1、 Standard Test Method Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Piping Systems This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance
2、does not in any respect 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 granti
3、ng any right, by 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 shou
4、ld in no way be interpreted 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 resp
5、onsibility for the 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 ind
6、ividual volunteers. 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
7、address all potential 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 e
8、nvironmental protection 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 m
9、ay be revised or withdrawn at any time in accordance with NACE technical committee procedures.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 reaffirm
10、ation or revision. 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 FirstService Department, 1440 South Creek Dr., Houston, Te
11、xas 77084-4906 (telephone +1 281-228-6200). Revised 2012-06-23 Reaffirmed 2002-04-11 Approved 1997-12-22 NACE International 1440 South Creek Drive Houston, TX 77084-4906 +1 281-228-6200 ISBN 1-57590-047-5 2012, NACE International NACE Standard TM0497-2012 Item No. 21231 TM0497-2012 NACE Internationa
12、l i _ Foreword This NACE International standard test method provides descriptions of the measurement techniques and cautionary measures most commonly used on underground and submerged piping other than offshore piping to determine whether a specific criterion has been met at a test site. Description
13、s of measurement techniques and cautionary measures used on offshore pipelines and structures can be found in NACE SP0607/ISO 15589-21 for offshore pipelines, and SP01762 for offshore structures. This standard includes only those measurement techniques that relate to the criteria or special conditio
14、ns, such as a net protective current, contained in NACE SP0169.3 This standard is intended for use by corrosion control personnel concerned with the corrosion of underground or submerged piping systems that transport oil, gas, water, or other fluids. The measurement techniques described require that
15、 the measurements be made in the field. Because the measurements are obtained under widely varying circumstances of field conditions and pipeline design, this standard is not as prescriptive as those NACE standard test methods that use laboratory measurements. Instead, this standard gives the user l
16、atitude to make testing decisions in the field based on the technical facts available. This standard contains instrumentation and general measurement guidelines. It includes methods for voltage drop considerations when structure-to-electrolyte potential measurements are made and provides guidance to
17、 minimize incorrect data from being collected and used. The measurement techniques provided in this standard were compiled from information submitted by committee members and others with expertise on the subject. Variations or other techniques not included may be equally effective. The complexity an
18、d diversity of environmental conditions may require the use of other techniques. Appendix A (mandatory) contains information on the common types, use, and maintenance of reference electrodes. Appendix B (nonmandatory) contains information for the net protective current technique, which, while not a
19、criterion, is a useful technique to reduce corrosion. Appendix C (nonmandatory) contains information regarding the use of coupons to evaluate cathodic protection (CP). While some engineers use these nonmandatory techniques, they are not universally accepted practices. However, there is ongoing resea
20、rch into their use. The test methods in this standard were originally prepared by NACE Task Group T-10A-3, “Test Methods and Measurement Techniques Related to Cathodic Protection Criteria,” a component of Unit Committee T-10A, “Cathodic Protection.” It was reviewed by Task Group (TG) 020, reaffirmed
21、 in 2002 by Specific Technology Group (STG) 35, “Pipelines, Tanks, and Well Casings,” and revised in 2012 by TG 020. This standard is issued by NACE 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 t
22、he 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. _ TM0497-2012 i
23、i NACE International _ NACE International Standard Practice Measurement Techniques Related to Criteria for Cathodic Protection on Underground or Submerged Metallic Piping Systems Contents 1. General . 1 2. Definitions . 1 3. Safety Considerations . 3 4. Instrumentation and Measurement Guidelines . 4
24、 5. Structure-to-Electrolyte Potential Measurements . 5 6. Causes of Inaccurate Measurements . 9 7. Voltage Drops Other Than Across the Pipe Metal/Electrolyte Interface . 11 8. Test Method 1Structure-to-Electrolyte Potential of Metallic Piping with CathodicProtection Applied . 13 9. Test Method 2Pol
25、arized Structure-to-Electrolyte Potential of Metallic Piping . 15 10. Test Method 3Cathodic Polarization of Metallic Piping . 17 References 22 Appendix A: Reference Electrodes (Mandatory) 23 Appendix B: Net Protective Current (Nonmandatory) . 25 Appendix C: Using Coupons to Determine Adequacy of Cat
26、hodic Protection (Nonmandatory) 26 Bibliography 22 FIGURES: Figure 1: Instrument connections 6 Figure 1 (a): Instrument connection (polarity option 1) . 6 Figure 1 (b): Instrument connection (polarity option 2) . 7 Figure 2: Structure-to-electrolyte potential corrections for pipeline current flow .
27、13 Figure 2 (a): Correction when pipeline current flows toward pipe test connection . 12 Figure 2 (b): Correction when pipeline current flows away from pipe test connection 13 Figure 3: Polarization decay . 19 Figure 4: Polarization formation 21 _ TM0497-2012 NACE International 1 _ Section 1: Genera
28、l 1.1 This standard describes and illustrates testing procedures for measuring potentials that are used to determine whether a CP criterion is achieved at a test site on underground or submerged metallic piping. 1.2 The provisions of this standard shall be applied by personnel who have the knowledge
29、 and understanding of the fundementals of cathodic protection of buried and submerged metallic piping systems acquired by education and related practical experience. 1.3 Special conditions in which a given test technique is ineffective or only partially effective sometimes exist. Refer to Paragraphs
30、 5.9 and 6.1. Deviation from this standard may be warranted in specific situations. _ Section 2: Definitions(1) Anode: The electrode of an electrochemical cell at which oxidation occurs. Electrons flow away from the anode in the external circuit. Corrosion usually occurs and metal ions enter the sol
31、ution at the anode. Cathode: The electrode of an electrochemical cell at which reduction is the principal reaction. Electrons flow toward the cathode in the external circuit. Cathodic Polarization: The change of electrode potential in the active (negative) direction caused by current across the elec
32、trode/electrolyte interface. See Polarization. Cathodic Protection: A technique to reduce the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. Cathodic Protection Coupon: A metal sample representing the pipeline at the test site, used for cathodic protectio
33、n testing, and having a chemical composition approximating that of the pipe. The coupon size should be small to avoid excessive current drain on the cathodic protection system. Coating: A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid prote
34、ctive, decorative, or functional adherent film. Conductor: A bare or insulated material suitable for carrying electric current. Corrosion: The deterioration of a material, usually a metal, that results from a reaction with its environment. Corrosion Potential (Ecorr): The potential of a corroding su
35、rface in an electrolyte relative to a reference electrode under open-circuit conditions (also known as Rest Potential, Open-Circuit Potential, or Freely Corroding Potential). Criterion: A standard for assessment of the effectiveness of a cathodic protection system. Electrical Isolation: The conditio
36、n of being electrically separated from other metallic structures or the environment. Electrode: A conductor 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 measur
37、ed against a reference electrode. (The electrode potential does not include any resistance losses in potential in either the electrolyte or the external circuit. It represents the reversible work to move a unit of charge from the electrode surface through the electrolyte to the reference electrode.)
38、 Electrolyte: A chemical substance containing ions that migrate in an electric field. For the purpose of this standard, electrolyte refers to the soil or liquid, including contained moisture and other chemicals, next to and in contact with a buried or submerged metallic piping system. (1) Definition
39、s in this section reflect common usage among practicing corrosion control personnel and apply specifically to how terms are used in this standard. As much as possible, these definitions are in accord with those in NACE/ASTM G193.4 TM0497-2012 2 NACE International Foreign Structure: Any metallic stru
40、cture that is not intended as part of a system under cathodic protection. Free Corrosion Potential: See Corrosion Potential. 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 current
41、 source 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 curre
42、nt for cathodic protection.) 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. Interference: An
43、y electrical disturbance on a metallic structure as a result of stray current. Isolation: See Electrical Isolation. Long-Line Current: Current through the earth between an anodic and a cathodic area that returns along an underground metallic structure. Off or On: A condition whereby cathodic protect
44、ion current is either turned off or on. Parallax Error: An apparent shift in the position of a needle on an analog display, caused by a change in the observers position that provides a new line of sight. Pipe-to-Electrolyte Potential: See Structure-to-Electrolyte Potential. Pipe-to-Soil Potential: S
45、ee Structure-to-Electrolyte Potential. Polarization: The change from the open-circuit potential as a result of current across the electrode/electrolyte interface. Polarized Potential: The potential across the structure/electrolyte interface that is the sum of the corrosion potential and the cathodic
46、 polarization. Potential Gradient: A change in the potential with respect to distance, expressed in millivolts per unit of distance. Protection Potential: A measured potential meeting the requirements of a cathodic protection criterion. Reference Electrode: An electrode whose open-circuit potential
47、is constant under similar conditions of measurement, which is used for measuring the relative potentials of other electrodes. Resistance to Electrolyte: The resistance of a structure to the surrounding electrolyte. Reverse-Current Switch: A device that prevents the reversal of direct current through
48、 a metallic conductor. Shielding: (1) Protecting; protective cover against mechanical damage. (2) Preventing or diverting the cathodic protection current from its natural path. For the purposes of this standard, only the second part of the definition applies. Shorted Pipeline Casing: A casing that is in metallic contact with the carrier pipe. Side Drain Potential: A potential gradient measured between two reference electrodes, one located over the pipelin
