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https://cathodic.ir/wp-content/uploads/2017/11/BS-7361-1-1991-WWW.CATHODIC.IR_.pdf
Part 1: Code of practice for land and marine applications — (formerly CP 1021)
Foreword
This Part of BS 7361 has been prepared under the direction of the General Electrotechnical Standards Policy Committee. It represents a revision of CP 1021:1973, which is withdrawn. BS 7361의 이 부분은 일반 전기 기술 표준 정책 위원회의 지시에 따라 준비되었다. 이는 철회된 CP 1021:1973의 개정판이다.
Cathodic protection is a means of preventing the corrosion of most metals wherever they are in contact with a mass of water or moist materials. 음극 보호는 다량의 물이나 습한 물질과 접촉하는 대부분의 금속의 부식을 방지하는 수단이다. It should not, however, be inferred that cathodic protection, wherever applicable, is necessarily advantageous. 그러나 적용 가능한 경우 음극 방식이 반드시 유리하다고 추론해서는 안 된다. Unless the need for cathodic protection is already established, every case should be carefully examined and an evaluation made of the economic advantage of cathodic protection, compared with other methods of avoiding or reducing corrosion, such as sheathing or coating, the use of other materials of construction etc. 음극 방식에 대한 필요성이 이미 확립되어 있지 않은 한, 모든 경우를 면밀히 검토하고 피복이나 코팅, 기타 건설 재료의 사용과 같은 부식을 방지하거나 감소시키는 다른 방법과 비교하여 음극 방식의 경제적 이점을 평가해야 한다. Included in the assessment should be the cost and consequences of allowing the expected corrosion to proceed. 예상되는 부식이 진행되도록 허용하는 데 따른 비용과 결과도 평가에 포함되어야 한다. This may be possible, for example, in the case of steel pilings, while entirely ruled out in the case of high pressure pipelines. 예를 들어 강철 말뚝의 경우 이는 가능할 수 있지만 고압 파이프라인의 경우에는 완전히 배제다.
This Part of BS 7361 covers good up-to-date practice and contains both guidance on general principles and detailed information on the cathodic protection of particular types of structure or plant, excluding those involved in off-shore applications. Even where sufficient evidence based on actual installations has not been obtained to enable detailed information to be given, it should not be assumed that cathodic protection is unsuitable if there is sufficient economic incentive. Lack of evidence has also prevented firm guidance being given at several points in this Part of BS 7361, notably on the test methods needed to avoid excessive error due to potential drop through the electrolyte when the effectiveness of cathodic protection is being assessed by measuring the potential of the metal relative to a reference electrode.
Attention is drawn to the importance of considering any measures necessary to prevent corrosion during the early stages of the design of structures and possible future extensions. Design to prevent corrosion, for example by selection of materials, avoidance of unsuitable shapes or combinations of metals, or by using metal spraying or protective coatings is important, but is outside the scope of this standard. The corrosion protection of iron and steel in this context is covered by BS 5493.
This revision has been occasioned by developments in a variety of industries since 1973, as well as increasing sophistication in the associated measuring techniques. Whilst the main body of the first edition has been found to be sound, detailed changes have been required throughout the document, and additional experience in areas such as pipe coatings, anode materials and the cathodic protection of reinforcing steel in concrete, and methods of assessing cathodic protection, has necessitated the introduction of new text. Despite further consideration by the committee no change is proposed to the 20 mV criterion for limiting corrosion interaction.
A major area for cathodic protection is that concerned with off-shore applications. The scale of this work and the size of the corresponding text to cover it requires the preparation of Part 2 of this standard and this is intended to be accomplished by participation in corresponding work that has been initiated in Europe under the aegis of CEN.
It has been assumed in the drafting of this British Standard that the execution of its recommendations is entrusted to appropriately qualified and experienced people, for whose guidance it has been prepared.
Section 1. General
1.1 Scope
This Part of BS 7361 covers the applications of cathodic protection for which principles of use have been established, i.e. the prevention of the corrosion of buried or immersed metalwork and the internal protection of containers for aqueous liquids. It does not deal with the cathodic protection of off-shore structures. The code indicates general circumstances in which the application of cathodic protection is likely to be economical as a method of corrosion prevention. It covers general principles, their application, the special problems arising in the protection of particular types of structure, the safeguarding of neighbouring structures, electrical measurements, the commissioning, operation and maintenance of cathodic protection systems, and safety aspects. Off-shore applications are to be covered in Part 2 (see foreword).
NOTE 1 Where detail of equipment is shown in the figures, the purpose is to assist in the reading of the text by indicating typical arrangements. The figures are not intended to establish preferred types of equipment. Similarly, any dimensions shown are to provide an indication of size, not to establish preferred dimensions.
NOTE 2 The titles of the publications referred to in this code are listed on the inside back cover. The titles of related British Standards are listed in Appendix B for information.
NOTE 3 The numbers in square brackets in the text refer to numbered references in Appendix C.
1.2 Definitions
For the purposes of this Part of BS 7361 the definitions given in BS 4727 apply together with the following. 1.2.1 anaerobic
the lack of free oxygen in the electrolyte adjacent to a metal structure
1.2.2 anodes
1.2.2.1 anode the electrode through which direct current enters an electrolyte
1.2.2.2 cantilever anode
an anode formed and supported as a cantilever NOTE This type of anode is used particularly for the impressed current protection of the inner surfaces of containers for liquids.
1.2.2.3 continuous anode
a long flexible anode
1.2.2.4 sacrificial anode
an anode used to protect a structure by galvanic action
NOTE Previously termed “galvanic anode” or “reactive anode”.
1.2.2.5 anode backfill
a low-resistance moisture-retaining material immediately surrounding a buried anode for the purpose of decreasing the effective resistance of the anode to the soil
1.2.2.6 anodic area
that part of a metal surface which acts as an anode
1.2.3 blistering (of paint film)
the formation of swellings on the surface of an unbroken paint film by moisture, gases, or the development of corrosion products between the metal and the paint film
1.2.4 bonds
1.2.4.1 bond
a piece of metal conductor, either solid or flexible, usually of copper, connecting two points on the same or on different structures, to prevent any appreciable change in the potential of the one point with respect to the other
1.2.4.2 continuity bond
a bond designed and installed specifically to ensure the electrical continuity of a structure NOTE This may be permanent or temporary. In the latter case it is used to connect two sections of a structure which would otherwise be disconnected during a modification or repair.
1.2.4.3 drainage bond
a bond to effect electric drainage
1.2.4.4 remedial bond
a bond installed between a primary and a secondary structure in order to eliminate or reduce corrosion interaction
1.2.4.5 resistance bond
a bond either incorporating resistors or of adequate resistance in itself to limit the flow of current
1.2.4.6 safety bond
a bond connecting the metallic framework or enclosure of electrical apparatus with earth, in order to limit its rise in potential above earth in the event of a fault, and so reduce the risk of electric shock to anyone touching the framework or enclosure
1.2.4.7 bond resistance
the ohmic resistance of a bond including the contact resistance at the points of attachment of its extremities
1.2.5 carbonation
the chemical reaction between atmospheric carbon dioxide and the calcium hydroxide present in Portland cement
1.2.6 cathode
the electrode through which direct current leaves an electrolyte
1.2.7 cathodic area
that part of a metal surface which acts as a cathode
1.2.8 cathodic disbonding
the failure of adhesion between a coating and a metallic surface that is directly attributable to cathodic protection conditions and that is often initiated by a defect in the coating system, such as accidental damage, imperfect application or excessive permeability of the coating
1.2.9 cathodic protection
a means of rendering a metal immune from corrosive attack by causing direct current to flow from its electrolytic environment into the entire metal surface
1.2.10 cell
a complete electrolytic system comprising of a cathode and an anode in electrical contact with an intervening electrolyte
1.2.11 conductor
a substance (mainly a metal or carbon) in which electric current flows by the movement of electrons
1.2.12 corrosion
the chemical or electrochemical reaction of a metal with its environment, resulting in its progressive degradation or destruction NOTE This standard is concerned with corrosion by electrochemical action.
1.2.13 corrosion product
the chemical compound or compounds produced by the reaction of a corroding metal with its environment
1.2.14 corrosion interaction
the increase or decrease in the rate of corrosion, or the tendency towards corrosion, of a buried or immersed structure caused by the interception of part of the cathodic protection current applied to another buried or immersed structure or current from other sources
NOTE 1 For convenience, also referred to as “interaction”.
NOTE 2 Also known as “corrosion interference”.
1.2.15 crossing point
a point where two buried or immersed structures cross each other when viewed in plan
1.2.16 current density
the current per unit geometrical area of the protected structure, coated and uncoated, in contact with the electrolyte
1.2.17 dielectric shield
a protective covering of insulating material applied to a painted structure in the immediate vicinity of an anode to prevent the paint being stripped by alkali produced by the high current density at the steel surface close to the anode NOTE This is usually applied to a ship’s hull.
1.2.18 differential aeration
the unequal access of air to different parts of a metallic surface NOTE This often results in the stimulation of corrosion at areas where access of air is restricted.
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