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:
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, simultaneously .
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 suitable PPE.
General Line Clearance Procedures
This procedure is to be followed whenever line clearance is being carried out by ship or shore.
All involved in line clearance should wear appropriate PPE.
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.
Precautions to Be Observed During Line Clearance Operations
- 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.
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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