Q71) Describe different methods of carriage of liquefied gases, what is

re- liquification of gas? How is it done on gas tankers? OR

Explain the operation of the re-liquefaction plant in liquefied gas
tanker?-------------------------- Q72) What is the information required prior to
loading of a given chemical information?
cargo in bulk? List the publications, which are referred to get this. -----------
------------ Q73) Write notes on following w.r.t. to chemical tankers:
Types of chemical tankers.---------------------------- Q74) Write notes on the
following w.r.t. to chemical tankers: P & A Manual.------------------------ Q75)
Write notes on following w.r.t. to Gas Tankers: Cooling down of tanks--
----------------------- Q76) Write notes on following w.r.t. to Gas Tankers:
SIGTTO --.------------------------------ Q77) Write notes on following w.r.t. to
Gas Tankers: Pre-Arrival Checklist------------------------- Q78) Write notes on
following w.r.t. to Gas Tankers: ICS data sheets-----------------------Q80)
State the cargo related documents required on board Chemical
Tankers.--------------------------- Q82) With reference to liquefied gas
carriers, write short notes on: Deep Well Pump.-------------------- Q83) With
reference to liquefied gas carriers, write short notes on: IGC Code. ------
------------------------------ Q84) Sketch and Describe typical tank and piping
arrangement of any one type of chemical tanker--------------------. Q85) A
Chemical Tanker discharges phosphoric acid at a port in Baltic Sea
and is bound for Houston. Describe the operations she will perform
with respect to cleaning of tanks so as to be ready on arrival to load
next Cargo.---------------------------- Q86) What are the various types of gas
carriers considering survival capability as defined in IGC Code. ------------
------------------ Q87) Describe the hazards involved with Tank Cleaning in
Type 1 Chemical Tankers.-------------------------- Q88) Who issues the
"Certificate of fitness" on a Gas / Chemical Carrier?-----------------------------
Q89) Describe with a diagram about LNG ships membrane tank
structure.--------------------------- Q90) Explain in proper sequence the
procedures of preparation and then loading operations of full cargo
of LNG.------------------- Q91) Explain a single stage reliquefication
plant found onboard fully pressurised LPG ship. --------------------------
---- Q92) Differentiate the following with respect to liquefied gas
tankers: Independent Type A, B & C tanks ---------------------------------- Q93)
Differentiate the following with respect to liquefied gas tankers:
Integral Tanks & Membrane Tanks----------------------------- Q94)
Differentiate the following with respect to liquefied gas tankers: Fully
Refrigerated & Semi - Refrigerated / Semi - pressurised gas carrier.---
------------------------ Q95) Describe the types of gas carriers with reference to
nature of cargo and its protection in case of accident as categorized
in IGC Code. ----------------------- Q96) Outline the procedure for tank
cleaning a cargo tank in a chemical tanker.-----------------------------------------
Ans71: - Methods of carriage of liquefied gases :->>>

I) Reliquefaction with Intercooling: - Intercooling is used in conjunction with two stage

compression. The first stage discharge is desuperheated in the intercooler and returned to the 2nd
stage. The discharge from the 2nd stage is condensed in the condenser, and thence to the intercooler
for further cooling. The condensate is returned to the cargo tank.
Non-condensable gases are separated out in the purge condenser and transferred by the
cross over line to the collector and mast, or via the stripping or bottom distribution lines back into
the cargo tank. If two or more tanks are being reliquefied simultaneously via one cargo system the
distribution of condensate between the tanks is to be controlled manually.

If, during intercooling, there is insufficient condensate in the intercooler drum, additional
liquid can be transferred from the cargo tank using the stripping/condensate line and a cargo pump.
This is more likely to occur during the early stages of intercooling, or if the 2nd stage compression
temperature is too high.

The condenser pressure is to be maintained at approximately 1 bar above the saturation

pressure of condensate at the condensate temperature.>>>>>

Reliquefaction without Intercooling:- Gas is drawn into the 1st stage of the compressor
from the tank, via the surge drum (if fitted), compressed and discharged through the intercooler, but
without cooling. The gas is liquefied in the condenser, expanded to tank pressure and returned via
the spray or stripping/condensate line.

When several tanks are being cooled simultaneously by one

reliquefaction plant, the operation should start with the tank having
the highest pressure. Pressure is to be equalised before the tanks are
interconnected. Also, when several tanks are be ing cooled
simultaneously a careful watch must be kept on the liquid return to
ensure equal filling.-----------------------------------
Ans72:- Information required prior to loading of a given Chemical Cargo in
Bulk :-

1) The correct chemical name of the cargo should be provided so that the appropriate data sheet
in the Tanker Safety Guide (Chemicals) can be consulted.
2) Quantity in Weight.
3) Required quantity control - Contamination is measured in parts per million (ppm). Thus tanks &
 pipelines must be practically spotless. Degree of wall-wash required.
4) Specific Gravity - This is required in order that an estimation can be made of the probable
volume that the weighed quantity will occupy.
5) Temperature - This is required for two purposes.
a. The loading temperature is used in conjunction with the specific gravity to obtain the
probable volume of the particular parcel.
b. The temperature at which the cargo is to be carried will indicate if heating will be
required on passage..
6) Compatibility - Certain chemicals react with other chemicals and thus may not be stowed in
adjacent compartments.
7) Tank coating compatibility - The tank coating must be suitable for the proposed cargo.
8) Corrosive Properties - This will also indicate the required tank coating and also possible damage
to ship fittings.
9) Electrostatic generation - Some chemicals can accumulate static, the principles which apply to
HC cargoes should be applied to chemical static accumulators.
10) Fire & Explosion Data - It has been previously noted that 50 % of the chemicals transported are
derived from hydrocarbon oil and thus fire hazards are similar to those which pertain to
petroleum products.
11) Toxicity - Chemicals which emit highly toxic vapours requires Closed Ventilation and Ullaging
System.
12) The Health Hazard of the particular parcel.
13) Reactivity.
14) Action to be taken in the event of particular emergencies - Most of the above information and
additional essential information can be found on the chemical data sheets in the safety
guide.>>>

Publications which are referred to get info prior loading chemical cargo :-

1) On receipt of the name of the cargo, the certificate of fitness must be checked to verify if the
said vessel is allowed to carry that particular cargo as enlisted in the COF.
2) Depending on whether the ship is constructed before / after 01-07-1986. The relevant IBC Code
/ BCH Code must be consulted..
3) Additional information can be obtained from the chemical data sheet pertaining to that cargo -
found in the ICS (International Chamber of Shipping) publication. Tanker Safety Guide .
4) Also added information can be obtained from USCG system. CHRIS - Chemical Hazard Response
Information System..
5) The "Procedure & Arrangement" (P & A) manual which is ship specific, gives information such as
tank arrangement, pumping & piping arrangements .
6) Annex 2 of the MARPOL 73/78 should be referred to obtain discharge criteria & procedure.
Paint compatibility guide - to check if the coating in the tank will
withstand with particular cargo to load.----------------------------------------
Ans73:- There are 3 basic types of Chemical Tankers, All 3 types are meant to carry chapter 17
cargoes of IBC code.>>>

Type I ships
> It must be able to survive assumed damage anywhere in their length. Cargo tanks for the
most dangerous products should be located outside the extent of the assumed damage
and at least 760mm from the ship's shell.
> IMO type 1, 2 and 3. Other cargoes, which present a lesser hazard may be carried in tanks next
to the hull - (incl diluted slops after tank washings)

> Some of the chemicals carried on type one ships are Chlorosulphonic acid, Dodecyl phenol,
Phosphorous yellow/ white, Tricresyl Phosphate (>1% orthoisomer), Trixylyl Phosphate.
> Maximum tank size is 1250 M3.
> Double side width B/5 or 11.5 mtrs which ever is less.
> DB depth B/15 or 6 mtrs at centre line, but not < 760mm .
> Auto ignition temperature of cargoes <65 deg C.
> Explosive range >50% by volume in air.
> Type 1 offers highest limit of containment.>>>>

Type II ships
> If more than 150m in length, must be able to survive assumed damage
anywhere in their length; if less than 150m, the ship should survive assumed damage anywhere
except when it involves either of the bulkheads bounding machinery spaces located aft. Tanks
for Type II cargoes should be located at least 760mm from the ship's shell and outside the
extent of assumed grounding damage.

> Maximum tank size is 3000 M3.

> Capable of stripping tanks <100 litres.
> Auto ignition temp of cargoes <200 deg C.
> Explosive range >40% by volume in air.>>>>

Type III ships

> If more than 125m in length, should be capable of surviving assumed damage anywhere in their
length except when it involves either of the bulkheads bounding the machinery space. If less
than 125m in length, they should be capable of surviving damage anywhere unless it involves
machinery spaces. There is no special requirement for cargo tank location. No limit for size of
tank.
> Capable of stripping tanks <300 litres with tolerance of 50 litres.
> Length > 125 m but < 225 m damage anywhere in length except including ER bulkheads.
Length <125 m damage anywhere in length except machinery space ---------
-------------------

Ans74:- P & A Manual :> MARPOL Annex II requires that each chemical tanker be provided with a
P&A Manual to achieve compliance with the regulations and to be able to demonstrate that
compliance has been considered from the earliest design stage. The format of the P&A Manual and
its contents must be as specified in MARPOL Annex II Appendix D, and be approved by the flag
administration of the ship.

> The P & A Manual is concerned with the marine environmental aspects of cleaning of cargo
tanks, and the discharge of cargo residues that may or may not be mixed with a washing
medium. The results of the stripping test are recorded in it.

> Ships' officers should familiarise themselves thoroughly with the P&A Manual, and adhere at all
times to operational procedures with respect to cargo handling, tank cleaning, stop handling,
 residue discharge, ballasting and deballasting. The master is obliged to ensure that the ship
does not discharge into the sea any cargo residues, or mixtures of residue with water, unless
such discharges are made in full compliance with the operational procedures contained in the
P&A Manual, and that the equipment required by the Manual for such discharge is used.
> The P & A Manual, together with the cargo record book and Certificate of Fitness, will be
checked by the ship's own flag administration and by port state control officers in order to
confirm full compliance with the requirements of MARPOL Annex II.

> It is now recognised that almost any discharge from a ship into the surrounding environment
needs to be carefully considered in advance. Not only are chemical cargo residues, oily
water from machinery room bilges and overboard disposal of
garbage strictly regulated, but funnel exhausts and ballast water have
now been identified as requiring control.-------------------------------------
Ans75:- Cooling down of tanks:

> Prior to loading if returned with insufficient heel.

> After dry-docking, off-hire or during initial commissioning.
> LNG carriers with a typical capacity of, say, 153,000 m3 are loaded at about 12,000 m3/h.
> The volume of liquid LNG loaded displaces an equivalent quantity of vapour in the ship's
empty cargo tanks which is returned to the LNG storage tanks for processing in the site's
fuel gas system.
> This BOG will be available for typically 12 hours in each loading cycle. If the ship's tanks are
warm, loading takes a longer period of time as initially volumes of LNG are vaporised when
they contact the warm sides of the LNG tanks, thereby cooling them.
> During loading, more than one LNG storage tank can be used simultaneously to load the
carriers.
> Where jetty lines are long, the loading line generates significantly more BOG due to heat
ingress from the pumps as a result of the larger duty.
> With relatively short jetty/transfer lines < 1 km, the heat component from LNG pumping is
relatively small (typically around 5% of total BOG).
However, for example where the LNG must move in excess of 7 km the
pumping component becomes significantly larger at an estimated 45% of
total BOG.----------------------------
Ans76:- SOCIETY OF INTERNATIONAL GAS TANKERS AND TERMINAL
OPERATORS (SIGTTO) was born out of a recognition that an industry specializing in the
transport of liquefied gas needed to establish and promote the adoption and implementation of the
very highest standards if it was first to win and then to maintain the confidence of the public at
large. In acting as a beacon for quality and best practices, SIGTTO and its members have done just
that, and that the excellent safety and pollution record of the sea borne gas transport industry to
date defines it quite categorically as a highly responsible and effective sector.

A number of involved companies were therefore concerned to agree essential common

standards for the industry, to aid its expansion, underpin public confidence and avoid a proliferation
of unilaterally defined regulations. This group resolved to establish a body to draw together industry
member companies in an effort to establish commonly agreed standards and best practice criteria.
Hence the Society was formed and registered as a Bermuda Exempted Company (non-profit making)
with limited liability in October 1979.
 The Society was granted consultative status at the IMO in 1982. >>>>

PURPOSE: - The Society is the international body established for the

exchange of technical information and experience, between members of
the industry, to enhance the safety and operational reliability of gas
tankers and terminals. The organization has been organized to encourage
safe and responsible operation of liquefied gas tankers and marine
terminals handling liquefied gas; to develop advice and guidance for
best industry practice among its members and promote criteria for best
practice to all who have responsibilities for, or an interest in, the
continuing safety of gas tankers and terminals----------------------------------
Ans77:- The daily operation of a liquefied gas carrier involved potential hazards. It should be noted
that cargo pipes, valves and connections and any point of leakage at the gas cargo may be intensely
cold and may cause severe cold burns.

Pressure should be carefully reduced and liquid cargo drained from any point of the cargo
transfer system, including discharge lines, before any opening up or disconnecting is begun. ^

Everyone involved in liquefied natural gas trans- portation takes safety very seriously.

The popular perception of liquefied natural gas is that it is inherently dangerous. While it
possesses a set of hazards that need to be managed.

Within 5 days of the ship's estimated time of berthing, the following checks and tests shall be carried
out, and the results recorded. These records are to be made available to the gas terminal upon
request.

(1) Deck water spray line

(2) Water curtain
(3) Gas free condition of hold space
(4) Alarm function of fixed gas detection equipment
(5) Cargo gauging system and alarm set points.
(6) Emergency Shutdown System (ESD), all the relevant system shall be tested prior to arrival port
and time needed to shut should be confirmed around 25 up to 30 seconds.
(7) Operation of cargo system remote control valves and their position indicating systems.
(8) Confirm Cargo transfer emergency stops fully operational and date of last test.
(9) Confirm tank high level and pressure alarms operational.
(10) Confirm that remotely operated manifold valves have been operated through a complete
open/closed cycle, functioning and advise valve type(ball, gate, etc)and actual closing time. The
corresponding records shall be produced by the master on the ship arrival at berth. Any defects or
deficiencies must be reported to the terminal as an addendum to the Pre-Arrival information notice.
Deep well cargo pump and booster pump mechanical seals are free of
oil leaks.----------------------------------- Ans78: - ICS data sheets: -
> ICS data sheets outlines the main characteristics of individual cargoes, and the action to be
taken in an emergency.
> Matters relating solely to maintenance of the purity of individual cargoes and their
condition during carriage have not been included.
> It's something like material safety data sheet of gas cargo.
 > With respect to ICS Data Sheet - The IMO Codes require the following information to be
available to every ship and for each cargo:
o The master must only load a cargo which is listed on his certificate of fitness.

o Data sheets for these cargoes should be on board.

o The master and all those concerned should use the data sheet and any other relevant
information to acquaint themselves with the characteristics of each cargo to be
loaded. If the cargo to be loaded is a mixture (e.g LPG), information on the
composition of the mixture should be sought; the temperature and pressure
readings in the shore tank can be used to verify this information.

o Special notes should be made of any contaminants that may be present in the cargo,
e.g."water".

o Ref: Sigtto publication for gas carrier appendix 1------------------------------ Q79) Describe the loading
procedure of a semi-refrigerated LPG tanker in accordance with the IGC Code and ISM Code? (Oct-
17, Oct-15, April-14, Oct- 12) OR

With reference to liquefied gas carriers, write short notes on: SemiRefrigerated ship. (April-15)

Ans79:- SEMI-REFRIGERATED OR PRESSURE CARGOES>>>

Loading

> This operation follows the general principles very closely. The shore loading hose, and, if
available, the vapour return line hose, are connected to the liquid and vapour line
connections at the cargo manifold.
> Loading is effected through the liquid line, and pressure relief, etc., through the vapour
return line. When the vessel arrives at the loading terminal, her tanks should be:
empty of liquid, but under suitable pressure of vapour from her previous cargo, gas-
free, but under the maximum vacuum .

> If the vessel's cargo tanks are full of vapour at a suitable pressure (gassed up), loading can
start at once.
> This being the simpler of the two cases given above, it will be described first.
> As the liquid enters the tank, the vapour trapped in the space above the liquid will be
compressed, become supersaturated and condense.
> If a vapour return line has been provided, any excess pressure can be returned ashore.
> If no vapour return line is provided, then the pressure can be relieved in the following ways:
firstly, by spraying part of the cargo into the tank, secondly by refrigeration and finally, if
these methods fail, by allowing the excess pressure to escape into another tank.
> In this connection, it is not advisable to attempt loading all the, cargo
through the sprays because to do so places an unnecessary restriction on the line.

> The sprays should be used only for the purpose of providing a larger surface area upon
which the supersaturated vapour condenses.
> In the second case, when the vessel arrives alongside gas-free and under an 80 per cent.
vacuum, the first step is to break the vacuum with vapour taken from shore, and raise the
pressure within the tanks to a suitable level.
 > If a vapour return line is provided, this is simple. If no vapour return line is provided, the
cargo tanks can be gassed-up by using the vaporiser.
> This effectively gasses-up the tank, but if the ship arrived with an 80% vacuum, 20 per cent.
of the ship's capacity will be occupied by incondensibles at atmospheric pressure, the
incondensibles being either air or inert gas (usually nitrogen).
> However, under pressure, the physical space occupied by these incondensibles is much less.
> If the incondensibles remaining in the tanks consist of air, the atmosphere within the tank
will be very "over-rich" after gassing-up.
> For this reason, some refineries insist on the cargo tanks being inerted prior to creating the
final vacuum before loading.
> The usual loading programme is to load the lower tanks first, and to complete
loading in the upper tanks. ^

> This is very important because it is an old maxim that it is the unmatched tank which always
overflows.
> To load a very warm cargo from fully pressurized storage at ambient temperature into a
semi-refrigerated ship, the reliquefaction plant must be started up and run at its maximum
capacity to cool the cargo as it comes on board.
> The usual technique is so to adjust the loading rate as to maintain a pressure in the tanks
below the safety valve relief setting.
> This can be achieved by maintaining a constant pressure at the loading manifold by
frequently adjusting the manifold valve.
> Experience will soon show the best pressure to maintain and it is usually very close to the
maximum pressure at which it is intended to load the product.
The loading manifold pressure gives a much better indication of the valve
adjustment needed, than watching the tank pressures, and adjusting the
loading rate by guesswork.--------------------------------------------
Ans80:- The vessel's management is presented with a great deal of documentation from parties to
the cargo, authorities, etc. Furthermore vessel's management must also issues papers serving to
record evidence, claims etc.

Following are most needed documents:-

1) Deck Log Book

2) Sea Passage Report
3) Port Log
4) Notice of Readiness
5) Deadfreight Statement
6) Protest of Difference Between Ship and Shore Figures
7) Pre arrival and Commencement - Cargo Operations Checklist
8) During Loading Ops Checklist
9) Completion of Cargo & Pre-departure Checklist
10) Prior to Use of Vapour Emission Control System Checklist
11) During Discharge Ops Checklist
12) Ullage Report
13) Pumping Record
14) Cargo Heating Report
15) Inert Gas Log
16) Tank Cleaning Record
17) ROB Report
18) Dry receipt
19) Vessel Experience Factor (Load)
20) Cargo Loading Plan
21) Cargo Discharge Plan
22) Chemical & Physical Properties
23) Pressure Log & O2 Log
24) Cargo Hose Record
25) Cargo Sampling Log
26) Tank Cleaning Plan
27) Tank Cleaning Schedule Checklist
28) Monitoring During Cleaning Operations
29) Wall Wash Test Results>>>>>

Documents provided by the Shipper :->

1) Cargo quality certificate (analysis report)

2) Cargo quantity certificate.
3) Certificate of origin.
4) Cleanliness report.
5) Heating instructions.
6) Inhibitor certificate.
7) Cargo manifest.
8) Vessel's experience factor.
9) Tank History.
10) Sample receipt.
Custom Clearance Reports / Papers.------------------------------------Ans:81:- Closed Cycle System
(re-circulation method) :-

1) Wash oil is supplied from the aftermost centre tank or slop tank and drained oil is collected in the
same tank, i.e., the same tank is used for both purposes.>> a. Precaution:-

i. Slop tanks loaded by the "Load-on-Top" procedure should be discharged entirely

and then filled with fresh oil (crude oil free from water and residue) prior to
COW.>>>>ii. It is considered better to discharge Driving Oil in Slop tank after
washing a few tanks, not more than six tanks, and replace to fresh oil again as it
may avoid the Driving oil to be sludge-full.>> Closed loading guideline
for various noxious liquid chemicals in bulk :> Closed
loading/discharge means loading or discharging with securely closed ullage,
sounding and sighting ports. > For gauging e.g. ullaging and sounding closed
devices must be used. The level alarm systems must be operated during the
entire closed cargo operation. Closed cargo operations must be stopped as soon
as any essential system for safe loading.>>

Gauging, sounding and sampling :> A closed gauging device penetrates the cargo tank,
but is part of a closed system and prevents the cargo or its vapour being released. Examples are the
float-type systems, radar systems.
> For sampling and sounding, the Dovianus or Hermetic portable gauging and sampling systems
may be used.
> Vapour locks, where fitted, are to be calibrated and certified by a recognised cargo inspection
company which will also approve the datum level corrections including list and trim corrections
for tank volumes.>>

Cargo tank venting : -

> Controlled venting must be established if closed cargo operations are required. A controlled tank
venting system is a system with pressure and vacuum-relief valves (P/V-valve) fitted on each
tank in order to limit the pressure or vacuum in the tank.

> Secondary venting system must also be operational Information on maximum loading rates and
venting capacities is to be readily available and displayed in the cargo control room.

Vapour emission control system onboard chemical tankers :> Where required,
VEC is to be used and operated in accordance with IBC Code, local regulations, and instructions
contained in the vessel's VEC System Operation Manual and in conjunction with the requirements
and provisions of the shore installation. ^V

The primary hazards include :

> The ship loses effective control of the tank atmosphere pressure, and is directly influenced by
any changes which may occur within the terminals system.
> Associated pressure sensing devices on the vessel are well maintained.
> It is also essential that individual cargo tank P.V. valves are properly maintained and operate
correctly.
> Check that the VECS alarms are correctly set and tested. (Secondary PV alarms are set 5-10%
above PV valves setting as per Oil Major Requirements for normal operations).-----------------------
----------Ans:82:- Deepwell pump is the pump type that is often used on gas tankers.
> Deepwell pumps are pumps with a long shaft between the driving motor and the pump.
> The shaft goes inside the tank's discharge pipe from the pump up to the tank dome.
> The discharge pipe is a solid pipe that goes up through the tank and out to the flange on the
tank dome to the liquid line.
> The discharge pipe is constructed with several lengths with pipes, and there is a shaft bearing on
each flange.
> The bearings are lubricated and cooled down by the liquid that is pumped from the tank.
> It is very important not to run the pump without liquid. This may result in damage of bearings
and then the shaft.
> The motor that drives the pump is either electric or hydraulic.
There is a mechanical sealing device between the motor and the discharge pipe in the cargo tank.----
--------------------------------------Ans:83:- :- IGC Code :- —

> The Code which applies to new gas carriers (built after 30th June 1986) is the International Code
for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk.
> In brief, this Code is known as the IGC Code.
> The IGC Code, under amendments to Safety of Life at Sea Convention (SOLAS),
is mandatory for all new ships. _ A
> As proof that a ship complies with the Code, an International Certificate of Fitness for the
Carriage of Liquefied Gases in Bulk should be on board.
> In 1993, the IGC Code was amended and the new rules came into effect on 1st
July 1994. \\\ ^

Ships on which construction started on or after 1st October 1994 should apply the amended version
of the Code but ships built earlier may comply with previous editions of the IGC Code.--------------------
-----------------------Ans:84-Piping Arrangement :-

The pipes leading from the cargo tanks to the pumps are termed as bottom lines, from the
pump-room up to deck are called risers. The lines on deck are termed as deck lines. The lines which
lead from the deck to the tanks are called drop lines.

In the cargo tanks, the pipes terminate in a bellmouth. A tank may have two bellmouths -
one main and one smaller stripper bellmouth. Alternatively, one bellmouth may serve the purpose
of main as well as stripping discharge. The piping system has evolved over the years to cater to
varying cargo requirements. In a product tanker which is designed to carry many grades, we see that
there are many more pipes so that many grades can be catered to. In a crude oil tanker, the piping is
straightforward and simple.>>

There are three basic types of pipeline systems :

1) Direct Line system

2) Ring main system
3) Free flow system.
Each system has their uses and is designed to fulfill a need in a particular type of vessel.>>

Direct Line svstem:-

It consists of lines running longitudinally in the centre tanks and branching out to bellmouths in the
centre and wing tanks. The system is uncomplicated and found on some crude carriers.>> The
advantages are that :

1) It is easy to operate and less training of personnel is required.

2) As there are fewer valves, it takes less time to set up the valve system before commencing a
cargo operation.
3) Contamination is unlikely, as it is easy to isolate each section.

The disadvantages are that :

109 | Page

1) The layout is not as versatile. 2) A very rigid system which makes it difficult to plan.>>

Ring-main svstems:-
> > It is also called the circular system. This type of piping system provides for the handling of
 several different types of oil. A particular tank can be pumped out either by a direct suction line
or through another line by use of a cross-over. The system is very versatile. The indirect suctions
for the port cargo tanks feed the starboard cargo line and the starboard cargo pump. Master
valves are provided on each line between the tanks, so as to isolate each tank from the other
when necessary.>>
Free-flow system :> In this system, the oil flows freely into the aft most tanks when the
interconnecting gate valves are opened.

> Main suction bellmouths in a full free flow tanker will only be provided in the aft tanks.
However, each tank is generally provided with a small stripping line.
This system has the distinct advantage of having lesser and less complicated piping system in the
tanks and is suitable for large tankers which usually do not carry many grades of oil.-----------------------
----------------Ans:85:- :- Phosphoric Acid Discharge & Tank Cleaning :.

> Phosphoric Acid is normally carried in rubber lined or Stainless Steel Tanks.
> Phosphoric Acid is generally carried on a "Type 3" Chemical tanker.
IMO Ship Type 3 :- is a Chemical Tanker intended to transport products with sufficiently severe
environmental & safety hazards. These products require a moderate degree of containment to
increase survival capability in a damaged.>> Some of the properties of Phosphoric
acid is listed below :-

Pollutant Category: Z

Sp. Gravity:- 1.685 @ 25OC (Water =1 )

Vapour Pressure: 0.3 k Pa (@ 20OC)

Vapour Density: 3.4 (Air = 1)

> Easily soluble in hot water. Soluble in cold water.

> Very hazardous in case of skin contact (irritant), of eye contact (irritant) of
ingestion.

> Phosphoric Acid is non-flammable.

> Reacts with metals to liberate flammable hydrogen gas.
> Minor corrosive effect on bronze. Sever corrosive effect on brass, corrosive to
ferrous metals & alloys.

> Polymerization will not occur.>>

Tank Cleaning :> Ensure the prewash after dischg is with fresh water. Then use sea water till the
pH is 7. Immediately after that wash again with fresh water to remove all chlorides from tank. This is
crucial to avoid elephant skin.

> Have a look at the first empty tank. If the sediment is too much --it is usual to recirc at end
of discharge of each tank.
> Acid/sea water mixture remaining in lines and stainless steel hoses will soon result in
pittings.
> For Stainless Steel (SS) Tanks : - After the tanks are thoroughly/finally cleaned,
 passivate the tanks with Nitric Acid as the Phosphoric destroys the passive oxide coating on
the stainless.
> Category Z :- Noxious Liquid Substances which, if discharged into the sea from tank
cleaning or deballasting operations, are deemed to present a minor hazard to either marine
resources or human health and therefore justify less stringent restrictions on the quality
and quantity of the discharge into the marine environment.>>
> .
Discharge Criteria for Tank wash residues into Sea :> If outside any S.A.
(Special Area)

o Discharge tank washing 12 NM from Nearest land. o

Depth of water must be more than 25 mt. o Speed. of
ship must be more than 7 kmts.

> S.A. designated for Annex II cargoes is Antartic Region.

Discharge of tank washings is not permitted in the Baltic Region.-------------------------------------
-Ans86:- :- Types of gas carriers:- Gas carriers range in capacity from the small pressurised
ships of between 500 and 6,000 m3 for the shipment of propane, butane and the chemical gases.
Between these two distinct types is a third ship type — the semi-pressurised gas carrier. These very
flexible ships are able to carry many cargoes in a fully refrigerated condition at atmospheric pressure
or at temperatures corresponding to carriage pressures of between five and nine bar.

Fully pressurised ships :>Today, most fully pressurised LPG carriers are fitted with two or
three horizontal, cylindrical or spherical cargo tanks and have capacities up to

6.0 m3.
> However, in recent years a number of larger capacity fully-pressurised ships have been built
with spherical tanks, most notably a pair of 10,000 m3 ships, each incorporating five
spheres, built by a Japanese shipyard in 1987.
> Fully pressurised ships are still being built in numbers and represent a cost- effective, simple
way of moving LPG to and from smaller gas terminals.

Semi-pressurised ships : -

> These carriers, incorporating tanks either cylindrical, spherical or bi-lobe in shape, are able
to load or discharge gas cargoes at both refrigerated and pressurised storage facilities.

> The ships can load or discharge at virtually all pressurised and refrigerated terminals,
making them the most versatile gas carriers in terms of cargohandling ability.

Fully refrigerated ships : -

> The 1960s also saw another major development in gas carrier evolution — the appearance
of the first fully refrigerated ship, built to carry liquefied gases at low temperature and
atmospheric pressure between terminals equipped with fully refrigerated storage tanks.
The first purpose-built, fully refrigerated LPG carrier was constructed by a Japanese
shipyard, to a United States design, in 1962.
> The ship had four prismatic-shaped (box-like) cargo tanks fabricated from31/2 per cent
 nickel steel, allowing the carriage of cargoes at temperatures as low as -48°C, marginally
below the atmospheric boiling point of pure propane.

> The main types of cargo containment system utilised on board modern fully refrigerated
ships are independent tanks having rigid foam insulation.>>>Liquefied natural gas
(LNG) carriers :> At about the same time as the development of fully refrigerated LPG
carriers was taking place, naval architects were facing their most demanding gas carrier
challenge, this was the transport of LNG.

Natural gas, another clean, non-toxic fuel, is now the third most important energy source in the
world, after oil and coal, but is often produced far from the centres of consumption. .--------------------
-----------------------Ans:87:- - A Hazard is a physical situation with a potential for human injury,
damage to property, damage to the environment, to capital investment or some combination of
these.

>Fire & Explosion Three elements are necessary to create a fire : Fuel, an
Oxidiser (usually air) and a Source of Ignition (energy). In theory, ignition is not possible, if any
one of the 3 is eliminated. During many tank cleaning operations the atmosphere in the tank
must be considered as flammable because the product to be cleaned is flammable and
inertisation is not possible. Under these circumstances the only way to guarantee that an
explosion cannot occur during cleaning is to make certain that there is no source of ignition. A
potential source of ignition during tank cleaning is Electrostatic discharge. Especially during
water spraying electrostatic charges could be induced.

> Undesired reactions Polymerization (Depletion of inhibitor or excessively high

temperature) Saponification , Drying/Hardening,Reaction with water .

> Corrosion - Corrosive substances destroy human tissue on contact (e.g. skin, eyes and
mucous membranes in the mouth and respiratory tract) Metal or other material used in ship
construction could be corroded at an excessive rate.

> Overexposure to toxic substances (Death of operator after wiping Phenol residues by tank
entry without wearing a full chemical suit and SCBA [self- contained breathing apparatus])

> Asphyxiation -Oxygen deficiency (Entry into a tank with an inert gas atmosphere)

> Emissions
o To the air: As always when ventilating, special care must be taken to prevent the risk of explosion
(flammable products) or with regard to toxic vapors. All normal safety precautions must be
taken.The wind strength and wind direction must also be a decisive parameter for the Master to
allow ventilation. To avoid a buildup of explosive or toxic vapors on deck the amount of gas to
be escaped from the tanks should be limited. -------------------------------------Ans:88:- :-
Certificate Of Fitness (COF) on chemical tankers

> An International Certificate of Fitness for the Carriage of Dangerous

> Chemicals in Bulk shall be issued after an initial or renewal survey to a chemical tanker
engaged in international voyages which comply with the relevant provisions of the Code.
 Classification society issues the certificate of fitness on behalf of the administration.
> An International Certificate of Fitness for the Carriage of Dangerous
Chemicals in Bulk shall be issued for a period specified by the Administration which shall not
exceed 5 years.

> All ships will get a new COF after 1.1.07, considering IBC code and Marpol rules are revised
as on 1.1.07. IMO has decided that Chemical carriers can carry COF or NLS, not both.
> For ships carrying IBC code chapter " Other Substances" OS, there is no need for COF, they
require only NLS certificate.
> COF is a certificate issued by Flag administration confirming that the structure , equipment
and materials used in the construction of the chemical tanker are in compliance to carry a
given list of chemicals and it gives the conditions of carriage.
> Upon receipt of cargo loading instructions, all products are to be checked against the
Certificate of Fitness. Any irregularities are to be reported immediately to the chemical
operator. >>>>Since new chemicals are being manufactured and re-evaluated for safe sea
carriage regularly it may be possible that some chemical is not included in the COF list. In
such a case permission may be obtained from flag administration or their representative for
this particular chemical and attached to the COF as an addendum.
The issuance of an Addendum to CoF may be done immediately based on the Tripartite Agreement.
The submission of data and evaluation by GESAMP and ESPH may come afterwards.-----------------
-----------------------Ans:89:- :- Membrane Tanks :

> Unlike independent tanks, membrane tanks are non-self-supporting structures. Their primary
barrier consists of a thin layer of membrane (0.7 to 1.5 mm thick).
> The membrane is supported to the inner hull structure through an insulation that can range upto
10 mm thickness as per IMO IGC Code. Due to their nonself-supporting nature, the inner hull
bears the loads imparted onto the tank.
> This way, the expansions and contractions due to thermal fluctuations are compensated by not
allowing the stress to be taken up by the membrane itself.
Membrane tanks are primarily used for LNG cargo.

> Often, there are two layers (primary and secondary) of insulation and membranes placed
alternatively.
> The most common types of membrane tanks are the ones designed and developed by two
French companies Technigaz and Gaz Transport. The Tehnigaz system makes use of a stainless
steel system that is constructed with corrugated sheets in such a way that one sheet is free to
expand or contract independent of the adjacent sheet. The Gaz Transport system uses Invar as
the primary and secondary membranes.
> Invar has low coefficient of thermal expansion, which makes corrugations unnecessary.
> The insulation is usually made of materials like Reinforced Polyurethane.

Some of the advantages of membrane tanks are as follows :

> They are generally of smaller gross tonnage, that is the space occupied within the hull is lower
for a given cargo volume.
> Due to the above reason, maximum space in the hold can be used for cargo containment.
Since the height of tanks above the main
deck is significantly lesser compared to the
cases of Moss tanks, membrane tanks
provide allow visibility from the
navigational bridge. This also allows a
lower wheelhouse.--------------------------------
--Ans:90:- :- Preparation for
loading LNG cargo :>Loading
LNG cargo after dry docking :

LNG is a cryogenic substance and its main component is methane. It gasifies

violently when directly introduced into a cargo tank at ambient temperature, rapidly increases the
internal pressure of the cargo tank and makes the atmosphere into a flammable condition. In
addition, the cargo tank is rapidly cooled, resulting tremendous thermal stress on cargo tank skins
and cargo piping systems.

To avoid such damages, the preparatory work for cargo loading after dry docking must be
done in the following sequence. During dry dock all the compartments of an LNG carrier are kept gas
free.

>Drying of Cargo Tank:

During dry docking or inspection, cargo tanks which have been opened and contained humid air,
must be dried to avoid the formation of ice when they are cooled down and the formation of
corrosive agents if the humidity combines with sulfur and nitrogen oxides which might be present in
excess in the inert gas. >Drying of Hold Spaces :

The drying operation of a hold space is carried out in order to prevent tank

i. insulation damage due to condensation of moisture inside it prior to initial cool down operation
and periodically during a voyage>> Operation procedures and precautions :-
Before delivering dry air into a hold space, completely dry up the bottom section of the hold
space, particularly the bilge well.
> When drying a hold space after completing the inerting operation of a cargo tank, purge
relevant equipments and Inerting/aerating lines with dry air to prevent the ingress of inert gas
into the hold space.>> Inerting of Cargo Tanks :
> Cargo tanks filled with air shall be dried and inerted with inert gas supplied from the inert gas
generator on board.>> Inerting of Annular Space for Moss type vessels
> The space between the surface of a cargo tank and insulation is called annular space, insulation
space or wedge space.>> Inerting Inter Barrier Spaces (IBS) and Insulation
Spaces (IS) for Membrane type vessels
> The space between the primary and the secondary barrier is called interbarrier space (IBS). The
space between the secondary barrier and the inner hull is called insulation space (IS).>> Gassing-
up :-
> After lay-up or dry dock, the cargo tanks are filled with inert gas or nitrogen. If the purging has
been done with inert gas, the cargo tanks have to be gassed up and cooled down when the vessel
arrives at the loading terminal.>>Supply of LNG for gassing up :-
> LNG liquid is supplied from the terminal to the liquid manifold where it passes to the
stripping/spray header via the appropriate ESDS liquid valve.>>Initial Cool Down
> Cool down is an operation to pre-cool cargo tanks and lines required before taking on cryogenic
LNG. Cargo tank cool down is carried out by spraying LNG through the spray nozzles of each cargo
tank, using LNG received from the shore terminal.>> Vapor generation :-
> If LNG is introduced directly into warm tanks, the LNG will almost immediately turn into vapour.
LNG has a liquid to gas expansion ratio 1: 600. Therefore, to enable the liquid to be loaded into the
tank at a reasonable loading rate, necessity of large compressors would be required to remove the
vapour generated in the process.>> Cargo tank Material
Most cargo tanks are constructed of stainless steel which is a material, that retains its flexibility and
strength characteristics over the temperature range being considered (-180°C - 50°C). >>Pipe
tower construction

The tower which supports the pipe-work within the tank is constructed of
stainless steel bars. If subjected to rapid cooling thermal stress
within the material can be excessive, leading to t he material
cracking. Loading Operation
LNG is loaded via the loading manifolds to the liquid header and then to each tank filling line. The
boil-off and displaced vapour leave each tank via the vapour suction to the vapour header As the
loading rate increases, it is important to monitor the tank pressures and to start one HD compressor.
Bulk loading

> When all lines and valves are fully cooled the vessel can commence ramping up the loading
rate in the sequence agreed with the terminal.
> Ensure the HD compressors are adjusted in line with loading rate to ensure that the tank.
> Topping off

As the vessel approaches completion of cargo operations the tanks should be staggered in line with
the cargo plan, typically this would leave a gap of 10 to 15 minutes between completion of each
tank. >>Deballasting

The deballasting operation is carried out simultaneously with the cargo loading operation. Before
any de-ballasting commences, all ballast surfaces should be visually checked and confirmed as
free from oil or other pollutants.>> Filling Rate of Cargo Tanks

> When loaded in the cargo tanks, the pressure of the vapour
phase is maintained substantially constant, slightly above
atmospheric pressure.
The external heat passing through the tank insulation generates
convection currents within the bulk cargo, causing heated LNG
to rise to the surface where it vaporizes. >>>> Behaviour of LNG
in the cargo tanks

> When loaded in the cargo tanks, the pressure of the vapour
phase is maintained substantially constant, slightly ab ove
atmospheric pressure.
> The external heat passing through the tank insulation
generates convection currents within the bulk cargo, causing
heated LNG to rise to the surface where it vaporizes.
------------------------------------------- Ans:91:- Single-Stage Direct Cvcle: -
 > The single-stage direct cycle system is particularly suited to the
semi- pressurised carrier.

> A simplified diagram of single -compression reliquefaction is

shown in Figures 4.11(a) and (b).
> This cycle is suitable where suction pressures are relatively
high, as in the carriage of semi -pressurised products. Boil -off
vapours from the cargo tank are drawn off by the compressor —
(a) in the diagrams. Compression increases the pressure and
temperature of the vapour — to (b) in the diagrams. Th e high
temperature allows it to be condensed against sea water in the
condenser — at (c) in the diagrams.
> The condensed liquid is then flashed back to the tank via a float
controlled expansion valve at (d) in the diagrams.
> The liquid/vapour mixture being returned the cargo tank may be
either distributed by a spray rail at the top of the cargo tank or
taken to the bottom of the tank to discourage re -vaporisation.
The spray rail is normally used when the tank is empty and bottom
discharge when the tank is fu ll.----------------------------------------- Ans:92:- :- Main
characteristics of the different tank types :->>TYPE A- Description:- Prismatic tank, adjustable
to hull shape; full secondary barrier.>> Pressure:- <0.7 bar g >>> Pros: space –efficient>> CONS:- Boil-off gas
handling. More complex fuel system required, high cost>>>>TANK TYPE B:- - Description:- Prismatic tank,
adjustable to hull shape; partial secondary barrier, Spherical tank; partial secondary barrier,>>>PRESSURE:- <0.7
Bar g,>>>PROSS:- Space- efficient , Reliably proven in LNG carriers,>>>CONS:- Boil-off gas handling.

More complex fuel system required. High costs, Boil-off gas handling. More complex fuel system
required,>>>>TANK TYPE C :- - Description:- Pressure vessel, cylindrical with dished
ends>>>PRESSURE:- >2 bar G>>>PROS:- Allows pressure increase.,simple fuel system, little
maintenance, Easy installation Lower costs.CONS :- On board space requirements -------------------------
-------------- Ans :93:- INTEGRAL TANKS- > Integral tanks form a structural part of the ship's hull and
are influenced by the same loads which stress the adjacent hull structure, and in the same
manner.>> This form of cargo containment is not normally allowed if the cargo temperature is below
-10OC.>>> This containment system is partly used on some LPG ships dedicated to the carriage of
butane.>>> MEMBRANE TANKS:- Membrane tanks are not self-supporting tanks; they consist of a
thin layer (membrane), Normally not exceeding 1 mm thick, supported through insulation by the
adjacent hull structure.>> The rounded parts of the layer are designed to accommodate thermal
expansion and contraction, and other types thereof.>>> The semi-membrane design has been
developed for carriage of LNG, and the material of construction is 9% nickel steel or aluminium. -----
-------------------------------------------------Ans:94:- FULLY REFRIGERATED GAS CARRIERS :->> Shape:- The
tankers have prismaticshaped cargo tanks>>> Cargo capacity: - The ships are typically in the range
15,000m3 - 85,000m3, with three common sizes for LPG/Ammonia trades of 30,000m3, 52,000m3 and
80,000m3.>>>>>> SEMI-REFRIGERATED/ SEMI PRESSURIZED GAS CARRIERS :->> Shape:- The tanks
are cylindrical in shape and of a thinner construction than the pressurised vessels.>> Cargo capacity:
- The Ships typically ranges up to 5,000 m3 in size. Their construction is based on carrying propane at
a pressure of 8.5 kg/cm2, and a temperature of -10°C.--------------------------------------------------------------
Ans:95:- :- The two main types of liquefied gas carriers are :-
1) LPG (Liquefied Petroleum Gas) Carriers, and
2) LNG (Liquefied Natural Gas) Carriers.>>
Liquefied Petroleum Gas (LPG) : Petroleum hydrocarbon products such as Propane and
Butane, and mixtures of both have been categorised by the oil industry as LPG. It is widely used in
domestic and industrial purposes today. The most important property of LPG is that it is suitable for
being pressurised into liquid form and transported. But there are conditions related to pressure and
temperature that need to be maintained for the above to be carried out without posing threat to
life, environment, and cargo.

At least one of the following conditions need to be complied with, for transportation of LPG:

> The gas should be pressurised at ambient temperature.

> The gas should be fully refrigerated at its boiling point. Boiling point of LPG rangers from -30
degree Celsius to -48 degree celsius. This condition is called fully-refrigerated condition.
> The gas must be semi-refrigerated to a reduced temperature and pressurised.>>>>

Liquefied Natural Gas (LNG) : Natural gas from which impurities like sulphur and carbon-
dioxide have been removed, is called Liquefied Natural Gas. After removal of impurities, it is cooled
to its boiling point (-165 degree Celsius), at or almost at atmospheric pressure. Note here, that unlike
LPG, LNG is cooled to low temperatures but not pressurised much above atmospheric pressure. This
is what makes the design of LNG carriers slightly different from LPG carriers. LNG, at this condition is
transported as liquid methane.LPG carriers are categorized into types.>>

Integral Tanks : They are mainly used for cases when LPG is to be carried at conditions close to
atmospheric condition, for example - Butane. That is because, in this case, there are no
requirements for expansion or contraction of the tank structure.

Independent Tanks : These tanks are self-supporting in nature, and they do not forman
integral part of the hull structure. Hence, they do not contribute to the overall strength of the hull
girder.---------------------------------------------------------------------Ans:96:- :- Procedure for Tank
Cleaning on Chemical Tanker :- No cleaning can take place unless the mandatory prewash
as required by MARPOL is done.>>

The master must enforce precautions like "no smoking "and "AC on recirc ". It is important
for all on a chemical tanker to know the location of AC fresh air intake, and the Anemometer, to use
the relative wind direction to advantage. Bioaccumulative vapours and carcinogenic fumes can enter
the engine room via intake vents and cause health problems for the engine staff. It is not all right to
say that just the deck crew are exposed to toxic vapors.>>

STAGES OF TANKCLEANING :--

1) Precleaning with sea water :- Pre cleaning is different from MARPOL mandatory
Prewash. Tank cleaning machines may have shadow sectors, and this can be rectified for main wash.
Non drying oils and fats can be steamed before the hot water precleaning.>>
2) Main wash with sea water : - Do not attempt to use tank cleaning chemicals unless the
cargo clingage is removed.>>
3) Tank Cleaning Chemical wash : - If cargo is not water soluble or residues remain , the
use of tank cleaning chemicals is justified. If the previous cargo is not water soluble using a 0.04%
detergent wash will be good enough for WW standard ( this is not WALL WASH .>>

4) Rinsing with sea water :- This is done with tank cleaning machines, the main purpose is
to get rid of the residues loosened up by the tank cleaning chemicals.>> 5) Flushing with
fresh water :- This is done with tank cleaning machine using a low throughput, to remove the salt
before they dry up .>> 6) Steaming tank and pipelines (to bring level of chlorides down
and wash down appendages):- Steaming is the introduction of saturated steam into the tank to
evaporate volatile residue (odour removal). The steam will condense on the tank surfaces. The
temperature should normally be as high as possible during steaming. >>
7) Draining tank sump :- Strip out the tank and the pump stack. Sometimes it will be
necessary to use a Wilden pump and sponges to save time. Mopping reduces drying time if there are
water pools on the tank bottom. Make sure no lint is left .>>

8) Drying tank with ventilation :- While venting please remember that warm moist air
condenses on a cold surface. Ventilation removes water, moisture and odor, which is usually done
by forced air circulation.---------------------------------------------