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2 CURRENT PRACTICES ON TANK VESSELS Barges and tankships differ substantially in size, complexity, man- ning requirements, and scheduling. River barges are relatively small, with uncomplicated cargo systems. They are generally unmanned except during loading and unloading when a Coast Guard certificated "tankerman" is required to perform operations. Tankships range upward in size and complexity to the extremes of maritime sophistication, with multiple- cargo capability, closed-loading facilities, segregated ballast tanks, and inert-gas cargo blanketing systems to prevent fires and explosions. Tankships carry dedicated crews, including skilled personnel to super- vise loading and unloading. (Their inert gas systems and flexible piping and pumping systems give tankships some ability to reduce vapor emissions by operational measures.) Operationally ? tankships and barges differ in many ways. A river barge may be thought of as comparable to a freight car in that--unlike self-propelled tankship--it may lie unattended for periods of time, may be passed from carrier to carrier as multibarge tows are assembled and dispersed, and may have less available documentation of its cargo and construction. The personnel who load and unload barges in the United States are less rigorously certified, and often less experienced, than those aboard tankships. For these reasons, the two types of vessels may require substantially different systems for vapor control. A few companies carry out vapor disposal or recovery when loading tankships with crude oil and gasoline (e.g., in the Santa Barbara chan- nel and the San Francisco Bay area), and certain hazardous substances, such as chlorine and acrylonitrile, are loaded in barges with vapor disposal or recovery. The technology for such operations is considered mature, but extending it to all marine terminals handling crude oil and gasoline would place increasing demands on safety systems and proce- dures, and would entail substantial costs to owners of both terminals and vessels. All tankships and tank barges are inspected and certificated by the Coast Guard under extensive regulatory requirements that control the design and construction of the vessels, their manning and operation, * For the purposes of this study, oceangoing integrated tug-barge units are considered tankships. 33
34 TABLE 2-1. Inland Tank Barge Pleet Profile: Number of Vessels Age of Barge Capacity (thousands of barrels) (years) 8 9-15 16-25 26-50 Total 0-15 148 656 292 313 1,408 16-30 198 612 388 211 1,409 > 30 284 245 193 30 752 Total 630 1,513 873 553 3,569a aThe Booz-Allen & Hamilton estimates are less than the Coast Guard estimates cited in the text, because Booz-Allen & Hamilton only counted barges where their computer files were sufficiently complete for their purposes. Source: U.S. Coast Guard Inspected Vessels Data Base, Maritime Administration, U.S. Army Corps of Engineers, and Booz-Allen & Hamilton analysis. (including handling and stowage of cargo), and certain duties of the officers and crew. Vessels are reinspected annually, and new certifi- cates are issued every 2 years following thorough inspection. INLAND TANK BARGES The inland waterway system encompasses 25,000 miles and includes the East and West coasts as well as the Mississippi River system, which is composed of the Allegheny, Monongahela, Kanawha, Ohio, Tennessee, Cumber- land, Missouri, Illinois, Arkansas, Warrior-Tombigbee, and Mobile rivers as well as smaller tributaries. The Gulf Intracoastal Waterway, which stretches along the Gulf Coast from Brownsville, Texas to Apalachicola, Florida, is also considered part of the inland system. In 1982 there were 1,800 companies operating on the inland river system. The de- pressed state of business since 1983 has reduced this number to less than 1,000. The largest 50 companies operate about three-fourths of the fleet. The 3,968 inland tank barges have a total capacity of 52 million barrels and an average individual capacity of 14,500 barrels. All are certificated to carry subchapter O or D cargoes. Their total market value is estimated by Booz-Allen & Hamilton (1987) at $730 million. The average 5-year-old, 10,000-barrel barge has a market value of about $250,000, but the typical inland barge is older than this. Table 2-1 categorizes the inland tank barge fleet by capacity and age. The industry operates mainly under short-term contracts, with only a small part in dedicated commodity trade. This means that the typical
35 barge carries a variety of products, depending on market demand, and moves flexibly through the inland waterway system, rather than traveling a regularly scheduled path. The inland tank barge industry is struggling to break even finan- cially. A study by Booz-Allen & Hamilton (1987) estimates that a typical inland barge loses about $1,000 per year before paying interest charges. Common service river barges carrying grain, coal, and other cargoes are moved long distances in so-called tows: groups of 10 to 12 barges lashed together securely and pushed by a single towboat. A tow may consist of barges from a variety of sources. While awaiting incorpora- tion in the tow, these barges are customarily stored temporarily in commercial "fleets," mooring areas under the supervision of local towing companies. Thus, a given barge may be brought to the fleet by one towing company, moored by another, assembled in a tow for long-distance transport by a third, and then routed to its final destination. To avoid accidents due to poor communications as barges are passed from hand to hand, barges carry diagrams of piping and tanks. They are also required to carry shipping papers showing cargo, consignee, and delivery point (46 CFR 35. 01-10) and a certificate of financial respon- sibility (46 CFR 542). Historically, liquid cargo has tended to move in "unit tows, " a string of barges and a tow boat serving one or several customers, with the boat and barges staying together as a unit. Many unit tank barge tows consist of two to four barges, are rarely "fleeted," and are handled with a dedicated towboat that stands by during loading and unloading. The towboat's crew often performs the tankerman's opera- tions. This results in high-speed product movement. The trend over the past several years has been toward less unit-tow business and more indi- vidual shipments. Tank barges differ from tankships in the absence of propelling ma- chinery and living spaces. River tank barges are rectangular or box- shaped, and may have a rake, or upward slope, to one or both ends. Tank barges range in length from less than 100 to several hundred feet. The simplest type, for petroleum and other liquids not considered I be highly dangerous, is a box divided by a longitudinal centerline bulkhead and several transverse bulkheads. All bulkheads are oil- tight, dividing the barge into a number of separate cargo tanks. The end spaces are left void, providing buoyancy when cargo tanks are full. Each tank has piping and venting systems and an access hatch. The barge may be fitted with double bottoms and side voids as well as with pumps and diesel engine drives. Cargo Handl ing The hazards of cargoes, such as flammability, reactivity, or toxic- ity, place different demands on the design of the barges that carry them . No matter what the particular hazard, tank barges mus t have fee - tures built in to reduce the hazards. In the case of accidental dis- charge into the waterway, because of the need for different levels of
36 safeguard against spills, the U. S . Coast Guard Rules and Regulations class barges according to whether their cargo requires moderate, signifi- cant, or maximum preventive measures against uncontrolled release into the water. Each dangerous cargo is then classified according to the needed amount of protection, which determines the type of barge used to carry it. The regulations also explain the differences in the three barge types in terms of protection against flooding, hull damage, and grounding. Depending on the severity of hazard, hazardous chemicals regulated under subchapter O must be carried in a barge with a type I, II, or III hull. A type I barge, for example, must remain afloat if a transverse bulkhead is damaged, with compartments on both sides of the bulkhead flooded; must have space between the cargo and the bow and sides of the hull to avoid collision damage; and must be able to run aground without overstressing the hull. A type II barge must remain afloat if any single compartment is flooded, and must have space between cargo and bow and between cargo and sides (but a smaller space than in a type I barge). Less rigorous requirements apply to type III barges. There are a number of common variations of tank barge arrangements (Figure 2-1~: (1) single skin, (2) double skin, (3) double wall, and (4) independent tank A single-skin tank barge is divided into cargo tanks by a number of transverse bulkheads and may also have a centerline bulkhead running fore and aft. Only the steel shell or single skin separates cargo from the river water. This type of arrangement is allowed only in Type III barges and barges designed for petroleum products. Double-skin tank barges have void spaces around the cargo tank sides and bottom. The double skin provides protection against cargo spills in case of grounding or collision and is, therefore, required when certain dangerous cargoes are carried. A double-wall barge is similar to a double-skin barge, except that only its sides, and not its bottom, are doubled. The independent-tank barge differs from the other three in that its cargo tanks are not designed as part of the hull structure, but are built separately and then installed in a barge hull, fitted with special saddles or supports shaped to hold the tanks. The independent tank is generally not considered as contributing to the structural strength of the barge. Most of these tanks are in the form of long cylinders. These barges are employed mainly in transporting liquefied gases such as liquefied petroleum gas, ammonia, and chlorine. Tank barges generally have simple piping systems. The main piping headers are used for both loading and discharge. One main header is located above deck and athwartship, and is flanged and valved for barge- to-shore connection with shoreside equipment. The other main header is oriented fore and aft, and is located inside the barge, just above the inner bottom. Lines from each tank, fitted with valves operated from the main deck via reach rods, are connected to this internal header. The above-deck header is connected to the internal header by a vertical riser that passes through the deck. During loading, cargo enters the above-deck header and flows by gravity through the the internal fore-and-aft header to the various cargo tanks. riser and During
at o En En En ° Single Double " Skin Skin FIGURE 2-1 Tank barge arrangements. Double Independent Wall Tank discharge, a deepwell pump, also connected to the fore-and-aft internal header, sucks cargo from the various tanks and pumps it through the above-deck header to shore. More complex piping systems may be installed for a number of rea- sons, such as the need to handle different grades of cargo (Figure 2-2~. A deepwell pump is a centrifugal pump with a long, vertical shaft. The impeller is located at the lower end of the shaft, near the bottom of the cargo tank. The prime mover is connected to the upper end of the shaft, above the deck. The drive shaft and impeller are enclosed in a discharge pipe, and the entire unit operates inside a larger suction barrel deepwell, extending from the deck to the bottom of the tank. Per- manently installed in the tank, deepwell pumps are greatly favored be- cause they are self-priming, since the impeller is in the lowest part of the tank. Pump rooms are not necessary when deepwell pumps are fitted. On barges certified to carry cargoes with an open-cup flashpoint of 80°F or less, cargo tanks are fitted at their tops with pressure/vacuum (PV) relief valves. The PV valve remains closed and seals the tank, as long as the pressure in the tank does not exceed the pressure for which the PV valve is set and as long as the vacuum in the tank does not ex- ceed the vacuum for which the PV valve is set. Normal diurnal tempera- ture variations cause the cargo in the tank to expand and contract. On tanks designed to operate at pressures of more than 10 pounds per square inch (psi), regulations require that safety relief valves, rather than PV valves, be installed.
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39 In vessels carrying the more dangerous grades of cargo, the vent pipes from the cargo tanks must be led high above the deck. The ver- tical part of the vent piping, leading up to the PV valve or flame arrestor, is called a riser. Depending on contractual agreements and the spot market, a typical inland barge operation carries gasoline on 50 percent of its petroleum movements, with the remaining 50 percent equally divided between No. 2 diesel fuel and jet fuel. There are occasional loadings of kerosene and natural gasoline. Manning Requirements for Loading and Unloading Cargo transfer operations involving unmanned barges are under the control of tankermen, certificated by the Coast Guard to handle certain liquid cargoes in bulk. Licensed masters, mates, pilots, and engineers are, by regulation, automatically certificated as tankermen. Tankermen are classified by the kinds of cargoes they are authorized to handle. More hazardous commodities require greater precautions and more training and knowledge. Two sets of regulations cover most require- ments for handling bulk hazardous liquid cargoes: 1. 46 CFR parts 30 through 40 (subchapter D)--''Rules and Regulations for Tank Vessels" (covering roughly 400 commodities, all of which have flammability as their main hazard). 2. 46 CER part 151 (subchapter O)--"Certain Bulk Dangerous Cargoes" (covering roughly 300 commodities with hazards other than, or in addi- tion to, normal flammability). The exact requirements to qualify as a tankerman are contained in the regulations and are subject to change. Qualification is based on experience, training, examination, and physical standards. A sufficient number of crewmen (as defined in the U.S. Coast Guard pollution and tankerman regulations) must be on duty to perform cargo transfers. At all times there must be a qualified person-in-charge on the vessel and on the dock. On tank vessels, this person will be a licensed officer or certificated tankerman. Tank-cleaning operations generally require the same qualified person-in-charge as cargo trans- fers. No one may connect, top off, disconnect, or take part in any other critical transfer procedure unless the person-in-charge supervises the operation. No one may start the flow of oil to or from a vessel unless instructed to do so by the person-in-charge, who must be in the immediate vicinity of the operation and immediately available to the transfer personnel. In addition, no one may serve as the person-in- charge of oil transfer operations on more than one vessel at a time, and no one may be in charge of both a vessel and the terminal facility, without the approval of the U.S. Coast Guard captain-of-the-port. Within this framework, cargo handling on barges adjacent to each other are routinely handled by one tankerman.
40 The terminal operations manual and posted vessel procedures, re- quired by regulation, indicate the minimum number of qualified personnel for transfer operations, as well as the number of ships and barges that can be handled at the same time. Tank barges need not be manned unless in the judgment of the marine inspection officer-in-charge such manning is necessary for the protec- tion of life and property and for the safe operation of the vessel. However, any towing vessels, while towing barges that are not required to be manned, must carry in its regular complement and have on board at all times at least one licensed officer or certificated tankerman. A strict watch of each unmanned barge in tow is required to be maintained from the towing vessel while underway. Appendix E summarizes the requirements for barge surveillance. When a barge is moored but not gas-free (flushed with air, as in cleaning), at least one of the following precautions shall be taken: 1. The barge shall be under the observation of a watchman who may be a member of the complement of the towing vessel, a terminal employee, or another competent person responsible for the security of the barge and for keeping unauthorized persons off the barge. 2. All cargo tank hatches shall be clearly marked in not less than 3-in. lettering, "Danger--Keep Out," and all hatch covers shall be closed and dogged down, or otherwise secured, by a tool-operated device, such as a length of pipe, so that no person can open the hatch by use of bare hands alone. Loading and Discharging Procedures Before a fleet operator ("fleeter") accepts a barge from a line ves- sel, his representative inspects the barge for damage and ensures that it has the proper Coast Guard documents (i.e., certificate of inspec- tion, certificate of financial responsibility, and information on the last cargo Bottoms. If these documents are in order, the barge is accepted into the fleet. The fleeter accepts full responsibility and must keep a site surveillance during the unit's stay. Depending on the product, the customer may require that the barge be cleaned before loading and will designate an inspector to ensure that it is cleaned properly. A local cleaning plant will be contacted. When the barge is delivered to the plant, the plant operator assumes full responsibility for the unit. After the barge is cleaned and accepted by the customer's inspector, it is sent back to the fleeter. The fleeter again checks the barge for damage. If all is in order, he accepts the barge into his fleet. When the loading facility is ready to accept the barge, it will contact the fleeter and request that the barge be delivered. On arrival at the dock, the barge is again inspected by both the loading foreman and the designated barge inspector, who also discuss loading procedures. A Coast Guard publication entitled A Manual for the Safe Handling of Flammable and Combustible Liqu i ds and Hazardous Products (U. S . Depart
41 ment of Transportation, 1975) describes the hazards in transfer opera- tions and identifies applicable requirements. Loading and unloading hydrocarbons from barges carries the inherent risk of fire and explosion. Vapor in the tanks may pass through the flammable or explosive ranges as the tanks are emptied or filled. Thus, a number of safety precautions are taken to avoid sources of spark or ignition. Appendix F sets forth gasoline loading procedures required by one large Ohio Valley towing company. Similar procedures are representa- tive of responsible operators in the industry. After loading, quantity and quality specifications are checked and the loading facility foreman places the proper loading manifest aboard. The loading manifest includes information on the product loaded, the loading port, the quantity loaded, the destination port, and any special handling hazards of the product. The barge is then released by the load- ing dock and returned to the fleeter, who again checks to be sure all required papers are aboard and the barge is in serviceable condition. The line vessel operator, prior to pickup, lays out his tow configu- ration to accommodate his future delivery and pickup schedule, and to ensure proper towing and handling characteristics. Finally, the barge is picked up from the fleeter by a line vessel, who again inspects it for proper papers and seaworthiness. The barge is transported either directly to the discharge terminal or to an intermediate fleeting opera- tion; the latter requires redispatching it to the discharge terminal, a procedure s imilar to that at the loading berth. At the discharge termi- nal, unloading is carried out according to set procedures. TANKSHIPS About 231 million tons of crude oil, refined products, and organic chemicals were loaded aboard tankships in the United States in 1984 (see Table 1-3~. While tankships are inherently more complex than barges, they present many of the same operational problems, particularly where loading and unloading are involved. Some of the operational differences between the two types of vessels are that most tankships practice closed loading (loading with hatches and ports, but not necessarily vents, closed to the atmosphere), carry seawater as ballast (which can generate emissions under some circumstances), are equipped with systems to blan- ket cargoes with inert gas to lessen the danger of fire or explosions, and are manned continuously by licensed officers, most of whom have college educations. National legislation and international regulations (summarized in Figure 1-3) are extending to more tankships the requirements for inert gas systems and closed loading, and for ballast tanks separate from cargo tanks (the latter under requirements for segregated ballast tanks and clean ballast tanks). These requirements are explained later in this chapter.
42 ,: ,'' fl ~ ~, ~ / a: a ~ 7 1 6 1 5 1 4 1 3 1 2 1 1 1 ~ = '-1 = = 1 . I FIGURE 2-3 General arrangement of typical tanker, with a side view, top view, and cross-section; (a) indicates the main cargo pump room and (b) the extra large tanks for special parcels. Arrangement of Typical Tankship A typical tankship in the crude or product trade has three parts: spaces forward of the cargo tanks for service, cargo-carrying tanks midship (the tank body), and propulsion machinery aft. Figure 2-3 shows the general arrangement of such a tankship. Vessels designed to operate mainly in the clean product trade usually have numerous cargo compartments to permit carrying multigrade cargoes. Crude-carrying vessels often have fewer separate cargo compart- ments5 since one grade of crude oil is often the only cargo carried. Most tankers are single-hull vessels with the cargo carried in the tanks and separated from the outside by a single steel hull. Combination Carriers In addition to conventional tank vessels, there are several other types of oil-carrying vessels. So-called combination carriers, for example, are constructed to carry either oil or dry bulk cargoes. Most combination carriers carry only crude oil when in petroleum service. Among the types of combination carriers are ore/oil carriers, bulk/ oil carriers, and product/bulk/oil carriers.
43 Ocean Barges Integrated tug barges (ITBs) are a relatively new type of tankship. Today 13 are in operation, all about 40,000 cwt. The tug and barge of an ITB are designed to operate as one unit, with the tug fitting into a specially designed slot in the stern of the barge. This arrangement improves the flow of water around the hull as compared with a tug towing a barge on a hawser. The barge component of an ITB is constructed simi- lar to the tank body of a conventional seagoing tankship, with essential- ly identical cargo piping and pumping arrangements, ballast tanks, inert gas systems, and vent lines, for example. There are a few seagoing barges towed by seagoing tugs delivering oil along the U.S. coasts. These barges are built similar to seagoing ships, except that they are usually unmanned and have no propulsion. The cargo-handling arrangements are very similar to river barges or to those of the ITB. Cargo Tank and Pipeline Arrangements Figure 2-4 is a simple drawing of a complete direct pipeline system on a nonsegregated ballast tankship with a pumproom forward of the engine room. Only the three main centrifugal pumps are shown. The stripping pumps have their own pipeline system, which can deliver into the main system, into the cargo tanks, or directly ashore. Also, the valves are not shown. _~~ PI Pumps FIGURE 2-4 General piping and pumping arrangements of a tankship.
44 To show the details, the pumproom in the sketch is considerably out of proportion to the cargo tanks. In reality the pumproom in a fore and aft direction is only a fraction of the size of a cargo tank. The sketch is of a modest-size product or crude carrier with three "natural segregations," meaning that the vessel can load or discharge simulta- neously three separate grades of oil. Three drop lines shown in the sketch, connecting the deck lines to the bottom suction lines, permit loading oil without going through the pumproom. Drop lines that are not connected to suction lines terminate a few inches from the bottom of the tank, so there is practically no free-falling liquid. Hoses or articulated metal arms are connected to the deck manifolds for transferring cargo during loading or discharging. The sea suctions in the bottom of the pumproom, installed at the turn of the bilge, permit ballast water to be taken into the cargo tanks. Ballast water can also be discharged through the sea suctions. Product and Chemical Carriers Figure 2-5 shows a typical product carrier. The complex piping on the deck gives flexible loading layouts that can accommodate several different types of oils or chemicals. Smaller tankships often carry chemicals. The sophistication of the cargo tank and pipeline arrange- ments increases with the requirement for a greater number of small parcels of chemicals. Some chemical carriers have as many as 60 natural segregations. The cargo tanks of chemical carriers often are made of stainless steel to carry corrosive chemicals. Double bottoms are usually installed in chemical carriers to ensure good drainage and easy tank cleaning. Sometimes a complete double hull is used. When many natural segregations are required, deepwell cargo pumps are installed in the cargo tanks. Crude Carriers Very large crude carriers (VLCC) have far fewer segregations, hence less complex piping and tank arrangements (Figure 2-61. The cargo is loaded through drop lines and flows through open sluice valves into other tanks. Essentially only one grade of oil can be carried in this type of vessel without significant commingling of different grades. Cargo Pumps Most main cargo pumps on crude and product tankers are gravity-fed centrifugal pumps. These pumps are compact and reliable, producing a steady rather than pulsating flow. They are easily adapted to different power sources such as steam turbines and electric or diesel motors.
45 _AI 1 . i ~ _Al , Did _ ~ ;1t p~ .. ..... _ ~ ~ i' ~ ~ ~ ` ~ ~ ~ ~:.:~ ~ - ' ~:$~ illlll~ . ~ ~.~ ~ ~' _ ilk ~ .. ..... : :: :9~ ~ ~ ~'~ :::: ~ A...,. ~ _ ~ . ~ ~./~ "A 1 ~ ~ ~ ~:_~-_ . ~ . ..~.$ ~ ~ ~ ~ ~ _ . ~ ~"~ ~ ~ ~ ~ Hi' ~'~'~'~'~ ~ ~ FIGURE 2-5 Typical product tanker. Source: Exxon Shipping Co. These pumps cannot be used to strip the last few feet of cargo out of tanks unless equipped with special recirculating devices. Positive displacement pumps are used as stripping pumps, since they can suck the remaining liquid from the tanks, even though some air becomes Entrained in the liquid. Reciprocating, gear, and screw pumps are of this type. On VLCCs, the cargo tanks are also fitted with eductors driven by the discharge from a cargo pump to perform stripping and tank cleaning. Eductors, having no moving parts, are almost trouble-free, but they do not have a very high ratio of mechanical energy to work. Deepwell cargo pumps are used extensively on chemical carriers or tankships carrying a great diversity of refined products. Each pump is installed in the cargo tank. Their impellers operate so close to the bottom of the tank that they can discharge nearly all cargo before losing suction. Additional stripping is usually unnecessary.
46 FIGURE 2-6 Typical medium-size crude carrier. Co . Tank Ventilation ~ a' ~:~.f Source: Exxon Shipping Most tankships have closed-loading equipment that permits keeping hatches closed during loading and ballasting. A vent line is installed in each cargo compartment so that vapors displaced during loading are released into the atmosphere. Similarly, when discharging, air or inert gas can enter the tank to replace the liquid discharged. Typically a vent line rises 8 ft above the deck. On some tankships the individual vent lines are connected to one or more common main vent lines that are carried up a king post or mast where the vapors are vented to the atmosphere. Flame screens are installed at the ends of these common vents. PV valves are installed at the tops of the vents to permit con- trolled breathing and minimize cargo losses from evaporation. These PV valves are bypassed or opened during loading. Individual tank vents also are fitted frequently with constant velocity (CV) vents at the tops of the vent lines. These devices in- crease the velocity of the emerging gas, throwing the vapors high off the deck, where they are diluted by air drawn into the plume by the velocity of the emission. The object is to lessen exposure of personnel to the vapors and to dilute the vapors so that they are no longer
47 flammable. CV vents also impart a velocity to the vapors that exceeds the unconfined flame speed in the event of an ignition on deck, and thus prevent a flame from entering the tank through the vent outlet. Inert Gas Systems All new tankships of 20,000 dwt or more ordered after 1980 are required to be equipped with inert gas (IG) systems, and most trading in U.S. waters are so equipped. Inert gas equipment, properly installed, operated, and maintained, is a safety feature. However, IG is not a panacea for tankship fires and explosions (see Chapter 49. There can be no explosion or fire in a tank if there is insufficient oxygen to support combustion. Therefore, inert gas with an oxygen con- tent of 5-8 percent is obtained from the uptakes of the ship's boilers or from an independent inert gas generator. The inert gas is scrubbed free of most impurities and then blown into the cargo tanks. The inert gas is maintained under a slight positive pressure in the tanks. Air is permitted into the tanks only after they have been gas-freed of all hydrocarbon vapors. Figure 2-7 illustrates the arrangement of a typical IG distribution system. When loading cargo or ballast into an inerted tank the dis- placed vapors are released through the vents (or a common header). The distribution lines for the IG system are connected to each cargo compart- ment. Ballast Arrangements Tankships without cargo carry water as ballast to ensure good sea- keeping characteristics. Ballast equivalent to 20-30 percent of the deadweight usually is required for operations in good-weather; it may be increased during bad weather. Ballast is carried in SBTs, CBTs, or cargo tanks. Ballast water, if placed in dirty cargo tanks, mixes with traces of the previous cargo clinging to the tanks and is called dirty ballast. Discharge of this dirty ballast at sea contributes to oil pollution. T minimize this pollution SBTs and CBTs have been mandated for certain tankships, while other operational controls apply to other tankships. Segregated Ballast Tanks The United States has adopted and supplemented international conven- tions that require new crude tankers of 20,000 (and product tankers of 30,000) dwt or more constructed after 1980 to have sufficient ballast capacity for good weather operations in U.S. waters that is completely separate and distinct from the cargo system. These SBTs have their own ballast pumps and suction lines separate from the cargo systems. Tank- ships and combination carriers fitted with double bott;ons or double sides use the spaces thus formed for some or all of tile SBT. If
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49 existing crude oil tankers of 20,000 dwt or more are fitted with crude oil washing (COW), they do not require SBT or CBT. Clean Ballast Tanks Existing product tankers of 20,000 dwt or more operating in U.S. waters are permitted to substitute CBTs for SBTs. CBT are cargo tanks reserved for ballast, without separate ballast pumps and suction lines. On CBT vessels the ballast is loaded and discharged using a cargo pump and suction line. Ballast in Cargo Tanks Tankships under 20,000 dwt generally put all ballast water into empty cargo tanks. On many of the existing larger tankers fitted with COW, part of the ballast is carried in SBT and the remainder in cargo tanks. Ballast water pumped into cargo tanks displaces the cargo vapors through the vent lines into the atmosphere. Coast Guard regulations governing departure from any U.S. port require each tank vessel having a COW system without sufficient SBT or CBT to have a means to discharge hydrocarbon vapors from each cargo tank that is ballasted to a cargo tank discharging crude oil. Using this arrangement, VOC emissions from ballasting are eliminated. The IG distribution lines are used to transfer vapors from one cargo tank to another. Figure 2-8 illustrates how a tankship with IG can load ballast into a cargo tank and transfer the ballast vapors into a tank discharging cargo. Figure 2-9 shows the arrangement when a tankship loads ballast into a cargo tank and puts the displaced vapors into one or more empty cargo tanks by compression. Ullaging During Loading and Discharging Ullage is the space between the tank top and the surface of the liquid in a tank. Tankships with IG are equipped with automatic ullag- ing devices that serve as "trend indicators" during loading and discharg- ing. Figure 2-10 shows one type of such device that has been in use for many years. The float rides up and down the guide wires, and the deck officer can read the ullage through the small window in the deck mounting near the tank hatch. This ullage measurement is not considered sufficiently accurate for cargo documentation purposes. A more sophisticated system employed on a few tank vessels uses a radar-like device to determine the ullage. The readout is often in a control room in the afterdeck house at the main deck level. Other devices operate on a pressure measuring instrument that is easily arranged to read remotely in a control room.
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52 . Hi, 6,.,.N Wr. /o o/ °A FIGURE 2-10 Typical ullage gauge (Strand and Jurs). Modern tankships are equipped with control rooms that permit the mate to load and-discharge cargo and ballast from one location. Remote reading ullage gauges, automated valves, and cargo pump controls in the control room improve efficiency and safety during the transfer of cargo. The trend is toward more automation of loading and discharging. Older and smaller tankships under 20,000 dwt not equipped with IG or not fitted with remote-reading ullage devices monitor cargo levels by looking into the cargo tank through ullage ports on the tops of the tank hatches (the ullage ports are fitted with flame screens, which are removed to permit viewing cargo levels). Manning and Personnel Manning levels aboard tankers have been declining for many years. Automation of engine rooms and use of long-lasting coatings on exposed hull and superstructure surfaces have permitted large personnel reduc- tions. The worldwide depressed tanker market during the past 10 years
53 has accelerated this trend. Additional automation of mooring winches, anchors, and gangways, with changes in work rules, could bring large further reductions. There is no relation between the size of a tanker and its crew complement; it is common today for a small product or chemical tanker to have a larger crew than a VLCC. Shipboard personnel can be grouped broadly into two classes: offi- cers (who are licensed) and unlicensed personnel, or seamen (who are usually certificated). Most maritime nations have similar standards for licensing and certification. About one-third of all seagoing tankers fly the flags of nations known as "open registry." These small nations usually issue licenses to officers already licensed by a recognized maritime nation. Deck and Engine Officers Most licensed officers have the equivalent of a college education. This formal education is usually undertaken at special maritime colleges with 4-year curricula. After completion of the formal training, includ- ing some time aboard ship, they are eligible to take the U.S. Coast Guard examination for deck officer (as a third mate) or engine officer (as third assistant engineer). Some officers have both deck and engine licenses. Each year they serve with their licenses, officers are eligi- ble to sit for the next higher rank until they achieve their master's or chief engineer's license. In the United States unlicensed personnel, after serving for several years aboard ship, may also take the examination for deck or engine offi- cer. About 10 percent of U.S. officers are such so-called hawse pipe officers. Regulations governing licensed officers are contained in 46 CFR part 10. Unlicensed Personnel Most unlicensed personnel have relatively minimal formal training and start aboard ship in the lowest job category, called ''entry ratings."' They usually are initially certificated only to show they are in reasonable health. After serving aboard ship for a period of time, U.S. seamen are eli- gible to take a Coast Guard test certifying to their increased compe- tence. After many years of shipboard experience, they may be assigned by the shipowner to higher ratings as petty officers. Usually there is no certification as petty officer. The regulations concerning unli- censed personnel are contained in 46 CFR part 12. Loading Procedures The chief mate, also called first mate or first officer, tradition- ally serves as the cargo officer. He is responsible for loading, dis- charge, and general stewardship of the cargo, assisted by the second and
54 third mates. A petty officer called the pumpman works for the chief mate in port; at sea he assists the engineers in maintaining the cargo equipment. On arrival at the loading terminal, a formal meeting is held with the responsible ship's officer and the terminal representative. Mean- while, the hoses or articulated metal arms are connected by dock work- ers. The loading terminal advises of cargo characteristics, preferred loading order, venting requirements, number and size of hoses or articu- lated arms, maximum loading rates and pressures, bunkering plans, and so on. The ship's officer advises of the general arrangement of cargo, ballast, and bunker tanks and other data pertinent to loading. On the basis of this information exchange, a written agreement is prepared and signed by both parties. If there is ballast in some of the cargo tanks, the vessel will use its cargo pumps to discharge this ballast. At most U.S. ports this ballast is discharged into ballast receiving facilities ashore, where the separation of any oil in the ballast is accomplished most effec- tively. Generally it takes about 6 hours to discharge the ballast from the cargo tanks. If the tanker has some or all of its ballast in segre- gated ballast tanks the delay for deballasting is reduced or eliminated entirely. Petroleum inspectors, paid by the vessel's charterer, inspect all tanks to be sure they satisfy the requirements for the cargo. When the inspection has been approved the vessel notifies the shore to start loading slowly using pumps at the terminal. The chief mate is on deck when loading begins. A check is made to ensure there are no leaks at the cargo manifolds and that the cargo is entering the tanks designated to receive it. The chief mate decides the sequence to be followed in the loading operation, taking into account stresses caused by the loading, and fills out a cargo plan that gives precise information to the other deck officers on the loading sequence, final ullages for each tank, final draft and trim, and so on. Frequent checks are made of the tank ullages during loading. As the cargo level in the first tanks loaded nears 10 ft from the tank top, personnel are alerted for the topping-off operation: bringing the level of liquid up to a foot or so below the main deck. The loading sequence is arranged so that only a few of the tanks reach the topping-off point at the same time. If the cargo will expand during the loaded trip the mate calculates the additional space required to permit expansion. When carrying a full cargo, the tankship is loaded to its draft marks. The bunkers are filled before loading is completed. The last of the cargo is usually loaded into fore and aft tanks to put the vessel on the proper trim for the voyage. When loading is completed, petroleum inspectors, accompanied by a ship's officer, check the ullage, cargo temperature, and any free water under the cargo in each compartment. If the ship measurements are in close agreement with the shore loading figures, the cargo documents are placed aboard and the vessel departs for the discharge port. in,
55 Unloading Procedures On arrival at the discharge berth, the hoses or articulated arms are connected while a petroleum inspector, accompanied by a ship's officer, repeats the check of ullage, temperature, and free water under the cargo in each compartment. Simultaneously, a formal meeting is held with the -responsible ship's officer and a terminal representative. All pertinent information about the cargo, proposed discharge arrangements, pumping rates, operation of any shipboard inert gas system, the ballasting plan, and so on are reviewed in considerable detail. When the hoses or arms are connected and all tests and meetings have been completed (these steps may take 30 to 45 minutes), the ship noti- fies the terminal that it is ready to discharge. When the shore facili- ty confirms its readiness to receive the cargo, discharge will start slowly, often using only one cargo pump at slow speed. The terminal makes sure the cargo is entering the correct shore tank. The ship checks the cargo manifold connections and the pump room for leaks. The chief mate leaves detailed written discharge instructions for the other mates. With only one grade of oil, the cargo is discharged in sets, with several tanks comprising one set. Set one is discharged with the main cargo pumps down to within 2-3 ft of the bottom of the tanks. Then the main cargo pumps are switched to the second set. At the same time, the stripper pumps are activated to take 2-3 ft of oil out of set one. Usually the stripper discharge is put into a partially filled cargo tank instead of trying to discharge ashore against the pressure of the main cargo pumps. Long before the main cargo pumps have finished discharging set two, the stripping has been finished from set one. This method minimizes the delay for stripping the last set to not more than 2-3 hours. If the vessel is equipped with an IG system, the cargo leaving the tanks is replaced with inert gas maintained under slight pressure. Bal- lasting is timed to be finished when the cargo discharge is completed. On tankers equipped with COW facilities, the vapor from ballast loaded into cargo tanks is either compressed into empty cargo tanks or transferred into tanks from which the cargo is being discharged. COW delays a tanker 2-10 hours beyond the normal discharging time, depending on the number of tanks washed. In the COW process, the tank atmosphere becomes saturated with hydrocarbon vapors. While hydrocarbon emissions at the ballasting port can be avoided through vapor balancing on a COW tankship, the total atmospheric emissions of hydrocarbons are higher than what would be emitted from a similar tankship not practicing COW. In COW operations, one or more of the tanks is washed with the crude oil cargo during discharge to minimize the amount of oil clingage in the cargo tanks. Cargo tanks selected to receive ballast water are usually crude oil washed during discharge. Also one or more other tanks are often washed on a regular pattern to minimize the buildup of sludge. The discharge from COW goes ashore with the cargo stream. Generally it will take 16-24 hours to discharge most single-grade cargoes; multigrade cargoes may take considerably longer. The petroleum inspector returns after discharge is completed, and checks all compart- ments to see if they are dry of cargo. Any small amounts of cargo
56 remaining in the tanks, if considered pumpable, are measured. In many of the smaller and older tankers not equipped with IG systems, ballast must be pumped into some of the cargo tanks after discharge is finished. Ballasting may take an additional 3-4 hours. Washing Cargo Tanks The cargo tanks are washed (1) to free the tanks of gas so personnel can perform repairs or remove sludge, (2) to remove traces of previous cargoes so ballast water will remain clean, (3) to remove traces of previous cargoes that might contaminate the next cargo, or (4) to remove all traces of previous cargoes so shipyard workers can perform welding or other hot work safely inside cargo tanks. Water Washing Water washing of some or all cargo tanks generally takes place at sea on the ballast passage. Tankships bound for loading ports without ballast receiving facilities wash 20-30 percent of their tanks during each ballast voyage, then fill the washed tanks with clean seawater ballast. Tankships proceeding to loading ports with dirty ballast receiving facilities may not wash any tanks for ballast. The washing on small- and moderate-size tankships is usually per- formed with portable machines attached to hoses connected to a water source and lowered into the cargo tanks. The machine sprays the inside of the tank with water at 150 psi. A pump in the engine room supplies the water to the machines through the fireline that runs the full length of the vessel. On the larger tankships, high-capacity washing machines (HCWM) semipermanently installed in the tanks receive water from a cargo tank filled with recirculating wash water. Tankers using HCWM are required to have IG systems, since the greater water volumes from the HCWM are more prone to sustaining electrostatic discharges. The stripping pump or eductor removes the dirty wash water and slop oil as the washing proceeds, to prevent buildup of water on the bottom of the tank being cleaned. The dirty wash water and slop oil are put into a cargo tank called the slop tank. The slop tank is allowed several hours to settle, and then the fairly clean separated water is pumped out. On most crude oil tankships, the next incoming cargo is loaded on top of the slop oil that has been separated from the water. Slop should be discharged ashore to slop oil or dirty ballast receiving facilities. If gas-freeing is required, portable blowers are installed in the deck openings and fresh air displaces the vapors in the washed tank. If sludge removal by hand is necessary, personnel enter the tanks and scoop the traces of sludge and oil off the bottom for disposal ashore.
57 Crude Oil Washing Crude oil washing is allowed on some existing crude oil carriers as an alternative to segregated ballast. Crude carriers fitted with HCWM and IG also use the equipment to wash the tanks with crude oil cargo during discharge. Crude oil is more effective than water because it removes clingage and sludge. The crude oil washings and sludge are discharged ashore mixed with the cargo. COW minimizes ocean pollution, but increases atmospheric emissions. COW is performed while the tanker is discharging its crude cargo. Vessels with COW must have IG systems. By this crude oil washing of a tank which is to be ballasted, the amount of oil which is discharged at sea as a result of ballasting is greatly reduced. Crude oil washing is also practiced on crude tankers with segregated ballast because it tends to improve overall efficiency. If additional cleaning is necessary for clean ballast, the vessel goes to sea and cleans the tanks with water. It takes considerably less time for water washing after crude washing, because most of the clingage has been removed.
