Taylor-Wharton VJ Bulk Tank - Manual (Page 17)

Try to determine the source of leakage in cases where the casing safety device has not ruptured;
visually inspect the exterior of the casing. Check the following areas in the order in which they are
listed:
a. Vacuum gauge tube,
b. Vacuum gauge tube valve (V-3),
c. Casing evacuation valve (V-4),
d. Casing bursting disk (R-1),
e. All liquid and gas phase lines at exit point from casing,
f. Any area of the casing that might have been exposed to cryogenic liquid spray or
contact.
Look for signs of damage, corrosion, operated valves, and other abnormal conditions. Make repairs
to any suspicious area and proceed with re-evacuation.
If there is complete loss of vacuum and rupture of the casing safety device accompanied by ejection
of perlite insulation, the cause is probably leakage from the liquid container or internal piping. Field
repair of such internal leakage is beyond the scope of these instructions. Contact the Customer
Service Department at the Theodore, Alabama factory for advice or assistance.
TESTING FOR CASING LEAKAGE
If leakage appears to be from atmosphere and there is no evidence of casing safety device failure,
check for leaks in the casing and/or casing/piping connection. This involves breaking any remaining
partial vacuum, pressurizing the casing, and checking all casing welds, especially those around
piping.
BREAKING VACUUM
If it is necessary to break vacuum (allow insulation space to return to atmospheric pressure) of a tank
that is still under partial vacuum, it is important to minimize the entry of moisture into the insulation
space. Removing such moisture during re-evacuation is difficult and time consuming. This problem
can be minimized by breaking vacuum with dry nitrogen gas admitted through the evacuation valve.
1. Remove the pipe plug from the evacuation valve inlet.
2. Connect a cylinder of dry nitrogen gas, equipped with a pressure regulator and an
accurate 0-5 psig (35 kPa) pressure gauge, to the evacuation valve inlet.
3. Open the cylinder valve and adjust the regulator to a delivery pressure of about 2 psig
(15 kPa).
4. Slowly open the evacuation valve to allow nitrogen gas to enter the insulation space.
5. When the vacuum has been broken, shut off the nitrogen supply and disconnect it from
the evacuation valve.
6. Leave evacuation valve open for at least 60 minutes to allow the insulation space
pressure to equalize. Then close the evacuation valve.
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