1、Designation: D 4787 93 (Reapproved 1999)Standard Practice forContinuity Verification of Liquid or Sheet Linings Applied toConcrete Substrates1This standard is issued under the fixed designation D 4787; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、 case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers procedures that may be used toallow the detection of discontinuit
3、ies in nonconductive liningsapplied to concrete substrates.1.2 Discontinuities may include pinholes, internal voids,holidays, cracks, and conductive inclusions.1.3 This practice describes detection of discontinuities uti-lizing a low voltage wet sponge holiday detector and a highvoltage pulsating or
4、 continuous dc spark tester. Linings withthickness in excess of 20 mils must be tested utilizing highvoltage spark testing equipment.NOTE 1For further information on discontinuity testing refer toNACE Standard RP0188-88 or Practice D 5162.1.4 This practice describes procedures both with and with-out
5、 the use of a conductive underlayment.1.5 The values stated in the inch-pound units are to beregarded as the standard. The values given in parentheses arefor information only.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibi
6、lity of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For a specifichazard statement, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D 149 Test Method for Dielectric Breakdown Voltage
7、 andDielectric Strength of Solid Electrical Insulating Materialsat Commercial Power FrequenciesD 5162 Practice for Discontinuity (Holiday) Testing ofNonconductive Protective Coating on Metallic Substrates2.2 NACE Standards:3RP0188-88 Discontinuity (Holiday) Testing of ProtectiveCoatings3. Terminolog
8、y3.1 Definitions of Terms Specific to This Standard:3.1.1 discontinuitya localized lining site that has a dielec-tric strength less than a determined test voltage.3.1.2 conductive underlaymenta continuous layer appliedto the prepared concrete surface prior to the application of anonconductive lining
9、 layer(s) that will allow high voltage sparktesting for discontinuities in the lining.3.1.3 spark-overthe distance a spark, from a high voltagetester, will jump across a space from a grounded surface at aspecific electrical voltage.3.1.4 high voltage spark testeran electrical device (inexcess of 800
10、 V) used to locate discontinuities in a noncon-ductive protective coating applied to a conductive substrate.3.1.5 low voltage testera low voltage wet sponge electri-cal detector used to locate discontinuities in nonconductivelinings applied to conductive substrates.3.1.5.1 DiscussionThis test instru
11、ment is not suitable fortesting linings in excess of 20 mils.3.1.6 test voltagethat electrical voltage established whichwill allow a discontinuity at the thickest lining location site tobe tested, but which will not damage the lining.3.1.6.1 DiscussionThe test voltage must always be setwell below th
12、e dielectric breakdown strength of the lining. Thisvoltage should be recommended by the lining manufacturer.The dielectric breakdown voltage strength of a solid can bedetermined by Test Method D 149.4. Summary of Practice4.1 This practice allows for high and low voltage electricaldetection of discon
13、tinuities in new linings applied to concretesubstrates through the utilization of a continuous conductiveunderlayment applied to the prepared concrete surface prior tothe application of the nonconductive lining layer(s) or bydetermining the conductivity of the concrete substrate to be1This practice
14、is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.46 on Industrial Protective Coatings.Current edition approved Jan. 10, 1999. Published September 1999. Originallypublished as D 4787 88. Last
15、previous edition D 4787 88.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from NationalAssociatio
16、n of Corrosion Engineers, P.O. Box 218340,Houston, TX 77218.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.tested. The conductivity of concrete varies, depending onmoisture content, type, density, and location of rebars. Test thecon
17、ductivity of the concrete by attaching the ground wire torebar or other metallic ground permanently installed in theconcrete. If a metallic ground is not available, the ground wireshall be placed directly against the bare concrete surface andweighted with a damp cloth or paper sand-filled bag. If th
18、e testindicates the concrete provides an insufficient ground, a con-ductive underlayment will be required if a continuity test is tobe conducted.5. Significance and Use5.1 The electrical conductivity of concrete is primarilyinfluenced by the presence of moisture. Other factors whichaffect the contin
19、uity of concrete include the following:5.1.1 Presence of metal rebars,5.1.2 Cement content and type,5.1.3 Aggregate types,5.1.4 Admixtures,5.1.5 Porosity,5.1.6 Above or below grade elevation,5.1.7 Indoor or outdoor location,5.1.8 Temperature and humidity, and5.1.9 Age of concrete.5.2 The electrical
20、conductivity of concrete itself may besuccessfully used for high-voltage continuity testing of liningsapplied directly with no specific conductive underlaymentinstalled. However, the voltage required to find a discontinuitymay vary greatly from point to point on the structure. Thisvariance may reduc
21、e the test reliability.5.3 Although the most common conductive underlaymentsare liquid primers applied by trowel, roller, or spray, and whichcontain carbon or graphite fillers, others may take the form ofthe following:5.3.1 Sheet-applied graphite veils,5.3.2 Conductive polymers,5.3.3 Conductive grap
22、hite fibers,5.3.4 Conductive metallic fibers, and5.3.5 Conductive metallic screening.5.4 Liquid-applied conductive underlayments may be desir-able as they can serve to address imperfections in the concretesurface and provide a better base for which to apply the lining.5.5 This practice is intended f
23、or use only with new liningsapplied to concrete substrates. Inspecting a lining previouslyexposed to an immersion condition could result in damagingthe lining or produce an erroneous detection of discontinuitiesdue to permeation or moisture absorption of the lining.Deposits may also be present on th
24、e surface causing telegraph-ing. The use of a high voltage tester on a previously exposedlining is not recommended because of possible spark throughwhich will damage an otherwise sound lining. A low voltagetester can be used but could produce erroneous readings.5.6 The user may consider this practic
25、e when performancerequirements of the lining in a specified chemical environmentrequire assurance of a lining free of discontinuities.5.7 Factors affecting the dielectric properties and test volt-age shall be considered. Some factors are the curing time ofliquid-applied linings; the possible presenc
26、e of electricallyconductive fillers or solvents, or both; the possible presence ofair inclusions or voids; and the compatibility of conductiveunderlayments with the specified lining.5.8 A continuous dc high voltage tester stresses a lining to agreater degree than the pulsating dc high voltage tester
27、.6. Apparatus6.1 High Voltage Spark TesterAn electrical detector witha voltage rating in excess of 800 V. The detector is to consistof an electrical energy source, an exploring electrode, a groundconnection, and ground wire. The detector shall be equippedwith a visual or audible indicator, or both.6
28、.1.1 Electrical Energy SourceEither a-c, d-c, or pulsat-ing d-c type with the appropriate test voltage.6.1.2 Exploring ElectrodeThe full length shall be capableof maintaining continuous contact with the surface beinginspected.6.1.3 Ground Wire, stranded 14 to 16 gage copper wire.6.1.4 Visual or Audi
29、ble Indicators, or both, to signal aclosed electrical circuit. Such signals shall be essential fortesting the underlayment for electrical conductivity and forexposing discontinuities in the lining after it has been applied.6.1.5 High Voltage Pulsating DC Spark TesterA deviceused to locate discontinu
30、ities where electrical pulses aregenerating between 20 and 60 cps. Each pulse is on for a periodof time between 20 and 200 s.6.1.6 High Voltage Continuous DC Spark TesterA deviceused to locate discontinuities where the voltage is continuouslypresent on the surface of the protective coating.6.2 Low V
31、oltage TesterAn electrical device powered by a5 to 90 volt battery. The detector consists of an electricalenergy source, an open-cell sponge electrode, a ground wire,and an audible indicator. The device may contain a variablerange selector that has no effect on the sensitivity of thedetector which m
32、ust range between 80 000 and 100 000 V.7. Hazards7.1 Solvents retained in the applied underlayment or liningmay create an explosive environment with the high voltagetesters as well as produce an erroneous result.8. Conductive Underlayments8.1 The conductive underlayment shall not rely on theconcrete
33、 substrates electrical properties.8.2 The specified lining shall be compatible with the speci-fied conductive underlayment.8.3 Application:8.3.1 The finished conductive underlayment surface shall berelatively smooth. The conductive underlayment shall beconsidered part of the lining system and must b
34、e installed inaccordance with the manufacturers latest published instruc-tions.8.3.2 Visually verify that the conductive underlayment cov-ers the entire area to be lined. Breaks at expansion joints andconstruction joints are allowable unless otherwise specified.8.4 Verification of Underlayment Condu
35、ctivity:D 4787 93 (1999)28.4.1 The surface of the applied conductive underlaymentshall be clean, dry, free of oil, grease, dirt, or other contami-nants and be sufficiently cured in accordance with the manu-facturers latest published instructions at the time the conduc-tivity testing is performed. (
36、WarningSee Section 7.)8.4.2 Verify the operation of the test instrument in accor-dance with Section 9.8.4.3 Adjust the high-voltage test instrument in accordancewith Section 12.8.4.4 Ground the test instrument to the installed underlay-ment or other appropriate ground. If electrical isolation across
37、an expansion joint is encountered, the ground wire must bemoved to an appropriate ground in the same section beingtested.8.4.5 Place the exploring electrode on a nonconductivespacer so that an air gap between the surface of the underlay-ment and the electrode is equal to the maximum thickness ofthe
38、lining.8.4.6 The underlayment is conductive if the visual oraudible indicator, or both, on the test instrument is activated.8.5 Test Sampling:8.5.1 A minimum of four test points shall be used for thefirst 100 ft2(9.2 m2). Test points shall be approximately equallyspaced within the test area. At leas
39、t one additional test pointshall be used for every 500 ft2(46.45 m2) thereafter.8.5.2 Test points most distant from the ground connectionshall be included in the test sampling.8.5.3 The specified lining shall not be applied until theconductivity of the underlayment or concrete has been verified.9. V
40、erifying Operation of High and Low Voltage Testers9.1 Test electrical source for proper voltage output of highvoltage testers.9.2 Check battery for proper operation of low voltagetesters.9.3 Follow the equipment manufacturers operating instruc-tions for verifying the operation of the tester.9.4 If t
41、he testers fail to signal, they shall be considereddefective.10. Adjustment of High-Voltage Spark Tester forVerifying Conductivity of Underlayment10.1 Establish the test voltage based on the maximumspecified thickness of the nonconductive lining, its dielectricstrength, and the lining manufacturers
42、recommendations.10.2 Following the equipment manufacturers instructions,set and check the test voltage established in 10.1.11. Procedures For Using Low Voltage Wet SpongeTester11.1 Attach the ground wire from the instrument groundoutput terminal to the conductive substrate and ensure positiveelectri
43、cal contact.11.2 Attach the exploring sponge lead to the other outputterminal.11.3 Saturate the sponge with a solution consisting of tapwater and a low sudsing wetting agent (such as used inphotographic film development), combined at a ratio of 1 fluidoz (29.5 mL) wetting agent to 1 gal (3.785 L) wa
44、ter. Thesponge shall be wetted sufficiently to barely avoid dripping ofthe solution while the sponge is moved over the coating.11.4 Sodium chloride (salt) shall not be added to the wettingsolution because of the potential erroneous indications ofdiscontinuities. The salt, after drying on the coated
45、surface,may form a continuous path of conductivity. It will alsointerfere with intercoat adhesion of additional coats.11.5 Contact a bare spot on the conductive substrate withthe wetted sponge to verify that the instrument is properlygrounded. This procedure shall be repeated periodically duringthe
46、test.11.6 Move the sponge over the surface of the coating at amoderate rate approximately 1 ft/s (0.3 m/s), using a doublepass over each area.Apply sufficient pressure to maintain a wetsurface. If a discontinuity is detected, turn the sponge on end todetermine the exact location of the discontinuity
47、.11.7 Discontinuities that require repair shall be identifiedwith a marker that is compatible with the repair coating or onethat is easily removed.11.8 To prevent telegraphing (current traveling through amoisture path to a discontinuity, giving an erroneous indica-tion), take care to ensure that the
48、 solution is wiped dry from apreviously detected discontinuity before continuing the test.11.9 The wetting agent must be completely removed byrinsing the holiday area prior to repair.11.10 When a test is conducted between coats of a multicoatsystem, a wetting agent shall not be used.12. Adjustment o
49、f High Voltage Spark Tester forVerifying Conductivity of the Applied Lining12.1 Select the proper test voltage to provide reliablespark-over to locate a holiday under normal test conditions.The voltage selected must jump an air gap equal to themaximum specified dry film thickness of the lining being testedand not arc through the lining at the minimum specified dryfilm thickness.12.2 Adjust the tester to the test voltage established in 12.1as follows:12.2.1 Connect a high-voltage voltmeter or a spark-gapcalibrator between the electrode and the ground wire.12.2
