentation for another possible

corrosion detection method, the measurement of electrochemical noise,

has been continued. A special potentiostat has been built at NBS

and tested, with encouraging results.

e) Electrochemical noise measurements have been made on a

number of electrodes, and experience in interpreting the experimental results is being accumulated.

- 10 -
3. Field Studies

During the first year specimens were prepared and buried at the

outdoor NBS test site, and preliminary electrochemical measurements

were made after burial. The results of this are described in the first

annual report.

This year, our objective has been to bring the findings in the

laboratory to bear on the measurements at the outdoor test site.

This section will deal with this and other aspects of the studies.

Through the year, the experimental procedure was continuously

being changed and improved. The main reason for these changes was

to raise the signal to noise ratio of our measurements with the bulk

of the interference being the background alternating current in the

cable. In principle, the solution to the problem is simply to separate

the dc signal of interest from the ac signal. In practice the difficulty is that the dc signal is less than 10 mV while the background signal is over three orders of magnitude larger or about

50 volts. Along with this ac voltage a dc component was discovered.

In addition, there are a number of "earth currents" at our

test site which emanate from a variety of sources some of which we

have identified. Three of these sources in decreasing order of importance are, 1. the grounding rod at the power supply transformer to

the test site, 2. the steam generating plant for the entire NBS

complex located about 200 meters north east of our test site, and, 3.

the cathodic protection system in operation on the utilitites distribution system for the NBS complex. Other sources of interference

such as a high frequency ac signal coming from the NBS broadcasting

system and a dc communication line that runs alongside our test site

are intermittent, low power signals which are of little significance.

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At the initial stages of the program, alternating current was

not imposed on the buried cables. Thus, the electrochemical measurements during this period were satisfactory. The only interference

in these measurements was the current from the grounding bar at the

power supply transformer for the test site.

3.1

Experimental Procedure

3.1.1 Potential Measurements

Open circuit potential surveys are made of each specimen at the

field site. This survey consists of making soil surface potential

measurements at the intersections of an 18m x 2m grid at lm intervals

along the length of the buried cable using a Cu-CuSO^ reference electrode.

Each point on the grid is marked at the field site with a permanent

aluminum marker imbedded in the ground. With these markers it is possible to make repeated measurements over several months at the same

point. The survey allows one to rapidly and simply detect the changes

that may occur along the length of the cable. It was from the potential

survey measurements that the earth currents were first detected.

In an effort to determine the relative amount of earth current

flowing on the NBS grounds compared to other sites, potential measurements between two like reference electrodes were made as shown in

figure 13. The potential on the perimeter of the circle was measured

with reference to the electrode located at the center of the circle.

Considering the earth between the two electrode as a simple resistor,

a qualitative evaluation of current flow can be surmised. This measurement was made at two sites in addition to the NBS site.

3.1.2 Soil Modification and Cable Inspections

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As a result of the laboratory studies which indicated that the

corrosion rate of the concentric neutral cable could be raised by

increasing aeration in the presence of chlorides, the soil at the

field test site was locally modified. An excavation was made on cables

3 and 4 that was 1 x 1m square and over 1m deep extending approximately

30 cm below both cables. While exposed, the 1 meter lengths of cable

were visually examined. One of the cables was cleaned with distilled

water prior to the inspection.

After visual inspection, the excavation was backfilled with a

mixture of equal volumes of the soil removed and sand. As the layers

of soil-sand mixture were added, a solution of sodium chloride was

poured over each layer. A total of four kilograms of sodium chloride

were added to the backfill material. Three months after the modification, the soil was qualitatively tested for chloride content and

the soil resistivity measured at three locations at the site, and at

three depths at each location. The chloride evaluation was made by

taking 100 g of soil and mixing it with 200 ml of distilled water.

After standing for 30 minutes the mixture was filtered so that a

clear solution resulted. 1 ml of a saturated solution of silver

nitrate was added to the filtrate causing any chloride to precipitate

as silver chloride.

3.1.3 Polarization measurements

The circuit diagram being used for polarization measurements is

illustrated in figure 14. This diagram can be thought of as two

separate circuits with the section to the left of the specimen providing

and measuring the current for polarization while the circuit to the

right measures the resultant potential change of the specimen.

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The section on the left has a DC power supply whose current output to the specimen is controlled by a voltage divider circuit not

shown in the illustration. In addition to this voltage divider there

is a variable resistor which also assists in current control. Two

switches in parallel, as illustrated, can completely isolate the specimen from the current circuit. The normally open (N.O) switch is a

push button microswitch used for intermittent current control. The onoff switch bypasses the N.O. switch when needed for longer term current

applications. The output of the DC power supply is measured by a zero

resistance ammeter. Notice that the ammeter is in parallel with a

capacitor which serves as an AC filter for the ammeter, and allows most

of the AC to travel to ground through the counter electrode without

affecting the DC current measurement.

The section of the circuit shown to the right of the specimen in

figure 14 is used to measure the potential of the specimen with respect

to the Cu-CuSO^ reference electrode. The potential is measured across

a Wheatstone bridge which is used to measure and compensate for any IR

error.

The high impedance voltmeter is isolated from the background AC

by means of a two-pole low-pass filter circuit which reduces the 60 Hz

signal by as much as a factor of 5000.

Measuring the corrosion rate of a finite length of a metallic

member in an electrolyte such as soil is, in general, not difficult

using techniques developed here and elsewhere (4). However, measuring

the corrosion rate of what amounts to an infinite length of metal poses

a special problem. The problem is that of not knowing how much of the

metallic specimen surface is being polarized. If the surface area being

polarized is not known, then corrosion current densities cannot be calculated.

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Fortunately there may be ways to get around this problem. For

example, polarization measurements can be made at several points along

a cable. The positions of the electrodes would be changed for each

measurement as illustrated in figure 15. The polarizability, the

current necessary to polarize a section of cable 6 mV, of each section

of cable would then be compared. The amount of current necessary to

polarize a section of cable 6 mV is directly related to the corrosion

rate of the section. Another approach is to distribute the current

uniformly over a length of cable and then look for any discontinuities

in potential along the cable. Such discontinuities would warrant

closer inspection.

In order to determine current distribution, current was

applied to a cable from a counter-electrode driven into the ground

at a given distance as shown in figure 16. Potential measurement

were then made over the length of the cable. The change in potential

with and without polarizing current applied was then plotted for

each point along the length of the cable.

3.2 Results and Discussion

A considerable amount of time and effort has been expended in

improving our ability to do measurements in the presence of interfering

signals. As mentioned earlier the sources of interference have been

numerous. Each had to be identified and eliminated by either removing

the source or filtering out its effects.

3.2.1 Potential Measurements

The first evidence of a problem appeared in the open circuit

potential measurements of the cables. The effect of the AC signal

on the potential readings of cable 3 is illustrated in figure 17

- 15 -
which shows that with AC the potential around position 10 of cable

3 is over 50 mV more noble than the end of the cable. Because this

variation in potential with position did not improve with time, it

was investigated further. Open circuit potential measurements made

along a line perpendicular to the length of the cable indicated an

increase in potential as one moved a short distance towards one

source of ac , cables 1 and 2, as shown in figure 18. As several

meters were traversed with the potential readings, a dramatic increase

in potential developed immediately over cables 1 and 2 as figure 17

shows. An even greater variation in potential (not shown) occurred as

the measurements were extended beyond cables 1 and 2 and approached

the area of the grounding rod for the field site power station.

It became apparent that this interference could not be tolerated,

and had to be removed before the electrochemical measurements could

proceed. Thus, the grounding rod was moved over 40 m away from the

nearest cable reducing the effect of this source of interference.

Once this massive interference was removed, it became possible

to analyze and correct the other sources. Using a portable oscilloscope

it was found that along with the ac signal there was a DC component.

This component was coming through a common ground that connected our

site to a distant building housing large power transformers for the

entire NBS site. This dc component was easily removed by inserting

an isolation transformer at our field site which filtered out all

unwanted dc signals from the transformer station. Moving the ground

rod and introducing the isolation transformer into the circuit resulted in reducing the total effect of interference by an order of

magnitude as shown in figure 19.

- 16 -
The oscilloscope also revealed an intermittent high frequency

ground signal which was eventually found to come from the NBS fire

and security broadcasting station whose antenna is located in the

same building that houses the power transformers and with whom we

have a common ground. This is a low order signal that would have

negligible effect on our site.

Using two reference electrodes in a circle it was possible to

trace earth current sources. As the field site was traversed it was

found that a current source came from the direction of the steam

generating plant located over 100 m from our field site. A second

possible source of this earth current is the NBS cathodic protection

ground bed located over 1000 m from our test site. The maximum

potential measured between the reference electrodes 5 m apart was

30 mV which for our soil results in a maximum current of approximately

0.3 mA assuming a soil resistivity of 10,000 ftcm. Relative earth

current measurements were made at two other sites as figure 20 illustrates.

At Lock Raven, north of Baltimore, Maryland, the earth current calculated was approximately 0.8 mA assuming a soil resistivity of 15,000

ftcm. The ocean beach at Dam Neck, Virginia, resulted in the lowest

earth current at 0.06 mA with a soil resistivity of 20,000 ftcm. On

the basis of these few measurements it was judged that the earth

currents at the NBS site were typical of those found in this region.

Since little can be done about these currents short of shielding the

entire field site with a buried conducting barrier, and because they

are expected to exist to some degree at all locations, it was decided

to monitor, but not eliminate these low order earth currents.

- 17 -
Through the combination of the ac filtering system described

earlier, the removal of the grounding rod from the vicinity of the

test site, and the i ncorporation of the isolation transformer, all

sources of interference were reduced to a tolerable level. Figure 21

illustrates the potential of cable 3 with and without ac on cables 1

and 2 with the filtering system in use. Similar data on cable 1

which has the ac signal imposed on it are shown in figure 22. The

instability in the potential readings after 8 days is clearly evident

in this figure. Three weeks later the potential stabilized and has

remained relatively unchanged for the first three months.

3.2.2 Soil Modification and Cable Inspection

The visual inspection of the exposed cables showed that some

loss of the tinning had occured. On some areas of the wire, the copper

was clearly visible through the coating. This is not necessarily

significant since the coating was extremely thin to begin with. Thus,

it was decided that little, if any, attack had developed on the concentric neutral wires during the eleven months of burial.

The chloride content evaluation made 3 months after the soil

was modified revealed that all soil samples contained some traces

of chloride, but only the intentionally modified soil contained significant concentrations detectable by the addition of silver nitrate to

the aqueous extract of the soil.

The soil resistance measurements of samples taken from the same

areas indicated that the resistivity of modified soil averaged 3,300 ficm

from 0.5 to 1 m below the surface while other soil samples located away

from the modified soil, but at the same depth, had soil resistivities

that averaged almost 12,000 ftcm. Clearly the soil modification was

- 18 -
still effective after 3 months. However, electrochemical measurements

indicate that in the area of the soil modification there has been no

discernible effect on the potential of the cables as shown in figure 23

3.2.3 Polarization Measurements

As indicated earlier, the initial polarization measurements were

made at four points along each cable. Figure 24 is a plot of the current

necessary to polarize the cable 6 mV, the polarizing current, for cables

3 and 4 at three different periods of time. The polarizing current for

the cables has increased slightly and uniformly with time. Of particular interest is the fact that no significant change in current is

observed where the soil is modified. There may be two reasons for

this lack of reaction at that section of the cable. First, during

this period the weather has been unseasonably dry. Second, because of

low diffusion rates in soil, it may take more time for the cable to

respond to the change in its environment.

Imposing an ac signal between cables 1 and 2, on the other hand,

has had a large effect on the polarizing current. The initial polarization measurements indicated that the polarizing current of cable 1

was comprable to cables 3 and 4. Since applying the ac the polarizing

current of cable 1 has been rising steadily as shown in figure 25. In

particular note the relatively high polarizing current around position

12 after approximately 2 months.

In order to evaluate the distribution of current over the cable

during polarization, the change in potential over the length of the

cable was measured as current was applied from a vertical steel rod

in the ground. The distance of the current source was varied from

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0.5 at to 1 m. The resulting data, illustrated in figure 26, indicate

that from a distance of 1 m the current is distributed over the 15 m

cable with little concentration of current in the vicinity of the source

located at position 5. As the current source (counter-electrode) is

moved to within 0.5 m of the trench the current distribution begins to

show a distinct concentration around the source. When a current of 900 mA

is applied and at a distance of 0.5 m, 85% of the current is concentrated

along 9 m of the 15 m cable. As the current is increased the distribution

becomes more uniform. This type of information which describes the

current distribution during polarization is necessary for corrosion rate

determi nations

3 . 3 Summary of Field Stu d ies

a) the electrical interference problems have been eliminated.

b) the soil has been locally modified around the set of cables,

that has no ac signal applied

c) visual examination of a section of cable without ac revealed

little corrosion after 11 months of burial.

d) polarization techniques are now being used in the field site

to evaluate the extent of corrosion on the cables.

e) these measurements indicate that the corrosion rate of the

cables with an imposed ac are corroding at a substantially

higher rate than those without ac.

4. Pla ns For Next Y ear

4 . 1 La boratory Studies

1) Comparison between polarization measurements and weight losses

2) Analysis of polarization measurements in the presence of large

ac signals
3) Noise measurements on Copper and tinned Copper

4) Work on overcoming problems arising from taking noise measurements in the field

4.2 Field Studies

1) Correlation of the electrochemical data with careful visual

examination of the cables in the field

2) Evaluation of the polarization techniques and their distribution

of current on longer cable in the field and application of these

techniques to real cables

3) Evaluation of the influence of the carbon impregnated polyethylene on the distribution of current

4) Modification (locally) of the soil on a set of cables with

ac

5) Evaluation of the noise technique on cables in the field.

- 21 -
References

1) F. Mansfeld, Corrosion, 29^ 397 (1973)

F. Mansfeld, in "Advanced in Corrosion Science and Technology",

M. G. Fontana and R. W. Staehle, eds. Vol. 6, p. 163, Plenum

Corp. , New York (1976)

.

2) M. Sluyters - Rehbach, J. H. Sluyters, in "Electroanalytical

Chemistry", A. J. Bard, ed. Vol. 4, p. 1, M. Dekker, New York (1970).

3) R. D. Armstrono, M. Henderson, H. R. Thirsk, J. Electroanal. Chem.

35, 119 (1972)

R. D. Armstrong, R. E. Firman, ibid. 34, 391 (1972).

I. Epelboin, M. Keddam, H. Takenouti, J. Appl. Electrochem. 2^, 71 (1972)

4)

Schwerdtfeger, W. J., A Study by Polarization Techniques of the

Corrosion Rates of Aluminum and Steel Underground for 16 months,

J. Res. Nat. Bur. Stand. (U.S.), 65C, No. 4, 271-276 (Oct. -Dec. 1961).

Jones, D. A. and Lower, T. A., ASTM Journal of Materials; "Polarization Methods for Measuring the Corrosion of Metals Buried Underground, p. 600, Sept. 1969.

- 22 -
List of Tables

Tab 1 e

Table

Table

Table

Table

Tab] e

I. Parameters obtained from polarization measurements on tinned CCN

wire. Cells without ac signal.

II. Parameters obtained from polarization measurements on tinned

CCN wire. Cells with ac signal superimposed.

2 III. Real ( Z

'

and imaginary (Z") values in ft

' cm“ of the electrode

impedance for tinned CCN wire in 2% Na^SO^. Nitrogen atmosphere.

2 IV. Real (Z') and imaginary (Z M

) values in ft * cm of the electrode

impedance for tinned CCN wire in 2% Na^SO^ . Oxygen atmosphere.

2 V. Real (Z '

and imaginary ( Z"

values in ft • cm“ of the electrode

impedance for tinned CCN wire in 2% Na9 S0 4> 1% NaCl. Nitrogen atmosphere.

9 VI. Real (Z') and imaginary ( Z"

values in ft • cm“ of the electrode

impedance tinned CCN wire in 2% Na^SO^ , 1% NaCl. Oxygen

atmosphere

- 23 -
List of Figures

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9.

Fig. 10.

Fig. 11.

Fig. 12.

Fig. 13.

Fig. 14.

Fig. 15.

Fig. 16 .

Fig. 17.

Fig. 18 .

Fig. 19.

Fig. 20.

Fig. 21.

Fig. 22.

Fig. 23.

Fig. 24.

Z" vs Z' for CCN in 0

2 atmosphere. Frequency as parameter.

Z" vs Z' for CCN in atmosphere. Frequency as parameter.

Z" vs Z' for CCN in N^ atmosphere at low v. Frequency as parameter

Z" vs Z' for CCN in 0

9 atmosphere at low v. Frequency as parameter

Noise spectrum of commercial potentiostat

.

Circuit for noise measurements under potentiostatic conditions.

Effect of simulator resistance on noise current.

Noise voltage across simulator resistor.

Noise spectrum of Cu in acidified CuSO „

.

r 4

Noise spectrum of Al in H^BO^: Na

2 B

4

^

7

*

Noise spectrum H of Al in K BC) : Na B 0_ with 0.01 M NaCl.

3 3 2 4 7 Peaks in noise voltage for Al in boric * borate + NaCl.

Earth current measurements.

Circuit diagram for polarization measurements.

The four positions for polarization measurements.

Graphic positions of counter £ reference electrodes with respect to

the cable.

The effect of ac on the potential readings.

The effect of ac on the potential readings.

The results of moving the ground rod and introducing the isolation

transformer

.

Earth current measurements at Loch Raven, MD and Dam Neck, VA.

The effects of stray currents on potential.

Stabilization of the dc potential.

The effects of modification of soil on potential.

Polarization of cables 3 and 4 without ac .

- 24 -
Fig. 25.

Fig. 26 .

The current produced by polarizing cable 1 to 6 mV.

Distribution of current along cable.

- 25 -

Table I•

Parameters

obtained

from

polarization

measurement:

on

tinned

CCN

wire.

Cells

without

ac

x

m o X r— c CO m c . — o 

* • o c c • X c 0-

05 4 O CJ

X X. + o —1 n r-H c c h- X CO c 0- IT, o • —I

to r-H o r- f

1 • n o o CJ X • 0 in c

>c 4 o COX

m C^H 4- C r-H rr

rTM‘ 0/. c m X X 0 00 in o h- 0 • r-. V—• r H • o in in o • 0 c 71 if* 4 oo r~H m X Q. 4 *—H m r- 8 ' ‘ c X m -a 0 3 X • r—' o 0 C 2 K •—<

CJ o o c3

X • in o C)

n + in r-H m OC X- + o r—•

in 01; *—

o in "O a 4 c r—H

in c c- in o o. *“H • O o o in • o rc c <— + m 4T 05 8 or 4 o CO X CJ Cl cX

C) 3 m T3 in OJ 0 If. in o o in c c

'S'. r—i <—• • 05 o o r- • o o X 3 1 + 0 m CT> 8 CX 4 o CJ X r-H u

CJ 40D£ T3 O o in i t X to X C X cn • i 1 CJ o O' • to o V + CO r-H £ + o oo X 8 CtC

4J 0 in Q£ o X

r c 0 i I X CJ o O . c oo • i 1 CJ o r-H • o o CJ

CTi + o r-4 £ + o oo

X CJ XD c in OO CO TJ c n- oc i I X o o c CM • i 1 CJ c 05 • oo c in c X 4 • O r-H c + o r-H X <

1 u 3 r-H T3 o o T. r- X o c r—H 3 •-H o OJ • o oo o r-H • m o r- CJ

LT, + 1 1 oo 1-1 8 0£ + o CO

X rH o OO X O

X c oo o o • H o 00 o O o

tn CO o rr CJ r-H • 05 r-H 0 + to r-H CO 8

<4- + o oo <

1 r—< Q.

x.

r* ' c in T3

m "tJ 2 c X X O O •T o O 'Z'. CM • r-H o O C r-H • oo O O 0 c 

CO + o CO

X to oc + o 00 0- CJ ct o O X O X

IT,

m

m o • rH 0 in o •rH

—«

CJ • in in c3 r—

H • in oo

C^3 + o r-H in r—H X + o 8 XX) X oo in X c 0 c- • f—< o m o . ^

oo • o in CJ OJ • X o c3

4- o CO O' X-h + o to r-H 8 XUJ XX 2 2

Cl

X > CO > CJ E E > o o o > O

O

O E \ o 0) \ V Q < TJ ~o < -o ~3 * H \ \ •> • •>

13.

x \ X> > • •* > > D. x > E E E E 71 • x E • X > _o o ' o - •» 4-> o o E * 4-> ~ • o •* CJ o • rH • o CJ o • H o O >rH — X' X X • rH OC X) JC Uh — c c — D GJ X xV , o

_2“ r— Cl C. X C ] 7J C) O o O 2

Er E

+~> 4-»
'l.'Mr II Parameters obtained from polarization measurements on tells with ae signal superimposed.

nmed (TN wire.

Sc 1 u t i on 2% Na SO

2 4 2

". Na.

? S °4 + ", NaCl

T

1 i me

,

h 1600 2400 4 200 6700 1 600 2400 4 200 6700

o.c.p. vs Mils + 275 + 260 + 26 7 + 170 + 200 + 250 t 2 2 5

J pA/em2 corr

,

0 . a 5 — 0.2 5 0.25 7) 2 0.

0.4

A t nosphere H , mV 21 — 16 17 4 0 20 8 1 1

0 ., b a> mV/dec 70 — 58 38 — 80 25 30

b , mV/dec 160 — 600 400 — 120 70 100

Fit good — good good poor fa i r fair fair

o.c.p. vs NIIK + 120 + 90 + 7 5 + 1 20 + 3 5 0 +40

j +4 5

I ,pA/cm

2 corr

c 0.2 0.1 0.15 0.14 0.2 0.1 0.3

At nospherc B, mV — — — — 1 7 — 15 25

N ) b, , mV/dcc

d — — — — 60 — 55 60

b , mV/dec

c — — large large 110 — 120 CO

Fit

t

no no no poor fai r poor fai r fa i r
Table

III.

Heal

(

'Z)

and

imaginary

(Z")

values

in

J2

'

err.

of

the

electrode

impedance

for

tinned

CCN

wire

in

2%

Na.

SO

with

nitrogen

atmosphere

X

I • r-H 1—

)

X

X 05 LO 05 oo • • • CO o OO X c oc .—

1

00 t—H X • • • L.O oo r—H X X —

*

oo OJ o

to • LO oo m •*r CO c - rr r—H • • • • • X X X

LO X c

)

.—

i

oo o X o o • • • 00 r—

'

OC or oo OO r—H oo t'- r -

c- oo oo ro X ro X

n: X to o- o X oo • • • • X

'sT LO r—1 Is- CO o ro r-H • • 05 oc oo r-H r-H OJ t—H t—H X t—H o r—H OC X 00 X X oo

C\] - t—H 00 X 'cr 00 CM

r—< X OO o LO X r-H o r-H ^r X • • • to LO to 1—

1

00 X X oo r-H CTi t-H 1—H

1—

1

a

3

c

QC •H

cn I x LO t—H CM X X 05 X

x o- to ^r oo X • • • • X • cc o O; o X t—H -cr X r-H • • o r-H i

1 oo X r-H r-H ^r OO t—H i—

1

to I—

1

C3 X X X o oo r—i CM X X

O x - 00 to X X t—H X

x cc X 0- o oo 00 00 X X o- o • • LO to to t—H r- X X OJ r-H t—1 X CM

X X oo X

X o- 00 r-H X • • • • r—H r-H

r—H ro x r-H 0- 05 o • • 00 LO or rH 00 X r—H r-H r-H

05 X o- o o X o

05 - o- X • • • • 05 • • OO X r 1 O- or i—1 05 X •M- • r-H 1—

1

v 03 r—H r-H X X X CM 05 1-1 r—H

X 05 Or X X X

X 05 c i—

i

oo oo coo to OO oo r-H X CM r-H OO • « oo X X r—H i—

I

05 X CO r-H t—H X r-H o X X X 00 05 oo X

x - r-H or X CO 05 x n; X r—H r

1 X X 00 X • • • x to CM OO r-H 00 ro CM r-H 05 1—

{

r-H

x X o X X

oj to LO X o X X • • • • X

CO 05 X '? X t-H 05 X X OJ • • r-H r- X O] r-H r-H X CM t—H r—H X r—H X 00 o • o o X -c 05 OJ o

oo - to oo X r—H X X

OJ N] 00 r-H 05 CM 0- 05 05 i—

H

O • •

.—

•

CM to to oo r—H 00 t'- X X r—

i

r—H X CM c

ec

• rH

C/) I r—H oo X X • N3 oc r- oo o • • • • X r—H o to LO X OO X r-H X • •

• X X —

(

00 oo t-H X t—H

03

LO LO

•sr • • X 05 r-H o 00 o X LO - CO o

LO O’ i—

'

o- 05 05 X 05 V c o t—

H

oo OJ t—

H

X ^r t-H r—H r—H t-H

+ N

LO oc o o c o o 5^ tsC

1—1 oc c X o *> «—

t

X •—

’

X c c o

1—1 X
T3

t>Cc• r—

+->

t-, O

<+hVuc

.-3 XJ

0)aEo

•a

t,

4-J o

0J

r—

<D

a; +J

Q-,ooac

rH

ino vu

c.

in

'Z' x' x

"3 cm C

03VO

.jC

<33

CM LO CO

X CD

r-H ro to LO i—i o* rr CM • lO CD 00 CC ro i—i t-- 'O c t—H o X • • to CM CM i—1 CO CM to rH to r“*

to to r- LO r—i

X CM - CM CO r- r 1 • • LO CM o a.

r-H n: h- or r—~i CD ro LO 1—1 00 • • • • X CM CM CM r- X- ro X ro CD •'D t—

o

r-Hc3 i 00 CD X- oo

X CD lO c X X Is- CT> CM X oo o • oo ac CD <y> LO ro LO r-H 03 CM ro 00 • • H to CM CM r-H 00 X CM 1 1 ro t—H ro

in• to CM 00 CM to CD Q to - rH co r—i CM rH r-H • • • oo oo • to X o io to LO LO r^ X CD t—H • • 03 IO to CM CM oo ^r ro X to rH LO ro O2 - oo o cs: <D X X T'- CD • 00 CM o CM to oo o 00 • • r-H 00 OJ r-H CO ro ro

CD oo

CD - r- CM CM LO CM o • • CD

CM n: LO LO r- ro r—

'O CM o • 00 oo X CM CM CM 1—

CD

00 CO r-H CD

X oo

X

X CO ro o CO 00 h- • • ro rH 00 X LO CD o X 00 CD • CM r-H r—

CD

X ro t

1 LO CM

CD CD r-H CD CM CM ro

CM - LO CO CD o LO CM • oc oc

ro

X 00

v CM o X LO t—

• • i to CM CM CM rH X CO r-H oc r-H r-H o 1

CM

X

X CM

X CO ^r IO CO CM r-H • • • o 'O oo rH CM CD CD ro oo ro • r-H CO to CM rH X X t—H r-H ro

r—

o CM o X - CD CO LO co ro • • • X r-H LO X X* LO o LO CO x- t—

to LO • • C3 CM 00 CO CO CM .H r—

LO ro t—

00 OJ c

CJj • rH

(f). - CM •O r-H t—H CD o LO LO r- X rH LO • • • X • LO oo LO o CM X X C] • 03 CM r-H t—H X ro ro CD IO t—H X

C"- CD CD OO 00 00

X io - LO to CM r- <D CD

LO n: CO r-H *r CM LO to o r-H o rrH i—

r-H CD ro 1-1 r-H OJ r—i •—

H t N

-C LO 00 o o o c o 1*3 1*3 1*3 t—H 00 c o o •* i-H LO r-H LO o O o

-H

—1 LO
Table

V.

Heal

(Z1)

and

imaginary

(/")

values

in

ft’

cm -

of

the

electrode

impedance

for

tinned

CCN

wire

in 2%

NaoS04

1%

NaC 1

with

nitrogen

atmosphere

O' oo o r-H CO X • 1 • to ro CM rH I 1 05 m OJ i—

o

r-H CM - LO N3 00 CM 1—1 CO 1 1 o

00 CO CM oo rH t rH oo

X

XX

X o 05 in

r

—

CO o co

X CO 05 05 in • • • • • oo 05

X CM i—

r—

CO o X ro c O • • CO v to i—

CO CO

r—

rH rH 05 CM 1—

rH

x in CO in o CO 05 o 00

cm - o to in • • • • • • 00 05 00 c rH X -c* 00 in CO 00 ro in ro fO • • • OG CM CM 1—

i—

co

X or CM CM rH

X CM o • H

C/3 o• I in co to ro 00 o rH CO X 00 to CM 05 • • • • • • o CM o cc 00 CM X X to co o o • • o X to rH X 'C CM 1—

rH rH ro rH 2

to o 05

X OO o ro 00 rH 05

ro - to LO CO • • • • • • o rH

ro

X CM 00 in in CO rH o in in • • in CM r—H .

i X in in to oo rH 05 to OO X X 05 in X rH • rH • • • 00 05 05 X 00 X X X o • • • CM X rH CO to ro oo CO o

05 CO , 1 X in

05 - CO in • • • • ro 05 to

CM

XX o o o CM

X • • • X '—

rH

X in ro rH 05 00 CO

CO co

X to ro rH rH 00 o X CM c LO • • • in in X in ,

i in X o X cc o oo

X* ro CM

XX to 05 CO CD co CM o

05 rH 05 o in 1—1 05 o 03 (H ro ro CM - x • • • CM o in

to

X CO oo 05 o X to co in o • • • to i—

cc in to CM CM rH i—rH CO rH o 1 1 C3c r in to oo X 00 r-H OJ 00 00 X to r—H X CM • • r rH CO 00 X o • rH o i—1 X o co X CM • • • • 73 X X ro rH in m rH 00 co CO OJ rH o x i—1 r—

i—to oo CO oo co 05 CO CO

X - • • • in CM

X

<3 inX i—

X

X 00 o oo

X in rH • • e CM 00 X X to ro oo 1—

1—

X CM

00 rH • • CO CO ro

X 00 o CM • • • 00

X

COX to 05 i—X • • CO rH r—H ro CM rH X oo o

cc 00 CM o CM o in - 3- o ro o in X c CO CO X OJ • • • ' 1 X to to rH rH 00 X CO in £ N

sc sc sc sc SC SC x: — -V in oo o o o o o O o 1—

ro in o o o o N i—

X 00 o o o o rH OJ in o -4—5 i—

CM

X in rH
Sho

<DOC

c3 T3

<DO,E• rH

1' T3CU

-H <D a

<D <D t—i

0) C,wo V E

-C 4->

4-> 03 4h C O <Dao

M >> E X

(J o

-r->

a • fHs

r" H r-H o W 03 O 2 31 1 03 r—1 >.—

o

CM C/3

•*

—

CM

03 >5 2 U

03

V oc C CM • H

Qfl c

e3 • rH E

•H <D

Sh T3 • H C s

03 2 -—

C_>

— o N

T3

<L> i—l C

03 c O • rH cc 4->

HH>V

—1

jo

03

oo M- ro •3 I in eo o o o • • • • ro x ro x eg in oo CO CO ro in o • h- in in eo rH rH co ro eg

or CD ro CD roo - r- c 00 CD in in • • • ro oo

r—1 X

—

H in CD r^. o in CO 00 co • • CO 00 CO LO eo eo rH CD CO r-H X c

rH

co CM OJ eo CD CD co eg CD o • • OC c oo ro co oo oo 00 X- eg 1 • CD 00 co in to eo eg rH i—H

^5* CM ro • rH

C/2 CD ro t"- r—

H

CD ro r-H • o - to eg eg o eg LO o • Is- CD a to n: CM o o 00 CD CO o • • • • in i—H

rH rH in ro r-H 00 00 eg rH

C3O2 z X e- rH

CM CO CD CD CD CD CM • • • in eo eo rH c o co X O eg eo eg eg eg r-H X rH

t-H

in oo rH to

h- - CD coX CM oc o • • • CM eo o o CD rH 00 X ro rH

•C CO CD CO to to eg 1—1 t—H i o r-H in • eg X c co CM 00 to eg 00 c • • CD o CO in CD in x 00 o CO to • eg rH rH 00 co in rH f—H

CM i—ieg

CD CM CO oo CM eo CO M"

CM - eg o 00 in eg t-H • • CD O'.

X

to N! o* CD cc to eg in

X

x • • e- to eg rH rH to I"- eg r-H •

CM CD o to r-H CM rH

X in CM 00 co ro h- 00 • • • CD

r—1 in r-H <J) o CD CD r- CO in ro • c3 eg eo rH rH co in r-H CD CM eg

r-ac

•fH ro i—i o 00 00 1 1 CM 00

c/: - cc in ro CD CM • • ro o in n: o to o 00 00 eg oo • • • CN] to eo eo X ro CM in eg oo CM o

c3

rH eg ro eg o X

X in ro oo CD i—

H

in oc in 00 co rH in 00 • • CM i rH co eg r-H eg

r- CD ro ro co t—

H

eg M- to - 00 cd cc eg in n: O LO to CM 00 eg CO t-H • • r—1

eg i“H i—i

e- in in eg CM IX + N bsC CX

JZ3 in a> c o o o o rH in o O rH oo o o f—! in

rs rH in -P > ,
Fig- I- Z" vs Z' for CCN in atmosphere. Frequency as parameter.
Z" vs Z' for CCN in

N 2 atmosphere. Frequency as parameter.
42000

38000 -

34000

30000 -

26000 -

oog 22000

Cj

N

18000 -

14000 -

10000 -

6000

2000

2000 6000 10000 14000 18000 22000

z\ D. —2 cm

Z" vs Z' for CCN in N

2 atmosphere at low V. Frequency as parameter. Fig. 3.
3 wo U‘„Z

ti

V-

<u

oG

cc O

czro

u

o

4-1

N3

in>M

<r

to

*(—< U-.

Frequency

as

parameter.
SPECTRAL

POWER

AMPLITUDE,

V//TTz

Fig. 5. Noise spectrum of commercial potentiostat

.
CELL

SIMULATOR

LU

or co

-ocou

CJ

CT3 j-i

(fi3o

•HU

vC

00

•H

U-4

P0TENTI0STAT

TESTING

CIRCUIT
NOISE

CURRENT,

A//Hz

Fig. 7. Effect of simulator resistance on noise current.
SPECTRAL

POWER

AMPLITUDE,

V//Hz

Fig. 8. Noise voltage across simulator resistor.
I I o o

ZH/^mo/V ‘A.11SN3Q lN3yyflO 3SION

FREQUENCY,

Hz
NOISE

CURRENT

DENSITY,

A/cm

2

/Hz

Al/H 3B0 3 Nq 2B4

0 7

. Ref. S.C.E.

Fig. 10. Noise spectrum of A1 in Na

2 R^O^.
NOISE

CURRENT

DENSITY,

A/cm 2

/Hz

T

I0' 8 -

UPPER: -120 mV vs. S.C.E.

i = + 7/x A / cm^

LOWER: -420 mV vs. S.C.E.

i = 0

Fig. 11. Noise spectrum in Al in H^BO^: Na2B^0_, with 0.01 M NaCl.
Ai/H 3

B03 + Na 2 B4 07

+ 0.01 M NaCI

Fig. 12. Peaks in noise voltage for A1 in boric borate + NaCI.
EARTH CURRENT MEASUREMENT

(POTENTIAL BETWEEN TWO Cu-CuS04 ELECTRODES)

Fig. 13. Earth current measurements.
SPFFTRAI

Dnu/ro

I

Circuit

diagram

for

polarization

measurements.
GEOMETRY OF POLARIZATION ELECTRODES

TOP VIEW

CABLES

/\

REFERENCE

ELEECTRODE

+

O -A

O

O

-A

+

+

1 1m 1 1m 1

COUNTER

ELECTRODE

Fig. 15. The four positions for polarization measurements.
GEOMETRY

OF

POLARIZATION

ELECTRODES

END

VIEW

QJ I < rO

rJu

oi jruo

d.Xo

4-1 2Xo

HZ)od

4—)

00

•H

Graphic

positions

of

counter &

reference

elei
CABLE

3

DATA

3 H N sa A 'ivslN310d

(/} toC £

•H*0

re

OJ

c

<D 4Jo

ocu X

c

ou

ex3

M-4

X

H

W)

•rH

[4_

POSITION.
CABLE

3

DATA

04

T3C

10

Ui

o

<# o

04 o

04

'30N3B3ddiG !VllN310d

200

100

0

100

200

DISTANCE

FROM

CENTER

OF

3-4

TRENCH,

cm
<3E

J-j o

>4-1 in5

u

0) JC

4J

OJj c

*rHu

3

"0o

4-J c

"Oc

tfl 33o

Vj

33c

3

O

>->

<3 x:

3

cn3

QJ 33H

or>

U-t
EARTH CURRENT MEASUREMENT

(POTENTIAL BETWEEN TWO Cu-CuS0 4 ELECTRODES)

Fig. 20.

CLEARING IN WOODED AREA - LOCH RAVEN. MD.

+ 0.100

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NBS-114A ip.ev. i 77)

w.s. DEPT. C F COMM. 1. PUBLICATION OR REPORT NO. 2. Gov’t Accession

BIBLIOGRAPHIC DATA No. SHEf T NBSIR-78-1486

4. TITLE AND '-UBTITLE Development of In-situ Techniques for the Detection and

Measurement of Corrosion of Copper Concentric Neutrals in

Underground Environments

7. AUTHOR(S)

J. Kruger-, U. Bertocci, E. Escalante, J. L. Mullen

3. R r !. i r . ; lit ’ •' At t'f -M'.'K

5. Publ it nr ion Datf.

6 . Performing Organization ( ode

8 . Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 5610442

11. Contract/Grant No.

E (49-1 ) -3800

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Energy Research and Development

Administration

Washington, D.C. 20545

13. Type of Report & Period Covered Annual Report

1/15/77-1/15/78

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The report describes the work done on the second year of a three-year project

whose purpose is to develop in-situ methods for detecting corrosion on buried copper

concentric neutral (CCN) wires. Potential and polarization measurements on buried

cables have been performed, and methods for distinguishing the signals of interest

from interference due to a.c. applied to the cables, as well as d.c. earth currents,

have been developed. The soil around one of the buried cables has been modified

in order to make the environment more corrosive.

Laboratory measurements to test possible corrosion detection techniques have

been performed. Current-potential data so far obtained have been analyzed. Impedance

measurements have also been tested, but results indicate that the method is not very

well suited for corrosion detection. Analysis of electrochemical noise has been

developed and tested, and measurements on some electrochemical systems carried out.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Buried cables; copper concentric neutral wires (CCN); corrosion detection methods;

current-potential measurements; underground corrosion

18. AVAILABILITY ££ Unlimited c For Official Distribution. Do Not Release to NTIS

I ! Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Stock No. SN003-0Q3

I I Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

60

22. Price

$5.25

USCOMM-DC 660 3S- P7 6
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