Cathodic protection of submarine pipelines
|Publication Date:||1 September 2019|
Scope of this document
The CP calculation procedures in this RP generally comply with the requirements and recommendations in the applicable sections of ISO 15589-2, although the approach to the importance of pipeline coating systems' design and the quality control of their application, especially for FJC, differs from that of the ISO standard. The same applies to the relative importance of seawater ambient temperature and internal fluid temperature on design current densities.
DNVGL-RP-F103 is applicable to submarine pipeline systems as defined in DNVGL-ST-F101, except riser sections above mean water level for which cathodic protection is not practical. For any landfall sections to be protected by impressed current CP, reference is made to the latest revisions of ISO 15589-1 and EN 12954.
The present document covers the detailed design of CP for submarine pipeline systems using galvanic anodes, either Al or Zn based, and the manufacture 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 DNVGL-RP-B401 is recommended for CP design. For conceptual CP design, Sec.6 is applicable to preliminary calculations of the anode net mass and anode distribution. For requirements to anode steel inserts and the inspection and testing during anode manufacture in Sec.7, reference is made to the applicable sections in ISO 15589-2.
By referring to requirements to the design and quality control of specific coating systems for linepipe, field joints and field repairs in DNVGL-RP-F102 and DNVGL-RP-F106, individual coating breakdown factors for linepipe and field joint coating, respectively are recommended in this RP (App.A). The primary purpose of this approach is to ensure that the CP design is adequate for the actual combination of coating systems to be applied and to enable a CP design without any arbitrary allowance for deficiencies associated with the design and quality control of such coatings. The RP emphasises the importance of documentation of quality control and gives comprehensive advice and guidance related to CP design, anode manufacture and installation. This guidance covers both purchaser's specification and contractor's execution of QA/QC.
Full conceptual design of CP, detailed design of impressed current CP systems, and the operation of pipeline CP systems are not addressed in this document. For these items, reference is made to the general guidelines in DNVGL-ST-F101 and the somewhat more detailed recommendations in ISO 15589-1, ISO 15589-2 and EN 12474. For electrochemical testing of galvanic anode materials for the purpose of either qualification or quality control, reference is also made to DNVGL-RP-B401 App.C and DNVGL-RP-B401 App.B, respectively.
Considerations related to safety and environmental hazards associated with galvanic anode manufacture and installation are beyond the scope of this document.