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Post What is the "Gas Free" Process for Cleaning Oil Tankers?
Created by John Eipper on 09/16/20 4:16 AM

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What is the "Gas Free" Process for Cleaning Oil Tankers? (Eugenio Battaglia, Italy, 09/16/20 4:16 am)

John E asked about the "gas free" process for cleaning oil tankers.  It is the most important job carried out by the crew.

After discharging the cargo, the ship is completely washed out.  But contrary to the practice until the early 1970s, no oil can be discharged at sea. All cleaning water sprayed into the tank from big pumps and rotating nozzles must be recovered in a special slop tank, where it can undergo decantation.  The clean water is then slowly discharged, with care taken not to discharge any oil. The sludge at the bottom of the tanks is then recovered by hand by the crew after going inside. Of course, prior to entering a cleaned tank, it has to be well ventilated, and then the atmosphere inside the tanks must be checked for the possible presence of gas with a special instrument handled by the Chief Officer (or Captain) who is also the first to enter. Generally, I wanted to go first unless my presence was required on the bridge. As you know if the crew is motivated, it works much better and the captain working first with the crew is the best way to motivate. Well, offering a beer or going to dinner with the crew also helps.

Prior to any shipyard work in port, all the sludge and slop (remaining oil) must be discharged and the slop tank completely cleaned discharging ashore.

On the occasion I mentioned in my post of September 15th, the new law had just been enacted.  Someone in the office (at the mid-levels)  was betting that I did not know about the new stricter law, as earlier it had been possible to discharge oil in the open seas provided that the ship was at least 50 nautical miles away from land and it could be shown that repairs were being performed on the ship.  Dumping at sea would save a lot of money.  A VLCC tanker could previously discharge up to 1000 tons of oil at sea, which it is frightful.

A port captain flew from Chicago to Tenerife to try to convince me that if I doctored the Ship's Log in a certain way I could have discharged oil and contaminated water.  Of course, he refused to give me a written order or a written specification on how to write the false log entry.  I did not carry out these illegal instructions.  This could have angered some in the company, but I had the law behind me.

I assume that I was the only captain who refused such a request, but I was betting on the support of Captain Phillips.

I hope to have explained this complex process. It is a specific job that can be difficult to explain to laypersons without tanker experience.

JE comments: Read WAIS every day, and you'll never fail to learn something! Imagine how many millions of gallons of gunky crude were intentionally dumped in the oceans in the old days.  Horrifying. Eugenio, you may have landed yourself in trouble with some of your unscrupulous supervisors, but Mother Earth and Father Neptune thank you.

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  • Environmental Regulations for Oil Tankers in the 1970s (Eugenio Battaglia, Italy 09/18/20 3:58 AM)
    As a followup to my post on the "gas free" process for cleaning oil tankers (September 16th), WAISers may be interested in the following:

    The 1970s were a revolutionary decade for the oil transportation industry, when the MARPOL 73/78 (International Convention for the Prevention of Pollution from Ships) finally declared that the pollution of the seas by oil, refuse, black waters, etc. was forbidden.

    But other important innovations came out during the decade:

    1) Crude Oil Washing. The term itself sounds astonishing. While two pumps discharge ashore, a third one pumps the crude oil through jet rotating nozzles into the tanks being discharged. The spreading oil significantly cleans the bulkheads, highly reducing the amount of sludge and the oil remaining on board.

    2) Inert Gas System. This system is deployed to prevent an explosion in the cargo tanks of a ship. In this integrated system, while pumping out the inflammable liquid cargo, an inert gas, generally flue gas from the ship's boilers, is pumped in. Also, a loaded ship tops off the loaded tanks with inert gas.

    In 1978 we had the disaster of the Amoco Cadiz, which ran aground on the coast of Brittany with the loss of the ship with 221 hundred metric tons of cargo and about 4000 tons of fuel. The ensuing inquiry discovered that the wreck was caused by the shearing of smaller than required (a shipyard mistake) threaded studs in the ram steering. Therefore a second redundant system was mandated.

    Years later, Regulation 19 Annex I to MARPOL specified that new tankers launched after 1996 should have double bottoms and double hulls separated from the cargo tanks, which can be used as clean ballast tanks.

    With the imposition of the above rules, the shipping industry is safer while the sea is cleaner.

    JE comments:  Despite the decade's reputation for economic stagnation and bad fashion, the 1970s were triumphant for the environment.  In 1969 we had burning rivers in Cleveland.  On January 1st, 1970, President Nixon signed the EPA into existence.  Somehow we missed this Golden Anniversary on WAIS.

    A few days ago I saw an article that reflected on where we'd be now if we hadn't tackled air pollution through intelligent laws and technical innovation.  (The focus was on vehicle emissions.)  Some cities such as Los Angeles would literally, not metaphorically, be unable to sustain human life.

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