ASTM G218-19

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G218 − 19
Standard Guide for
External Corrosion Protection of Ductile Iron Pipe Utilizing
Polyethylene Encasement Supplemented by Cathodic
Protection
This standard is issued under the fixed designation G218; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 The most recent version of the following documents
1.1 This guide will discuss standard practices which have
should be consulted as references by those using this guide:
been successfully utilized in the field for over 35 years to
provide external corrosion protection of polyethylene encased 2.2 ASTM Standards:
ductile iron pipe supplemented with cathodic protection (CP).
A674 Practice for Polyethylene Encasement for Ductile Iron
This guide may also be used for ductile iron fittings, valves, Pipe for Water or Other Liquids
and other appurtenances specific to ductile iron pipe systems. A746 Specification for Ductile Iron Gravity Sewer Pipe
D149 Test Method for Dielectric Breakdown Voltage and
Casehistoriesandpublicationsreportingontheuseofcathodic
DielectricStrengthofSolidElectricalInsulatingMaterials
protection to supplement polyethylene encasement are in-
at Commercial Power Frequencies
cluded as an Appendix in this guide.
D882 Test Method for Tensile Properties of Thin Plastic
1.2 Other external corrosion control methods which have
Sheeting
been used for ductile iron pipe include, but are not limited to:
D1709 Test Methods for Impact Resistance of Plastic Film
cathodic protection, metallic zinc coatings, bonded dielectric
by the Free-Falling Dart Method
coatings, dielectric coatings with cathodic protection, and
D1922 Test Method for Propagation Tear Resistance of
trench improvement. Detailed information on these methods of
Plastic Film and Thin Sheeting by Pendulum Method
protection are available from other sources and are beyond the
D4976 Specification for Polyethylene Plastics Molding and
scope of this guide.
Extrusion Materials
G51 Test Method for Measuring pH of Soil for Use in
1.3 The values stated in inch-pound units are to be regarded
Corrosion Testing
as standard. The values given in parentheses are mathematical
G57 Test Method for Field Measurement of Soil Resistivity
conversions to SI units that are provided for information only
Using the Wenner Four-Electrode Method
and are not considered standard.
G97 Test Method for Laboratory Evaluation of Magnesium
1.4 This standard does not purport to address all of the
SacrificialAnode Test Specimens for UndergroundAppli-
safety concerns, if any, associated with its use. It is the
cations
responsibility of the user of this standard to establish appro-
G187 Test Method for Measurement of Soil Resistivity
priate safety, health, and environmental practices and deter- Using the Two-Electrode Soil Box Method
mine the applicability of regulatory limitations prior to use. G193 Terminology and Acronyms Relating to Corrosion
G200 TestMethodforMeasurementofOxidation-Reduction
1.5 This international standard was developed in accor-
Potential (ORP) of Soil
dance with internationally recognized principles on standard-
G215 Guide for Electrode Potential Measurement
ization established in the Decision on Principles for the
2.3 ANSI/AWWA Standards:
Development of International Standards, Guides and Recom-
ANSI/AWWA C105/A21.5 Polyethylene Encasement for
mendations issued by the World Trade Organization Technical
Ductile-Iron Pipe Systems
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Metals and is the direct responsibility of Subcommittee G01.10 on Corrosion in Standards volume information, refer to the standard’s Document Summary page on
Soils. the ASTM website.
Current edition approved Oct. 1, 2019. Published October 2019. DOI: 10.1520/ Available fromAmerican Water WorksAssociation (AWWA), 6666 W. Quincy
G0218-19. Ave., Denver, CO 80235, http://www.awwa.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G218 − 19
ANSI/AWWAC110/A21.10 Ductile-Iron and Gray-Iron Fit- polyethylene raw material with additives designed to control
tings generalized corrosion and microbiologically induced corrosion
ANSI/AWWA C111/A21.11 Rubber Gasket Joints for Duc- (MIC).
tile Iron Pressure Pipe and Fittings
3.1.7 ER probe—an ER (electrical resistance) corrosion
ANSI/AWWA C151/A21.51 Ductile-Iron Pipe, Centrifu-
measurement probe that has been adapted for use in soil-side
gally Cast, for Water
applications (also known as SCP – soil corrosion probe).
ANSI/AWWA C600 Installation of Ductile-Iron Mains and
3.1.8 free-corrosion coupon (also known as native
Their Appurtenances
coupon)—a coupon that is immersed in the soil or aqueous
2.4 NACE International Standards:
environment adjacent to the structure but is not connected to
SP0169 Control of External Corrosion on Underground or
the structure.
Submerged Metallic Piping Systems
3.1.9 high-density, cross-laminated (HDCL) polyethylene
SP0104 The Use of Coupons for Cathodic Protection Moni-
film—film extruded from virgin high-density polyethylene raw
toring Applications
material, which is then molecularly oriented by stretching; the
TM0497 Measurement Techniques Related to Criteria for
finalproductisthenformedbytwosingle-plylayersofthefilm
Cathodic Protection on Underground or Submerged Me-
thatarethenlaminatedtogetherwiththeirorientationsat90°to
tallic Piping Systems
one another using molten, high-density, virgin resin.
Publication 05107 Report on Corrosion Probes in Soil or
3.1.10 linear low-density (LLD) polyethylene film—film ex-
Concrete
truded from virgin linear low-density polyethylene raw mate-
Publication 10A292 Corrosion and Corrosion Control for
rial.
Buried Cast- and Ductile-Iron Pipe
3.1.11 LPR probe—a linear polarization resistance (LPR)
2.5 ISO Standards:
ISO 8180 Ductile iron pipelines – Polyethylene sleeving for probe which determines the corrosion rate on its metal elec-
trode or electrodes by measuring the polarization resistance
site application
ISO 8179 Part 1 Ductile iron pipes, fittings, accessories, and under the application of a small applied potential, typically 10
to 20 mV, above the free corroding potential of the electrode or
their joints – External zinc-based coating – Part 1: Metal-
lic zinc with finishing layer electrodes; the probe elements are generally made of the same
2.6 Various additional publication references related to spe- or similar material as the structure to be monitored.
cific topics discussed in this guide are included as Appendix
3.1.12 polyethylene encasement—polyethylene material, in
X1.
tube or sheet form, that is used to encase ductile iron pipe and
fittings for the purposes of corrosion protection or stray current
3. Terminology
mitigation, or both.
3.1 Definitions of Terms Specific to This Standard:
3.1.12.1 Discussion—See Section 6 of this guide.
3.1.1 100 mV criterion—a specific degree of cathodic po-
3.1.13 shopcoat—the standard external coating for ductile
larization between the pipe surface and a stable reference
ironpipeasdescribedinANSI/AWWAC151/A21.5;itconsists
electrode, both in contact with the electrolyte; the degree of
of a painted coating approximately 1 mil (0.025 mm) thick
polarization can be measured during formation or decay.
which is normally applied to the outside of ductile iron pipe
3.1.2 –850 mV criterion—the degree of polarized potential and fittings.
measured relative to a saturated copper/copper sulfate refer- 3.1.13.1 Discussion—See 5.4 of this guide.
ence electrode, which is used to verify cathodic protection has
3.2 General terminology and acronyms relating to corrosion
been achieved.
are defined in Terminology G193.
3.1.3 annealing oxide—a layer of tenacious and complex
oxides of iron and silicon formed on ductile iron pipe during
4. Significance and Use
the annealing process.
4.1 Thisguideprovidesbasicinformationontheapplication
3.1.3.1 Discussion—See 5.3 of this guide.
ofcathodicprotectiontopolyethyleneencasedductileironpipe
3.1.4 cathodic protection coupon—a metal sample repre-
for engineers, owners, water companies, corrosion consultants,
senting the pipeline at the site, used for cathodic protection
ductile iron (DI) pipe manufacturers and others who have an
testing, and having a chemical composition approximately the
interest in providing underground corrosion protection to
same as the pipe.
ductile iron pipe.
3.1.5 ductile iron pipe—see Section 5 of this guide.
4.2 There are many publications, standards, recommended
3.1.6 enhanced linear low density (ELLD) polyethylene practices, and specifications for the application of coatings and
encasement film—film extruded from virgin linear low density cathodic protection to steel pipe. However, the metallurgy,
chemistry, physical properties, surface composition and
texture, coating requirements and electrical continuity of stan-
AvailablefromNACEInternational(NACE),15835ParkTenPl.,Houston,TX
dardproductionductileironpipearesignificantlydifferentthan
77084, http://www.nace.org.
those of steel pipe, and coating and cathodic protection
Available from International Organization for Standardization (ISO), ISO
specifications written specifically for steel pipe may not be
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Geneva, Switzerland, http://www.iso.org. directly applicable to ductile iron pipe. The latest revision of a
G218 − 19
commonly accepted cathodic protection specification (NACE of the pipe resists introduction of chlorides and other com-
SP0169) states the following in the forward: “This standard pounds from contacting this protective oxide layer on the pipe
does not include corrosion control methods based on injection surface.
of chemicals into the environment, on the use of electrically
5.4 Shopcoat—An exterior coating approximately 1 mil
conductivecoatings,orontheuseofnon-adheredpolyethylene
(0.025 mm) thick is normally applied on the outside of ductile
encasement (refer to NACE Publication 10A292).” It is the
ironpipeandfittings.AWWAandASTMspecificationscallfor
purposeofthisguidetosummarizepublications,casehistories,
the finished coating to be continuous, smooth, and strongly
and studies which are available regarding cathodic protection
adherent to the pipe. While primarily applied for esthetic
installations of polyethylene encased ductile iron pipe to give
purposes, studies have shown asphaltic and other shopcoats do
the reader guidance on this unique method of protection.
offer limited corrosion protection in conjunction with the
annealing oxide and have been shown to reduce current
4.3 This guide may be utilized with galvanic or impressed
requirements on CP systems (X1.2, X1.18). Shopcoats have
current cathodic protection.
also been shown to be compatible with metallic zinc coatings
4.4 This guide is written specifically for ductile iron pipe
onductileironpipe,andhavebeenreportedtoimprovethelife
and does not apply to any other type of piping material. It may
and performance of these coatings (X1.3).
also be used for ductile iron fittings, valves, and appurtenances
5.5 Metallic Zinc Coating—Prior to the application of the
specific to ductile iron piping systems.
shopcoat, a metallic zinc coating is sometimes applied to the
4.5 This guide references requirements for vendor provided
exteriorofductileironpipeforexternalcorrosionprotection.It
information which should be requested and reviewed by the
is normally applied in accordance with ISO 8179 Part 1
user.
utilizing arc spray or flame spray methods. The metallic zinc
coating is typically applied on top of the inherent annealing
5. Ductile Iron Pipe (DIP)
oxide layer on ductile iron pipe. In severely corrosive soils,
metallic zinc coating is normally utilized in conjunction with
5.1 Metallurgy—Ductile iron is a novel ferrous product
polyethylene encasement, or an enhanced polyethylene
containing approximately 93 % iron (Fe), with sufficient car-
encasement, and may be used with or without additional
bon (C) and silicon (Si) to qualify as a eutectiferous material.
external cathodic protection (X1.5).
Ithasbeentreatedintheliquidstatesoastocausethemajority
of the carbon to occur as substantially equiaxed particles
6. Polyethylene Encasement
appearingasspheroidsornodulesintheas-caststructureofthe
6.1 Description and Properties:
pipe. Ductile irons can be viewed as a family of alloys which
6.1.1 General Description—Polyethylene encasement has
combine the principal advantages of gray cast iron with the
been the primary asset preservation method utilized for gray
engineering advantages of steel; that is, good fluidity,
castability, machinability, great strength, toughness, and duc- and ductile iron pipe since 1958. In the 60+ years of use, over
300 million feet of iron pipe have been installed with polyeth-
tility. Ductile iron pipe is typically specified to meet the
minimum requirements of ANSI/AWWA C151/A21.51 and ylene encasement and over 300 miles of encased pipe installed
with supplemental cathodic protection (X1.1, X1.5).
Specification A746.
6.1.2 Mechanisms of Protection:
5.2 Joints—Joints are the device by which an essentially
6.1.2.1 Polyethylene encasement is an engineered corrosion
leak-free connection is produced between two lengths of
control system for ductile iron pipelines. The film is manufac-
ductile iron pipe. The joint may be mechanical, push-on, or
tured using specially designed virgin material with specific
restrained, and is typically specified to meet minimum require-
minimumthicknessandmechanicalrequirements,forexample,
ments of ANSI/AWWA C111/A21.11. Bolts used for securing
tensilestrength,elongation,propagationtearresistance,impact
mechanical joints are also typically specified to conform to the
resistance, and dielectric strength, which are specified in
requirementsofthesamestandard,andpipewithothertypesof
national and international standards. In those standards, re-
joints specified to comply with the joint dimensions and
cycled polyethylene is specifically proscribed from use in the
weights agreed upon at the time of purchase.
manufacture of the film. Protection is achieved by encasing the
5.3 AnnealingOxide—Modernproductionpracticesforduc- pipe with a tube or sheet of loose polyethylene at the trench
tile iron pipe include an annealing heat treatment to allow the during the pipe installation process. Once installed, polyethyl-
materialtoachievetheoptimumbalanceofmaterialproperties. ene encasement acts as an unbonded film, which prevents
When iron or steel are heat treated in air an oxide film is direct contact of the pipe with the corrosive soil. It also limits
formed. Unlike mill scale on carbon steel which flakes away, the electrolyte available to support corrosion activity to the
the annealing oxide on ductile iron pipe exhibits a tenacious moisture that might be present in the thin annular space
layer that adheres to the base metal due to the presence of betweenthepipeandwrap.Althoughpolyethyleneencasement
silicon in the oxide structure. Under burial conditions, pores in isnotawatertightsystem,intypicalinstallations,theweightof
the annealing oxide film become plugged by relatively in- the earth backfill and surrounding soil after installation nor-
soluble corrosion products. This oxide film protects the under- mally prevents any significant exchange of groundwater be-
lying metal as long as the oxide layer is protected from the tween the wrap and the pipe (X1.1). Although some ground-
introductionofotherspecies,likechlorides,whichcanresultin water will typically seep beneath the wrap, the water’s
partialdissolutionoftheoxide.Intactpolyethyleneencasement corrosive characteristics are depleted by initial corrosion
G218 − 19
reactions, usually reduction of oxygen in the presence of water 6.2.2 High-density Cross Laminated (LLD) Polyethylene
to form hydroxyl ions. In areas of fluctuating water table or Film—Polyethylene film described in Specification D4976 as
tidal action, additional installation procedures are described in
in 6.2.1 except with density of 0.940 to 0.960 g/cm .
ASTM and AWWA standards to minimize water exchange
6.2.3 Enhanced Linear Low-density Polyethylene Film—
under the wrap.
Linear low density polyethylene film as described in 6.2.1
6.1.2.2 Once the available dissolved oxygen in the moisture
utilizesadditivesdesignedtocontrolgeneralizedcorrosionand
or groundwater between the pipe and the wrap has been
microbiologically induced corrosion (MIC). These additives
consumed,furthercorrosionactivityiseffectivelyhalted,anda
utilize a specifically engineered co-extruded polyethylene ma-
uniform environment created around the pipe. This, in turn,
trix as the carrier.
helps eliminate the formation of localized corrosion cells that
typically occur on the surface of a pipe exposed to a non-
7. Inspection, Testing, and Verification of Polyethylene
homogeneous soil environment.Additionally, the polyethylene
Encasement
film provides an essentially impermeable barrier that restricts
7.1 Materials:
the access of additional oxygen to the pipe surface and the
diffusion of corrosion products away from the pipe surface 7.1.1 Polyethylene Film—Only virgin polymers meeting the
(X1.9). The film also has a high dielectric strength that minimum properties described in Practice A674, Table 1 for
mitigates the pick-up of stray electrical currents and minimizes
linear-low density polyethylene film, or Table 2 for high-
currentrequiredforcathodicprotectionapplications(X1.7).To
density cross laminated polyethylene film, are considered to be
summarize,polyethyleneencasementisolatesthepipefromthe
compliant with this guide. These properties are summarized in
soil and replaces a corrosive non-homogeneous environment
6.2 of this guide. Virgin polyethylene polymers are critical as
(soil) with a non-corrosive homogeneous environment (passi-
some non-virgin polymers or films containing post-consumer
vated water) (X1.8, X1.9).
waste products (that is, recycle polyethylene) can contain
6.1.2.3 To enhance corrosion protection of linear low den-
deleterious materials such as biodegradable elements, binders,
sity polyethylene encasement, incorporation of an anti-
starches, and other components which can affect film
microbial and a corrosion inhibitor into the film at the time of
properties, cause deterioration with time, or serve as food
manufacture can be considered as an improvement to tradi-
sources for bacteria associated with MIC, or combinations
tionalpolyethyleneencasement.Theanti-microbialisdesigned
thereof. Non-compliant polyethylene films may not only de-
to control microbiologically induced corrosion (MIC) which
grade with time, but generally do not meet all the minimum
mayoccurinsomeenvironments,andthecorrosioninhibitoris
physical requirements for new film and are difficult to install
designed to control the initial corrosion rate until the deoxy-
without significant damage.
genation process takes place under the film. This material is
7.1.1.1 Quality Control and Inspection—Practice A674 re-
commercially available and is described in 6.2.3.
quires the manufacturer of polyethylene film for corrosion
6.1.3 Polyethylene Encasement with Cathodic Protection—
protection encasement of ductile iron pipe systems to have a
Polyethylene encasement has been used successfully in con-
documented Quality Control System or a current compliance
junction with cathodic protection and this combination is
certificate from an accredited QualityAuditing organization to
discussed in Section 9 (X1.1, X1.2, X1.4, X1.5, X1.6, X1.7,
assure that it complies with all requirements of the standard.
X1.8, X1.10, X1.11, X1.12, X1.13, X1.14, X1.16, X1.17).The
7.1.1.2 Manufacturer’s Statement—Practice A674 requires
primary purpose of cathodic protection is to provide protection
the film manufacturer, the film distributor, or both, to maintain
to the pipe surface at areas of unrepaired damage to the
accessible quality records for a minimum period of one year
encasement. Polyethylene encasement with an anti-microbial
from date of manufacture. In lieu of the above records, the
has also been used in conjunction with cathodic protection to
manufacturer may elect to test a customer selected film sample
addressMICconcernsatareasundertheencasementwherethe
provided that proof of manufacturer and the date of manufac-
cathodic protection currents may not reach (X1.4, X1.5,
ture (DOM) are verifiable to the sample.
X1.16). As both standard polyethylene and enhanced polyeth-
7.1.1.3 Freedom from Defects—Practice A674 requires the
ylene films meet the dielectric requirements of Practice A674,
polyethylene film to be manufactured and used in accordance
cathodic protection design and operation requirements are
with the standard, not be made from recycled materials, and to
typically the same for both types of film.
be clean, sound, and without defects.
6.2 Physical Properties—Physical properties and test meth-
7.2 Installation – Polyethylene Encasement Installation—
ods are described in detail in Practice A674. They include
thickness, tensile strength (machine and transverse direction), Installation practices are described in Practice A674. Failure to
elongation (Test Method D882), dielectric strength (Test follow these installation practices can significantly limit the
Method D149), impact resistance (Test Methods D1709), and effectiveness of the installed polyethylene encasement system.
propagation tear resistance (Test Method D1922).
Enhanced LLD Polyethylene Encasement installation practice
6.2.1 Linear Low-Density (LLD) Polyethylene Film— per this guide encompasses all of the practice defined in
Practice A674 and should include manufacturers defined in-
PolyethylenefilmdescribedinSpecificationD4976iscategori-
cally described as Group 2 (linear) with a density of 0.910 to stallation practice as well. Recommended installation practices
3 15
0.925 g/cm and dielectric strength, volume resistivity of 10 are also described in ANSI/AWWA C105/A21.15 and ANSI/
ohm-cm, minimum. AWWA C600.
G218 − 19
8. Cathodic Protection tection specialist. During design of the CPsystem, it should be
recognized that properly installed, undamaged polyethylene
8.1 Description—Cathodic protection is an electrochemical
encasement shields the ductile iron pipe from cathodic protec-
technique used to reduce the corrosion rate of a metal surface
tion currents. The primary purpose of applying cathodic
by making it the cathode of an electrochemical cell. When a
protection to polyethylene encased ductile iron pipe is to
metallic structure, such as ductile iron piping, comes in contact
provide cathodic protection to damaged areas of the encase-
with an electrolyte, through burial or other means, anodic and
ment.
cathodic areas may form at the metallic surface exposed to the
electrolyte,whichcreateslocalelectrochemicalcells.Atanodic
9. Need for Polyethylene Encasement with Cathodic
areas,currentflowingfromthestructurethroughtheelectrolyte
Protection
causes corrosion. At cathodic areas, current flowing from the
soiltothemetallicsurfacecausesasignificantdropofthelocal
9.1 Description/Discussion—The appendix of Practice
corrosion rate. Therefore, cathodic protection can make a
A674 includes a detailed description of soil survey tests,
structure cathodic by forcing the current to flow through the
observations, and interpretations used to determine if polyeth-
electrolyte, from an external anodic site to every exposed areas
ylene encasement is recommended. In addition to these areas,
of this structure. CP can be used in conjunction with coatings
some installations may need polyethylene encasement supple-
or wrappings in order to minimize to exposed area of a pipe,
mented with cathodic protection. These include but are not
therefore reducing the total current required to achieve ad-
limited to: (1) installations where soils are corrosive and there
equate polarization of the structure. Cathodic protection sys-
isaconcernthatareasofdamagetotheencasementmaynotbe
tems can be subcategorized into two distinct techniques: (1)
repaired, (2) areas of high density stray current where stray
galvanic anode CP systems, and (2) impressed current CP
current mitigation is needed, and (3) “uniquely severe” soils as
systems.
described in Practice A674.
8.2 Galvanic Anode CP Systems—In galvanic anode CP
9.2 Site Assessment—There are many factors which must be
systems, current is generated by connecting to the structure a
consideredwhenevaluatingthepotentialforexternalcorrosion
less noble (or more active) metal. The driving voltage (differ-
duringasiteassessment.Someofthesefactorsarediscussedin
ence of potential between the anode and the structure) depends
the following sub-sections. Testing should only be accom-
on the nature of the anode. Typical materials used for galvanic
plished by qualified personnel who are experienced in soil
anodes underground are magnesium and zinc. Aluminum
analysis and evaluation of conditions potentially corrosive to
anodes have sometimes been used for special environments
ductile iron pipe.
such as salt water.
9.2.1 Soils—The most common tests normally conducted to
8.2.1 Galvanic Anodes—Galvanic anodes for use with poly-
evaluate soil corrosivity include resistivity (Test Methods G57
ethylene encasement are typically recommended to be of
and G187), oxidation-reduction potential (Test Method G200),
quality material and to comply with all design requirements
pH (Test Method G51), presence of sulfides/sulfates, presence
which include, but not be limited to composition, electrode
of chlorides, moisture content, and presence of corrosion
(oxidation potential), and electrical charge (ampere hours)
related bacteria.
obtained per unit mass of specimen consumed. Test Method
9.2.2 Stray Current—Sources of stray electrical currents
G97 may be used to verify magnesium anode properties.
include but are not limited to: cathodic protection systems,
8.3 Impressed Current CP Systems—In impressed current
cathodically protected pipelines, electric railways, welding
CP systems, the structure is connected to a more noble metal,
equipment, direct current transmission systems, and mine
and the current is forced to circulate from the anode to the
transportation equipment. Normally, the amount of stray cur-
cathode(intheelectrolyte)byanexternalpowersourcesuchas
rent influence from cathodic protection systems is insignificant
a transformer rectifier or batteries. The driving voltage there-
for galvanic CP systems but can be significant for impressed
fore depends on the power source used and can easily be
current systems. Analysis and mitigation of stray current
adjusted. Many different materials can be used as impressed
environments should be conducted by a trained and certified
current anodes such as high silicon cast iron, graphite, mixed
professional engineer, NACE corrosion specialist, or NACE
metal oxide, platinum, etc.
cathodic protection specialist.
8.4 Accepted Criteria—Accepted cathodic protection crite-
9.2.3 Environmental Conditions—Certainsoilsandenviron-
ria utilized on regulated pipelines are discussed in Section 10.
mental conditions are known to be potentially corrosive to iron
Although ductile iron pipe are typically not considered for
pipe based on experience and thus do not require evaluation.
regulated pipelines such as oil and gas lines, much of the same
These include but are not limited to: coal, cinders, muck, peat,
criteria for verifying adequate cathodic protection has been
mine wastes, and landfill areas high in foreign materials.
utilized (X1.2, X1.4, X1.5, X1.6, X1.8, X1.10, X1.11, X1.12,
9.2.4 Likelihood of Future Changing Conditions over Pro-
X1.13, X1.17).
jected Life Span—It should be recognized and considered
8.5 Installation of Cathodic Protection System—Design and during design that environmental conditions may change over
installation of cathodic protection systems are beyond the the projected life span of the system. One such example is the
scope of this guide. Cathodic protection systems should be addition of road salts on roadways for de-icing purposes. This
designed and installed by a trained and certified professional practice will normally change a relative non-corrosive soil to a
engineer, NACE corrosion specialist, or NACE cathodic pro- very corrosive environment over time. Installation of new
G218 − 19
pipelines with cathodic protection systems, roads, industries, 10. Cathodic Protection Criteria
etc. may also change environmental conditions.
10.1 General—The most generally utilized criteria for ca-
9.3 Risk Assessment: thodic protection (to ferrous materials) is described in Section
6 of NACE SP0169 (formerly RP0169) developed by NACE
9.3.1 General—An engineer or certified corrosion profes-
International (National Association of Corrosion Engi-
sional should perform a risk assessment considering the areas
neers) – Houston, Texas.Although the criteria included in that
described in 9.1 and 9.2. Selection of the proper corrosion
standard were developed in 1969 primarily for the regulated
control method and design should be project specific and
OilandGasIndustry,andthescopeofthatdocumentstatesthat
should address the likelihood and consequence of corrosion
it does not include corrosion control methods based on the use
failure (X1.1, X1.7, X1.15).
of non-adhered polyethylene encasement, portions of this
9.3.2 Implications of Failure—Although the proper treat-
document have been successfully applied to gray and ductile
ment and transport of water and wastewater are critical
iron pipe for decades (X1.6). Publications and case histories
components of maintaining a healthy society, the implications
have documented the successful use of the polyethylene
or risks associated with the failure of a water or wastewater
encasement plus CP corrosion control strategy to protect over
piping system are generally not as severe or life threatening as
300+ miles of ductile iron pipe constructed over the last 30+
a failure in an oil, fuel, or gas pipeline (X1.11). For these
years (X1.1, X1.6). Many of these case histories are referenced
reasons, corrosion control systems are not federally regulated
and summarized in Appendix X1 of this guide. A commonly
in the water and wastewater industry as they are in the energy
used benchmark for effective external corrosion control is (a
industry. Risk associated with failures in a water or wastewater
reductioninthecorrosionrateto)0.025mmperyear(1milper
piping system are generally related to water loss, possible
year) or less. Numerous case histories document ductile iron
reduction in water quality, property damage, disruption of fire
pipe encased in polyethylene encasement with CP have met
protection systems, temporary disruption of service to
this benchmark (X1.1, X1.5, X1.6, X1.8, X1.10, X1.16).
customers, sink hole development, and traffic re-routing. Po-
Electrical resistance corrosion probes are sometimes installed
tential risk of failure in wastewater piping systems may also
under polyethylene encasement to verify the effectiveness of
include environmental contamination of soil and waterways,
the polyethylene encasement + CPsystem (refer to Section 11)
health concerns, environmental fines and/or mandates, and
(X1.5, X1.8, X1.9, X1.10, X1.14, X1.16, X1.18, X1.19).
extensive clean-up costs.While all of these risks/consequences
of failure are potentially severe, rarely does a failure in a water
10.2 Criteria—The two most commonly utilized criteria for
or wastewater piping system result in the loss of life. Rather,
determining adequate cathodic protection for iron or steel
the primary reasons for installing and maintaining a cathodic
piping, or both, are (1) a structure-to-electrolyte potential of
protection system on water or wastewater piping are typically
–850 mV or more negative as measured with respect to a
for economic, sustainability, and reliability issues rather than
saturated CSE (copper/copper sulfate) reference electrode (that
safety concerns.
is, –850 mV criterion), and (2) a minimum of 100 mV of
9.3.3 Areas of High Risk—Areas with a high risk of failure cathodic polarization (that is, 100 mV shift criterion). Of these
may include but are not limited to: hospitals and health care two methods, the one which has been utilized most often for
facilities, single source transmission mains, heavily congested verifying effective cathodic protection of polyethylene encased
areas, river crossings, deep bury installations, under heavily ductile iron pipe is the 100 mV cathodic polarization criterion
traveled roadways, under airport runways, power plants, under (that is, 100 mV shift) (X1.11). Detailed discussions and
railroad crossings, certain industrial facilities, and other areas
descriptions of cathodic protection instrumentation and mea-
based on economic and reliability considerations. surement procedures are beyond the scope of this guide. For
this information, the reader is referred to Guide G215 and
9.3.4 Historical Performance—Historical performance of
NACE TM0497. As stated in the NACE standard, “The
old iron or metallic pipelines in the area of new pipelines to be
provisions of this standard shall be applied by personnel who
installed can provide valuable information and guidance re-
have the knowledge and understanding of the fundamentals of
garding the corrosivity of the soil and expected performance of
cathodic protection of buried and submerged metallic piping
pipe with and without corrosion protection. Whenever
systems acquired by education and related practical experi-
possible, a review of historical performance of metallic pipe-
ence.”
lines in the area should be considered in the risk analysis and
design of corrosion protection systems for new pipelines. 10.2.1 Cathodic Polarization of 100 mV (that is, 100 mV
Shift Criterion)—The100mVshiftfromthenativepotentialof
9.3.5 Potential Third-party Damage—In spite of all efforts
the pipe may be measured as the formation or the decay of
to properly design, install, and maintain a cathodic protection
polarization between the native potential of the pipe and the
system, the risk always exists regarding the possibility of
polarized CP potential.
damagebyathirdparty.Thismayincludebutnotbelimitedto:
cuttingofanode,anodebed,orteststationconnectionwiresby
10.2.2 –850 mV Potential Criterion—Structure-to-
third party excavation or brush cutting, vandalism of rectifiers, electrolyte potential of –850 mVor more negative with respect
installation of other underground facilities between anodes or to a saturated copper/copper sulfate (CSE) reference electrode.
anode beds and the pipe, and loss of power to rectifiers. Future To meet this requirement, potential measurements are allowed
installation of other nearby cathodically protected pipelines to be taken either as a direct measurement of the polarized
may also result in stray current interference problems. potential or a current applied potential. However, if a current
G218 − 19
applied potential is utilized, most procedures require the and is connected to one terminal of the voltmeter. The two
significance of voltage drops in the earth and metallic paths to primary reference electrodes utilized for cathodic protection
be considered.
field measurements are the copper-copper sulfate (Cu-CuSO )
electrode, and the silver-silver chloride (Ag-AgCl) electrode.
10.3 Special Considerations—Special conditions in which
Saturated calomel reference electrodes which consist of a
CPcriteria may need to be adjusted include but are not limited
platinum wire in contact with a mercury/mercurous chloride
to: areas where MIC (microbiologically influenced corrosion)
mixture and saturated KCL solution are also available and are
is active, elevated temperatures (that is, >40°C (104°F)), weak
used primarily for laboratory measurements. Zinc reference
acid environments, and area of high AC current densities. In
electrodes are sometimes used as a permanently installed
these environments, a polarized potential more negative than
reference electrode. General comments regarding reference
–850 mV or a cathodic polarization higher than –100 mV may
electrodes (cells or half-cells) are as follows:
be required. Also, special cathodic protection current design
considerations may apply when applying impressed current 11.2.2.1 The accuracy of the reference electrode should be
cathodic protection to metallic zinc coated iron pipe. periodically verified against a master reference electrode in a
common solution, measuring the voltage difference between
11. Monitoring and Verification
the two electrodes. A maximum voltage variance of 5 mV
between the electrodes is usually satisfactory.
11.1 General Description—This section gives a brief over-
view of monitoring and verification methods. For more in-
11.2.2.2 The negative structure-to-electrolyte potential is
depth discussion, refer to NACE TM0497, NACE SP0104
the value commonly used for cathodic protection measure-
(formerly RP0104), and NACE Publication 05107. General
ments. This requires that the meter polarity be set with the
comments regarding monitoring and verification are as fol-
positive lead of the voltmeter connected to the reference
lows:
electrode, resulting in the instrument indicating the reference
11.1.1 Monitoring and verification activities are essential to
electrode is positive with respect to the pipe, meaning the pipe
determine that protection has been established and that each
potential is negative with respect to the reference electrode.
part of the system is functioning properly.
When using a digital voltmeter, some users have adopted the
11.1.2 Initial testing will provide baseline data for compari-
practice of hooking the reference electrode to the negative
son to subsequent results and establish that the protection is
terminal of the voltmeter giving a negative number on the
within the desired limits.
meter display. Once a decision has been made on the polarity
11.1.3 Corrosion monitoring may include the use of ca-
of the connection, this polarity should be continued for all
thodic protection coupons or corrosion probes, or both, to
testing.
verify the effectiveness of the protection system.
11.2.2.3 In seawater or brackish water, silver-silver chloride
11.1.4 Test equipment should be of the appropriate type and
reference electrodes are normally utilized in lieu of copper-
voltage range(s) for the measurement being made, verified
copper sulfate reference cells.
against known standards prior to use, and maintained in good
11.2.2.4 Depending on the design of the system, perma-
operating condition.
nently installed reference electrodes may be used. If so,
11.2 Potential Measurements—NACE TM0497 lists three
accuracy should be verified initially and periodically.
test methods which have been used to determine if cathodic
11.2.2.5 Two characteristics of a copper-copper sulfate ref-
protection is adequate. The selection of the proper method to
erence electrode should be considered – temperature effect and
use is dependent upon the circumstances associated with each
photoelectric effect.Apotential measurement change observed
installation.
with temperature is approximately –0.5 mV per degree above
11.2.1 Instruments—Ahigh resistance voltmeter is required
70°F, and +0.5 mV per degree below 70°F. A change in
because of the normally high resistance of the earth side
potential due to photoelectric effect as also been observed by
circuit. Digital meters used for monitoring typically have an
sunlightstrikingthecoppersulfateelectrode.Thiseffectcanbe
input impedance of 10 megaohms or more. Instruments should
easilycheckedbyshadingtheelectrodetoseeifachangeinthe
have test leads easily identifiable with clips allowing connect-
potential reading is observed.
ing to the pipeline and the reference electrode. Instruments
11.2.2.6 When making potential measurements utilizing a
should also be kept clean, maintained and handled with care,
reference electrode, contact resistance between the soil and the
and be checked and calibrated before use. Batteries should be
reference electrode should be minimized. High contact resis-
removed when not in use to prevent possible leakage and the
tance may be reduced by using a reference cell with a larger
resultant corrosive damage. For impressed current systems,
contact surface. Sources of high contact resistance may be dry
current interrupters may be required to cycle the influential
or frozen soil, asphalt or concrete paving material, rocks,
cathodic protection current source(s).
vegetation, etc. Readings should not be taken through asphalt
11.2.2 Reference Electrodes—A reference electrode is one
or concrete. In dry soil conditions wetting the surface with
half of a corrosion cell consisting of a metal in solution of
water may be necessary to reduce the contact resistance.
metalions.Adetaileddiscussionofreferenceelectrodesforuse
11.2.3 Types of Potential Measurements—There are three
in the laboratory and field studies is given in Guide G215.
When the concentration of the metal ions remains constant generally accepted test methods for measuring potential of a
cathodically protected pipeline system (refer to Section 10). In
around the metal the “half cell” potential remains constant.
This “half cell” then provides contact to the electrolyte (soil) all three methods, potential measurements are taken between
G218 − 19
the buried structure and a reference electrode contacting the The probe elements are generally made of the same or similar
surface of the earth (soil). material as the structure to be monitored.
11.3.1.2 LPR Probe—Alinear polarization resistance (LPR)
11.2.3.1 Test Method 1 described in Section 8 of NACE
TM0497 is a procedure for measuring structure to electrolyte probe determines the corrosion rate on its metal electrode or
electrodes by measuring the polarization resistance under the
potential with cathodic protection applied (known as “on
application of a small applied potential, typically 10 to 20 mV,
potential”). This test method records all voltage drops, includ-
above the free corroding potential of the electrode or elec-
ing contributions from potential stray current sources.
trodes. The probe elements are generally made of the same or
11.2.3.2 Test Method 2 described in Section 9 of NACE
similar material as the structure to be monitored.
TM0497isaprocedureformeasuringthepolarizedstructureto
11.3.2 Cathodic Protection Coupons—CP coupons have
electrolyte, using current interruption (known as “instant off
been shown to be a simple tool for determining the level of
potential”).This test method accounts for the unknown voltage
polarization of a pipeline and to confirm the IR drop in a
drops but may not be practical on extended, multi-rectified
potential measurement. CP coupons are installed in the soil or
systems, systems with galvanic anodes attached, or zinc coated
electrolyte near the pipeline and then connected to it through a
ductile iron pipe.
test station. The CP coupon can then be easily disconnected
11.2.3.3 Test Method 3 of NACE TM0497 (Section 10) is a
from the pipeline for periodic monitoring of “instant off” and
procedure using either pipeline polarization decay or pipeline
depolarization potential measurements. General characteristics
polarization formation. This method normally takes more time
of the coupon are that it is nominally the same metal and
than either Method 1 or 2.
surface condition of the pipe, it is small to avoid excessive
11.3 Corrosion Probes and Cathodic Protection Coupons—
current drain on the system, it is placed at pipe depth in the
Both corrosion probes and cathodic protection coupons are
same backfill as the pipe. A second, freely corroding (native)
used to monitor and evaluate cathodic protection effectiveness.
coupon not connected to the pipe may be installed adjacent to
The use of corrosion probes is discussed in detai
...