CTM 9.6	Chemical Tanker Manual CTM Cargo Discharging Operations	Doc No.: CTM 9.6 Revision: 01 Date: 15 Oct 2024 Issued by: DPA Approved by: MD

1. APPLICATION

This document applies to all Chemical Tankers managed by the Company.

2. PURPOSE

The purpose of this document is to provide guidelines and instructions for the safe and efficient discharging of cargo from chemical tankers.

3. CARGO HANDLING PLAN

3.1 Basic Information

The Chief Officer shall prepare a Cargo operation plan that provides a detailed sequence of cargo and ballast operations. It shall cover the following:

• Quantity and grade of each parcel
• Density, temperature and other relevant properties
• A plan of the distribution lines and pumps to be used
• Transfer rates and maximum allowable pressures
• Cargo pollution category
• Flammability and toxicity; (including antidotes if applicable)
• Fire protection including fire-fighting agent
• Miscibility
• Critical stages of the operation
• Notice of rate change
• Venting requirements
• Stability and stress information
• Drafts and trims
• Ballast operations
• Emergency stop procedures
• Action to be taken in the event of a spill
• Protective equipment requirements
• Hazards of the particular cargoes.
• Inert gas requirement

Additionally, as required or applicable:

• Inhibitor requirements
• Inerting and padding
• Cargo viscosity
• Cargo melting point
• Cooling
• Tank coating material compatibility
• Precautions against static generation
• Control of cargo heating systems
• Line clearing
• Under keel clearance limitations
• Bunkering
• Special precautions required for the particular operation

3.2 Discharging methods

The Cargo Operation plan shall clearly specify:

• Manifold/line to be used
• Connecting method for jumping hoses or spool pieces

3.3 Involvement of Engine Department

The Chief Officer shall discuss relevant items of the Cargo Operation plan with the Engine Department, which shall include the following:

• When and how ballast / Cargo pumps are used
• Steam arrangements required during cargo discharging
• Check the compressor’s air charge for air blow
• Stress and Stability with regard to Bunker tanks distribution
• If bunkering is scheduled, planning both operations so as not to interfere with one another

4. REFERENCES

Follow precautions as detailed in the following Industry guides:

• International Safety Guide for Oil Tankers and Terminals (ISGOTT)
• ICS Tanker Safety Guide Chemicals

5. ULLAGING PRIOR TO DISCHARGE (CDI 5.1.6)

Before commencing discharge of cargo and in conjunction with the surveyor/receiver’s representative:

• Take ullages and temperatures of all tanks
• Calculate cargo quantities

If discrepancy exceeds 0.5%:

• Determine the cause
• Retake ullage/temperatures
• Check void spaces

In taking ullages and temperatures, Chief Officer shall consider the following points:

• Take ship's draught readings immediately before cargo measurement
• Use correct ullage datum
• If there is movement on the surface of the cargo, obtain a true mean ullage
• Correct the measured ullages for ship's trim and list
• Take cargo temperature readings from the top, middle, and bottom of each tank
• Apply corrections for the UTI being used, as applicable
• On vessels fitted with remote gauges, take both manual ullage and gauge readings

6. PRIOR TO DISCHARGE (CDI 5.1.6)

6.1 Information to be exchanged with terminal before unloading operation

The Chief Officer shall ensure the following information is exchanged:

• Kinds and the properties of the cargoes to be discharged
• Arrangement and capacity of vessel's cargo line and venting system and shore's cargo lines and tanks
• Maximum discharge capacity and pressure of cargo pump to be used and discharge rate and pressure
• Maximum allowable pressure of vessel/shore hoses or loading arms to be used
• Discharging sequence
• Necessary precaution to avoid electrostatic ignitions
• Movement or operations which may change flow rates
• Kinds and numbers of safety equipment to be prepared or used
• Proper name of Consignee/Charterer/Receiver for each cargo, especially in case of discharging the same kind of cargo
• Max time allowed for stripping

6.2 Preparation prior to discharge

Prior to discharge, the Chief Officer shall ensure:

• Fire-fighting/pollution prevention equipment is kept in readiness
• Cargo pumps are ready and emergency stops tested
• Identification tags are put up at manifold for identification
• Inert gas system is ready. I.G. branch valves are locked open (If Applicable)
• Cargo tank vents are set correctly
• Pump room fans are put on well in advance

7. PUMPING SYSTEMS

7.1 Speed of discharge

• The vessel shall be ready to discharge on completion of checking cargo figures.

Note:

• If delay encountered from the terminal, Issue a Letter of Protest.
• Upon commencement of discharge:
  • Initiate a cargo pump discharge log
  • Note and record pressure at manifold at intervals not exceeding one hour

7.2 Cargo pumps

Chief Officer shall ensure that the flow to the pump suction does not fall below the pumping rate.

7.3 Submerged centrifugal pumps

7.3.1 Control and operation of centrifugal pumps

During operation, Chief Officer/OOW shall give due consideration to:

• The prevailing suction and discharge conditions in relation to pumps' performance characteristics

Information:

• This is particularly important when operating cargo pumps where the rated capacity is achieved at a relatively high total head
• Operation of these pumps with a low total head can grossly exceed the pumps’ rated capacity and cause excessive liquid velocities in piping systems

7.3.2 Discharge valves

Chief Officer shall ensure proper control of the discharge valves. Information:

• Control of a centrifugal pump can be achieved by:
  • Adjusting the pump discharge valve and/or
  • Restricting the pump speed
• The discharge control valve has three main functions. They can be used:
  • To regulate pumping rates in variable and constant speed pumps and to prevent overloading in constant speed pumps
  • In conjunction with self-priming systems to provide a self-priming capability in centrifugal pumps
  • To reduce the throughput of a pump and so reduce the Net Positive Suction Head required

7.3.3 Cavitation

Chief Officer/OOW shall avoid cavitation as far as possible. Information:

• A pump is said to cavitate when the pressure at the pump suction has fallen to such an extent that bubbles of vapour are formed in the fluid being pumped.
• In a centrifugal pump, bubbles can form with great rapidity at the pump suction and may be carried away to regions of higher pressure within the pump.
• The bubbles then collapse rapidly and in the process of collapsing create a hammer effect.
• This effect, though minute, if repeated frequently, may cause damage to the pump.
• The residual effects of cavitation, as well as the cavitation itself, are harmful and include:
  • Erosion of metallic surfaces which, if severe, may create flow disturbances.
  • Vibration, which may damage the pump or, more commonly, the instrumentation connected with the pump and installation.

7.3.4 Discharging using more than one pump

When cargo is being discharged from more than one tank simultaneously through the common line or jumping hose:

• Ensure that there is no backflow from one tank to another due to imbalance in delivery pressure or mishandling of valves.

7.4 Positive displacement pumps

7.4.1 General

This type of pump includes:

• Reciprocating type – mainly used for stripping tanks
• Screw type – used as specialized cargo pumps

7.4.2 Reciprocating pumps

Chief Officer/OOW shall take precautions to avoid racing, if necessary by slowing the pump.

7.4.3 Screw pumps

Information:

• Screw pumps give a steady flow but are less efficient than reciprocating pumps because of the large areas with running clearance exposed to differential pressure between suction and discharge.
• Wear increases the clearance with consequent loss of efficiency, especially when handling low viscosity liquids.
• The prime mover for a screw pump is invariably a diesel engine driving through a gearbox and clutch system.

Chief Officer/OOW shall ensure:

• Before clutching in a screw pump, the pump shaft is to be turned by hand to ensure free movement of the pump motors.

7.4.4 Operation

Chief Officer/OOW shall ensure:

• The suction and discharge valves of a positive displacement pump:
  • Are always open before starting the pump and
  • Must remain open until the pump is stopped
• These types of pumps are not operated more than their design speed
• Particular care is taken to avoid that these pumps overspeed when they lose suction.
• Pressure relief devices must be checked at regular intervals (as per PMS) to ensure their correct operation

8. CARGO DISCHARGING

8.1 General

When deep well cargo pumps are used in parallel to discharge a group of tanks into a common discharge line, Chief Officer/OOW shall ensure:

• The discharge pressures of all pumps in the group are balanced.

Note:

• This is to prevent the backfilling and possible pressurisation and overflow of one or more tanks in the group.

Note:

• In some vessels, Non-return valves are fitted downstream of the pumps
• The non-return valves are not relied upon to prevent backfilling.

8.2 Commencing a transfer using deep well pumps

The following procedure is common to all types of deep well pumps. Chief Officer and OOW shall follow the steps below when commencing discharge:

1. The number of full tanks (98% capacity) to be commenced as a group must not exceed.

Note:

• In case of bulk discharging with deep well pumps, all tanks should be dropped to below 95 percent alarm level, one by one.
  In case ship needs to start more than one tank, this should be carefully evaluated and a risk assessment done. Approval from Master must be taken.
2. Ensure that cargo tanks, which are not part of the group to be initially discharged, are isolated from the group.
3. Start the pumps in pairs at a minimum 100 bar hydraulic pressure and open the pump discharge valves. At that pressure, the pump will run smoothly but produce minimal cargo backpressure.
4. Monitor the ullage levels in all tanks in the group while starting the pumps.
5. When all pumps are running at 100 bar hydraulic pressure, check:
   • Ullage levels in all tanks in the group and
   • The cargo back pressure at the pump gauges and/or the manifold.
6. When satisfied that the situation is stable, increase the hydraulic pressure to each pair of pumps in turn in increments of 10-20 bar until:
   • All pumps in the group are running at the same hydraulic pressure and
   • The required cargo back pressure at the manifold has been achieved.
7. Reduce the level of all cargo tanks with the same cargo to below 90% prior to increasing the discharge rate to the agreed maximum rate.
8. To add additional pumps to the group at a later stage in the discharge operation, reduce the hydraulic pressure of the pumps already running to the level specified in step IV above. Open the isolator valves of the additional pumps and start them at the same pressure, then open their discharge valves.
9. Tanks are to be discharged as quickly as possible to achieve backpressure as agreed between vessel and shore.

8.3 Final Stages of Discharging - Trim and List of Vessel

At the final stage of discharging (stripping and/or squeezing (sweeping) the cargo), achieve correct trim and list to obtain maximum out-turn in minimum time. This shall be achieved by:

• Ballasting or transferring ballast between tanks, or
• By controlling discharging sequences.

9. TANK INSPECTION

Information:

• Upon completion of discharge, receiver’s representative or surveyor will:
  • Inspect the cargo tanks to determine whether the tanks have been properly drained after discharge, and
  • Issue a Tank Inspection Certificate.
• The results of this survey will largely determine whether receivers/charterers have a valid claim against the vessel.

Chief Officer shall:

• When part cargo remains onboard for discharge elsewhere:
  • Take ullages and dips of all tanks in conjunction with the receiver’s representative or surveyor, and
  • Calculate the quantity discharged/remaining on board.
• After satisfactory completion of tank inspection:
  • Disconnect the discharging hose.
  • Enter the exact time of disconnection in the Deck Log Book or Port Log.

10. OUTTURN

Chief Officer/ Master shall ensure:

• Cargo tanks are discharged and stripped in accordance with the P & A manual.
• Heated cargoes are kept at required temperatures to ensure:
  • Best possible discharge rate, and
  • Minimum of residues in the tank.

11. CARGO RESIDUE

Chief Officer shall ensure:

• In case of heated cargoes, cargo temperature is maintained to properly assist draining.
• On completion of discharge, all lines and tanks are stripped as dry as possible. This to ensure that the maximum amount of cargo is delivered and "in transit" losses are minimized.
• The cargo hoses and cargo lines including the common line are drained as much as possible, as soon as a cargo operation has been completed.
• This is especially important if cargo has a high freezing point or is of polymerizing nature.
• When the lines are cleared by draining the cargo residue into other tanks, these tanks have sufficient ullage to accept such residues.
• Segregation of the cargo residue is maintained from those which react dangerously when mixed.
• Cargoes which react dangerously with water:
  • Are never drained into a wet tank or one containing water.
  • Water is never used for cleaning such lines and tanks unless required procedure is followed and necessary precautions are taken.
• Pressure on the cargo hoses and lines is released prior to disconnection.

12. SWEEPING (SQUEEGING) OF CARGO TANKS

Master/Chief Officer shall ensure the following prior to/during entry into any tank:

• The tank is well ventilated with a forced draught fan.
• Oxygen content is monitored and maintained at 21%.
• The tank atmosphere is checked for carbon monoxide (CO), H2S, and LEL.
• Steam to heating coils is stopped and pressure is released to prevent scorching.
• Self-contained breathing apparatus, lifeline, and harness are kept at the tank entrance, ready for immediate use.
• The tank is well illuminated.
• A responsible person attends the tank entrance throughout the sweeping operation.



Note:

• `Issue Enclosed space entry permit HSSEQ-11 - Enclosed Space Entry Permit. Carry out a Risk Assessment.


• Visual contact is always maintained with sweeping personnel in the tank.
• Frequent reporting of sweeping progress is made to the CCR.
• If other tanks are discharging cargo using the same shore manifold, due consideration is given to the possibility of backflow from high tanks into the tank being stripped.
• Shore back pressure is considered. If required, the tank being stripped is isolated.
• One person is exclusively assigned to look after stripping and cargo pumping out rate and adjust it as required by the sweeping gang.

In case shore contractors are used:

• Master/Chief Officer shall:
  • Review the procedures with them.
  • Address the need for proper PPE.
  • Check the quality of PPE used by shore contractors.
  • Review and observe contractor tank entry to ensure this is in line with company requirement.
  • Evaluate and assess hazards prior to tank entry of the shore gang.

13. PORTABLE CARGO PUMP

Storage on Board Forecastle / Bosun store

The portable pump and flexible hoses must be cleaned and ready for a new pumping job before the equipment is placed in the storage room onboard.

The storage room must be clean and dry, and the pumping equipment must have easy accessibility.

• The flexible hoses are filled with hydraulic oil. Drain off approx. one cup of oil from the hoses before storage (when disconnecting from the main system).
• Control bend radius for the flexible hoses during storage (min 800 ml).
• Control that the units are safely supported and check that the Snap-On coupling and starting head/flow control valves are greased and protected.

The hydraulically driven portable cargo pump:

• Is considered to be a part of the standard cargo handling equipment, and
• Can be used to supplement the fixed pumping system.
• Is also an emergency system in case of main pump breakdown, space flooding, and salvage operations.

Officers shall familiarize themselves with the use of the portable cargo pump by referring to the maker’s manuals. A quarterly drill on the actual rigging and operation of the portable cargo pump should be carried out as per Drill schedule HSSEQ-03. During the drill, the portable pump should be rigged and tried out as it will be done in an emergency scenario.

The portable pump must be tested regularly as per the PMS. Prior to rigging the portable pump, the vessel should carry out a risk assessment and send it to the respective MSI for review.

14. EMERGENCY SHUTDOWN PROCEDURE

• Chief Officer shall agree to an emergency shutdown procedure with the terminal.



Note:

• Record same in Ship/Shore Safety Checklist and Cargo Operation Plan.


• The agreement shall designate circumstances in which operations must be stopped immediately.



Coution:

• Give due regard to the possible dangers associated with the emergency shutdown procedure.




Coution:

• The incorrect operation of pumps and valves can produce pressure surges in a pipeline system. These surges may be sufficiently severe to damage the pipeline, hoses or metal arms.


• Chief Officer shall have a written agreement with the terminal concerning the control of flow rates, the rate of valve closure, and pump speeds.
• This shall include the closure period of remote controlled and automatic shutdown valves.

15. BUTTERFLY AND NON-RETURN (CHECK) VALVES

• Chief Officer shall arrange for thorough checking that such valves are fully open when they are passing cargo or ballast.
• This is to prevent large surge pressures from forming, with the possible resulting line, hose, or metal arm failures.

16. VALVE OPERATION

Chief Officer and OOW shall:

• Not close valves at the downstream end of a pipeline system against the flow of liquid, except in an emergency. This is to avoid pressure surges.
• In general, where pumps are used for cargo transfer, keep all valves in the transfer system open before pumping begins.



Note:

• The discharge valve of a centrifugal pump may be kept closed until the pump is up to speed and the valve then opened slowly.


• In the case of ships loading by gravity, discuss with terminal representatives such that the final valve to be opened is that at the shore tank end of the system.
• Ensure, if the flow is to be diverted from one tank to another:
  • Either the valve on the second tank is opened before the valve on the first tank is closed, or
  • Pumping is stopped while the change is being made.

17. REFERENCED FORMS AND CHECKLISTS

• CHEM 06A - Ship Shore Safety Checklist
• CHEM 01 - Cargo Operation Plan
• CHEM 04 - Hourly Monitoring Record