1、 Standard Practice Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates 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 anyon
2、e, 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 otherw
3、ise, 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 restr
4、iction 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 u
5、se 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 NACE
6、 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 safet
7、y 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, in
8、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 CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time
9、 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 International
10、 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). Reaffirmed 2006-12-27 Revised March 1999 Reaffirmed Septe
11、mber 1990 Approved 1988 NACE International 1440 South Creek Drive Houston, Texas 77084-4906 +1 281/228-6200 ISBN 1-57590-074-2 2006, NACE International NACE SP0188-2006 (formerly RP0188-99) Item No. 21038 SP0188-2006 NACE International i _ Foreword A coating is applied to a substrate to prevent corr
12、osion, reduce abrasion, and reduce product contamination. The degree of coating continuity required is dictated by service conditions. Discontinuities in a coating are frequently very minute and not readily visible. This standard practice provides a procedure for electrical detection of minute disco
13、ntinuities in new coating systems that are applied to conductive substrates. The user should refer to NACE Standards RP0274,1RP0490,2and/or TM03843for procedures specific to electrical inspection of pipeline coatings. This standard describes procedures for determining discontinuities using two types
14、 of test equipment: low-voltage wet sponge testers and high-voltage spark testers. This standard is intended for reference in coating specifications or other documents and may be used by specifiers, applicators, and coating inspectors if a specification requires holiday detection on conductive subst
15、rates. For the purposes of this standard, the term “coating” can refer either to atmospheric or immersion service. This standard was originally prepared in 1988 by Task Group T-6A-37, a component of Unit Committee T-6A on Coating and Lining Materials for Immersion Service. It was reaffirmed in 1990,
16、 revised in 1999, and reaffirmed in 2006 by Specific Technology Group (STG) 03. This standard is issued by NACE International under the auspices of STG 03 on Protective Coatings and Linings: Immersion and Buried. It combines the input of representatives of coating manufacturers, applicators, inspect
17、ion agencies, architectural engineers, equipment manufacturers, and general consumers. 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, 4th ed., Paragraph 7.4.1.9. Shall and must are used to st
18、ate mandatory requirements. The term should is used to state something considered good and is recommended but is not mandatory. The term may is used to state something considered optional. _ SP0188-2006 ii NACE International _ NACE International Standard Practice Discontinuity (Holiday) Testing of N
19、ew Protective Coatings on Conductive Substrates Contents 1. General . 1 2. Definitions . 1 3. Low-Voltage Wet Sponge Testing 1 4. High-Voltage Spark Testing 3 5. Testing of Repaired Area 5 6. Safety 5 References 5 _ SP0188-2006 NACE International 1 _ Section 1: General 1.1 This standard provides pro
20、cedures for low-voltage wet sponge testing and high-voltage spark testing of new coatings on conductive substrates. 1.2 Electrical testing to determine the presence and number of discontinuities in a coating is performed on a nonconductive coating applied to a conductive substrate. The allowable num
21、ber of discontinuities should be determined prior to conducting this test, because the acceptable number of discontinuities varies depending on coating thickness, design, and service conditions. 1.3 This standard is not intended to provide data on service life, adhesion, or film thickness of an appl
22、ied coating system. Electrical testing does not detect areas where the coating is thin (even as thin as 25 m 1.0 mil). 1.4 This standard is intended for use only with new coatings applied to conductive substrates. Inspecting a coating previously exposed to an immersion condition could result in dama
23、ge to the coating or could produce an erroneous detection of discontinuities due to permeation or moisture absorption of the coating. Deposits may also be present on the surface, causing telegraphing. The use of a high-voltage spark tester on previously exposed coatings can result in a spark that da
24、mages an otherwise sound coating. A low-voltage wet sponge tester may be used without damaging the coating but can produce erroneous readings. 1.5 To prevent damage to a coating if a high-voltage spark tester is being used, the total film thickness and dielectric strength of the coating system shall
25、 be considered in selecting the appropriate voltage for detection of discontinuities. 1.6 The coating manufacturer shall be consulted to obtain the following information, which can affect the accuracy of the tests described in this standard to determine discontinuities: (a) The length of time requir
26、ed to adequately dry or cure the applied coating prior to testing. Solvents retained in an uncured coating may form an electrically conductive path through the film to the substrate. (b) Whether the coating contains electrically conductive fillers or pigments that may affect the normal dielectric pr
27、operties. _ Section 2: Definitions Coating: A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film. Discontinuity: (1) An interruption in the normal physical structure or configuration of a coat
28、ing such as cracks, laps, seams, inclusions, or porosity. A discontinuity may or may not affect the usefulness of the coating. (2) A condition in which the electrical path of a structure is interrupted by a device that acts as a dielectric or insulated fitting. May also be identified as a holiday or
29、 pinhole. Holiday: A discontinuity in a protective coating that exposes unprotected surface to the environment; in this standard, a term used interchangeably with discontinuity. Holiday Detector: A device that locates discontinuities in a coating applied to a conductive substrate. Pinhole: A minute
30、hole through a coat or coats that exposes an underlying coat or the substrate. Telegraphing: Current that travels through a moisture patch to a discontinuity, causing an erroneous discontinuity test result. _ Section 3: Low-Voltage Wet Sponge Testing 3.1 Equipment 3.1.1 A low-voltage wet sponge test
31、er is an electronic device powered by a self-contained battery with voltages ranging from 5 to 90 V direct current (DC), depending on the manufacturers circuit design. It is used to locate discontinuities in a nonconductive coating applied to a conductive substrate. Operation includes the use of an
32、open-cell sponge electrode saturated with a solution for exploring the coating surface, a ground connection, and an audible or visual indicator for signaling a point of coating discontinuity. 3.1.2 The operating voltage of a low-voltage wet sponge tester is a function of the particular electronic SP
33、0188-2006 2 NACE International circuit design and does not affect the sensitivity of the device. 3.1.3 A number of industry accepted, low-voltage wet sponge testers are commercially available. The following electronic principles describe two types of devices generally used; others may be available b
34、ut are not described in this standard. 3.1.3.1 One type of low-voltage wet sponge tester is a lightweight, self-contained, portable device based on the electrical principle of an electromagnetic sensitive relay or solid-state electronic relay circuit that energizes an audible or visual indicator whe
35、n a coating discontinuity is detected. Generally, this type of tester can be recalibrated in the field by the user. 3.1.3.2 Another type of low-voltage wet sponge tester is a lightweight, self-contained, portable device based on the principle of an electronic relaxation oscillator circuit that react
36、s significantly to the abrupt drop in electrical resistance between the high dielectric value of the coating and the conductive substrate at the point of coating discontinuity. This results in a rise in oscillator frequency as well as in the audible signal from the device. Generally, this type of te
37、ster cannot be recalibrated in the field by the user. 3.2 Procedures for Use 3.2.1 Sufficient drying or curing of the coating shall be allowed prior to conducting a test. The length of time required for drying or curing shall be obtained from the coating manufacturer. Solvents retained in the coatin
38、g could produce erroneous indications. 3.2.2 The film thickness of the coating shall be measured with a nondestructive dry film thickness gauge. If the coating exceeds 500 m (20 mil), the procedures for high-voltage spark testing described in Section 4 shall be used. A low-voltage wet sponge tester
39、shall not be used for determining the existence of discontinuities in coatings having a total thickness greater than 500 m (20 mil), due to the relative inaccuracy and lack of sensitivity of low-voltage wet sponge testers. 3.2.3 The tester shall be tested for sensitivity in accordance with Paragraph
40、 3.3. 3.2.4 The ground wire from the tester ground output terminal shall be attached to the conductive substrate, and positive electrical contact shall be ensured. 3.2.5 The exploring sponge lead shall be attached to the output terminal. 3.2.6 The sponge shall be saturated with tap water. The sensit
41、ivity of the test may be increased by adding a low-sudsing wetting agent (such as that used in photographic film development), combined at a ratio of 30 mL (1 fl oz) wetting agent to 3.8 L (1 gal) water. The sponge shall be wetted sufficiently to barely avoid dripping while it is moved over the coat
42、ing. 3.2.7 If a wetting agent is used, it must be completely removed by rinsing the holiday area prior to repair. Additives can leave contaminants on the surface that can interfere with adhesion of topcoats or repair coats and may contaminate stored product. 3.2.8 If a test is conducted between coat
43、s of a multicoat system, a wetting agent shall not be used. 3.2.9 Sodium chloride (salt) shall not be added to the water because it can cause erroneous indications of discontinuities. The salt, after drying on the coated surface, can form a continuous path of conductivity. It also interferes with in
44、tercoat adhesion of additional coats. 3.2.10 A bare spot on the conductive substrate shall be contacted with the wetted sponge to verify that the tester is properly grounded. This procedure shall be repeated periodically during the test. 3.2.11 The sponge shall be moved over the surface of the coati
45、ng at a moderate rate of approximately 0.3 m/s (1 ft/s), using a double pass over each area. Sufficient pressure shall be applied to maintain a wet surface. If a discontinuity is detected, the sponge should be turned on end to determine the exact location of the discontinuity. 3.2.12 Discontinuities
46、 that require repair shall be identified with a marker that is compatible with the repair coating or one that is easily removable. 3.2.13 To prevent telegraphing, care should be taken to ensure that the solution (tap water) is wiped dry from a previously detected discontinuity before continuing the
47、test. 3.3 Verifying Sensitivity of Equipment 3.3.1 The tester shall be tested for sensitivity prior to initial use on each project and periodically thereafter during the project, in accordance with the manufacturers instructions. 3.3.2 The battery shall be tested for proper voltage output according
48、to the manufacturers instructions. 3.3.3 The ground cable shall be connected to the tester ground output terminal. 3.3.4 The tester shall be switched to the “on” position, if neccessary. SP0188-2006 NACE International 3 3.3.5 The sponge shall be saturated with a wetting solution consisting of tap water and a wetting agent (see Paragraph 3.2.6). 3.3.6 The ground-cable alligator clip
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