ASTM G218 - 25 用聚乙烯包裹外加阴极保护的球墨铸铁管外部腐蚀保护的标准指南

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Designation: G218 −25
Standard Guide for
External Corrosion Protection of Ductile Iron Pipe Utilizing
Polyethylene Encasement Supplemented by Cathodic
Protection
1
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
1.1 This guide will discuss standard practices which have
been successfully utilized in the ﬁeld for over 35 years to
provide external corrosion protection of polyethylene encased
ductile iron pipe supplemented with cathodic protection (CP).
This guide may also be used for ductile iron ﬁttings, valves,
and other appurtenances speciﬁc to ductile iron pipe systems.
Case histories and publications reporting on the use of cathodic
protection to supplement polyethylene encasement are in-
cluded as an appendix in this guide.
1.2 Other external corrosion control methods which have
been used for ductile iron pipe include, but are not limited to:
cathodic protection, metallic zinc coatings, bonded dielectric
coatings, dielectric coatings with cathodic protection, and
trench improvement. Detailed information on these methods of
protection are available from other sources and are beyond the
scope of this guide.
1.3 The values stated in inch-pound units are to be regarded
as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only
and are not considered standard.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 The most recent version of the following documents
should be consulted as references by those using this guide:
2.2 ASTM Standards:
2
A674 Practice for Polyethylene Encasement for Ductile Iron
Pipe
A746 Speciﬁcation for Ductile Iron Gravity Sewer Pipe
D149 Test Method for Dielectric Breakdown Voltage and
Dielectric Strength of Solid Electrical Insulating Materials
at Commercial Power Frequencies
D882 Test Method for Tensile Properties of Thin Plastic
Sheeting
D1709 Test Methods for Impact Resistance of Plastic Film
by the Free-Falling Dart Method
D1922 Test Method for Propagation Tear Resistance of
Plastic Film and Thin Sheeting by Pendulum Method
D4976 Speciﬁcation for Polyethylene Plastics Molding and
Extrusion Materials
G51 Test Method for Measuring pH of Soil for Use in
Corrosion Evaluations
G57 Test Method for Measurement of Soil Resistivity Using
the Wenner Four-Electrode Method
G97 Test Method for Laboratory Evaluation of Magnesium
Sacriﬁcial Anode Test Specimens for Underground Appli-
cations
G187 Test Method for Measurement of Soil Resistivity
Using the Two-Electrode Soil Box Method
G193 Terminology and Acronyms Relating to Corrosion
G200 Test Method for Measurement of Oxidation-Reduction
Potential (ORP) of Soil
G215 Guide for Electrode Potential Measurement
2.3 ANSI/AWWA Standards:
3
ANSI/AWWA C105/A21.5 Polyethylene Encasement for
Ductile-Iron Pipe Systems
1
This guide is under the jurisdiction of ASTM Committee G01 on Corrosion of
Metals and is the direct responsibility of Subcommittee G01.10 on Corrosion in
Soils.
Current edition approved Oct. 1, 2025. Published October 2025. Originally
approved in 2019. Last previous edition approved in 2019 as G218 – 19. DOI:
10.1520/G0218-25.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at www.astm.org/contact. For Annual Book of
ASTM Standards volume information, refer to the standard’s Document Summary
page on the ASTM website.
3
Available from American Water Works Association (AWWA), 6666 W. Quincy
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
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.
1

ANSI/AWWA C110/A21.10 Ductile-Iron and Gray-Iron
Fittings, 3 In. Through 48 In. (76 mm Through 1,219 mm),
for Water
ANSI/AWWA C111/A21.11 Rubber Gasket Joints for
Ductile-Iron Pressure Pipe and Fittings
ANSI/AWWA C151/A21.51 Ductile-Iron Pipe, Centrifu-
gally Cast
ANSI/AWWA C600 Installation of Ductile-Iron Mains and
Their Appurtenances
2.4 ISO Standards:
4
ISO 8179 Part 1 Ductile iron pipes, ﬁttings, accessories and
their joints – External zinc-based coating – Part 1: Metal-
lic zinc with ﬁnishing layer
ISO 8180 Ductile iron pipelines – Polyethylene sleeving for
site application
2.5 NACE International Standards:
5
SP0169 Control of External Corrosion on Underground or
Submerged Metallic Piping Systems
SP0104 The Use of Coupons for Cathodic Protection Moni-
toring Applications
TM0497 Measurement Techniques Related to Criteria for
Cathodic Protection on Underground or Submerged Me-
tallic Piping Systems
Publication 05107 Report on Corrosion Probes in Soil or
Concrete
Publication 10A292 Corrosion and Corrosion Control for
Buried Cast- and Ductile-Iron Pipe
2.6 Various additional publication references related to spe-
ciﬁc topics discussed in this guide are included as Appendix
X1.
3. Terminology
3.1 Deﬁnitions of Terms Speciﬁc to This Standard:
3.1.1 100 mV criterion, n—a speciﬁc degree of cathodic
polarization between the pipe surface and a stable reference
electrode, both in contact with the electrolyte; the degree of
polarization can be measured during formation or decay.
3.1.2 –850 mV criterion, n—the degree of polarized poten-
tial measured relative to a saturated copper/copper sulfate
reference electrode, which is used to verify cathodic protection
has been achieved.
3.1.3 annealing oxide, n—a layer of tenacious and complex
oxides of iron and silicon formed on ductile iron pipe during
the annealing process.
3.1.3.1 Discussion—See 5.3 of this guide.
3.1.4 cathodic protection coupon, n—a metal sample repre-
senting the pipeline at the site, used for cathodic protection
testing, and having a chemical composition approximately the
same as the pipe.
3.1.5 ductile iron pipe, n—see Section 5of this guide.
3.1.6 enhanced linear low density (ELLD) polyethylene
encasement ﬁlm, n—ﬁlm extruded from virgin linear low
density polyethylene raw material with additives designed to
control generalized corrosion and microbiologically induced
corrosion (MIC).
3.1.7 ER probe, n—an ER (electrical resistance) corrosion
measurement probe that has been adapted for use in soil-side
applications (also known as SCP – soil corrosion probe).
3.1.8 free-corrosion coupon (also known as native coupon),
n—a coupon that is immersed in the soil or aqueous environ-
ment adjacent to the structure but is not connected to the
structure.
3.1.9 high-density, cross-laminated (HDCL) polyethylene
ﬁlm, n—ﬁlm extruded from virgin high-density polyethylene
raw material, which is then molecularly oriented by stretching;
the ﬁnal product is then formed by two single-ply layers of the
ﬁlm that are then laminated together with their orientations at
90° to one another using molten, high-density, virgin resin.
3.1.10 linear low-density (LLD) polyethylene ﬁlm, n—ﬁlm
extruded from virgin linear low-density polyethylene raw
material.
3.1.11 LPR probe, n—a linear polarization resistance (LPR)
probe which determines the corrosion rate on its metal elec-
trode or electrodes by measuring the polarization resistance
under the application of a small applied potential, typically
10 mV to 20 mV, above the free corroding potential of the
electrode or electrodes; the probe elements are generally made
of the same or similar material as the structure to be monitored.
3.1.12 polyethylene encasement, n—polyethylene material,
in tube or sheet form, that is used to encase ductile iron pipe
and ﬁttings for the purposes of corrosion protection or stray
current mitigation, or both.
3.1.12.1 Discussion—See Section 6of this guide.
3.1.13 shopcoat, n—the standard external coating for ductile
iron pipe as described in ANSI/AWWA C151/A21.5; it consists
of a painted coating approximately 1 mil (0.025 mm) thick
which is normally applied to the outside of ductile iron pipe
and ﬁttings.
3.1.13.1 Discussion—See 5.4 of this guide.
3.1.14 uniquely severe environment, n—an environment
where all the following characteristics co-exist: (1) soil resis-
tivity ≤500 ohm-cm, (2) anaerobic conditions in which sulfate
reducing bacteria thrive (neutral pH of 6.5 to 7.5, low or
negative redox potential, and the presence of sulﬁdes), and (3)
salt/brackish water tidal area where the water table is intermit-
tently or continually above the invert of the pipe.
3.2 General terminology and acronyms relating to corrosion
are deﬁned in Terminology G193.
4. Signiﬁcance and Use
4.1 This guide provides basic information on the application
of cathodic protection to polyethylene encased ductile iron pipe
for engineers, owners, water companies, corrosion consultants,
ductile iron (DI) pipe manufacturers, and others who have an
interest in providing underground corrosion protection to
ductile iron pipe.
4
Available from International Organization for Standardization (ISO), ISO
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Geneva, Switzerland, http://www.iso.org.
5
Available from Association for Materials Protection and Performance (AMPP),
15835 Park Ten Place, Houston, TX 77084, https://www.ampp.org (formerly NACE
International).
G218 − 25
2

4.2 There are many publications, standards, recommended

practices, and speciﬁcations for the application of coatings and

cathodic protection to steel pipe. However, the metallurgy,

chemistry, physical properties, surface composition and

texture, coating requirements, and electrical continuity of

standard production ductile iron pipe are signiﬁcantly different

than those of steel pipe, and coating and cathodic protection

speciﬁcations written speciﬁcally for steel pipe may not be

directly applicable to ductile iron pipe. The latest revision of a

commonly accepted cathodic protection speciﬁcation (NACE

SP0169) states the following in the foreword: “This standard

does not include corrosion control methods based on injection

of chemicals into the environment, on the use of electrically

conductive coatings, or on the use of non-adhered polyethylene

encasement (refer to NACE Publication 10A292).” It is the

purpose of this guide to summarize publications, case histories,

and studies which are available regarding cathodic protection

installations of polyethylene encased ductile iron pipe to give

the reader guidance on this unique method of protection.

4.3 This guide may be utilized with galvanic or impressed

current cathodic protection.

4.4 This guide is written speciﬁcally for ductile iron pipe

and does not apply to any other type of piping material. It may

also be used for ductile iron ﬁttings, valves, and appurtenances

speciﬁc to ductile iron piping systems.

4.5 Properly installed and undamaged polyethylene encase-

ment shields the ductile iron pipe surface from cathodic

protection currents. The primary purpose of applying cathodic

protection to polyethylene encased ductile iron pipe is to

provide cathodic protection to unrepaired damaged areas of the

encasement.

4.6 This guide references requirements for vendor provided

information which should be requested and reviewed by the

user.

5. Ductile Iron Pipe (DIP)

5.1 Metallurgy—Ductile iron is a novel ferrous product

containing approximately 93 % iron (Fe), with sufficient car-

bon (C) and silicon (Si) to qualify as a eutectiferous material.

It has been treated in the liquid state so as to cause the majority

of the carbon to occur as substantially equiaxed particles

appearing as spheroids or nodules in the as-cast structure of the

pipe. Ductile irons can be viewed as a family of alloys which

combine the principal advantages of gray cast iron with the

engineering advantages of steel; that is, good ﬂuidity,

castability, machinability, great strength, toughness, and duc-

tility. Ductile iron pipe is typically speciﬁed to meet the

minimum requirements of ANSI/AWWA C151/A21.51 and

Speciﬁcation A746.

5.2 Joints—Joints are the device by which an essentially

leak-free connection is produced between two lengths of

ductile iron pipe. The joint may be mechanical, push-on, or

restrained, and is typically speciﬁed to meet minimum require-

ments of ANSI/AWWA C111/A21.11. Bolts used for securing

mechanical joints are also typically speciﬁed to conform to the

requirements of the same standard, and pipe with other types of

joints speciﬁed to comply with the joint dimensions and

weights agreed upon at the time of purchase.

5.3 Annealing Oxide—Modern production practices for duc-

tile iron pipe include an annealing heat treatment to allow the

material to achieve the optimum balance of material properties.

When iron or steel are heat treated in air an oxide ﬁlm is

formed. Unlike mill scale on carbon steel which ﬂakes away,

the annealing oxide on ductile iron pipe exhibits a tenacious

layer that adheres to the base metal due to the presence of

silicon in the oxide structure. Under burial conditions, pores in

the annealing oxide ﬁlm become plugged by relatively in-

soluble corrosion products. This oxide ﬁlm protects the under-

lying metal as long as the oxide layer is protected from the

introduction of other species, like chlorides, which can result in

partial dissolution of the oxide. Intact polyethylene encasement

of the pipe resists introduction of chlorides and other com-

pounds from contacting this protective oxide layer on the pipe

surface.

5.4 Shopcoat—An exterior coating approximately 1 mil

(0.025 mm) thick is normally applied on the outside of ductile

iron pipe and ﬁttings. AWWA and ASTM speciﬁcations call for

the ﬁnished coating to be continuous, smooth, and strongly

adherent to the pipe. While primarily applied for esthetic

purposes, studies have shown asphaltic and other shopcoats do

offer limited corrosion protection in conjunction with the

annealing oxide and have been shown to reduce current

requirements on CP systems (X1.2,X1.18). Shopcoats have

also been shown to be compatible with metallic zinc coatings

on ductile iron pipe, and have been reported to improve the life

and performance of these coatings (X1.3).

5.5 Metallic Zinc Coating—Prior to the application of the

shopcoat, a metallic zinc coating is sometimes applied to the

exterior of ductile iron pipe for external corrosion protection. It

is normally applied in accordance with ISO 8179 Part 1

utilizing arc spray or ﬂame spray methods. The metallic zinc

coating is typically applied on top of the inherent annealing

oxide layer on ductile iron pipe. In severely corrosive soils,

metallic zinc coating is normally utilized in conjunction with

polyethylene encasement, or an enhanced polyethylene

encasement, and may be used with or without additional

external cathodic protection (X1.5).

6. Polyethylene Encasement

6.1 Description and Properties:

6.1.1 General Description—Polyethylene encasement has

been the primary asset preservation method utilized for gray

and ductile iron pipe since 1958. In the 60+ years of use, over

300 million feet of iron pipe have been installed with polyeth-

ylene encasement and over 300 miles of encased pipe installed

with supplemental cathodic protection (X1.1,X1.5).

6.1.2 Mechanisms of Protection:

6.1.2.1 Polyethylene encasement is an engineered corrosion

control system for ductile iron pipelines. The ﬁlm is manufac-

tured using specially designed virgin material with speciﬁc

minimum thickness and mechanical requirements, for example,

tensile strength, elongation, propagation tear resistance, impact

resistance, and dielectric strength, which are speciﬁed in

G218 − 25

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摘要：

ASTM G218 - 25 是一项针对球墨铸铁管外部腐蚀保护的标准指南，重点规范了采用聚乙烯包裹层与外加阴极保护系统相结合的综合防护方法。该标准适用于埋地或浸水环境中的球墨铸铁管道，旨在通过物理隔离与电化学保护的协同作用，有效抑制土壤或水介质对管体造成的腐蚀损伤。指南中详细阐述了聚乙烯包裹材料的性能要求、施工工艺、质量检验标准，以及阴极保护系统的设计准则、安装调试和运行维护要点。同时，标准还提供了两种防护方式相互配合时的兼容性评估方法，帮助工程人员规避因材料老化、剥离或保护电位不当而引发的失效

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