scope:

This Recommended Practice (RP) has been prepared to facilitate the execution of detailed CP design and the specification of galvanic anode manufacturing and installation. While the requirements and recommendations are general, the document contains advice on how amendments can be made to include project specific requirements. The document can also easily be amended to include requirements/guidelines by a regulating authority, or to reflect the pipeline operator's general philosophy on pipeline corrosion control.

Guidance note:

It is recommended that any additional conservatism is introduced by use of a "design factor" rather than modification of one or more of the many design parameters used for CP calculations. For example, it may be specified that the design life shall be based on the maximum estimated lifetime of the pipeline multiplied with some constant larger than 1 (one).

The document covers the detailed design of CP for submarine pipeline systems (see 1.3.1) using galvanic anodes, either Al - or Zn -based, and the manufacturing and installation of such anodes. For CP of subsea manifold templates, riser bases and other subsea structures where components of a pipeline system are electrically connected to major surfaces of structural C-steel, use of DNV-RP-B401 is recommended for CP design (see 1.5.3). For conceptual CP design, Sec.5 is applicable to preliminary calculations of the anode net mass and anode distribution. This RP is based on the sections in ISO 15589-2 that are applicable (see 1.3.1). For compliance with the general philosophy in DNV-OS-F101, primarily with respect to procedures for quality control, or for the purpose of clarification and guidance, some amendments are given. This RP further contains some formula for calculation of CP protective range from adjacent structures and minimum distance between pipeline anodes that are not included in the ISO standard. Default values for galvanic anode performance and design current densities that do not require any special qualification or field testing are also recommended.

By referring to specific pipeline coating systems for linepipe, field joints and field repairs in DNV-RP-F102 and DNV-RP-F106, and implementing the detailed requirements for the quality control of their manufacturing as defined in these documents, specific design parameters for calculation of current demands for CP are recommended in this RP. This is to enable a CP design without any arbitrary allowance for deficiencies associated with the design and quality control of such coatings, reducing the need for excessive conservatism in the design. In this RP, and contrary to ISO 15589-2, the current demands for cathodic protection are calculated for specific combinations of linepipe and field joint coating.

Guidance note:

In case certain deviations from the requirements to coating design and/or quality control of manufacturing in DNV-RP-F106 and DNV-RP-F102 are identified, the CP design parameters associated with pipeline coatings in this document (i.e. "coating breakdown factors") may still be applicable. However, the user of this document should then carefully assess the significance of any such deviations.

Full conceptual design of CP (see 1.1.3 and 1.2.2), detailed design of impressed current CP systems, testing of galvanic anode material for the purpose of either qualification or quality control, and the operation of pipeline CP systems are not addressed in this document. For these items, reference is made to the general guidelines in DNV-OS-F101 and the more detailed recommendations in ISO 15589-1, -2.

Although considerations related to safety and environmental hazards associated with galvanic anode manufacturing and installation are of great importance, such are never-theless beyond the scope of this document.