1、 Standard Practice External Corrosion Control of Underground Storage Tank Systems by Cathodic Protection 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 respect preclude any
2、one, 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 implication or othe
3、rwise, 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 interpreted as a res
4、triction 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 the interpretation or
5、 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 volunteers. Users of this NA
6、CE 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 potential health and saf
7、ety 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 protection practices, i
8、n 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 CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any ti
9、me 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. The user is cautioned to obtain the latest edition. Purchasers of NACE Internation
10、al standards may receive current information on all standards and other NACE International publications by contacting the NACE International FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281-228-6200). Revised 2011-03-13 Revised 2002-04-06 Revised February
11、1995 Approved March 1985 NACE International 1440 South Creek Dr. Houston, Texas 77084-4906 +1 281-228-6200 ISBN 1-57590-143-9 2011, NACE International NACE SP0285-2011 (formerly RP0285) Item No. 21030 SP0285-2011 NACE International i _ Foreword This standard presents standard practices for effective
12、 control of external corrosion of underground storage tank (UST) systems by cathodic protection (CP). It is intended to be used by corrosion professionals as a guideline to establish minimum requirements for using CP to control external corrosion of metallic UST systems, including those used to cont
13、ain oil, gas, and water. Specifically addressed is CP of: (a) Existing bare and externally coated steel USTs; (b) New externally coated steel USTs; (c) Metallic piping and flexible connectors; and (d) Other metallic components. For further information on testing CP systems for UST systems, refer to
14、NACE Standard TM0101.1 This standard was originally published in 1985 by Task Group (TG) T-10A-14, Control of External Corrosion on Metallic Buried, Partially Buried, or Submerged Liquid Storage Systems. The standard was revised in 1995 by TG T-10A-14, Corrosion Control of Underground Storage Tank S
15、ystems, a component of Unit Committee T-10A, Cathodic Protection. It was revised in 2002 and in 2011 by TG 011, Corrosion Control of Underground Storage Tank Systems by Cathodic Protection. TG 011 is administered by Specific Technology Group (STG) 35, Pipelines, Tanks, and Well Casings, and is spons
16、ored by STG 05, Cathodic/Anodic Protection. This standard is issued by NACE International under the auspices of STG 35. In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual. The terms shall and must
17、 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. _ SP0285-2011 ii NACE International _ NACE International Standard Practice
18、 External Corrosion Control of Underground Storage Tank Systems by Cathodic Protection Contents 1. General 1 2. Definitions . 1 3. Cathodic Protection of New Underground Storage Tank Systems . 3 4. Cathodic Protection of Existing Underground Storage Tank Systems . 6 5. Criteria for Cathodic Protecti
19、on 9 6. Cathodic Protection System Design . 10 7. Installation of Cathodic Protection Systems . 14 8. Operation and Maintenance 18 References 20 TABLES Table 1: Conversion of Other Potential Measurements to CSE Equivalents 10 _ SP0285-2011 NACE International 1 _ Section 1: General 1.1 Introduction 1
20、.1.1 This standard presents standard practices for effective control of external corrosion of UST systems by CP. It is intended to serve as a guideline to establish minimum requirements for using CP to control external corrosion of metallic UST systems, including those used to contain oil, gas, and
21、water, and that are buried, partially buried, or in contact with the soil. 1.1.2 When designing the CP system, the designer shall provide the owner with the design life and the assumptions used to develop the CP system design. If conditions change at the UST site, the original CP system design life
22、may also change. Some examples of UST system changes include fluctuation in soil resistivity, UST system coating failure, adding/removing components of the UST system or site, and electrical shorting or isolation of UST components. This information should be kept as part of the permanent UST system
23、records. 1.1.3 This standard does not designate specific practices for every situation because the complexity of some environmental conditions in which UST systems are buried precludes standardization of corrosion control practices. 1.1.4 This standard does not include corrosion control methods base
24、d on chemical control of the environment, internal linings, or the use of UST construction materials other than steel. 1.1.5 This standard does not override applicable safety codes and should not be used to infringe on the primary requirement of protecting personnel, the environment, and equipment.
25、In any situation, the CP system design for UST systems should incorporate all requirements of any applicable codes, standards, and regulations as determined by authorities having jurisdiction. 1.1.6 The provisions of this standard shall be applied under the responsible direction of competent individ
26、uals. Such individuals must either be registered professional engineers, NACE International certified Corrosion Specialists or CP Specialists, or individuals qualified by professional education and related practical experience. All of the above individuals must be able to demonstrate suitable experi
27、ence in corrosion control of UST systems. 1.1.7 Deviation from this standard may be warranted in specific situations provided the objectives expressed in this standard have been achieved. 1.1.8 For accurate and correct application of this standard, this standard must be used in its entirety. Using o
28、r referring to only specific paragraphs or sections can lead to misinterpretation and misapplication of the standard practices contained in the standard. _ Section 2: Definitions Anode: The electrode of an electrochemical cell at which oxidation occurs. (Electrons flow away from the anode in the ext
29、ernal circuit. It is usually the electrode where corrosion occurs and metal ions enter solution.) Backfill: Material placed in a hole to fill the space around the anodes, vent pipe, and buried components of a cathodic protection system. Cathode: The electrode of an electrochemical cell at which redu
30、ction 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. Cathodic Polarization: (1) The change of electrode potential caused by a
31、 cathodic current flowing across the electrode/electrolyte interface; (2) a forced active (negative) shift in electrode potential. (See Polarization.) Cathodic Protection: A technique to reduce the corrosion rate of a metal surface by making that surface the cathode of an electrochemical cell. SP028
32、5-2011 2 NACE International Coating: (1) A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film; (2) (in a more general sense) a thin layer of solid material on a surface that provides improved
33、protective, decorative, or functional properties. Continuity Bond: A connection, usually metallic, that provides electrical continuity between structures that can conduct electricity. Corrosion: The deterioration of a material, usually a metal, that results from a chemical or electrochemical reactio
34、n with its environment. Corrosion Potential: (Represented by the symbol Ecorr) The potential of a corroding surface in an electrolyte measured under open-circuit conditions relative to a reference electrode. (Also known as Electrochemical Corrosion Potential, Free Corrosion Potential, Open-Circuit P
35、otential.) Current Density: The electric current flowing to or from a unit area of an electrode surface. Dielectric Coating: A coating that does not conduct electricity. Dissimilar Metals: Different metals that could form an anode-cathode relationship in an electrolyte when connected by an electron-
36、conducting (usually metallic) path. Driving Potential: Difference in potential between the anode and the steel structure. Electrical Isolation: The condition of being electrically separated from other metallic structures or the environment. Electrochemical Cell: (1) an electrochemical reaction invol
37、ving two half reactions, one of which involves oxidation of the reactant (product) and the other of which involves reduction of the product (reactant). (The equilibrium potential of the electrochemical cell can be calculated from the change in free energy for the overall electrochemical reaction. Th
38、e equilibrium potential of the electrochemical cell can be measured by separating the oxidation and reduction half reactions into individual compartments and measuring the voltage that develops between them under conditions that virtually no charge passes between them.) thermodynamic use; (2) an ele
39、ctrochemical system consisting of an anode and a cathode in metallic contact and immersed in an electrolyte. (The anode and cathode may be different metals or dissimilar areas on the same metal surface.) common use Electrode Potential: The potential of an electrode in an electrolyte as measured agai
40、nst a reference electrode. Electrolyte: A chemical substance containing ions that migrate in an electric field. For the purposes of this standard, electrolyte refers to the soil or liquid adjacent to and in contact with a buried or submerged metallic UST system, including the moisture and other chem
41、icals contained therein. Foreign Structure: Any metallic structure that is not intended as a part of a system under cathodic protection. 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
42、 the electron source in one type of cathodic protection. Groundbed: One or more anodes installed below the earths surface for the purpose of supplying cathodic protection current. Impressed Current: An electric current supplied by a device employing a power source that is external to the electrode s
43、ystem. (An example is direct current 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 reas
44、on, is not corroded appreciably.) Instant-Off Potential: The polarized half-cell potential of an electrode taken immediately after the cathodic protection current is stopped, which closely approximates the potential without IR drop (i.e., the polarized potential) when the current was on. Interferenc
45、e Bond: An intentional metallic connection, between metallic systems in contact with a common electrolyte, designed to control electrical current interchange between the systems. IR Drop: See Voltage Drop. SP0285-2011 NACE International 3 Isolation: See Electrical Isolation. Polarization: The change
46、 from the corrosion potential as a result of current flow across the electrode/electrolyte interface. For the purposes of this standard, polarization is considered to be the change of potential of a metal surface resulting from the passage of current directly to or from an electrode. Polarized Poten
47、tial: (1) (general use) the potential across the electrode/electrolyte interface that is the sum of the corrosion potential and the applied polarization; (2) (cathodic protection use) the potential across the structure/electrolyte interface that is the sum of the corrosion potential and the cathodic
48、 polarization. Potential Gradient: A change in the potential with respect to distance, expressed in millivolts per unit of distance. Reference Electrode: An electrode having a stable and reproducible potential, which is used in the measurement of other electrode potentials. Stray Current: Current flowing through paths other than the intended circuit. Stray-Current Corrosion: Corrosion resulting from stray cur
