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Portable
Manual Sampling Unit (PSU)
The
portable manual sampling unit (PSU) is designed to obtain samples under
closed or restricted system conditions and to be compatible with vapor
control valves fitted on the vessel. Some PSUs are capable of
accepting various types of samplers and of taking the various types of
samples.
Maintenance/Verification
When
measurement equipment is first put into service, it must be carefully
inspected and checked for any signs of damage or construction
flaw. The measurement tapes of all PMUs should be compared
against a verified steel gauge tape to be certain the linear markings
on the tape are correct in accordance with API MPMS Chapter
3.1A. PSUs should be checked for proper size, operation,
seating, and any signs of wear before each use.
The manufacturer's instructions
and warranties should be carefully reviewed and followed throughout the
use of the equipment and, if required, sufficient replacement batteries
kept available. In addition, the manufacturer's maintenance
schedule must be followed and a log kept of all maintenance and
verifications performed. UTIs and single function PETs must
be verified and records kept in accordance with API MPMS Chapter 7.3.
CAUTION:
Although UTIs and single function PMUs have been designed to withstand
the rigors of shipboard operation, they are sensitive electronic
measurement devices. As such, they must always be handled
with care and properly maintained throughout their use.
It
may be noted that from time to time it may become necessary to use a
vessel's PMU that does not have adequate documentation of its
verification and calibration. In those instances, it is
acceptable to use such unit provided it is field verified as follows:
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The tape function is visually
verified against a manual steel gauge tape that has been calibrated to
API MPMS Chapter 3.1A.
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The thermometer function is
verified as per section 5.3.1.2 of this standard.
Procedures for
Measurement-Closed and Restricted
When
vessels are fitted with vapor control valves, portable electronic
gauging equipment can be used to measure free water, petroleum liquid
levels, and temperature. It may also be used for measuring
liquid
ROB/OBQ. Special PMUs and/or techniques may be used for taking samples
and for measuring non-liquid ROB/OBQ. Use of this equipment
requires observance of safety procedures outlined in the International
Safety Guide for Oil Tankers and Terminals, (ISGOTT), the International
Maritime Organization (IMO), Inert Gas Systems (IGS), and other
applicable International Chamber of Shipping, the Oil Companies
International Marine Forum (OCIMF) publications and manufacturer's
instructions.
Prior to boarding a vessel
equipped with VCVs, attempt to determine the manufacturer and size of
the VCVs so that compatible equipment or adapters can be taken on board.
In addition, before gauging,
verify that:
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All cargo operations have been
stopped, and no cargo is being transferred.
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The IGS pressure in the cargo
tanks has been lowered sufficiently to minimize vapor loss.
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The gauging equipment has been
calibrated and the calibration/verification log reviewed.
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The equipment is free of
breaks, kinks, and signs of wear which might affect measurement
accuracy.
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The equipment is suitably clean
for the product to be measured. I.e. aIl numbers and
graduations on the tape are legible.
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The batteries are charged
(replace if necessary).
It may be noted that for best
accuracy, trim and list should be eliminated. When both
conditions exist; every effort should be made to eliminate at least one
condition, preferably list. Conditions of trim and list must
be noted and corrections made for their affect on measurements and! or
volumes.
Sections of text taken from API - MPMS Chapter 17 Marine Measurement
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