-
Record
the reference gauge height indicated for each vessel's tank on the
vessel's capacity tables. Note any corrections for individual
standpipes and/or adapters and calculate the actual reference height
for the reference gauge point used.
-
Determine
if tank capacity tables include volumes within vessel lines in each
tank. If they do not, so note and record.
-
Prior
to gauging, verify with vessel's officer that no cargo is being
transferred and request an estimate of the cargo level in each tank.
-
Verify
that the vapor control valve is closed.
-
Place
the gauging tape assembly onto the vapor control valve and screw it
down tightly (or lock firmly, if quick- release type).
-
To
measure oil, open the vapor control valve and slowly unwind the tape
until the oil indicating tone is heard. When the sensor on the probe
indicates an oil level according to the manufacturer's operation
instructions, read the tape at the reference gauge point to the nearest
tape graduation (1/8th-in., 1-mm, 0.01-ft). See
API MPMS Chapters 3.IA.
-
Repeat
the gauging procedure until two identical readings are obtained out of
three consecutive gauges. If three gauges are required to
obtain two alike, all three must fall within a 1/8th-in.
(3-mm) span. Record the liquid level.
It
may be noted that persistent variance between gauges usually indicates
movement of the tank contents. If cargo movement in a tank is
unavoidable, at least five measurements should be taken, the highest
and lowest readings dropped and the remaining three averaged.
-
When
cargo level measurement is complete, determine the free-water ullage by
lowering the sensor to approximately 1 ft (300 mm) above the bottom of
the tank. Determine the oil/water interface by lowering and
raising the sensor until the water interface is found according to the
manufacturer's operation instructions: For added evaluation,
water-finding paste may be applied to the probe.
It
may be noted that due to varying gauge locations and trim conditions,
the detection of cargo and free water at the specific gauge locations
on a vessel is not always possible. For more information on
gauge
point location, See MPMS Chapters 2.8B and 3.lA.
It
may be noted that if such soundings indicate emulsion or if emulsion is
expected to exist, alternate methods of water measurement such as
bottom sampling may be used. (See API MPMS Chapter 8.1.)
-
Lower
the probe slowly to the bottom of the tank. Record the gauge at which
the bottom of the tank is found to the nearest whole tape
graduation. This is the observed reference height of the
tank. The difference between the ullage of the free-water
interface and the observed reference height is the free-water innage.
Refer to API MPMS Chapter 3.1A, paragraph 11.2.3 for guidance when the
observed or published reference height as stated on the tank capacity
table is either exceeded or not reached.
It
may be noted that because of the design of the probe used, the tip of
the probe may not be the zero point of the gauge tape. In
that situation, an adjustment to the gauge must be made to convert the
observed reference height to the corrected reference height.
It
may be noted that heavy bottom sludge may make the tank bottom
difficult to feel, necessitating the use of a specially designed
weighted bob. Also, the probe end of the PMU can become
blocked by the sediment-which can seriously affect the sensitivity of
the probe.
-
Raise
the probe back into the oil and recheck the interface level. Once the
interface level is verified, record the free water ullage reading to
the nearest tape graduation 1/8th-in., 1-mn,
0.01-ft) at the reference gauge point.
-
When
all measurements are complete, wind the tape until the bob is fully
retrieved above the valve. Then close the vapor control valve
and disconnect the gauging equipment from the valve.
-
Verify
that the batteries have sufficient charge after each tank is gauged.
Closed and Restricted Measuring
of Small Quantities
Measurement
of small quantities on board marine tank vessels, including OBQ and
ROB, volumes is performed in the same manner as that of gauging liquid
levels described in earlier. However, unless reference gauge points are
properly located on the cargo tanks, small quantities may not be
detectable under all conditions of trim and list. To handle
varying trim conditions, gauge points must be located as close to the
aft and forward bulkheads as possible. In placing the gauge
points, care must be given to assure their location will not cause the
measurement equipment to touch the tank bulkhead when in use.
On
vessels where only a single trim condition (aft or forward) is
experienced, the vessel need only have a single gauge point located in
the direction of the normal operational trim of the vessel.
For more information on gauge point location, see API MPMS Chapters
2.8B and 3.1A. Also see Appendix B.11.
The
following actions should be considered when the existence of ROB, OBQ,
or free water is likely, but not detectable, at the reference gauge
point because of the location of the VCV - but only when they can be
done safely and when operating regulations permit:
-
Request
the vessel's officer to reduce tank pressure to a safe level at which
the tank can be opened at a point closer to the aft bulkhead.
-
File
a protest against the vessel for having a VCV in a location not
suitable to allow proper marine custody transfer measurements.
It
may be noted that because of the design of the probe used, the tip of
the probe may not be the zero point of the integrated gauge tape (see
Figure 11). Therefore, in that situation an adjustment to the gauge
must be made.
Procedures
outlined in API MPMS Chapter 17.4 should be followed for calculating
small quantities on board vessels.
Temperature Measurement Using PETs
PMUs
that can take temperatures are a special type of portable electronic
thermometer (PET) designed to be used in conjunction with
VCVs. Such PMUs may be of the single function type or
integrated into a multifunction measurement unit. As such,
temperatures are to be obtained in conjunction with the measurement of
liquid levels in the tank.
Sections of text taken from API - MPMS Chapter 17 Marine Measurement
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