On completing this chapter you will have an understanding of why the startup
stage is extremely critical how the proven pressure capacity of the pumps
valves and line systems is important when discharging at full rate the aims
of the ballasting stage the main aims and concerns of crude oil washing why
ships trim and the discharge pressure of cargo pumps is important during
stripping the key features of the three cargo stripping systems and their use by
pressing up of ballast tanks is important before departure the ship's
main concern during the final gauging of cargo tanks after discharge the
importance of the final line clearing of the cargo hose
in the startup phase of the discharge operations what extremely critical
measures ensure that tanks atmosphere does not go into negative pressure and
that any leaks into dry pipes and valves are quickly detected the discharge
operation normally commences according to the following procedure formalities
with port authorities and terminal loading master completed cargo hoses
arms well-connected cargo surveys completed tank survey and calculation of
the cargo arrival figures lining up of lines valves and pumps to be used both
onshore and onboard under the supervision of the chief officer the
loading master
line up and start inert gas plant with the recirculation valve returning gas to
the funnel until the pumps start running when lining up is completed and it is
confirmed the inert gas plant is running satisfactorily the chief officer reports
to the loading master that the vessel is ready to start pumping the loading
master orders the vessels manifold valves to be opened according to the
agreed discharge plan when the manifold valves are confirmed open the loading
master orders discharge to commence at slow rate for line displacement the
cargo pump or pumps are now being started either by the chief officer pump
man or Duty deck officer in close cooperation with the Duty engineer in
the engine control room at slow rate until correct flow is confirmed when the
cargo pump or pumps are running the inert gas is opened to the deck lines
the Duty deck officer pump man and bosun with deck crew must during this sequence
check that the cargo oil is passing through the manifolds and check valves
and lines in use to ensure that no malfunction or leaks occur when the
cargo oil enters
you
once all lines and valve settings have been proved to be free of leaks and the
discharge operations have stabilized at a low rate what is the main risk when
pump revolutions are raised to the full discharge rate when the loading well
stir confirms that the oil flow is as planned and that the line displacement
is completed he instructs the vessel to slowly increase the discharge rate to
the maximum as agreed upon in the discharge plan
in order to utilize the conquer pasty and operate them correctly either
in series or in parallel it is important to understand the pumps characteristics
and though the shorelines and reception facility at this stage as the discharge
has reached the maximum agreed capacity it is important to check the pumps and
cargo lines in order to discover any leaks caused by damaged flange gaskets
or pipes hold due to corrosion or pitting
for further information on operation of cargo pumps see cbt number zero seven
eight
you
what are the four main aims of taking in water ballasts considered at the
discharge plan which decide when to start taking in ballast during
discharging when to start taking on ballast depends on the discharge rate
whole stress
air draft or free board or limitations on fixed discharge arms on the terminal
trim requirements for stripping and also often a terminal requirement that the
vessel may leave the berth immediately in an emergency this was considered in
the ship Shore meeting and will be found in the discharge plan
you
in order to save fuel cost taking on ballast by gravity in the first few
hours of the ballasting operation may be considered ballast in the double hull
ballast tanks is completely segregated from the cargo tanks and piping and is
therefore ideal for adjusting the trim in connection with crude oil washing and
final stripping of cargo tanks all ballast handling is required to be
recorded in the vessels ballast water management plan according to IMO
resolution a 868 20 convention adopted June 2010
you
what are the six main aims and concerns washing operation the crude oil washing
operation is a demanding task that requires full attention from all Duty
deck personnel the terminal requires to be informed when crude oil washing
starts and to be updated during the operation and when completed before
departure on a ballast voyage after the complete discharge of cargo sufficient
tanks shall have been proved or washed in accordance with the procedures
specified in the crude oil washing operations and equipment manual
designated heavy weather banners touch cleaned to take on ballast in that
weather for the new double hull tankers the required number of tanks to be crude
or washed every discharge are approximately one-quarter of the total
number of tanks including the tanks which are dedicated to take on heavy
weather ballasts the remaining tanks to be crude oil washed on a rotation basis
sludge control routines for sludge control purposes no tank
needs to be crude or washed more than once in every four months static
electricity to avoid excessive electrostatic
generation in the washing process due to the presence of water in the crude oil
washing fluid the contents of any tank to be used as a source of crude oil
washing fluid must first be discharged by at least one meter before being so
used any tank used as a slop tank on the previous ballast voyage shall be
completely discharged and refilled with dry crude oil if that tank is to be used
as a source of washing fluid vapor generation and VOC emission in order to
minimize the vaporization of volatile organic compounds while crude or washing
closed-cycle washing from a dedicated slop tank reusing a fixed quantity of
oil is preferable to bleeding off fresh crude oil from a tank during its
discharge inert gas pressure and oxygen content before starting crude oil
washing it is required to measure the tank atmosphere to ensure that oxygen
content does not exceed 8% and that the oxygen content in the inert gas supply
does not exceed 5% throughout the entire discharge and crude oil washing
operation it is important to monitor the inert gas pressure if the inert gas
system fails the discharge and crude oil washing operation must be stopped and
cannot be resumed until the inert gas system is working satisfactorily again
all crude oil washing machines need to be regularly function checked during the
operation and necessary adjustment of the drive unit program for correct
washing person and cycles are to be carried out according to the discharge
plan affected stripping throughout finally the sludge sediment at the
bottom is effectively removed only if it is stripped out immediately
and not allowed to accumulate
you the crude oil washing requirements of
multiple and x1 are comprehensive and covers detailed technical and design
criteria minimum coverage of area to be washed capacity of supply pumps as well
as stripping plants the STCW code defines special competence levels for
personnel responsible and involved in crude oil washing operations for
detailed information on crude oil washing c c bt number zero five four
how does a good trim by the stern help in the stripping of cargo tanks and how
can a duty officer tell when a cargo pumps efficiency is dropping due to gas
accumulation and the vacuum stripping system is to be started the stripping or
final draining of the cargo tanks is an important phase of the discharge
operation in order to achieve a satisfactory out turn of the cargo it is
necessary to document that the remaining quantity in the cargo tanks lines and
pumps are as close to zero as possible prior to reaching the stripping level in
the cargo tanks the vessel should be trimmed to a certain trim on the stern
in order to obtain a natural free liquid flow to the suction area in the after
part of the tanks by observing the cargo pump pressure gauges the Duty deck
officer or pump man who is operating the cargo pump console will get an
indication by Falling pumping pressure that the pump or pumps efficiency are
dropping because of gas accumulation at this stage it is necessary to assist the
pump or pumps by starting the vacuum strip system
what are the three main cargo stripping systems in use on crude oil tankers on
crude oil carriers there are three different draining and stripping systems
fitted
system
the stripping adductor and the stripping pump for line stripping through the
small diameter line or marple line click on the buttons to learn more
goon stripping system
where does the gas removed by the vacuum pump from the separated tanks of the
cargo pumps get discharged to what prevents the oil in the separator tank
from being vacuumed out together with the gas the vacuum strip composition is
a system which is fitted on the suction line and close to each cargo pump the
system consists of a separator tank forming part of the suction line to each
cargo pump the purpose of this separator tank is to support the cargo pump with
liquid the separator tank one for each cargo pump has a pipe connection to a
vacuum tank located at a higher level in the pump room
further the vacuum tank is connected to a vacuum pump briefly explained the
liquid level inside the separated tank will fall when the liquid level in the
cargo tank becomes lower than the height of the separator tank and the void space
above the liquid inside the separator tank will increase at this stage falling
pump pressure should be observed and the vacuum system started at a fixed liquid
level in the separator tank a signal is given to the vacuum pump to start and
vacuum is created in the vacuum tank the valve opens between the vacuum tank and
the top of the separator tank and by that the vacuum effect in the void space
on top of the liquid level inside the separator tank will lift the liquid
level that assists the cargo pump the gas accumulation on top of the liquid
inside the separator tank will at the same time be evacuated by a separate
line into the slop tank as the oil level in the separator rises to a cut-off
point the signal shuts off the valve connecting to the vacuum tank and liquid
cargo is prevented from being vacuumed up assisted by the vacuum strip system
the cargo tanks can be satisfactorily emptied by the cargo pumps in addition
the suction area for the stripping suction Bell mouth from the double hole
tankers is formed as a sump called the suction well which allows the suction
Bell mouth to be fixed inside a restricted area and lower than the tank
bottom for further details regarding vacuum strip systems see separate
documentation
mr. thing a doctor
why is the stripping adductor specially preferred for draining tanks during
crude oil washing during crude oil washing the washing fluid is discharged
to shore with the BOC cargo in the final stage of the crude oil washing bottom
crude oil washing for removal of sludge and sediments the stripping adductor is
used as well as for final draining of all cargo tank bottoms and lines the
stripping adductor is driven by either a cargo pump or a separate crude oil
washing pump the driving fluids and the drainage from the tanks are delivered
into the primary slop tank the slop tank will then be the last tank to discharge
with one cargo pump the stripping adductor is designed to a capacity 1.25
times higher than the combined throughput of all crude oil washing
machines designed to be used simultaneously that is why it is
preferred for stripping during crude oil washing another reason is that it
creates a vacuum continuously for fluids as well as gas directly in the cargo
tank if the tank becomes dry temporarily and gas pockets form in the suction pipe
a stripping pump would stop and start and a vac strip pump would need a good
quantity of oil in the pipe when the crude oil washing is completed the
monster crude oil washing checklist is to be completed
you
when finally stripping the main cargo lines why should inert gas be allowed to
enter from a cargo tank at the highest point of the mela fold when the slop
tanks are empty the Box discharged is completed and the manifold valves are to
be closed the final draining of the vessels cargo
pumps and lines in the Pump Room and on deck shall be carried out by means of a
stripping pump normally a steam driven pump which can deliver the remaining oil
to shore through a small diameter line also called a MARPOL line this line is
connected to one of the manifold lines and outside of the manifold gate valve
in order to enable direct discharge to shore after the manifold valves have
been closed when the final draining through the small diameter line is
completed and its valve that the manifold is closed the remainder in the
same line as dropped via a small branch pipes to the nearest cargo tank the
discharging operation is completed when draining the main cargo lines it is
important to break the vacuum caused at the top of the manifold by the stripping
pump taking suction at the lowest point of the pipelines for this purpose a
2-inch line with a gooseneck is provided from the highest point of the manifold
to the inert atmosphere at the top of a cargo tank the valves in the line should
be opened to break the vacuum during final line stripping
give two reasons why to the maximum level possible before
sailing out the forward ballast tanks will normally remain to be topped up
when the discharge operation is completed as these tanks may have been
used for trimming the vessel by Stern for cargo stripping the ballast tanks
should always be filled to the maximum allowance in order to minimize the void
space between the ballast water and deck from experience it is well known that
this area in the ballast tanks is exposed to air and splash of seawater
which results in corrosion this also helps to minimize free surface effects
due to slack ballast tanks when the last ballast tank is topped up the vessel
should be in a seaworthy condition as prescribed by the IMO or SOLAS
regulations the ballast operation is now to be recorded in the ballast water
management plan
you
what if the ship's major commercial concern when the tank is being finally
surveyed on completion of discharge as soon as the discharge is completed the
cargo surveyors start surveying the cargo tanks together with the duty deck
officer and deck crew this survey consists of dipping the
tanks in order to confirm that all cargo is discharged all tank dipping must be
through dipping pipes or hatches with vapor locks after completion of the tank
survey layers calculate the remaining onboard quantity and all documentation
is signed by the chief officer and cargo severe
if an unacceptable quantity oil remains on board the cargo surveyor
will issue a letter of protest on behalf of the cargo receivers and charges which
is to be signed by the monster
you
what is the main environmental concerns poses and what action is to be insured
to mitigate it as soon as the final stripping through the small diameter
line is completed the terminal staff will drain the cargo hoses arms and then
the disconnection will be initiated if the draining or blowing with nitrogen is
not effective there is an immediate danger of an oil spill into the drip
tray and outside it to prevent small quantities of oil dirtying the tip tray
and creating a pollution hazard from weather at sea empty half cut drums
should be placed under the flange when breaking it the disconnection should be
supervised by the Duty deck officer until all hoses arms are off and the
manifold blanks fitted if the vessel has discharged via an SPM boy the
disconnection operation is more demanding and as for berthing requires
experienced hands