DNVRPB401 Cathodic Protection Design.docx

1、DNVRPB401 Cathodic Protection DesignDNV-RP-B401 Cathodic Protection Design1. General1.1 Introduction1.1.1Cathodic protection (CP) can be defined as e.g. electrochemical protection by decreasing the corrosion potential to a level at which the corrosion rate of the metal is significantly reduced (ISO

2、8044) or a technique to reduce corrosion of a metal surface by making that surface the cathode of an electrochemical cell (NACE RP0176). The process of suppressing the corrosion potential to a more negative potential is referred to as cathodic polarization. 1.1.2For galvanic anode CP systems, the an

3、ode of the electrochemical cell is a casting of an electrochemically active alloy (normally aluminium, zinc or magnesium based). This anode is also the current source for the CP system and will be consumed. Accordingly, it is often referred to as a sacrificial anode, as alternative to the term galva

4、nic anode consistently used in this Recommended Practice (RP). For impressed current CP, an inert (non-consuming) anode is used and the current is supplied by a rectifier. In this RP, the cathode of the electrochemical cell (i.e. the structure, sub-system or component to receive CP) is referred to a

5、s the protection object. 1.1.3For permanently installed offshore structures, galvanic anodes are usually preferred. The design is simple, the system is mechanically robust and no external current source is needed. In addition, inspection and maintenance during operation can largely be limited to per

6、iodic visual inspection of anode consumption and absence of visual corrosive degradation. However, due to weight and drag forces caused by galvanic anodes, impressed current CP systems are sometimes chosen for permanently installed floating structures. 1.1.4Cathodic protection is applicable for all

7、types of metals and alloys commonly used for subsea applications. It prevents localised forms of corrosion as well as uniform corrosion attack, and eliminates the possibility for galvanic corrosion when metallic materials with different electrochemical characteristics are combined. However, CP may h

8、ave certain detrimental effects, for example hydrogen related cracking of certain high-strength alloys and coating disbondment as described in 5.5. 1.1.5Cathodic protection is primarily intended for metal surfaces permanently exposed to seawater or marine sediments. Still, CP is often fully effectiv

9、e in preventing any severe corrosion in a tidal zone and has a corrosion reducing effect on surfaces intermittently wetted by seawater. 1.2 Scope1.2.1This Recommended Practice (RP) has been prepared to facilitate the execution of conceptual and detailed CP design using aluminium or zinc based galvan

10、ic anodes, and specification of manufacture and installation of such anodes. Whilst the requirements and recommendations are general, this document contains advice on how amendments can be made to include project specific requirements. The RP can also easily be amended to include requirements or gui

11、delines by a regulating authority, or to reflect owners general philosophy on corrosion control by CP. 1.2.2Some of the design recommendations and methods in Sections 5, 6 and 7 are also valid for CP systems using other current sources such as magnesium anodes and rectifiers (i.e. impressed current)

12、. 1.2.3This RP is primarily intended for CP of permanently installed offshore structures associated with the production of oil and gas. Mobile installations for oil and gas production like semi-submersibles, jack-ups and mono-hull vessels are not included in the scope of this document. However, to t

13、he discretion of the user, relevant parts of this RP may be used for galvanic anode CP of such structures as well. 1.2.4Detailed design of anode fastening devices for structural integrity is not included in the scope of this RP. Considerations related to safety and environmental hazards associated w

14、ith galvanic anode manufacture and installation are also beyond its scope. 1.2.5Compared to the 1993 edition of DNV-RP-B401, design considerations for impressed current CP have been deleted from the scope of the 2004 revision whilst the sections on anode manufacture and installation are made more co

15、mprehensive. CP of submarine pipelines is further excluded from the scope (see 1.5). However, this RP is applicable for CP of components of a pipeline system installed on template manifolds, riser bases and other subsea structures when such components are electrically connected to major surfaces of

16、structural C-steel. In this revision, guidance and explanatory notes are contained in a Guidance note to the applicable paragraph in Sections 6, 7, 8 and in Annex B and C. (Most of the Guidance notes are based on queries on the 1993 revision of DNV-RP-B401 and other experience from its use. Furtherm

17、ore, some informative text in the old revision has been contained in such notes). All tables and figures associated with Sec.6 are contained in Annex A. The document has further been revised to facilitate specification of Purchaser information to Contractor, and optional requirements associated with

18、 CP design, manufacture and installation of anodes (see 1.3). Additional comments on revisions in this 2004 issue are made in the Introduction (last paragraph) of Sections 6, 7, 8 and Annex B and C. 1.3 Objectives and Use1.3.1This RP has two major objectives. It may be used as a guideline to Owners

19、or their contractors execution of conceptual or detailed CP design, and to the specification of galvanic anode manufacture and installation. It may also be used as an attachment to an inquiry or purchase order specification for such work. If Purchaser has chosen to refer to this RP in a purchase doc

20、ument, then Contractor shall consider all requirements in Sections 6-9 of this document as mandatory, unless superseded by amendments and deviations in the specific contract. Referring to this document in a purchase document, reference shall also be made to the activities for which DNV-RP-B401 shall

21、 apply, i.e. CP design in Sections 6 and 7, anode manufacture in Sec.8 and/or anode installation in Sec.9. 1.3.2CP design, anode manufacture and anode installation are typically carried out by three different parties (all referred to as Contractor). Different parties issuing a contract (i.e. Purchas

22、er) may also apply. The latter includes Owner, e.g. for CP design and qualification of galvanic anode materials. For definition of contracting parties and associated terminology, see Sec.3. 1.3.3Specification of project specific information and optional requirements for CP detailed design, anode man

23、ufacture and anode installation are described in 7.1.2, 8.1.2 and 9.1.3, respectively. 1.4 Document Structure1.4.1Guidelines and requirements associated with conceptual and detailed CP design are contained in Sections 5, 6 and 7, whilst galvanic anode manufacture and installation are covered in Sec.

24、8 and Sec.9, respectively. Tabulated data for CP design are compiled in Annex A. Annex B and C contain recommended procedures for laboratory testing of anode materials for production quality control and for documentation of long-term electrochemical performance, respectively. 1.5 Relation to Other D

25、NV Documents1.5.1Cathodic protection of submarine pipelines is covered in DNV-RP-F103. 2. References2.1 GeneralThe following standards (2.2-2.7) are referred to in this RP. The latest editions apply. 2.2 ASTM (American Society for Testing and Materials)ASTM G8 Test Method for Cathodic Disbonding of

26、Pipeline Coating ASTM D1141 Specification for Substitute Ocean Seawater2.3 DNV (Det Norske Veritas)DNV-RP-F103 Cathodic Protection of Submarine Pipelines by Galvanic Anodes2.4 EN (European Standards)EN 10204 Metallic Products - Types of Inspection Documents2.5 NORSOKNORSOK M-501 Standard for Surface

27、 Preparation and Protective Coating2.6 ISO (International Organization for Standardisation)ISO 3506 Mechanical Properties of Corrosion-Resistant Stainless Steel Fasteners ISO 8044 Corrosion of Metals and Alloys; Basic Terms and Definitions ISO 8501-1 Preparation of Steel Substrates for Application o

28、f Paint and Related Products - Visual Assessment of Surface Cleanliness. Part 1: Rust Grades and Preparation Grades of Uncoated Steel Substrates. ISO 10005 Quality Management- Guidelines for Quality Plans ISO 10474 Steel and Steel Products - Inspection Documents2.7 NACE InternationalNACE RP0176 Corr

29、osion Control of Steel Fixed Offshore Structures Associated with Petroleum Production NACE RP0387 Metallurgical and Inspection Requirements for Cast Sacrificial Anodes for Offshore Applications3. Terminology and Definitions3.1 TerminologyOwner Party legally responsible for design, construction and o

30、peration of the object to receive CP. Purchaser Party (Owner or main contractor) issuing inquiry or contract for CP design, anode manufacture or anode installation work, or nominated representative. Contractor Party to whom the work (i.e. CP design, anode manufacture or anode installation) has been

31、contracted. shall indicates a mandatory requirement. should indicates a preferred course of action. may indicates a permissible course of action. agreed/agreement refers to a written arrangement between Purchaser and Contractor (e.g. as stated in a contract). report and notify refers to an action by

32、 Contractor in writing. acceptedacceptance refers to a confirmation by Purchaser in writing. certificatecertified refers to the confirmation of specified properties issued by Contractor or supplier of metallic materials according to EN 10204:3.1.B, ISO 10474:5.1-B or equivalent. purchase document(s) refers to an inquiry/tender or purchase/contract specification, as relevant.3.2 DefinitionsF