Category X:
Noxious Liquid Substances which, if discharged into the sea from tank cleaning or deballasting operations, are deemed to present a major hazard to either marine resources or human health and, therefore, justify the prohibition of the discharge into the marine environment.
Examples are Acetone Cyanohydrin, Carbon Di Sulphide, Nonyl Phenol, Di Butyl Pthalate, Epichlorohydrin, Ethyl Acrylate Monomer, Vinyl Toluene, Butyl Benzyl Pthalate, Alpha Methyl Styrene, Calcium Naphthalate etc. Cumene has been down graded from 1st Jan 2007 from A to Y—however more stringent stripping is required.
You are not allowed to discharge Cat X washings into the sea. A tank from which a substance in Category X has been unloaded, shall be prewashed before the ship leaves the port of unloading. The resulting residues shall be discharged to a reception facility until the concentration of the substance in the effluent is below 0.1% by weight. When the required concentration level has been achieved, remaining tank washings shall continue to be discharged to the reception facility until the tank is empty. See P&A manual for the water quantity and number of cycles.
The Govt Surveyors sign and stamp has to be endorsed on the Cargo record book entry. For prewash one cleaning cycle is defined as two consecutive identical rotations of 360 degrees . Any water subsequently introduced into the tank may be discharged into the sea in accordance with the discharge standards in regulation
When discharging Cat X cargoes superstrip is not mandatory as you are prewashing ashore till the tank is empty.
To find out how much water to use in prewash for 0.1% conc by weight—
Find out how many m3 of water is ejected in one cycle. At 13 m3 /hr and 7.5 min for one cycle, it is 1.63 m3 ( 13/60 X 7.5 )
1.63 X no of cycles X no of machines ( as per P&A manual )
The residual quantity of pre-wash tank washings in:--
1) Volume of water to use ( CuM )
2) Duration of wash in minutes
is tabled in the P&A manual for each cargo tank .
Both tables will have the value K on the X axis and the ships cargo tanks on the Y axis.
k = a factor having values as follows:
Category X, non-Solidifying, Low-Viscosity Substance, k = 1.2
Category X, Solidifying or High-Viscosity Substance, k = 2.4
Category Y, non-Solidifying, Low-Viscosity Substance k = 0.5
Category Y, Solidifying or High-Viscosity Substance k = 1.0
Typical pre-wash volumes in CuM / times in minutes---------- for a SS tank of 1500 cum with portable machines (15 cum/ hour ) would be:--
Proforma--- K/ Volume in CuM / Duration in Minutes
0.5/ 1.02 / 4.1
1.0/ 2.03 / 8.1
1.2/ 2.44 / 9.8
2.4/ 4.88 / 19.5
A cleaning machine cycle is defined as the period between two consecutive identical orientations of the machine (rotation through 360°).
After washing, the cleaning machine(s) shall be kept operating long enough to flush the pipeline, pump and filter,and discharge to shore reception facilities shall be continues until the tank is empty.
Number of cleaning machine cycles to be used in each location
Category of substance | Number of cleaning machine cycles | |
Non-Solidifying Substances | Solidifying Substances | |
Category X | 1 | 2 |
Category Y | 1/2 | 1 |
Prewash procedures for non-Solidifying Substances : Tanks shall be washed by means of a rotary water jet, operated at sufficiently high water pressure. In the case of Category X substances cleaning machines shall be operated in such locations that all tank surfaces are washed. In the case of Category Y substances only one location need be used.
Prewash entries in Oil record book –Annex 2:
Identify port---Identify tank(s), substance(s), category(ies) discharged ashore---Have tank(s), pump(s), and piping system(s) been emptied?---Has a prewash in accordance with the ship’s procedures and arrangements manual been carried out?---Have tank washings resulting from the prewash been discharged ashore and is the tank empty?---An exemption has been granted from mandatory prewash---Reasons for exemption----Name and signature of authorized surveyor.----Organization, company, government agency for which surveyor works.
Category Y –
Noxious Liquid Substances which, if discharged into the sea from tank cleaning or deballasting operations, are deemed to present a hazard to either marine resources or human health or cause harm to amenities or other legitimate uses of the sea and therefore justify a limitation on the quality and quantity of the discharge into the marine environment;
Examples are Acrylonitrile, Biodiesels, Carbon Tetrachloride, Caustic coda , Ethylene di Chloride , MDI, Lub Additives, Phenol, Sulphuric acid, Benzene, Toluene, Xylene, Ethylene Glycol , Methanol, Lard, Palm Oils, All VEG OILS and FATS, Hexane, Vinyl acetate etc.
For High-Viscosity or Solidifying Substances in Category Y the following shall apply ( note –the values are given in the cargo list of P&A manual ) :
1 a prewash procedure shall be applied;
2 the residue/water mixture generated during the prewash shall be discharged to a reception facility until the tank is empty; and
.3 any water subsequently introduced into the tank may be discharged into the sea
High-Viscosity Substance means a noxious liquid substance in Category X or Y with a viscosity equal to or greater than 50 mPa.s at the unloading temperature.
Solidifying Substances and substances with viscosity equal to or greater than 50 mPa.s at 20°C shall be washed with hot water (temperature at least 60°C) when water is used as the washing medium, unless the properties of such substances make the washing less effective.
Only solidifying and viscous Category Y cargoes need to be prewashed ashore (with >60 deg C water) prior departure discharge port.
Solidifying means –---if MP>15C and dischg temp of cargo is within 10 deg C/ if MP<15C and dischg temp of cargo is within 5 deg C.
Prewash procedures for Solidifying Substances
1 Tanks shall be washed as soon as possible after unloading. If possible tanks shall be heated prior to washing.
2 Residues in hatches and manholes shall preferably be removed prior to the prewash.
3 Tanks shall be washed by means of a rotary water jet operated at sufficiently high water pressure and in locations to ensure that all tank surfaces are washed.
4 During washing the amount of water in the tank shall be minimized by pumping out slops continuously and promoting flow to the suction point (positive list and trim). If this condition cannot be met, the washing procedure shall be repeated three times with thorough stripping of the tank between washings.
5 Tanks shall be washed with hot water (temperature at least 60°C) unless the properties of such substances make the washing less effective.
6 The number of cycles of the cleaning machine used shall not be less than that specified in table 6-1. A cleaning machine cycle is defined as the period between two consecutive identical orientations of the machine (rotation through 360°).
7 After washing, the cleaning machine(s) shall be kept operating long enough to flush the pipeline, pump and filter,and discharge to shore reception facilities shall be continues until the tank is empty.
Table 6-1 -- Number of cleaning machine cycles to be used in each location
Category of substance | Number of cleaning machine cycles | |
Non-Solidifying Substances | Solidifying Substances | |
Category X | 1 | 2 |
Category Y | 1/2 | 1 |
Those substances which have a viscosity equal to or greater than 50 mPa.s at 20°C shall be washed with hot water (temperature at least 60°C), unless the properties of such substances make the washing less effective.
Prewash procedures for non-Solidifying Substances : Tanks shall be washed by means of a rotary water jet, operated at sufficiently high water pressure. In the case of Category X substances cleaning machines shall be operated in such locations that all tank surfaces are washed. In the case of Category Y substances only one location need be used.
Recycled medium prewash—Can be adopted for washing more than one tank. The cargo concentration in the water / medium 5% based on stripping test quantities of the P&A manual.
Every ship constructed on or after 1 July 1986 but before 1 January 2007 shall be provided with a pumping and piping arrangement to ensure that each tank certified for the carriage of substances inCategory X or Y does not retain a quantity of residue in excess of 100 litres in the tank and its associated piping
The definition of high viscosity in the revised Annex II would mean that a lot of vegetable oils (primarily the soft oils) could be required to be prewashed.
It has been suggested that for certain oils, such as Soyabean oil, the discharge temperature could be raised slightly to bring the product out of the high viscosity range, thus obviating the need for a prewash, and the vegetable oil industry has been considering the issue. FEDIOL (the European refiners association) have, however, recently advised that they are not prepared to alter the heating instructions in respect of vegetable oils. This will mean that a prewash is inevitable for a number of oils.
It should be noted that the revised Annex II requires that the prewash and discharge ashore should be carried out in the port of unloading unless a port that the vessel is due to call at later has confirmed in writing that it has a reception facility available that is adequate for the purpose. The unloaded tank must be neither washed nor ballasted at sea before the prewash can be carried out.
Prudent masters must ensure the availability of shore reception facilities, till all are familiar will the new regulations.
Regarding the DH ( discharge temperature ), --for solidifying or high viscosity cargoes which have been identified as being required to be a certain minimum temperature during unloading-- If P-Xylene was discharged at temperature of 17°C, the tank cleaning slop of the cargo should be discharged to a reception facility because it is a solidifying cargo defined as Solidifying substance.
It means --in case of substances with melting points less than 15°C, is at a temperature, at the time of unloading, of less than 5°C above its melting point.
