NBSIR 77-1232 (ERDA)

Development of In-Situ

Techniques for the Detection

and Measurement of Corrosion

of Copper Concentri(^ Neutrals

in Underground Environments

Corrosion and Electrodeposition Section

Metallurgy Division

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

April 1977

Annual Report

Prepared for Energy Research and Development Administration

Washington, D. C. 20545

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

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NBSIR 11-M22 (ERDA)

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

Metallurgy Division

institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

April 1977

Annual Report

DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

Prepared for Energy Research and Development Administration

Washington, D. C. 20545

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

Dr. Betsy Ancker-Johnson, Assistant Secratary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director
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Development of IN-SITU Techniques for the Detection and Measurement

of Corrosion of Copper Concentric Ileutrals in Underground Environments

Annual Technical Report for Period January lb, 1976 to January 15, 1977

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

1. Introduction

1 . Laboratory Experiments

2.1 Corrosion Tests

2.1.1 Experimental Conditions

2.1.2 Experimental Results

2.1.3 Examination of the Results

2. 1.3.1 Effect of Solution Composition and Atmosphere

2. 1.3. 2 Effect of Convective Motion

2. 1 . 3. 3. Effect of a . c

2. 1.3. 4. Effect of Coupling with CPE

2.2 Current-Potential Measurments

2.2.1 Potentiodynamic Scans

2.2.2 Long-Term Current-Potential Data

2.3 Chemical Analysis of the Surface

2.4 t^oise Measurements

2.5 Discussion of the Laboratory Experiments

3. Fielu Experiments

3.1 Material Selection and Specimen Design

3.2 Experimental Procedure

3.3 Results and Discussion

3.4 Summary of the Field Experiments

4. Plans for Future Work

5. Executive Summary
Jevelopment of IN-SITU Techniques for the Detection ana Measurement

of Corrosion of Copper Concentric iJeutrals in Underground environments

Annual Technical Report for Period January 15, 1976 to January 15, 1977

J. Kruger, U, uertocci , L. Escalante, and J. L. Mullen

1. Introduction

This is the first annual report of a three-year project, whose objective

is to develop techniques and instrumentation for detecting and measuring the

extent of corrosion of the copper concentric neutral (CCN) wires of buried

electric cables without removal of the cables from the soil, by being able to

locate the sites where the rate of corrosion is high, preventive measures

sucri as altering the environment (e.g. , by oackfilling witli different soils),

application of cathodic protection, or otner yet to be determined ways, can

De applied.

Tiie approach to this problem consists in finding first, oy means of

laboratory tests, the conditions that promote a nigh corrosion rate, and

subsequently to create those conditions on buried cables in order to compare

laboratory and field results.

Measurement methods such as the recording of polarization curves and

electrode potential are to be evaluated with respect to their ability to

detect and measure corrosion of buried cables. Also, at the same time, other

proposed methods, such as a.c. impedance and electrochemical noise measurements,

would first be developed in the laboratory and subsequently, if found

promising, field-tested.

The measurement techniques eventually will be applied in the field to

corroding and non-corrodi ng cables, and then potential for detecting corrosion

assessed

.

A major effort of the first year's work was directed at finding, by means of laboratory experiments, which conditions favor the onset of the rapid,

localized corrosion that it is the aim of the project to detect in the field.

Also, development of new measurement techniques has been initiated.

In the field, burial of the cable and related materials as well as all

necessary electrical connections were completed, and systematic measurements

on the underground specimens were initiated.

2. Laboratory Experiments

2.1 Corrosion Tests

2.1.1 Experimental Conditions

A number of specimens of copper concentric neutral (CCW) wire made of

tinned copper underwent long term corrosion tests for times of order of 2000 h.
Development of IN-SITU Techniques for the Detection and Measurement

of Corrosion of Copper Concentric Neutrals in Underground Environments

Annual Technical Report for Period January 15, 1976 to January 15, 1977

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

1. Introduction

This is the first annual report of a three-year project, whose objective

is to develop techniques and instrumentation for detecting and measuring the

extent of corrosion of the copper concentric neutral (CCN) wires of buried

electric cables without removal of the cables from the soil. By being able to

locate the sites where the rate of corrosion is high, preventive measures such

as altering the environment (e.g. , by backfilling with different soils),

application of cathodic protection, or other yet to be determined ways, can be

applied.

The approach to this problem consists in finding first, by means of

laboratory tests, the conditions that promote a high corrosion rate, and

subsequently to create those conditions on buried cables in order to compare

laboratory and field results.

Measurement methods such as the recording of polarization curves and

electrode potential are to be evaluated with respect to their ability to

detect and measure corrosion of buried cables. Also, at the same time, other

proposed methods, such as a.c. impedance and electrochemical noise

measurements, would first be developed in the laboratory and subsequently, if

found promising, field-tested. The measurement techniques eventually will be

applied in the field to corroding and non-corroding cables, and then potential

for detecting corrosion assessed.

A major effort of the first year's work was directed at finding, by means of laboratory experiments, which conditions favor the onset of the

rapid, localized corrosion that it is the aim of the project to detect in the

field. Also, development of new measurement techniques has been initiated.

In the field, burial of the cable and related materials as well as all

necessary electrical connections were completed, and systematic measurements

on the underground specimens were initiated.

2. Laboratory Experiments

2.1 Corrosion Tests

2.1.1 Experimental Conditions

A number of specimens of copper concentric neutral (CCN) wire made of

tinned copper underwent long term corrosion tests for times of order of 2000 h.
Several environmental variables were tested for their influence on corrosion

susceptibility. They were:

a) Composition of the electrolytic solution. Four solution compositions

were extensively tested: 2% Ha 2 S04 » 2% Na

2 S 04 + 1% NaCl , 0.42 M NaC 104

and 0.42 M NaC 104 + 1% NaCl. The pH of all solutions was approximately

neutral. These solution compositions were chosen so as to test the

influence of two salts, sulfate and perchlorate, thought not to be

particularly aggressive, both in the presence and in the absence of

chloride ions, which are supposed to be corrosive in the soil.

b; Composition of the gaseous atmosphere in contact with the solution,

both an oxygen and a nitrogen atmosphere were tested, the latter

representing poor soil aereation.

c) Convective motion in solution. Since in the soil convective transport

is negligible compared with a liquid, some corrosion tests were carried

out in 1% Agar gel, with the solution having the same compositions given

in d) in order to simulate soil conditions.

d) Superimposed a.c. signal. In order to investigate the effect of a.c. current flowing between the wire and the soil, tests were performed where

a 60 Hz a.c. signal was applied between the test specimen and a large

surface area counterelectrode. In order to approximate a potentiostatic

condition without entailing the use of a potentiostat for each test cell,

a circuit scheme such as that of Fig. 1 was used. The resistance R is

used to measure the current, and the capacitor C is inserted to prevent

circulation of a d.c. current. In order to approximate a potentiostatic

behavior, the voltage V supplied by the variable transformer should be as close as possible to the voltage between the electrode under study t and

the solution in its immediate vicinity. In other words, all other voltage

drops in the circuit should be as small as possible. In the practical

case the resistance R was chosen as 10 Q, and the capacitance was made

by two 220 mF electrolytic capacitors put in series so as to block all

d.c. components. In separate experiments it was found that the d.c.

resistance of the two capacitors at low voltages is greater than 1 G fi. The impedance of the two capacitors is of the order of 24 at 60 Hz.

The counterelectrode CE is made of a stainless steel sheet of large

surface area (75 cm^ compared with about 2 cm^ for the working electrode).

In a number of experiments it was found that 60 to 80% of the total

impedance was found between E and the adjacent solution (the measurement

was carried out by means of a third electrode inserted in the cell).

- 2

-
here are two examples of how the voltage drop is distributed:

Cu in 2% Na^bO^ Tinned Cu in 2% iia^SO^

A=5 cm^, c.d. =0.447 mA/cm^ A=2.2 cm^ c.d. =0.215 mA/cm^

Voltage drop. 0 0

II E> -e- =9U° /Z/, n

0 0

II

-e- <t>=90° /Z/,

Total 146 97 78.4 71 82 229

R - 1.5 22.3 10.0 - 1.5 4.5 10.0

C 53 4.75 23.8 10.5 4.0 23.7

CE 6.5 9.5 5.15 1 .0 1 .8 4.34

E 87 63 48.1 61 71 197

/Z/^//Z/^, % 61 86

Fig. 2 shows voltage and current signal for the cell whose data are in Col . 1

.

ihe distortion of the current signal from a si nusoi dal one is considerable.

With sucn a circuit the cell voltage and current density could not be maintained

as constant and nave varied between 150 and 450 mV and 1 and 8 mA/cni2,

respecti vely . In the tables that summarize our results, an a.c. resistance

has been reported, calculated as the ratio between the average cell voltage

and trie electrode current density. This number is an indication of the ease for the a.c. to flow between the wire and the solution. A smaller

resistance, therefore, entails a larger current density, and vice versa.

e) Coupling with conducting polyethylene (CPt). The outer part of the insulating

sheath of the cable is covered with CPt, formed by carbon powder embedded

in polyethylene, which is in electric contact with the neutral wire. Since

the open circuit potential of CPt tends to be fairly positive, as shown in

Fig. 16, the effect of coupling the CCH wire with CPt was also examined.

In these experiments the short circuit current flowing between CCH wire and

CPt was periodically measured by inserting a current-to-vol tage converter

between the two. Since the internal resistance of the instrument is

effectively zero, it was possible to measure the short circuit current

without affecting its magnitude.

2.1.2 txperi mental Results

The results obtained from the corrosion tests are presented as follows:

igs. 3, 4, 5, and 6 give the potential of the tinned CCN wire vs. SCt in

olutions containing Wa2S0^ with and without iJaCl and under an O 2 ^^2 atmosphere,

igs. 7, 8, 9, and 10 are the analogous graphs for solutions containing

jaC 104 . Also, Tables I-VIII summarize the results by giving average values

f the electrode potential, of the a.c. resistance and of the short circuit

Urrent density uetween specimen and CPt when appropriate, as well as a description

f trie appearance of the wire after the test as obtained by visual inspection

-3-

1
under a low power microscope. Finally, Figs. 11, 12, 13, 14, and lb show some color photographs of the wires after the test.

2.1.3 Examination of the Results

2. 1.3.1 Effect of bolution Composition and Atmoshpere

Under a nitrogen atmosphere the rate of corrosion is slower than in the

presence of oxygen. The electrode potentials, as a consequence, tend to be more negative; if the tinning coat is continuous, the potential can remain at

low voltages, -400 to -500 vs. SCE for fairly long periods of time, as it had

been found in preliminary experiments. The tinning coat on the CCN wire in use now always presents many small flaws, and very low potentials have never

been maintained for long times. The steady state values obtained on this wire

(see Figs. 3, 4, 7, and 8) are higher in the absence of Cl~ ions (about 0 mV

in NaC 104 ana -50 in Na 2 S04 ) than in their presence (from -130 to -220 mV in

Na 2 b04 ana from -100 to -200 mV in i'iaCl 04 ). Potentials are shifted towards

more positive values by oxygen, and they are higher in the absence of

chlorides, where NaC 104 solutions show, as in N2> higher values (+40 to 80 mV)

than Wa 2 S04 solutions ^from 0 to +30 mV). When chlorides are present, the

aifferences are much less pronouncea, also because the spread is larger. In

sulfate, the potential ranges from +30 to -60 mV and in perchlorate from +50

to -ttO mV, with the solutions containing agar showing the lowest values

because of the lower availability of oxygen.

The a.c. resistance shows a definite tendency towards lower values in

nitrogen than in oxygen. Chloriae in solution has the effect of decreasing

even more the resistance of the electrode. If these findings are compared

with the results of the visual inspection of trie wires after the test, it is

clear that a high a.c. resistance is associated with and probably caused by

extensive scale formation. Low resistance specimens in general look only

slightly corroded. Chlorides, on the other hand, promote corrosion but

evidently contribute to the formation of more conductive reaction products than

those formed in their absence.

Comparison of the specimens kept in sulfate and perchlorate solutions

show that, all other conditions being equal, the extent of corrosion is

greater in perchlorate. In particular the tinning coat can be removed more easily in a number of cases (see Figs. 13 e) and f)), from wires tested in

rlaC 104 .

2. 1.3. 2 Effect of Convective Motion

Preliminary experiments had shown that corrosion in agar under a N

2

atmosphere was very small, and, therefore, it had been decided to examine

the effect of preventing convective motion only under oxygen. Corrosion was found to be rather small in the absence of chlorides altnougn some pit initiation

was detected. In solutions containing chlorides, however, extensive pitting

was found towards the bottom of the wire, with a pattern suggesting differential

aeration. This was true both in sulfate isee Fig. 12a) and perchlorate (see

Figs. l4 e) and f; and Fig. 15 f)).

- 4 -
^ . 1 . 3 . J tffect of a . c

.

The superposition of an a.c. signal did not have a clear effect on the

electrode potential but has definitely enhanced the corrosion of the wire.

In particular, pitting as opposed to a more uniform attack, has been detected

almost exclusively on specimens tested with a.c. tven for the tests in the

milder ^2 atmosphere, corrosion and pitting could be found (see, for instance.

Figs. 14 a) and b)). It must be kept in mind that a.c. current in N 2 atmosphere

was often much larger than under oxygen, as discussed in 2. 1.3.1, and this may

nave enhanced the affect of a.c. On the other hand, in Oo a smaller current

did not prevent the enhancement of the attack and pit formation.

2. 1.3. 4 Effect of Coupling with CPE

Since the potential of CPt is more positive than that of the CCN wire,

as shown in Fig. 16, it was expected that coupling between CPt and wire would

shift the potential toward more positive values and that an anodic short

circuit would flow in the electrolyte from the wire to the CPt. These

expectations have been largely fulfilled. In nitrogen the electrode

potentials of the wires coupled to CPE almost without exception are 20 to 100 mV more positive than the correspondi ng wires tested without coupling. In oxygen

trie situation is less clear, but wires coupled to CPE tend to be more positive.

As far as the direction of the short circuit current is concerned, a few

exceptions tiave been found where a cathodic current, always very small, was measured. There is no simple explanation for it. It is possible that the

reversal was caused by transport of some of the corrosion products to the CPt,

providing an anodic reaction there. This explanation is suggested by the fact

that some Cu products have been found on the CPE and also that in the corresponding

tests in agar, where such a transport could not occur, the short circuit current

was anodic on the wire.

Coupling to CPt increased somewhat the rate of attack of the wires: under

N 2

, attack occurred under the tinning coat so that often it could be removed by

gentle scratching or even by brushing with a soft brush (see, for instance.

Figs. 13 e) and f)). Cases where there was attack under the tinning were associated with relatively high short circuit current densities, that is larger

than 1 pA/cm^ and up to 6 uA/cm^ in one instance. In general, however, this

attack was not associated with pit formation.

Trie short circuit current density is influenced by botn the availability

of oxygen that shifts the potential in a positive direction and by the

formation of a resistive layer on the wire as iriaicated by the a.c. resistance.

Trie two factors work against each other, but the second seems to be more

important. Therefore, short currents in il^ atmosphere were often larger than

in O

2 in spite of the fact that the potential was more tnan 100 mV higher in the

latter condition.

- 0

-
2.2 Current-potenti al Measurements

2.2.1 Potentiodynamic Scans

Potentiodynamic scans afford a useful way to examine quickly the main

features of the current-potential behavior of an electrode. For this reason,

scans on CCN wire were taken in Na2S04» both in the presence and in the absence

of NaCl. The results, given in Figs. 17 and lii, show a number of peaks, with a very large one in NaCl at about -150 mV vs. SCt. The wires showed loss of the

tinning coat during the measurements, and in order to clarify the contribution

of copper and of the tinning coat to the electrochemical behavior, potentiodynamic

scans were taken both on pure copper and on a piece of alloy having the same composition, about 90% Pb and 10% 5n, of the tinning bath used by the manufacturer

of the cable.

The results obtained on pure copper are shown in Figs. 19 to 24. In the

absence of chlorides no detectable formation of a passive, protecting film is

observed, whether in Na2Su4 or in NaC104. Fig. 19 shows the scans in sulfate in

oxygen or in nitrogen over the scan range of greatest interest for our study

from -800 to +200 mV vs. SCL. Fig. 20 shows the monotonic increase of anodic

current with the extension of the range up to +800 mV. The curve in Fig. 21

shows tnat the same behavior, with even larger current densities, is observed

in perchlorate. From these data, and from visual observation of the solution

in the cell, it is quite clear that the Cu"'"'' ion produced anodically is precipitated

as hydroxide away from the electrode surface and never forms any protective

layer on the metal surface. As a consequence, no cathodic reduction takes place,

in the absence of oxygen, until hydrogen can evolve during the cathodic sweep.

In the presence of chlorides in solution, a precipiate is formed during

anodic attack, sufficiently adherent to produce a cathodic peak during tfie

negative sweep. However, the precipitate is very ineffective in protecting

the metal, and although causing some poorly reproducible peaks and inflections

on the anodic branch, it fails to limit the anodic current density which can reach 60 mA/cm2 at +800 mV as shown in Fig. 23. Comparison between Figs. 22, 23,

and 24 shows that the position of the cathodic peak is shifted toward more negative values by extending the anodic range as well by increasing the scan

rate. The anodic branch, on the contrary, is little affecteo by changes in scan rate indicating that the behavior is not a transient one.

The electrochemical behavior of the 90% Pb-10% Sn alloy, both in the

absence an in the presence of chlorides, is described in Figs. 25, 26, and 27.

Scans were carried out changing the range and the rate in chloride containing

solutions. Tiie results have confirmed that the more negative of the cathodic

peaks corresponds to the anodic peak and is caused by the irreversible reduction

of a PbS04 film. The more positive of the cathodic peaks is absent if the scan

does not exceed -200 mV (see dashed curve in Fig. 27) and corresponds to an anoaic oxidation occurring between -200 mV ana +200 mV, probably the formation

of lead cnloride. The metal exhibits passive behavior up to 800 mV vs. SCt.

- 6-
The results show, at least qualitatively, that some of the features seen

on the potentiodynami c scan on tinned wire (Figs. 17 and Id) are indeed due

to the tinning coat. However, it must be kept in mind that the alloy used

in these experiments does not correspond to the composition of the tinning

coat as discussed in Section 2.3.

2.2.2 Long-Term Current-Potential Data

The current-potential data described in the preceding section have been

obtained from freshly prepared samples where no accumulation of corrosion

products has taken place. In order to monitor the change in electrochemical

behavior with time of exposure of the CCN wires to the environment for a better

correlation with the field measurements, cells similar to those used for the

corrosion tests but with provision for applying current and recording the

potential have been set up. The data are being taken at intervals of the order

of a month. The measurements are done potentiostati cal ly , shifting the

potential by small increments from the open circuit potential, and waiting

several minutes for every point in order to stabilize the current.

Values obtained in December 1976 are shown in Fig. 28 and those obtained

in January 1977 in Fig. 29. For the moment ttie open circuit potentials have

shifted somewhat, out there are not significant changes in the curves. The

corrosion current densities, estimated roughly from the curves, are of the order

of 1 )jA/cm^.

2.3 Chemical Analysis of the Surface

In order to determine the extent of removal of the tinning coat during

corrosion tests, some specimens have been analyzed in a scanning electron

microscope using energy dispersive x-ray detection.

In Fig. 30 are the spectra of an untouched tinned wire as well as comparison

spectra of copper and two compositions of Pb-Sn alloy. It is evident that on the tinned wire the Sn/Pb ratio is larger than in either one Pb-Sn alloy tested,

90% Pb-10% Sn being the composition of the tinning bath. The tinning layer,

therefore, consists mainly of Sn with probably only 20 to 30% Pb. This is not

surprising, since Sn forms i ntermetal 1 i c compounds with Cu, and it is taken

up preferential ly during the tinning process. Figs. 31 and 32 show spectra of

corroded specimens, all of them after tests in sulfate solutions. Spectrum

31 a) was taken on specimen #1 (see Table III) where the surface was covered

with a CU 2 O layer, ilo tinning was detected, although the tinning coat was

still present in some areas. Spectrum 31 b) was taken on specimen #101 (see

Table I). The only effect of the corrosion tests was some loss of Pb on trie

surface. Spectrum 31 c) was taken on specimen #5 (see Table III), exposed

to conditions quite similar to 31 a), except that it was coupled with CPt.

Its potential tended to be about 100 mV more positive than 31 a) throughout

the tests. The analysis results show a significant amount of Sn still present

as well as formation of PbCl

2

> indicated by the presence of a small Cl peak.

The tinning is still largely present on 31 d) ^specimen #104, see Table III)

where no a.c. was applied. Also no Cl peak can be seen. The wire whose

- 7

-
analysis is shown in Fig. 32 see Table VII) was exposed in agar to an oxygenated solution containing chlorides. The Sn has disappeared, but both

Pb and Cl are visible. It is likely that because of lack of convection,

in spite of the thorough attack of the tinning coat, the PbCl

2 formed remained

on the surface.

2.4 Hoise Measurements

In our proposal , we have mentioneu that the detection and analysis of

voltage fluctuations will be tested as a possible means of finding areas of

high corrosion rate in the field. The amplitude and the frequency of the

noise generated by corroding metals lias been shown in some cases to be

correlated with the corrosion rate or to change in a significant way above and

below the pitting potential. The method is, however, a novel one, and a large

amount of preliminary laboratory work is expected before the method can be

field-tested.

During this year the equipment necessary for the measurement of noise

by two methods has been assembled and tested. The first method is essentially

based on using a spectrum analyzer. The schematic circuit is shown in Fig. 33.

In this method the potential of the electrode is varied by applying a constant

current. However, it would be better if the noise measurements could be

carried out under potentiostati c conditions. For this purpose, a special low

noise potentiostat is being developed and built at NdS and should shortly be

ready for testing.

Preliminary measurements of the noise of electrochemical systems has been

carried out in order to examine the capabilities and limitations of the system.

Fig. 34 shows two spectra for electrode systems that are expected to have a low

noise. The lower spectrum coincides essentially with the background instrumental

noise.

borne measurements have been carried out on an iron electrode in a solution

where pitting can occur. Under anodic polarization a significant increase of

the noise was observed when the electrode potential was above the pitting

potential. Fig. 35 shows the spectra obtaineu at different potentials, and

Fig. 36 shows the time recordings of the electrode potential above and below the

pitting potential.

The second method for noise measurements is supposed to allow the

measurement of a source lower than the noise level of the electronic equipment

employed. The method consists in sending the noise signal to be measured on two parallel amplifying and filtering channels as shown in Fig. 37 . The

output signals of the two channels are fed to a multiplying amplifier with

averaging capability. Each channel signal is the sum of the source noise and

of the instrument noise, but since the instrument noise is uncorrelated, the

average of its product is zero, and the output of the multiplying amplifier

should be only the square of the source noise.

- 8-
I Fifj. Jc shows some results of prel iiniriary tests. On it is reported

the instrument noise as well as the noise generated by a 10 Ki/ resistor. At

jhigh frequencies, the thermal noise of the resistor is, as expected, higher than

jthe instrumental noise. The larger peak is caused by some 60 Hz pickup, but

from approximately 10 riz down, the noise is lower than the instrument noise.

This method is expected to be usable above 0.2 hz.

Iz.b Discussion of the Laboratory Experiments

The results obtained from the long exposure time corrosion tests give

useful guidelines on ways to artificially cause corrosion in buried cables. It

is evident that the application of an a.c. signal is a powerful means to cause pitting, however, a.c. is probably not absolutely necessary, as shown

by some cases when extensive corrosion occurred without it, but causes a considerable increase in the rate of attack.

The presence of a reducible species such as oxygen was expected to enhance

I corrosive attack, and this has been verified experimental ly to a certain extent.

•However, the effect of the attack is the formation of layer of reaction products

that can slow down considerably further corrosion. Which of the two effects

of the availability of oxygen, thermodynamic factors favorable to corrosion or kinetic factors opposed to it, will be predominant in a certain instance may

I depend on subtle differences in the environment and may be difficult to predict.

Trie presence or absence of a protective scale influences the amount of a.c. leakage and probably explains why extensive pitting was found in tests where

oxygen was kept low by a nitrogen blanket; in these conditions, no protective

scale was found, and extensive pitting occurreu in many cases. Analogous

conclusions can be drawn from those tests in agar where oxygen could not

readily reach the bottom part of the specimen, and the attack there was quite

severe. These tests also point to differential aeration as a possible cause

of failure in the field.

The addition of chloride ions also enhances corrosive attack, since they

tend to reduce the resistance of the protective layer.

A few months ago it was pointed out by Ur. Nesslage of Phel ps-Dodge

,

j that sulfates, or perhaps other sulphur-containing materials, may play an

I important role in the corrosion of CCM wire in the field. To examine this

possibility, corrosion tests employing NaClOA instead of lla 2

S 0

^ as the main

electrolyte were carried out. From the results reported here it appears that

no special role is played by sulfates in the laboratory tests. Although the

effect is quite minor, the NaC 104 solutions seem to be a slightly more corrosive environment than Na 2 SU 4

, perhaps because all perchlorates of the

heavy metals (including Pb) are more soluble than the corresponding sulfates.

j The crude measurements of the electrode impedance obtained by monitoring

'the a.c. voltage and current have given some interesting clues concerning the

I susceptibi 1 i ty of the CCW wire to undergo rapid attack. This seems to be an encouraging result that may point to a.c. impedance measurements as a useful

diagnostic tool. It is our intention to start soon more extensive measurements

I of the impedance at various frequencies with the aim of developing i t as a

I field measurement method.

- 9-
3. Field Experiments

3.1 Material Selection and Specimen Design

Considerable time and effort was spent in trying to determine whether

any particular cable design or combination of cable components was more susceptible to corrosion deterioration than others and, therefore, better

suited for field testing. This search developed inconclusive information

since apparently failures due to corrosion have occurred in all designs and

component combinations. It was then decided that we adopt the underground

cable design that is most widely used. The following specifications were finally accepted.

#2 AWG stranded aluminum conductor in cross-linked, thermosetting

polyethylene insulation with ten strands of #14 AWG coated copper

concentric neutral wires manufactured within AEIC #5 and IPCEA S-61-402

specifications

.

1100 feet of cable were ordered from the Reynolds Metals Company. A

significant reason for placing this order with Reynolds was that they

supplied a bulk sample of the coating alloy and over one hundred meters

(300 ft.) of bare copper wire.

The cable was cut to desired lengths but otherwise used as received.

For the field study, cable lengths of 15 meters 45 ft.) were used. An

insulated conductor was attached midway between the two ends of the cable and, once buried, extended above ground to a terminal block.

The cable components (i.e., bare or coated copper wire, coating alloy,

carbon impregnated plastic) were handled in the following way. One meter (39

inches) length sections of cable were cut with cable shears. The coated CCN

wires were removed from these sections and soldered together as shown in Fig.

39a. Each specimen had an insulated electrical lead attached to it which

extended above ground after burial. All solder joints were coated with silicon

rubber adhesive to avoid undesirable galvanic effects.

Similarly the bare copper wire was cut to a length equivalent to one meter (39 inches) of cable and assembled as shown in Fig. 39 b.

The one meter length of cable component that remained after the CCN

wires were removed had the conducting polyethylene (CPE) film on the outside.

The ends of these pieces of cable were sealed with silicon rubber adhesive.

Electrical contact was made to the CPE by tightly wrapping bare wire around

its circumference at a point midway between the two ends as shown in Fig. 40 a. This binding was also coated with silicon rubber adhesive.

The resistivity of the CPE was measured to be 55 cm. It was observed

that mechanical flexing during handling increased the resistivity of the CPE

by as much as a factor of two in an irreversible way.

- 10-
1

The 90% lead (Pb) 10% tin (Sn) coating alloy ingot was cold rolled into

sheet with a thickness of 0.5 mm (0.02 inches). Specimens cut from this sheet were such that their total surface area equaled the surface area of the CCN

wires on a meter (39 inches) length of cable. Fig. 40 b illustrates the

geometry of this specimen whose total surface area is 512 cm^. In addition,

the alloy was spectrographical ly analyzed. Other than Pb and Sn, the total’

sum of other constituents is less than 2%. Neither of the two major

j impurities, antimony (Sb) and copper (Cu), form intermetal 1 ics with lead as

I indicated by their phase diagrams.

! 3.2 Experimental Procedure

The field specimens were buried at our NBS site in November 1976. The

burial plan is illustrated in Fig. 41.

Four trenches each approximately 0.6 m (25 in.) wide, 1 m (3 ft.) deep

and from 17 to 30 m (50 to 90 ft.) long were dug with a back hoe. Three of

these trenches hold the 15 m (45 ft.) cables as shown. The first of these

three trenches contains the cables with the superimposed alternating current

I (AC). The current density on the CCN wires of these cables is 1 mA/cm^. The

fourth, and longest trench, contains the cable components which are buried

alone or galvanically coupled to another component.

j Corrosion data has been gathered in the field by electrochemical

: techniques initially at intervals of two weeks. These preliminary measurements

consisted of potential measurements of all specimens, galvanic current measurements of all coupled specimens, and corrosion rate measurements of the 15 m

(45 ft.) cables and the noncoupled components.

Potential measurements were made using a high input impedence (10^^ ohm)

voltmeter and a Cu-CuSO^ reference electrode.

The galvanic current measurements on the cable components were made with

a zero input impedence ammeter. This measurement indicates not only the amount

of current flowing, and, thus, the amount of metal dissolution resulting

between two components, but also its direction of flow so that the anode-cathode

relationship can be identified.

j Corrosion rate measurements were made by conventional polarization

i methods. Up to this time only the linear polarization technique has been

used. In this case the potential of the specimen is polarized by not more

than 10 mV in the cathodic (active) direction and the current required to do

this noted. The Stern-Geary equation (1) is used as follows:

'a " Ai =

1^CORR

- 11 -
In this equation At is tne overvoltage of the corroding electrode produced by

the polarizing current Al; and are the slopes of the anodic and cathodic

polarization curves, respecti vely , in the Tafel region, and IroRR is the corrosion

current. The constants Bg and Bq are both assumed to be equal to 0.1 in this

equation. This assumption results in the following equation:

r =

21 .7 Al (mA)

^CORR(mA) aE (mV)

Through the use of this equation the corrosion rate is then calculated.

The counterelectrode was a rod driven into the ground some 15 or 20 m

(45 or 55 ft.) from the specimens. Likewise, the reference electrode was

15 or 20 m (45 or 55 ft.) on the opposite side of the specimens. IR-DROP

compensation was necessary.

3.3 Results and Discussion

The field study is a relatively long term program in that once the

specimens are buried, they will remain in the ground from one to three years.

During this time, as has already been described, electrochemical measurements

will be carried in situ on the specimens. Since the specimens have only been

in the ground about ten weeks, the data presented here are very preliminary

in nature and subject to change.

Previous experience has shown that settling of the soil continues for

several weeks after burial. During this settling period, electrochemical data

tend to be unstable.

The potential measurement data collected during the first ten weeks and

listed in Table 9, for example, show a general shift in a negative (active)

direction. The potentials appear to be approaching some equilibrium level

with time.

The specimens listed in Table 9 are separated into three groups. The

first group is the uncoupled cable components. The second group is the

galvanically coupled cable components. The last group is the 15 m (45 ft.)

cables with or without imposed alternating current.

The galvanic currents listed in group 2 show some general tendencies.

In practically every case the conducting polyethylene (CPE) is cathodic to

the other materials. That is, it causes the metal to which it is connected to corrodt

The larger the galvanic current the greater is the rate of reaction. One can

see that the lead-tin coating alloy sheet (CAS) is corroding about ten times

faster than the bare copper wire (BCW) or the coated copper wire (CCW). In the case where the BCW is connected to the CAS, the CAS is acting as the

anode and, hence, corroding. This in turn is cathodically protecting the

copper wire.

- 12 -
Tile corrosion rate measurements made on the uncoupled cable components

after forty days of burial indicate that the bare copper wire is corroding

at a rate of less than 1 mdd*. The coated copper wire during the same time

period is deteriorating at a rate that is four times greater or 3.7 mdd. The

corrosion rate of the coating alloy is only slightly less at 2.5 mdd.

3.4 Summary of the Field Studies

1) The field study specimens have now been in the ground for over ten

weeks.

2) Potential measurements indicate that settling of the soil is just

beginning to stabilize.

3) The galvanic current measurements reveal that 90% lead-10% tin coating

alloy is cathodically protecting the copper wire. These measurements also

show that when the conducting polyethylene is galvanically connected to

the bare copper wire, the coated wire, or the coating alloy, they are sacrificial ly corroded.

4) After forty days of burial the polarization data of the cable

components show that the corrosion rate of the bare copper wire is less than

1 mdd, and the corrosion rate of the coated copper wire and the coating alloy

is two to four times greater.

4. Plans for Future Work

During the next year of this project, the following work is planned:

Activity Expected Completion

Introduce corrosive conditions identified in

the laboratory to the field studies in order

to make measurements under corrosive conditions 3 months

Complete examination by retrieval of 6 months

exposed cables 6 months

Complete evaluation of polarization and

potential techniques in field 9 months

Complete examination in laboratory of AC and

noise techniques 10 months

Start adoption of laboratory developed techniques

to field tests 12 months

Complete examination by retrieval of one year

exposed cables 12 months

*mg/dm^/day -13-
5. Lxecuti ve Summary

The first year's work of a three-year project aimed at developing

techniques and instrumentation for detecting and measuring corrosion in buried

copper concentric neutral (CCN) wires has been completed.

Laboratory corrosion tests and electrochemical measurements have given

information on which environmental conditions are likely to cause corrosion

similar to that of concern in the field. This knowledge is necessary in

order to be able to cause corrosion at will in buried CCN wires used to test

detection and measurement techniques. Presence of chlorides, availability of

oxygen and a.c. leakage from wires to the electrolyte are the major factors

in causing rapid corrosion. Preliminary examinations of polarization as impedance and corrosion "noise" in the laboratory were initiated.

A field test site has been set up, and a number of cables buried.

Polarization and potential measurements on these specimens to provide base

line data were initiated.

Milestones for the coming year were set involving: a) application of

the first year results to provide corroding systems for field testing of

detection techniques; b) testing of new detection and measuring techniques

in the laboratory; and c) two retrievals and examinations of buried cables.

- 14-
REFEREflCES

(

1 ) M. Stern and A.L. Geary, J. Electrochem. Soc., (1), 55 (1957)
, 1

+-> 1 rtj 1 (Uc 1 s- M

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«o

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cz OJ 1 > cu to 1 s- o •r“ 1 O) X +J !5 to OJ to $- i JD o OJ • O +-> o to

(O +-> c 1

o c • o o

fO

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OJ to 1— c -M c

>> 5^^ -o o £= 3 1 03 S- -r- 0) -r- OJ 11 1

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*r“ •r" r— to 1 o c > >^"o OJ o

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$- Z3 3 o •1- o X 1

O)O (_) 2: hU UJ <

a.

i/) oE ZJ

+-> o to ' +-> O =»t- CM

CM ; 2T Q. i • O • 1 t/1 “O <N 1 CM • E «o- fO o o o o 2T • • 1 • <c t— o O 3- 4- C to 1 O i •r"

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Qc: CM 1 o E o trj ' • o oc CO 1 o • 1

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CM \J)1 • 0 1 i f— +J <o <o <o

C_) 0 1— CSJ 1 <o r— r— r—

Q. + ]1 J- 11 o • )I oo “O CM

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TABLE

IV

Solution:

NaC104 +

NaCl • N2

Atmosphere •

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Excellent.
TABLE

VI

Solution:

NaC

104•

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coat

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LlJ r“ r“

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f— 1— r— 1“ 1“

-90±5

+6.4

12d

Brittle

surface

layer

than

can

be

broken

off

easily.

Red

crystals

underneath,

but

no

pits.
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+-> -•-> ^ sT3 +-> CM E to c

(T3 o o . O)

C i- 3 S- c to > s- ca >— T3 . o to CJ o to OJ CJ

S- CL+J <u c 0) C3 CL t4- U 1— • O) +J > 3 -o r— 4-> to

to -C ro cu XI E • c +-> -*-> CO +J

+-> 1— to to

O

O CD 3 • to •>- o o O) -t-> £1 O +-> C c O r— a Q. S E QJ - 1- •r— CD -)-> T- +J •f— a ,

O C Q- O -C 3 CO +-> c O

ra i~ to

O

T3 03 CJ .Q

C 3 • r— z 3 Ol Q. (U . -(-> s- JD 4-> to >> to -t-> • O S- 4-> CO ^ O) 1—

•I— CO 1— (O to +-> r— • S- +-> o XJ . > 1— (O r— rt ' CO XJ O to c: CD c CD

OJ ^ (O -M to to

O to

O 3 • C to E 0) c > O +J CO o o u S- -r- • r—

s- O) to to c c CD >, c OJ -C +-> sz

(1) O) s- +J >,

C 3 OJ JDC o >> CJ 1—

u

sz s- . +-> S- o o (U +-> •!- •r— to +-> to -M CL CD CD CD CO U T- E i- S- X3 +-> +J 1— to . to to to 1 C C 4-> CD to OJ to S- s- E o ^ - 1— •r— >> C -r- C CL > S- •r— E O OJ c CJ E U -C -(-> > <U "O (U OJ o ai +-> OJ to CL OJ to

+-> CO

O +-> CO O)C (U E CL E X3 •r“ OJ CL OJ

+-> <D SO SO o <u c C S- >, o S- >> CQ LU Q. :i: CD o CD OO 1— S_ 3 •f— CD -Q U CD JD

CM Oo(T3 +

J- o o

+Jo =»»= Q.

(U T3O

LD

CU un

CD X3 CM CO • E Z CJ O CM • < O • • U 3- + E . O to

•r— +J3 .* O OCcM

t/J E o o O • o CD CM CM o • t

t—< • G t—H

CO t ( >

LU_J XJ CD > o E o c CM OJ r—

t— • > O +1 +1 o o E r— O o o o LD

O • +1 LD CM CD r—

1—

-o o 1 1 + + 1 +

UOOO o o( +1 + o oLD + + I 1i

lOCD

K

K

O

«a

LU

Q_O

•KK * -*t

CT> C\J

LT) O

03O + M

CO CTi

-80±10

+4.4

15f

Brittle

layer.

Copper

corroded

underneath.
CQcC I

hr

(/> +JC i

*1)

Potential

vs.

Cu-CuSO.

REFERENCE

ELECTRODE
Figure Captions

1. Schematic circuit for corrosion tests with superimposed a.c.

2 . Voltage signal (upper trace) and current signal (lower trace) for Cu in

I n Na

2

S0 ^.

; 3. Electrode potential vs. time for tinned Cu wire in 2% MapSO^. Np atmosphere.

! 4. Electrode potential vs. time for tinned Cu wire in 1% NapSO. + 1% NaCl.

Np atmosphere. ^

5. Electrode potential vs. time for tinned Cu wire in 2% NapSO^. Op atmosphere.

6 . Electrode potential vs. time for tinned Cu wire in 2% NapSO. + 1% NaCl.

Op atmosphere. ^

I 7. Electrode potential vs. time for tinned Cu wire in 0.42 M I'laC 104 * ^^*2 atmosphere

8 . Electrode potential vs. time for tinned Cu wire in 0.42 M NaClO^ + 1% NaCl.

Np atmosphere.

' 9. Electrode potential vs. time for tinned Cu wire in 0.42 M NaClO^. Op atmosphere

10. Electrode potential vs. time for tinned Cu wire in 0.42 M NaClO^ 1% NaCl.

Op atmosphere.

11. Corrosion tests with superimposed a.c.

12. Corrosion tests without superimposed a.c.

13. Corrosion tests in Na 2^^4 NaCl 04 -

i

I

14. Corrosion tests in NaCl 04 -

I 15. Corrosion tests in NaC 104 -

I 16. Rest potentials vs. time of CPE and Pb-Sn alloy in 2% Na 2^^4 NaCl.

1

17. Potentiodynami c scans for tinned Cu in 2 % Na 2

^®

4

* ^ mV/sec.

Dashed curve is expansion of solid curve and rerers to c.d. scale on left.

18. Potentiodynami c scans for tinned Cu in 2 % Na 2^04 1^ NaCl. Scan rate

I 4 mV/sec. Dashed curve is expansion of solid curve and refers to c.d.

I scale on left.

I

I 19- Potentiodynami c scans for Cu in 2% Na 2 ^^

4

* i^ate 4 mV/sec.

j 20. Potentiodynami c scans for Cu in 2% Na 2

S04 up to +800 mV. Scan rate 4 mV/sec.

I 21. Potentiodynami c scan for Cu in 0.42 M NaCl 04 - Inert atmosphere.
22 . Potentiodynami c scans for Cu in 2% Na2S0^ + 1% NaCl. Scan rate 4 mV/sec.

23. Potentiodynami c scans for Cu in 2% Na2S0^ + 1% NaCl. Inert atmosphere.

24. Potentiodynami c scan for Cu in 2% Na2S04 + 1% NaCl. Inert atmosphere.

25. Potentiodynami c scans for Pb-Sn alloy in 2% Na2S0^. Scan rate 4 mV/sec.

26. Potentiodynami c scans for Pb-Sn alloy in 1% Na2S0^ + 1% NaCl. Scan rate

4 mV/sec. Inert atmosphere.

27. Potentiodynami c scans for Pb-Sn alloy in 2% Na2^®4 NaCl. Oxygen

atmosphere. Scan rate 4 mV/sec.

28. Polarization curves for tinned Cu wire in 2% Na2^*^4> ^^ken in December 1976.

29. Polarization curves for tinned Cu wire in 2% Na2^^4» taken in January 1977.

30. X-ray spectra of various control specimens.

31. X-ray spectra of corroded neutral wires.

32. X-ray spectrum of corroded CCN wire #11Q. Solution 2% Na2S0^ + 1% NaCl,

O2 atmosphere, CPE coupling. Agar, 1600 h.

33. Schematic circuit for noise measurements.

34. Noise spectrum at open circuit.

35. Noise spectra of Fe in 1:1 H3B02-Na2B^O^+0. 01 M NaCl at various potentials.

36. Oscillographic record of electrode potential of Fe in 1:1 H3B03-Na2B40y+

0.01 M NaCl above and below the pitting potential.

37. Noise measuring circuit.

38. Spectral power amplitude vs. frequency. Noise generated by the instrumentation

and by a 10 resistor.

39. a) Coated copper wire specimen,

b) bare copper wire specimen.

40. a) Conducting polyethylene specimen,

b) Coating alloy sneet specimen.

41. Plan of NBS underground corrosion test site.
Fig. 1 Schematic circuit for corrosion tests with superimposed a.c.
I

Sweeprate 5 ms/div

1

Fig. 2. Voltage signal (upper trace) and

current signal (lower trace) tor

Cu in 2 % Na^ S0«.
I

O O O QO

*7 cvj lO

'

I

I ‘3'0'S SA AUJ ‘3

Electrode

potential

vs.

time

for

tinned

Cu

wire

in

2%

NapSO..

N„

atmosphere.
Electrode

potential

vs.

time

for

tinned

Cu

wire

in1

%

Ha2S0^

+

II

NaCl.

atmosphere.
OD

Nd^SU..

0,.

atinosptiere .
3 D'S SA AUJ ‘3

I I

tlectrode

potential

vs.

time

for

tinned

Cu

wire

in2

%

+

1%

daCl

.

0,,

atmosphere.

^

^
0

1 0

CM

1 ‘3 0*S AUJ ‘3

o

tlectrode

potential

vs.

time

for

tinned

Cu

wire

in

0.42

m

NaClO-.

H

atmosphere.
'3 *0*S SA AUJ ‘3

hlectrode

potential

vs.

time

for

tinned

Cu

wire

in

0.42 M

NaClO

Np

atmosphere.
blectrode

potential

vs.

time

for

tinned

Cu

wire

in

0.42 M

NaClO..

0^

atmosphere.
001 o

u>

CVJ o

CVJ o

00

CO

UJ2

I- oo

CVJ oCVJ o

CVJ

10.

Electrode

potential

vs.

time

for

tinned

Cu

wire

in

0.42 M

NaClO^ +

1%

NaCl.

0^

atmosphere.


Fig.

12.

Corrosion

tests

witl.out

superimposed

a

•2. Sulfate, flj). Cl , a.c. 210n h

ir scratchinQ arid cleaning in acid.

b) Sulfate, O 9 , CPE, Cl", a.c. 1720 h

After scratching and cleaning in acid.

--12. Sulfate, Go, Cl", a.c. 2100 h

.er scratching ana cleaning in acid.

d) -^117. Sulfate, 02* CPE, 2100 h

Perchlorate, ll;,, Cr, CPE, 2100 h f) "H3. Perchlorate, II;., Cl , CPE, 21

After brushing.

Fig. 13. Corrosion Tests in ^32^0^ and liaClO^.
I
-'8. Op, Aga>% a.c. 2 TOO h d) -8. ATfter scratching and cleaning in

acid.

n

2

* CV a .c. Agar. 2100 h f)#9. After scratching and cleaning in h iUp

Fig. 14. Corrosion Tests in OaCl'^i.

-‘116. 0^, CPH, Cl", 2100 h f) /'119. 0,, CPC, Aoar, Cl". 2200 h. Scale

partially rcp'ovcd.

Fip. 15. Corrosion Tests in HaClO^.
1 M

i'1

ji
200 O O OO

CM M-

• I •3*0 -S SA AUJ ‘3

o

o

CO

JC

o<D

>=^ o

inCM

fO

CM

o

fOc

I -Q

O

14-0

01E

to>

to

03C

O) +Jo

a.

4-> to

O)

to

I

I

I

TIME,

i, mA/cm^

LU

cn

tf) >>E

LU

OJ o

<u c

to

O > <u E —

fOu

to

a

+j • 03 "O

s_ • u c

03

O

U -M OO

to

5- • CD O OJ

./o s_

cvj 03 -O

7^

C

03

C\J <U> c s-o

t_> T3 I—

O)O

C to c

•I- It- +J o

i- c: o o

4- -1-to to :i C 03

03 Q. U X

to OI 0 to 1

03 <U C >

>1 s- TD =3 O U

4-> -O C GJ

QJ -C

-(-> to O 03

Cl. "13

ro CVJ

— o — CVJ fO 6 6 6 61 6 d

gUJO/VUJ *!
If) kO

i, mA/cm^ o mI oI inI

CVJ Oo

(OI

00 0) o

c. o

<0 4J o

OO 00

i.a>

(D oto TD

C.

l.'S ro

cy - >

i- •;S-3 o o u

oo o llJ CNX3

CVJ 03 -r- 1 o o

to CO rvj Q- c o

«D r— > 3 O

C_J •>- oo >E

oo

O

C

QJ 03 C Cl

•»

C

X 1 UJ

•1— QJ

•*-> oo O

»4- O)>

</) i-

:: 3

to

u

u

00 "O

QJ

O JZ

•I— 00 E •tJ <T3 S- ^ OJ >> '

ZJ • o u :: QJ o

-t-> 00 e \ QJ QJ > •—

-*-> E <o o u

Q. oo

ZD I i
Putentiodyriamic

scans

for

Cu

in

1

%

da,.S0.

.

Scan

rate

4

mV/sec.
oCM

Potciitiodynami

c

scans

for

Cu

in

2

I'la^SO^

up

to

+800

mV.

Scan

rate

4

n)V/sec.
o

o

GO

o

o

'd'

LiJ

ui

>

>

E

m UJ

o

o

CM

cr> o

ID

tf> CJ

^ujo/\;in

o m

CJ

I

Potentiodyiiani

c

scan

for

Cu

in

d.42

M

naClO^.

Inert

atmosphere.

Scan

rate

4

inV/sec.
uJ

d

CO

>

E

UJ

gUJO/ vuLi ‘

!

CNJ

C\J

Poteiitiociynamic

scans

for

Cu

in

2

.

iJa^SO.

+

I'/o

naCl

.

Scan

rate

4

mV/sec.
Fiy.

Potent!

odyiiaiiiic

scans

for

Cu

in

da^SU^

+

NaCl.

Inert

a

uiiospiiere

.
001 I ^uJO/Vtu *!

ui6

CO

vi>>E

LiJ

Fig.

24.

Potentiodynamic

scan

for

Cu

in

2%

Na^SO- +U

NaCl.

Inert

atmosphere.

Scan

rate

40

mV/sec.
LU

d

d

<o>

>

E

UJ

2b.

Poteiitioaynamic

scans

for

Pb-Sn

alloy

in

2V.

ila^SO..

Scan

rate

4

mV/sec.
uJ

• o

cn

>

>

E

iiJ

>x> c^o

gUJO/x/uj ‘

j

J

Potentiodynamic

scans

for

Pb-Sn

alloy

in

2%

iJa^SO.

+

1;.

NaCl

.

Scan

rate

4

mV/sec.

Inert

atmosphere.

^^
8

O

O

oCVJ

8

I

O

O

CD

I

uJ

d

d

(A

>

>

E

LU

Poteiiti

odynami

c

scans

for

Pb-Sn

alloy

in

Wa^SO^

+

1%

daCl

.

Oxygen

atmospliere.

Scan

rate

4

mV/sec.
o

o

O CVJ “ E

o\

o

=L

CO

LxJ Q

UJ

(T

a:3O

«5T o00

CM

(O

CM

O)

S_

3

(_) •O

O)

s_o

I/) cu>

s-3

u

co

+-> (BM

s_fOo

QCO

CM

o

GO

I o O

CJ

I 3*o*s *SA snoAnnii^

taken

in

December

1976.
CVJ CNJ o z

(T

<

O

<

55

•_ I u o

CM CM Z O

9000 11^ II 5|- 11 ^

(O a> (7) (o

cr»

>>

<03

c

fOc

c

cu

to

O)>

3u

co

Nl

'TS o

cx

'NJ

3*o*s 'SA snoAmiiN

CURRENT

DENSITY

(^a/cm^)
o

<T3 C

uo

I

;

» ;• V. I.O uj ir:

' I •is< c:>

oi cti.i U_ CT i . ii :• icC CT | •s:* Cil<

t'. ^=-

•«.' txJ

C-.J a.i •s» ':t» rH .

I r- -

:r:> ft lii' !>:;

I - c::<

»• j> ij I

I I i « >j;

I . ,.:> « • I « >

:i

j

" ’**>

. --y ;-* - i

"

r'*i -O 1

* '

, r CJ O)

1

* '*

. I.K >

. .J •Tii;*

* C->

' r *1

QJO

o>

I-.,.,

1 1 1 V:r:

.""*1

V;'

.

W. -T“f

LxJ

i;

, > i_ri

ito

• <:J>

.'V; '••• :i. I— i:s:' ?

j y a D£> «s:i ff

i i :•

. ;v -

’

Fiq. X-ray spectra of various control specimens

.

30

c)

Pure

copper

wire

d)

60%

Sn40%

Pb

alloy
CPE.

1700

h.
CH.. 16K FS 10 Ev/.'r

C:jRS0R=68. y5KE V'j . yyl26i;.CUUNT.!:-

-t- -.-4

',4

' ' \

• ’ V .=V' '

?> :V. . V' '

'

'J-

• -V'-' -

,

' •'

•• ; -V »

1*'

1 RS i.=

. N 1 = 8 8 E1 ti B s *3

' A l5 1= d - 1 13 Z‘ t L- L- U K

#119

Fiq. 32. X-ray spectrum of corroded neutral wire. Solution Na^SO^+NaCl .

0^ atmosphere. CPE coupling. Agar. 1600 h.
Input

signal

i
ZH/ /A *apn^i[duiB jawod iej^Dad$

o CO

M

C.<u3

CT

<U

L.

O)

Noise

spectrum

at

open

circuit.
SPECTRAL

POWER

AMPLITUDE,

V/\/Hi

Fig. 35. lioise spectra of Fe in 1:1 various potentials.
C.25-10'"

V/div.

V/div.

Fe/H3 B 03-Na2 B407 + 0.01 m NaCI

Above Pitting Potential

Open Circuit

0- 3b. Usci 1 1 ograptii c record of electrode potential of Fe in

U.Ol H HaCl above ana below the pitting potential.
ACTIVE

PREAMPLIFIER

—

POSTAMPLIFIER

FILTER

Fig.

37.

Noise

measuring

circuit.
SPECTRAL

AMPLITUDE,

V/

/h1

10

'®

5

3

2

lo-"^

5

3

2

I0-®

5

3

2

10-9

10"^ 10’

' I 10 10^ 10^ 10^

FREQUENCY, Hz

r FiQ- J8. Spectral power amplitude vs. frequency. Noise generated by the instrumentation

and by a 10 i^Q resistor.

\

V

A

\

\.

\

if

INSTRUMENT NOISE

O 10 KO. RESISTOR

/ \

li
a) Coated Copper Wire

b) Bare Copper Wire

Figure 39
a) Conducting Polyethylene (CPE)

b) Coating Alloy Sheet

Figure 40
a>

NBS

UNDERGROUND

CORROSION

TEST

SITE
NBS-1 14A (REV. 7-731

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1, PUHI.K ATION OR REPORT NO.

NBSIR 77-1232 (ERDA)

2. Ciov *t Accf.s.sion No.

4. TITLE AND SUBTITLE

Development of IN-SITU Techniques for the Detection and

Measurement of Corrosion of Copper Concentric Neutrals in

Underground Environments

3. Roi" ipirni 's Accession No.

S. Publication Hate

6. Perfortning Organization Code

7. AUTHOR(S) 8. Performing Organ. Report No. Krug

FORlCfler, [J. £firtnrx.i.^F. Escalante, and J.L. Mullen

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract /Grant No. E(49-l)-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 Annual Report

1/15/76-1/15/77

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 first year of a three-year project, whose

purpose is to develop in-si tu methods for detecting corrosion on buried copper

concentric neutral (CCN) wires.

Specimens of the wire underwent long term corrosion tests. Environmental variables

examined were: a) composition of electrolyte, b) composition of the gaseous

atmosphere, c) convective motion in solution, d) superimposed a.c. signal, and

e) coupling with conducting polyethylene (CPE).

The results showed that accelerated attack with pit formation was caused by a.c. signal and that oxygen availability and presence of chloride ions in solution

favored the attack of the wires.

Potentiodynamic scans on the wires as well as on pure copper and tinning alloy were performed in various solutions.

The development of a new measurement method, the analysis of the fluctuations of

the corrosion potential, has been initiated in the laboratory with the aim of

testing its potentiality as a corrosion detection method in the field. A burial site

on NBS grounds has been prepared, and several lengths of cable as well as some other

pertinent materials have been laid underground. Data collection from the buried

s pacimens ha s been initiated,

17. rEY words (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; seoarated by semicolons

)

Buried cables; copper concentric neutral wires; corrosion detection methods; corrosion

tests; current-potential measurements; underground corrosion

18. AVAILABILITY Unlimited

d For Official Distribution. Do Not Release to NTIS

I

^ Order F rom Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CH

Order F rom National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

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UNCLASSIFIED

21. NO. OF PAGES

69

22. Price

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