1、StandardRecommended PracticeExternal Cathodic Protection of On-Grade CarbonSteel Storage Tank BottomsThis NACE International standard represents a consensus of those individual members who havereviewed this document, its scope, and provisions. Its acceptance does not in any respectpreclude anyone, w
2、hether he 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, byimplication or otherwise, to manufa
3、cture, sell, or use in connection with any method, apparatus, orproduct covered by Letters Patent, or as indemnifying or protecting anyone against liability forinfringement of Letters Patent. This standard represents minimum requirements and should in noway be interpreted as a restriction on the use
4、 of better procedures or materials. Neither is thisstandard intended to apply in all cases relating to the subject. Unpredictable circumstances maynegate the usefulness of this standard in specific instances. NACE International assumes noresponsibility for the interpretation or use of this standard
5、by other parties and acceptsresponsibility for only those official NACE International interpretations issued by NACEInternational in accordance with its governing procedures and policies which preclude theissuance of interpretations by individual volunteers.Users of this NACE International standard
6、are responsible for reviewing appropriate health, safety,environmental, and regulatory documents and for determining their applicability in relation to thisstandard prior to its use. This NACE International standard may not necessarily address allpotential health and safety problems or environmental
7、 hazards associated with the use ofmaterials, equipment, and/or operations detailed or referred to within this standard. Users of thisNACE International standard are also responsible for establishing appropriate health, safety, andenvironmental protection practices, in consultation with appropriate
8、regulatory authorities ifnecessary, to achieve compliance with any existing applicable regulatory requirements prior to theuse of this standard.CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may berevised or withdrawn at any time without prior notice. NACE Intern
9、ational requires that action betaken to reaffirm, revise, or withdraw this standard no later than five years from the date of initialpublication. The user is cautioned to obtain the latest edition. Purchasers of NACE Internationalstandards may receive current information on all standards and other N
10、ACE Internationalpublications by contacting the NACE International Membership Services Department, 1440 SouthCreek Dr, Houston, Texas 77084-4906 (telephone +1281228-6200).Revised 2001-06-15Approved October 1993NACE International1440 South Creek DriveHouston, Texas 77084-4906+1 281/228-6200ISBN 1-575
11、90-014-92001, NACE InternationalNACE Standard RP0193-2001Item No. 21061RP0193-2001NACE International i_ForewordIt is extremely important to maintain the integrity of on-grade carbon steel storage tanks for botheconomic and environmental reasons. The proper design, installation, and maintenance ofcat
12、hodic protection (CP) systems can help maintain the integrity and increase the useful servicelife of on-grade carbon steel storage tanks.The purpose of this standard recommended practice is to outline practices and procedures forproviding cathodic protection to the soil side of bottoms of on-grade c
13、arbon steel storage tanksthat are in contact with an electrolyte. Recommendations for both galvanic anode systems andimpressed current systems are included. Design criteria for the upgrade of existing tanks as wellas for newly constructed tanks are included. This standard is intended for use by pers
14、onnelplanning to install new on-grade carbon steel storage tanks, upgrade cathodic protection onexisting storage tanks, or install new cathodic protection on existing storage tanks.This NACE standard was originally prepared by Task Group T-10A-20, a component of NACE UnitCommittee T-10A on Cathodic
15、Protection, in 1993. It was technically revised by Task Group 013in 2001. Task Group 013 is administered by Specific Technology Group (STG) 35 on Pipelines,Tanks, and Well Casings and sponsored by STGs 03 on Protective Coatings and LiningsImmersion/Buried and STG 05 on Cathodic/Anodic Protection. Th
16、is standard is issued by NACEInternational under the auspices of STG 35 on Pipelines, Tanks, and Well Casings.In NACE standards, the terms shall, must, should, and may are used in accordance with thedefinitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shallan
17、d must are used to state mandatory requirements. The term should is used to state somethinggood and is recommended but is not mandatory. The term may is used to state somethingconsidered optional._RP0193-2001ii NACE International_NACE InternationalStandardRecommended PracticeExternal Cathodic Protec
18、tion of On-Grade Carbon SteelStorage Tank BottomsContents1. General . 12. Definitions 13. Preliminary Evaluation and Determination of the Need for Cathodic Protection. 24. Criteria for Cathodic Protection. 55. General Considerations for Cathodic Protection Design . 76. Design Considerations for Impr
19、essed Current Cathodic Protection 97. Design Considerations for Galvanic Anode Cathodic Protection . 118. Design Considerations Cathodic Protection for Tanks with Replacement Bottoms orRelease Prevention Barriers . 129. Installation Considerations 1510. Energizing and Testing . 1711. Operation and M
20、aintenance of Cathodic Protection Systems 1812. Recordkeeping . 19References 19Bibliography 20FiguresFigure 1: Soil Resistivity Testing (Four-Pin Method) 3Figure 2: Temporary Groundbed for Current Requirement Testing 5Figure 3: Stray Current Corrosion 6Figure 4: Vertically Drilled Anode CP System 9F
21、igure 5: Angled Anode Cathodic Protection System 10Figure 6: Deep Anode Groundbed. 10Figure 7: Horizontally Installed Anode Groundbed 10Figure 8: Typical Double-Bottom Cathodic Protection Layout (Impressed or Sacrificial) 13Figure 9: Typical Double-Bottom Galvanic Anode Design. 14Figure 10: Typical
22、New Tank or Double-Bottom Impressed Current Anode Design . 14Figure 11: Perforated Pipe Installed for Reference Electrode . 16_RP0193-2001NACE International 1_Section 1: General1.1 This standard presents guidelines for the design,installation, and maintenance of cathodic protection for theexterior b
23、ottoms of on-grade carbon steel storage tanks.Cathodic protection can be installed to protect new orexisting tanks, but cannot protect carbon steel surfaces thatare not in contact with an electrolyte.1.2 This standard is applicable to welded, bolted, andriveted carbon steel tanks that are either fie
24、ld- or shop-fabricated.1.3 It is understood in this standard that cathodic protectionmay be used alone or in conjunction with protectivecoatings.1.4 All cathodic protection systems should be installed withthe intent of conducting uninterrupted, safe operations.When cathodic protection is applied, it
25、 should be operatedcontinuously to maintain polarization.1.5 The criteria for cathodic protection are based oncurrent industry standards.1.6 Corrosion control must be a consideration during thedesign of on-grade carbon steel storage tanks._Section 2: DefinitionsAmphoteric Metal: A metal that is susc
26、eptible to corrosionin both acid and alkaline environments.Anode: The electrode of an electrochemical cell at whichoxidation occurs. Electrons flow away from the anode in theexternal circuit. Corrosion usually occurs and metal ionsenter the solution at the anode.Backfill: Material placed in a hole t
27、o fill the space aroundthe anodes, vent pipe, and buried components of a cathodicprotection system.Cathode: The electrode of an electrochemical cell at whichreduction is the principal reaction. Electrons flow toward thecathode in the external circuit.Cathodic Protection (CP): A technique to reduce t
28、hecorrosion of a metal surface by making that surface thecathode of an electrochemical cell.Cell: See Electrochemical Cell.Current Density: The current to or from a unit area of anelectrode surface.Deep Groundbed: One or more anodes installed verticallyat a nominal depth of 15 m (50 ft) or more belo
29、w the earthssurface in a drilled hole for the purpose of supplyingcathodic protection.Differential Aeration Cell: An electrochemical cell, theelectromotive force of which is due to a difference in air(oxygen) concentration at one electrode as compared withthat at another electrode of the same materi
30、al.Electrical Isolation: The condition of being electricallyseparated from other metallic structures or the environment.Electrochemical Cell: A system consisting of an anodeand a cathode immersed in an electrolyte so as to create anelectrical circuit. The anode and cathode may be differentmetals or
31、dissimilar areas on the same metal surface.Electrolyte: A chemical substance containing ions thatmigrateinanelectricfield.External Circuit: The wires, connectors, measuringdevices, current sources, etc., that are used to bring aboutor measure the desired electrical conditions within anelectrochemica
32、l cell. It is this portion of the cell throughwhich electrons travel.Foreign Structure: Any metallic structure that is notintended as a part of a system under cathodic protection.Galvanic Anode: A metal that provides sacrificial protectionto another metal that is more noble when electricallycoupled
33、in an electrolyte. This type of anode is the electronsource in one type of cathodic protection.Groundbed: One or more anodes installed below theearths surface for the purpose of supplying cathodicprotection. For the purposes of this standard, a groundbedis defined as a single anode or group of anode
34、s installed inthe electrolyte for the purposes of discharging direct currentto the protected structure.Impressed Current: An electric current supplied by adevice employing a power source that is external to theelectrode system. (An example is direct current for cathodicprotection).On-Grade Storage T
35、ank: A tank constructed on sand orearthen pads, concrete ringwalls, or concrete pads.RP0193-20012 NACE InternationalOxidation: (1) Loss of electrons by a constituent of achemical reaction. (2) Corrosion of a metal that is exposedto an oxidizing gas at elevated temperatures.Piping: For the purposes o
36、f this standard, this term refersto all piping associated with the transfer of products in andout of storage tanks.Reduction: Gain of electrons by a constituent of a chemicalreaction.Reference Electrode: An electrode whose open-circuitpotential is constant under similar conditions ofmeasurement, whi
37、ch is used for measuring the relativepotentials of other electrodes.Stray-Current Corrosion: Corrosion resulting from currentthrough paths other than the intended circuit, e.g., by anyextraneous current in the earth._Section 3: Preliminary Evaluation and Determination of the Need for Cathodic Protec
38、tion3.1 This section outlines the information that should beconsidered prior to designing a cathodic protection systemto protect on-grade carbon steel storage tank bottoms incontact with an electrolyte.3.2 Site Assessment Information3.2.1 Prior to designing a cathodic protection system,the following
39、 information should be obtained:(a) Tank, piping, and grounding constructiondrawings, including dimensions, etc.(b) Site plan and layout(c) Date of construction(d) Material specifications and manufacturer(e) Joint construction (i.e., welded, riveted, etc.)(f) Coating specifications(g) Existing or pr
40、oposed cathodic protection systemsin the area(h) Location of electric power sources(i) Electrochemical properties of the tank bedding orpadding material(j) History of the tank foundation (i.e., whether thetank has been jacked up/leveled, etc.)(k) Unusual environmental conditions(l) Operating history
41、 of the tank, including leakinformation (internal and external)(m) Maintenance history of the tank(n) Containment membranes/impervious linings(o) Secondary bottoms(p) Water table and site drainage information(q) Liquid levels maintained in the tank(r) Nearby foreign structures(s) Typeofliquidstored(
42、t) Operating temperature(u) Electrical grounding3.3 Predesign Site Appraisal3.3.1 Determining the Extent of Corrosion on ExistingSystems3.3.1.1 Information regarding the degree oftank-bottom corrosion is useful becauseconsiderable bottom damage may requireextensive repairs or replacement prior to th
43、einstallation of cathodic protection.3.3.1.2 Field procedures for determining theextent of existing corrosion may include:(a) Visual inspection(b) Tank bottom plate-thickness measurements(ultrasonic testing, coupon analysis, etc.)(c) Estimation of general corrosion ratesthrough the use of electroche
44、mical procedures(d) Determination of the magnitude anddirection of galvanic or stray current transferredto or from the tank through piping and otherinterconnections(e) Determination of soil characteristicsincluding resistivity, pH, chloride ionconcentration, sulfide ion concentration, andmoisture co
45、ntent(f) Estimation of the degree of corrosiondeterioration based on comparison with datafrom similar facilities subjected to similarconditions3.3.1.3 Foundation characteristics are alsoimportant factors in the assessment of the extentof existing corrosion. The pad material ofconstruction, thickness
46、 of ringwalls, and waterdrainage should all be considered.3.3.1.4 Data pertaining to existing corrosionconditions should be obtained in sufficientquantity to permit reasonable engineeringjudgments. Statistical procedures should beused in the analysis, if appropriate.RP0193-2001NACE International 33.
47、3.2 Electrical Isolation3.3.2.1 Electrical isolation facilities must becompatible with electrical groundingrequirements conforming to applicable codesand safety requirements. If the tank bottom is tobe cathodically protected, the use of alternativeelectrical grounding materials, such asgalvanized st
48、eel and galvanic anodes, should beconsidered.3.3.2.2 The designer of a cathodic protectionsystem should consider the possible need forelectrical isolation of the tank from piping andother interconnecting structures. Isolation maybe necessary for effective cathodic protection orsafety considerations.3.3.2.3 Electrical isolation of interconnectingpiping can be accomplished through the use ofiso
