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Cargo line clearance safe procedure for chemical tankers
Why line clearance ? :
The lines used for cargo operations must be cleared and the pressure released to prevent
solidification, polymerisation, reaction, pitting and danger to personnel connecting and disconnecting
hoses or taking samples.
The final onboard cargo line and systems clearance after the hoses / chicksans have been removed
and the cargo systems secured is the responsibility of the vessel.
Line clearance should be carried out immediately after any of the following, unless safety or pollution
concerns dictate otherwise:
In order to prevent blockages from freezing it is important that lines, drain cocks / plugs are cleared
from such cargoes as Phenol, Caustics, Acetic Acid, Benzene, Paraxylene, Cresols, Vegoils etc in cold
- On the completion of loading (each line system).
- After any internal transfer of cargo (tank to tank).
- After cargo recirculation operations via the manifold or any part of the line being used.
- After a part discharge from any of the tank(s).
- On completion of discharge each line system must be cleared according to Regulations
- As a result of prolonged stops in the cargo handling operations which may cause line
solidification due to high melting point or freezing weather condition.
All cargo manifold lines to be checked by knocking to ensure they are clear prior vessel arriving port.
All line clearance operations must be carefully planned to ensure safe and proper execution. Critical
Operation Checklists should be created and utilised to assist.
Special care must be taken to
ensure that cargo tank and line systems are not over-pressurised or overfilled during such operations
After clearing the cargo lines, the respective valves to be kept closed.
In freezing weather the
vacuum formed in the lines may suck the cargo from the cargo tanks and causing solidification of
pipe lines. Hence it is imperative that the cargo pipe lines are checked daily.
Clearing the Line from the Terminal / Barge or Coaster
Normally the Terminal / Barge / Coaster will clear their lines into the loading vessel’s tanks.
If line clearance into the vessel’s tanks is not possible the line should be cleared into a Slop Tank
(bearing in mind possible reactions with other chemicals / materials which may already be in the
tank) or other suitable containers.
Normally the cargo lines are steamed on the outside of pipe line with live steam and drained into the
tank via drop and delivery lines of respective tanks by blowing with air/nitrogen , as appropriate,
Deepwell Pump Line Clearance
Before putting pressure on the cargo line systems, the lines should be completely secured with all
valves closed and all flanges bolted. When the cargo line system is being pressurised the pump stack
valve or drop line valve should be carefully controlled, the valve should be opened and closed
repeatedly until the line is clear of all cargo (an indication of this can be obtained by listening for the
flow of cargo passing the valve). On completion of the line clearance any residual line pressure must
be released into the drip tray or other suitable container in a controlled manner wearing
General Line Clearance Procedures
This procedure is to be followed whenever line clearance is being carried out by ship or
The operation will be supervised by a responsible officer and the procedure clearly agreed
with the terminal representative. A record of this agreement is to be recorded in the Port
Log and Ship/Shore Checklist.
All involved in line clearance should wear appropriate PPE.
The vessel’s list / trim may complicate the line clearance procedure and special care must be
taken under such circumstances to ensure that lines and systems are clear of residues.
Ensure that the tank into which the line(s) are to be cleared has sufficient ullage to prevent
Ensure a crew member remains at the vessel’s manifold valve for controlling pressure.
Tank vent to be kept open to prevent over tank pressurization. During line clearance
monitor tank vapour pressure continuously to avoid over pressurization.
On completion of clearing the hoses / chicksans systematically close all valves starting at the
Ensure that no pressure remains in the ship’s lines by closing the pump stack or drop line
Ensure no pressure remains in the hoses / chicksans by opening the drain cock outboard of
the manifold valve.
If further line clearance is required (solidifying cargoes, freezing conditions or low freezing
point cargoes) first disconnect the hoses / chicksans, the necessity for further clearance can
be ascertained by knocking the pipeline with a suitable instrument, paying particular
attention to low points in the system.
If the cargo has been loaded via individual manifolds and lines then each system must be
cleared into its individual tanks.
The off shore manifold section shall also be cleared.
Prepare for the displacement by placing blind flanges with suitable connections (steam, air,
Nitrogen) on each side of the manifold.
Ensure that the medium chosen for the line displacement is suitable for the particular cargo
Connect the hoses and supply the selected medium from both sides of the manifold
Ensure that the tank / system is not over pressurised and that there is sufficient ullage
space in the receiving tank to prevent an overflow, by ensuring that tank vent is open
during line clearance and tank vapour pressure is being continuously monitored.
Open the pump stack or drop line valves.
Slowly open the valves on both sides of the manifold controlling the selected cleaning
medium and checking the tightness of all connections.
When clearing each line system, open and close the pump stack or drop line valve
repeatedly until the flow of liquid is no longer detected passing the valve.
When the line is determined as clear, firstly close the supply valve of the purging medium
then close the pump stack or drop line valve.
Ensure that “dead ends” of pipeline systems and vent systems are cleared also.
On completion of each line clearing operation ensure that all valves, flanges and dust caps
are properly sealed and secured.
Precautions to Be Observed During Line Clearance Operations
Clear instructions must be issued with regards to the Procedures and Safety issues to be
observed during clearing operations.
The plan of line clearing must be systematically followed in order to be effective.
Good communications between all parties involved in the line clearing operations are of
The appropriate PPE must be worn by all personnel involved in the cleaning operations; any
personnel not involved in the operation must be kept clear of the area.
The choice of clearance medium (steam / air / Nitrogen) must be considered carefully as the
choice of the wrong medium may affect both the safety of the vessel and the cargo quality
- Compressed Air: may contain water/oil vapour / droplets; static electricity hazards
- Steaming, condensed water will introduce / increase water content of the cargo;
static electricity hazards ; heat may have an
adverse effect on some cargoes and tank/pipeline coatings.
- Nitrogen: this is the most commonly used medium for clearing lines, however
consideration must be given to both the purity of the Nitrogen used and also its use
for line clearance when Oxygen dependent inhibitors have been added to the cargo.
When applying steam to the inside of pipelines always make sure that the condensate and
melted product have an escape route.
Risk Assessments must be carried out for Line Clearance operations and maintained on file.
Although the line clearance procedure should, if correctly and methodically carried out after each
cargo operation, remove all liquid from the cargo lines, the following checks must be carried out in
ample time prior to arrival at the discharge port:
Check the entire cargo lines including the manifold crossovers for possible blockages by
tapping with a suitable instrument.
Check that all cargo valves are moveable and not “frozen”.
Check that vent systems are free to operate and are not blocked.
Ensure that manifolds are free of liquid by opening the drain valves and loosening the
flanges (these must be secured after the checks are completed).
When dealing with cargoes which freeze at ambient temperatures it is important to check
and prevent the cargo lines and valves from becoming blocked or “frozen”. Pay particular
attention to PV lines also and continuously monitor vapour pressure in each tank
particularly when tanks are heated. During heavy weather freezing temperature,
it is possible for PV and IG lines to be filled with solidified cargo blocking these
Voyage planning and related considerations
Preparation for cargo operation
Preparing a cargo tank atmosphere
Cargo unloading operation safety precautions
Liaison between ship and shore
Cargo line leakage countermeasures
Checklist for handling dangerous liquid chemicals in bulk
Recommended temperature monitoring equipments onboard
Practical example of solving tank cleaning problems
Pre-cleaning /washing of cargo tanks
Risk & hazards of chemical contamination onboard
Cargo compatibility and reactivity of various chemical cargo
Poisoning and required first aid treatment onboard
Chemical tanker safe mooring practice
Determining presence of contaminants
in chemical cargo
Handling various grade liquid chemicals during loading
How to prepare a cargo loading or discharge program ?
How to avoid solidification in cargo tanks ?
Cargo segregation requirement for chemical tankers
How to take cargo samples ?
How to arrange disposal of tank cleaning waste ?
Restrictions on discharge cargo residue into sea
Retention of slops on chemical tankers
Vapour emission control requirement for chemical tankers
Handling self reactive chemicals
Handling of toxic chemical cargoes
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