7 Anode Bed Design
7.1 Anodes shall be designed prior to the rectifier sizing.
The anode bed design shall:
a. Avoid stray current interference with off-site structures.
b. Avoid physical interference with adjacent facilities.
c. Provide uniform current distribution.
7.2 The anode system shall provide protection against corrosion for the specified design life of
the CP system for a particular structure, i.e. minimum for a period of 25 years for ICCP and
15 for SACP.
7.3 The anode quantity and distribution shall ensure sufficient and good current distribution to all
parts of structure requiring protection.
7.4 Design and installation of all elements shall be such that no major maintenance or
replacement shall be required during the design life period unless otherwise specified or
required for particular applications.
7.5 Ground bed systems shall be located strategically to minimize shielding and to provide
optimum protection levels.
7.6 The current capacity of an anode bed shall be equal to or greater than the rated capacity of
the DC power source and shall be calculated based on the total anode surface area
multiplied by the applicable maximum current density shown in the respective anode.
7.7 Anode Bed Circuit Resistance:
7.7.1 All DC cable resistances shall be considered part of the anode bed circuit resistance.
7.7.2 The maximum acceptable operating circuit resistance for a new CP system shall be
defined as the DC power source rated voltage, divided by, the design current required to
achieve adequate protection.
7.7.3 The maximum acceptable operating circuit resistance for a new CP system shall be 1.0
ohm or less.
7.7.4 Anode beds shall be designed for a circuit resistance of 70% or less of the maximum
acceptable operating circuit resistance for the CP power source.
7.7.5 Anode beds that are commissioned at circuit resistances greater than the design
resistance but less than the maximum acceptable operating resistance shall not be
considered out of compliance.
7.7.6 The practice of one header cable from the positive junction box feeding all anodes
around a structure is not allowed.
7.8 Earth potential rise for horizontal and vertical distributed anodes shall be used to determine
the anode spacing.
7.9 The distributed anode distance from buried pipelines/piping shall vary from one to three
meters for sacrificial anode, and from three to five meters for impressed anodes.
7.10 Distributed single impressed anode output shall not exceed 1.5 Ampere.
7.11 The CP designer shall calculate the actual sacrificial anode efficiency instead of using
the maximum efficiency.
7.12 The location of each distributed anode shall be marked.
7.13 All anodes shall be from the SABIC approved manufacturers. Anodes from other
manufacturers will not be acceptable.
7.14 The contractor shall use material types which have proven track record in use for a
minimum of 10 years. The materials shall be NACE certified and tested by an
independent laboratory using NACE Standard Test Methods. Prior to procurement of
these anodes, independent laboratory testing certification shall be submitted to SABIC
STC for review and approval.
7.15 The contractor shall use materials (for the approved anode system) which have been in
use for a minimum of 10 years and have extensive and proven track records in the Gulf
countries.