T.O. 33B-1-1
4-83
4.7.7
Inspection Procedures.
4.7.7.1
Conductivity Procedure Requirements.
Procedures for conductivity measurement should take into account the varieties of environments and test part
conditions which might be encountered. In preparing for conductivity measurement, the following steps should be
considered:
a. Background and objectives of the inspection.
b. Equipment requirements.
c. Part preparation.
d. Instrument calibration.
e. Conductivity measurement procedures.
f. Acceptance/rejection criteria.
4.7.7.2
Background And Objectives.
An understanding of the problem that initiates a conductivity measurement requirement enables the inspector to better
interpret inspection results and handle unexpected test conditions. The purpose of the test can be separation of mixed
or improper alloy, determination of improper heat treatment, and detection of heat or fire damaged material. The types
of material involved and the location of the inspection should be specifically established. Heat and/or fire damage may
be confined to a portion of a part and may vary in the degree of damage. These variables must be considered during
conductivity measurement.
4.7.7.3
Part Preparation.
As with all types of eddy current inspection, areas on which conductivity measurement is to be performed must be free
of any sharp slivers or foreign material that could damage a probe or cause lift-off changes. Such conditions can be
removed with fine emery paper or other approved means. Conductivity measurements can be performed through
nonconductive coatings that have thicknesses equal to or less than the amount of lift-off adjustment on meter type
equipment. Both the thickness and uniformity of the coating thickness and the amount of lift-off adjustment provided
should be checked prior to measuring conductivity through nonconductive coatings. If lift-off adjustment cannot be
obtained, correction factors can be determined for uniform coatings by establishing the change in conductivity readings
caused by the coating and adding this change to each of the measured values. Nonuniform coatings in excess of lift-off
adjustment must be removed prior to measuring conductivity. Excessively rough surfaces should be smoothed with
emery paper to provide a surface finish 250 RMS or better before performing conductivity measurements.
4.7.7.4
Calibration For Measuring Conductivity Values.
NOTE
US Navy - PD-214 Follow instructions in the: instruments’ conductivity program.
To calibrate a general purpose instrument for measuring conductivity directly, the following procedures should be
followed:
a. Select a sufficient number of standards to obtain a smooth continuous curve over the range of
conductivity to be measured. The actual number of samples will depend on the expected range to be
measured and the accuracy required.
b. Adjust the instrument for lift-off, if applicable, and a standard representing approximately mid-range of
the conductivities to be measured.
