Chapter 21 High and Low Voltage Holiday Testing Instrumentation

Question 1

1. General types of holiday detectors include:

Answer 1

• Low-voltage DC
• High-voltage DC
• High-voltage pulsed DC
• High-voltage AC

Question 2

2. Low-Voltage (wet sponge) holiday detectors are powered by a battery with output voltages ranging:

Answer 2

5 – 120 V DC

Question 3

3. Describe low-voltage (wet sponge) holiday detectors:

Answer 3

Portable battery-powered electronic instrument
Nonconductive handle with clamps (to hold the sponge)
Open-cell sponge (cellulose)
Ground wire
Solvents retained in the protective coating film can cause erroneous indications (false holidays) during electrical testing
4. High-voltage DC holiday detector types include:

Question 4

4. High-voltage DC holiday detector types include:

Answer 4

High-Voltage Constant Current DC Holiday Detector- used to detect coating holidays in dielectric coatings.

High-Voltage Pulse-Type DC Holiday Detector- ideal for use in moist conditions.

Question 5

5. Describe high-voltage DC holiday detectors:

Answer 5

Ground connection must be made direct to metal substrate (preferred) or indirectly when necessary (e.g., to soil for pipeline measurement). Rule of thumb: 100V/mil (4V/um). Electrode rate of 0.3 m/s (1 ft/s) in a single pass (according to NACE Standard SPO 188). Voltage output range from 800 to 60,000 V

Question 6

6. The type of high-voltage holiday detector used for concrete is a:

Answer 6

High-Voltage Constant Test Current DC holiday Detector

Question 7

7. Excess moisture can cause erroneous indications by creating a path across the surface of the coating to pinholes previously detected, or directly to the signal return connection. This is often referred to as

Answer 7

“telegraphing”