1、d Standard Practice High-Voltage Electrical Inspection of Pipeline Coatings 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 anyone, whether he or she has ad
2、opted 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 otherwise, to manufacture, sell,
3、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 restriction on the use of better
4、 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 use of this standard by othe
5、r 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 NACE International standard are
6、 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 safety problems or environmental
7、 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, in consultation with appropria
8、te 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 CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time in accordance with NACE te
9、chnical 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. The user is cautioned to obtain the latest edi
10、tion. 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, Texas 77084-4906 (telephone +1 281-228-6200). Reaffirmed 2011-28-10
11、 Reaffirmed 2004-03-31 Reaffirmed 1998-25-03 Reaffirmed 1993 Approved 1974-08 NACE International 1440 South Creek Drive Houston, Texas 77084-4906 +1 281-228-6200 ISBN 1-57590-064-5 2011, NACE International NACE SP0274-2011 (formerly RP0274) Item No. 21010 SP0274-2011 NACE International i _ Foreword
12、Detection and correction of defects in protective coatings are important factors in an effective corrosion-control program. High-voltage electrical inspection of pipeline coatings is one commonly used method of detecting such defects. Before the first issuance of this standard practice, there had no
13、t been a national standard for electrical inspection of pipeline coatings other than Section 3.13 of the 1966 edition of AWWA(1) Standard C203,1 which was only applicable to coal-tar coatings. Several specifications have been written by operating companies for high-voltage electrical inspection of p
14、rotective coatings, but these apply only to specific coatings. Following the principles of this standard will improve holiday detection of pipeline coatings. This standard is intended to be used by pipeline operating companies, pipeline contractors, pipeline inspection services, and pipeline coating
15、 mills. This standard was developed through the joint efforts of representatives of coating manufacturers, coating applicators, holiday detector manufacturers, corrosion specialists, and other personnel concerned with the construction of underground pipeline facilities. This standard involves testin
16、g all pipeline coatings, including coatings on in-service pipelines and new or replacement coatings. Procedures for low-voltage wet sponge testing and high-voltage spark testing of new coatings on conductive substrates are provided in NACE SP0188.2 This standard was originally prepared in 1974 by Ta
17、sk Group (TG) T-10D-9, “Coating Inspection,” and Work Group T-10D-9a, “Electrical Inspection,” components of Unit Committee T-10D, “Protective Coating Systems.” It was reaffirmed in 1993 and 1998 by Unit Committee T-10D. It was reaffirmed in 2004 and 2011 by Specific Technology Group (STG) 03, “Coat
18、ings and Linings, ProtectiveImmersion and Buried Service.” This standard is issued by NACE International under the auspices of STG 03. 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
19、 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. _ (1) American Water Works Association (AWWA), 6666 W. Quin
20、cy Avenue, Denver, CO 80235. SP0274-2011 ii NACE International _ NACE International Standard Practice High-Voltage Electrical Inspection of Pipeline Coatings Contents 1. General . 1 2. Definitions . 1 3. Testing Voltages . 1 4. Grounding . 2 5. Electrode . 2 6. Electrode Travel Speed 3 7. Voltage Me
21、asurements . 3 8. Condition of the Coating Surface 3 9. Care of Equipment 3 References . 4 TABLES Table 1: Minimum Testing Voltage for Various Coating Thickness 2 _ _ Section 1: General 1.1 Electrical inspection (holiday detection) is a test of the continuity of a protective coating. This type of in
22、spection does not provide information concerning coating resistance, bond, physical characteristics, or the overall quality of the coating, nor is it intended to do so. It detects bubble or blister-type voids, cracks, thin spots, and foreign inclusions or contaminants in the coating that are of such
23、 size, number, or conductivity as to significantly lower the electrical resistance or dielectric strength of the coating. 1.2 An initial electrical inspection, performed as soon after the application of the coating as practical, serves to check the materials and the application procedures. A final c
24、oating inspection, performed before lowering-in operations, will disclose any defect or damage (except disbonding) that has occurred during the construction period. 1.3 This standard presents acknowledged techniques for the use of holiday detectors currently used on pipeline coatings and presents a
25、table of minimum testing voltages for various coating thicknesses. These minimum testing voltages do not apply to thin-film coatings (i.e., coating materials usually applied by a fusion-bonding process). Thin-film pipeline coatings are generally applied to a dry film thickness less than 0.5 mm (20 m
26、il). _ Section 2: Definitions Holiday: A discontinuity in a protective coating that exposes unprotected surface to the environment. Holiday detector: A device for locating discontinuities in a coating. Pulse-type detector: A type of holiday detector that supplies a high-voltage pulse of very short d
27、uration (e.g., a pulse duration of 0.0002 seconds at a rate of 30 pulses per second). _ Section 3: Testing Voltages 3.1 All testing voltages in this standard refer to direct current (DC) or peak alternating current (AC) values. 3.2 The minimum testing voltage in volts (V) for a particular coating th
28、ickness shall be within 20% of the value determined using Equation (1) or (2), or as shown in Table 1: t7 ,9 0 0V o lta g e Te s tin g (1) where t = average coating thickness in mm; t1 ,2 5 0V o lta g e Te s tin g (2) where t = average coating thickness in mil. SP0274-2011 NACE International Table 1
29、 Minimum Testing Voltage for Various Coating Thicknesses(A) Average Coating Thickness (t) Minimum Testing Voltage (mm) (mil) (V) 0.51 20 6,000 0.79 31 7,000 1.6 62 10,000 2.4 94 12,000 3.2 125 14,000 4.0 156 16,000 4.8 188 17,000 13 500 28,000 16 625 31,000 19 750 34,000 (A) Thin-film coatings are n
30、ot covered by this standard _ Section 4: Grounding 4.1 Both the pipe metal and the ground terminal of the holiday detector must be grounded to complete the circuit. This should be done through a direct-wire connection or by connecting both to earth as a common ground. If not in contact with the eart
31、h, the pipe metal should be connected to the earth by a driven ground rod or metal pin. In most cases, the holiday detector can be effectively grounded by the use of a flexible, bare wire of approximately 9 m (30 ft) in length that is connected to the ground terminal of the holiday detector and trai
32、led along the earth. 4.2 In arid, sandy, or rocky areas of high electrical resistivity, a direct-wire connection between the pipe metal and detector ground terminal shall be maintained. _ Section 5: Electrode 5.1 The electrode of the holiday detector is the means by which the electrical testing pote
33、ntial is applied to the surface of the coating. 5.2 The construction of the electrode shall be such that for each 1,000 V of testing potential there will be no more than 0.25 mm (10 mil) lateral distance between the points where the electrode contacts the coated surface. 5.3 The electrode shall main
34、tain contact with the coated surface at all times. 5.4 The electrode shall not adversely distort the coating. 5.5 To prevent causing a decrease in the coating thickness, the electrode should not be moved back and forth excessively on a soft coating. 5.6 The electrode should always be in motion when
35、the testing voltage is applied. _ Section 6: Electrode Travel Speed 6.1 Pulse-type detector: The pulse rate should be considered in the determination of the electrode travel speed over the coated surface. Higher pulse rates allow a higher speed of travel. 6.2 Non-pulse-type detector: The electrode t
36、ravel speed is limited by the mechanics of application and the response time of the detector. Some detectors are spring-type, some use a conductive rubber, and others use brass brushes. The speed of the electrode is limited by the type of detector. 6.3 The proper electrode travel speed for a particu
37、lar set of conditions should be determined by making holidays in the coating and attempting to detect the holidays at various electrode travel speeds. _ Section 7: Voltage Measurements 7.1 Voltage measurements of non-pulse-type detectors shall be made with a high-resistance kilovolt meter, or with a
38、 high-resistance voltage divider in conjunction with a high-resistance voltmeter. 7.2 Voltage measurements of pulse-type detectors shall be made with a high-impedance peak-reading kilovolt meter or with a high-impedance capacitance or resistance voltage divider and suitable indicator, such as an osc
39、illoscope or voltmeter. 7.3 The electrode must be in the normal operating position on the coated surface in a holiday-free area. 7.4 All components must be properly grounded. 7.5 The voltage shall be measured between the electrode and the pipe. 7.6 In the absence of a suitable means of voltage measu
40、rement, the operation of the holiday detector (but not necessarily the proper testing voltage) should be determined by making a small holiday in the thickest portion of the coating to be inspected. The holiday-detector voltage shall then be adjusted to locate this holiday at normal electrode travel
41、speeds (see Paragraph 6.3). _ Section 8: Condition of the Coating Surface 8.1 Excessive moisture or any electrically conductive material in or on the surface of the coating system can cause appreciable leakage currents, which may lower the effective testing voltage or cause erroneous holiday indicat
42、ion. Drying and cleaning of the coated surface may be necessary (see Section 9). 8.2 Any surface condition that causes an increase in the distance between the electrode and the metal must be corrected (see Paragraphs 5.3 and 9.2). _ Section 9: Care of Equipment 9.1 All parts of the holiday detector
43、shall be kept clean and free of moisture at all times. 9.2 The electrode shall be kept free of coating material and in such mechanical condition as to maintain contact with the coated surface at all times. 9.3 All electrical contacts shall be kept clean and free of corrosion. SP0274-2011 NACE Intern
44、ational _ References 1. ANSI(2)/AWWA Standard C203 (latest revision), “Coal-Tar Protective Coatings and Linings for Steel Water PipelinesEnamel and TapeHot-Applied” (Denver, CO: AWWA). 2. NACE SP0188 (formerly RP0188) (latest revision), “Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates” (Houston, TX: NACE). (2) American National Standards Institute (ANSI), 25 West 43rd St., 4th Floor, New York, NY 10036. ISBN 1-57590-064-5
