Risk of tank over pressurisation & cargo tank lid / Hatch securing methods
Improper closing and sealing of cargo tank hatches can be a major cause of cargo contamination. A
properly closed and sealed tank hatch/opening will prevent sea water ingress and maintain a positive
pressure Nitrogen blanket in the ullage space. Cargo tank hatches must be properly maintained, with
the correct type of tank packing fitted and in good condition (no visible damage/deformation, clean
and free from cargo odours), any doubt as to the suitability or condition of the hatch closing
arrangements must be reported to the Management Office.
Non-Flanged Hatches/Openings
If the hatch cover is fitted with a stong bar, ensure that the securing end is correctly hooked. As the packing is about to make contact with the coaming, visually inspect contact points to insure that the packing is exactly centred on the top of the coaming edge. When hatch cover is properly aligned, correct pressure must be applied to ensure an even tightness between the hatch coaming and the lid.
Fig:Modern Chemical tanker underway
For hatches with more than one securing dog, the dogs must be tightened sequentially in a
criss-cross pattern (12 & 6 o`clock, 9 & 3 o`clock)
When the hatch is properly secured, inspect the actual sealing
Flanged Tank Washing Openings
For hatches with bolts and studs, the bolts must be tightened sequentially in a crisscross pattern (12 & 6 o`clock, 9 & 3 o`clock)
Whenever there is a doubt regarding the tightness of the tank packing, silicon sealer may be applied (silicon may, in some cases, damage packing and should not be used on packing that provide proper sealing in itself). The silicon sealer should be applied on the edge of the hatch coaming before closing down the hatch cover (ensure the hatch is clean and free of rust particles). Whatever action is necessary to prevent water ingress to the tank lid must be taken
When replacing packing on tank hatches, the instruction given by hatch and packing manufacturer must be followed and the edge of the tank hatches/openings must be clean and free from corrosion. Carry out tank Vapour tightness test as per USCG 40 CFR.61.304(f)
Risk of tank over pressurisation
Tank over pressurisation accident the resulting damage could be significant, taking a vessel out of service for several months. In an incident a chemical tanker was loading ethanol in the USA and due to winter conditions the ambient temperature was below zero degrees Celsius. At this time the vessel involved in an accident of tank over pressurisation. The resulting conclusion :
P/V Valves - to be inspected regularly and thoroughly overhauled and decarbonised at least every six months, or more frequently, if specified by the manufacturers’ instructions. In addition. annual testing of each PV valve is to be carried out in the workshop to ensure that both sides of the valve open at the specified pressure and vacuum. All such maintenance is to be recorded in the ships PMP.
With regards to this particular incident it is suspected that the PV valves may have been frozen due to ambient temperatures. Vessels trading in cold weather areas it is essential to check that PV valves and any deck seal heating systems are fully operational.
Loaded Passage
Particular attention to carriage instructions during the loaded voyage is essential in order to maintain product quality integrity which may be affected by variations of temperature, inhibitor levels, moisture and/ or the oxygen content of the containment tank vapours.
Certain chemical products are shipped with specific requirements for the minimum and/or maximum allowable temperatures of both the commodity in question and those parcels stowed in adjacent cargo tanks to ensure that each does not affect the other.
Chemicals sensitive to degradation by oxygen are usually required to be loaded into tanks which have previously been purged with nitrogen to a specified reduced oxygen level. The inert atmosphere must be restored on completion of loading and, by routine monitoring, maintained inert throughout the voyage.
Chemically unstable products, notably those which polymerise over the passage of time are normally shipped with an inhibitor added to prevent the reaction. The inhibitor system may require specific tank atmosphere conditions and during a long voyage it may be necessary to add extra inhibitor if routine cargo tests indicate a decline in inhibitor activity. It is also essential to monitor the temperature of such cargoes.
Related Info:
Types of Chemical tankers at Sea
Available shipbuilding materials for modern chemical tankers
Pre-cleaning /washing of cargo tanks
Final cleaning of cargo tanks prior loading
Tank cleaning and posoning hazards
Testing of tanks and cargoes
Practical tank cleaning methods for various noxious liquid cargo
Special tank cleaning method
Determining proper tank cleaning by acid wash method
Supervision of all tank cleaning and gas freeing operations
Disposal of tank washings, slops and dirty ballast - safe method
Chemical Tanker Guide !
Shipboard safe practice relating to seagoing chemical tankers
Home page ||| Chemical hazards ||| Cargo planning & Stowage ||| Cargo loading ||| Cargo documents ||| Safe stability ||| Cargo care ||| Preparation for unloading ||| Inert gas systems |||Gas freeing ||| Nitrogen handling ||| Chemical handling Safe practice |||Handling equipments ||| Cargo & Ballast pumps ||| Cargo tanks |||Tank cleaning |||Special cargoes |||Spills emergencies |||Fire protection
Chemicaltankerguide.com is merely an informational site about various aspects of chemical tankers and safety tips that may be particular value to those working in: Chemical Handling, Chemical Storage, Liquefied Chemical Suppliers, Chemical Shipping, Chemical Transportation, Chemical Terminals, Bulk Chemical Services and Chemical Processing. If you are interested in finding out more about chemical tanker guideline please visit IMO official website. For any comment please Contact us
Copyright © 2011 Chemical Tanker Guide.com All rights reserved.
If the hatch cover is fitted with a stong bar, ensure that the securing end is correctly hooked. As the packing is about to make contact with the coaming, visually inspect contact points to insure that the packing is exactly centred on the top of the coaming edge. When hatch cover is properly aligned, correct pressure must be applied to ensure an even tightness between the hatch coaming and the lid.
Fig:Modern Chemical tanker underway
When the hatch is properly secured, inspect the actual sealing
Flanged Tank Washing Openings
For hatches with bolts and studs, the bolts must be tightened sequentially in a crisscross pattern (12 & 6 o`clock, 9 & 3 o`clock)
Whenever there is a doubt regarding the tightness of the tank packing, silicon sealer may be applied (silicon may, in some cases, damage packing and should not be used on packing that provide proper sealing in itself). The silicon sealer should be applied on the edge of the hatch coaming before closing down the hatch cover (ensure the hatch is clean and free of rust particles). Whatever action is necessary to prevent water ingress to the tank lid must be taken
When replacing packing on tank hatches, the instruction given by hatch and packing manufacturer must be followed and the edge of the tank hatches/openings must be clean and free from corrosion. Carry out tank Vapour tightness test as per USCG 40 CFR.61.304(f)
Risk of tank over pressurisation
Tank over pressurisation accident the resulting damage could be significant, taking a vessel out of service for several months. In an incident a chemical tanker was loading ethanol in the USA and due to winter conditions the ambient temperature was below zero degrees Celsius. At this time the vessel involved in an accident of tank over pressurisation. The resulting conclusion :
- The vessel did not comply with procedures for testing and maintenance of Pressure / Vacuum valves
- The vessel did not comply with procedures for testing of secondary venting system
- The vessel did not comply with procedures and checklists for loading operations, e.g. an approved loading plan was not available at anytime during loading operations.
- The vessel was aware of the predicted sub-zero temperature but no additional precautions were undertaken to verify correct operation of PV valves.
P/V Valves - to be inspected regularly and thoroughly overhauled and decarbonised at least every six months, or more frequently, if specified by the manufacturers’ instructions. In addition. annual testing of each PV valve is to be carried out in the workshop to ensure that both sides of the valve open at the specified pressure and vacuum. All such maintenance is to be recorded in the ships PMP.
With regards to this particular incident it is suspected that the PV valves may have been frozen due to ambient temperatures. Vessels trading in cold weather areas it is essential to check that PV valves and any deck seal heating systems are fully operational.
Loaded Passage
Particular attention to carriage instructions during the loaded voyage is essential in order to maintain product quality integrity which may be affected by variations of temperature, inhibitor levels, moisture and/ or the oxygen content of the containment tank vapours.
Certain chemical products are shipped with specific requirements for the minimum and/or maximum allowable temperatures of both the commodity in question and those parcels stowed in adjacent cargo tanks to ensure that each does not affect the other.
Chemicals sensitive to degradation by oxygen are usually required to be loaded into tanks which have previously been purged with nitrogen to a specified reduced oxygen level. The inert atmosphere must be restored on completion of loading and, by routine monitoring, maintained inert throughout the voyage.
Chemically unstable products, notably those which polymerise over the passage of time are normally shipped with an inhibitor added to prevent the reaction. The inhibitor system may require specific tank atmosphere conditions and during a long voyage it may be necessary to add extra inhibitor if routine cargo tests indicate a decline in inhibitor activity. It is also essential to monitor the temperature of such cargoes.
Related Info:
Types of Chemical tankers at Sea
Available shipbuilding materials for modern chemical tankers
Pre-cleaning /washing of cargo tanks
Final cleaning of cargo tanks prior loading
Tank cleaning and posoning hazards
Testing of tanks and cargoes
Practical tank cleaning methods for various noxious liquid cargo
Special tank cleaning method
Determining proper tank cleaning by acid wash method
Supervision of all tank cleaning and gas freeing operations
Disposal of tank washings, slops and dirty ballast - safe method
Chemical Tanker Guide !
Shipboard safe practice relating to seagoing chemical tankers
- Cargo calculation & related guideline
- Signing a Bill of lading & related problems
- Issuing notice of readiness and related guideline
- Cargo claims and issuing letter of protest
- Statement of facts
- Avoiding cargo claims - Chemical tanker procedure
Home page ||| Chemical hazards ||| Cargo planning & Stowage ||| Cargo loading ||| Cargo documents ||| Safe stability ||| Cargo care ||| Preparation for unloading ||| Inert gas systems |||Gas freeing ||| Nitrogen handling ||| Chemical handling Safe practice |||Handling equipments ||| Cargo & Ballast pumps ||| Cargo tanks |||Tank cleaning |||Special cargoes |||Spills emergencies |||Fire protection
Chemicaltankerguide.com is merely an informational site about various aspects of chemical tankers and safety tips that may be particular value to those working in: Chemical Handling, Chemical Storage, Liquefied Chemical Suppliers, Chemical Shipping, Chemical Transportation, Chemical Terminals, Bulk Chemical Services and Chemical Processing. If you are interested in finding out more about chemical tanker guideline please visit IMO official website. For any comment please Contact us
Copyright © 2011 Chemical Tanker Guide.com All rights reserved.