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Extracted from "A Half Century of Maritime Technology 1943-1993". Reprinted with the permission of the Society of

Naval Architects and Marine Engineers (SNAME). Material originally appearing in SNAME publications cannot

be reprinted or reproduced without written permission from the Society, 601 Pavonia Ave., Jersey City, NJ 07306.

Refined Product and Speci -ty TankersMAURICE GORDONPetrolewn Product TankersD URING WORLD WAR II there was a considerablemovement of refined products from the GulfCoast refineries to the East Coast and to Europe. Thistrend cont inued until the late 1950s. Most of thetankers built in that period were similar in arrangement to crude oil tankers and, in many cases, theywere used interchangeably. Cargo in those ships wascarried in :2.4 to 30 tanks arranged in four isolatedsystems with double valved crossover piping. Thispermitted the ship to handle up to four grades ofcargo with a minimum possibiliry of contamination. Large quantities of gasoline, diesel oil, aviationfuel, kerosene, heating oil, and similar productswere moved on those ships. Some built during thatperiod had dry cargo holds forward. These were usedfor carrying specialry cargoes such as lube oils indrums.

From 1943 to 1970, product tankers increased insize from the 16,000 dw! MarAd T:2. design to the75,000 dw! Exxon San Francisco-class. As requirements for larger tankers grew, many ships built duringthe 1940S and 1950S were enlarged by adding new fore-

or mid-bodies, or both. Another trend during that period was a reduction in the number of cargo tanks-from 30 to about 15. That simplified cargo handlingsignificantly.

Also during that period, the oil companies and independen ts undertook some major pipeline conStruction. Many of the pipelines extended from the GulfCoast to the northeast. Advances in pipeline technology permitted different products to be sent throughthe same pipeline with minimal mixing. Also, thediscovery of oil on Alaska's North Slope shifted thefocus of the tanker owners to crude oil. As a result,most of the U.S.-flag tankers built or convened after1968 were intended solely for crude oil.

Today, in 1993, the main uses of product tankersare to: Transport clean products to terminals that are not

yet served by a major pipeline. Transport products (such as heavily leaded aviation

gasoline) that cannot be sent through a pipeline. Carry productS to alleviate spot shortages. This is

most notable in the winter when tankers carryheating oil to the northeast terminals.

Fig. 1 The chemical tanker SS Manne Dow-Chem: length 55 1 ft, beam 68 ft, deadweight 16,200 tons. Delivered in 1954, theMarine Dow-Chem was the first oceangoing vessel specifically constructed for the transportation of liquid chemicals in bulk.

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282 PART VI SHIPS OF COMMERCE

Fig. 2 The l iquid sul fu r carner 55 Marine Flondlan: length 612 ft, beam 42 ft, -deadweight 24,412 tons. The Manne Floridian, ajumbolzed vessel, has a cargo capacity 50 percent greater than that of the T-2 tanker from whlc I It was bUilt (In 1967). Constructionof the new tanker required extensive modification work on the ex-Paoli stern and ship's systems.

Specialty Product TankersSolvents, lube oil blending stocks, waxes and otherspecialry products are also t ranspor ted by tanker.These specialry tankers or "drugstore ships" carry awide variery of products, perhaps as many as 30 ot 40different ones on a trip. The tank arrangements onthese ships vary widely but there are generally nospecial conrainmenr or isolation requiremems as theremay be on chemical ships. Also, cargo compatibiliryis such that some of the cargoes can be dischargedsequenrially through the same cargo pumping system.

Only a few ships of this rype have been built new,but several have been converred from product tankers.The most recent new buildings were the 42,000 dwtExxon Charleston and Exxon Wilmington built byAvondale Shipyards in 1983-84. These ships have 42cargo tanks, each capable of carrying a separate gradeof cargo [3].

The main reason for the exisrence of these shipsis that the products they carry require more protection from cOntamination than a pipeline can provide,or they require other special treatment such as heating. These ships are classified as product tankers, andcransporr their catgoes in compliance with 46 CFRSubchapter D ("Tank Vessels") of the Coast GuardRules.

The Noxious Liquid Substance (NLS) provisionsofMARPOL Annex II have shaded the division be[Ween specialry tankers and chemical tankers. AnnexII classifies the pollution and roxic potential of many

products and chemicals. Some solvenrs that had beencarried as pertoleum products under Subchapter 0were labeled NLS and are now transpotted under theproviSIOns of 46 CFR Subchaptet 0 ("Ha2ardousCargoes").

Chemical TankersIn the past half cemury, the transport ofchemicals bywater has increased dramatically. At this writing, however, the largest chemical tanker Beets are nOt underU.S.-Bag. Chemical tankers have some of the mostsophisticated tank and pumping arrangements. Special coatings and linings are required for some products. In addition, many of rhe chemicals react withothers and with water. The violence of one of thesereactions resuJced in the loss of the Puerto Rican in1983. In tha t case, caUStic soda corroded a damagedarea in its t ank and leaked inro an adjacent cofferdam. coated with inorganic zinc. The caustic soda andthe zinc reacted to form hydrogen gas, which subsequentlyexploded.

Chemical tankers have three basic types ofcontainmenr, which are mainly related to damaged StabilityThe mOSt stringentsystem,Type I, requires protectionfrom grounding and collis ion damage. Type II requires protection only from grounding damage. TypeIII requires only protective PoS! tioning of cargo tanks.Type I and II systems aJso require that the tankbulkhead be at least 76 em (30 in.) awayfrom the ship's

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shell. Most chemical tankers have a combination ofcontainment systems.Cargo handling arrangements vary, but the cutrent

standard arrangement is to have a cargo pump, eitherdeepwell or submerged type, in each tank with a dedicated line to the loading manifold. A highly effectivestripping arrangement is also required, so as to discharge themaximum amount ofhigh value cargo, andto meet the requirements ofMARPOL Annex II.Some chemicals have properties requiring unusual

discharge arrangements. On theManne Dow-Chern, forexample, six rubber lined pressure tanks were installedfor hydtochloric acid [1]. The tank surface was pressurized with compressed air to force the liquid dlroughthe ship's piping to the suction of a pump ashore.In 1954, Bethlehem Steel's Quincy yard delivered

the 16,625 dwt Manne Dow-Chern to Marine TtansPOrt Lines and Dow Chemical. This was the firsttanker bui lt from the keel up as a chemical tanker.Unti l tha t time, tankers and barges had been converted from other uses to carry chemicals.TheMarineDow-Chern had 24 chemical tanks served by 11 totallyisolated cargo systems. In addition, therewere 18 wingtanks that could be used for petroleum producrs, andfive double botrom tanks. The ship carried perchlorerhylene, methylene chloride, styrene, glycol, carbontetrachloride, and chloroform. Six of the cargo tankswere 100 psig pressure vessels for hydrochloric acid.Four other tanks, clad with 50 tOns of nickel, wereinstalled fot caustic soda.Another notable U.s.-built chemical tanker was

the 37,100 dwt Edgar M. Queeny, built in 1970 byBethlehem Steel, Sparrows Point for Keystone andMonsantO. The ship was capable of carrying up to 26separate cargoes, including liquid naphthalene andcaustic soda. In 1971, the same yard delivered the34,600 dwt Puerto Rican to Hendy (now West CoastShipping) and Union Carbide. This ship includedcryogenic tanks and handling arrangements for uninhibited vinyl chloride and butadiene. It also carriedsuch products as caustic soda, ethylene glycol, rrichloroethylene, pylene and merhyl-chloroform.In 1983, Newport News delivered the 35,000 dwtChemical Pioneerro Marine Transport Lines and Un

ion Carbide for service between Texas and New Jersey.This ship was, in fact, a conversion using the afterbody from the Sea Witch, which had been all butdestroyed in a fiery collision with the Esso Brussels in1973. Newport News built a new forebody, whichincorporated the latest chemical tanker technology.The ship has a double hull and 48 cargo tanks. Each

REFINED PRODUCT TANKERS 283

Fig. 3 The Chemical Pioneer. Cones that resemble large eyesprotrud ing port and starboard from the bow are inexpensivealternatives to flaring the upper hull enough to protect the bulbousbow against damage when the anchors are lowered.

tank has a submetged hydraulic pump with a dedicated discharge to the loading manifold. All piping isself draining to the cargo pump. Product is strippedfrom each tank using compressed nitrogen throughan eductor syStem. The ship also has a liquid nitrogensystem to supply nitrogen for tank atmosphere padding, stripping and instrumentation.

Edib Liquid TankersWhile not a mode for transpOrting the finest wines,one tanker was built in the United States to carrywineas its main catgo. In 1957, the Bethlehem Steel SanFrancisco yard converted the 15.343 dwt T-2 AngekJPetTi by building a new midbody. The ship was arranged to carry 26 different wines in stainless steelvats. Another product transpOrted by this tanker isorange juice. This requires stainless steel COntainmentand special inert gas arrangements.

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284 PART VI SHIPS OF COMMERCEElevated Temperature ProducrsTwo elevated temperarure products are notable forbeing transported by tanker. These are asphalt andliquid sulfur. Asphalt is a residual of the petroleumrefining process. It must be maintained at about300 oF. Bur, even at this temperature it is quite viscousand generally requires positive displacement pumps,special seals and heat tracing. It has generally beencarried in single hull vessels and the temperaturedifferential with the seawater has made thermal hullstress a serious consideration.

Liquid sulfur also requires special consideration.The main reason for carrying sulfur as a liquid is thatthe end user needs it in that form. Moreover, stOringir as a liquid eliminates a number of hazards that arisewhen s roring i t in solid form. Liquid sulfur is carriedat 260-280 OF [4]. It solidifies ar 238 oF.

The U.S. Coast Guard requires that liquid sulfurtanks be independent of the hull. They are also insulated. The vapor space above rhe cargo is ventilated comaintain hydrogen sulfide concentration at half its 37percent lower explosive limie. In addit ion, sulfur reaces with copper, so no copper bearing materials areused in the ca rgo sys tem and special provisions aremade in the machinery space co protect equipmentfrom damage.

References1 Danielson, R.., and McDonald, A, "The Design ofthe 5.5. Dow-Chern Tankship for Special Commodities," New England Secrion, SNAME, Sept. 1954.

2 Price, R. 1., Goldbach, R. D., Dyer, A E, andWheeler, F. ]., "Sending Chemicals ro Sea," Metropolitan Section, SNAME, May 1967.

3 Koops, Coldwell, and Gordon, "Two Stare-of-the-ArtProduct SpecialcyShips," Tram. SNAME, Vol. 92,1984, pp. 51- 83.

4 Johnson, L., "Sulphur Vessels," GuJfcoast Secrion,SNAME, Feb. 1972.

MAURJCE GORDON graduared from Case Instirute in1970 wirh a degree in mechanical engineering. Followingeight years of tanker design experience wirh BerhlehemShipbuilding, he spenr two years managing mainrenanceand repairs for Atlanric Richfield and EI Paso Marine. Since1980 he has been with the Exxon Shipping Company,largely as a projecr engineer for new construction. In 1984he was given rhe SNAME Linnard prize as co-author of thebest annual meeting paper (on specialcy product ships). Heis a life member of SNAME, a fellow of rhe Insriture ofMarine Engineers, a member of ASME, and a registeredProfessional Engineer.