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5.17 LINING UP THE SHIP'S DISCHARGE SYSTEM
Before cargo discharge can begin, the appropriate cargo valves must
be opened so that the cargo will flow to the pumps and from the pumps
ashore. Careful attention to the proper setting of the valves is required,
as the following case studies indicate.
Case studies
A 90,000 DWT crude oil tanker began discharging cargo at a Trieste terminal
shortly after midnight. At 0300 oil was discovered on the sea surface
and pumping was stopped. The source of the oil was traced to one loose
sea valve and one loose line valve in the pumproom. Several tons of oil
had escaped, contaminating the harbour, nearby beaches, yachts and small
fishing craft. A bond of USD 170,000 was required to be posted to permit
the vessel to depart. Final costs of USD 540,000 were paid.
A 120,000 DWT crude oil tanker began discharging crude oil at Quebec in
the morning and discovered oil on the nearby sea surface 24 hours later.
Oil leakage was traced to a valve in the pumproom not being properly closed.
The vessel owner's P&I Club posted a letter of undertaking to permit
the release of the vessel. Clean up costs and fines totalling USD 275,000
were paid.
Case analyses
Overboard discharge valves are frequently the cause of pollution incidents
and claims against tankers. To minimise the chances of leakage while
discharging, they should be subjected to a routine proof test programme
to provide early indication of defects. (See section 2.18.1)
When the ship's valves are being set for discharge, the overboard discharge
valves in the pumproom should be checked with a valve wrench to see
that they are firmly seated. It is obvious that in the cases above,
neither of these tests were applied. The result of this neglect was
a cost to owners and their liability insurers of more than USD 800,000!
5.17.1 Valve setting programme
Cargo valves will normally be set for the discharging operation while
the transfer hoses/arms are being connected. The setting of valves should
be done according to a written plan. Each valve to be opened should
be identified by a unique identity number or other code. When the cargo
system has been set for discharging, the ship's manifold valve at the
transfer arm/hose connection should be the only valve closed against
cargo flow.
5.17.2 Valve setting procedure
The basic rule for setting cargo valves is that 'any valve not required
for the discharging operation must be closed'. The easiest way to ensure
this condition is to first close all cargo valves in the ship, then
systematically open only those valves to be used for the first step
of the discharging operation. This is easily done from an automated
tanker's CCR, but more difficult on tankers where manual valves are
still used.
The valve setting orders should be used as a checklist. The completed
checklist should be signed by the officer in charge of setting the valves.
5.17.3 Valves and valve position indicators
Each cargo watch officer must understand the types of valves used in
the cargo system, their correct method of operation, their modes of
failure and indications of possible failure.
The cargo officers and pumpmen must fully understand the functioning
of the ship's valve position indicators and the modes of failure of
the indicators. This is particularly important on automated vessels
with CCR operation. Wherever possible, critical valves should be examined
visually to ensure that they are in the position indicated by the remote
indicator in the CCR. Any valve which shows an ambiguous position signal
when operated from the CCR should be considered suspect and not used
until it can be examined. It may be necessary to disable the remote
function of the valve and operated it locally by hand until necessary
repairs can be made. When a valve actuator is disabled a notation on
the CCR valve control board, on the CCR status board and in the cargo
orders is required.
5.17.4 Independent check
An independent check of the valve alignment must be performed to discover
any one-man-errors in the cargo system discharging alignment. After
the valves have been set, their positions should be verified by an officer
who did not participate in the initial valve setting. Once again, the
valve alignment orders should be used as a checklist and the completed
audit signed by the verifying officer. Particular care should be taken
to check that all drain valves, bypass valves and crossover valves are
closed unless indicated to be open.
5.17.5 Pumproom check
The case studies indicate the importance of verifying that the pumproom
valves are properly set. Checking that the overboard valves are tightly
seated is essential to avoiding accidental overboard leakage while discharging
cargo. The closed overboard valves must be sealed and the seal numbers
recorded in the log prior to beginning discharge. The independent petroleum
inspector should request to see the sealed overboard valves in the pumproom.
If he does not, ask him to witness the fact that the valves are sealed
and to record the seal numbers and time in his report.
Verify that the cargo pump bypass valves are closed, that the bilges
are clear of oil and that no immediate repairs are needed. No repairs
to pumproom equipment should be undertaken while discharging. Any necessary
repairs should be completed before the pumps are started.
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