1、Designation: D 4787 08Standard 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 case of revision,
2、 the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 discontinuities in nonconductiv
3、e liningsor other non-conductive coatings applied to concrete sub-strates.1.2 Discontinuities may include pinholes, internal voids,holidays, cracks, and conductive inclusions.1.3 This practice describes detection of discontinuities uti-lizing a high voltage spark tester using either pulsed orcontinu
4、ous dc voltage.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 the use of a conductive underlayment.1.5 The values stated in SI units are to be regarded asstandard. The values give
5、n in parentheses are for informationonly.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory
6、 limitations prior to use. For a specifichazard statement, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D 5162 Practice for Discontinuity (Holiday) Testing ofNonconductive Protective Coating on Metallic SubstratesG 62 Test Methods for Holiday Detection in Pipeline Coat-ings2.2 NACE Stand
7、ards:3RP0188-88 Discontinuity (Holiday) Testing of ProtectiveCoatings3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 conductive underlayment, na continuous layer ap-plied to the prepared concrete surface prior to the application ofa nonconductive lining layer(s) that will allo
8、w high voltagespark testing for discontinuities in the lining, as it will conductthe current present when the spark is generated.3.1.2 current sensitivity, nsome high voltage testers haveadjustable current sensitivity that can be used to prevent lowlevels of current flow activating the audible alarm
9、. The alarmsensitivity control sets the threshold current at which theaudible alarm sounds. If the high voltage can charge the lining,a small amount of current will flow while this charge isestablished. If the lining contains a pigment that allows alow-level leakage current to flow from the probe wh
10、ile testingthe threshold current can be set so that the alarm does notsound until this current is exceeded, that is, when a holiday orflaw is detected. Increasing the current threshold setting makesthe instrument less sensitive to this low level current flow,decreasing the current threshold setting
11、makes the instrumentmore sensitive to current flow.3.1.3 discontinuity, na localized lining site that has adielectric strength less than a determined test voltage.3.1.4 high voltage spark tester, nan electrical device(producing a voltage in excess of 500 V) used to locatediscontinuities in a noncond
12、uctive protective coating applied toa conductive substrate. The high voltage is applied to thecoating or lining using an exploring electrode and any currentresulting from the high voltage passing through a discontinuityin the coating or lining is passed to the device via a signalreturn cable (also k
13、nown as a ground or earth wire).3.1.5 holiday, nsmall faults or pinholes that permit cur-rent to flow through the conductive substrate, also known as adiscontinuity.3.1.6 spark-over, nthe distance a spark, from a highvoltage tester, will jump across a space from a groundedsurface at a specific elect
14、rical voltage.1This practice 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 June 1, 2008. Published July 2008. Originally appro
15、vedin 1988. Last previous edition approved in 1999 as D 4787 93 (1999).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 AST
16、M website.3Available from NACE International (NACE), 1440 South Creek Dr., Houston,TX 77084-4906, http:/www.nace.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.7 telegraphing, ncurrent traveling through a moisturepath across
17、 the surface of the coating to a discontinuity, givingan erroneous indication of a fault.3.1.8 test voltage, nthat electrical voltage establishedwhich will allow a discontinuity at the thickest lining locationsite to be tested, but which will not damage the lining. Table 1is based on the minimum vol
18、tage for a given thicknessdetermined by the breakdown voltage of air, which is typically4 kV/mm (100 V/mil) and the maximum voltage to preventdamage assuming a dielectric strength of 6 kV/mm (150V/mil).Alternatively the test voltage can be calculated using thefollowing expression:V 5 M=Tcwhere:V = t
19、est voltage,Tc = coating or lining thickness, andM = a constant dependant on the thickness range and theunits of thickness as follows:Coating Thickness Units Coating Thickness Range M Valuemm 1.00 (1.000 m) 7843mil 40.0 1250Examples:1) For a lining of 500 m, Tc = 0.5 and M = 3294ThereforeV 5 3294 =0
20、.5 5 3294 * 0.707 5 2329 V 3.3 kV!2) For a lining of 20 mil, Tc = 20 andM=525ThereforeV 5 525 =20 5 525 * 4.472 5 2347 V 3.3 kV!3) For a lining of 1500 m, Tc = 1.5 and M = 7843ThereforeV 5 7843 =1.5 5 7843 * 1.224 5 9599 V 9.6 kV!4) For a lining of 60 mil, Tc = 60 and M = 1250ThereforeV 5 1250 =60 5
21、 1250 * 7.745 5 9681 V 9.7 kV!4. Summary of Practice4.1 This practice allows for high voltage electrical detectionof discontinuities in new linings applied to concrete substratesthrough the utilization of a continuous conductive underlay-ment applied to the prepared concrete surface prior to theappl
22、ication of the nonconductive lining layer(s) or by deter-mining the conductivity of the concrete substrate to be tested.The conductivity of concrete varies, depending on moisturecontent, type, density, and location of rebars. Test the conduc-tivity of the concrete by attaching the signal return cabl
23、e torebar or other metallic ground permanently installed in theconcrete. If the concrete is sufficiently grounded a signal returncable may be placed with its electrical contact against thestructure and held in place using a wet sand bag. If the testindicates the concrete provides an insufficient sig
24、nal return thetest cannot be conducted. A conductive underlayment will berequired if a continuity test is to be conducted and it is notpractical to add this conductive layer for the purpose of the test.5. Significance and Use5.1 The electrical conductivity of concrete is primarilyinfluenced by the p
25、resence of moisture. Other factors, whichaffect the electrical continuity of concrete structures, includethe 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 within the concrete,5.1.6 Above or below grade elevation,5.1.7 Ind
26、oor or outdoor location,5.1.8 Temperature and humidity, and5.1.9 Age of concrete.TABLE 1 Suggested Voltages for High Voltage Spark TestingTotal Dry Film ThicknessSuggested Inspection, Vmm mils0.5000.590 19.723.2 27000.6000.690 23.627.2 33000.7000.790 27.631.1 39000.8000.890 31.535.0 45000.9000.990 3
27、5.439.0 50001.0001.090 39.442.9 55001.1001.190 43.346.9 60001.2001.290 47.250.8 65001.3001.390 51.254.7 70001.4001.490 55.158.7 75001.5001.590 59.162.6 80001.6001.690 63.066.5 85001.7001.790 66.970.5 90001.8001.890 70.974.4 100001.9001.990 74.878.3 108002.0002.090 78.782.3 115002.1002.190 82.786.2 1
28、20002.2002.290 86.690.2 125002.3002.390 90.694.1 130002.4002.490 94.598.0 135002.5002.590 98.4102.0 140002.6002.690 102.4105.9 145002.7002.790 106.3109.8 150002.8002.890 110.2113.8 155002.9002.990 114.2117.7 160003.0003.090 118.1121.7 165003.1003.190 122.0125.6 170003.2003.290 126.0129.5 175003.3003
29、.390 129.9133.5 180003.4003.490 133.9137.4 185003.5003.590 137.8141.3 190003.6003.690 141.7145.3 195003.7003.790 145.7149.2 200003.8003.890 149.6153.1 210003.9003.990 153.5157.1 218004.0004.190 157.5165.0 225004.2004.290 165.4168.9 230004.3004.390 169.3172.8 240004.4004.490 173.2176.8 250004.5004.59
30、0 177.2180.7 258004.6004.690 181.1184.6 264004.7004.790 185.0188.6 268004.8004.890 189.0192.5 274004.9004.990 192.9196.5 280005.0005.290 196.9208.3 285005.3005.500 208.7216.5 290005.6008.000 220.5307.1 30000D47870825.2 The electrical conductivity of concrete itself may besuccessfully used for high-v
31、oltage 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 reduce the test reliability.5.3 Although the most common conductive und
32、erlaymentsare 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 graphite fibers,5.3.4 Conductive metallic fibers, and5.3.5 Conductive
33、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 for use only with new liningsapplied to concrete substrates. Inspec
34、ting 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 the surface causing telegraph-ing. The use of a high voltage tester
35、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 practice when performancerequirements of the lining in a specified chemic
36、al 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 presence of electricallyconductive fillers or solvents, or both; the poss
37、ible presence ofair inclusions or voids; and the compatibility of conductiveunderlayments with the specified lining.5.8 A pulsed dc high voltage may cause a lining to break-down at a lower voltage than would be the case for acontinuous dc voltage.6. Apparatus6.1 High Voltage Spark TesterAn electrica
38、l detector witha voltage rating in excess of 500 V. The detector is to consistof an electrical energy source, an exploring electrode, a signalreturn cable connection, and wire. The detector shall beequipped with a visual or audible indicator, or both.6.1.1 Electrical Energy SourceEither d-c or pulsa
39、ting d-ctype with the appropriate test voltage.6.1.2 Exploring ElectrodeA metal brush or conductiverubber strip, the full length of which shall be capable ofmaintaining continuous contact with the surface being in-spected.6.1.3 Signal Return Cable, Wire, typically stranded 14 to 16gage copper wire.6
40、.1.4 Visual or Audible 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 t
41、o locate discontinuities 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 protectiv
42、e coating.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 substrates electrical proper
43、ties.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 be installed inaccordance with
44、 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 Conductivity:8.4.1 The surface of
45、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. (WarningSee Section 7.)8.4.2 Verify the operatio
46、n of the test instrument in accor-dance with Section 9.8.4.3 Adjust the high-voltage test instrument in accordancewith Section 11.8.4.4 Connect the test instrument to the installed underlay-ment or other appropriate ground using the signal return cable.If electrical isolation across an expansion joi
47、nt is encountered,the signal return cable must be moved to an appropriate groundin the same section being tested.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 lining.8
48、.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 10 m2(100 ft2). Test points shall be approximately equallyspaced within the test area. At least one add
49、itional test pointshall be used for every 50 m2(500 ft2) thereafter.8.5.2 Test points most distant from the signal return con-nection shall 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.D47870839. Verifying Operation of High Voltage Testers9.1 Test electrical source for proper voltage output of highvoltage testers.9.2 Follow the equipment manufacturers ope
