After successfully completing this lesson you should understand the special
circumstances that require a cofferdam to be filled and be familiar with the
procedures involved in filling and circulating the cofferdam
to gain maximum benefit from this lesson you should successfully have completed
the previous lessons this lesson discusses the special
circumstances that require the cofferdam to be filled with liquid in order to
prevent damage to the pump including listing the cargoes involved it then
explains the techniques involved in filling and circulating the cofferdam
the practical sections consist of two parts
first there is a demonstration of the procedures this is followed by an
interactive guided walkthrough of the same procedures
due to their particular properties some cargoes require special handling in
order to avoid damage to the pump and lines standard operating procedures
requires that the cofferdam is clean dry and vented to atmosphere through the
exhaust trap vent line this permits leakages to be easily detected
however with certain cargoes it is actually advantageous to fill the
cofferdam with liquid the working lifetime of the seals may be extended
and blockages of solidified cargo in the cofferdam can be avoided the liquid used
in the cofferdam varies depending on the cargo carried in the tank as reaction
between the two must also be considered normal purging routines will be
suspended when the cofferdam is filled the fram-o purging report should be
endorsed indicating that the cofferdam has been filled and noting which liquid
has been used this lesson must be considered as general advice only and
specific company operating guidelines must always be followed with the older
open loop systems where there is no feed pump to maintain the pressure in the
hydraulic circuit when the cargo system is not in use there is a risk of
contaminating the hydraulic oil when filling liquid into or circulating
liquid around the cofferdam in such systems it is important that the
hydraulic oil returned pressure is always higher than the pressure in the
liquid filled cofferdam the following cargoes require the cofferdam to be
filled with liquid connect the buttons to see more details
after discharging is completed and the pump cofferdam has been purged it is
recommended that fresh water is circulated through the cofferdam to
remove any traces of acid if they are allowed to remain and any
moisture forms such as from condensation the mixture will become aggressive
abrasive granules such as from phosphoric acid will also be washed away
a minimum of 5 to 10 liters of dioctyl phthalate should be added to the
cofferdam this should be done prior to commencement of loading and remain until
tank cleaning is almost completed without it ingress of cargo is a slight
possibility if the cargo seal was to fail and should there be any moisture
present the product would then solidify and block the cofferdam the dop will
ensure that any leakage remains in a liquid state
a blocked cofferdam is an extremely serious situation which will lead to
heat generation and a possible violent reaction indeed a fram-o deep well pump
with a blocked cofferdam must not be run as a minimal precaution 5 to 10 litres
of fresh water should be added to the cofferdam this should be done prior to
commencement of loading and remain until tank cleaning is well underway if
possible it is even better to fill the cofferdam completely rig a reservoir
drum and small portable pump and circulate the water during cargo
discharge the cofferdam should be filled with hot fresh water and circulated
during loading and discharge to prevent ingress and possible blockage from
solidified product phenol has a melting point of approximately 45 degrees
Celsius so the heat is critical to this operation the water may be heated by
trickle feeding a live steam hose lashed into the drum for resting a small
custom-built heating coil in the bottom the cofferdam should be filled with hot
fresh water and circulated to prevent ingress and possible blockage from
solidified product caustic soda 50 percent solution has a melting point of
approximately 16 degrees Celsius so the heat is important to this operation
especially in low ambient temperatures the water may be heated by trickle
feeding a live steam hose lashed into the drum
resting a small custom-built heating coil in the bottom five to ten liters of
diesel oil or mineral spirit should be added to the cofferdam this should be
done prior to commencement of loading and remain until tank cleaning is almost
completed once the cofferdam is emptied it should be thoroughly cleaned and
dried water heated if necessary can be circulated and air or nitrogen can be
blown through to drive the cofferdam and associated piping when filling the
cofferdam it is preferable to add the liquid by gravity if a pump is used to
transfer the liquid it is essential to use low pressure maximum three-bar in
ordered not to damage the seals or exceed the hydraulic oil return pressure
small traces of cargo residue may of course be expelled as the cofferdam is
filled or recirculated the appropriate personal protective equipment must
always be used this section deals with the addition of liquid to the cofferdam
either to partly or completely fill the cofferdam and its associated piping and
which then remains as a static preventative measure while the cargo or
residues from the cargo are on board you will now see a demonstration of the
procedure to be followed when filling the cofferdam click on the buttons in
numerical order disconnect the exhaust trap piping from
the cargo pump top cover plate using a suitable adapter fill the liquid through
the cofferdam check pipe open the purging connection to ventilate the
cofferdam during filling this completes the demonstration of the procedure to be
followed when filling the cofferdam click you will have noted in the
previous section that the cofferdam was filled down the check pipe with the
displaced air being released up through the purge pipe this is the easiest and
most practical method to adopt when filling liquid that is going to remain
as a static preventative barrier while a particular cargo is in the tank in
practice however the cofferdam can be filled from either direction when the
liquid is going to be continuously circulated around the cofferdam an
adapter must be fitted to the purging connection and it then becomes easier to
both fill and circulate in that direction with the liquid returning out
and back to the reservoir through the check pipe and exhaust trap connection
the aim is to add an circuit consisting of a reservoir and
circulating pump onto the cargo pump the reservoir may be a purpose-built header
tank or simply an open drum placed on deck adjacent to the top cover plate the
pump will typically be a small portable pump commonly air driven and capable of
adjustment to regulate the flow small bore flexible rubber hoses are usually
employed to feed and return the liquid with the appropriate fittings and
connections additional equipments such as a steam supply or specially made
heating coil may also be added you will now see a demonstration of the procedure
to be followed when circulating liquid through the cofferdam click on the
buttons in numerical order prepare the reservoir adjacent to the top cover
plate fill with the required liquid add heating facility if necessary prepare
and connect the circulating pump connect a flexible supply hose between the pump
outlet and the purging connection connect another flexible hose from the
exhaust trap drain valve and secure it so that it flows back into the reservoir
slowly fill the cofferdam and associated piping topping up the reservoir as
required a just pump regulator to achieve a slow steady circulation this
completes the demonstration of the procedure to be followed when
circulating liquid through the cofferdam