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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
rise above a reference 30 degrees C. The cause of
are available. These vary from a simple hand-held
the heat rise should be identified such as phase
instrument similar to a gun, through which the op-
unbalance, overload, poor connections, or other heat
erator can detect hot spots and note their locations,
producing conditions.
to complex equipment requiring qualified operators
(2) Test parameters. Equipment must detect
and product photographs as a permanent record of
emitted radiation and convert to a visual signal. A
the area being checked. The simpler detectors are
detection ability of a one degree C rise between the
usually sold outright, while the complex items are
hot spot area and the 30 degree reference area is
usually used by infrared detection services which
required.
contract to do the work. Having an instrument
readily available can be justified for a large instal-
(3) Hot spot indications. NETA-MTS indicates
lation with several substations, while a contract to
that temperature gradients as shown in table 3-l
have a survey performed would probably be better
will require the following actions.
for a small installation. However, as a low cost al-
ternative, a camera with infrared sensitive film
Table 3-l. Infrared hot spot gradients1
may be used, or a self-calibrating portable indicat-
ing unit can be coordinated with a Polaroid camera.
Temperature
c. Surveys. When infrared (thermographic) sur-
Deficiency
gradient
Action
veys are made, the equipment to be scanned must
0" to 3C
Possible
Investigate
4" to 3C
Probable
Repair as time permits
be identified. Scanning should be made after visual
16C and above
Major
Repair immediately
and mechanical conditions have been observed. Re-
port all areas scanned.
1
Consider providing photographs an&or thermograms as seen on
(1) Reports. If hot spots are found the report
the imaging system in reports where appropriate to the size and
should locate the problem area and the temperature
criticality of the equipment examined.
Section II - STRUCTURE MAINTENANCE
3-8. Importance of maintenance.
b. Painting. If required spot painting covers more
than 5 percent of the visible surfaces, the entire
The useful life of a substation structure is directly
structure probably should be painted.
dependent upon the care it receives. Surface preser-
vation is of prime importance.
(1) Priming coat. Apply a priming coat to the
clean dry surface using a good zinc dust/zinc oxide
3-9. Galvanized steel structures.
paint. Allow ample time for the paint to dry before
The protective coating produced by the galvanizing
applying the finish coats.
process normally has a long life; however, the coat-
(2) Finish coats. Two finish coats should be ap-
ing will eventually fail and rust will appear. The life
plied using the same type paint used for priming.
of the coating on structural steel used in substa-
Ample drying time should be allowed between fin-
tions should generally be longer than 12 years ex-
ish coats. Only one finish coat is needed for areas on
cept possibly for the upper flat surfaces of horizon-
which the galvanized coating remains intact. Other
tal members. Any failure of the coating will usually
paints normally used as final coats for metal (such
occur in spots rather than over an entire surface.
as aluminum paint) may be used as the final coat in
Refer to chapter 4, section VII for self-weathering
place of the zinc dust/zinc oxide paint.
steel requirements.
a. Cleaning. Clean the surface with a wire brush
(3) Temperature. Painting of outdoor metal
or by other mechanical means to remove rust and
work is recommended only when the temperature is
dirt. If the surface is contaminated with grease or
above 45 degrees F (7 degrees C) and when the
oil, a solvent should be used to remove those con-
relative humidity is below 80 percent.
taminants. Mineral spirits or one ounce (28.4
(4) Durability. The d urability of a paint coat-
grams) of trisodium phosphate in one gallon (3.8
ing depends on thickness, cohesion, and contin-
liters) of warm water can be used as the solvent. If
uity. Generally, 5 mils or 0.005 inch (0.125 milli-
it is uneconomical or impractical to remove all rust,
meters) is an adequate thickness. The thickness
a reasonably satisfactory job can be obtained by
should be uniform, and paint should not be
deactivating the rust through chemical treatment. A
easily scraped off the metal. Welds, edges, and other
weak solution of phosphoric acid is suggested for
deactivating rust. Use proper skin and eye protec-
hard-to-coat areas should be given particular at-
tion.
tention.
3-2
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