United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/056 Sept. 1986
£EPA Project Summary
Copper-Induced Corrosion of
Galvanized Steel Pipe
Katherine P. Fox, Carol H. Tate, Gordon P. Treweek, R. Rhodes Trussed,
A. Eugene Bowers, Michael J. McGuire, and Dale D. Newkirk
An investigation was conducted to
determine the cause* of rapid pitting
failure of galvanized steel pipe used in
consumer plumbing systems. The pres-
ence of copper in water and the charac-
ter of the galvanized steel pipe were
factors examined in detail.
Pipe manufactured in Korea, Aus-
tralia, and in the United States was
compared for pipe structure and zinc
coating. The pipe manufactured in
Korea by electrical resistance welding
had a pronounced weld seam, whereas
U.S. and Australian pipes manufac-
tured with Diittwelding had only small
or nonexistent seams. Furthermore, the
zinc coating on the Korean pipe failed
to meet the weight of coating standard
(1.8 oz/ft2) in 11 of 14 samples. Exami-
nation of the iron/zinc interface on the
Korean pipe revealed possible sites of
poor adhesion of the coating to the
base metal.
In pilot testing, increasing copper
concentrations (from 0.0 to 5.0 mg/L)
produced increased corrosion activity
on the pipe surface, as measured by
greater deposition of scale, calcium,
iron, zinc, and copper. Also, the ratio of
iron surface to zinc surface area in-
creased. Other factors such as the
mode of exposure and the addition of
citrate had no measurable Impact. The
corrosion activity measured by scale
formation was greatest on the Korean
pipe, followed by the U.S. and Aus-
tralian. Rapid pitting of the sort ob-
served In several southern California
homes did not occur under any of the
conditions tested.
Thla Project Summary was dovol-
ofMMf by EPA'f Water Engineering Re-
search Laboratory, Cincinnati, Off, to
announce key findings of the research
project that la fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Over the past two decades, several
occurrences of accelerated pitting cor-
rosion of small-diameter, galvanized
steel pipe have been investigated. Pit-
ting is a term used to describe a form of
corrosion wherein a concentrated attack
occurs at small sites, often perforating
the pipe. Pitting typically causes leaks
and destroys a pipe's usefulness long
before the end of its rated economic life.
Recent episodes of this type of corro-
sion have taken place in large housing
tracts where widespread pitting failure
of household plumbing occurred within
5 years of construction.
Several factors have been alleged to
cause or enhance the corrosion prob-
lem, including the presence of copper in
the water, the surface character of the
pipe, base metal and/or zinc composi-
tion and integrity, and water tempera-
ture and quality. A common factor in
failures that have occurred in a variety
of water sources, building types, and in
both hot and cold waters is the presence
of copper in the water. A number of in-
vestigations into housing tract failures
seem to bear out this hypothesis.
Table 1 summarizes the conditions ob-
served and failures investigated by sev-
eral studies. As the table shows, copper
in the water was associated with each
case, either through its use as an algi-
cide or through dissolution of copper
piping. The variety of water sources in-
cluded local well water, Owens River
water with low total dissolved solids
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Table 1. Summary of Copper-Related Corrosion of Galvanized Steel Water Pipes
Affected Units
Year
Source of
Water Supply
Source of
Copper
Surface
Copper Copper
Concentration Concentration
in Water on Pipe
Img/U (mo/dm2) Corrective Action Recommended
Comment
Apartment Houses (9) 1961 Local wells and Reservoir
Colorado River algicide
Lodge (75 units)
Motel (21 units)
Apartment Hotel
144 units)
Tract Homes
(39 units)
Tract Homes
(100+ units)
Tract Homes
(500+ units)
Tract Homes
(340 units)
1962 Local wells
1965 Local wells
1968 Owens Valley
1973 Local wells
Reservoir
algicide
Dissolution of
copper pipe
Copper tubes in
heat exchangers
Reservoir
algicide
1973 Colorado River Reservoir
algicide
1977 Colorado River Reservoir
algicide
1978 Colorado River & Reservoir
Northern algicide
California
N/A* 12-25 Install new copper pipes. Dis-
continue the use of CuSO4 algi-
cide. Reduce dissolved O2 by
blending.
N/A 11-26 Reduce reservoir aeration. Re-
duce intake of highly mineral-
ized water. Reduce hot water
temperature.
0.01-0.08 0.84 Reduce velocity of circulation.
Avoid mixing of copper and iron
piping systems. Continue
pofyphosphate treatment.
0.05 9.6 Replace corroded galvanized
steel hot water piping with cop-
per system.
0.029-0.063 N/A Adjust pH to positive Langelier
Index. Aerate supply to remove
hydrogen suffide. Cease use of
polyphosphate inhibitor. Discon-
tinue CuSO4.
0.1-0.5 N/A Replace galvanized pipe with
copper pipe. Use greater care in
application of copper sutfate-
citric acid complex as algicide.
0.01-0.4 15-34 Replace galvanized pipe with
copper pipe. Use greater care in
application of copper sulfate-
citric acid complex as algicide.
0.3-4.3 2.5-12.3 Replace galvanized pipe with
copper pipe.
Pipe failure through pitting
corrosion in 18-36 months.
Hot (140-160^) water sys-
tem pipe failure through
pitting corrosion in
18 months.
Circulating hot (150'F)
water system. Red water
and iron particles from pit-
ting corrosion in
18 months.
Circulating hot (130°F)>
water system. Pipe failure
through pitting corrosion
in 108 months.
Pipe failure through pining
corrosion in 24-36 months.
Pipe failure through pitting
corrosion in 12-24 months.
Pipe failure through pitting
corrosion in 12-24 months.
Pipe failure through pitting
corrosion within 24-
60 months; 90% of leaks
in horizontal pipes, 72% of
leaks in hot water pipe.
*N/A means not analyzed.
(TDS), and Colorado River water with
high TDS. The latter four cases shown
involved housing tracts with up to 500+
units affected.
To investigate further the factors that
are important in this type of corrosion, a
pilot-scale facility was designed, con-
structed, and operated in which the ef-
fects of copper dose, pipe type, mode of
exposure of the pipe to test solutions,
and water quality could be tested over a
period of 3 years. During that period,
ancillary bench and laboratory studies
were also carried out on the effects of
pipe structure, iron-zinc polarity rever-
sal, and pipe surface anomalies. The full
report contains findings made in each of
these areas. Readers interested in ob-
taining the complete report with color
illustrations should contact the senior
author for details.
Results and Discussion
The first phase of this investigation
concentrated on determining the char-
acteristics of the galvanized steel pipe
structure and the zinc coating. The re-
sults of this phase are summarized in
Table 2. With respect to the elemental
composition of the base metal, emis-
sion spectroscopy determined that the
base steel used by each of the three
manufacturers (Australian, Korean, and
U.S.) was satisfactory for trace ele-
ments in the steel. The Korean pipe had
a lower carbon content than either the
Australian or the U.S. pipe, but this fact
should not affect its corrosion potential.
Microscopic examination of a cross-
section of Korean pipe revealed a pro-
nounced weld seam, probably pro-
duced during electrical resistance
welding, whereas the U.S. and Aus-
tralian pipes had only a small or nonex-
istent seam, respectively. The weld
seam on the Korean pipe produced a
discontinuity in the otherwise smooth
interior surface.
The zinc coating on pipe samples
from each of the three manufacturers
was examined by energy dispersive X-
ray (EDX) to determine the elemental
composition of the zinc/iron layers at
the interface. No abnormal components
were found in any of the three layers,
which consisted primarily of zinc and
iron with trace amounts of lead. The
thickness of the zinc coating was deter-
mined by three tests: the weight of coat-
ing test (ASTM A90-81), the Preece test
(ASTM A239-73), and microscopic ex-
amination. The Korean pipe failed to
meet the weight of coating standard
(1.8 oz/ft2) in 11 of 14 samples. The Aus-
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Table 2. Summarized Characteristics of Galvanized Steel Pipe Structure and Coating
Pipe Manufacturer
Characteristic
Pipe Structure
Base metal chemical composition
Fabrication anomalies
Australian
Satisfactory
None
Korean
Satisfactory
Pronounced weld seam
U.S.
Satisfactory
Slight weld seam
Pipe Coating
Thickness
Weight of coating test
Preece test
Microscopic test
Chemical composition
Adhesion
Uniform coating
All samples >1.8 oz/ft2
Uniform, smooth coating
2 to 3 dips for 10 of 14 samples
Average coating
Satisfactory
Satisfactory
Uniform coating
11 of 14 samples < 1.8 oz/ft2
Blemishes
1 dip for 12 of 14 samples
Thin coating
Satisfactory
Variable coating
All samples > 1.8 oz/ft2
Variable coating
More than 2 dips for 12 of 14
samples
Thick coating
Satisfactory
Separation zone between base metal Satisfactory
and coating
tralian and U.S. pipes met this standard
in all instances. In the Preece test, 12 of
the 14 Korean pipe samples required
only one dip in copper sulfate solution
to reveal the base metal. Ten of the 14
Australian pipe samples required two to
three dips to reveal the base metal, and
12 of the 14 U.S. pipe samples required
more than two dips to reveal the base
metal. As would be expected from the
weight of coating test and the Preece
test, the microscopic examination of
three samples revealed that the total
zinc coating on the Korean pipe was the
thinnest. Furthermore, each of the three
layers that make up the zinc/iron inter-
face (the delta, zeta, and eta layers)
were thinner for the Korean pipe than
for the Australian or U.S. pipe. From
these three tests, a picture emerged of
the Australian pipe with a uniform,
smooth coating of the proper thickness,
the Korean pipe with a uniform thin
coating containing occasional blem-
ishes, and the U.S. pipe with a more
variable but thick coating containing oc-
casional blemishes and irregularities.
Subsequent etching and microscopic
examination of the iron/zinc interface
on all three pipes revealed sites where
the zinc coating adhered poorly to the
base metal on the Korean pipe. In some
instances, a thin gap appeared to exist
between the zinc coating and the under-
lying base metal.
Because premature pitting failure of
Table 3. Results of Bench-Scale Testing for Potential Reversal and Unusual Corrosion at Pipe Surface Anomalies*
Water Source
Characteristic
Control Water+
State
Water
Project
Colorado
River
Water
Pasadena Tap#
1. Potential Reversal
2. Water Quality Impact
Pipe Surface Anomalies
Control
Acid etched
Acid etched and drilled
Drilled
Reversal occurred
No reversal
No reversal
No reversal
Distilled Water Plus Constituent
Control
CuS04
Citrated
CuS04
Cu
Plated
None
None
Localized
Loalized
None
None
Localized
Localized
None
None
Localized
Localized
None
None
Localized
Localized
Pasadena Tap Plus Constituent*
3. Pipe Surface Anomalies
Control
Acid etched
Drilled
Black iron
Control
None
None
None
Generalized
CuSO4
None
None
None
Generalized
Citrated
CuS04
None
None
None
Generalized
Azurite
Zinc loss
Zinc loss
Zinc loss
Generalized
CuSO4
with
Azurite
Zinc loss
Zinc loss
Zinc loss
Generalized
Citrated
CuSO4
with
Azurite
Zinc loss
Zinc loss
Zinc loss
Generalized
* All tests used Korean galvanized pipe samples except as noted.
+Distilled water plus 110 mg/L HCO* 10 mg/L SO* 10 mg/L NO*
# Local groundwater source.
S The same tests but with salts added to create high TDS (2000 mg/L) water showed no localized corrosion.
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galvanized pipe has been demonstrated
to occur as a result of potential reversal
between the iron and zinc, bench-scale
testing was conducted to determine
whether such potential reversal was oc-
curring at the elevated temperatures of
hot water systems. Additional tests
were run to determine whether unusual
corrosion would occur at specially cre-
ated pipe surface anomalies. The re-
sults of the bench-scale testing are sum-
marized in Table 3. As shown, potential
reversal occurred in the water solution
matched to that used by earlier investi-
gators. However, for water supplies cur-
rently available in southern California
(the two surface water sources, State
Water Project and Colorado River water.
and one groundwater source, Pasadena
tap water), no potential reversal oc-
curred over the temperature range and
time interval tested.
Pipe surface anomalies were created
on Korean galvanized steel pipe by acid
etching and/or by drilling a small hole
into the zinc layer. While localized corro-
sion was enhanced in the drilled areas,
the acid etching of the zinc surface had
no measurable impact. Similarly, the
addition of copper sulfate or citrated
copper sulfate to the solution did not
noticeably increase the localized corro-
sion over that recorded for the control,
which consisted of distilled water. Cop-
per plating portions of the sample (both
clean and clean with acid etching) had
little effect. Similar results were
recorded when Pasadena tap water was
substituted for distilled water. Azurite
crystals placed on the bottom of the in-
terior pipe surface did accelerate the
loss of zinc from the surface. In general,
the addition of copper sulfate or citrated
copper sulfate did not have corrosion
impact that was obviously different
from that of the control solution without
these chemicals.
Pilot plant testing was undertaken to
determine the impact of five major vari-
ables on the corrosion rate of galva-
nized steel pipe: copper dose (0.0 to
5.0 mg/L), pipe manufacturer (Aus-
tralian, Korean, U.S.), initial mode of ex-
posure (static, flowing), water quality
(Colorado River water, State Water Pro-
ject), and complexing agent (citrated,
uncitrated). Table 4 summarizes the re-
sults of this pilot plant testing.
Pipes from all three countries were
exposed to Colorado River water for up
to 20 months and to increasing copper
doses from 0.0 to 5.0 mg/L. The effect
on the galvanized steel pipe was deter-
mined by measuring the extent of scale,
calcium, iron, zinc, and copper deposi-
tion on the interior pipe surface. In addi-
tion, the iron-to-zinc ratio was deter-
mined for the interior surface area after
the scale had been removed. Irrespec-
tive of the pipe manufacturer, increased
copper doses invariably led to in-
creased scale and increased iron-to-zinc
ratios. Increasing the exposure time
from 8 to 20 months generally resulted
in overall increased scale deposition,
but the amount of calcium in the scale]
showed no difference. The iron-to-zinc
ratios also showed no consistent in-
crease with increased exposure time. Fi-
nally, the mode of exposure (static ver-
sus flowing test solution) made no
apparent difference on the extent of cor-
rosion.
As with the Colorado River water ex-
periment, pipes from all the manufac-
turers exposed to State Water Project
water with increasing doses of copper
produced increasing deposition on the
interior pipe surface. As the copper
dose increased from 0.0 to 5.0 mg/L, the
scale, calcium, iron, zinc, and copper de-
position on the interior pipe surface
similarly increased. The iron-to-zinc
ratio of the exposed surface also in-
creased. The addition of 2.5 mg/L of cit-
rate to the solution containing 5.0 mg/L
of copper produced no apparent differ-
ence compared with the solution con-
taining only the 5.0 mg/L of copper. Fi-
nally, the mode of exposure (static
versus flowing test solution) showed no
difference in terms of the extent of cor-
rosion.
The results from 8 months of expo-
sure to Colorado River water were com-
pared with those from 7 months' expo-
sure to State Water Project water for all
the pipe manufacturers. At each copper
Table 4. Results of Pilot Plant Testing of Galvanized Steel Pipe Corrosion"
Effects on Pipe
Item tested and test conditions
Scale
Deposition
Calcium
Deposition
Iron
Deposition
Zinc
Deposition
Copper
Deposition
Surface
Exposed
Fe/Zn
1. Colorado River Water Exposure tall pipe manufacturers)
Increase Cu dose (0.0 to 5.0 mg/L) Increase
Increase exposure time (8 to 20 months) Increase
Mode of exposure (static vs flowing)
Section of pipe (top or bottom)
2. State Water Project Exposure
Increase Cu dose (0.0 to S.O mg/L) Increase
Addition of citrate (2.5 mg/L to S.O mg/L Cu)
Mode of exposure (static vs flowing)
3. Comparison of Colorado River water (8 months' exposure)
Increase Cu dose (0.0 to S.O mg/L) CRW > SWP+
4. Comparison of Pipe Manufacturers
Increase Cu dose (0.5 to 5.0mg/L) K>US>A#
Increase
Unchanged
Increase
Increase Increase
Increase Increase
No apparent difference
No apparent difference
Increase
Increase
Increase Increase Increase
No apparent difference
No apparent difference
with State Water Project water (7 months' exposure)
CRW>SWP CRW>SWP Variable CRWUS>A US>K>A K>US>A K>US>A
Increase
Variable
Increase
CRW^SW,
Variable
"All tettf were carried out utlng the pipe from Korei. Auttnlle, end the United Stete$.
+CRW - Colorado River weter; SWP - Stete Weter Project water.
*K - Korea; US. - United Stetee; A * Auttrelle-
-------
dose, the scale formed in the Colorado
supply was greater than the scale
formed in the State supply, a result ex-
pected from the more positive Langelier
Index of the Colorado supply. The ex-
tent of zinc removal and deposition
varied among the different pipe manu-
facturers with no consistent pattern,
whereas the extent of copper deposi-
tion was always less from the Colorado
supply than from the State supply. The
iron-to-zinc ratios for the exposed sur-
face area indicated that the Colorado
supply was at least as aggressive in re-
moving the zinc layer as the State sup-
ply, and in some instances, it was more
aggressive.
With respect to the different pipe
manufacturers, the Korean pipe gener-
ally produced the greatest scale, cal-
cium, zinc, and copper deposition,
whereas the U.S. pipe deposition was
between that of the Korean and Aus-
tralian samples. The U.S. pipe appeared
to produce the greatest iron deposition,
with the Korean pipe between the U.S.
and Australian samples. The iron-to-
zinc ratio of exposed surface area varied
between the different pipe manufactur-
ers with no consistent pattern.
The pilot plant testing demonstrated
increased corrosion activity associated
with two variables—increasing copper
dose (0-5 mg/L) and pipe manufacturer
(Korean pipe showed the most corro-
sion and Australian the least). This cor-
rosion activity was evidenced by the re-
moval of zinc and iron from the pipe
surfaces and the formation of deposits
containing calcium, iron, zinc, and cop-
per. Pits that did occur on the pipe sur-
faces were scattered over the entire sur-
face of the pipe and were generally
superficial, never becoming deep
enough to warrant depth measurement.
The 2 years of pilot testing produced no
deep isolated pits of the type that origi-
nally motivated the study. Perhaps a
longer test period or more severe test
conditions (such as longer exposure
time in hot water) would have resulted
in eventual pitting failure, but such re-
sults are not clearly predictable.
Conclusions and Recommenda-
tions
Given past observations of the influ-
ence of copper on galvanized steel pipe
and our findings regarding the differ-
ences in pipe quality among Korean,
U.S., and Australian manufacturers,
these results are unexpected. Based on
the galvanic series, copper is known to
be aggressive to less noble metals such
as zinc and iron, and pitting failure of
galvanized, recirculating hot water sys-
tems as a result of copper contamina-
tion is quite common. The large-scale
pitting failures that were found in
houses during field studies and that pre-
cipitated this study appeared to match
the failures of the recirculating hot
water systems. However, our testing of
copper in both pilot- and bench-scale
facilities, coupled with a host of other
variables, did not demonstrate this
phenomenon. Use of Korean pipe with
its substandard zinc coating did not pro-
duce this result either. Thus the recom-
mendations below are directed toward
re-evaluating field occurrences of this
type of corrosion and attempting to de-
termine whether flaws in the experi-
mental designs of the pilot plant and
bench tests precluded expected results.
1. Retain samples from bench and
pilot testing for further analyses.
Of specific concern is whether the
rapid scale build up on the pipe
during the pilot testing interfered
with the action of copper on the
pipe surfaces.
2. In this same context, a comparison
is warranted of the form of copper
precipitated on the pilot-plant
pipes with the copper found on
pipes that have failed in the field in
housing tracts and in recirculating
hot water systems. Possibly pilot-
plant conditions resulted in a pre-
cipitate that is less intensively cor-
rosive than that observed under
these other conditions.
3. More thorough scrutiny should be
provided for the conditions under
which failures in housing tracts
have occurred and may occur in
the future. A group of experts from
several fields such as chemistry,
metallurgy, and corrosion should
examine any future occurrences
and concur as to the significant
variables.
The full report was submitted in fulfill-
ment of Cooperative Agreement No.
807446-02 by Metropolitan Water Dis-
trict of Southern California under the
sponsorship of the U.S. Environmental
Protection Agency.
-------
Katharine P. Fox, Carol H. Tata, Gordon P. Trewaak, and R. Rhodes Trussell are
with James M. Montgomery, Consulting Engineers, Inc., Pasadena, CA91101;
and A. Eugene Bowers, Michael J. McGuire, and Dale D. Newkirk are with the
Metropolitan Water District of Southern California, Los Angeles, CA 90054.
Marvin Gardel* is the EPA Project Officer (see below).
The complete report, entitled "Copper-Induced Corrosion of Galvanized Steel
Pipe," (Order No. PB 86-208 717/AS; Cost: $ 16.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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flgjtt
IRARIAN
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U.S. GOVERNMENT PRINTING OFFICE; 1986 — 646-017/47155
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