tea
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-023 Mar 1981
Project Summary
Field Test of Corrosion
Control to Protect
Asbestos-Cement Pipe
Gary S. Logsdon
This research program was initiated
to determine whether adding zinc
orthophosphate to potable water
would sufficiently coat an asbestos-
cement pipe with zinc to prevent
asbestos fibers from entering the
water.
Storage tanks and chemical and
feed pumps were set up at each of the
Greenwood, SC, water treatment
plants, and zinc orthophosphate was
fed into the system at an average rate
of 0.3 mg/L. Two sections of new
asbestos-cement pipe were installed
to represent a low-flow and a high-
flow water condition; they were
removable for testing. Samples were
periodically tested to determine the
number of asbestos fibers in the
water. The two pipe sections were
removed and examined for the
amount of zinc deposited on the
surface.
Although routine tests, such as pH
and alkalinity, showed no significant
changes during the study period,
asbestos fibers in the water decreased
substantially. Electron microscope
photographs and energy dispersive X-
ray spectra analyses showed coatings
of zinc products on the two pipe
samples. Thus, adding zinc ortho-
phosphate under the existing water
quality conditions reduced or pre-
vented corrosion of asbestos-cement
pipe.
This Project Summary was devel-
oped by the EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati, OH 45268, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Asbestos-cement (A/C) pipe has
been used in the United States since the
1930's Because this pipe does not rust
and cause "red water" or rusty water
problems for water users, some water
utilities have used A/C pipe as an
alternative to cast iron when the treated
water has had a history of corroding cast
iron water mams. In some instances,
using A/C pipe to carry aggressive or
corrosive water has deteriorated the
A/C pipe.
Zinc orthophosphate, developed as a
corrosion control additive for water
distribution systems, has been used
successfully in the 1970's to control
problems of corrosion m cast iron
mams The Greenwood study was con-
ducted to evaluate its use for controlling
deterioration of A/C pipe exposed to
aggressive water The pipe, much of
which had been installed in Greenwood
in the late 1940's and 1 950's, had been
attacked by the water carried by the
pipes During the study, the water leav-
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ing the treatment plant had a pH of 8 2
to 8 3, alkalinity of 20 mg/L as CaCO3,
total hardness of 10 mg/L as CaCO3,
and an iron content of 0.1 mg/L. As the
water passed through the A/C pipes,
the pH increased—an indication that
constituents of the A/C pipe were being
dissolved by the water.
Methodology
After the equipment was installed,
zinc orthophosphate was injected into
the system just ahead of the clearwell at
each of the two treatment plants, begin-
ning on October 11, 1977. The initial
feed rate for passivation was 3 0 mg/L.
The passivation period was ended after
3 days on October 14, 1977, short of the
intended date of October 15, because of
problems encountered at one of the
system's larger users, a pharmaceutical
company. This firm, which processes
gauze and surgical supplies, used a
cotton-filament, wound filter to remove
rust or iron particles as well as other
particles in the water. The high concen-
trations of zinc orthophosphate clogged
the filters sufficiently for the company to
change filters every 2 to 3 days during
the initial periods, normally, a set of
filters would have lasted 6 to 7 months.
The feed rate was reduced to 0 5 mg/L
in an effort to ease the filter problem
When zinc was found at 0.17 mg/L at
the low-flow location, it was concluded
that zinc was present throughout the
system.
The clogged filter problem at the phar-
maceutical company continued how-
ever, and on November 21, the zinc feed
rate was lowered to 0.3 mg/L. The
concentration of zinc at the low-flow
location decreased to less than 0 1
mg/L. This rate was continued until the
end of the study, although problems
were still encountered with the filters.
Water from two test locations (one
high-flow, one low-flow) where A/C
pipe is used, was routinely sampled for
zinc content, pH, alkalinity, and calcium
as CaCOs. Water samples werealspfor-
warded to the EPA laboratory in
Cincinnati to determine the number of
asbestos fibers present.
The high-flow test site (a 20-cm (8-
inch) A/C pipe servicing other mains in
a subdivision) was selected because it
represented a flow-through situation
This location was about 1.7 km (1 mile)
from one of the two treatment plants
where zinc was added. The low-flow
sampling location (a 15-cm(6-mch) A/C
main) was on a looped dead end line
about 5 km (3 miles) from the same
treatment plant
At each of thetwosampling locations,
a section of new A/C pipe was installed
so that it could be removed at the end of
the experiment.
Throughout the study period, water
quality was monitored at both locations.
When the water had been tested on
March 2, 1976, no asbestos fibers were
found in the well water but 022 x 106
fibers/liter were found in water that
had passed through about 2 miles of
A/C pipe. The finished water had an
Aggressiveness Index (Al) of about 104
to 105 The tendency of a water to
deteriorate the structure of asbestos-
cement pipe has been described by the
Al as
tapping'
Al = pH + log (AH)
where
pH = -log a(-T (-log of the hydrogen
ion activity)
A = total alkalinity in mg/L as
CaC03
H = calcium concentration in mg/L
as CaCO3
Waters possessing an Al >120 are
considered to be "nonaggressive",
those where Al < 10.0 are said to be
"highly" aggressive," and those with an
Al between 10 and 12 are "moderately
aggressive." During the study, the Al of
the water at the closer, high-flow loca-
tion ranged from 10.6 to 11.2, which is
somewhat above the Al at the treatment
plant. At the more distant, low-flow
location, the Al varied from 11 2 to 11 9
during the study—a range considerably
higherthanthe 104 to 105AI values at
the treatment plant
Results
After the initial passivation period,
zinc concentration at the closer location
averaged about 0.2 mg/L; at the distant
location, it was generally less than 0.2
mg/L, averaging 0 1 mg/L These con-
centrations were not sufficient to
prevent a rise in pH and calcium
between the two sampling locations.
Most of the calcium increase in the
distribution system occurred between
these sites, where zinc concentration
was lowest
Two times after A/C pipe had been
tapped in the sample location vicinity,
high asbestos fiber counts were ob-
served. Because pipe
operations can temporarily raise the
fiber count in the distribution system,
the use of tapping machines equipped to
flush away drilling and tapping debris is
recommended.
The scanning electron microscope
(SEM) was used to examine the interior
pipe wall of pipe samples removed from
both sample locations. The interior sur-
face of the 20-cm (8-mch) pipe was
smooth, and some coating resulting
from zinc treatment could be identified.
The interior of the 15-cm (6-inch) pipe,
with a lower concentration of zinc (0.1
mg/L), had much larger uncoated areas
on the pipe surface.
Regardless of which portion of the
pipe was examined, the 20-cm (8-inch)
pipe always showed better coverage
than the 15-cm (6-inch) pipe. This indi-
cates that the zinc or zinc compounds do
adhere to the A/C pipe, and that to be
effective, the zinc concentration should
be 0 2 mg/L, or higher if possible
Energy-dispersive, X-ray spectro-
metric elemental analyses were made
on the surfaces of the two test pipes,
these analyses were compared with
that for a new, unused piece of pipe. Orj
the unused pipe, the only large peak
shown was calcium High peaks were
seen for iron and zinc on the 20-cm (8-
inch) test pipe and the low peak seen for
calcium could indicate that t'ie pipe is
well protected and the calcium is
masked at this location. High silica and
calcium peaks and a low zinc peak were
observed for 1 5-cm (6-inch) pipe at the
low-flow locatom. This again indicates
that the low zinc concentration of 0.1
mg/L in the 1 5-cm (6-inch) A/C pipe is
not adequate to provide a protective
coating—certainly not as effectively as
the higher concentration (10.2 mg/L)a1
the other site.
In the energy-dispersive, X-ray
spectrornetric analyses, the peak size
for zinc and iron varied with location ir
the pipe. A comparison of these peakj
from the 15-cm (6-inch) and the 20-crr
(8-inch) pipes showed, however, tha
the highest peaks of the 20-cm (8-mch
pipe were always higher than the high
est peaks of the 1 5-cm (6-inch) pipe, anc
the lowest peaks of the 15-cm (6-mch
pipe were always lower than the lowes
peaks of the 20-cm (8-inch) pipe Th<
results for the iron peaks suggest tha
iron in the water provides a partial pro
tective coating to the A/C pipe in thi:
system.
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Conclusions
The study results of using zinc ortho-
phosphate to protect A/C pipe suggest
that this treatment will cause A/C pipe
to be coated with a protective com-
pound. A zinc concentration of 0.2 mg/L
was adequate to provide a coating on
the pipe wall, but pH and calcium
increases occurred at this concentra-
tion of zinc The concentration of zinc
reaching the end of the distribution
system should exceed 0.2 mg/L.
Because zinc precipitates in the system,
the amount of zinc orthophosphate
dosed at the treatment plant to obtain
the desired zinc residual would have to
be determined for each system.
The full report, submitted in fulfill-
ment of Grant No R804888-01 by Com-
missioners of Public Works,
Greenwood, CA, under the sponsorship
of the U.S. Environmental Protection
Agency, was authored by Clarence E.
Grubb
Gary S. Logsdon is with the U.S. Environmental Protection Agency (see below).
Ralph W. Buelow was the EPA Project Officer.
The complete report, entitled "Field Test of Corrosion Control to Protect
Asbestos-Cement Pipe." (Order No. PB 81-152 878; Cost: $5.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
Gary Logsdon. the present contact, can be reached at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
I US GOVERNMENT PRINTINQ OFFICE 1961 -757-01Z/7016
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