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Procedure for testing of tanks and cargo onboard chemical tankers

The range of chemicals shipped in bulk has increased enormously in modern days .The need to maintain product quality, to minimise the potential for discoloration, and to facilitate tank cleaning between cargoes it is essential to test tanks and cargo at times and when required.

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.

Chemical tanker pipeline system
Fig : Chemical tanker pipeline system

If possible one of the ship's deck officers should take part in the cargo sampling, cargo testing, tank cleanliness examination etc. He should make notes and observations on the work of the surveyor with a view of protecting his party's interests. It is therefore necessary to have a general knowledge of the various procedures, without necessarily being able to carry them out himself. Some tests which are easily carried out by the ship's staff by relatively simple means. A small laboratory with a stainless steel sink, a rack for 10 - 20 bottles of chemical reagents, test tubes (Nessler tubes) and a supply of distilled water are an advantage to have on board.

In some remote ports independent surveyors may not be available. This gives the chief officer added responsibility in following the shipper's or receiver's instructions, particularly if he is requested to sign their protocols etc.

There are number of tests, which are commonly used by surveyors. Most of the tests are of a physical nature and are relatively easy to carry out on board. Normally the test results do not give any exact answers as to contaminations etc but have to be judged in relation to commonly accepted standards in industry or agreed values between the parties. Furthermore, the answers are often only indices of contaminations. In case of any disagreement full laboratory examinations may have to be carried out. It is then of the outmost importance that the ship secures samples, sealed by an independent surveyor or by both parties, of the cargo parcel in question for further analysis.

ASTM (American Society for Testing and Materials) - standards are contained in a series of updated books, obtainable through good bookstores or from: American Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103, USA.

Similarly API (American Petroleum Institute) issues various standards, which are generally applied. All measurements and tests have their tolerances, usually rather widespread and with correspondingly great economic consequencies. It is good practice to take all readings twice, repeat important tests twice etc!

With ships engaged in special trades it might be useful to be able to carry out the more common tests on board and to train personnel correspondingly. This refers in particular to the testing of tank walls for cleanliness. Many delays can be avoided if the ship's officers can satisfy themselves that the tanks are properly cleaned before entering port, using the same methods as the surveyor coming on board does.

Cargo Lines and Fittings

Inspection of the cargo pumping, piping and tank heating equipment is an essential part of the preloading survey for determining a vessel's suitability to load a sensitive chemical product. Although many chemical parcel tankers have dedicated cargo piping and individual submersible cargo pumps and heating coils for each tank, it is still possible for the residues of a previous cargo, tank washing solutions, water and/or heat exchange fluid to be retained in drained piping, cargo pump cofferdam spaces and leaking heating coils.

It is therefore essential that tank cleaning operations include thorough line cleaning, draining of cargo piping and heating coils, blowing of cargo pump cofferdam spaces, as well as pressure testing of heating coils and submersible cargo pump seals.

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Tank cleaning and risk with cargo contact

Securing tank lids & safety precautions

Practical example of solving tank cleaning problems

Tank cleaning fatality- case study & lessons learned

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

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Determining proper tank cleaning by acid wash method

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Disposal of tank washings, slops and dirty ballast - safe method

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Use of liquid level gauges determining tank levels in cargo tanks

Requirement of Gas freeing prior entering in a cargo tank

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