Foreword
ISO 15589-2:2004(E)
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 15589-2 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries, Subcommittee SC 2, Pipeline transportation systems.
ISO 15589 consists of the following parts, under the general title Petroleum and natural gas industries —
Cathodic protection of pipeline transportation systems:
— Part 1: On-land pipelines
— Part 2: Offshore pipelines
Introduction
Pipeline cathodic protection is achieved by the supply of sufficient direct current to the external pipe surface,
so that the steel-to-electrolyte potential is lowered to values at which external corrosion is reduced to an
insignificant rate.
Cathodic protection is normally used in combination with a suitable protective coating system to protect the
external surfaces of steel pipelines from corrosion.
External corrosion control in general is covered by ISO 13623.
Users of this part of ISO 15589 should be aware that further or differing requirements may be needed for
individual applications. This part of ISO 15589 is not intended to inhibit alternative equipment or engineering
solutions to be used for the individual application. This may be particularly applicable where there is innovative
or developing technology. Where an alternative is offered, any variations from this part of ISO 15589 should
be identified.
Deviations from this part of ISO 15589 may be warranted in specific situations, provided it is demonstrated
that the objectives expressed in this part of ISO 15589 have been achieved.
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Examples of Design for Cathodic Protection Systems
From Estimated Exposed Surface Area
Estimating current requirements from expected exposed surface is always subject to
error. There are many factors, which affect the results.
Consider:
• Total surface area in contact with soil or other electrolyte.
• Dielectric properties of any protective coating.
• Factors which may damage a protective coating during installation.
• Expected protective coating life under service conditions.
• Expected percentage coverage by protective coating.
• Past experience with coating applicators and construction contractors.
• Current density required for cathodic protection of the metal(s) in the
environment.
In the end, the expected current requirement depends on calculating the area of
exposed metal in contact with the electrolyte and multiplying it by the “best estimate”
of current density for the conditions present.
There is an alternate approach for coated electrically isolated structures (pipes, under-
ground storage tanks, etc.) where there is data available on existing cathodic protection
systems.
The approach requires reliable local data on:
• Expected leakage conductance (Siemens/unit area) in 1000 ohm cm. soil for a
class of coating (epoxy, polyethylene tape, etc.) and type of service
(transmission pipeline, gas distribution, fuel tank).
• Soil resistivity in the service area.
• Structure to soil potential shift required to produce polarization needed to meet
cathodic protection criteria. This is the immediate change in potential of an
isolated structure measured to a point at “remote earth” when cathodic
protection is applied.
The value is not a criteria for protection. However, under a given set of operating and exposure conditions, a potential shift will provide a good estimate of current needed to meet accepted criteria.
The approach is best understood by using an example.
Example 5.1
A gas utility is planning to install 3049 meters (10,000 feet) of 5.1 cm (2 inch) coated
steel distribution mains in a new development. The average soil resistivity in the area
is 5,000 ohm cm. The corrosion engineer wishes to estimate the approximate current
required to cathodically protect the pipes.
Experience in the utility has developed the following data on cathodic protection
current requirements:
Average leakage conductance G for distribution type service is 2.14 × 10−3S/m2in
1000 ohm cm soil.
Average potential shift measured to “remote earth” to achieve protection is −0.250
volt.
Calculations:
Total surface area of the proposed pipe.
As=πd L = (5.1 × 3.1416/100) × 3049 = 488 sq. meters
Estimated leakage conductance of new pipe in 1000 ohm cm soil.
g = G × A = 2.14 × 10−3×488 = 1.04 Siemens
Since resistance = 1/conductance
Resistance to remote earth = 1/1.04 = 0.96 ohm
Estimated resistance to remote earth in 5000 ohm cm soil. (Resistance is directly pro-
portional to resistivity).
0.96 × 5 = 4.8 ohms
Estimated current to shift pipe potential to remote earth −0.250 volt. From Ohm’s
Law (I = E/R)
0.250/4.8 = 0.052 A.
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Estimating current requirements from expected exposed surface is always subject to
error. There are many factors, which affect the results.
Consider:
• Total surface area in contact with soil or other electrolyte.
• Dielectric properties of any protective coating.
• Factors which may damage a protective coating during installation.
• Expected protective coating life under service conditions.
• Expected percentage coverage by protective coating.
• Past experience with coating applicators and construction contractors.
• Current density required for cathodic protection of the metal(s) in the
environment.
In the end, the expected current requirement depends on calculating the area of
exposed metal in contact with the electrolyte and multiplying it by the “best estimate”
of current density for the conditions present.
There is an alternate approach for coated electrically isolated structures (pipes, under-
ground storage tanks, etc.) where there is data available on existing cathodic protection
systems.
The approach requires reliable local data on:
• Expected leakage conductance (Siemens/unit area) in 1000 ohm cm. soil for a
class of coating (epoxy, polyethylene tape, etc.) and type of service
(transmission pipeline, gas distribution, fuel tank).
• Soil resistivity in the service area.
• Structure to soil potential shift required to produce polarization needed to meet
cathodic protection criteria. This is the immediate change in potential of an
isolated structure measured to a point at “remote earth” when cathodic
protection is applied.
The value is not a criteria for protection. However, under a given set of operating and exposure conditions, a potential shift will provide a good estimate of current needed to meet accepted criteria.
The approach is best understood by using an example.
Example 5.1
A gas utility is planning to install 3049 meters (10,000 feet) of 5.1 cm (2 inch) coated
steel distribution mains in a new development. The average soil resistivity in the area
is 5,000 ohm cm. The corrosion engineer wishes to estimate the approximate current
required to cathodically protect the pipes.
Experience in the utility has developed the following data on cathodic protection
current requirements:
Average leakage conductance G for distribution type service is 2.14 × 10−3S/m2in
1000 ohm cm soil.
Average potential shift measured to “remote earth” to achieve protection is −0.250
volt.
Calculations:
Total surface area of the proposed pipe.
As=πd L = (5.1 × 3.1416/100) × 3049 = 488 sq. meters
Estimated leakage conductance of new pipe in 1000 ohm cm soil.
g = G × A = 2.14 × 10−3×488 = 1.04 Siemens
Since resistance = 1/conductance
Resistance to remote earth = 1/1.04 = 0.96 ohm
Estimated resistance to remote earth in 5000 ohm cm soil. (Resistance is directly pro-
portional to resistivity).
0.96 × 5 = 4.8 ohms
Estimated current to shift pipe potential to remote earth −0.250 volt. From Ohm’s
Law (I = E/R)
0.250/4.8 = 0.052 A.
for detail you can buy PEABODY or cantact me for getting ebookthks for all
bajakz
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