DIN EN 12495-2000 Cathodic protection for fixed steel offshore structures German version EN 12495 2000《海上固定钢结构的阴极保护》.pdf

1、DEUTSCHE NORM Atxi12000 Cathodic protection for fixed steel offshore structures English version of DIN EN 12495 DIN EN 12495 - ICs 47.020.01; 77.060 Kathodischer Korrosionsschutz von ortsfesten Offshore-Anlagen aus Stahl European Standard EN 12495 : 2000 has the status of a DIN Standard. A comma is

2、used as the decimal marker. National foreword This standard has been prepared by CEN/TC 21 9. The responsible German body involved in its preparation was the Normensfelle Schiffs- und Meeresfechnik (Shipbuilding and Marine Technology Standards Committee), Technical Committee Korrosionsschufz. EN com

3、prises 32 pages. No pari of this standard may be reproduced without the prior permission of Ref. No. DIN EN 12495 : 2000-0 Y Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany, s the exclusive right of sale for German Standards (DIN-Normen). English price group 13

4、Sales No. 11 13 09.00 EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 12495 January 2000 ICs 47.020.01 : 77.060 English version Cathodic protection for fixed steel offshore structures Protection cathodique des structures en acier fixes en mer Kathodischer Korrosionsschutz von ortsfesten Offsh o

5、re-An lagen aus Stahl This European Standard was approved by CEN on 1999-1 2-03 CEN members are bound to comply with the CENKENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bib

6、liographical references concerning such national stand- ards may be obtained on application to the Central Secretariat or to any CEN member. The European Standards exist in three official versions (English, French, German). A version in any other language made by translation under the responsibility

7、 of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, the Neth

8、erlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels O 2000. CEN - All rights of exploitation in any form and by

9、 any means reserved worldwide for CEN national members. Ref. No. EN 12495 : 2000 E Page 2 EN 12495 : 2000 Contents Page Foreword 4 Introduction . 5 1 1.1 1.2 1.3 2 3 4 4.1 4.2 4.3 4.4 4.5 5 5.1 5.2 5.3 5.4 5.5 6 6.1 6.2 6.3 6.4 7 7.1 Scope 5 Structural parts 5 Materials . 5 Environment 6 Normative r

10、eferences 6 Terms and definitions . 6 Design basis 8 Objectives 8 Cathodic protection criteria . 9 Electrical current demand 9 Coatings . 10 Cathodic protection systems - Anode dimensions . 11 Design of galvanic anodes system . 11 General . 11 Design considerations 12 Galvanic anode materials . 12 L

11、ocation of anodes . 13 Anodes inserts and attachments design . 14 Design of impressed current system 15 General . 15 Design considerations 15 Equipment considerations . 16 Location considerations . 17 Design of monitoring systems . 17 Objectives 18 7.2 7.3 7.4 7.5 7.6 8 9 9.1 9.2 9.3 10 10.1 10.2 10

12、.3 11 11.1 11.2 11.3 11.4 Page 3 EN 12495 : 2000 Description . 18 Potential measurements . 19 Measurement of the anode electrical current output 19 Transmission of data 20 Control and monitoring of impressed current generators . 20 Installation of cathodic protection and monitoring systems . 20 Comm

13、issioning and surveying of cathodic protection systems . 20 Objectives 20 Galvanic anode system 21 Impressed current system . 21 Documentation 21 General . 21 Galvanic anodes system 21 Impressed current system . 22 Safety and cathodic protection 22 Objectives 22 Physical obstructions . 23 Electric s

14、hock 23 Gas evolution 23 Annex A (informative) Guidance on current requirement for cathodic protection of fixed steel off shore structures . 24 Annex B (informative) Anode resistance and life duration formulae . 26 Annex C (informative) Recommendations for anode installation 29 Annex D (informative)

15、 Safety precautions for impressed current system 30 Annex E (informative) Typical electrochemical characteristlcs for commonly used impressed current anodes . 31 Bibliography 32 Page 4 EN 12495 : 2000 Foreword This European Standard has been prepared by Technical Committee CENTTC 21 9 “Cathodic Prot

16、ection“, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by July 2000, and conflicting national standards shall be withdrawn at the latest by July 2000. Accor

17、ding to the CENICENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal

18、, Spain, Sweden, Switzerland and the United Kingdom. The Annexes A,B,C,D, and E of this European Standard are informative. Page 5 EN 12495 : 2000 Introduction Cathodic protection, possibly together with protective coating or paint, is usually applied to protect the external surfaces of fixed steel o

19、ffshore structures and appurtenance from corrosion due to sea water or marine sediments. The general principles of cathodic protection are detailed in prEN 12473:1999. The cathodic reaction ensures the protection from corrosion of the submerged areas of the structure and associated appurtenances whi

20、ch are exposed to the marine environment. Cathodic protection involves the supply of sufficient direct current to the external surface of the structure in order to reduce the steel to electrolyte potential down to values where corrosion is insignificant. 1 Scope This European Standard defines the me

21、ans to be used to cathodically protect the submerged areas of fixed steel offshore structures and appurtenances. 1.1 Structural parts This European Standard defines the requirements for the cathodic protection of fixed structures, including sub sea production and related protective structures whethe

22、r connected or not to each other by pipelines and/or walkways. It also covers the submerged areas of appurtenances attached to the structure, when these are electrically connected to the structure. It does not cover the cathodic protection of floating structures such as ships, semi-submersible units

23、, or elongated structures such as pipelines or cables. This European Standard concerns only the cathodic protection of external surfaces, in contact with the sea water or with the sea bed. It covers the immersed or buried external surfaces of the jacket, conductor pipes, well casings, piles, J-tubes

24、, production or utility risers, etc. It does not cover the corrosion protection of the sections of the structure above the sea level : .e. the splash zone and atmospheric zone. This standard does not include the internal protection of any components such as jacket members, legs, conductor pipes; the

25、 protection of these is often performed using chemicals. 1.2 Materials This European Standard covers the cathodic protection of bare or coated steels with a specified minimum yield strength (S.M.Y.S.) not exceeding 500 N/mm2. 1.2.1 Overpolarisation by reducing the number of ancillary surfaces ; by l

26、imiting the ratio of steel surfaces over electrolyte volume in congested areas. Minimum negative potential volt Table 1 - Summary of potential versus silver/silver chloride/sea water reference electrode recommended for the cathodic protection of steel materials in sea water Maximum negative potentia

27、l volt Material Carbon / low alloy steels aerobic environment anaerobic environment -0,80 -0.90 Stainless steel Austenitic steel - (PREN240) - (PREN40) Duplex -0,30 -0,60 (see note 1) -0,60 (see note 1) no limit no limit (see note 2) _ NOTE 1 For most applications these potentials are adequate for t

28、he protection of crevices although higher potentials can be considered. NOTE 2 Depending on metallurgical structure these alloys can be susceptible to cracking and high negative potentials must be avoided (see prEN 12473:1999). 4.3 Electrical current demand In order to achieve the cathodic protectio

29、n criteria on the whole structure it is necessary to consider the electrical current demand on each part of the structure. The electrical current demand of each pari of the structure is the product of its steel surface area multiplied by the electrical current density required. The current density r

30、equired is not the same for all parts of the structure as the environmental conditions are variable. Therefore, the following areas and parts should be considered, referring to zones as defined in clause 3 : - areas located in the tidal and transition zones (usually coated or cladded) ; - areas loca

31、ted in the immersed zone : - areas located in the buried zone ; Page 10 EN 12495 : 2000 - wells to be drilled ; a current allowance per well shall be considered, depending on projected sizes, depth and cementing of the wells (see A.4 in annex A) ; neighbouring structures and pipelines in electrical

32、contact with the fixed steel offshore structure to be protected. The selection of design current densities may be based on experiences from similar structures in the same environment or from specific tests and measurements (typical values are given in annex A). - The electrical current density requi

33、red for cathodic protection depends upon the kinetics of the electrochemical reactions and varies with parameters such as the electrode potential of the steel, the dissolved oxygen content of the sea water, the water flow rate, the temperature, and, possibly, the water depth. Furthermore, the build

34、up of calcareous deposits and the settlement of marine growth modify the surface conditions for the cathodic reactions. For each particular set of environmental condition and surface condition of the steel (such as rusted, blast cleaned, coated with organic or metallic coating), the following electr

35、ical current densities shall be evaluated : - initial electrical current density required to achieve the initial polarisation of the structure, .e. to achieve the lowering of the steel potential down to value within the range recommended in table 1; maintenance electrical current density required to

36、 maintain this polarisation level on the structure ; - - final or repolarisation electrical current density required for a possible repolarisation (.e. for re-establishing the potential to the initial polarisation level) of the structure after severe storms or cleaning operations. As the initial pol

37、arisation period preceding steady state or maintenance conditions is normally short compared to the design life, the time weighted electrical current density becomes very close to maintenance electrical current density. A proper evaluation of the current densities required shall be carried out to op

38、timise the cathodic protection system. Interactions A platform may be permanently or temporarily connected to other neighbouring structures. These structures should be fitted with their own cathodic protection system which shall be checked before electrically connecting them to the platform consider

39、ed. If temporary structures are not fitted with a cathodic protection system or if this is ineffective, the cathodic protection of the platform should be checked to ensure its efficiency during the connection period and the influence of this foreign structure should be evaluated. 4.4 Coatings The ca

40、thodic protection system may be combined with suitable coating systems. The coating reduces the electrical current demand and improves the electrical current distribution on the structure due to its insulating properties. This reduction of the electrical current demand may be in a ratio of 100 to 1

41、or even more. However, the current demand of coated steel will increase with time as the coating deteriorates. An initial coating breakdown factor related mainly to mechanical damage occurring during the installation of the structure should be considered and a coating deterioration rate shall be the

42、reafter evaluated in order to take into account the coating ageing and possible small mechanical damage occurring to the coating during the structure life. These values are closely dependent on the actual installation conditions and operation conditions. Guidelines for the values of coating breakdow

43、n factors are given in annex A. The resultant electrical current density needed for the protection of coated steel is therefore equal to the product of the electrical current density for bare steel and the coating breakdown factor. Page 11 EN 12495 : 2000 Due to possible interactions between the cat

44、hodic protection and the coating, all coatings to be used in combination with cathodic protection should be tested beforehand to establish that they have adequate resistance to cathodic disbondment. 4.5 Cathodic protection systems - Anode dimensions Cathodic protection can be achieved using : - the

45、galvanic anodes system ; - the impressed current system ; - a combination of both cathodic protection systems (hybrid systems). When using hybrid systems the galvanic anodes should provide cathodic protection during float out, initial installation and subsequently during the impressed current system

46、 shutdowns. Galvanic anodes should also be installed in areas where it may be difficult to achieve adequate level of polarisation by the impressed current system due to shielding effects. As the electrical current demand is not constant with time, the cathodic protection system shall be able to deli

47、ver the re-polarisation current density required for short periods throughout the life of the structure. The number of anodes required in any particular zone of the structure will be determined by the cathodic protection current demand in that zone and the individual anode current output. The curren

48、t output from each individual anode is calculated by Ohms law: /= AWR where : AV is the driving voltage between the anode potential and the protection potential of steel, in volts ; R is the circuit resistance, usually taken as the anode resistance, in ohms. The anode resistance is a function of the

49、 resistivity of the anodic environment and of the geometry (form and dimensions) of the anode. The anode resistance may be calculated using one of the empirical formulae given in annex B. If the anodes are grouped in arrays and close to each other, mutual interference between anodes should be considered when calculating the anodic resistance. The cathodic protection system should be designed to minimise the risks of affecting associated pipelines or any other neighbouring structure. All components of the cathodic protection system should be installed at locations where the prob