More D The degree of coating continuity required is dictated by service conditions. Discontinuities in a coating are frequently very minute and not readily visible. This practice provides a procedure for electrical detection of minute discontinuities in nonconductive coating systems.
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A number in parentheses indicates the year of last reapproval. For concretesurfaces, refer to Practice D The values given in parentheses are for informationonly. It is theresponsibility 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.
Referenced Documents2. A discontinuity may also be identified as aholiday or pinhole. A pinhole in the finish coat may not appear as adiscontinuity. Significance and Use4. The degree of coating continuity required is dictatedby service conditions. Discontinuities in a coating are fre-quently very minute and not readily visible. This practiceprovides a procedure for electrical detection of minute discon-tinuities in nonconductive coating systems.
The allowable number of discontinuities should be determinedprior to conducting this test since the acceptable quantity ofdiscontinuities will vary depending on coating film thickness,design, and service conditions.
Highvoltage spark test equipment is generally used for determiningthe existences of discontinuities in coating films having a totalthickness of greater than 0. Consult the coating manufac-turer for proper test equipment and inspection voltages.
Current edition approved June 1, Published July Originally approvedin Last previous edition approved in as D — DOI: United States1strength in a coating system shall be considered in selecting theappropriate voltage for detection of discontinuities. Atmo-spheric conditions shall also be considered since the voltagerequired for the spark to gap a given distance in air varies withthe conductivity of the air at the time the test is conducted.
Suggested starting voltages are provided in Table 1. Solventsretained in an uncured coating film may form an electricallyconductive path through the film to the substrate. Its use on a coating previouslyexposed to an immersion condition has often resulted indamage to the coating and has produced erroneous detection ofdiscontinuities due to permeation or moisture absorption of thecoating.
Deposits may also be present on the surface causingtelegraphing current traveling through a moisture path to adiscontinuity, giving an erroneous indication or current leak-age across the surface of the coating due to contamination.
Theuse of a high voltage tester on previously exposed coatings hasto be carefully considered because of possible spark-through,which will damage an otherwise sound coating. Although a lowvoltage tester can be used without damaging the coating, it mayalso produce erroneous results. It is used to locate discontinuities in a noncon-ductive coating applied to a conductive substrate.
Operationincludes the use of an open-cell sponge electrode wetted witha solution for exploring the coating surface, a signal returnconnection, and an audible or visual indicator, or both, forsignaling a point of coating discontinuity.
The following electronic principle describes two types ofdevices generally used; others may be available but are notdescribed in this practice. Generally this equipment is capable of being recali-brated in the field by the user. This results in a rise in oscillator frequency aswell as in the audible signal from the device.
Generally, thisequipment is incapable of being recalibrated in the field by theuser. The length of time requiredshall be obtained from the coating manufacturer. Solventsretained in the coating film could produce erroneous indicators.
If the coatingfilm exceeds 0. Anexample of a low sudsing wetting agent is one used inphotographic development. The sponge shall be wetted suffi-ciently to barely avoid dripping of the solution while thesponge is moved over the coating. The wetting agent residuemust be removed prior to executing repairs to the coating. The salt, after drying on the coated surface,may form a continuous path of conductivity across the surface.
It will also interfere with intercoat adhesion of additional coats. This procedure shall be repeated periodically dur-ing the test. Apply sufficient pressure to maintain a wetsurface. If a discontinuity is detected, turn the sponge on end todetermine the exact location of the discontinuity. Improvedaccuracy of location can be achieved using a corner of thesponge if practical. However, when a test isconducted between coats of a multicoat system, a wetting agentshall not be used and all residue left by the test water must becompletely removed prior to applying additional coats.
A certificate of calibration, renewedannually, may be required if the quality management systemthat controls the testing dictates. Itconsists of an electrical voltage source, an exploring electrode,and a signal return wire connection from the indicator, signal-ing current flow through a coating film discontinuity, to thesubstrate.
The detector shall be equipped with a visual oraudible indicator, or both. It shall be kept cleanand free of coating material. A pulse type detectordischarges a cycling, high voltage pulse, while a direct currenttype discharges continuous voltage.