Item No. 24250
NACE International Publication 10A292 (2013 Edition)
This Technical Committee Report has been prepared by NACE
International Task Group (TG) 014,* “Corrosion Control of
Ductile and Cast Iron Pipe.”
Corrosion and Corrosion Control
for Buried Cast- and Ductile-Iron Pipe
© May 2013, NACE International
This NACE International (NACE) technical committee report represents a consensus of those
individual members who have reviewed this document, its scope, and provisions. Its acceptance
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Foreword
The purpose of this technical committee report is to review data on corrosion and corrosion protection of ductile and gray cast-iron
pipe from literature in the U.S. and abroad (gray-iron pressure pipe is no longer produced in North America). Throughout this
report, gray cast iron is referred to as “cast iron.” The following subjects are covered in this technical committee report:

Engineering practices with respect to ductile- and cast-iron pipe;

Reported protective measures and results obtained by their use;

Influence of the different properties of the two types of iron pipe; and

Case histories of installations spanning decades in a wide range of soils.
This report provides the user, owner, engineer, contractor, and other interested parties with technical and general information as
to the state-of-the-art with regard to understanding techniques and methods used to mitigate corrosion of iron pipe and fittings. It
includes discussions of both historical and recent practices in which corrosion is a potential problem. This technical committee
report is not a standard, and as such, it does not cover compliance with any particular specifications, although specifications and
standards are cited as references.
____________________________
*Chair Ronald L. Bianchetti, Russell Corrosion Consultants, El Dorado Hills, CA
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There are a variety of opinions concerning the benefits of various corrosion control systems for cast- and ductile-iron pipe, which
are discussed in pertinent sections of this report. Each method or technique presents the designer and the user with numerous
factors that have an impact on installation and operating costs. It is intended that the reader use the report in its entirety and use
the information as well as the cited resources when he or she makes decisions about corrosion control for his or her particular
situation, and that he or she finds this report a useful source of information and an engineering tool in making decisions
associated with corrosion protection.
This report was originally prepared in 1992 by NACE Task Group T-10A-21, a component of Unit Committee T-10A, “Cathodic
Protection.” It was revised in 2012 by Task Group (TG) 014, “Corrosion Control of Ductile and Cast Iron Pipe.” TG 014 is
administered by Specific Technology Group (STG) 35, “Pipelines, Tanks, and Well Casings,” and is sponsored by STGs 02,
“Protective Coatings and Linings—Atmospheric,” 03, “Protective Coatings and Linings—Immersion/Buried,” 05, “Cathodic/Anodic
Protection,” and 39, “Process Industry—Materials Applications.” This report is published by NACE under the auspices of STG 35.
NACE technical committee reports are intended to convey technical information or state-of-the-art
knowledge regarding corrosion. In many cases, they discuss specific applications of corrosion
mitigation technology, whether considered successful or not. Statements used to convey this
information are factual and are provided to the reader as input and guidance for consideration when
applying this technology in the future. However, these statements are not intended to be
recommendations for general application of this technology, and must not be construed as such.
Historical Perspective on Iron Pipe
The earliest recorded installation of cast-iron pipe occurred in 1455 at the Dillenburg Castle in Germany. In 1664, French King
Louis XIV ordered the construction of a cast-iron pipeline extending 24 km (15 mi) from a pumping station at Marly-on-Seine to
Versailles to supply water for the fountains and town. Sections of this cast-iron pipeline are still functioning after more than 340
1
years of service (as of 2005).
2
Cast-iron pipe was installed in the U.S. in Philadelphia, Pennsylvania, as early as 1804. Currently, more than 600 utilities in the
U.S. and Canada have cast-iron pipe that has provided service for 100 years or longer. Currently, at least 22 utilities in the U.S.
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and Canada have cast-iron mains that have served continuously for 150 years or more.
Over the years, cast-iron pipe has been manufactured in sizes ranging from 50 to 2,100 mm (2 to 84 in) nominal diameter, and in
various laying lengths from 0.9 to 6 m (3 to 20 ft). The first cast-iron pipes were statically cast in horizontal molds. The position of
casting the molds changed from a horizontal position to a sloping position, and finally to a vertical position around the year 1850.
Centrifugal casting methods have been in the process of commercial development and refinement since 1925.
The first ductile-iron pipe was cast experimentally in 1948 and entered the marketplace in 1955. Since 1965, ductile-iron pipe has
(1)
(2)
4
been manufactured in accordance with ANSI /AWWA C 151/A 21.51 by centrifugal casting methods. In the centrifugal
casting process, a controlled amount of molten metal that has the proper characteristics is introduced into a rotating mold, fitted
with a socket core in such a way as to distribute the metal over the interior of the mold surface by centrifugal force. This force
holds the metal in place until solidification occurs. Pipe removed from the mold is furnace annealed to produce the prescribed
physical and mechanical properties and to eliminate any casting stresses that are present.
By 1979, ductile-iron pipe had succeeded cast-iron pipe as the predominant water and wastewater piping material. Ductile-iron
pipes are manufactured in standard sizes ranging from 80 to 1,600 mm (3 to 64 in) nominal diameter with nominal lengths of 5.5
m (18 ft) and 6.0 m (20 ft) and employ rubber-gasket jointing systems. Although several types of restrained joints are available for
ductile-iron pipe, the push-on joint and the mechanical joint are the most prevalent.
For water applications, ductile-iron pipe is typically furnished with cement-mortar lining to prevent internal corrosion. The exterior
of the pipe normally has a 1.0 mil (25 m) thick asphaltic coating that offers some protective value, but is not intended to provide
long-term corrosion protection.
(1)
(2)
American National Standards Institute (ANSI), 25 West 43rd St., 4th Floor, New York, NY 10036.
American Water Works Association (AWWA), 6666 Quincy Ave., Denver, CO 80235.
2
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Metallurgical Differences and Similarities Between Ductile and Cast Iron
The mechanical properties of iron-based alloys are largely dependent on their microstructures. Ductile and cast iron have similar
chemical analyses including carbon contents, but very different microstructures. During solidification of cast iron, the carbon
precipitates in the form of an interconnected continuous phase of graphite flakes intermixed with the iron matrix. The weak
graphite phase provides a continuous path for crack propagation and is responsible for the brittle nature of this alloy. While
detrimental to mechanical strength and ductility, the flakes provide excellent vibration damping and thermal conductivity, which
are utilized in cast iron machine tool bases, dryer drums, engine blocks, and similar applications. During solidification of ductile
iron, graphite precipitates as discrete spheroids and does not form a continuous phase. The mechanical properties of ductile iron
reflect those of the continuous iron matrix phase and have yield and tensile strength similar to mild steel. However, ductility and
impact strength of mild steel are higher than those of ductile iron.
The small amount of sulfur that is normally present in cast iron plays a major role in graphite morphology, as it precipitates from
the molten iron during solidification. In the presence of sulfur, carbon precipitates from solution in the form of graphite flakes. By
the introduction of a small amount of magnesium into the molten iron, sulfur is effectively removed, and carbon precipitates as
graphite spheroids. Figure 1 shows the differences in the microstructures of these two different forms of iron.
(3)
If less than an appropriate amount of magnesium (or magnesium and cerium) is introduced into the iron, the ASM Metals
5
Handbook indicates that graphite shapes intermediate between a true nodular form and a flake form are possible and yield
6
inferior properties compared to those of a typical ductile-iron structure. The ASM Specialty Handbook on Cast Irons states, “It is
common to attempt to produce greater than 90% of the graphite in this form (> 90% nodularity), although structures between 80
and 100% nodularity are sometimes acceptable.”
During the long history of iron pipe, numerous iron ore deposits all over the world were used to make pig iron that went into pipe
making. Each iron ore deposit has its own unique chemistry. In the early 1900s, only five elements were routinely analyzed in
iron: carbon, silicon, manganese, sulfur, and phosphorus. With the many sources of iron ore and only basic chemical analysis, it
would only be speculation as to what other elements and concentration were present in pig iron before the 1940s. Whereas in
the early days of ductile iron production, more pig iron was used, scrap iron usage now approaches 80%; trace quantities from the
7
scrap possibly affect corrosion properties for the better in some instances and for the worse in others. It has been reported that
chemical composition sometimes varies among pipe from the different pipe companies and even between different pours from the
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5
same company. As stated in the ASM Metals Handbook, “most of the specifications for standard grades of ductile iron are
based on properties; that is, strength and/or hardness is specified for each grade of ductile iron, and composition is either loosely
specified or made subordinate to mechanical properties.”
(4)
Today, even though AWWA and ASTM do not specify a particular chemistry for a particular grade of ductile iron, strict chemical
limits are used to achieve the desired mechanical properties. Industry representatives report that spectrographic analyses
routinely provide the concentrations of more than 15 elements from each ladle of iron used in pipe production. Also, care
normally is taken to prevent elements that might have undesirable effects on the strength of the pipe or quality of the potable
water being transported from being introduced into the iron.
4
ANSI/AWWA C151/A21.51 includes the minimum mechanical properties for ductile-iron pipe. The standard does not mention
chemical limits and processing parameters. ANSI/AWWA pipe standards rely on the improved mechanical properties, modern
manufacturing processes, and sound engineering design principles with significant factors of safety to determine the appropriate
wall thickness for different classes of ductile-iron pipe. As a result, ductile-iron pipe has been produced in thinner sections over
the years. For instance, while a 36 in (910 mm) cast-iron pipe designed to hold up to 150 psig (1 MPa), pressure would have
been 1.58 in (40.1 mm) thick in 1908. A 36 in (914 mm) ductile iron pipe today rated for 150 psig (1 MPag) is 0.38 in (9.7 mm)
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thick, with both types of pipe having varying thicknesses in spots as a result of manufacturing tolerances.
Significant differences exist between both the metallurgy (cast and ductile iron) as well as pipe production techniques from the era
of cast iron to today’s ductile iron.
(3)
(4)
ASM International, 9639 Kinsman Rd., Materials Park, OH 44073.
ASTM International, 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.
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Figure 1(a): Cast iron (polished sample).
Figure 1(b): Ductile iron (polished sample).
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Internal Corrosion
General
This state-of-the-art report primarily covers external corrosion of cast- and ductile-iron pipe. For those concerned with internal
corrosion, this section provides a brief overview of common corrosion problems and the solutions that are often applied.
Potable Water Systems
The first cast-iron water mains were not lined, but they were installed, following cleaning, in the same condition in which they
came from the molds. After many years, it became evident that certain types of water might affect the interior of the pipe. The
use of bituminous coatings was proposed, and most of the cast iron sold for waterworks service after about 1860 was provided
with a hot-dip bituminous lining and coating, usually made of molten tar pitch. In those systems in which water was relatively hard
and slightly alkaline, bituminous linings were generally considered satisfactory. When soft or acidic waters were encountered,
however, problems such as the water being red or rusty and a gradual reduction of the flow rate through the pipe frequently
occurred. Aggressive water penetrated pinholes in the tar coating, resulting in corrosion and tuberculation. The need for a better
pipe lining to combat tuberculation led to experiments and research with cement mortar as a lining material. In 1922, the first
8
cement-lined cast-iron pipe was installed in the water distribution system of Charleston, South Carolina.
Cementitious linings prevent tuberculation by creating a high pH at the pipe wall and by providing a physical barrier to the water.
The protective properties of cement linings are the result of two properties of cement. The first is the chemically alkaline reaction
of the cement, and the second is the gradual reduction in the amount of water in contact with the iron. When a cement-lined pipe
is filled with water, water permeates the pores of the lining, thus freeing a considerable amount of calcium hydroxide. The
calcium hydroxide reacts with the calcium bicarbonate in the water to precipitate calcium carbonate, which tends to clog the pores
of the mortar and prevent further passage of water. The first water in contact with iron through the lining dissolves some of the
iron, but free lime tends to precipitate the iron as iron hydroxide, which also closes the pores of the cement. Sulfates are also
precipitated as calcium sulfate. Through these reactions, the lining provides a physical as well as a chemical barrier to the
9
corrosive water.
10
(5)
Cement mortar linings are covered in ANSI/AWWA C 104/A 21.4. They have been tested and certified to comply with NSF
11
61. From 1953 to 1995, ANSI/AWWA C 104/A 21.4 stated that unless otherwise specified, the cement mortar lining is given a
seal coat of asphaltic material. This thin asphaltic paint coating, applied to the freshly placed cement-mortar lining, would greatly
minimize moisture loss during hydration, thereby resulting in controlled cure of the mortar. The seal coat also provided a
secondary benefit in that, as a barrier coating, it helped slow the leaching of the cement by soft, aggressive waters. The 1995
edition of the standard was revised so that the manufacturer had the option of providing the cement-mortar lining with or without a
seal coat unless otherwise specified. One of the primary reasons for the change was to minimize the use of seal coat and
thereby help reduce air pollution resulting from volatile organic compounds (VOCs).
Ductile-iron pipe installed in water systems today is normally furnished with a cement-mortar lining, unless otherwise specified by
the purchaser. Epoxy and polyurethane have also been utilized as lining materials for aggressive waters, seawater, and highvelocity service. For existing unlined cast-iron pipe, on-site cleaning and lining to restore hydraulic capacity is often economically
feasible. Also, additives such as phosphate and silicate are used to prevent red water in old unlined cast-iron mains.
In addition to potable water, cement-mortar linings have had a very good history in salt water service.
cement mortar is sometimes used for seawater service.
8
Type V sulfate-resistant
Wastewater Piping
Hydrogen sulfide (H2S) gas poses a problem in gravity sewers and at high points in force mains if the pipe has an air space.
Because H2S is extremely hazardous to personnel, the designer typically provides adequate slope and maintains a velocity of at
least 0.61 m/s (2.0 ft/s) in the piping system, which helps prevent the waste stream from becoming anaerobic and generating H2S
(i.e., becoming septic). pH values approaching zero have been observed in septic wastewater lines. In instances in which H2S is
a problem, special linings such as novolac ceramic-filled epoxy, coal tar epoxy, epoxy, polyurethane, fusion-bonded polyethylene,
calcium aluminate cement mortar, and glass have been used. Chemical treatment of the waste stream is sometimes an effective
means for controlling H2S-related corrosion. Care is generally taken in the selection of the chemicals used so as not to damage
the pipe, linings, or rubber gaskets.
(5)
NSF International (NSF), 789 N. Dixboro Rd., Ann Arbor, MI 48113-0140.
5
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External Corrosion
Graphitic Corrosion
A form of corrosion unique to cast- and ductile-iron pipe is referred to as “graphitic corrosion,” which is technically correct, but is
commonly referred to as “graphitization.” In this report, the term “graphitization” is sometimes used when quoting reference
materials, but “graphitic corrosion” is actually meant; in the water industry, the terms are sometimes used interchangeably, even
though they actually refer to dramatically different forms of corrosion. In this report, the terms “graphitization” and “graphitic
12
corrosion” are used in place of each other and are intended to mean the same thing. NACE/ASTM G193 contains standard
terminology and acronyms related to corrosion.
Graphitic corrosion is the selective dissolution of iron that leaves behind a graphite network. Many reports of graphitic corrosion
13-15
of cast-iron pipe concur in characterizing the attack as caused by galvanic action.
When soil conditions are corrosive and the
pipe is unprotected, graphitic corrosion is typically expected. Because the graphite content of cast iron is cathodic to the iron and
is distributed in the mass, there is selective attack on the iron. If the ferrous corrosion products do not leach out, the result is a
15
matrix consisting of graphite, silica, and oxides of iron. This residue is described by King, et. al as “a network of interlocking
graphite flakes and phosphide eutectoid products which bond corrosion products.” King, et. al also states that pipe walls
sometimes appear to be relatively noncorroded when exhumed, and they often have sufficient strength to carry water.
16
Gummow states, “When this occurs, the pipe wall appears to be sound, but the remaining uncorroded metal [is] extremely thin
and brittle [in some cases], and it [is possible for it to] fracture completely from excessive loads.” Gummow further reports the
failure of municipal authorities to recognize that corrosion was the primary cause of most cast-iron watermain breaks and is at the
root of the failure of ductile-iron piping. He states, “…[I]t is understandable that the corrosion was not recognized [because] with
16
cast iron, the corrosion pattern is well camouflaged.”
Various studies describe corrosion products of ductile iron as being the result of graphitic corrosion, while others state that
graphitic corrosion is specific to cast iron. The nodules of ductile iron do not have the interlocking capabilities to form a network
17-20
like the flakes found in cast iron.
In a selective leaching process, a more active component of an alloy is galvanically corroded
away, leaving the more noble material behind. In the case of cast iron, the more noble, interconnected-continuous phase of
graphite flakes is left behind by the graphitic corrosion; the structure is likely to be porous if the iron corrosion products dissolve
away or rust plugs the pores. In the case of ductile iron, the graphite precipitates as discrete spheroids, and the iron matrix forms
the continuous phase. Thus, the continuous phase in ductile-iron corrosion mass is rust with embedded nodules of graphite; if
these iron corrosion products dissolve away, the graphite nodules do not hold together. In addition, an analysis of corrosion
21
products published by Smith showed that while ductile iron and cast iron corrosion products are similar, ductile-iron corrosion
products contain only about 5% of the iron phosphide and about 75% more silica than is found in cast-iron corrosion products, as
well as other minor composition variations. The corrosion products of ductile iron typically do not have the strength of cast iron
7
graphitic corrosion and tend to be in the form of plugs that are possibly still able to prevent leaks to some lesser degree.
22,23
Woodcock
has expressed that difference in metallurgy of ductile irons possibly explains instances of graphitic corrosion and
varying corrosion behaviors.
It is generally accepted that when corrosion of either cast- or ductile-iron pipe occurs, the graphite present remains as an integral
part of the corrosion byproducts that adhere firmly to the metal substrate. General agreement has not been reached on the
integrity of the behavior of the corrosion product layer formed. Some believe that these byproducts provide a barrier against
further corrosion attack, which, if left undisturbed, slow or even stop the corrosion process in many soil environments. Although
the graphite corrosion products are weaker than the original iron structure, they have provided sufficient strength in many
instances to maintain liquid tightness in the absence of elevated internal or external pressures such as caused by water surges,
mechanical loads, and/or freeze/thaw earth movements.
18
For cast iron, LaQue states, “The firmness of the attachment and compactness or permeability of the graphitic residue are
influenced by the strengthening effect of other insoluble constituents of the iron, such as carbides, siliceous compounds, and
phosphide eutectic stringers or insoluble corrosion products that [are] precipitated within the graphitic corrosion product layer.
The graphitic layer with its intermixed insoluble corrosion products, etc., [sometimes] become[s] so impermeable to the further
penetration of corrosive liquids that it [. . .] form[s] an excellent protective coating that [. . .] stifle[s] further attack.” When
24
comparing cast iron to steel, LaQue reported, “The volume of graphite in cast iron is greater and is more likely to remain in place
as a protective residue after the iron associated with it has been removed by corrosion [ . . .] In addition to their protective value,
the graphitic corrosion products that form on cast iron also have appreciable mechanical strength reinforced by the insoluble iron
and silicon compounds, phosphide networks, and so forth that combine with the carbon to make up the graphitic residue. The
development of graphite residues that [are possibly] protective occurs in ductile (spheroidal graphite) irons as it does with ordinary
(flake graphite) cast irons.”
19
Denison and Romanoff tested sections of cast-iron pipe in soils of varying corrosiveness for periods up to 11 years at pressures
up to 3.4 MPa (500 psi) and concluded, “[. . .] most of the test specimens withstood a maximum pressure of 3.4 MPa (500 psi
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[34.5 bar]). Removal of the corrosion products revealed numerous holes of various diameters [. . .] Hence, it is reasonable to
conclude that cast-iron pipe in an advanced stage of graphitic corrosion is able to withstand the minimum pressure [. . .] of
Pressure Class 150 psi (1.0 MPa) pipe.”
(6)
In another test made in cooperation with the Cast Iron Pipe Research Association (CIPRA), pipe sections closed at both ends
21
and fitted with means of applying hydraulic pressure were buried. At two-year intervals or until the pipe ruptured, 2.8 MPa (400
psi) pressure was applied. At the time of the report (1954), no section had failed after 24 years, even though some were buried in
extremely corrosive soils.
25
Sears reported on 152 mm (6.0 in) cast-iron and ductile-iron pipes that were placed in a severely corrosive environment to
develop complete penetration of the pipe wall. They were then hydrostatically tested to evaluate the strength of the corrosion
products. The average bursting pressure of the ductile-iron specimens was 1.97 MPa (286 psi), compared to an average of 1.28
MPa (185 psi) for the cast-iron samples. Also, a comparison of the chemical analyses of the corrosion products was performed.
Sears concluded, “The corrosion products of ductile-iron pipe are similar in nature to those of cast-iron pipe and have strength
and adherence equal to or somewhat better than those of cast-iron pipe.”
(7)
The National Bureau of Standards (NBS), now the National Institute of Standards and Technology (NIST), began corrosion tests
of pipe in 1958 at six sites using 0.30 m (1.0 ft) long samples of 50 mm (2.0 in) pipe. In 1967, after 4 and 8 years of exposure, it
was reported that “the graphite corrosion products of ductile-iron specimens have the same general characteristics and adhesive
19
26
properties as those of cast iron.” In 1976, Gerhold reported that data for 14 years of exposure reaffirmed the conclusion given
in 1967 by Denison and Romanoff.
Dissimilar Metal Corrosion Cells
Buried cast- or ductile-iron pipe electrically connected either intentionally or unintentionally to metals to which it is anodic, such as
copper service mains in water systems, sometimes suffer attack as a function of the following factors:
1.
Potential differences of the two metals;
2.
Relative areas exposed to the environment;
3.
Environmental resistivity;
4.
Corrosion product characteristics;
5.
Aeration; and
6.
Temperatures.
27
Gummow, describing corrosion of municipal water mains, states, “Copper piping is used universally for customer services. This
mixed metal system accelerates corrosion of the iron piping which participates as the anode of a galvanic corrosion cell in which
the copper acts as the cathode.” The size ratio between the anode (iron pipe) and cathode (copper) [is generally] considered in
the anode/cathode relationship. The larger the anode (iron pipe) in relation to the cathode (copper) results in a lesser effect on
the bi-metallic connection. Also, in industrial plants or similar facilities, copper grounding systems connected to metallic pipes can
cause accelerated corrosion.
Iron pipe connected to metals that are anodic to the pipe, such as some types of steel bolts, causes premature failure of the
28
anodic materials in some situations. To avoid this situation, fasteners are generally used as specified in ANSI/AWWA C 111.
Corrosion problems caused by dissimilar metal cells are common in underground construction, and iron pipe is no exception.
When dissimilar metal cells are discovered, a common solution is to electrically isolate the metals from each other. When this
method is impractical, galvanic anodes are frequently used to bring the cathodic metal closer to the potential of the anodic
29
member of the couple. Other options include coating or wrapping the more noble material (the one that is not corroding) or
using polyethylene encasement to isolate the affected area from the soil.
(6)
Cast Iron Pipe Research Association (CIPRA), predecessor to the Ductile Iron Pipe Research Association (DIPRA), 245 Riverchase
Parkway East, Suite O, Birmingham, AL 35244.
(7)
National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070.
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An example of unintentionally causing a galvanic corrosion problem is the use of bare copper to electrically bond joints of iron
piping. Bare copper bonding straps across joints in a ductile-iron water main system (installed in anticipation of an induction
30
heating system against freezing) caused 23 leaks in a 3.60 km (2.24 mi) water main installation in Bayside, Wisconsin. Leaks
began to occur close to the bonds six years after installation, and the system was never activated. Investigation showed that all
leaks resulted from galvanic action between the copper bonds and the pipe. The use of insulated (coated) copper bonds in these
types of applications would have helped resolve this problem.
Nonhomogeneous Environments
Differences in the texture and content of backfill in contact with buried pipe potentially contribute to corrosion. Price states, “[The]
corrosive action of soils conducive to graphitic corrosion of cast iron is sometimes delayed [. . .] by surrounding the pipe with a
blanket of river sand to isolate the metal from direct contact with the corrosive soil. [. . .] [The] sand [. . .] tends to filter out solid
14
particles and to equalize concentrations of solutions of soil electrolytes.”
31
British studies show that it takes as long as 15 years for complete settling of soil backfill. Because backfill is less consolidated
than undisturbed soils outside the trenches, the trenches sometimes fill with water or retain water longer than adjacent
undisturbed soil. Wet soil is more corrosive than dry soil, all other factors being equal.
32
Fitzgerald noted that differential aeration attack causes corrosion along the bottom of iron pipe. When the pipe rests on native
soil, a differential oxygen cell is created in some cases because of the native soil containing less oxygen than the backfill placed
around and above the pipe.
13
Evans reported that “clods” in the backfill determine the location of corroded patches because of oxygen concentration cells.
According to Evans, they make “intimate contact with the pipe, excluding the air there-from, so that the pipe suffers anodic attack.
The voids between the clods ensure a plentiful supply of oxygen, and the moistened metal becomes cathodic.”
Changes in environmental conditions over time potentially change the corrosiveness of the environment. In some buried or
submerged conditions, leaks at joints or from corrosion penetration(s) allow waste water or other transported corrosive liquids to
collect. Additionally, the influence of salt contamination from salting roads and the resulting increased corrosiveness is
33
summarized by Gummow.
Microbiological Activity
Both micro and macroorganisms contribute to the corrosion of buried metal pipes. Bacteria often identified in connection with
microbial processes include Desulfovibrio desulfuricans, Ferrobacillus ferroxidans, Gallionella, Sphaerotilus natans, and
Pseudomonas. Microbes of various species and numerous fungi and algae are also frequently involved. The effects of biological
activity include the development of oxygen concentration cells under filamentous or single-cell mats and reductions in pH.
13
Aerobes and anaerobes are often found in symbiotic relationships that contribute to these effects. Evans described biological
attack as resulting from the anaerobes’ ability to “render the oxygen present in sulfates, nitrates, and carbonates available for the
acceleration” of the cathodic reaction. This means that corrosion proceeds even in the absence of dissolved oxygen. According
to Evans, conditions for anaerobic attack are:
1.
Absence of oxygen;
2.
Presence of assimilable organic compounds and physiological elements needed for growth; and
3.
Large amounts of sulfates, nitrates, or carbonates.
Electrical, chemical, and microbiological analyses assist with, but are not conclusive in predicting anaerobic attack. One study
has indicated that polyethylene encasement is helpful in reducing biological damage, but the author (Harris) states that additional
34
testing is generally conducted.
Experience with steel pipe has indicated that disbonded coatings allows or promotes
microbiologically influenced corrosion (MIC) if it creates an anaerobic environment with an adequate food source. Polyethylene
encasement that is not intended to be a bonded coating can be supportive of an anaerobic environment.
13
According to Evans, iron sulfates are reduced to sulfides, and “if subsequently the conditions become aerobic, the iron sulfide is
oxidized to ferric sulfate, which acts as an oxygen carrier.” He also cited research showing that the corrosion rate of iron under
13
biologically active anaerobic conditions is as much as 19.5 times greater than that under anaerobic sterile conditions.
15
King, et. al conducted tests on the resistance of ductile- and cast-iron test specimens in aqueous and soil environments to
anaerobic bacterial attack. The tests were conducted under specialized laboratory conditions of sustained high levels of sulfide
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and microbial activity. Tests were conducted on sandblasted test specimens with the shopcoat and annealing oxide layer
removed, specimens with only the shopcoat removed, and specimens with the shopcoat and annealing oxide layer intact (the
15
latter being representative of as-received pipe). Regarding the sandblasted specimens, King, et. al concluded that “both ductileand cast-iron pipe suffer extensive corrosion by sulfate reducing bacteria. The metals corrode at similarly high rates.” King, et. al
attributed the corrosion to the presence of galvanic cells between cathodic adherent sulfide-rich deposits and anodic substrate
metal. He and his associates concluded, with respect to ductile iron, that “corrosion performance of this new, mechanically
superior material [had] not been as good as expected.” King, et. al further reported that the unblasted test specimens with the
shopcoat and annealing oxide layer intact had very low rates of corrosion. He confirmed “the slow degradation of the bitumen
coating” and summarized that signs of distress (deterioration) of the bitumen coating were evident at the end of the test period
(250 days). King, et. al observed that the quality of the bitumen and oxide layer appear to contribute to delaying the onset of
microbiological corrosion. The thickness of the annealing layer seemed to influence the corrosion resistance of the iron pipe, with
cast-iron oxide layer generally two and up to three times that of the ductile iron. Microbial corrosion rates were compared for cast
15
and ductile iron by King, et. al. The data resulted in the following conclusions:
1.
Corrosion rates for bare metal (annealing oxide and shopcoat removed by sandblasting) of both ductile and cast iron
types in soils inoculated with bacteria were approximately 1,240 to 1,500 m/y (49 to 59 mpy), in soils were more than two
times greater than those in aqueous environments;
2.
Bituminous coatings delayed onset of attack;
3.
Oxide layers influenced attack rates more on cast iron than on ductile iron because the layer on cast iron was thicker;
4.
Ductile iron was slightly more resistant in aqueous media but was attacked more in soils;
5.
Corrosion was dominated by diffusion processes;
6.
Sulfate bacteria attacked both types of iron;
7.
Local cells developed between cathodic sulfide deposits and anodic substrate metal;
8.
Both corroded at similar rates;
9.
General attack predominated in later attack stages (250 days); and
10. Specimens with the shopcoat and annealing oxide layer intact showed a delay before active corrosion began, but once
corrosion was initiated corrosion rates rose rapidly to 50 to 90% of the bright metal corrosion rate.
17,35
Suspected MIC failures on polyethylene-encased wastewater lines have been reported.
This raises concern as to whether
there is an increased risk of MIC when sewage (a food source) is trapped inside the polyethylene encasement, either from
previous corrosion wall penetrations or leaks at joints. In an attempt to minimize MIC concerns, a polyethylene encasement with
36
anti-MIC additives was developed to try to minimize possible MIC problems. These anti-MIC polyethylene encasement materials
37
have been installed on various projects. Additional independent testing and long-term evaluations still remain to be completed to
35
confirm the influence of MIC under polyethylene encasement on both water and wastewater lines. Szeliga and Simpson state
that polyethylene encasement typically is not used for sewer mains where corrosion penetrations in the piping can result in the
retention of raw sewage between the polyethylene encasement and the pipe.
Stray Current
Stray currents pertaining to underground pipelines are currents flowing through the earth from a source not related to the pipeline
being affected. When these stray direct currents are discharged from a metallic pipeline or structure, they cause accelerated
electrolytic corrosion of the metal or alloy. Sources of stray current include cathodic protection (CP) systems; direct current (DC)
powered trains or streetcars, arc-welding equipment, and DC or alternating current (AC) electric transmission systems.
Factors that influence the probability of stray current include orientation and distance from the stray current source, magnitude of
the current, soil resistivity, and electrical continuity of the pipeline (welded, bonded, unbonded). When stray current is
encountered, however, three main techniques have been used to control stray current corrosion on underground pipelines. One
technique involves insulating or shielding the pipeline from the stray current source. Because of their high dielectric properties,
polyethylene encasement as well as bonded coatings are often used to shield the pipeline from stray currents. Although coatings
and polyethylene encasement reduce stray current pickup, they sometimes do not eliminate the problem. Accelerated corrosion
rates occur at holidays or damaged areas in the coating or polyethylene encasement at locations of current discharge. A second
technique is draining the collected current by means of either electrically bonding the pipeline to the negative side of the stray
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38
current source or installing grounding cell(s). This allows the current flow to be collected and mitigated. A third stray current
control technique that has been successfully used is the application of CP to offset the corrosive effects caused by stray current.
The approach and specific measures used to mitigate stray current corrosion are typically based on site-specific conditions and
determined by personnel experienced in this area.
Ductile-iron pipe is manufactured with a rubber gasket jointing system. Although several types of joints are available for ductileiron pipe, the push-on joint and the mechanical joint are the most prevalent. Rubber gasket joints exhibit electrical resistance that
varies from a fraction of an ohm to several ohms, yet is of sufficient magnitude for ductile-iron pipelines to be considered
39
electrically discontinuous. Because the joints are electrically discontinuous, resulting in increased longitudinal resistance, the
pipeline has a greater resistance to the flow of stray current. The electrical resistance characteristics of the pipe system have an
39
impact on the extent of stray current corrosion damage that occurs. Corrosion can range from virtually nonexistent to severe,
depending on the magnitude and source of stray earth current, soil conductivity, pipeline electrical resistance, and other site39
specific factors.
In areas of stray current influences, electrically continuous pipelines can accumulate a greater magnitude of stray current flow
than an electrically discontinuous pipeline. On electrically discontinuous pipelines, it is more difficult to detect and mitigate
interference. As more and more service station tanks are cathodically protected and cities turn to DC-powered mass transit, the
ability to test for and mitigate stray current becomes increasingly critical. The bonding of pipe joints typically provides good
control of stray current corrosion by reducing or eliminating current discharges at pipe joints and by providing a return path to a
40
location in which the current is managed more effectively.
41
Szeliga and Silhan comment that installation of test facilities to existing piping in suspected stray current areas is often used so
that accurate test data can be collected and that the test facilities are especially used for existing piping that was not installed with
electrical bonding across pipe joints to assure electrical continuity. The authors further state that new piping in stray current areas
are normally installed with pipe joint bonding, test facilities, and electrical sectionalization in selected locations to minimize stray
current pickup and discharge as well as to facilitate accurate monitoring of stray current activity and allow for flexibility in
responding to changes in stray current activity.
One report on an unbonded sewer main installed close to the groundbed of an impressed current CP system tells of substantial
42
damage from interference. It was concluded that the sewer system’s anticipated service life of 20 years was reduced to 8 to 12
years. The two million dollar wastewater pipeline system picked up current from the groundbed at one end and discharged it at
the other end where an uninsulated coated steel gas line was located. The current “jumped around the joints.” Leaks stopped
when the groundbed was moved, but more leaks were expected from the previous stray current damage.
Induced AC plays a role in the corrosion process and sometimes causes a dangerous electrical shock hazard on pipes paralleling
43,44
or crossing AC power lines.
If ductile iron lines are bare and not electrically continuous, the chance of problems from steady
state AC interference is minimized compared to a coated pipeline. If the ductile iron line is coated with either polyethylene
encasement or bonded coatings and electrically continuous, additional AC interference mitigation is sometimes necessary to
reduce higher voltages. The amount and type of AC mitigation depends on site-specific conditions.
Evaluation of Corrosiveness
There are no universally agreed-upon factors or methodologies for determining soil corrosiveness. Several methods are
described as part of this report. In situ testing and the number of soil samples that are normally procured and tested depend on
many factors such as geology, topography, and subsurface conditions. The following list identifies many of the most frequently
mentioned factors for iron pipe corrosion:
1.
Alignment Corrosiveness Factors
(a) Resistivity/conductivity;
(b) pH and alkalinity;
(c) Soil type and gradation;
(d) Microbiological activity;
(e) Moisture;
(f)
Nonhomogeneous environments;
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(g) Changing groundwater conditions;
(h) Dissolved salts (chlorides, sulfates, etc.);
2.
(i)
Cinders and carbon deposits; and
(j)
Chemical contaminants.
Design and Construction Factors
(a) Dissimilar metal corrosion cells;
(b) Stray current;
(c) Soil contamination from external factors;
(d) Damage to pipe encasement or coating during installation;
(e) Improper installation and maintenance of CP systems;
(f)
Bedding and backfill material;
(g) Restrained joints; and
(h) Joint integrity.
There is disagreement about the exact resistivity levels at which to differentiate among corrosive soils; however, low-resistivity soil
45
is generally accepted as a major factor in the corrosion of iron pipe. Although there are widely used methods that address only
low resistivity, it is not the sole criterion by which a decision to provide corrosion protection has been made. Also, any expected
future soil contamination such as the introduction of deicing salts is generally taken into consideration.
Rough indications of soil corrosiveness versus resistivity are listed by A.W. Peabody.
factors such as depth and temperature sometimes influence the corrosiveness.
46
Additionally, Peabody notes that other
47
In a report by Romanoff on tests made under the auspices of NBS (now NIST) on the corrosion of cast-iron pipe after burial for
intervals up to 30 years, the relationship between soil resistivity and the corrosion of ferrous metals is discussed. In their analysis
of corrosion rates on water distribution iron piping, some authorities report that soil resistivity is an important factor along with pipe
48-50
.
type and wall thickness and the presence of copper services.
They found that soil resistivity below 2,000 Ω cm is the most
51
corrosive to iron pipe. An article by Szeliga and Simpson, “Evaluating Ductile Iron Pipe Corrosion,” relates the authors’
experiences, evaluation of soil resistivity, and its correlation to the time period when ductile iron corrosion failures have been
.
observed and found that soil resistivity below 5,000 Ω cm can be very corrosive to ductile iron pipe.
Although there is no universally accepted corrosion risk assessment methodology for iron pipe, there are a number of different
procedures that have been utilized for evaluating the corrosive conditions and their influence on the corrosiveness for pipelines in
order to evaluate corrosion control methods. Rather than assessing the corrosiveness of a soil based solely on its resistivity,
others have devised methodologies for rating the soil’s overall corrosiveness. These include the soil evaluation system for ductile
52
iron pipe (ductile iron 10 point system), as included in Appendix A of the ANSI/AWWA Standard C105/A21.5. This procedure
uses soil analysis and evaluation of environments to identify those that are potentially corrosive to iron pipe. It was originally
developed by CIPRA in 1964. The evaluation is based on measurements drawn from five soil tests and observations: soil
resistivity, pH, redox potential, sulfides, and moisture. For a given sample, each parameter is evaluated and assigned points
according to its contribution to corrosiveness. The points for all five soil characteristics are totaled. If the sum is 10 or more, the
soil is considered corrosive to ductile-iron pipe and corrosion is likely to occur unless protective measures are taken. This 10
point procedure also states that a description of the soil, possibility of stray DC, and experience with existing installations are
normally utilized as part of the evaluation process of whether polyethylene encasement is necessary or not. In uniquely severe
environments, additional corrosion control options other than just polyethylene encasement are considered if specific
53
characteristics are present. Bonds, et. al summarized the effectiveness of the 10 point system as an accurate and dependable
49
35,50-51,54
method in evaluating soils for their corrosiveness to iron pipe. However, Wakelin and Gummow and Szeliga, et. al
have
reported on their evaluations of the ineffectiveness of the 10 point system in predicting corrosion activity on ductile iron piping.
Szeliga, in his analyses of data from operating mains, reported that the 10 point system did not correlate with the actual rate of
35,54
corrosion on ductile iron mains.
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Kroon, et. al utilized the10 point soil evaluation system as a basis to develop a model. This risked-based model was the result of
a three-year study undertaken in conjunction with DIPRA to evaluate corrosion and corrosion protection of ductile-iron pipe.
Included were field and laboratory evaluations of short-term and long-term cathodic polarization rates of ductile iron under varying
soil conditions; corrosion rate reduction and corresponding cathodic current densities; the performance of polyethylene
encasement in preventing corrosion of ductile-iron pipe; and the corrosion protection benefits of the traditional, standard asphaltic
coating applied to the typical annealing oxide formed during pipe manufacturing. The extensive field and laboratory test data were
analyzed in conjunction with test measurements from 1,379 physical inspections. The result of the study is a proprietary riskbased corrosion protection design strategy for buried ductile-iron piping.
The risk model considers both the likelihood and consequence of pipe failure as a result of external corrosion. This model then
determines the most cost-effective corrosion control option to achieve a pipeline service life of 75 to 100 years or more, including
pipe as manufactured with standard asphaltic coating and annealing oxide; polyethylene encasement; polyethylene encasement
with joint bonding, supplemented at times with corrosion monitoring; life extension cathodic currents with or without polyethylene
encasement; and CP. The information specific to this model is not available for third-party evaluation to determine its
effectiveness.
Another method that was developed in Australia, called the observation and resistivity, sulfide, and total acidity determination
56
(ORSTAD) chart, is also utilized. Ferguson and Nicholas, describing experiences with corrosion in Australia, proposed the
following soil categories and two major accelerators:
Soils:
1.
Acidity;
2.
Neutral or alkaline; and
3.
Anaerobic.
Accelerators:
1.
Stray current; and
2.
Galvanic coupling.
They concluded that (1) acidic corrosion implies reduction of hydrogen ions, (2) hydrogen evolution occurs at a much higher pH
for weak acids than for strong acids, and (3) total acidity is more important than the concentration of dissociated hydrogen. They
also reproduced the 10 point soil evaluation system and used it to develop a cumulative score from five categories of tests to
indicate whether or not a soil is corrosive and pipes are to be protected. Normally, the need for polyethylene encasement is the
only supplemental corrosion control method considered under the 10 point system and the ORSTAD evaluation results.
Others have expanded these two corrosiveness evaluation procedure results (ORSTAD and 10 point system) to include
additional corrosion control methods and use the anticipated level of corrosiveness to determine whether as-manufactured,
corrosion monitoring (joint bonds and test stations), polyethylene encasement with or without CP, or tight-bonded coatings with
CP are justified. Some do not allow use of polyethylene encasement as the only corrosion control method in all cases and
23,32,37,44,57-59
typically use tight-bonded coatings in their most corrosive areas.
A large water and wastewater utility in the U.S.
60
employs the point values such as those presented by Dillon in his book Corrosion Control in the Chemical Process Industries,
61
along with a decision tree that evaluates whether there is water in the borehole and the size of the pipeline. This water and
wastewater utility uses a decision tree that not only uses polyethylene encasement as a corrosion control method, but also uses
tight-bonded coatings and CP based on their evaluation of the anticipated level of risk and size and function of the pipeline being
considered.
Another corrosion risk assessment method that has been proposed is called the ductile iron 25 point risk assessment analysis,
(8)
which modified and expanded the Washington Suburban Sanitary Commission (WSSC) risk assessment method and decision
37
tree to include additional factors. This 25 point risk assessment procedure was summarized in the July 2002 issue of MP by
62
Spickelmire and incorporated soil corrosiveness factors from the Dillon assessment method along with factors from the 10 point
procedure. In addition, this risk-assessment procedure included other additional soil corrosiveness factors as well as additional
pipe design/function factors along with difficulty in leak repairs and possibility of interference.
(8)
Washington Suburban Sanitation Committee (WSCC), 14501 Sweitzer Ln., Laurel, MD 20707.
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The 25 point process evaluates not only risk of failure, but also the consequences of failure and it allows various corrosion control
possibilities to be evaluated and selected based on the perceived degree of risk. Available corrosion control methods vary from
the standard manufactured ductile-iron pipe with standard asphaltic coating (as-manufactured), to polyethylene encasement
alone or with CP, to use of tight-bonded coatings with CP. Because the different levels of corrosion control methods do not cost
the same amount or provide equal levels of corrosion protection, selection is therefore based on specific project requirements and
the 25 point risk assessment evaluations or soil corrosiveness zone. For smaller distribution-type piping, the levels of corrosion
control methods are one or two levels less conservative than for ductile iron transmission-type pipelines.
A document published in July 2004 by a federal agency dealing with water projects in the western U.S. provides guidelines for an
overall corrosion prevention strategy, and corrosion control methods are based, in part, on a 10% probability of encountering soils
63-64
with a given in situ resistivity.
In this document, soils with resistivity values below certain levels generally use more stringent
corrosion protection methods; higher resistivity soils normally use less stringent levels of corrosion control. For ductile iron, a
bonded dielectric coating, corrosion monitoring, and CP is specified in that document for soil resistivity evaluations that yield a
.
.
10% probability below 2,000 Ω cm. The minimum corrosion control for soil resistivity between 2,000 and 3,000 Ω cm is typically
an unbonded wrap (polyethylene encasement) for ductile iron with corrosion monitoring and CP. For soil resistivity above 3,000
.
63
Ω cm, the minimum corrosion control often used is polyethylene encasement with corrosion monitoring for ductile-iron pipe. The
63
publication also advises the engineer to consider known corrosion performance with the same or similar type installations in
64
nearby or similar soils, other test data, and pertinent factors in addition to the 10% probability soil resistivity number.
Relative Corrosion Rates for Iron Pipe
Corrosion of iron pipe is typically in localized patches or pits, and its progress is a fairly complicated issue. The literature
generally considers that the corrosion rate varies with time. When corrosion takes place, it is also common to see an increasing
23,49,65-67
68
numbers of perforations per time interval the longer a pipe is in the ground.
Rossum has developed a theoretical model
that provides equations and factors for estimating time to the first leak and the number of leaks in a given period of time, within
limitations.
Corrosion kinetics are known to be nonlinear with an incubation period before corrosion starts. However, most corrosion rates are
reported as linear (constant rate over time) because of the wide range of conditions encountered that can change with time and
are not comparable or definable. For these reasons and to simplify comparisons and to be more conservative, a linear straight
23,53
line corrosion rate is typically used in the absence of more comprehensive data.
Typically, all factors presented below or in other reports are considered. Attempting to predict pipe service life for any pipeline
based on the literature without knowing all the facts relative to the reported corrosion rate(s) can lead to an incorrect analysis.
49
69
70
Studies published on corrosion rates of cast and ductile-iron pipe include Gummow, Jakobs and Hewes, Bonds, et. al,
71
17
50,54
72
73
74
65
26
Wakelin and Gummow, Spicklemire, Szeliga,
Horton, et. al, Schiff and McCollom, Bell, et. al, Romanoff, Gerhold,
75
23
(9)
Fuller, and the National Academies National Research Council (NRC).
52
In this section, for the terms “10 points” and “uniquely severe,” refer to Appendix A of ANSI/AWWA C105/A21.5.
As-Manufactured in Accordance with AWWA C 151
There have been a number of studies published on the corrosion rate of ductile-iron pipe and cast-iron pipe. Approaches and
65
conclusions have varied. Romanoff compared earlier NBS cast-iron studies to later studies of ductile-iron pipe and reported,
“[c]ast iron and ductile iron [sometimes] corrode at nearly the same rate in the same soil environment.” Regarding pitting rate,
39
75
Stroud reported a “distinct advantage of ductile iron over cast iron in test site environment[s] for a period of eight years.” Fuller
reported, “With both pipe materials, the rate at which local deeper corrosion attack penetrates the pipe wall decreases as the
exposure time increases. With cast pipe, the rate of decrease is relatively small, but with ductile pipe, the rate of decrease is
much greater, even though the initial attack is sometimes slightly faster.”
53,70
Bonds, et. al
compiled a database of DIPRA test site research programs and in-service inspections involving more than 2,000
70
specimens over a 75 year period. Information published was a subset of calculated linear corrosion rates for iron pipe in soils of
differing corrosiveness. Regarding cast- vs. ductile- iron pipe, the authors in the Bonds study concluded that the mean maximum
pitting rate of ductile-iron pipe is typically less than for cast-iron pipe and, to an extent, is soil specific. However, in the interest of
conservatism, they considered the mean maximum pitting rates for both ductile- and cast-iron pipe to be the same. Bonds, et. al
state that based on their data that “overall results indicated that the corrosion pitting rates of ductile iron versus gray-iron pipe
were soil specific to an extent but were essentially the same statistically (t-tests, 95% confidence). For this reason, the ductile-
(9)
National Research Council (NRC), 500 5th St., NW, Washington, DC 20001.
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and gray-iron pipe data were combined to obtain the benefits on an increased sample size in subsequent analysis.” Based on
23
the NBS and Bonds, et. al data, the NRC committee also considered cast-iron and ductile-iron corrosion rates to be similar.
Nevertheless, without appropriate corrosion protection, ductile-iron pipe can experience through-wall penetration faster than castiron pipe because of the ductile iron pipe’s thinner wall.
53,70
To consider the frequency of pitting as well as the rate, incidences of nonpitting pipe samples in the Bonds, et. al
study were
averaged with incidences of actual pitting, providing mean maximum pitting rates in the report’s terminology. The reported mean
maximum pitting rate corresponds to approximately 0.0105 in/y (10.5 mpy) (267 µm/y) for as-manufactured (asphaltic shop
coated) iron pipe in soil conditions greater than or equal to 10 points (not uniquely severe). For as-manufactured (asphaltic shop
coated) iron pipe in soils under 10 points, the reported mean maximum pitting rate corresponds to approximately 0.0007 in/y (0.7
mpy) (18 µm/y).
23
66
70
In a presentation for an NRC committee report, Cowan performed analyses of the Bonds, et. al corrosion data on behalf of
70
DIPRA that evaluated corrosion rates considering that they tend to decrease over time. The Bonds, et. al paper involved a large
database that allowed for a statistical evaluation of mean maximum pitting rates. Cowan’s analyses of DIPRA’s data provided a
statistical evaluation of different conditions of ductile iron pipe (i.e., as-manufactured and polyethylene-encased).
23
53,70
66
67
54
The NRC report evaluated information from a number of sources, including the Bonds study,
Cowan, Woolley, Szeliga,
23
70
66
and others. The evaluation, in the NRC report applied a different type of analysis approach from the Bonds, et. al, Cowan,
67
and Woolley studies.
The NRC committee reviewing the Bonds, et. al data as part of their study believed that the first failures and the estimated life of a
pipeline is based on the corrosion behavior at the tail of the distribution, where the corrosion is the fastest (maximum observed
23
corrosion rate), and not by averages of averages (mean maximum corrosion rates). The NRC report states, “The committee
believes that is the extreme values (Data Types 1 and 2) that need to be need to be considered rather that the reported mean
maximum pitting rates (Data Type 4), because it will always be the point of most rapid corrosion on a length of pipe that will lead
to the first failure.” The NRC report includes statements about what the committee does and does not endorse in terms of various
methods to evaluate data.
Therefore, the NRC committee used an approach based on the linear maximum observed corrosion rate to determine when a
23
pipe first leaks. The NRC committee determined maximum observed pitting rate corresponds to approximately 34 mpy (0.86
mm/y) for as-manufactured (asphaltic shop coated) ductile-iron pipe in soil conditions greater than or equal to 10 points (not
uniquely severe).
54
Szeliga provides examples of maximum observed pitting rates based on his and others’ experiences. His paper contained inservice installations of as-manufactured (asphaltic shop coated) iron pipe corrosion. Pipe ages reported in this paper ranged from
five to 35 years. The reported maximum pitting rates ranged from 3.0 to 68 mpy (0.08 to 1.7 mm/y) for the as-manufactured iron
pipe examples.
Polyethylene-Encased Pipe
70
In their statistical analysis summary of 75 years of data, Bonds, et. al also reviewed cast- and ductile-iron pipe protected with
damaged and undamaged polyethylene encasement. A study included more than 300 polyethylene-encased cast- and ductileiron pipe and pipe specimens exposed for varying periods of times and excavated between 1952 and 2004. The corrosion rates
were reported as a combined mean deepest pitting rate for undamaged polyethylene-encased iron pipe buried in both uniquely
severe corrosive soils and not uniquely severe corrosive soils (above 10 points). The reported mean maximum pitting rate was
approximately 0.0005 in/y (0.5 mpy) (12.7 µm/y) for iron pipe (151 examples), with undamaged polyethylene encasement in soil
conditions greater than or equal to 10 points (not uniquely severe). For undamaged polyethylene encasement in uniquely severe
soil conditions, the reported mean maximum pitting rate was approximately 0.0068 in/y (6.8 mpy) (172.7 µm/y) for 85 iron pipe
examples.
70
The Bonds, et. al study reported mean maximum pitting rate for 62 iron pipe with damaged polyethylene encasement was
approximately 0.0112 in/y (11.2 mpy) (284 µm/y) for five different test site locations with soil resistivities ranging from 68 to 1,600
.
Ω cm conditions. The authors also report that their data did not indicate accelerated corrosion at areas of intentional damage to
the polyethylene encasement.
66
67
70
As previously noted, Cowan and Woolley conducted statistical analyses of the Bonds, et. al corrosion data, and their findings
23
are described in an NRC report.
Cowan took into account that corrosion rates tend to decrease over time. As part of his
evaluations, Cowan analyzed the corrosion found on 151 pipes from test site and in-service inspections involving iron pipe
installed in corrosive soils (not uniquely severe) with undamaged polyethylene encasement. Cowan’s statistical analysis of those
specimens resulted in a projected mean maximum pitting depths of less than 0.10 in (2.5 mm) in 100 years (less than 1 mpy
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[0.02 mm/y.] As summarized in the NRC study, of the 151 inspected pipe, Woolley noted that only 14 exhibited pitting corrosion
(9%); his analysis showed a 4.9 mpy (0.12 mm/y) mean maximum pitting rate for these 14 corroding samples only.
23
The NRC report, using Woolley’s information, concluded that the years to penetration reported for polyethylene-encased pipe in
70
the Bonds, et. al paper would be reduced by over an order of magnitude based on the approach of using the linear maximum
53,70
66
67
54
pitting rate. This and other similar information from the Bonds, et. al papers,
Cowan, Woolley, Szeliga, and others was
also shown in the NRC report as maximum observed pitting rates for both intact (undamaged) and damaged polyethyleneencased pipe examples. The NRC committee, having some data distribution information for the DIPRA research in a letter by
67
Woolley, found that the data for undamaged polyethylene-encased pipe in particular were bimodal (91% of the data exhibited
no corrosion, 9% exhibited corrosion). The NRC determined the linear maximum observed pitting rate corresponds to
approximately 8 mpy (0.20 mm/y) for iron pipe with undamaged polyethylene encasement in soil conditions greater than or equal
to 10 points (not uniquely severe). The NRC report also describes measured corrosion from the field for iron pipes protected in
23
various ways for differing exposure periods and various soil conditions.
54
Szeliga compiled a list of maximum observed pitting rates for 14 polyethylene-encased pipe examples based on his and others’
experiences. These included 12 in-service inspections and two examples of a pipe sample. The reported pitting rates ranged
35,51,54,76
from 3 to 68 mpy (0.08 to 1.7 mm/y) for the ductile-iron pipe examples with polyethylene encasement. Szeliga, et. al
reported that the rate of corrosion of ductile-iron piping under undamaged polyethylene encasement is similar to or greater than
the rate that occurs at tears or damage in the polyethylene encasement.
17
Spickelmire reported that the rate of corrosion of ductile-iron piping under undamaged polyethylene encasement is sometimes
37
the same as at tears or damage in the polyethylene encasement, but sometimes greater. Spickelmire further reported that on a
(10)
77
Denver Water Board
test site, several pipe samples indicated that corrosion was observed under undamaged polyethylene
encasement on the same pipe specimen at a location away from where the polyethylene encasement was deliberately damaged
for three of the intentionally damaged samples. For one pipe sample, measured corrosion of 43 mil (4.91 mpy) (0.1247 mm/y)
was observed at the intentionally damaged polyethylene location with actual deeper corrosion of 68.0 mil (7.77 mpy) (0.195
mm/y) observed at the undamaged polyethylene location on the opposite side of the pipe. This represented a difference of 150%
(68 mil [1,727 µm], compared to 43 mil [1,092 µm] in 8.75 years of burial).
External Corrosion Control Systems for Ductile-Iron Pipe
General
In the early days of cast iron, wall thickness used for pipe strength also provided a defense against corrosion. However, this
practice might not be economical or reliable because there is no assurance that corrosion attacks the pipe wall in a uniform
fashion.
Corrosion protection systems described herein for ductile-iron pipe in buried service often vary substantially and are dependent
on soil conditions, environmental factors, the designers’ or operators’ experience, professional judgment, desired service life, and
whether applied to new or existing pipe systems. For new piping systems, consideration of corrosion during the design and
construction phases of the project has greatly reduced corrosion problems. The use of polyethylene encasement, bonded
coatings, joint bonding, and the possible implementation of CP is most appropriately considered at the time of design. The
responsible owner or owner’s representative typically makes the final decision based on requirements and information relative to
the project.
For existing pipe systems, corrosion control options are limited. In many cases, the need for corrosion control manifests itself as
a high leak rate. For these situations, CP in the form of sacrificial anodes has been utilized by attaching the appropriately sized
anode to each segment of pipe located in a corrosion “hot spot” or to each pipe in a region of the pipeline where leak repairs are
frequent. The installation of the sacrificial anodes usually occurs when leaks are being repaired or as a preventive measure to
each pipe segment in a region or zone of concern. Impressed current CP has been effectively used to control corrosion-caused
leaks of an existing iron pipe system. For both new and existing iron pipe systems, a life-cycle cost analysis is helpful in making
corrosion control decisions.
Trench Bedding
78
79
AWWA C 150 and C 600 cite five types of trench bedding. Each type influences the corrosion potential depending on the type
of bedding selected and homogeneity. Select fill does not always negate corrosive soil conditions, because soil constituents
infiltrate the fill over time.
(10)
Denver Water Board, 1600 W. 12th Ave., Denver, CO 80204.
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Portland cement slurry controlled density fill/controlled low-strength mortar (CDF/CLSM) backfill has recently been promoted for
23,80
use in municipal areas.
Possible corrosion of as-manufactured ductile-iron pipe from constituents of the slurry fill or from
differential conditions caused by the slurry fill is typically considered. Special attention is often given to transition areas from the
CDF/CLSM to native soil environments.
Galvanic Considerations
Although boltless push-on joints are the prominent joint used with ductile iron pipe, mechanical joints utilizing T-bolts made of low28
alloy steel in accordance with AWWA C 111, which are close in galvanic potential with ductile-iron pipe, are used. Brass
corporation stops and copper tube service pipe are more cathodic than ductile-iron pipe. Additionally, copper services often
connect the pipe main to the electric grounding of the service customer. These connections are readily isolated using corporation
or meter fittings with integral dielectric insulation. This provides a design choice for corrosion control. The designer sometimes has
the galvanic effect of the large ductile-iron main protecting the thin-walled copper tube. If localized corrosion is problematic in a
particular soil, then the first few feet (meters) of the service are sometimes wrapped or coated to foster more uniform galvanic
effect on the large bare pipe section. Alternately, the designer occasionally isolates the ductile-iron main to allow the copper to
stand on its own, separately protects the copper service with galvanic anodes, or selects plastic service pipe. Galvanic corrosion
is sometimes less pronounced on as-manufactured pipe than on a coated pipe because of the increased anode/cathode surface
ratio.
Continuity
Push-on gasketed joints are not generally considered electrically continuous. Mechanical and restrained joints are incidentally
electrically continuous but the lengths are not typically of concern regarding long-line corrosion.
It is possible for joints of ductile-iron pipe to be electrically continuous when the joints are deflected to the maximum, resulting in
incidental metal-to-metal contact between the spigot end and the bell socket or on restrained pipe sections. This contact provides
for electrical continuity, but is typically not counted on to be sustained over a long period of time. As the pipe moves, the contact
“makes” and “breaks.” In addition, because of oxidation of the contact surfaces, shorted joints sometimes develop sufficient
38
resistance and become electrically discontinuous with regard to stray currents.
The practice of joint bonding as a standard precautionary measure for monitoring and possible corrosion mitigation is a matter of
value engineering and the preference of the pipeline owner. In environments in which as-manufactured ductile-iron pipe has
demonstrated satisfactory performance and where failures can be tolerated, joint bonding might be unwarranted. Others maintain
that electrical continuity is normally necessary to monitor corrosion activity, mitigate interference, or more easily accommodate CP
37,44,51,57,61,63,81
during construction or at some time in the future.
When electrical continuity is desired, joint bonds are used. Typical impressed current CP systems and some galvanic current CP
systems establish that positive electrical continuity through the use of appropriately sized insulated copper conductors. The
number and size of conductors across each joint vary, mainly depending on pipe size. A minimum of two conductors is typically
installed across each joint for redundancy. Cast-iron type exothermic charges are the most reliable and are typically used for
40
cast- and ductile-iron pipe. Steel-type exothermic charges on iron pipe have frequently been known to fail.
Joint bond
connections are generally coated and protected during pipe installation and before backfilling is performed. Methods to minimize
damage to internal dielectric linings from exothermic weld connections, such as use of steel weld plates on the spigot end and
direct exothermic connection to selected locations on the bell end, are typically considered.
It is much less costly to establish electrical continuity at the time of pipeline installation than to retrofit the pipeline. An electrically
continuous pipeline long enough to traverse areas of differing environments could be subject to long-line corrosion cells. This
type of corrosion cell is rarely an issue for unbonded piping. Long-line corrosion caused by joint bonding is minimal, and it is often
difficult to accurately locate the length and location of the corrosion cell. In areas in which there is such a concern, bonded pipe is
sometimes dielectrically isolated in select sections.
For existing ductile-iron pipe that was installed without joint bonds, electrical continuity has sometimes been established by
excavating each pipe joint and attaching bond wires. In some systems, there has been success with the use of vacuum
excavation techniques to minimize the extent and cost of the excavations. For larger-diameter pipe, joint bonding has sometimes
been accomplished internally.
The electrical continuity of a circuit (including the test stations, the pipeline, and the joint bonds) is normally verifiable. There are
82
methods of locating open joints on underground pipelines. Brass wedges have been used for continuity, but they have typically
been found to be unreliable because they sometimes become loose and fall out because of ground/pipe movements.
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Maintenance
Maintenance requirements for CP systems vary based on the level and type of corrosion protection selected.
As-Manufactured in Accordance with AWWA C 151
General
Ductile-iron pipe has directly replaced cast-iron pipe in the water and wastewater industry. The first installation of ductile-iron pipe
was circa 1955. The majority of buried pipe is supplied as-manufactured with approximately 1.0 mil thick (25 µm) standard
asphaltic coating and no supplemental corrosion protection. The asphaltic coating offers protection from superficial rusting during
transportation and storage. The coating is not intended for long-term protection in soils, for stray current protection, or for later
retrofit with CP.
55
Kroon, et. al documented the inherent corrosion resistance provided by the standard asphaltic coating and annealing oxide
included in the standard manufacture of ductile-iron pipe. Kroon, et. al estimated the annealing oxide had a specific coating
51
resistance of 1.4 to 1.5 times that of the theoretical resistance-to-ground value for bare pipe. Szeliga and Simpson reported
evaluations of failed ductile iron mains with the standard asphaltic coating, which provided no appreciable long-term protection
from external corrosion. Szeliga and Simpson also reported on corrosion beneath undamaged standard asphaltic coatings.
In relatively benign soil environments, as-manufactured ductile-iron pipes can provide suitable corrosion resistance for the desired
design life. In corrosive soils, ductile-iron pipe, because of thinner wall section, is more susceptible to pitting perforation than
cast-iron pipe. Additional corrosion measures are normally taken where soils are determined to be corrosive to ductile-iron pipe,
depending on the operational consequences of failure and cost/benefit of providing corrosion mitigation measures. The levels of
supplemental protection are normally based on local experiences with cast- and ductile-iron pipe, corrosiveness evaluations, and
risk assessment. Additional corrosion measures are also taken in stray-current environments or for critical facilities.
Coating/Encasement Systems for Ductile-Iron Pipe
General
A variety of external coatings and encasement barrier systems have been applied to help isolate iron pipe from a corrosive
environment. As technologies evolve, new and improved systems continue to become available. The intent of this section is to
provide a state-of-the-art report on the coating and encasement systems currently being utilized and an overview of some of the
types of coating and encasement systems that have been utilized for iron pipe in the past. NACE does not currently have a
standard for polyethylene encasement, although some international, AWWA, and NACE bonded coating standards may be
applicable for ductile-iron pipe, as summarized in Appendix A.
The earliest record of a protective coating being applied to iron pipe is around 1860, when it became general practice to dip pipe
83
in a bituminous molten tar to provide protection to both internal and external surfaces. In the 1940s, hot tar coatings began to be
replaced with sprayed asphaltic cutback coatings. Prior to the 1950s, coatings and linings in the cast-iron pipe industry were
84
primarily cement-mortar linings and bitumastic external coatings. Beginning in the 1950s, polymeric bonded coatings, such as
85
coal tar epoxy and extruded polyolefin systems, primarily developed for steel pipe, began to appear in the marketplace.
After polyethylene film became commercially available in 1950, testing of polyethylene-encased iron pipe exposed to various
86
types of soils was initiated.
The first commercial application of polyethylene-encased cast-iron pipe was in 1958 in a very
corrosive, swampy area in Lafourche Parish, Louisiana. Excavations of that pipeline in 1988, 1993, 1998, 2003, and 2008
revealed this polyethylene-encased pipe was still in excellent condition after more than 50 years of service in a severely corrosive
87-90
environment.
Three different approaches in the use of coatings/encasement for external corrosion control were summarized in a 2003 article in
91,92
the AWWA Journal on Ductile Iron Corrosion.
This article states that there are three general categories with markedly
different corrosion control coating/encasement approaches currently being utilized in the industry today. The first, represented
primarily by the ductile-iron pipe manufacturers and DIPRA, promotes the use of a passive protection system (polyethylene
encasement), and often advocates against the use of joint bonds, except in interference areas. The second is represented by the
traditional corrosion engineering approach, which is utilized in the regulated oil and gas industry (bonded coatings, CP, and joint
bonding). This approach often avoids polyethylene encasement, with or without CP. The third, represented more by the
Europeans and Japanese, utilizes a combination of zinc-rich coatings with “an additional synthetic polymer coating, such as coal
91,92
tar enamel and a polyethylene wrap (for extra protection).”
The AWWA article also reports that this last group uses tightbonded coatings and CP in some extreme situations.
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Polyethylene Encasement
In the U.S., from 1958 to present, the most common method of external corrosion protection utilized by the water and wastewater
industry for protecting cast- and ductile-iron pipe has been polyethylene encasement.
39,86-100
Polyethylene encasement is a common method of corrosion mitigation for cast- and ductile-iron pipe.
A pilot survey of 21
utilities conducted by the AWWA Engineering and Construction Division reported that 95% of those 21 utilities use polyethylene
101
encasement for corrosion protection. Polyethylene encasement involves enveloping or wrapping the pipe and appurtenances
with a tube or sheet of polyethylene at the job site. The polyethylene serves as an unbonded film to prevent direct contact
between the pipe and the surrounding soil. The electrolyte available to support corrosion is minimized. Because polyethylene
encasement is not a watertight system, some seepage of groundwater typically occurs beneath the wrap.
39,70,86-87,93
Various authors
state that the initial corrosion reactions can subside, possibly because of a depletion of the available
dissolved oxygen in the annular space. Intact and properly installed polyethylene film then provides an impermeable barrier that
restricts the access of additional oxygen to the pipe surface. The pressure of surrounding compacted backfill compresses the
polyethylene against the pipe, which reduces the exchange of groundwater between the wrap and the pipe. As a result, the
polyethylene is thought to provide an essentially uniform environment around the pipe, thereby reducing local galvanic cells
caused by variations in soil composition, pH, aeration, etc.
The mechanism of this protection method has been summarized as, “polyethylene encasement isolates the pipe from the soil and
replaces a corrosive, nonhomogenous medium—soil with a noncorrosive homogenous medium—passivated water [oxygen
86-87
deficient].”
DIPRA has reported that since 1958, over 100 million ft (30,000 km) of cast- and ductile-iron pipe have been
102
23
installed with polyethylene encasement with minimal reported problems.
A recent report by the NRC states that polyethylene
encasement is an improvement to bare or as-manufactured ductile iron pipe, but cites a number of cases that indicate that
performance can vary from the high success of that which is reported above.
76
Szeliga reported that corrosion can occur under intact polyethylene encasement and that “[t]he theory that areas between the
wrap and the pipe will be oxygen-free and therefore not conducive to corrosion activity appears to be flawed.” However, most
103
utilities do not track or report their main failures, so the actual number of failures is not known. Szeliga reported on a review of
technical papers published from 1987 through 2007 that indicated that hundreds of failures of polyethylene-encased pipe have
occurred.
52
Polyethylene encasement that adheres to AWWA Standard C 105 is a specially designed material with minimum mechanical
23,97,104-108
requirements such as strength, elongation, propagation tear resistance, impact resistance, and dielectric strength.
The
use of recycled polyethylene in the manufacture of the film is not a common practice. Some post-consumer waste (i.e., recycled
polyethylene) contains materials including biodegradable elements, binders, starches, and other components often resulting in
cloudiness, lumps, blisters, and cracking, all of which are capable of affecting film properties and causing deterioration with time.
52
To facilitate proper installation and long-term effectiveness, only those films meeting or exceeding the AWWA C 105 standard
are typically used by the ductile-iron pipe industry. Polyethylene encasement is normally sampled, inspected, and independently
tested to ensure compliance with all applicable standards. Polyethylene encasements usually can be visually inspected during
52,72
installation and any damage repaired. Installation procedures and materials provided typically also meet AWWA C 105.
The
52
polyethylene encasement is sometimes certified by the pipe and polyethylene manufacturer in accordance with AWWA C 105.
23,37
As reported,
in an effort to offer options to pipeline designers, one polyethylene manufacturer offers polyethylene encasement
52
materials with volatile corrosion inhibitors (VCI) and anti-MIC inhibitors that typically meet or exceed AWWA C 105.
37
Spickelmire reports, “one polyethylene encasement manufacturer is experimenting with perforated polyethylene encasement
(similar to perforated rock shield concept) in an attempt to minimize (concerns) about CP shielding.”
Appurtenances such as bends, reducers, offsets, etc., can be encased in the same manner as the pipe in accordance with
52
AWWA C 105. Odd-shaped appurtenances such as valves, tees, and crosses are encased with a flat sheet or split length of
polyethylene tube by passing the sheet under and then over the appurtenance and bringing it together around the body of the
appurtenance.
The typical method of tapping polyethylene-encased ductile-iron pipe involves wrapping two or three layers of polyethylene
adhesive tape completely around the pipe to cover the area in which the tapping machine and chain are to be mounted. The
corporation stop is installed directly through the tape and polyethylene. After the tap is made, the entire circumferential area is
inspected for damage, and any repairs are made. Some of the reported failures of polyethylene-encased iron pipe have involved
service taps in which the film had been cut and torn back to make taps and not repaired, exposing the pipe to aggressive soils.
As with any corrosion protection system, use of specified materials and proper installation is a factor in a polyethylene
encasement’s success. Some known failures of polyethylene-encased cast and ductile-iron pipe have been caused by improper
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installation or poor workmanship. Examples of such problems include improper overlap at the joints, incomplete encasement of
the pipe, damage as a result of handling (e.g., chains, dragging, cables), failure to repair rips or damage in the film prior to
backfilling, dirt and mud not being cleaned from the pipe prior to installation of the encasement, improper installation and repair
100
techniques at corporation stop connections, and large, sharp rocks or debris in the backfill.
35
Szeliga and Simpson report on a water main that was installed with bonded joints, test stations, and double polyethylene
encasement. The main was closely inspected during installation to prevent damage to the polyethylene encasement. A closeinterval potential survey conducted immediately after installation detected damaged areas in the polyethylene encasement. They
concluded that polyethylene encasement is likely to be damaged during installation or handling, regardless of how well an
109
inspection is performed. Crabtree, et. al
reports that potential surveys might not confirm the condition of the polyethylene
35,51,54,76
encasement, and confirmation with actual pipeline excavations is typical. Szeliga, et. al
report that potential surveys are
effective in locating corroding areas on pipelines and provided case histories of pipe excavations that were selected based on the
76
analysis of potential data. Szeliga also reports that potential testing is necessary to locate areas of active corrosion on a ductileiron main and when potential data are correlated with in situ soil resistivity data, the most seriously corroded areas along a main
35,50-51,54,76,103,110
can be located. Szeliga, et. al
report corrosion under both damaged and undamaged polyethylene-encased
ductile-iron pipe. Others report corrosion under undamaged polyethylene encasement on both cathodically protected and
23,37,57
103
unprotected ductile-iron pipe.
Szeliga reported on the evaluation of the effectiveness of polyethylene encasement based
on a review of technical papers for 1987 through 2007 and provides his conclusions.
81
Bell and Romer state that additional attention to design and installation items not described in relevant national standards are
also typically used for polyethylene-encased pipelines. They state that it is normal for electrical isolation from attachments and
appurtenances to be provided, the joints are intentionally bonded to provide electrical continuity, corrosion monitoring stations are
installed, and CP is provided. Considerations for polyethylene-encased pipelines to monitor and preserve corrosion control
options in the future are included in Appendix B.
An evaluation of the corrosion benefits of polyethylene encasement in a tidal muck environment in the Florida Everglades is
72,111
reported by Horton, et. al.
Based on three years of test data, corrosion rates under the encasement are compared to those
outside the encasement with the use of electrical resistance-type corrosion rate probes. The corrosion of the probes under the
encasement was, on average, one tenth of those in direct contact with the soil environment. As expected, the corrosion rate of the
probes under the encasement decreased over time as conditions under the encasement stabilized.
58
Brander reported that polyethylene encasement only offered an average 30% reduction in leaks compared to bare ductile-iron
pipe and therefore, a tight-bonded coating (40 mil [1 mm] extruded polyethylene) and CP for their ductile-iron pipe are typically
used.
A discussion of documented research and field applications for polyethylene encasement of iron pipe is provided in Appendix C.
Bonded Coatings
General
Bonded coating systems that have been specified for iron pipe include coal tar epoxy, coal tar enamel, extruded polyolefin,
23,37,44,58-59,64,84,112-113
sprayed polyolefin, polyurethane, hot- and cold-applied tapes, and cement coatings.
Additionally, wax114
115
37,81
petrolatum tapes (AWWA C 217 and NACE Standard RP0375 ) have also been used on iron pipe and fittings.
Extruded
polyethylene-type coatings have been adapted for bell and spigot-type ductile-iron pipe joints and have been utilized since
17,58
17
1975.
Tape coatings have been used since the mid-1970s, with polyurethane coating use beginning in 1988. In one report,
a bonded thermoplastic coating for ductile-iron piping was utilized in Seattle, and this type of coating had been previously used in
59
Europe.
Liquid epoxy, fusion-bonded epoxy, and thermoplastic-type coatings have been used for ductile-iron and cast-iron
fittings. Spray-applied coatings, tape, or heat-shrink sleeves have historically been utilized for pipe joint coatings. A wider variety
of tight-bonded coatings have been used outside North America to protect buried ductile-iron pipe.
During this same time period, to a much lesser degree, bonded coatings have also been furnished. A review of production
records of the U.S. ductile-iron pipe manufacturers for a 10 year period, between 1990 and 2000, indicates less than 1% of
ductile-iron pipe production had been furnished with a special bonded exterior coating. Historically, as in instances of
polyethylene encasement noted above, the use of tight-bonded coatings on the exterior of ductile-iron pipe has been largely
23,37,44,58-59,64,112-113
39,84,116
successful.
Others have reported problems.
The majority of reported problems have been primarily
related to application by inexperienced vendors.
After 2000, most U.S. ductile-iron pipe manufacturers have chosen to not provide bonded coatings on buried ductile-iron pipe,
with the exception of fittings (some ductile-iron manufacturers provided bonded coatings in aboveground applications), nor
provide or sell their pipe to a purchaser/end user who wishes to coat it, citing technical application issues and the higher initial
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costs for a bonded coating system. During that time, with the exception of aboveground applications and fittings, coating of
ductile-iron pipe, according to the U.S. ductile iron pipe manufacturers, would void their warranties. In addition to special handling
and installation requirements, some of the factors that U.S. pipe manufacturers cite as limiting the feasibility of a bonded coating
for ductile-iron pipe are discussed in the following sections under Surface Preparation, Surface Roughness, Coating Thickness,
and Holiday Detection, Coating Application, and Special Consideration—Joints. However, bonded coatings are still used outside
the U.S. and were used for many years in the U.S. Recently, a few U.S. ductile-iron pipe manufacturers have begun to provide
external coated ductile-iron pipe in limited quantities. There are also some international ductile iron pipe manufacturers that are
now offering coated ductile iron pipe in the U.S.
23
The NRC report summarizes the different types of bonded coatings used for ductile iron along with a partial list of bonded
coated ductile-iron pipelines for North America alone, which included over 877 miles (1,410 km). The committee could not find
any reported failures of ductile-iron pipe with bonded coatings and CP. In 1999, there were no reported failures on 860 miles
(1,380 km) of bonded, coated ductile-iron pipe. In 2008, the NRC committee confirmed that 526 miles (847 km) of the 860 miles
(1,380 km) had not experienced any corrosion leaks. For the remaining 334 miles (538 km), it was not possible to obtain updated
information. The committee also received information that more than 3,000 miles (4,800 km) of ductile-iron pipe have been
coated in the Asian market alone. One pipe manufacturer in Europe indicated to the NRC committee that approximately 3 to 5
percent of their ductile iron pipe in the U.K. is still coated with a bonded coating (extruded polyethylene or polyurethane).
Typically, CP and/or joint bonding are not used in the European market.
In Europe, the primary external coating for corrosion control since the 1960s has been metallic zinc spray with a bitumen topcoat.
(11)
117
This method of protection, covered by ISO
8179,
is used by most European iron pipe manufacturers for mildly and
moderately corrosive soils. In more corrosive soils, the metallic zinc coating is typically supplemented by polyethylene
118
encasement.
Other protective coating systems utilized by European pipe manufacturers include, but are not limited to,
extruded polyethylene, polyurethane, zinc-aluminum metallic spray with epoxy topcoat, tape, and reinforced cementitious
coatings.
Numerous coating standards for material, application, inspection, and surface preparation on steel surfaces are available through
(12)
(13)
organizations such as NACE, SSPC,
ISO, BSI,
ASTM, and AWWA. For the reasons discussed in the following sections,
84
standards and specifications for smooth carbon steel surfaces might not be directly applicable for ductile-iron pipe. There are
currently only a few coating standards for the application of a bonded coating to ductile-iron pipe that are specific to underground
use, with the exception of the aforementioned AWWA and NACE coating standards, and some international standards that have
been developed for coating of ductile iron as listed in Appendix A. There are some coating manufacturer standards or product
specifications that have been developed specifically for ductile iron; other standards or product specifications might not be
applicable, and sometimes there is coordination between the customer and the individual coating manufacturers/experienced
112
119
applicators that have developed procedures for application of their coatings to ductile-iron pipe. Guan, Noonan, and Bradish
discuss some of the design factors that are often considered for coating different water pipeline types (e.g., steel, ductile iron, and
concrete).
Because ductile iron has a rougher surface than steel, adjustments in the coating thickness and the amount of holidays allowed
are normally considered in the selection of the tight-bonded coating. As with other types of pipelines, consideration of coating
thickness and type utilized is typically given to fittings and joints so as not to restrict the function of the piece being coated. Some
major coating manufacturers have developed specific coating application techniques and specification considerations specific to
ductile iron or cast iron to minimize surface porosity, holidays as a result of surface roughness (orange peel), out-gassing, and
other unique coating problems associated with ductile-iron pipe.
Many corrosion professionals and owners maintain that the higher initial cost for additional corrosion mitigation measures such as
a bonded coating or CP is justified, as a life-cycle cost analysis indicates that just as with oil and gas pipelines, the better coatings
provide a lower long-term cost. An economical analysis comparison for different types of coatings for prestressed concrete
120
cylinder pipe (PCCP), ductile iron, and steel water pipelines by Noonan showed that the better the coating quality, the less the
life-cycle costs. This included examples and comparisons of bare, polyethylene-encased, and bonded tape-coated ductile iron,
bonded tape coated steel, and bare and coated PCCP.
121
Bianchetti, et. al studied the installation costs combined with the net present value operation costs associated with a single mile
(1.6 km) of ductile iron and of steel transmission-type pipelines employing varying corrosion mitigation measures. In this instance,
they considered the estimated numbers of leaks that the varying options often entail over a 75 year service life. They did not,
however, consider additional costs, such as possible additional leaks as a result of shielding of pipe areas under polyethylene
encasement or disbonded coatings and structural losses as a result of corrosion, nor did they consider the cost of retrofitting CP if
(11)
International Organization for Standardization (ISO), 1 ch. de la Voie-Creuse, CP 56, CH 1211, Geneva 20, Switzerland.
Society for Protective Coatings (SSPC), 40 24th St., 6th Floor, Pittsburgh, PA 15222-4656.
(13)
British Standards Institute (BSI), British Standards House, 389 Chiswick High Road, London W4 4AL, United Kingdom.
(12)
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it is not installed initially. They provided their conclusions regarding the use of coating plus corrosion monitoring systems and the
installation of CP.
In a 100 year life-cycle cost analysis in which the initial and long-term cost of different corrosion control strategies for ductile-iron
122
pipe were evaluated, Kroon
states, “There are other more practical and effective corrosion control techniques that [are
sometimes] implemented at a considerably lower total cost of ownership (TCO).” These corrosion control techniques, individual
or in combination, include polyethylene encasement, CP, and life-extension cathodic currents reduce corrosion rates for achieving
the desired service life. This study asserts that unlike natural gas and hazardous pipelines in which CP is regulated and corrosion
failures are not acceptable, in the case of ductile-iron pipe used in water and waste water, some corrosion is tolerable, and the
122
pipeline still achieves the desired pipeline service life.
In this analysis, the use of strategies that included a wax petrolatum
tape coating have a notably higher life-cycle cost. However, there was no inclusion of such expenses as varying cost of pipeline
repairs given the various options or of replacement for unprotected or less protected mains if corrosion failures become frequent.
Kroon concludes that a properly maintained cathodically protected pipeline can remain in operation idefinitely largely free of
corrosion and corrosion-related failures. Because of corrosion failures to pipelines, replacement of a cathodically protected
pipeline is not always done.
Surface Preparation
The surface profile of ductile iron is different from that of steel pipe, so modifications in the degree of surface preparation are
typically used. For ductile-iron pipe, obtaining the surface condition specified by some coating manufacturers can cause
delamination, slivering, or damage to the pipe surface from overblasting, high nozzle velocities, and excessive blast times for
certain types of ductile-iron pipe if the blasting is not performed properly. The outer oxide layer on some ductile-iron pipe
manufactured by the DeLavaud process is softer and susceptible to damage if overblasted. Typically, this is not a problem on the
ductile-iron pipe interior or on pipe or fittings made with sand molds or pipe cast using a wet-spray process. Ductile-iron pipe
coated with a special bonded coating is normally provided bare, with no asphaltic coating or provided with a primer compatible
with the top coating.
116
123
Some of these problems are discussed in an article by DIPRA and also in the guidelines for a surface preparation standard
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developed by the National Association of Pipe Fabricators (NAPF).
Different surface preparation considerations for bonded
112
coatings were summarized in a 2001 article by a coating manufacturer for several different types of pipelines.
This article
states that the general surface preparation requirements for steel pipe are usually followed for ductile iron pipe. Even when a
123
reference to the NAPF 500-3 standard guidelines is included, the amount and grade of cleanliness is typically agreed on with
the coating manufacturer and specified for the specific ductile-iron pipe coating to be used, similar to the NACE and SSPC
124-127
surface preparation standards.
Because of the differences between pipe manufacturers, often a prebid meeting to discuss
surface preparation requirements has been found to be extremely beneficial.
The Fall 2005 NAPF Newsletter comments on the suggestion that this standard might be used as the basis for surface
preparation scenarios for bonded coatings in buried pipe applications. However, they believe that the conditions of exposure are
substantially different. Typically, discussions with the manufacturer are used to work out an agreement.
To minimize surface preparation issues, several tape coating manufacturers have developed specifications for application of
tightly bonded coatings for ductile-iron pipe without the removal of the oxide layer.
Surface Roughness, Coating Thickness, and Holiday Detection
Both the DeLavaud and wet-spray manufacturing processes for ductile-iron pipe produce a surface texture on the exterior of the
pipe that is significantly rougher than the smooth surface normally found on steel products. The majority of technical data sheets
for protective coatings have been developed and written for smooth steel surfaces. Some coating manufacturers have developed
specific specifications and products for ductile-iron pipe. Because of the rough, “orange peel” external surface inherent with
ductile-iron pipe manufactured using the DeLavaud casting process and surface porosity, an excessive number of holidays
occasionally occur in the coating. In general, liquid coatings to be applied to the exterior surface of ductile-iron pipe are thicker
than those for steel. These thicknesses for ductile-iron pipe have typically been obtained only from coating or pipe manufacturers,
who are knowledgeable about the surfaces unique to this piping material. Special procedures and coating materials are normally
used to minimize out-gassing and other specific application problems associated with ductile-iron pipe.
Because of the rough surfaces that are inherent in the manufacture of ductile-iron pipe, holiday test procedures developed and
written for smooth steel surfaces have not always been applicable. High-voltage spark testing methods in accordance with ASTM
128
129
G 62, Method B and NACE SP0274 have been found to damage coatings on the rough “orange peel” surface of ductile-iron
pipe, if the coating thickness is not sufficient over the rougher surface texture. The test voltage is normally in accordance with the
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National Association of Pipe Fabricators (NAPF), 1901 NW 161st St., Edmond, OK 73013.
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coating manufacturers’ recommendations for ductile-iron pipe. For thin-film coatings, low-voltage holiday detection in accordance
128
130
with ASTM G 62 Method A or NACE SP0188 has normally been used. Pipe manufacturers, coating applicators, and coating
system manufacturers knowledgeable about the unique surface texture and coatings used on ductile-iron pipe have typically been
consulted regarding holiday testing of the specific coating system being applied.
Coating Application
Application procedures for coating materials have normally been published by the coating material manufacturer. As previously
discussed, procedures that are based on the application of coating to a smooth steel surface have not always been applicable to
ductile-iron pipe. Application procedures developed specifically for ductile-iron pipe have typically been provided on the technical
data sheet or in the manufacturer’s literature. In cases in which these procedures are not provided, the coating manufacturer or
ductile-iron pipe manufacturer has typically been contacted.
Special Coating ConsiderationsJoints
Ductile-iron pipe is available with numerous types of joints (e.g., push-on, restrained push-on, mechanical joint, restrained
mechanical joint, flange, and ball joint). Each manufacturer has proprietary designs. For the purposes of CP, none of these joints
is considered electrically continuous.
For CP installation of ductile-iron pipe, the joints are normally bonded together in the field after assembly using an exothermic
welding process to attach cables having insulation suitable for underground use across the joint. In these installations, the
bonded exterior coating and interior lining, if damaged by the high-temperature welding procedure, are typically repaired.
Many automatic coating lines at applicators are designed for “no-socket” steel pipe. Depending on the joint configuration, it
sometimes is not possible to coat ductile-iron pipe using standard automatic line coating equipment. In these cases, another
coating has been selected or special hand-applied application procedures have been utilized.
Ductile-iron pipe with push-on joint designs typically have the last few inches (about 50 mm) of the spigot end inserted into the bell
end during assembly. In order to provide for proper leak-free assembly, the coating thickness in these critical dimensional areas
is normally 0.15 mm to 0.20 mm (6.0 to 8.0 mil) nominal, with a 0.25 mm (10 mil) maximum. Greater thicknesses are sometimes
used when it is demonstrated that dimensional tolerances of the joint components are not exceeded. When a specially coated
push-on joint ductile-iron pipe is cut in the field, the bonded coating on the sealing area of the pipe barrel is normally removed in
order to meet joint dimensional requirements. This is sometimes a problem for some thick-film systems such as hot enamel,
polyurethane, cementitious coatings, and tape wraps.
Some after-market restraint joint effectiveness is not compatible with bonded coatings. Use of these types of restraints on tightbonded coated pipe is typically considered during the design.
Because several inches (about 50 mm) of the external surface of the pipe spigot end are in contact with the liquid inside the pipe,
11
consideration is normally given to the suitability of the coating for that specific liquid on this part of the pipe exterior. NSF 61
mandates that all coating materials in contact with potable water be certified.
Inspection
Inspection during surface preparation, application, shipment, storage, and installation helps to assure the coating meets
specifications. As with any bonded coating, inspections of coatings applied to ductile-iron pipe have typically been conducted
during surface preparation, application, final acceptance, and installation. Coating inspection standards and coating manufacture
recommendations are generally followed.
Types of Coatings
Appendix A lists brief comments about some of the bonded coatings that have been utilized for application to the exterior of
ductile-iron pipe and fittings. Coating manufacturers, knowledgeable applicators, and ductile-iron pipe manufacturers have
typically been consulted regarding coating systems to be applied to ductile-iron pipe.
Cathodic Protection
General
CP is one method available for corrosion control of ductile- and cast-iron piping. For new installations, CP of buried piping has
been applied in conjunction with bonded protective coatings, polyethylene encasement, and on bare pipe. However, NACE
131
SP0169 notes concerns for the use of loose wrappers, which can shield metal surfaces from receiving CP.
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Corrosion failures can occur on cathodically protected pipe. These types of failures are typically limited in number and are the
result of (1) improper design, (2) improper installation, (3) lack of system maintenance, (4) improper testing and adjustment, (5)
electrical shielding, (6) coating failures or disbondment, and (7) MIC.
In the design of any CP system, the selection and specification of materials and installation practices that ensure the dependable
and economical operation throughout the intended operating life of the piping system have typically been considered. Criteria,
131
design, installation, operation, maintenance, etc., of CP of metallic structures is covered in NACE SP0169.
In some cases, the use of retrofitting the existing pipe system with a CP system provides some economical alternative to pipe
replacement. Studies in Canada and the U.S. show that installation of CP using distributed anodes have typically been successful
33,132
in slowing the development of new leaks and extending the service life of the pipe.
CP with Galvanic Anodes
Galvanic anode systems are often referred to as sacrificial anode systems. They provide CP by the use of a metal that is
electrochemically more active than the structure being protected. Galvanic anodes are typically used when CP current densities
are low and/or in areas in which soil resistivity is low enough to obtain the desired current output with a reasonable number of
133
anodes. Magnesium and zinc are the common anode materials for underground pipe applications. Anodes are often installed
individually along the pipe or in groups with particulars dependent on such factors as the presence and quality of a protective
coating/encasement and maintenance and monitoring plans. In some cases, an easily bendable zinc or magnesium ribbon
anode is laid along the entire length of pipe section and attached to the piping at predetermined intervals.
CP with Impressed Current
Impressed current systems normally utilize a transformer-rectifier as a power source. Commonly referred to as a rectifier, it is a
device that simply converts AC electric power to DC power. DC current is discharged from the anodes and collects on the
structure. When impressed current CP is implemented, the pipeline joints are bonded for electrical continuity. Impressed current
systems are typically used in cases requiring larger amounts of current or where other factors cause galvanic anode systems to
133
be impractical.
Anode materials generally used for impressed current are manufactured of graphite, high-silicon cast-iron,
platinum-coated, or precious metal oxide-coated materials. Impressed current anode beds have been distributed along the piping
system, concentrated at one location some distance from the piping being protected, or placed in a vertically installed deep anode
bed.
CP Current Demand
In this section, design current densities are determined for the total surface area of the pipeline (i.e., coated or encased and bare
areas). Design current densities for achieving full CP for buried as-manufactured ductile-iron or cast-iron piping without
2
supplemental coatings or encasement (i.e., bare pipe) are often assumed to be similar to that of steel, which is in the 1 to 3 mA/ft
2
134
(11 to 32 mA/m ) range, depending on soil corrosiveness, temperature, surface texture, etc.
When bonded coatings or encasement are used, the total CP current requirement is reduced because of the reduction in pipe
73,135
metal surface exposed to the environment. Schiff and McCollom
reported that on a project employing both ductile iron and
steel pipe, the average current density for approximately five years following installation of ductile-iron pipe with polyethylene
2
2
2
2
encasement was 0.0233 mA/ft (0.2500 mA/m ), compared to 0.000832 mA/ft (0.090000 mA/m ) for the steel pipe with a bonded
coating. Ductile-iron pipe with polyethylene encasement used 28 times as much current per total surface area as compared to a
7
2
2
tight-bonded coated steel pipe in similar soils. Spicklemire reports a current density requirement of 0.103 mA/ft (1.10 mA/m ) to
2
2
2
2
0.137 mA/ft (1.50 mA/m ) for parallel polyethylene-encased force mains and current requirements up to 0.670 mA/ft (7.2 mA/m )
136
2
in low-resistivity, salt-contaminated (sea coastal) soils. Schramuk and Rash report that a current density of 0.065 mA/ft (0.700
2
mA/m ) was used for CP of a new polyethylene-encased ductile iron water transmission pipeline.
55
Kroon, et. al summarized the use of life-extension current densities and criteria strategy for ductile-iron pipe. This approach
acknowledges that some corrosion of water and wastewater pipeline is often tolerated, yet still allows for a suitable service life to
be realized. This life-extension CP current density method operates by controlling (reducing) the rate of corrosion to acceptable
levels, often achieved through the application of cathodic current densities less than those used to realize a near-zero corrosion
55
rate. For as-manufactured ductile-iron pipe with the standard asphaltic coating, Kroon, et. al reported that a design current
2
2
density of about 0.10 mA/ft (1.08 mA/m ) causes a polarized potential shift of about 70 mV and effectively quadruples the pipe
service life based on E-log-I laboratory and field studies, in some cases. Current densities for polyethylene-encased and tightbonded coated pipe depend on site-specific conditions and the condition of the polyethylene encasement or bonded coating.
Higher current densities are generally used for locations of MIC and graphitized pipe.
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Polyethylene-Encased with CP
135
137
Applying CP to polyethylene-encased pipe has been reported by Schiff and McCollom, and Lindemuth and Kroon report that
pipeline designs dating back to at least the 1970s for more than 300 miles (500 km) of construction have included this corrosion
control methodology. Some projects were designed and constructed under the auspices of government agencies and other
agencies, dating back to the early 1980s, include CP and polyethylene encasement as the corrosion control strategy. In 2004,
63
23
there were no known corrosion problems on these government projects. However, as summarized in the NRC report, there
has since been a corrosion failure on one polyethylene-encased, cathodically protected government project pipeline (North
Dakota, October 2004).
As of 2012, there are no national standards for CP of polyethylene-encased pipe. The effectiveness of CP with polyethylene
encasement is widely debated in the corrosion field. This is because polyethylene encasement is a possible cause of shielding of
131
the CP current. NACE SP0169 covers control of external corrosion on underground or submerged metallic piping and supports
138
the application of bonded pipe coatings, such as a polyolefin coating system (e.g., see NACE SP0185, and NACE SP0169).
131
NACE SP0169 states that care is typically taken when using loose wrappers like polyethylene encasement because they might
cause shielding that is detrimental to CP effectiveness.
It is generally accepted that CP protects ductile-iron pipe with polyethylene encasement where the pipe surface is exposed to the
55
soil. After a two-year study, Kroon, et. al reported, “Cathodic currents improve the effectiveness of polyethylene encasement.
The methods are not exclusive and [are sometimes] used in combination.” CP of ductile-iron pipe with and without polyethylene
73-74,135
encasement with a variety of backfill conditions has been investigated using electrical resistance probes.
Two excavations
conducted in 2004 of a 15 year old, 30 in (762 mm) pipeline revealed no measurable corrosion, both at damaged and undamaged
139
140
areas of the polyethylene encasement.
In 2009, Lindemuth and Kroon reported similar results from the inspection of four
pipelines involving six total excavations of polyethylene-encased, cathodically protected ductile-iron pipelines ranging in age from
20 to 26 years.
23
The NRC report compiled a partial list of known cathodically protected polyethylene-encased ductile-iron pipelines in North
America, which consisted of approximately 370 miles (600 km) of pipe. Of these 16 systems, some dating back to 1975, four
reported corrosion leaks and two of the pipelines were replaced. Additionally, the NRC report calculated a failure rate of 0.00038
failures per mile (1.6 km) per year for cathodically protected polyethylene-encased ductile-iron pipe (one failure in 50 years for
every 53 miles [82 km] of pipe).
23
Also, the NRC report states that bonded coatings with CP can provide better ductile-iron pipe performance than polyethylene
encasement with CP. The report describes instances of iron pipe corrosion when buried as manufactured, with polyethylene
encasement, and with polyethylene encasement with CP. The report’s basic conclusions were that, even with CP, polyethylene.
encased ductile iron pipe is not likely to provide a reliable 50 year service life in highly corrosive soils (< 2,000 Ω cm) (one
corrosion failure in 454 miles [731 km] of pipe in 50 years). However, such measures can sometimes provide adequate corrosion
23
mitigation over bare or as-manufactured ductile iron pipe.
Spickelmire has documented that corrosion sometimes still occurs under undamaged polyethylene encasement on cathodically
protected pipelines. CP that is applied to polyethylene-encased pipeline does not always prevent the corrosion that occurs under
37
the polyethylene encasement, and failure of the pipeline still occurs, in some cases. McCollom has questioned the success of
CP levels under undamaged polyethylene encasement because of electrical shielding concerns. CP and electrical shielding
effects with polyethylene encasement continue to be studied and the full effects are not understood at this time.
Additional research and evaluations relating to the effectiveness of this corrosion control strategy is currently being conducted
139
74,81
137
37
72
independently by DIPRA, Bell, et. al,
Lindemuth and Kroon, Spickelmire, Horton, et. al, as well as others. Currently,
there is a lack of long-term documented experience and difficulty in accurately monitoring protection levels under unbonded films.
Additional monitoring techniques consisting of reference electrodes, plastic monitoring reference pipes, coupons, and resistance
probes are occasionally used in an effort to verify accurate protection levels.
Bonded Coatings with CP
When bonded coatings have been used on ductile-iron pipe and fittings, they are typically used together with impressed current or
17
63
galvanic anode CP systems. Spickelmire and a federal agency indicate that electrical shielding concerns are typically
minimized when tight-bonded coatings in conjunction with CP are used in more corrosive conditions. As a result of concerns
about electrical shielding, some proponents believe that bonded coating provides a higher degree of protection in some
37,44,57-58
23
environments with CP than does polyethylene encasement with CP.
The NRC report reached a similar conclusion.
Some authorities and utilities have specified tight-bonded coatings and CP measures similar to those normally used for steel
37,44,58
lines.
Corrosion studies were conducted, and specifications for both tight-bonded coatings and CP on ductile-iron pipe were
adopted, depending on route corrosiveness. They concluded that while there is a higher cost associated with the application of
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tight-bonded coatings, the major benefit is a longer anticipated life of pipelines with the ability to accurately monitor the condition
57,141
37,44,58-59,112-113
of the ductile-iron pipelines.
Bonded coatings with CP on iron pipelines have been successful.
The committee working on the NRC report found more cathodically protected ductile-iron pipe with a bonded coating in North
23
America than polyethylene-encased and cathodically protected ductile-iron pipe. Information provided in the report indicated
that there had been no failures on 525.9 miles (846.3 km) of ductile-iron pipe with CP with a bonded coating.
Future Considerations
Corrosion of buried iron pipe is a long-term issue, typically involving a required service life of 50 to 100 years. Because of the
number of controversial subjects and/or conflicting viewpoints on the type and success of different corrosion control methods for
ductile iron pipe, additional studies are being conducted to clarify what does and does not work. Additional areas of study to the
benefits of various corrosion mitigation measures include:

Development of quality programs for construction and maintenance of waterline corrosion protection systems;

Cost-benefit studies for various corrosion mitigation measures;

Additional studies of polyethylene encasement with CP for in-service pipelines using advanced monitoring techniques
(including, but not limited to, ductile-iron resistance probes, reference electrodes, plastic monitoring pipes, and smart
pigging);

Studies and testing of bonded coatings on ductile iron pipe;

Use of micro-perforated polyethylene encasement with CP;

Use of anti-MIC polyethylene encasement with and without micro-perforations;

Long-term effectiveness (e.g., physical, dielectric strength, etc.) of polyethylene encasement; and

Use of controlled low-strength material (CLSM) as a backfill material.
References
1. R.W. Bonds, Correspondence to TG 014, Birmingham, Alabama, referencing a December 16, 2005 letter from SaintGobain PAM, 2008.
2. T.F. Stroud, “Infrastructure: Is the Problem Being Blown Out of Proportion?” Ductile Iron Pipe News, Fall/Winter 1985: p. 9.
3. DIPRA, Cast-Iron Pipe Century and Sesquicentury Club records, correspondence to Task Group 014 and postings on the
DIPRA Web site, ongoing.
4. ANSI/AWWA C 151/A 21.51 (latest revision), “American National Standard for Ductile-Iron Pipe, Centrifugally Cast, for
Water” (Denver, CO: AWWA).
th
5. L.R. Jenkins, R.D. Forrest, “Ductile Iron,” Metals Handbook, Vol. 1, 10 ed. (Metals Park, OH: ASM, 1990).
6. J.R. Davis, ed., “Metallurgy and Properties of Ductile Irons,” Cast Irons (ASM Specialty Handbook) (Metals Park, OH:
ASM, 1996), pp.65-68.
7. B. Spickelmire, “Ductile Iron Corrosion Risk Assessment and Corrosion Control Design Considerations,” NACE Northern
Area Western Conference, Victoria, BC (Houston, TX: NACE, 2004).
8. R.W. Bonds, “Cement-Mortar Linings for Ductile Iron Pipe,” DIP-CML 3-05/3.5 M (Birmingham, AL: DIPRA, March 2005).
9. B. Helton, “Cracks and Looseness in Cement Linings of Cast-Iron and Ductile-Iron Pipe and Fittings” (Birmingham, AL:
(15)
American Cast-Iron Pipe Company, 1979).
(15)
American Cast Iron Pipe Company, 1501 31st Ave. North, Birmingham, AL 35207.
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10. ANSI/AWWA C 104/A 21.4 (latest revision), “American National Standard for Cement-Mortar Lining for Ductile-Iron Pipe
and Fittings for Water” (Denver, CO: AWWA).
11. NSF 61 (latest revision), “Drinking Water System Components—Health Effects” (Ann Arbor, MI: NSF).
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and West Conshohocken, PA: ASTM).
nd
13. U.R. Evans, Metallic Corrosion, Passivity and Protection, 2
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1986), pp. 83-91.
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AWWA Ontario Section meeting, Ontario, Canada (Denver, CO: AWWA, 1979).
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Western Area Corrosion and Educational Conference, Tigard, Oregon (Houston, TX: NACE, 2001).
18. F.L. LaQue, “Corrosion Resistance of Ductile Iron,” Corrosion 14, 10 (1958): p. 55.
19. I.A. Denison, M. Romanoff, “Corrosion of Nickel Cast Iron in Soils,” Corrosion 10, 6 (1954): p. 199.
20. H.L. Hamilton, “Effects of Soil Corrosion on Cast-Iron Pipe,” Journal AWWA 52, 5 (1960): p. 639.
21. W.H. Smith, “A Report on Corrosion Resistance of Cast Iron Pipe and Ductile Iron Pipe,” Cast Iron Pipe News 35, 3
(1968): p. 16.
22. M. Woodcock, “To Review Other Relevant Data Regarding Ductile Iron Pipe, Corrosion, and Coatings,” presentation at
NRC committee meeting (Washington, DC: NRC, 2008).
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of the National Academies (Washington, DC: The National Academies Press, January 2009).
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25. E.C. Sears, “Comparison of the Soil Corrosion Resistance of Ductile Iron Pipe and Gray Cast Iron Pipe,” MP 7, 10 (1968):
p. 33.
26. W.F. Gerhold, “Corrosion Behavior of Ductile Cast-Iron Pipe in Soil Environments,” Journal AWWA 68, 12 (1976): pp.
674-678.
27. R.A. Gummow, “Corrosion of Municipal Iron Watermains,” MP 23, 3 (1984): p. 39.
28. ANSI/AWWA C 111/A 21.11(latest revision), “Rubber-Gasket Joints for Ductile-Iron Pressure Pipe and Fittings” (Denver,
CO: AWWA).
29. J. Lichtenstein, “Grounding Design and Corrosion Control,” presented at NACE Western States Corrosion Seminar,
Pomona, CA (Houston, TX: NACE, 1981).
30. F.E. Steltler, “Case Histories: Accelerating Leak Rate in Ductile Cast Iron Water Mains Yields to Cathodic Protection,” MP
19, 10 (1980): p. 15.
31. H.H. Collins, “Anti-Corrosion Methods and Materials,” Anti-Corrosion Methods and Materials 11, 10 (1964), pp. 35-37.
32. J.H. Fitzgerald, “Corrosion as a Primary Cause of Cast-Iron Main Breaks,” Journal AWWA 60, 8 (1968): p. 883.
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33. R.A. Gummow, “Corrosion Control of Iron and Steel Water Piping—A Historical Perspective,” NACE Northern Area
Eastern Conference, Quebec City, Canada (Houston, TX: NACE, 2002).
34. J.O. Harris, The Efficiency of the Polyethylene Sleeve over Cast Iron Pipe in Relation to Sulfate Reducing Bacteria
(Manhattan, KS: Kansas State University, 1972).
35. M. Szeliga, D. Simpson, “Corrosion of Ductile Iron Pipe: Case Histories,” MP 40, 7 (2001): p. 22.
36. G. Ash, Fulton Enterprises, Correspondence to Task Group 014 from Fulton Enterprises, Birmingham, Alabama, 2001.
37. B. Spickelmire, “Corrosion Control Considerations for Ductile Iron Pipe—A Consultant’s Perspective,” 52
Underground Corrosion Control Course, Morgantown, West Virginia (Houston, TX: NACE, 2007).
nd
Appalachian
38. R.W. Bonds, “Causes, Investigation, and Mitigation of Stray Current Corrosion on Ductile Iron Pipe,” CORROSION/91,
paper no. 516 (Houston, TX: NACE, 1991).
39. T.F. Stroud, “Corrosion Control Measures for Ductile Iron Pipe,” CORROSION/89, paper no. 585 (Houston, TX: NACE,
1989).
40. W.C. Robinson, “Stray Current Analysis—Ductile Iron Water Mains,” CORROSION/93, paper no. 581 (Houston, TX:
NACE, 1993)
41. M.J. Szeliga, J. Silhan, “New Developments in the Collection of Stray Current Field Data,” CORROSION/94, paper no.
582 (Houston, TX: NACE, 1994).
42. P. Hort, “Case Histories: Lack of Predesign Corrosion Survey Proves Costly (Early Corrosion Failures in Sewage
Treatment Plant),” MP 14, 1 (1975): p. 37.
43. J. Lichtenstein, “Safety Consideration While Working Near Powerlines,” CORROSION/90, paper no. 241 (Houston, TX:
NACE, 1990)
44. D. Lieu, M. Szeliga, “Protecting Underground Assets with State-of-the-Art Corrosion Control,” MP 41, 7 (2002): p. 24.
45. M.J. Schiff, “What is Corrosive Soil?” presented at NACE Western States Corrosion Seminar, in Pomona, CA (Houston,
TX: NACE, 1981).
46. A.W. Peabody, Principles of Cathodic Protection, NACE Basic Corrosion Course (Houston, TX: NACE, 1970).
47. M. Romanoff, “Exterior Corrosion of Cast-Iron Pipe,” Journal AWWA 56, 9 (1964): pp. 1129-1143.
48. G. Kozhushner, R. Brander, B. Ng, “Use of Pipe Recovery Data and the Hydroscope NDT Inspection Tool for Condition
Assessment of Buried Water Mains,” proceedings from the 2001 AWWA Infrastructure Conference, Orlando, Florida (Denver,
CO: AWWA, 2001).
49. R.A. Gummow, “Corrosion Control of Iron and Steel Water Piping – A Historical Perspective,” NACE International
Northern Area Eastern Conference, Quebec City, Canada (Houston, TX: NACE, 2002).
50. M. Szeliga, “Analysis of Ductile Iron Pipe Corrosion Data from Operating Mains,” MP 46, 2 (2007): p. 22.
51. M. Szeliga, D. Simpson, “Evaluating Ductile Iron Pipe Corrosion,” MP 42, 7 (2003): p. 22.
52. ANSI/AWWA C 105/A 21.5 (latest revision), “Polyethylene Encasement for Ductile-Iron Pipe Systems” (Denver, CO:
AWWA).
53. R.W. Bonds, M. Barnard, A.M. Horton, G.L. Oliver, “Corrosion and Corrosion Control of Iron Pipe—75 Years of
Research,” Journal AWWA 97, 6 (2005): p. 88.
54. M. Szeliga, “Analysis of Ductile Iron Corrosion Data from Operating Mains and Its Significance,” presentation at ASCE
Pipelines, Advances and Experiences with Trenchless Pipeline Projects Conference, Boston, MA, 2007.
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55. D.H. Kroon, D. Lindemuth, S. Sampson, T. Vincenzo, “Corrosion Protection of Ductile Iron Pipe,” CORROSION/2004,
paper no. 46 (Houston, TX: NACE, 2004).
56. P. Ferguson, D. Nicholas, “Corrosion Protection of Buried Cast-Iron Water Mains,” Australian Corrosion Association,
Conference 23, Corrosion Australia (Mount Waverley, Australia: ACA, 1984), pp. 12-1739.
(16)
57. B. Bradish, M. Szeliga, G. Hart, “The Application of Corrosion Control Methods to Large Diameter Water Mains,”
presented at the Tri-Association Conference AWWA Chesapeake Section, Elliott City, MD, August 16-19, 1993.
58. R. Brander, “Water Pipe Materials in Calgary, 1970-2000,” Proceedings from the 2001 AWWA Infrastructure Conference,
Orlando, Florida (Denver, CO: AWWA, 2001).
59. J.R. Pimentel, “Bonded Thermoplastic Coating for Ductile Iron Pipe,” MP 40, 7 (2001): p. 36.
nd
60. C.P. Dillon, “Corrosion Control in the Chemical Process Industries,” 2
ed. (St. Louis, MO: MTI, 1994): p. 212.
61. D. Newell, Washington Suburban Sanitation District, correspondence to Task Group 014, 1999 through 2003.
62. B. Spickelmire, “Corrosion Considerations of Ductile Iron Pipe,”’ MP 41, 7 (2002): p.16.
63. “Corrosion Considerations for Buried Metallic Water Pipe,” Technical Memorandum No. 8140-CC-2004-1, Bureau of
Reclamation, July 2004.
64. Technical Memorandum No. MERL-05-19, Bureau of Reclamation, December 2005.
65. M. Romanoff, “Performance of Ductile-Iron in Soils,” Journal AWWA 60, 6 (1968): pp. 645-655.
66. C. Cowan, “Measurements and Standards,” presentation at NRC committee meeting, Washington, DC (Washington, DC:
NRC, 2008).
67. T. Woolley, letter and data presentation, “Corrosion Database Statistical Analysis,” presentation at NRC committee
meeting, Washington, DC (Washington, DC: NRC, 2008).
68. J. Rossum, “Prediction of Pitting Rates in Ferrous Metals from Soil Parameters,” Journal AWWA 61, 6 (1968): pp. 305310.
69. J.A. Jakobs, F.W. Hewes, “Underground Corrosion of Water Pipes in Canadian Cities, Case: The City of Calgary, Final
Report,” Caproco Corrosion Prevention, Ltd., August 31, 1983.
70. R.W. Bonds, A.M. Horton, G.L. Oliver, L.M. Barnard, “Corrosion Control Statistical Analysis of Iron Pipe,” MP 44, 1 (2005):
p. 30.
71. R. Wakelin, R.A. Gummow, “A Summary of the Findings of Recent Watermain Corrosion Studies in Ontario,” presented at
International Symposium of Materials Performance Maintenance, Ottawa, Ontario (Westmount, Quebec: The Metallurgical
(17)
Society of CIM, 1991).
72. A.M. Horton, D. Lindemuth, G. Ash, “Ductile Iron Pipe Case Study: Corrosion Control Performance Monitoring in A
Severely Corrosive Tidal Muck,” CORROSION/2005, paper no. 05038 (Houston, TX: NACE, 2005).
73. M.J. Schiff, B. McCollom, “Impressed Current Cathodic Protection of Polyethylene-Encased Ductile Iron Pipe,” MP 32, 8
(1993): pp. 23-27.
74. E.D. Bell, C.G. Moore, S. Williams, “Development and Application of Ductile Iron Pipe Electrical Resistance Probes for
Monitoring Underground External Pipeline Corrosion,” CORROSION 2007, paper no. 335 (Houston, TX: NACE, 2007).
75. A.G. Fuller, “Corrosion Resistance of Ductile Iron Pipe,” British Cast Iron Research Association Report 1442, November
1981.
(16)
Australasian Corrosion Association, P.O. Box 2340, Mount Waverley, Victoria 3149, Australia.
The Canadian Institute of Mining, Metallurgy, and Petroleum (CIM), Suite 1250, 3500 de Maisonneuve Blvd. W., Westmount, QC, Canada
H3Z 3C1.
(17)
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76. M. Szeliga, “Ductile Iron Pipe Failures,” MP 44, 5 (2005): p. 26.
77. D. Fowles, “Report of Pipe Inspection Denver Test Site (Marston Lake) in Conjunction with Denver Water Board”
(Birmingham, AL: DIPRA, July 15, 1983).
78. ANSI/AWWA C 150/A 21.50 (latest revision), “Thickness Design of Ductile-Iron Pipe” (Denver, CO: AWWA).
79. ANSI/AWWA C 600 (latest revision), “Installation of Ductile-Iron Water Mains and Their Appurtenances” (Denver, CO:
AWWA).
80. K.J. Folliard, D. Trejo, S. Sabol, D. Leshchinsky, “NCHRP Report 597 Development of a Recommended Practice for Use
of Controlled Low-Strength Material in Highway Construction (Washington, DC: National Cooperative Highway Research
Program, Transportation Research Board, 2008).
81. E.C. Bell, A.E. Romer, “Making Baggies Work for Ductile Iron Pipe,” presented at PIPELINES 2004, ASCE Annual
(18)
Conference, San Diego, CA (Reston, VA: ASCE, 2004).
82. L. Manian, “Locating Open Joints in Bell and Spigot Type Buried Pipelines,” MP 36, 5 (1997): p. 18.
th
83. E.F. Wagner, “Corrosion Control with Cement Mortar-Lined Pipe,” NACE 25 Annual Conference, paper no. 24 (Houston,
TX: NACE, 1969).
84. A.M. Horton, “Special Protective Coatings and Linings for Ductile Iron Pipe,” Proceedings from Second International
Conference, Pipeline Division and ASCE-TCLEE, Reston, VA (Reston, VA: ASCE-TCLEE, 1995), pp. 745-756.
85. R.N. Sloan, “50 Years of Pipe Coatings—We've Come a Long Way,” CORROSION/93, paper no. 17 (Houston, TX:
NACE, 1993).
86. E.F. Wagner, “Loose Plastic Film Wrap as Cast-Iron Pipe Protection,” Journal AWWA 56, 3 (1964): pp. 361-368.
87. A.M. Horton, “Protecting Pipe with Polyethylene Encasement, 1951-1988,” AWWA Water World News 4, 3 (1988): p. 2628.
88. “Inspection Report of Cast-Iron Pipe Encased in Loose Polyethylene, LaFourche Parish, Louisiana” (Birmingham, AL:
DIPRA, May 28, 1998).
89. “Inspection Report of Cast Iron Pipe Encased in Loose Polyethylene – LaFourche Parish, Louisiana” (Birmingham, AL:
DIPRA, May 28, 2003).
90. “Installation Report of Cast Iron Pipe Encased in Loose Polyethylene – LaFourche Parish, Louisiana” (Birmingham, AL:
DIPRA, June 24, 2008.
91. B. Rajani, Y. Kleiner, “Protection of Ductile Iron Water Mains: What Protection Method Works Best for What Soil
Condition?,” Journal AWWA 95, 11 (2003): pp. 110-125.
92. B. Rajani, Y. Kleiner, “Protection of Ductile Iron Water Mains Against External Corrosion: Review of Methods and Case
Histories,” NRCC-45225, Institute for Research in Construction, National Research Council Canada, May 6, 2011.
93. H.H. Collins, “The Use of Polyethylene Sleeving for the Protection of Buried Spun Iron Pipes,” British Cast Iron Research
Association, Report 1465, March 1982.
94. R. Oliphant, “Corrosion Protection of Iron Pipes by Polythene Wrapping,” Water Research Centre, Report 38E, September
1981.
95 A. Brown, “Loose Polyethylene Sleeving as a Corrosion Preventive,” British Gas Engineering Research Station, Report
R739, August 1974.
(18)
American Society of Civil Engineers (ASCE), 1801 Alexander Bell Dr., Reston, VA 20191.
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96. D.R. Whitchurch, J.G. Hayton, “Loose Polyethylene Sleeving for the Protection of Buried Cast-Iron Pipelines,” presented
at the Conference on the Corrosion and Protection of Pipes and Pipelines, Vienna, Italy (London, UK: Brintex Exhibitions Ltd.,
1968), pp. 71-78.
97. JDPA Z 2005 (latest revision), “Polyethylene Sleeves for Corrosion Protection of Ductile Iron Pipes” (Tokyo, Japan:
(19)
JSA).
98. “Corrosion Protection for Ductile Iron Pipe by Polyethylene Sleeves,” Kubota Ltd. Report, October 1986.
99. W. Wolf, W.D. Gras, “The Use of Polyethylene Sleeves for the Corrosion Protection of Cast-Iron Pressure Pipes in
Special Cases,” presented at the Information of the Fachgemeinschaft Gusseiserne Rohre, Berlin, Germany (Dresden,
Germany: Fachgemeinschaft Gusseiserne Rohre, 1971).
100. A.M. Horton, “Polyethylene Encasement as an Asset Preservation Method for Ductile Iron Pipe,” presented at
PIPELINES 2008, Atlanta, GA (Reston, VA: ASCE, 2008).
101. AWWA Engineering and Construction Division Survey, October 2000.
102. DIPRA, teleconference with Task Group 014, March 2007.
103. M. Szeliga, “An Independent Evaluation of the Effectiveness of Polyethylene Encasement as a Corrosion Control
Measure for Ductile Iron Pipe,” presented at PIPELINES 2008, Atlanta, GA (Reston, VA: ASCE, 2008).
104. ASTM A 674 (latest revision), “Standard Practice for Polyethylene Encasement for Ductile Iron Pipe for Water or Other
Liquids” (West Conshohocken, PA: ASTM).
105. BS 6076 (latest revision), “Specification for Polymeric Film for Use as a Protective Sleeving for Buried Iron Pipes and
Fittings” (London, UK: BSI).
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106. AS
3680 (latest revision), “Polyethylene Sleeving for Ductile Iron Pipelines” (North Sydney, Australia: SAA).
107. AS 3681 (latest revision), “Guidelines for the Application of Polyethylene Sleeves to Ductile Iron Pipelines and Fittings”
(North Sydney, Australia: SAA).
108. ISO 8180 (latest revision), “Ductile Iron Pipes—Polyethylene Sleeving for Site Application” (Geneva, Switzerland: ISO).
109. D. Crabtree, M. Breslin, C. Sordelef, J.T. Terrazas, J. Von Deusen, “Investigating Ductile Iron Pipelines,” CORROSION
2007, paper no. 127 (Houston, TX: NACE, 2007).
110. M.J. Szeliga, “Corrosion Failures in the Water Industry Case Histories,” presented at the AWWA 1992 Distribution
System Symposium, Philadelphia, PA (Denver, CO: AWWA, 1992).
111. A.M. Horton, D. Lindemuth, G. Ash, “Corrosion Control Performance Monitoring of Ductile Iron Pipe in Severely
Corrosive Tidal Marsh,” MP 45, 5 (2006): p. 50-54.
112. S. Guan, “Corrosion Protection by Coatings for Water and Wastewater Pipelines,” presented at Appalachian
Underground Corrosion Short Course, Water and Wastewater Program, West Virginia University, Morgantown, West Virginia,
2001.
113. R. Brander, “Water Pipe Materials in Calgary, 1970-2000,” Proceedings from the 2001 AWWA Infrastructure Conference,
Orlando, Florida (Denver, CO: AWWA, 2001).
114. ANSI/AWWA C 217 (latest revision), “Cold-Applied Petrolatum Tape and Petroleum Wax Tape Coating for the Exterior of
Special Sections, Connections, and Fittings for Buried Steel Water Pipelines” (Denver, CO: AWWA).
115. NACE Standard RP0375 (latest revision), “Field-Applied Underground Wax Coating Systems for Underground Pipelines:
Application, Performance, and Quality Control” (Houston, TX: NACE).
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(20)
Japanese Standards Association (JSA), 4-1-24 Akasaka, Minato-KU, Tokyo 107-8440, Japan.
Standards Australia (SA), P.O. Box 1055, Strathfield, NSW 2135, Australia.
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116. “Surface Preparation of Ductile Iron Pipe to Receive Special Coatings,” Ductile Iron Pipe News, Fall/Winter (1993): p. 17.
117. ISO Standard 8179 (latest revision), “Ductile Iron Pipe—External Zinc Coating,” (Geneva, Switzerland: ISO).
118. J.E. Drew, Pipe Materials Selection Manual (Swindon, UK: WRc, 1995), p. 128.
119. J.R. Noonan, B.M. Bradish, “New Bonded Tape Coating System and Cathodic Protection applied to Non-Steel Water
Pipelines; Quality Through Proper Design Specifications,” presented at PIPELINES 1995, Bellevue, WA (Reston, VA: ASCE,
1995).
120. J.R. Noonan, “Proven Economic Performance of Cathodic Protection and Anticorrosion Systems in the Water Pipeline
Industry,” Steel Water Pipe Bulletin, no. 6-6, June 1996.
121. R.L. Bianchetti, et. al, “Economic Considerations of Corrosion Control Strategies for Water and Wastewater Transmission
Pipelines,” presented at PIPELINES 2009, San Diego, CA (Reston, VA: ASCE, 2009).
122. D.H. Kroon, “Life-Cycle Cost Comparisons of Corrosion Protection Methods for Ductile Iron Pipe,” CORROSION/2005,
paper no. 37 (Houston, TX: NACE, 2005).
123. NAPF 500-03 (latest revision), “Surface Preparation Standard for Ductile Iron Pipe and Fittings Receiving Special
External Coatings and/or Special Internal Linings” (Edmond, OK: NAPF).
124. NACE No. 1/SSPC-SP 5 (latest revision), “White Metal Blast Cleaning” (Houston, TX: NACE and Pittsburgh, PA: SSPC).
125. NACE No. 2/SSPC-SP 10 (latest revision), “Near-White Metal Blast Cleaning” (Houston, TX: NACE and Pittsburgh, PA:
SSPC).
126. NACE No. 3/SSPC-SP 6 (latest revision), “Commercial Blast Cleaning” (Houston, TX: NACE and Pittsburgh, PA: SSPC).
127. NACE No. 4/SSPC-SP 7 (latest revision), “Brush-Off Blast Cleaning” (Houston, TX: NACE and Pittsburgh, PA: SSPC).
128. ASTM G 62 (latest revision), “Standard Test Methods for Holiday Detection in Pipeline Coatings” (West Conshohocken,
PA: ASTM).
129. NACE SP0274 (latest revision), “High-Voltage Electrical Inspection of Pipeline Coatings” (Houston, TX: NACE).
130. NACE SP0188 (latest revision), “Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates”
(Houston, TX: NACE).
131. NACE SP0169 (latest revision), “Control of External Corrosion on Underground or Submerged Metallic Piping Systems”
(Houston, TX: NACE).
132. D.J. Klopfer, J. Schramuk, “A Sacrificial Anode Retrofit Program for Existing Cast-Iron Distribution Water Mains,” Journal
AWWA 97, 12 (2005): pp. 50-55.
133. A. W. Peabody, R.L. Bianchetti, eds., Control of Pipeline Corrosion, 2
134. J. Morgan, Cathodic Protection, 2
nd
nd
ed. (Houston, TX: NACE, 2001).
ed. (Houston, TX: NACE, 1993), p. 51.
135. M.J. Schiff, B.F. McCollom, “Impressed Current Cathodic Protection of Polyethylene-Encased Ductile Iron Pipe,”
CORROSION/93, paper no. 583 (Houston, TX: NACE, 1993).
136. J. Schramuk, V. Rash, “Cathodic Protection for a New Ductile Iron Water Transmission Main,” MP 44, 10 (2005): p. 20.
137. D. Lindemuth, D. Kroon, “Cathodic Protection of Pipe Encapsulated in Polyethylene Film,” CORROSION 2007, paper no.
40 (Houston, TX: NACE, 2007).
138. NACE SP0185 (latest revision), “Extruded Polyolefin Resin Coating Systems with Soft Adhesives for Underground or
Submerged Pipe” (Houston, TX: NACE).
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139. “Inspection Report—Cathodically Protected Ductile Iron Pipe Encased in Loose Polyethylene Film—Dickinson, ND”
(Birmingham, AL: DIPRA, April 21, 2004).
140. D. Lindemuth, D. Kroon, “Case Histories: Cathodic Protection of Pipe Encapsulated in Polyethylene Film,” MP 65, 1
(2009): p. 63.
141. B. Bradish, M. Szeliga, “Corrosion Control Systems Acceptance and Maintenance Testing for Large Diameter Water
Mains,” presented at the 1994 Annual Conference AWWA Chesapeake Section, Annapolis, MD (Denver, CO: AWWA, 1994).
142. ISO 2531 (latest revision), “Ductile Iron Pipes, Fittings, Accessories and Their Joints for Water or Gas Applications”
(Geneva, Switzerland: ISO).
143. BS EN 545 (latest revision), “Ductile Iron Pipes, Fittings, Accessories and Their Joints for Water Pipelines.
Requirements and Test Methods” (London, England: BSI).
144. BS EN 15189 (latest revision), “Ductile Iron Pipes, Fittings, and Accessories. External Polyurethane Coating for Pipes.
Requirements and Test Methods” (London, England, BSI).
145. BS EN 14901 (latest revision), “Ductile Iron Pipes, Fittings, and Accessories. Epoxy Coating (Heavy Duty) of Ductile Iron
Fittings and Accessories. Requirements and Test Methods” (London, England: BSI).
146. ANSI/AWWA C 116/A 21.16 (latest revision), “Protective Fusion Bonded Epoxy Coating for the Interior and Exterior
Surfaces of Ductile-Iron and Gray-Iron Fittings for Water Supply Service” (Denver, CO: AWWA).
147. NACE Standard RP0394 (latest revision), “Application, Performance, and Quality Control of Plant-Applied, FusionBonded Epoxy External Pipe Coating” (Houston, TX: NACE).
148. BS EN 15542 (latest revision), “Ductile Iron Pipes, Fittings, and Accessories. External Cement Mortar Coating for Pipes.
Requirements and Test Methods” (London, England: BSI).
149. NACE SP0109 (latest revision), “Field Application of Bonded Tape Coatings for External Repair, Rehabilitation, and Weld
Joints on Buried Metal Pipelines” (Houston, TX: NACE).
150. BS EN 14628 (latest revision), “Ductile Iron Pipes, Fittings, and Accessories. External Polyethylene Coating for Pipes.
Requirements and Test Methods” (London, England: BSI).
151. A.G. Fuller, “A Review of Current Knowledge Concerning the Corrosion of Ductile Iron Pipe,” British Cast Iron Research
Association Report, June 1978.
152. E.C. Potter, Closing commentary at European Federation of Corrosion Conference, Vienna, Austria, 1968.
153. S. Nagao, “Corrosion and Corrosion Protection of Underground Pipes,” presented at the International Water Supply
Association, 12th Congress, held October 2-6, 1978 (Kyoto, Japan: International Water Supply Association, 1978).
154. Ductile Iron Pipe Compendium (Nancy, France: Pont-A-Mousson S.A., 1986).
155. J.A. Jakobs, F.W. Hewes, “Underground Corrosion of Water Pipes in Calgary, Canada,” MP 26, 5 (1987): p. 42.
156. “Underground Corrosion of Water Pipes in Canadian Cities: Case: the City of Calgary, Final Report” (Birmingham, AL:
DIPRA, November 1984).
157. B.R. Marchal, J. Mailliard, “Comments on the Article by J.A. Jakobs and F.W. Hewes— Underground Corrosion of Water
Pipes in Calgary, Canada,” Pont-a-Mousson, May 20, 1988.
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Appendix A
Bonded Coatings That Have Been Used
on Ductile-Iron Pipe and/or Fittings
This appendix is intended to provide supplementary information only, although it may contain mandatory or recommending
language in specifications or procedures that are included as examples of those that have been used successfully. Nothing in
this appendix shall be construed as a requirement or recommendation with regard to any future application of this technology.
The various types of bonded coatings that have been used on ductile iron pipe and/or fittings are listed below along with the
NACE, AWWA, BS, and ISO standards where applicable.
142
INTERNATIONAL The international standard for coating of ductile iron pipe, fittings and accessories is covered by ISO 2531.
23
As summarized in the NRC report, this ISO standard provides a list of external coatings that can be supplied depending on the
external conditions and taking into account existing national standards. These coating options include metallic zinc with finishing
layer, zinc-rich paint with finishing layer, thicker metallic zinc with finishing layer, polyethylene sleeving, polyurethane,
polyethylene, fiber cement mortar, adhesive tapes, bituminous paint, and epoxy. This ISO 2531 standard states that when ISO
standards do not exist, these coatings shall comply with national standards or with an agreed technical specification. The NRC
143
report summarizes that BS EN 545
states that specific coatings may be used in different soil conditions with different
corrosiveness ratings. This British standard allows the more robust type of coatings (extruded polyethylene, polyurethane, fiber
cement or adhesive tapes) to be used for all levels of corrosive soils.
Asphaltic Shopcoat—ANSI/AWWA C 151
4
Unless otherwise specified by the customer at the time of manufacturing, a 25 m (1.0 mil) minimum thickness of asphalt cutback
is applied as the standard exterior coating on ductile-iron pipe and fittings. This thin coating is normally for aesthetic purposes only
during aboveground storage. In the past, it has been considered to offer no significant long-term protection against attack by
aggressive soils.
Once applied, the thin asphalt penetrates the microscopic pores on the surface of the ductile-iron pipe and is difficult to remove
completely. For this reason, ductile-iron pipe and fittings that receive a special exterior bonded coating are usually ordered from
the ductile iron pipe manufacturer bare, without exterior coating. Polyethylene encasement is unaffected by the asphalt coating
and is usually applied directly to asphalt-coated pipe as received from the factory.
Polyurethane
Some polyurethanes are formulated to be high-build coatings (i.e. >20 mil, 0.020 in [0.508 mm] thick). They are normally highsolids, two-component coatings that cure quickly to form a hard, yet flexible film. Polyurethane coating of ductile iron is covered by
144
BS EN 15189.
Coal Tar Enamel
Coal tar enamel coatings usually consist of a liquid primer, followed by a hot coat of coal tar enamel and felt or fiberglass wrapper.
This is covered with a single layer of kraft paper for protection during transportation.
Coal-Tar Epoxy
Coal-tar epoxy has been used to protect both the interior and exterior of iron pipe and fittings. Coal-tar epoxies are comprised of
coal tar, filler materials, and epoxy. The specific formulation of coal-tar epoxies varies with manufacturer.
Epoxy
Epoxies include both two-component or fusion bonded epoxy systems. Epoxy coating of ductile iron is covered by BS EN
145
14901.
Metallized Zinc/Asphalt Topcoat
Metallized zinc exterior coatings are supplied on ductile-iron pipe for use outside the U.S. The coating is generally top coated with
thin asphaltic or synthetic resin paint. In corrosive soils, this system is normally used in conjunction with polyethylene
encasement.
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Zinc/Epoxy/Polyurethane
This system is sometimes used for aboveground installations where appearance and gloss retention are factors (e.g., bridge
crossing, pipe on piers, pipe in treatment plants, etc.). It consists of a zinc-rich primer for sacrificial corrosion protection and
undercutting resistance, an epoxy middle coat for corrosion protection, and a thin topcoat of polyurethane for gloss retention and
weathering resistance.
Fusion-Bonded Epoxy (FBE)
Fusion-bonded epoxies are routinely used for steel pipe, but they are not normally used for ductile-iron pipe because of issues
relative to surface roughness, holidays, and application methods. FBE is frequently applied to 16 in (406 mm) and smaller
146
smooth, sand-cast, ductile-iron surfaces such as those found on fittings. This is covered in AWWA C 116/A 21.16.
NACE
147
Standard RP0394 covers the use of this type of coating for various substrates including water pipelines, which can include
ductile iron.
Fusion-Bonded Polyolefin Coatings
Thermoplastic powder coating is based on an alloy of acid-modified polyolefins developed to achieve long-term adhesion to
85
ductile-iron and steel substrates without an adhesive primer.
Cementitious Coatings
Cementitious external coatings have been supplied on ductile-iron pipe. Modified cement mortar is reinforced using fibers or
148
other material and then sprayed onto the pipe surface. Fiber cement coating is covered by BS EN 15542.
Tape Systems
General
Several tape coating manufacturers have developed specifications for application of tightly bonded coatings for ductile-iron pipe
without the removal of the oxide layer. Specific coating systems are listed below.
Cold Applied
Cold-applied single and multi-layered tape systems consist of a liquid primer, an inner layer of tape for corrosion protection, and
one or more outer layer(s) of tape for mechanical protection. These tape-wrap systems are generally not as effective on fittings
because of the irregular shapes. NACE SP0109 covers the use of this type of coating for various substrates including water
149
pipelines and specifically mentions ductile iron and cast iron.
Petrolatum
Pliable wax-tape/petrolatum tape systems are surface and moisture tolerant and a moldable coating alternative for straight pipe
114
and irregular-shaped fittings. AWWA C 217 covers the use of this type of coating for steel fittings, while NACE Standard
115
RP0375
covers the use of this type of petrolatum wax tape coating for underground metallic pipe, fittings, and valves for
various substrates, which sometimes include ductile iron.
Extruded Polyolefin/Polyethylene Systems
Extruded polyolefin/polyethylene coatings normally incorporate an extruded butyl rubber adhesive to bond polyethylene to the
138
pipe. This system is not available for fittings. NACE SP0185 covers the use of this type of coating for various substrates
150
including water pipelines which can include ductile iron. Extruded polyethylene coating is covered by BS EN 14628.
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Appendix B
Considerations for Polyethylene-Encased
Pipelines for Effectively Monitoring and Preserving
Corrosion Control Options
This appendix is intended to provide supplementary information only, although it may contain mandatory or recommending
language in specifications or procedures that are included as examples of those that have been used successfully. Nothing in
this appendix shall be construed as a requirement or recommendation with regard to any future application of this technology.
81
The following are some of examples of corrosion control considerations for polyethylene-encased ductile iron.

Use of wax tape type coating of fittings to protect the fitting and minimize tears to the polyethylene encasement,
 Tape the joint ends with two complete wraps of appropriate polyethylene tape (AWWA 105), continuously seal the
seams, and overlap the tube form encasement and secure in place with tape wraps at 2.0 ft (0.61 m) increments in a
spiral winding.
52
 Always bond the joints for electrical continuity to allow future monitoring and to allow application of CP if required.
Only joint bonds with exothermic type welds can be relied on for permanent electrical joint continuity. Bond plates might
be recommended on polymeric lined pipe (polyurethanes, epoxies) to minimize damage to the internal lining from the joint
bond exothermic welds.

Apply CP (if required).
 Use select backfill to minimize possible damage to the polyethylene encasement and reduce the corrosiveness of the
environment.

Wrap the appurtenances including the tees, taps, valves, and copper services.

Special care should taken at protrusions, such as bolting, specialty restrained joints, etc.

Electrical isolation of services and laterals.
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Appendix C
Polyethylene Encasement Documented
Research and Field Applications
This appendix is intended to provide supplementary information only, although it may contain mandatory or recommending
language in specifications or procedures that are included as examples of those that have been used successfully. Nothing in
this appendix shall be construed as a requirement or recommendation with regard to any future application of this technology.
UNITED STATES In the U.S., polyethylene encasement of iron pipe is covered by two national standards: ANSI/AWWA C 105/A
52
104
21.5 and ASTM A674.
The AWWA C 105/ANSI A21.5 standard provides typical material and installation procedures for
polyethylene encasement of ductile-iron pipe. There are three methods of installing polyethylene encasement: two methods (A
and B) use polyethylene tubes, and one method (C) uses polyethylene sheets. Method A uses one length of polyethylene tube,
overlapped at the joints, for each length of pipe. Because installation is faster and easier, most utilities and contractors choose
some form of Method A. Method B uses a length of polyethylene tube for the barrel of the pipe and a separate length of
polyethylene tube or sheet for the joint. In Method C, each section of pipe is completely wrapped with a flat polyethylene sheet.
For installations below the water table or in areas subject to tidal actions, ANSI/AWWA C 105/A 21.5 discusses the typical use of
tube form polyethylene with both ends thoroughly sealed with adhesive tape or plastic tie straps at the joint overlap. Also, the
standard discusses placing circumferential wraps of tape at 2 ft (0.61 m) intervals along the barrel of the pipe to minimize the
space between the polyethylene and the pipe.
The most extensive research and field investigations regarding corrosion protection by polyethylene encasement have been
conducted by the DIPRA. Since 1951, DIPRA has been conducting research on polyethylene encasement for iron pipe in various
environments with excellent results. DIPRA has also reported on favorable inspections in operating systems throughout the U.S.
38
A partial list of 69 such inspections conducted from 1963 to 1988 is found in a paper by T.F. Stroud (to date, the list is over 100).
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Horton reports on 22 exhumations of polyethylene-encased iron pipe that were documented by an independent international
engineering consulting firm, and he states, “The pipe at each of the 22 exhumations was found to be in excellent or very good
condition and no significant corrosion attack was evident. In addition, the polyethylene film (including a 28 year old sample)
appeared to be unaffected and was demonstrated to meet the requirements for new polyethylene as specified in ANSI/AWWA C
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105/A 21.5.”
In 1964, Wagner reported, “The use of a loose wrap of polyethylene film to protect cast-iron pipe in highly corrosive environments
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has been under test for 10 years and the results to date have shown it to be highly effective.”
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More recently, Szeliga reported on the evaluation of the effectiveness of polyethylene encasement based on a review of
technical papers for 1987 through 2007 that included hundreds of examples of failures of polyethylene-encased pipe. He states,
“polyethylene encasement is not adequate for corrosion control of ductile iron pipe in corrosive soils if the risk of failure is not
acceptable.” He further states, “CP does not prevent corrosion under intact polyethylene encasement.”
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UNITED KINGDOM In the United Kingdom, polyethylene encasement is covered by BS 6076.
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Collins, with the British Cast Iron Research Association, reported in 1982: “Since its first use in the United Kingdom in 1964,
polyethylene sleeving has [often] been [. . .] recommended by [a major company] for the protection of pipelines laid in aggressive
soils, and the present extent of its use is very considerable [. . .] In view of the very considerable amount of polyethylene-sleeved
pipe laid, for the most part in aggressive soils, the number of failures that have so far been reported (two in Britain and one in
Germany, all [because of] improper installation) is very small indeed. Since the mechanisms of these failures are now well
understood and [able to be guarded against], there is a good reason to expect that this record of success [to] be maintained in the
future.”
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Fuller, also with the British Cast Iron Research Association, showed a comparison in 1978 of polyethylene-sleeved pipe and
unsleeved pipe in three soil environments and concluded that polyethylene sleeving is an effective means of reducing corrosion
attack on buried pipe in even the most highly aggressive environments.
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Other documentation in the United Kingdom includes that of the Water Research Centre
(WRc), which states in 1981,
“Consideration [is typically] given to using polyethylene sleeving on all buried iron pipes and fittings as a matter of course thereby
obviating the need to assess soil corrosiveness so as to decide which parts of the line require protection.” Documentation of the
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British Gas Engineering Research Station in 1974 states, “On technical grounds, [. . .] loose [polyethylene] sleeving be [is
(21)
British Cast Iron Research Association, Alvechurch, Birmingham B48 7QB, UK.
Water Research Centre (WRc), Frankland Rd., Blagrove, Swindon, Wiltshire, SN5 8YF.
(23)
British Gas Engineering Research Station, UK. Station Road, Killingworth, North Tyneside, U.K.
(22)
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NACE International
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generally] used to protect all iron mains laid in underground environments.” Whitchurch and Hayton reported in 1968, “The use
of poly[ethylene] sleeving has [typically] proved to be a cheap and efficient means of providing protection for iron pipes buried in
aggressive soils.”
Whitchurch and Hayton also reported that small punctures, tears, or holidays in the film did not produce accelerated corrosion,
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and, if small enough to prevent direct contact between the pipe and the soil, had little deleterious effect. Dr. E.C. Potter,
summing up after the international conference in which Whitchurch’s and Hayton’s paper on polyethylene sleeving was
presented, states in 1968: “This technique seems to disobey the rules, particularly concerning its reported success even when
perforated. Thus, it appears that the rules are wrong and that some rethinking is needed. One must surely concede that loose
polyethylene sleeving as a protective method lacks elegance [. . .] Nevertheless, if one is in an impecunious situation. . . it is
reassuring to know there is a handy means to avoid the worst excesses of pipeline corrosion.”
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JAPAN In Japan, polyethylene encasement is covered by the standard JDPA Z 2005. Documentation in Japan includes a
publication by a major company that describes the results of tests using the polyethylene sleeve method on actual pipelines in
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1986 and concluded, “The polyethylene sleeve method is effective against highly corrosive soil conditions.”
Also, Nagao
reported on the effectiveness of polyethylene encasement in protecting ductile-iron pipe in a corrosion test site at Amagosaki City,
Japan in 1978.
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AUSTRALIA In Australia, polyethylene encasement is covered by the standards AS 3680 and AS 3681.
Ferguson and
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Nicholas reported test results of aggressive soils in Australia beginning in 1966. Exhumation of sections of pipes starting in
.
1979 showed that during burial intervals of 6 to 13 years in 300 to 3,000 Ω cm soils, in some cases with sand backfill, very little
corrosion was found. Unprotected pipes from the same sites were replaced in less than 10 years. The authors conclude in 1984,
“Thirty years of experience has confirmed that loose polyethylene sleeving is the most cost-effective method of protecting castiron pipes in all soil conditions.”
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FRANCE The Ductile-Iron Pipe Compendium stated in 1986: “A large number of polyethylene sleeved cast- and ductile-iron
pipelines have been inspected in several countries, especially in the U.S., in the United Kingdom, and in France. In all cases of
severely corrosive soils, good protection was evidenced: the pipes were intact or exhibited only superficial corrosion damage.”
CANADA Canadian experience with polyethylene-encased ductile-iron pipe has not been entirely satisfactory. In an effort to
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better define the extent and mechanisms of underground corrosion for various pipe types, CANMET
commissioned a 1983
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study of pipes in Calgary, Canada. That study did not detect that pipes protected with polyethylene encasement corroded at a
155
lower rate than those which were placed in the soil without a wrap. Jacobs and Hewes state in 1987 that “the ineffectiveness of
PE wrap observed in present and earlier studies contradicts the information published.”
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In response to the Calgary study, DIPRA issued a technical review of the study in 1984 stating that a thorough investigation of
polyethylene encasement as a capable protective means had been avoided and the study had failed to explain the real reasons
for the corrosion failures in Calgary. Also in response to the Calgary study, a review was published in 1988 by Marchal and
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Mailliard, titled “Comments on the Article by J.A. Jakobs and F.W. Hewes,” which states the following: “The [Calgary] study
summarized in this article is based on “statistics” of little reliability analyzed in a very debatable manner. Furthermore, the real
causes of the corrosion: Fe/Cu galvanic couples aggravated by electrical bonding and inadequate use of PE sleeving, particularly
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on ductile iron, have not been seriously analyzed.”
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Brander indicated in 2001 that Calgary had moved away from using encased (wrapped) ductile-iron pipe, having concluded that
they were averaging only a 30% reduction in corrosion rate, or corrosion break rate, with polyethylene-encased ductile iron pipe
compared to bare ductile iron pipe, where no nonisolated copper services were involved.
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In a separate field study of 14 to 16 year old polyethylene-encased ductile-iron pipe in Vancouver, B.C., Spickelmire reported in
2007 that three corrosion penetrations were found that were still holding up to 600 psi (4.1 MPa) pressure as a result of the
cement lining and graphization. The corrosion consultant was not able to definitively ascertain that the corroded areas were
associated with damaged areas in the polyethylene, and felt that some corroded areas were under undamaged polyethylene.
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INTERNATIONAL The international standard for polyethylene sleeving, ISO 8180,
was adopted in 1985. As mentioned
previously, in Europe, the primary external coating for corrosion control since the 1960s has been metallic zinc spray with a
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bitumen topcoat. This method of protection, covered by ISO Standard 8179,
is used by most European iron pipe
manufacturers and the WRc for mildly and moderately corrosive soils. In more corrosive soils, the metallic zinc coating is typically
supplemented by polyethylene encasement or other type of topcoats. Other protective coating systems utilized by European pipe
manufacturers, often on top of zinc, include, but are not limited to, extruded polyethylene, polyurethane, tape, and reinforced
cementitious coatings. Zinc-aluminum metallic spray with epoxy topcoat, with and without polyethylene encasement, has also
been used.
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Canadian Centre for Mineral and Energy Technology (CANMET), 1 Haanel Dr., Ottawa, Ontario, Canada K1A 1M1.
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