1、 Standard Practice Performing Close-Interval Potential Surveys and DC Surface Potential Gradient Surveys on Buried or Submerged Metallic Pipelines This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its accep
2、tance 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
3、granting 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 an
4、d should 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 n
5、o responsibility 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
6、by individual 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 necess
7、arily 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,
8、 and environmental 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,
9、 and may be revised or withdrawn at any time in accordance with NACE technical committee procedures.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 re
10、affirmation 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 First Service Department, 1440 South Creek Dr., Hous
11、ton, Texas 77084-4906 (telephone +1 281/228-6200). Approved 2007-03-10 NACE International 1440 South Creek Drive Houston, Texas 77084-4906 +1 281/228-6200 ISBN 1-57590-211-7 2007, NACE International NACE SP0207-2007 Item No. 21121 SP0207-2007 NACE International i _ Foreword This standard practice pr
12、esents procedures for performing close-interval direct current (DC) structure-to-electrolyte potential surveys, DC surface potential gradient surveys, and hybrid surveys such as trailing-wire direct current voltage gradient (DCVG) surveys or intensive measurement surveys, on buried or submerged meta
13、llic pipelines. Cell-to-cell surveys used to evaluate coating effectiveness are described in other NACE publications.1This standard is intended for use by corrosion control personnel involved with operating pipelines, contractors performing close-interval survey (CIS) and other surveys, corrosion pr
14、ofessionals interpreting CIS and other survey data, and regulatory agencies. Included are definitions, pre-job considerations, instrumentation and equipment guidelines, methods for IR drop correction, pipe location and marking procedures, survey procedures, hybrid survey procedures, offshore and dyn
15、amic stray-current survey procedures, cell-to-cell surface potential gradient surveys, and data validity and post-job considerations. For accurate and correct application, this standard must be used in its entirety. Using or citing only specific paragraphs or sections can lead to misinterpretation a
16、nd misapplication of the recommendations and practices presented. Specific practices are not designated for every situation because of the complexity of conditions to which buried or submerged piping systems are exposed. This standard was prepared by Task Group (TG) 279 on Pipelines: Close-Interval
17、Potential Surveys on Buried or Submerged Metallic Pipelines. TG 279 is administered by Specific Technology Group (STG) 35 on Pipelines, Tanks, and Well Casings, and sponsored by STG 05 on Cathodic/Anodic Protection. This standard is issued by NACE International under the auspices of STG 35. In NACE
18、standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall and must are used to state mandatory requirements. The term should is used to state something good and is recommended
19、but is not mandatory. The term may is used to state something considered optional. _ SP0207-2007 ii NACE International _ NACE International Standard Practice Performing Close-Interval Potential Surveys and DC Surface Potential Gradient Surveys on Buried or Submerged Metallic Pipelines Contents 1. Ge
20、neral . 1 2. Definitions . 3 3. Pre-Job Considerations 7 4. Instrumentation and Equipment 9 5. Minimizing IR Drop . 11 6. Pipe Location and Marking Procedures 16 7. CIS Procedures 18 8. Hybrid CIS Procedures . 22 9. Offshore Close-Interval Survey Procedures . 23 10. Dynamic Stray Current Considerati
21、ons 25 11. DC Cell-to-Cell Surface Potential Gradient Surveys. 28 12. Data Validity and Post-Job Analysis . 32 References 35 Bibliography 35 Appendix A: Pipe IR Drop Calculation (Nonmandatory). 36 Figure 1: Dynamic Stray Current as a Result of Electric Transit System. 26 Figure 2: Dynamic Stray Curr
22、ent as a Result of Telluric Currents . 27 Figure 3: Hot-Spot Survey 31 Figure 4: Side-Drain Survey . 31 Figure 5: Plot of “On” and Instant-Off Potentials vs. Distance with Scatter 33 Figure 6: Plot of “On” and Instant-Off Potentials vs. Distance with Unmatched Reference Electrodes . 34 _ SP0207-2007
23、 NACE International 1 _ Section 1: General 1.1 Introduction 1.1.1 This standard defines the requirements for performing close-interval potential surveys and DC surface potential gradient surveys on buried or submerged metallic pipelines. For the purposes of this standard, the terms close-interval po
24、tential survey (CIPS) and close-interval survey (CIS) are used interchangeably. Procedures for performing hybrid close-interval surveys are given in Section 8. Procedures for performing CIS in marine conditions are given in Section 9. Considerations for dynamic stray current are given in Section 10.
25、 Procedures for performing DC cell-to-cell surface potential gradient surveys are given in Section 11. Methods for calculating the net current based on measured voltage drop and pipeline geometry are included in Appendix A (nonmandatory). 1.2 Scope 1.2.1 CIS is used to designate a potential survey p
26、erformed on a buried or submerged metallic pipeline, in order to obtain valid DC structure-to-electrolyte potential measurements at a regular interval sufficiently small to permit a detailed assessment. 1.2.1.1 Types of CIS include data collection prior to application of cathodic protection (CP) (na
27、tive-state survey), as well as data collection with the CP systems in operation (“on” survey), with the CP current sources synchronously interrupted (interrupted or “on/off” survey), with asynchronous interruption of CP current (waveform analyzer survey), and with CP currents turned off for some tim
28、e to allow the structure to depolarize (depolarized survey). 1.2.2 A hybrid survey is a CIS combined with other types of measurements such as side drains, lateral potentials, or cell-to-cell surface potential gradients along the pipeline. 1.2.2.1 This standard addresses hybrid survey techniques such
29、 as trailing-wire DCVG or intensive measurement surveys (CIS with side drains). 1.2.3 Surface potential gradient surveys are a series of surface potential gradients measured along or normal (perpendicular) to a pipeline. 1.2.3.1 This standard addresses DC cell-to-cell surface potential gradient surv
30、eys (e.g., hot-spot surveys, side-drain surveys) used to evaluate the direction of current in the earth and to identify possible anodic areas on a pipeline. AC-voltage gradient surveys (such as ACVG) and cell-to-cell surveys (such as traditional DCVG) used to evaluate the effectiveness of the coatin
31、g are described in other NACE publications.11.2.4 This standard includes procedures to perform these types of surveys along a buried or submerged pipeline. The standard acknowledges that all potential measurements contain error, and includes some guidance to minimize the error in each measurement. T
32、he standard does not address interpretation of survey data. A qualified person must determine whether the data contain an acceptable amount of error and can be used to evaluate the level of cathodic protection. 1.3 Qualifications 1.3.1 The provisions of this standard should be applied under the dire
33、ction of competent persons who, by reason of knowledge of the physical sciences and the principles of engineering and mathematics acquired by education and related practical experience, are qualified to engage in the practice of corrosion control on buried or submerged metallic piping systems. Such
34、persons may be registered professional engineers or persons recognized as Corrosion Specialists, CP Specialists, or Corrosion or CP Technologists by NACE if their professional activities include suitable experience in the collection and evaluation of these types of data used to monitor external corr
35、osion control of buried or submerged metallic piping systems. 1.3.2 Persons performing these types of surveys (for the purposes of this standard, called surveyors) must be qualified to understand and follow the applicable procedures contained in this standard or work under the direct supervision of
36、a person that is qualified. Such persons may be recognized as NACE CP Testers, Corrosion or CP Technicians, Technologists, Specialists, or equivalent if their professional activities include suitable experience in performing surveys of buried or submerged metallic piping systems. 1.4 Survey Impedime
37、nts 1.4.1 Certain conditions can make the data from a survey difficult to interpret properly, or make the survey impractical to perform. Examples include: 1.4.1.1 Areas of high contact resistance: 1.4.1.1.1 Pipe located under concrete or asphalt pavementContact resistance may be reduced by drilling
38、through the paving to permit electrode contact with the soil (see Paragraph 7.3.2). SP0207-2007 2 NACE International 1.4.1.1.2 Frozen groundContact resistance may be reduced by removing the frozen soil to permit electrode contact with unfrozen soil (e.g., drilling), or heating the soil to the meltin
39、g point of water. Because this is often difficult or impractical, surveys should be scheduled, when possible, to avoid unfavorable seasons. 1.4.1.1.3 Very dry conditionsIf the surface soil is dry enough to cause the electrical contact of the reference electrode with the electrolyte to be impaired, t
40、he soil around the electrode may be moistened with water until the contact is adequate (see Paragraph 7.3.4.6). Because this is often difficult or impractical, surveys should be scheduled, when possible, to avoid unfavorable seasons. 1.4.1.2 Adjacent buried or submerged metallic structures; 1.4.1.3
41、Surface conditions limiting access to the electrolyte: 1.4.1.3.1 Backfill with significant rock content or rock ledges; 1.4.1.3.2 Gravel; and 1.4.1.3.3 Dry vegetation. 1.4.1.4 Telluric or other dynamic stray currents; 1.4.1.5 High levels of induced alternating current (AC) that could influence poten
42、tial measurements or present a safety hazard; 1.4.1.6 Pipelines buried very deep; 1.4.1.7 Locations at which coatings cause electrical shielding; and 1.4.1.8 Lack of electrical continuity, such as with some forms of mechanically coupled pipe that have not been made electrically continuous through th
43、e use of bonding cables or straps welded across each coupling. 1.5 Applications of Surveys 1.5.1 CIS provides a detailed assessment of CP system performance and operation in accordance with established criteria for CP such as those in NACE SP0169.2A near-continuous evaluation is possible when perfor
44、med with a suitable survey interval (see Paragraph 7.2.1). 1.5.2 The objective of a CIS is to measure the structure-to-electrolyte potential at sufficient points along a pipeline. Interpreting the data can provide additional benefits such as: 1.5.2.1 Identifying areas outside the range of potential
45、criteria of a pipeline not identified by test point surveys; 1.5.2.2 Determining the extent of areas outside the range of potential criteria; 1.5.2.3 Locating medium-to-large defects in coatings (isolated or continuous and typically 600 mm21 in.2)1; 1.5.2.4 Locating areas of stray-current pickup and
46、 discharge or at risk for interference corrosion; 1.5.2.5 Determining the area of influence of CP; 1.5.2.6 Identifying possible shorted casings, defective electrical isolation devices, or unintentional contact with other metallic structures; 1.5.2.7 Locating areas of geologic shielding of CP; 1.5.2.
47、8 Measuring the level of CP in conducting current demand testing, and evaluating the effectiveness of current distribution along a pipeline; 1.5.2.9 Locating possible high-pH stress corrosion cracking (SCC) risk areas: the level of CP has been shown to be a factor in the susceptibility of pipelines
48、to high-pH SCC. CIS may assist in locating areas along a pipeline at which structure-to-electrolyte potentials fall in the susceptibility range for SCC; and 1.5.2.10 Locating and prioritizing areas of risk of external corrosion as part of an integrity management program, or a component of an external corrosion direct assessment (ECDA). 1.5.3 DC cell-to-cell surface potential gradient surveys may be used to evaluate the direction of current in the earth and to identify possible anodic areas on a pipeline. 1.5.3.1 Side-drain or latera
