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Cargo tank damage during pigging operations on a chemical tanker

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.

The pre-cargo meeting shall include full information regarding the final stage of cargo operations - any blowing or pigging. Standard procedures must be followed, including throttling the manifold valve and venting the tank. Line clearing shall be considered as critical operation and subject of risk assessment . Vessel should confirm during the pre-operation meeting with the terminal if the pigging / blowing operation would be towards the ship’s tank. This should be avoided if the ship’s tanks are nearly full.



chemical tanker navigation at sea
Maintenance of cargo monitoring equipment, such as pressure sensors, must be done at the earliest opportunity after any defects are found. Ship’s manifold must not be left unattended during blowing or pigging operations and manifold valves must be closed during idle periods.


Buckled Slop Tank Bulkhead
Fig: Buckled Slop Tank Bulkhead

Onboard a chemical tanker an incident occurred during loading operations at a US Gulf port.

The port slop tank (PST) had been nominated for loading of Crude Degummed Soybean Oil. The cargo equipment was checked and inspected as per company requirements prior to arrival, during which the PST remote pressure transducer was found inoperative.

Bulk loading into the port side tank was completed at 0615 on the day of the incident with the ship lines and shore hose blown shortly after.

At 1830 the Terminal asked the vessel to re-open the PST for further blowing and commenced blowing the shore line into PST. The Terminal advised the vessel to keep the manifold open. At 2315 the Duty Officer heard a heavy striking noise on deck and noticed air blowing out of the PST pressure valve under high pressure. Cargo operations were stopped immediately. On investigation it was found that cargo was migrating from PST into COT 6 port. All adjacent tanks were inspected and cargo was also found in the WBT 6 port.

What Went Wrong ( Critical Factors ):

Although the terminal advised they were blowing the lines, actually the terminal was pigging the line. The terminal incorrectly considered blowing and pigging as similar operations.

Communication and information from the terminal to the ship interface was inadequate

The ship’s PST manifold valve was kept opened from 1830 till the time of the incident. This was requested by the terminal. The terminal did not provide an estimated time of completion for the clearance of the shore pipeline system, thus the ship’s crew did not know when to anticipate completion. The manifold valve was left unattended during mentioned period.

Whilst the pressure transmitter in the PST was inoperative, the pressure in the tank was monitored on the local tank gauge. A spare pressure transmitter was available on board but it had not been fitted.



Related info:
  1. 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.

  2. 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).

  3. 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.

  4. 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.

  5. 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.

  6. Final cleaning of cargo tanks prior loading
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  7. Tank cleaning and posoning hazards
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  8. Testing of tanks and cargoes
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  9. Practical tank cleaning methods for various noxious liquid cargo
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  10. Special tank cleaning method
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  11. Determining proper tank cleaning by acid wash method
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  12. Supervision of all tank cleaning and gas freeing operations
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  13. Disposal of tank washings, slops and dirty ballast - safe method
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  14. 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.

  15. 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.

  16. 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.

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  19. Loading, discharging & care of Phenol - Safety guideline
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  20. Hazards of Phenol - safe handling of Phenol on chemical tankers.
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  21. Handling benzene & methanol safety precautions
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  22. Personal protective equipments for carcinogens & cyanide-like cargoes onboard chemical tankers
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  23. Handling ACRYLONITRILE safety precautions
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  24. 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.

  25. 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.



Reference publications



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