1、 Standard Practice Impressed Current Cathodic Protection of Internal Submerged Surfaces of Carbon Steel Water Storage Tanks This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any r
2、espect preclude anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by
3、implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be i
4、nterpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for th
5、e interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteer
6、s. Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all poten
7、tial health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental prot
8、ection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or
9、withdrawn at any time in accordance with NACE technical committee procedures. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication and subsequently from the date of each reaffirmation or revision
10、. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International First Service Department, 1440 South Creek Dr., Houston, Texas 77084-4906 (
11、telephone +1 281-228-6200). Reaffirmed 2014-01-09 Reaffirmed 2007-09-20 Revised 2001-11-07 Reaffirmed March 1995 Reaffirmed April 1990 Approved November 1988 NACE International 1440 South Creek Drive Houston, Texas 77084-4906 +1 281-228-6200 ISBN 1-57590-138-2 2014 NACE International NACE SP0388-201
12、4 (formerly RP0388) Item No. 21040 SP0388-2014 NACE International i _ Foreword The purpose of this NACE standard is to present the recommended practices for providing impressed current cathodic protection (CP) to the normally submerged steel surfaces inside water storage tanks. It contains recommend
13、ations for the design and installation of these cathodic protection systems and methods for determining the effectiveness of these systems. Recommendations for the operation and maintenance of both automatic and manual systems are provided. This standard is applicable to relatively large water stora
14、ge tanks used in municipal water supply and fire protection, including elevated and on-grade tanks. Although the general principles outlined in this standard are applicable to all such tanks, the impressed current cathodic protection system described in this standard may not be practical for smaller
15、 tanks. This standard is intended for use by engineers, water utilities, tank erectors and other contractors, and owner operators of steel water storage tanks. This standard was originally prepared in 1988 by Task Group T-7L-1, a component of Unit Committee T-7L, “Cathodic Protection.” The task grou
16、p was composed of corrosion engineers and others experienced in the design, installation, and maintenance of impressed current cathodic protection systems for water storage tanks. It was reaffirmed by T-7L in 1990 and 1995, revised in 2001 by Task Group (TG) 167 (formerly T-7L-14), and reaffirmed by
17、 Specific Technology Group (STG) 05 in 2007 and 2014. TG 167 is administered by STG 05, “Cathodic/Anodic Protection.” This standard is issued by NACE International under the auspices of STG 05. In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of t
18、hese terms in the NACE Publications Style Manual. The terms shall and must are used to state a requirement, and are considered mandatory. The term should is used to state something good and is recommended, but is not considered mandatory. The term may is used to state something considered optional.
19、_ SP0388-2014 ii NACE International _ Standard Practice Impressed Current Cathodic Protection of Internal Submerged Surfaces of Carbon Steel Water Storage Tanks Contents 1. General 1 2. Definitions 1 3. Determination of the Need for Cathodic Protection . 2 4. Design of Impressed Current Cathodic Pro
20、tection Systems . 3 5. Installation of Impressed Current Cathodic Protection Systems . 6 6. Criteria for Cathodic Protection and Measurement Procedures 7 7. Automatic Impressed Current Systems 8 8. Operation and Maintenance 9 References 11 _ SP0388-2014 NACE International 1 _ Section 1: General 1.1
21、This standard presents recommended practices for applying impressed current cathodic protection to the internal submerged surfaces of steel tanks used for the storage of natural waters. These tanks may be provided with an interior barrier coating. This standard is not intended for use with metallic
22、coatings or linings, such as zinc or aluminum. 1.2 It is recognized that galvanic anode systems can, at times, be used for cathodic protection of the internal surfaces of water storage tanks;(1)however, this standard addresses only impressed current systems. 1.3 Natural waters, as used in this stand
23、ard, include both potable and nonpotable fresh waters associated with water supply systems and fire protection. 1.4 The ground level and elevated storage tanks considered in this standard are of welded, bolted, or riveted steel construction and include many shapes and sizes. 1.5 Cathodic protection,
24、 as described in this standard, may be used alone to control corrosion of submerged steel surfaces or used as a complement to the protection afforded by protective coatings. Cathodic protection cannot protect surfaces that are not submerged. Non-submerged surfaces must be protected by coatings alone
25、. Cathodic protection does not reverse structural damage already caused by corrosion. 1.6 Cathodic protection may be installed to control corrosion in both newly constructed and existing tanks. When cathodic protection is used on existing tanks, it is not necessary to prepare the surfaces to be prot
26、ected; however, it may be necessary to drain the tank during installation. 1.7 It is recognized that the tanks under consideration are often associated with potable water and fire protection systems, which may be subject to public health and safety regulations. This standard should not infringe upon
27、 those regulations. Proper disinfection of the tanks may be required after installation. Any applicable regulations such as those from the U.S. Environmental Protection Agency (EPA)(2)and ANSI(3)/NSF(4)-612should be checked. In the United States, all materials in contact with potable water or expose
28、d to the interior of potable water tanks must be classified in accordance with ANSI/NSF-61. 1.8 The provisions of this standard should be applied under the direction of a competent corrosion engineer. The term “corrosion engineer,” as used in this standard, refers to a person who, by reason of knowl
29、edge of the physical sciences and the principles of engineering and mathematics, as acquired by professional education and related practical experience, is qualified to practice corrosion control and cathodic protection for water storage tanks. Such persons may be registered professional engineers o
30、r persons certified by NACE International as Cathodic Protection or Corrosion Specialists, if their professional activities include suitable experience in corrosion control and cathodic protection. 1.9 This standard may not be applicable in all situations. The responsible corrosion engineer may cons
31、ider alternate corrosion control methods. _ Section 2: Definitions Anode: The electrode of an electrochemical cell at which oxidation occurs. (Electrons flow away from the anode in the external circuit. It is usually the electrode where corrosion occurs and metal ions enter solution.) Calcareous Coa
32、ting: A layer consisting of calcium carbonate and other salts deposited on the surface. When the surface is cathodically polarized as in cathodic protection, this layer is the result of the increased pH adjacent to the protected surface. Cathode: The electrode of an electrochemical cell at which red
33、uction is the principal reaction. (Electrons flow toward the cathode in the external circuit.) Cathodic Disbondment: The destruction of adhesion between a coating and the coated surface caused by products of a cathodic reaction. (1)Information regarding galvanic cathodic protection of water storage
34、tanks may be found in NACE SP0196.1(2) U.S. Environmental Protection Agency (EPA), 401 M Street SW, Washington, DC 20460. (3) American National Standards Institute (ANSI), 25 W 43rd St., Fourth Floor, New York, NY 10036.(4) NSF International, P.O. Box 130140, Ann Arbor, MI 48113-0140. SP0388-2014 2
35、NACE International Cathodic Protection: A technique to reduce the corrosion rate of a metal surface by making that surface the cathode of an electrochemical cell. Coating: (1) a liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, dec
36、orative, or functional adherent film. (2) (in a more general sense) a thin layer of solid material on a surface that provides improved protective, decorative, or functional properties. Conductivity: (1) a measure of the ability of a material to conduct an electric charge. (2) the current transferred
37、 across a material (e.g., coating) per unit area per unit potential gradient. (Conductivity is the reciprocal of resistivity.) Corrosion: The deterioration of a material, usually a metal, that results from a chemical or electrochemical reaction with its environment. Current Density: The electric cur
38、rent flowing to or from a unit area of an electrode surface. Electrode: A material that conducts electrons, is used to establish contact with an electrolyte, and through which current is transferred to or from an electrolyte Electrode Potential: The potential of an electrode in an electrolyte as mea
39、sured against a reference electrode. Electrolyte: A chemical substance containing ions that migrate in an electric field. Galvanic Anode: A metal that provides sacrificial protection to another metal that is more noble when electrically coupled in an electrolyte. This type of anode is the electron s
40、ource in one type of cathodic protection. Holiday: A discontinuity in a protective coating that exposes unprotected surface to the environment. Impressed Current: An electric current supplied by a device employing a power source that is external to the electrode system. (An example is direct current
41、 for cathodic protection.) Impressed Current Anode: An electrode, suitable for use as an anode when connected to a source of impressed current. (It is often composed of a substantially inert material that conducts by oxidation of the electrolyte and, for this reason, is not corroded appreciably.) IR
42、 Drop: The voltage across a resistance when current is applied in accordance with Ohms Law. Polarization: The change from the corrosion potential as a result of current flow across the electrode/electrolyte interface. Reference Electrode: An electrode having a stable and reproducible potential, whic
43、h is used in the measurement of other electrode potentials. Resistivity: The electrical resistance between opposite faces of a unit cube of material. Tank-to-Water Potential: The voltage difference between a submerged metallic portion of the tank and the electrolyte (water), which is measured with a
44、 reference electrode in contact with the electrolyte. _ Section 3: Determination of the Need for Cathodic Protection 3.1 Introduction 3.1.1 Steel tank surfaces submerged in natural waters are subject to corrosion. The methods and procedures used to control corrosion should be governed by the rate of
45、 corrosion and the cost of maintaining the tank, including the hydraulic and aesthetic effects of corrosion debris in the tank and piping. 3.1.2 All coatings are subject to damage and deterioration. Therefore, corrosion control by use of coatings alone on the submerged surfaces of a steel water stor
46、age tank is usually not possible. SP0388-2014 NACE International 3 3.1.3 Cathodic protection is effective in controlling corrosion only on the submerged metal surfaces. 3.2 Cathodic Protection of Coated Tanks 3.2.1 In almost all cases, natural waters are sufficiently corrosive to require the use of
47、protective coatings and cathodic protection for corrosion control. Protective coatings and cathodic protection are synergistic, with the combination of the two methods providing a greater degree of corrosion protection than either method used alone. 3.2.2 Properly designed and maintained, cathodic p
48、rotection systems can extend the useful life of the water tank and its coating system. 3.2.3 The current required for cathodic protection is lowered significantly when coatings are used. 3.2.4 The coating system should be compatible with cathodic protection. 3.3 Cathodic Protection of Uncoated Steel Tanks 3.3.1 It is feasible to design a cathodic protection system to provide complete prot
