FED-STD-791D
NOTE 3:
It is advisable to cut open lines and critical fittings periodically to check
on the efficiency of cleaning. The most critical section is between the
coking head and the cooler.
i. Clean glass coker-assembly body and glass oil-filler tube with scouring powder,
rinsing afterwards with water then with isopropyl alcohol. Air dry and immerse
both in glass-cleaning solution for at least 1 h. Rinse thoroughly using distilled
water for the final rinse, then oven dry at 99 to 104.4C (210 to 220F).
j. Clean glass feeder flask and its connection by rinsing thoroughly with isopropyl
alcohol and air dry.
k. Store all parts in a clean, dust-free location until ready for reassembly.
6.4 Check the water side of the oil cooler for cleanliness, and clean as necessary.
(The frequency of the cleaning depends on the hardness of the water used.) With very
hard water it may be necessary to de-lime the inside of the cooling-water tube after each
test. Cleaning is best accomplished by corking the bottom end of the tube and filling it
with dilute acetic acid (25%), allowing it to stand for 15 to 30 min as needed, and then
flushing thoroughly with water. This cleaning is in addition to the regular cleaning
procedure for the removal of deposits from the oil side.
6.5 Prepare the coking tube as follows:
a. Clean the coking tube by hand abrasion with No. 400 silicon carbide paper
holding the tube by the top end in a jig or fixture designed to avoid marring or
distorting the tube. (To avoid getting dust in the thermocouple wells it is best to
plug them with paper during this operation.)
b. Inspect the surface of the tube for pits. If the tube is pitted, turn it down in a
lathe. (However, when the diameter has been reduced from its original 2.984 to
2.883 cm [1.175 to 1.135 in] or less, replace the tube.) Then repolish it by
hand.
c. After the final polishing with silicon carbide paper, wipe free of dust with clean
rags. Then rinse thoroughly with n-hexane (including thermocouple wells).
Blow dry with clean, dry air. (Thermocouple wells should also be swabbed out
with clean pipe cleaners.)
CAUTION:
After final cleaning, the coking tube must be handled only by the top
end to avoid contamination of the coking surface.
d. Inspect the thermocouple wells for residual oil. If there is any evidence of oil,
repeat the
n-hexane rinse and swab with pipe cleaners until all oil is removed.
e. Install a clean coking-tube thermocouple in one of the wells, and heat the tube to
204C (400F) by plugging in the power rig.
f. Allow the tube to cool, and store it in a dust-free location.
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