How to determine proper tank cleaning by acid wash onboard chemical tankers ?
The range of chemicals shipped in bulk now has been increased enormously and to maintain product quality proper tank cleaning is essential prior loading cargo.
The acid wash method is used if there is any suspicion that a cargo of aromatics may have been contaminated by a previous oil cargo.
The method is also used as a check that a tank is sufficiently cleaned before loading aromatics. A surface of about one m2 is carefully cleaned with clean cotton and an aromatic, e g toluene, and the liquid wrung out and tested as the cargo sample mentioned above. One can also take rust sediments (uncoated tanks) and dissolve any oil contaminants by means of toluene, which is then tested by this method.
The acid wash method is used if there is any suspicion that a cargo of aromatics may have been contaminated by a previous oil cargo.
The method is also used as a check that a tank is sufficiently cleaned before loading aromatics. A surface of about one m2 is carefully cleaned with clean cotton and an aromatic, e g toluene, and the liquid wrung out and tested as the cargo sample mentioned above. One can also take rust sediments (uncoated tanks) and dissolve any oil contaminants by means of toluene, which is then tested by this method.
This method is used to determine if petroleum hydrocarbons are present in aromatic compounds. Aromatics (e.g
toluene, xylene, benzene) are unaffected by sulphuric acid, but oils and most other contaminants are affected,
causing a discolouration. The method is suited for application on board and can be used as a check that proper tank
cleaning has been accomplished.
A test tube is filled with 7 cc conc (96 %) sulphuric acid, on top of which is filled 21 cc of the product sample. The tube is then shaken 40 - 50 seconds (150 times) and is then left to settle for a period of time. The colour of the acid in the bottom of the tube is then compared with the standard shades where 0 corresponds to water and 14 to a dark yellow colour.
Finally a difficult question arises: how much of cargo contaminants can be tolerated on the tank wall? Make tests and train your own judgement!
Hydrocarbons in methanol - "water miscibility test"
Methanol is very sensitive to oil contaminants. The following test method uses methanol as a testing medium. The methanol must therefore be guaranteed free from any hydrocarbon contaminants.
About one m2 of the tank wall is carefully washed with cotton and about 40 cc methanol. The methanol is wrung out and put into a test tube. Then 60 cc distilled water is added. The mixture is well shaken and left to settle for 20 min. If the solution remains a clear liquid the tank wall can be considered to be clean, but if the solution has turned milky or only slightly milky it is an indication that the tank should be cleaned again before loading methanol or any other oil-sensitive cargo.
This method should be a standard practice to be carried out by the ship's personnel. The method can, of course, also be used as a check on the cargo upon loading and discharging.
Related info:
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A test tube is filled with 7 cc conc (96 %) sulphuric acid, on top of which is filled 21 cc of the product sample. The tube is then shaken 40 - 50 seconds (150 times) and is then left to settle for a period of time. The colour of the acid in the bottom of the tube is then compared with the standard shades where 0 corresponds to water and 14 to a dark yellow colour.
Finally a difficult question arises: how much of cargo contaminants can be tolerated on the tank wall? Make tests and train your own judgement!
Hydrocarbons in methanol - "water miscibility test"
Methanol is very sensitive to oil contaminants. The following test method uses methanol as a testing medium. The methanol must therefore be guaranteed free from any hydrocarbon contaminants.
About one m2 of the tank wall is carefully washed with cotton and about 40 cc methanol. The methanol is wrung out and put into a test tube. Then 60 cc distilled water is added. The mixture is well shaken and left to settle for 20 min. If the solution remains a clear liquid the tank wall can be considered to be clean, but if the solution has turned milky or only slightly milky it is an indication that the tank should be cleaned again before loading methanol or any other oil-sensitive cargo.
This method should be a standard practice to be carried out by the ship's personnel. The method can, of course, also be used as a check on the cargo upon loading and discharging.
Related info:
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Fixed and portable tank cleaning equipments
The installation of fixed tank washing machines within a cargo tank allows an inert atmosphere to be maintained during the washing operation, and thus permits cleaning in a closed mode in compliance with port regulations prohibiting release of noxious vapours. Their installation and use also reduces crew exposure to cargo vapours and inert gas.
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Tank cleaning and risk with cargo contact
Different chemicals affect the human body in many different ways. A general information and some practical advice are available in Appendix,7, of "Medical first aid guide for use in accidents involving dangerous goods" published by IMO, WHO and ILO ref (36). -
Practical example of solving tank cleaning problems
Cleaning of tanks is usually the responsibilty of the ship. Tank cleaning and the cleanliness involved have different standards depending upon the previous cargo and the cargo to be loaded. But the matter can be still more complicated, as cleanliness for one and the same product may vary, depending on who the receiver is and for what purpose the cargo is finally intended. -
Tank cleaning fatality- case study & lessons learned
In the trade practice onboard chemical tankers, it is not uncommon that the use of methanol or other chemical/detergents is undertaken to achieve the required standard of cleanliness inside the cargo tank, pipelines, cargo hoses, manifold adaptors/reducers, gauging equipment, etc. Industry publications clearly highlight and caution regarding their use due to their flammability and toxicity hazards. -
Pre-cleaning /washing of cargo tanks
Washing between different grades of cargo is the most common reason for tank cleaning. In most cargo sequences on chemical tankers, this cleaning may consist of no more than a simple hot or cold seawater wash. A simple water wash will disperse many types of chemicals and has been found effective between clean petroleum products such as gas oil and kerosene. - Final cleaning of cargo tanks prior loading
Method of final cleaning to be used depends on both previous cargo and cargo to be loaded. As a general rule the tanks and piping shall be completely drained of water or residues before loading. The bottom of the tanks may have to be dried up with rags. - Tank cleaning and posoning hazards
Certain substances affect the tissues locally as an irritant (cashew nut shell oil) or cause grave damage to the eyes, skin or mucous membranes (e g strong acids and caustic). Other substances may be absorbed by contact to the skin without local effects (e g nitrobenzene, aniline). - Testing of tanks and cargoes
Most common tests and checks for oil and chemical cargoes include testing tank walls for cleanliness. Testing is normally carried out by independent surveyors who, according to local practice or a written agreement in the charter party, are accepted by shipper, receiver and owner. -
Practical tank cleaning methods for various noxious liquid cargo
Tanks that may have contained monomer or drying oils should first be cleaned with sufficient cold water quantities to avoid polymerization of cargo residues. In some cases, it is necessary to employ tank cleaning chemicals, but their use is generally limited as it may be difficult to dispose of slops. -
Special tank cleaning method
If a special method involving cleaning agents is to be used, it may create an additional hazard for the crew. Shipboard procedures should ensure that personnel are familiar with, and protected from, the health hazards associated with such a method. The cleaning agents may be added to the wash water or used alone. The cleaning procedures adopted should not entail the need for personnel to enter the tank. -
Determining proper tank cleaning by acid wash method
The acid wash method is used if there is any suspicion that a cargo of aromatics may have been contaminated by a previous oil cargo. The method is also used as a check that a tank is sufficiently cleaned before loading aromatics. -
Supervision of all tank cleaning and gas freeing operations
Tank cleaning is essential on-a chemical tanker, but it must be recognised as a potentially hazardous operation, and rigorous precautions should be observed throughout the process. Together with gas freeing, it is probably the most hazardous operation routinely undertaken on a chemical tanker. -
Disposal of tank washings, slops and dirty ballast - safe method
During normal operations of a chemical carrier, the main need to dispose of chemical residues, slops or water contaminated with cargo will arise during or immediately after tank cleaning. Final disposal of slops or washwater should be in accordance with the ship's P&A Manual. Tank washings and slops may be retained on board in a slop tank, or discharged ashore or into barges. -
Cargo tank damage during pigging operations
Blowing and pigging of pipelines at terminals poses inherent risks for the terminal and a chemical tanker. Frequent damages to tanks have occurred. If there are doubts about the shore operation or signs of problems ashore the OOW must immediately request clarification. -
Determining water contamination in chemical cargo
Presence of free water in non water-soluble products can, very roughly be determined on board by warming a sample of the product in a test tube or in a bottle. Water will then collect at the bottom of the tube and can be seen after some time. -
Determining Sulphur contamination (sulphides) in chemical cargo
Certain products, in particular "virgin naphta feedstock'' (petroleum naphta) are severely contaminated by minor amounts of sulphides (and also lead compounds), which poison catalysts in further processing. Previous heavy oils or dirty harbour ballast water may have left traces of sulphides in the cargo tanks. -
Chloride contamination in chemical cargo - how to resolve?
Certain cargoes are very senstive to chloride contamination, in particular glycols, methanol, ethanol . The tanks should be finally washed with fresh water. However, chlorides (salt) may still be present and a check might be useful. The greatest risk for salt deposits is on horizontal surfaces. -
APHA (Hazen) method for determining color of very light chemical products
A method called APHA (Hazen) is often used for very light products, defined in ASTM D-1209, viz aromatics, ketones. This colour scale is defined with an origin in 100 cc distilled water (value 0) to succesively higher values (max 500) by adding APHA-solution (a platinum-cobolt salt solution). -
Loading, discharging & care of Phenol - Safety guideline
PHENOL is carried at sea in a generally pure state. As a result, it has a high freezing point of approximately 40~ 41deg C. PHENOL is also extremely dangerous when it comes into contact with the eyes or skin and can be fatal. -
Hazards of Phenol - safe handling of Phenol on chemical tankers.
Phenol must be carried at temperatures within charterers instructions, typically between +50 and + 60 degrees C. Heating instructions of the Shipper or Owners must be followed to avoid protests and delays in the port of discharge. Overheating can damage this cargo. A full cargo heating log must be maintained. -
Handling benzene & methanol safety precautions
Benzene is known as a strong carcinogen and known to cause leukaemia. When handling cargoes with more than Benzene concentration of 0.5%, the Master is to ensure that all personnel involved are aware of the long term hazards. -
Personal protective equipments for carcinogens & cyanide-like cargoes onboard chemical tankers
A carcinogen is a substance that may cause cancer by contact or by inhalation. It is therefore essential that the highest safety precautions are taken when handling these cargoes. Access to deck areas must be restricted to duty personnel only. All accommodation doors and ports must be closed and ventilation put on recirculation. Any member of crews involved in cargo operations must wear chemical protective suits and breathing apparatus -
Handling ACRYLONITRILE safety precautions
ACRYLONITRILE are high value and require sophisticated handling for safety, health and loss prevention reasons. They need careful consideration prior loading , tank coating compatibility, cross compatibility with other cargoes carried, environmental controls if required (inerting). -
handling ISOCYANATES safety precautions
Product safety data sheets may be available from various sources. For safety preparation, until the specific product safety data sheet can be obtained, Chemical Data Guide for Bulk Shipment by Water (U.S. DoT), should be used. -
Loading, carrying & discharging of Sulphuric acid - regulatory requirements & special handling methods
IBC code compatibility chart strictly prohibits water in adjacent compartment to Sulphuric acid as you are aware if both come in contact with each other will generate a violent reaction. It is therefore recommended that the during loading of sulphuric acid adjacent ballast tanks to be always stripped dry to the maximum efficiency of the deballasting equipment used.
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 |||Enclosed space Procedures |||Hot work Precautions ||| Shipbuilding |||
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
Terms of use |||Privacy policy||| Home page
Copyright © 2011 Chemical Tanker Guide.com All rights reserved.