1、Designation: D4787 08D4787 13Standard Practice forContinuity Verification of Liquid or Sheet Linings Applied toConcrete Substrates1This standard is issued under the fixed designation D4787; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, 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 to allow the detection of discontinuities in nonco
3、nductive linings or othernon-conductive coatings applied to concrete substrates.1.2 Discontinuities may include pinholes, internal voids, holidays, cracks, and conductive inclusions.1.3 This practice describes detection of discontinuities utilizing a high voltage spark tester using either pulsed or
4、continuous dcvoltage.NOTE 1For further information on discontinuity testing refer to NACE Standard RP0188-88SP0188-2006 or Practice D5162.1.4 This practice describes procedures both with and without the use of a conductive underlayment.1.5 The values stated in SI units are to be regarded as standard
5、. The values given in parentheses are for information only.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicabil
6、ity of regulatorylimitations prior to use. For a specific hazard statement, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D5162 Practice for Discontinuity (Holiday) Testing of Nonconductive Protective Coating on Metallic SubstratesG62 Test Methods for Holiday Detection in Pipeline Coating
7、s2.2 NACE Standards:3RP0188-88SP0188-2006 Discontinuity (Holiday) Testing of Protective Coatings3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 conductive underlayment, na continuous layer applied to the prepared concrete surface prior to the application of anonconductive lini
8、ng layer(s) that will allow high voltage spark testing for discontinuities in the lining, as it will conduct thecurrent present when the spark is generated.3.1.2 current sensitivity, nsome high voltage testers have adjustable current sensitivity that can be used to prevent low levelsof current flow
9、activating the audible alarm. The alarm sensitivity control sets the threshold current at which the audible alarmsounds. If the high voltage can charge the lining, a small amount of current will flow while this charge is established. If the liningcontains a pigment that allows a low-level leakage cu
10、rrent to flow from the probe while testing the threshold current can be setso that the alarm does not sound until this current is exceeded, that is, when a holiday or flaw is detected. Increasing the currentthreshold setting makes the instrument less sensitive to this low level current flow, decreas
11、ing the current threshold setting makesthe instrument more sensitive to current flow.3.1.3 discontinuity, na localized lining site that has a dielectric strength less than a determined test voltage.1 This practice is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materia
12、ls, and Applications and is the direct responsibility ofSubcommittee D01.46 on Industrial Protective Coatings.Current edition approved June 1, 2008Feb. 1, 2013. Published July 2008March 2013. Originally approved in 1988. Last previous edition approved in 19992008 asD4787 93 (1999).D4787 08. DOI: 10.
13、1520/D4787-08.10.1520/D4787-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from NACE Internat
14、ional (NACE), 1440 South Creek Dr., Houston, TX 77084-4906, http:/www.nace.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequat
15、ely depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken
16、, PA 19428-2959. United States13.1.4 high voltage spark tester, nan electrical device (producing a voltage in excess of 500 V) used to locate discontinuitiesin a nonconductive protective coating applied to a conductive substrate. The high voltage is applied to the coating or lining usingan exploring
17、 electrode and any current resulting from the high voltage passing through a discontinuity in the coating or lining ispassed to the device via a signal return cable (also known as a ground or earth wire).3.1.5 holiday, nsmall faults or pinholes that permit current to flow through the conductive subs
18、trate, also known as adiscontinuity.3.1.6 spark-over, nthe distance a spark, from a high voltage tester, will jump across a space from a grounded surface at aspecific electrical voltage.3.1.7 telegraphing, ncurrent traveling through a moisture path across the surface of the coating to a discontinuit
19、y, giving anerroneous indication of a fault.3.1.8 test voltage, nthat electrical voltage established which will allow a discontinuity at the thickest lining location site tobe tested, but which will not damage the lining. Table 1 is based on the minimum voltage for a given thickness determined by th
20、ebreakdown voltage of air, which is typically 4 kV/mm (100 V/mil) and the maximum voltage to prevent damage assuming adielectric strength of 6 kV/mm (150 V/mil).Alternatively the test voltage can be calculated using the following expression:V 5M=TcTABLE 1 Suggested Voltages for High Voltage Spark Te
21、stingTotal Dry Film Thickness Suggested 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 35.439.0 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 7500
22、1.5001.590 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 120002.2002.290 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 14500
23、2.7002.790 106.3109.8 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 175003.3003.390 129.9133.5 180003.4003.490 133.9137.4 185003.5003.590 137.8141.3 190003.6003.690 141.7145.3 195003.7003.790 145.7149.2 200003.8
24、003.890 149.6153.1 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 250004.5004.590 177.2180.7 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
25、.290 196.9208.3 285005.3005.500 208.7216.5 290005.6008.000 220.5307.1 30000D4787 132where:where:V = test voltage,Tc = coating or lining thickness, andM = a constant dependant on the thickness range and the units of thickness as follows:Coating Thickness Units Coating Thickness Range M Valuemm 1.00 (
26、1.000 m) 7843mil 40.0 1250Examples:Examples:1) For a lining of 500 m, Tc = 0.5 and M = 32943294ThereforeV 53294=0.5 53294*0.707 52329 V 3.3 kV!ThereforeV 5 3294 =0.5 5 3294*0.707 5 2329 V 3.3 kV!2) For a lining of 20 mil, Tc = 20 and M = 525ThereforeV 5525=20 5525*4.472 52347 V 3.3 kV!ThereforeV 5 5
27、25 =20 5 525*4.472 5 2347 V 3.3 kV!3) For a lining of 1500 m, TcTC = 1.5 and M = 7843ThereforeV 57843=1.557843*1.224 59599 V 9.6 kV!ThereforeV 5 7843 =1.5 5 7843*1.224 5 9599 9.6 kV !4) For a lining of 60 mil, Tc = 60 and M = 1250ThereforeV 51250=6051250*7.745 59681 V 9.7 kV!ThereforeV 5 1250 =60 5
28、1250*7.745 59681 V 9.7 kV !4. Summary of Practice4.1 This practice allows for high voltage electrical detection of discontinuities in new linings applied to concrete substratesthrough the utilization of a continuous conductive underlayment applied to the prepared concrete surface prior to the applic
29、ationof the nonconductive lining layer(s) or by determining the conductivity of the concrete substrate to be tested. The conductivity ofconcrete varies, depending on moisture content, type, density, and location of rebars. Test the conductivity of the concrete byattaching the signal return cable to
30、rebar or other metallic ground permanently installed in the concrete. If the concrete issufficiently grounded a signal return cable may be placed with its electrical contact against the structure and held in place usinga wet sand bag. If the test indicates the concrete provides an insufficient signa
31、l return the test cannot be conducted. A conductiveunderlayment will be required if a continuity test is to be conducted and it is not practical to add this conductive layer for thepurpose of the test.5. Significance and Use5.1 The electrical conductivity of concrete is primarily influenced by the p
32、resence of moisture. Other factors, which affect theelectrical continuity of concrete structures, include the following:5.1.1 Presence of metal rebars,5.1.2 Cement content and type,5.1.3 Aggregate types,D4787 1335.1.4 Admixtures,5.1.5 Porosity within the concrete,5.1.6 Above or below grade elevation
33、,5.1.7 Indoor or outdoor location,5.1.8 Temperature and humidity, and5.1.9 Age of concrete.5.2 The electrical conductivity of concrete itself may be successfully used for high-voltage continuity testing of linings applieddirectly with no specific conductive underlayment installed. However, the volta
34、ge required to find a discontinuity may vary greatlyfrom point to point on the structure. This variance may reduce the test reliability.5.3 Although the most common conductive underlayments are liquid primers applied by trowel, roller, or spray, and whichcontain carbon or graphite fillers, others ma
35、y take the form of the 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 metallic screening.5.4 Liquid-applied conductive underlayments may be desirable as they can serve to address imperfecti
36、ons 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 linings applied to concrete substrates. Inspecting a lining previously exposedto an immersion condition could result in damaging the lining or produce an erroneous d
37、etection of discontinuities due topermeation or moisture absorption of the lining. Deposits may also be present on the surface causing telegraphing. The use of ahigh voltage tester on a previously exposed lining is not recommended because of possible spark through which will damage anotherwise sound
38、 lining. A low voltage tester can be used but could produce erroneous readings.5.6 The user may consider this practice when performance requirements of the lining in a specified chemical environmentrequire assurance of a lining free of discontinuities.5.7 Factors affecting the dielectric properties
39、and test voltage shall be considered. Some factors are the curing time ofliquid-applied linings; the possible presence of electrically conductive fillers or solvents, or both; the possible presence of airinclusions or voids; and the compatibility of conductive underlayments with the specified lining
40、.5.8 A pulsed dc high voltage may cause a lining to breakdown at a lower voltage than would be the case for a continuous dcvoltage.6. Apparatus6.1 High Voltage Spark TesterAn electrical detector with a voltage rating in excess of 500 V. The detector is to consist of anelectrical energy source, an ex
41、ploring electrode, a signal return cable connection, and wire. The detector shall be equipped witha visual or audible indicator, or both.6.1.1 Electrical Energy SourceEither d-c or pulsating d-c type with the appropriate test voltage.6.1.2 Exploring ElectrodeA metal brush or conductive rubber strip,
42、 the full length of which shall be capable of maintainingcontinuous contact with the surface being inspected.6.1.3 Signal Return Cable, Wire, typically stranded 14 to 16 gage copper wire.6.1.4 Visual or Audible Indicators , Indicators, or both, to signal a closed electrical circuit. Such signals sha
43、ll be essential fortesting the underlayment for electrical conductivity and for exposing discontinuities in the lining after it has been applied.6.1.5 High Voltage Pulsating DC Spark TesterA device used to locate discontinuities where electrical pulses are generatingbetween 20 and 60 cps. Each pulse
44、 is on for a period of time between 20 and 200 s.6.1.6 High Voltage Continuous DC Spark TesterA device used to locate discontinuities where the voltage is continuouslypresent on the surface of the protective coating.7. Hazards7.1 Solvents retained in the applied underlayment or lining may create an
45、explosive environment with the high voltage testersas well as produce an erroneous result.8. Conductive Underlayments8.1 The conductive underlayment shall not rely on the concrete substrates electrical properties.8.2 The specified lining shall be compatible with the specified conductive underlayment
46、.8.3 Application:8.3.1 The finished conductive underlayment surface shall be relatively smooth. The conductive underlayment shall beconsidered part of the lining system and must be installed in accordance with the manufacturers latest published instructions.D4787 1348.3.2 Visually verify that the co
47、nductive underlayment covers 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 the applied conductive underlayment shall be clean, dry, free of oil, grease, dirt,
48、or other contaminants andbe sufficiently cured in accordance with the manufacturers latest published instructions at the time the conductivity testing isperformed. (WarningSee Section 7.)8.4.2 Verify the operation of the test instrument in accordance with Section 9.8.4.3 Adjust the high-voltage test
49、 instrument in accordance with Section 11.8.4.4 Connect the test instrument to the installed underlayment or other appropriate ground using the signal return cable. Ifelectrical isolation across an expansion joint is encountered, the signal return cable must be moved to an appropriate ground in thesame section being tested.8.4.5 Place the exploring electrode on a nonconductive spacer so that an air gap between the surface of the underlayment andthe e
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