Common Errors and Causes extreme care at all times.

21.3.2.8 Common Errors and Causes extreme care at all times.

Common operator-based errors include the operator’s failure to keep the probe in con-

21.3.3.1 Proper Use of Instrument

tact with the surface and moving the elec- The high-voltage AC holiday detectors oper- trode either too quickly or slowly across the

ate on a different electrical principle, but the testing surface.

testing procedure is generally the same as Some equipment-based errors include:

for high-voltage DC holiday detectors.

• Lack of display: due to low battery or bad/

As with all instruments, refer to the manu-

missing fuse (depending on model).

facturer’s operating instructions for model-

• Continuous alarm: due to a damp surface

specific detailed instructions for use.

or moving the probe too quickly across surface.

21.3.3.2 Standards

• No alarm on fault: due to a too low volt-

Standards that may need to be consulted

age/sensitivity setting or bad ground con-

(depending on specification requirements,

nection.

coating and substrate type) include:

• No spark at the tip: caused by lead or con-

• AS3894.1-2002

nection.

• ASTM G62-07

• Incorrect voltage generated: Some

• NACE RP0274-04

21-12 High Voltage and Low Voltage Holiday Testing Instrumentation

• NACE SP0490-2007 achieve better results on certain substrates • NACE SP0188-2006

or with certain coating types. • ANSI/AWWA C214-07

• Anticipated coating thickness. As men- tioned earlier, use low-voltage (sponge)

• ANSI/AWWA C213-07 holiday detectors on coatings up to 20 • ISO 2746:1998

mils (500 µm) thick and the high-voltage detectors on higher film thicknesses. (This

21.3.3.3 Calibration and Frequency

is a general rule and does not always

The instrument comes calibrated from the

apply)

manufacturer and cannot be calibrated by

• Specification requirements. Some specifi-

the user. Check the voltage output periodi-

cations may require special procedures or

cally, following manufacturer’s suggested recommend a specific type of holiday

detector to be used.

method. If there is ever a question about the accuracy of the holiday detector, take it out

Example: The specification may call for a low-voltage detector on a film thickness

of service and return to the manufacturer or

over 20 mils (500 µm), which contradicts

supplier for service.

the general rule.

21.3.3.4 Operating Parameters

• Standards to follow. Depending on some of the other factors listed above, there are

Use AC-type holiday testers to test noncon-

specific standards that should be referred

ductive linings on steel substrates (e.g., rub-

to in order to ensure proper procedures are

ber, glass, or sheet linings). AC testers have

followed.

a variety of voltages but typical use is for very thick coatings, with test voltages in the

21.5 Inspector’s Checklist

range of 25,000–60,000V. Before testing for holidays, check the fol- lowing items:

21.4 Inspection Considerations

• Are non-intrinsically safe instruments

There are many factors inspectors must con-

allowed in the work environment?

sider before performing holiday detection.

• What are the grounding and safety issues

Some factors affect what instrument and/or

• Have the specification and standards that

procedure are chosen to perform the test.

govern how to conduct the testing been

Some of the factors include:

thoroughly reviewed and understood? • Work Environment. The high-voltage AC

• Is the proper instrument for the anticipated holiday detectors are not intrinsically safe

DFT at hand?

and cannot therefore be used in a hazard- • Is the battery charged and in satisfactory ous environment. Any instrument that can

working condition?

generating a spark when a flaw is detected is not intrinsically safe.

• Has the operations manual for the holiday detector been thoroughly reviewed and

• Type of Substrate and/or Type of Coating.

understood?

Although all the instruments are designed to locate holidays in nonconductive coat-

• Has the voltage output been checked to ings applied over a conductive substrate, a

ensure accurate readings? particular type of holiday detector may

High Voltage and Low Voltage Holiday Testing Instrumentation 21-13

• Have the signal return cable and electrode connections been checked to ensure there is no electrical resistance in the circuit?

21-14 High Voltage and Low Voltage Holiday Testing Instrumentation