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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.

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.

Chemical Tanker Guide !
Shipboard safe practice relating to seagoing 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

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Handling self reactive chemicals

Handling of toxic chemical cargoes

Risk with noxious liquid cargo contact

The biggest risk of a chemical cargo spill

Cargo handling equipments for handling noxious liquid substances in bulk

Cargo handling safe practices onboard modern chemical tankers

Product information required for various chemical cargo prior loading

Restriction on discharge of cargo residues into sea from chemical tankers

Risk & hazards of chemical contamination onboard

Cargo handling safe practices onboard modern chemical tankers

Cargo hoses handling ,connection and use

Checklist for handling dangerous liquid chemicals in bulk

Ship shore safety checklist

Recommended temperature monitoring equipments onboard

Practical example of solving tank cleaning problems

Pre-cleaning /washing of cargo tanks

Voyage planning and related considerations

Cargo sampling safety precautions

Preparation for cargo operation

Preparing a cargo tank atmosphere

Cargo unloading operation safety precautions

Liaison between ship and shore

Rubber lined tanks, for the transport of phosphoric acid, waste acids and hydrochloric acid.

How to determine the level of a liquid in a chemical tank

Poisoning and required first aid treatment onboard

Reference publications

Main Info pages!

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Chemical Tanker Guide !
Shipboard safe practice relating to seagoing chemical tankers 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

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