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If
examination of the sample clearly indicates the existence of free
water, further steps should include the following:
-
Advise
principals.
-
Advise
vessel.
-
Take
additional samples for testing and retention.
-
Document
steps taken and findings.
When
a high-viscosity or high-pour-point crude can be cut with
water-indicating paste, at least one minute should be allowed for the
paste to react with the oil/water emulsion.
HEATED CARGOES
Heating
of cargoes may cause unusual temperature stratification. In
such cases, additional temperatures may be required to get a good
average temperature of the cargo.
Heated
cargoes sometimes present problems with respect to the type of
water-indicating paste being used. Some pastes do not withstand higher
temperatures and are either dissolved or washed off before readings can
be taken.
MEASUREMENT ON BOARD ROLLING
MARINE TANK VESSELS
During
offshore operations or lightering, or when the vessel is at an exposed
berth, cargo may be in motion within the vessel's tanks. In
such
situations, at least five successive gauge readings should be taken,
the highest and lowest readings dropped and the remaining three
averaged and recorded. The successive gauges should be taken
as
quickly as is practical and a description and extent of the adverse
measurement conditions recorded.
SPIKED CRUDES
Some
crudes are injected with light hydrocarbons such as butanes, liquefied
petroleum gas, or condensate. Special care should be taken with these
crudes because of potential vapor buildup, especially after long
voyages. In addition, in-transit vapor loss may be higher
than usual.
HIGH RVP CARGOES
High
RVP cargoes such as gasoline and other light products, some very light
crude oils, and condensates all have potential problems as those
indicated in 'Spiked Crudes'. As such, special care should be
used when taking open hatch measurements, especially on hot days.
SOLIDIFIED OBQ/ROB
If
the OBQ/ROB quantities are solidified (non-liquid), a trim and/or list
correction may still be applied if the material is in contact with all
four bulkheads and the angle of solidification can be
determined.
If the solidified material is not in contact with all bulkheads, a
wedge calculation may be done. However, wedge calculations
and/or
wedge tables can only be used to calculate the volume of the solid
OBQ/ROB if it can be determined that the solid has taken, and is in,
the shape of a wedge. It must be noted that such
determinations
usually involve taking measurements at more than one place in the tank
and that it may not always be possible to do so because of physical
restrictions presented by the tank or because of operating
conditions. In all circumstances, the cargo documents should
include the vessel's trim and list and should note that material was
solidified. Solids and small quantities of liquid for which
temperatures cannot be obtained may be assumed to be at standard
temperature. For calculations of small quantities see API MPMS Chapter
17.4.
OUT-OF-TRIM VESSELS
When
a marine tank vessel is out of trim, oil and free water may not be
measurable at the usual gauge points. Although the oil or water should
be found in the general direction of the trim or list, it may be
trapped in segregated areas of the tank. In these
circumstances, more extensive methods of liquid determination may be
employed if safety and operational conditions permit. In such
circumstances, the cargo documents should include the vessel's trim and
list, as well as any other pertinent facts.
STATIC ACCUMULATOR CARGOES
Some
cargoes have a tendency to accumulate a static charge during the
loading or discharge process and need a relaxation time for the charge
to dissipate before measurement equipment can be safely introduced into
the tank. Most clean products are static accumulators while
most black oils are not. In addition, static inhibitors may
be added to some cargoes to reduce the risk of static charge.
To determine which cargoes are accumulators and for special
considerations to be taken during the measurement and sampling of them,
refer to ISGOTT for full details.
Sections of text taken from
API - MPMS Chapter 17 Marine Measurement
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