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1、MANUAL CATHODIC PROTECTION DEP 30.10.73.10-Gen. June 1983 (DEP Circular 11/84 has been incorporated) DESIGN AND ENGINEERING PRACTICE USED BY COMPANIES OF THE ROYAL DUTCH/SHELL GROUP This document is confidential. Neither the whole nor any part of this document may be disclosed to any third party wit
2、hout the prior written consent of Shell Internationale Petroleum Maatschappij B.V., The Hague, the Netherlands. The copyright of this document is vested in Shell Internationale Petroleum Maatschappij B.V., The Hague, the Netherlands. All rights reserved. Neither the whole nor any part of this docume
3、nt may be reproduced, stored in any retrieval system or transmitted in any form or by any means (electronic, mechanical, reprographic, recording or otherwise) without the prior written consent of the copyright owner. PREFACE DEP (Design and Engineering Practice) publications reflect the views, at th
4、e time of publication, of: Shell International Oil Products B.V. (SIOP) and Shell International Exploration and Production B.V. (SIEP) and Shell International Chemicals B.V. (SIC) The Hague, The Netherlands, and other Service Companies. They are based on the experience acquired during their involvem
5、ent with the design, construction, operation and maintenance of processing units and facilities, and they are supplemented with the experience of Group Operating companies. Where appropriate they are based on, or reference is made to, national and international standards and codes of practice. The o
6、bjective is to set the recommended standard for good design and engineering practice applied by Group companies operating an oil refinery, gas handling installation, chemical plant, oil and gas production facility, or any other such facility, and thereby to achieve maximum technical and economic ben
7、efit from standardization. The information set forth in these publications is provided to users for their consideration and decision to implement. This is of particular importance where DEPs may not cover every requirement or diversity of condition at each locality. The system of DEPs is expected to
8、 be sufficiently flexible to allow individual operating companies to adapt the information set forth in DEPs to their own environment and requirements. When Contractors or Manufacturers/Suppliers use DEPs they shall be solely responsible for the quality of work and the attainment of the required des
9、ign and engineering standards. In particular, for those requirements not specifically covered, the Principal will expect them to follow those design and engineering practices which will achieve the same level of integrity as reflected in the DEPs. If in doubt, the Contractor or Manufacturer/Supplier
10、 shall, without detracting from his own responsibility, consult the Principal or its technical advisor. The right to use DEPs is granted by SIOP, SIEP or SIC, in most cases under Service Agreements primarily with companies of the Royal Dutch/Shell Group and other companies receiving technical advice
11、 and services from SIOP, SIEP or SIC. Consequently, three categories of users of DEPs can be distinguished: 1)Operating companies having a Service Agreement with SIOP, SIEP, SIC or other Service Company. The use of DEPs by these Operating companies is subject in all respects to the terms and conditi
12、ons of the relevant Service Agreement. 2)Other parties who are authorized to use DEPs subject to appropriate contractual arrangements. 3)Contractors/subcontractors and Manufacturers/Suppliers under a contract with users referred to under 1) or 2) which requires that tenders for projects, materials s
13、upplied or - generally - work performed on behalf of the said users comply with the relevant standards. Subject to any particular terms and conditions as may be set forth in specific agreements with users, SIOP, SIEP and SIC disclaim any liability of whatsoever nature for any damage (including injur
14、y or death) suffered by any company or person whomsoever as a result of or in connection with the use, application or implementation of any DEP, combination of DEPs or any part thereof. The benefit of this disclaimer shall inure in all respects to SIOP, SIEP, SIC and/or any company affiliated to the
15、se companies that may issue DEPs or require the use of DEPs. Without prejudice to any specific terms in respect of confidentiality under relevant contractual arrangements, DEPs shall not, without the prior written consent of SIOP and SIEP, be disclosed by users to any company or person whomsoever an
16、d the DEPs shall be used exclusively for the purpose for which they have been provided to the user. They shall be returned after use, including any copies which shall only be made by users with the express prior written consent of SIOP and SIEP. The copyright of DEPs vests in SIOP and SIEP. Users sh
17、all arrange for DEPs to be held in safe custody and SIOP or SIEP may at any time require information satisfactory to them in order to ascertain how users implement this requirement. All administrative queries should be directed to the DEP Administrator in SIOP. NOTE: In addition to DEP publications
18、there are Standard Specifications and Draft DEPs for Development (DDDs). DDDs generally introduce new procedures or techniques that will probably need updating as further experience develops during their use. The above requirements for distribution and use of DEPs are also applicable to Standard Spe
19、cifications and DDDs. Standard Specifications and DDDs will gradually be replaced by DEPs. DEP 30.10.73.10-Gen. June 1983 Page 2 TABLE OF CONTENTS 1.INTRODUCTION.5 1.1GENERAL 5 1.2DEFINITIONS 5 1.3RELATED DOCUMENTS5 2.NATURE OF CORROSION AND PRINCIPLES OF CATHODIC PROTECTION 7 2.1ELECTROCHEMICAL NAT
20、URE OF CORROSION7 2.2FACTORS AFFECTING CORROSION.8 2.3CATHODIC PROTECTION.10 3.SURVEY METHODS AND PRELIMINARY INVESTIGATIONS.16 3.1ASSESSING THE NEED FOR CATHODIC PROTECTION.16 3.2SOIL RESISTIVITY17 3.3POTENTIAL MEASUREMENTS.19 3.4CURRENT-DRAINAGE TESTS21 4.PROTECTION BY SACRIFICIALANODES.29 4.1GENE
21、RAL 29 4.2ANODE MATERIALS.30 4.3ANODE CHARACTERISTICS.32 4.4PRACTICAL APPLICATION35 4.5ANODE DISTRIBUTION.37 4.6ANODE SPECIFICATION.38 5.PROTECTION BY IMPRESSED CURRENT41 5.1GENERAL 41 5.2CURRENT SUPPLY41 5.3ANODE MATERIALS.42 6.COATINGS AND CATHODIC PROTECTION45 6.1INFLUENCE OF COATINGS ON CATHODIC
22、 PROTECTION CURRENT REQUIREMENTS45 6.2INFLUENCE OF CATHODIC PROTECTION ON COATINGS.45 7.INSULATING FLANGES AND RESISTANCE BONDS46 7.1INSULATING FLANGES.46 7.2RESISTANCE BONDS46 7.3USE OF INSULATING FLANGES AND RESISTANCE BONDS46 8.ELECTRICAL INTERFERENCE EFFECTS.52 8.1STRAY CURRENTS52 8.2OTHER CATHO
23、DIC PROTECTION SYSTEMS.52 8.3REMEDIAL MEASURES.52 8.4OTHER SOURCES OF INTERFERENCE53 9.MONITORING CATHODIC PROTECTION SYSTEMS55 9.1GENERAL 55 9.2IMPRESSED-CURRENT SYSTEMS55 9.3SACRIFICIAL ANODES55 9.4LINE CURRENT MEASUREMENTS.56 10.PROTECTION OF BURIED PIPELINES57 10.1GENERAL 57 10.2CHOICE OF SYSTEM
24、.57 10.3COATINGS 58 10.4ATTACHING CABLES.58 10.5TELLURIC CURRENT.58 10.6ALTERNATING-CURRENT EFFECTS.59 10.7PIPELINE GROUNDING.60 11.PROTECTION OF UNDERGROUND TANKS63 11.1GENERAL 63 11.2PROTECTION BY SACRIFICIAL ANODES63 DEP 30.10.73.10-Gen. June 1983 Page 3 11.3PROTECTION BY IMPRESSED CURRENT64 11.4
25、INSULATING FLANGES AND JOINTS.64 12.PROTECTION OF SUBMARINE PIPELINES65 12.1GENERAL 65 12.2METHODS OF APPLICATION65 13.PROTECTION OF MARINE STRUCTURES68 13.1GENERAL 68 13.2METHODS OF PROTECTION68 13.3PRECAUTIONS.68 13.4EXAMPLE: OFFSHORE STRUCTURE CATHODIC PROTECTION DESIGN.69 14.PROTECTION OF HEAT E
26、XCHANGERS72 14.1BOX COOLERS.72 14.2SHELL-AND-TUBE HEAT EXCHANGERS.72 15.PROTECTION OF OIL WELL CASING74 15.1GENERAL 74 15.2METHODS OF PROTECTION74 15.3STRAY CURRENTS75 15.4APPLICATION.75 16.PROTECTION OF CRAFT76 16.1GENERAL 76 16.2EXTERNAL PROTECTION OF HULLS76 16.3EFFECT OF CATHODIC PROTECTION ON H
27、ULL PAINT .77 16.4PROTECTION OF CARGO AND BALLAST TANKS77 17.SAFETY PRECAUTIONS.78 18.ECONOMIC CONSIDERATIONS.79 18.1APPLICATION AND ECONOMIC JUSTIFICATION.79 18.2COST OF CATHODIC PROTECTION79 19.REFERENCES80 20.STANDARD DRAWINGS81 21.APPENDICES82 APPENDICES APPENDIX 1SPECIFICATION FOR THE SUPPLY, I
28、NSPECTION, AND TESTING OF SACRIFICIAL ANODES.83 APPENDIX 2POWER GENERATORS.86 DEP 30.10.73.10-Gen. June 1983 Page 4 1.INTRODUCTION 1.1GENERAL This manual, which is a revision of an earlier publication dated December 1970, describes the basic principles, advantages and limitations for the control of
29、corrosion of immersed, submerged or buried metal by cathodic protection, and gives guidance for the design of the installations required. It is intended for use in oil refineries, chemical plants, gas plants and, where applicable, in exploration, production and new ventures. This manual should enabl
30、e staff at locations in the absence of a specialist to decide when cathodic protection may be technically feasible and economically justifiable and also to deal effectively with specialist consultants and contractors normally called in to carry out cathodic protection work. Although the principle of
31、 cathodic protection is simple, its practical application calls for a certain skill and experience, and in all but the most straightforward cases it is wise to employ people who have this, rather than to attempt the work with inexperienced staff. Unless otherwise authorized by SIPM, the distribution
32、 of this manual is confined to companies belonging to or managed by the Royal Dutch/Shell Group. All publications referred to in this manual are listed in Section 19; the relevant standard drawings in Section 20. Where cross references are made, the number of the section or subsection referred to is
33、 shown in brackets. 1.2DEFINITIONS For the purpose of this manual the following definitions shall hold: Shall and Should - the word shall is to be understood as mandatory and the word should as strongly recommended to comply with the regulations of this manual. 1.3RELATED DOCUMENTS This manual is to
34、 be used for guidance, other documents such as those listed below provide useful guidelines for cathodic protection. In some countries operators are required to follow the local rules unless proof can be shown that the proposed method will be adequate under the circumstances envisaged. It should be
35、realized, that for offshore, the assumptions made are based on the fact that no problems have ever been reported when systems were designed along the guidelines given in this manual. It is most complicated and expensive to monitor cathodic protection systems effectively in the deeper and hostile wat
36、ers. It is therefore often recommendable to adopt conservative approach if authorities so require. The related documents often referred to are: British Standard CP 1021: latest revision: Code of Practice for cathodic protection. NACE Standard RP-01-76: Control of corrosion on steel, fixed offshore p
37、latforms associated with petroleum production. NACE Standard RP-06-75: Control of corrosion on offshore steel pipelines. NACE Standard RP-01-77: Mitigation of alternating current and lightning effects on metallic structures and corrosion control systems. NACE Standard RP-05-75: Design, installation,
38、 operation and maintenance of internal cathodic protection systems in oil treating vessels. NACE Standard RP-05-72: Design, installation, operation and maintenance of impressed current deep groundbeds. NACE Standard RP-01-69: Control of external corrosion on underground of submerged DEP 30.10.73.10-
39、Gen. June 1983 Page 5 metallic piping systems. Det Norske Veritas: Rules for the design, construction and inspection of offshore structures (with appendices). Det Norske Veritas: Rules for the design, construction and inspection of submarine pipelines and pipeline risers. Det Norske Veritas: TN-A 70
40、2: Installation of sacrificial anodes. Det Norske Veritas: TN-A 703: Fixed offshore installations cathodic protection evaluation. IEC publication 529: Classification of degrees of protection provided by enclosures. DEP 30.10.73.10-Gen. June 1983 Page 6 2.NATURE OF CORROSION AND PRINCIPLES OF CATHODI
41、C PROTECTION 2.1ELECTROCHEMICAL NATURE OF CORROSION At atmospheric temperatures the corrosion of metals is an electrochemical process, in which the metal surface is in contact with an electrolyte. The electrolyte may be a film of moisture containing dissolved salts, e.g. as in the case of corrosion
42、in the atmosphere, or may constitute the whole or part of the surrounding medium, e.g. when metal is immersed in fresh water, sea water or buried in the soil. In the last case the electrolyte is the soil water, containing dissolved salts. At the surface of a metal corroding in an electrolyte there a
43、re active electrochemical cells in which current flows between anodic and cathodic areas. The distribution of the anodic and cathodic areas depends on the metal surface (included impurities, oxide films such as millscale, variations in physical state, etc.), and also on the nature of the surrounding
44、 medium. Owing to the potential differences existing between the anodic and cathodic areas, positively charged metal ions leave the metal surface at the anodes while electrons leave the surface at the cathodes. Thus corrosion takes place at the anodic areas where metal ions react with the electrolyt
45、e to form the typical corrosion products. At the cathodic areas dissolution of metal does not take place, but reactions occur in the electrolyte. Although the basic principles of corrosion apply to all metals, illustration is simpler if discussion is restricted to iron and steel, which are the most
46、commonly used metals in the petroleum industry; they are considered specifically in most of the sections which follow. In this manual potential values will be referred to either a copper/copper sulphate half-cell or silver/silver chloride half-cell. The first is used mainly in soil, the second in se
47、a water. The natural surface potentials of iron and steel in contact with soil or water are always negative when referred to either of these halfcells; nevertheless different areas of the same piece of metal surface may have different potentials. DEP 30.10.73.10-Gen. June 1983 Page 7 2.2FACTORS AFFE
48、CTING CORROSION 2.2.1Steel surface conditions If a steel surface is partially covered with millscale, it is cathodic with respect to the surrounding areas of bare steel. Corrosion occurs, therefore, on the relatively lower- potential bare metal as shown in Fig. 2-1, and is particularly severe when t
49、he area of the millscale is large in relation to the area of the bare metal. If impurities, which are usually anodic with respect to steel, are occluded in the metal surface, corrosion in the form of pitting may take place at these points as shown in Fig. 2-1. When dissimilar metals are in contact and are surrounded by an electrolyte, the less noble metal tends to corrode more severely, and the nobler one less severely than they would if there was no contact. A common example of this is the deterioration of the zinc coating on a galvanized pipe when connected to a bare steel pipe, see Fig.