Taylor-Wharton High Capacity GST Storage Tanks - Manual (Page 21)

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PRODUCT SUPPLY VALVE,
All other valves should be closed.
TAKING A TANK OUT OF SERVICE
Schedule shutdown operation to coincide with low liquid level in the tank. If a large
quantity of liquid is in the tank, drain it into a trailer for use elsewhere or for disposal at a safe
location. For tanks so equipped, small quantities of liquid can be vaporized by the PRESSURE
BUILDING COIL and vented through the TANK BLOWDOWN VALVE, provided appropriate
safety precautions are taken.
For shutdowns of short duration, retain residual liquid in the tank. Close all valves except
tank VAPOR and LIQUID PHASE ISOLATION VALVES.
For shutdowns of a prolonged duration, perform the following steps.
TANKS IN OXYGEN SERVICE
1.
Drain liquid from tank. Open the TANK BLOWDOWN VALVE and reduce tank pressure
to atmospheric. Close the TANK BLOWDOWN VALVE.
2.
Connect a source of warm nitrogen gas to tank FILL CONNECTION. Admit nitrogen
purge gas through tank BOTTOM FILL VALVE. Vent tank through the TANK
BLOWDOWN VALVE. Two or three times during purge, close the TANK BLOWDOWN
VALVE and build tank pressure to about 10 psig (0.7 bar/70 kPa). Release pressure and
continue purge.
3.
Open the tank TRYCOCK VALVE and the PRESSURE BUILDING ISOLATION
VALVE and check exit gas with a nitrogen gas analyzer. Allow one hour between samples
reading for the gas to adequately mix. Discontinue purge when only nitrogen gas is
indicated. Close tank TRYCOCK VALVE.
4.
Close the TANK BLOWDOWN VALVE. Build tank pressure to 20 psig
(1.38 bar/138 kPa). Close tank BOTTOM FILL VALVE. Disconnect nitrogen gas hose
from tank FILL CONNECTION.
5.
Warm tank inner vessel before shipping to a new location.
TANKS IN NITROGEN/ARGON SERVICE
1.
Drain liquid product from tank. Open tank TANK BLOWDOWN VALVE and reduce tank
pressure to 20 (1.4 bar/140 kPa). Close tank TANK BLOWDOWN VALVE.
2.
Warm tank inner vessel before moving to a new location.