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– 2 –
CORROSION
MITIGATION
INSTRUMENTATION
2828
FM
758,
N
EW
B
RAUNFELS
,
TX
78130 T
EL
:
(909)
890-0700
P
RODUCT
I
NSTRUCTIONS
•
The Model AP/AC Holiday Detector is now ready to operate.
•
SELECT the HIGH or LOW position. Adjust the voltage setting, using the
digital display for reference.
NOTE: Digital display and actual output may differ as much as 5% due to manufacturer’s
specifications of display.
4.
OPERATING METHODS
A good ground return system for both the pipe and the detector will always provide the
best and most reliable inspection. The pipe to be inspected must be grounded from
the bare pipe to earth at some point along the pipe. If individual joints of the pipe are
to be inspected that are not electrically connected, each joint must be grounded. The
speed of the electrode's travel along the pipe should never be excessive, since faulty
inspection may result. Occasional checks of the detector operation should be made,
particularly if no holidays are being found. This can be accomplished by testing for the
spark and signal at the edge of the coating where bare pipe exists or by touching the
probe end to the bare pipe and noting the length of the spark and the signal
effectiveness. If the signal does not occur when the spark discharges from the
electrode into a known holiday, the ground return (i.e. the path between the metallic
pipe and earth and the earth to the ground trail of the detector) is of high resistance.
In this case, a better ground is required and a direct connection between the metal
pipe and the ground wire may be necessary. This type of grounding is extremely
uncommon unless the soil is very dry (if using a grounding rod) or the detectors output
is low.
Correct voltage output for a given thickness of coating has long been a matter of
controversy. However, recent formulas have been suggested which may be used as a
guide for correct peak voltages on various coating thickness. The calculation is as
follows:
V
=
K √ T
WHERE
V
=
Peak voltage in volts.
T
=
Thickness of bonded coating in mils (not
including outer wrappers).
K
=
Constant of 1,250 for coatings over 30 mils
and 525 for fusion bonded epoxy coatings
under 30 mils.
These formulas, when applied to a coating of 3/32” thickness and with a constant of
1,250, would indicate an applied voltage of 12,500 volts peak or a coating of 16 mil
