Oil tankers are purpose-built ships designed to transport crude oil or petroleum products. Tanker navigation at sea requires some basic safety precautions to be observed. Following are the most common matters that require crew to take care:
Avoidance of Thunder Storms::
Navigating through thunderstorms should be avoided as far as practically possible by changing of course while cargo related activities are carried out which may result in discharge of flammable vapors.
If the passing through thunderstorms cannot be avoided, all open cargo oil tank hatches should be closed until the vessel has passed through the thunderstorm
The valves in the main vent lines may be temporarily secured in locked position, but must be opened immediately after passing through the thunderstorm.
Cautions about Sparks from Funnel
At sea, where sparks / burning soot are observed being emitted from the funnel, measures to avoid such sparks falling on deck such as course alteration, where possible, should be considered.
Any special operations such as cargo tank cleaning, purging and gas freeing operations should be ceased and all tank opening closed.
Boiler tubes should be soot blown prior to arrival and after departure from a port. Boiler tubes soot blowing should not be carried out at berth. At sea, the officer of navigational watch should be consulted, prior to such activity, and suitable measures adopted.
Duty deck personnel shall watch for sparks or soot emitting from the funnel.
If sparks from the funnel are observed, the duty engineer or Chief Engineer must be notified immediately.
Facing rough seas
Closure of Tank Openings
Ensure that all cargo oil tank hatches and access openings / ports are tightly closed to prevent escape of oil and vapors.
Maintenance of Vent Line System
All P/V valves must be checked during ballast voyages to ensure proper and safe operation.
Record of maintenance shall be as per “Maintenance Record of Cargo Oil Tanks (COT) Pressure-Vacuum Valves”
Metal wire mesh in flame arrestors must be inspected only during ballast voyages as per the planned maintenance system, and kept clear of dirt and rust accumulation. Their specification of construction should be verified in accordance with related drawings.
Metal wire mesh in flame arrestors must be inspected.
Void Spaces/Duct Keels Ans Pipe Tunnels
Because of restricted natural ventilation these spaces may be oxygen deficient. In addition, they are adjacent to cargo holds and ballast tanks, so both hydrocarbon vapour and inert gas may leak into them. It must be recognised that the rescue of an unconscious or injured person may be very difficult.
Hydrocarbon vapours may also be released from adjacent cargo tanks due to leaks in pipelines or hairline cracks in the tank structure. It is therefore essential that checks are made of these spaces for the presence of hydrocarbons. Some ships will be equipped with automatic detectors and recording devices for this purpose. Ships that do not have such equipment must carry out manual checks at least weekly and the results recorded in the table within the deck log book.
Where the Classification Society rules do not require the permanent lighting systems in these spaces to be isolated during oil trading, the following procedures are to be complied with in order to eliminate the hazards that could result from damaged flame proof fittings:-
- The space must be tested and proven gas free, before the lights are switched on.
- The mechanical ventilation system is to be in operation before the lights are switched on, and must remain in operation until after the lights are switched off.
Leakage Into Void And Ballast Spaces
Leakage of cargo from the cargo tanks into the permanent ballast tanks or void spaces can create a potentially serious pollution problem. Structural failure at known weak points therefore requires monitoring. The generally recognised weak points are as follows:
- On vessels with vertically corrugated transverse bulkheads, cracks may occur in the welded seams between these bulkheads and the upper hopper tanks.
- On vessels where the upper hopper tank is connected to the lower hopper by a trunk way or pipe, any leakage will affect the lower hopper in addition to the area around the fracture.
- In double-hulled vessels, leaks may be found around the upper welded seams of the longitudinal bulkhead between the ballast tank and the cargo tank abutting the sloped deckhead of the cargo tank.
In order to monitor the integrity of double hull spaces a procedure for checking these spaces for the presence of hydrocarbon gases is to be established. Where this is impractical due to short voyage trading then a visual inspection of the surface of the ballast water, if carried, is to be made. Such an inspection is to be carried out in any case, to check whether oil is present on the surface of the ballast after loading ballast and before discharge of the ballast.
As a back-up, a system of sounding round all spaces is to be employed. This system may be established as part of the daily sounding routine. During the ballast voyage the cargo spaces are to be checked for the ingress of water from the ballast tanks.
Depending on the cargo carried it is essential not only to test the ballast tank for oil content but also the atmosphere for toxic gases and/or oxygen deficiency before entering the tank to carry out repairs. It must be remembered that the requirements of the Work Permit Entry into enclosed spaces must be complied with.
Inerting
Ballast and void space are to be inerted where fitted with IGS if there is flammable cargo leakage.
Double hull vessels => 20,000 DWT are required to be fitted with suitable connections for the supply of inert gas in double hull spaces in case of cargo leakage into such spaces. Refer to ISGOTT 11.7.
Whilst there may be a hard piping connection possible through portable spools which could connect inert gas supply to the bottom ballast piping, there must also be the possibility to supply the inert gas over the top in cases where tanks contain ballast. This is usually achieved by connecting portable hoses from provided connection flanges on the inert gas piping (usually valved) to similar flanges located on each ballast tank. These portable connections must be electrically bonded to the connecting flanges when installed.
The hoses shall be individually identified and subject to electrical continuity checks in a dry condition on a 3 monthly basis, results being recorded within the PMP. It must be confirmed that the hose string is properly earthed before inerting commences. Until the tank is fully inert, precautions against electrostatic hazards must be implemented.
Exhaust outlet from ballast tanks being inerted is to be through a portable stand pipe. The cross sectional area of such gas outlet pipe is to be such that an exit velocity of at least 20 m/s is obtained and outlets are to extend not less than 2 m above deck level.
When inerting ballast tanks in such circumstances, the oxygen content in any part of any ballast tank shall be reduced to below 8% by volume and tanks shall be maintained inert to this level and at a positive pressure at all times. Blinds shall be fitted to tank outlets accordingly to maintain pressure.
After inerting is completed, careful consideration should be given to keeping the tank connected to the inert gas system and hence to the cargo tanks. This should be risk assessed, the advantages being constant pressure monitoring, over-pressure protection and ease of topping up against the vulnerability of the hose to heavy seas damage.
Vessels are provided with P/V valves which are mounted on top of the 2-meter standpipes to ensure the tank cannot be pressurised outside design limits if the connection to the inert gas system is removed and the tank isolated.
All equipment including isolating valves , flange bolts , hoses , blanks , standpipe and P/V valves shall be included in the vessels PMP for routine 3 monthly readiness checks. The ballast tank P/V valve shall be subject to the same maintenance requirements as cargo tank P/V valves
Electrical Continuity: Bonding and Earthing
Static accumulator oils may be electrostatically charged by pipeline flow. Pipeline bonding is required to prevent electrostatic charge accumulation. Bonding does not prevent accumulation, however, assists in relaxation of any charge accumulation. Pipelines in the cargo system through which static accumulator oils flow must be bonded to each other and to the ships structure which in turn is naturally earthed through the hull to sea. This bonding is normally achieved by metallic connection between the pipelines and to the ships structure (usually by bonding wires or metal straps). These connections must be inspected regularly and maintained in good condition.
Flexible hoses used on board shall be electrically continuous. Generally the bonding of the metal reinforcement in the hoses to their flanges will ensure this.
Ship / Shore Electrical Isolation (applies also to vapour connections).
Differences in electrical potential between the ships and shore installation can result in electrical arcing at the manifold during connection and disconnection. This is entirely a separate issue from static electricity.
Metal loading / discharging arms provide low resistance and there is risk of an incentive arc occurring when the current is suddenly interrupted during manifold connection / disconnection. Similar arcs can occur with flexible hose strings containing metal connections between the flanges of each length of hose.
To prevent this the terminal should provide means of electrical isolation within the connection to ensure electrical discontinuity between ship and shore.
This is normally achieved by an insulating flange, alternatively, in flexible hose strings one length of non-conducting hose without internal bonding is provided. This protects against low voltage but high amperage circuits caused by stray currents, cathodic protection and galvanic cells. It does not protect against high voltage low current sparking associated with static discharge.
The whole connection remains earthed, either to the ship on the ship side of the isolation, since all parts are electrically continuous, or to the shore on the shore side of the isolation for similar reasons.
The following points must be verified to ensure the isolation is not compromised –
- The insulating flange (which should be clearly labelled) or single length of non-conducting hose must not be short circuited by contact with external metal i.e. a metallic hose flange on the ship side of the isolation must not make contact with the jetty structure or short circuit by wire guys on metal arms. The insulating flange should be inserted at the jetty end where it is not likely to be disturbed.
- When the connection is partly flexible and partly metal arm the insulating flange is fitted to the metal arm.
- The insulating flange must be clean, unpainted and ice free.
When ship hoses are to be used for cargo transfer, the Chief Officer is to ensure that electrical bonding is checked prior to commencing operations to ensure intermediate flanges in the ship / shore hose will still be earthed by the continuous path to earth via the ship's manifold and hull.
Ship / Shore Bonding Cables ( use not recommended)
Investigations have proved that ship / shore bonding wires are ineffective and serve no useful purpose and they are only to be connected on the insistence of the terminal or required by local regulations. A ship / shore bonding cable does not replace the requirement for an insulating flange.
The following points must be verified if a bonding cable is to be used –
- The cable to be visually inspected to be mechanically sound
- The connection point shall be well clear of the manifold
- The switch in the bonding circuit must be off before permitting connection / disconnection to the ship and the cable is to be attached before the manifold arm / hose connection is made and removed only after manifold arm / hose disconnection is completed.
- All ullage ports must be securely closed and no sampling, sounding or dipping of tanks is in progress during connection / disconnection of the bonding cable to the ship
- No cargo, ballasting, tank cleaning or gas freeing operations are in progress during connection / disconnection of the bonding cable to the ship.
Flame Arrestors
All flame arrestors and screens, if fitted, must be maintained, in good condition and replaced if they deteriorate to the point where they will become ineffective. Passage of gas may be dangerously restricted if these devices become blocked. Flame screens must never be painted.
Radio Equipment And Radar
When berthed the ship’s normal communications equipment must not be used unless certified as being safe. This also applies to mobile telephones, pagers, loudhailers and searchlights etc.
Main radio transmitters are not to be used in port and all aerials must be disconnected and earthed. Usually this does not apply to, satellite equipment and permanently correctly installed VHF equipment, however, Masters must be aware that many ports, as a national requirement, do not permit the use of satellite equipment.
Whilst the vessel is alongside and engaged in cargo operations the ship’s radar equipment is not to be operated.
Electrical Equipment / Fittings
All electrical equipment and fittings outside the accommodation and machinery spaces must be intrinsically safe. Damaged electrical fittings must be isolated and not used until they are repaired. Particular care must be taken to ensure that portable electrical equipment such as radio telephones, pagers and electrical equipment cameras etc. are not used in hazardous areas. Conventional battery powered watches can be used in a gas hazardous area as there is no risk of the watch causing an explosion.
Smart Watches / Fitness bands have far greater power and are not considered safe and therefore prohibited for use in gas hazardous areas.
The batteries for portable equipment must not be changed on the open decks, and strict control to be put in place to ensure that the following are intrinsically safe:
- Hermetic Ullaging Equipment
- VHF/UHF radios
- Torches
- Gas detection Equipment
- Cameras when used in any dangerous areas, must not contain batteries or other electrical circuits, unless intrinsically safe
- Smart watches / Fitness bands
Damaged portable equipment must not be used until it is repaired.
The level of protection provided by explosion-proof or intrinsically safe electrical equipment may be compromised by incorrect maintenance procedures.
Even the simplest repair and maintenance operations must be carried out in strict compliance with the manufacturer’s instructions so that such equipment remains in a safe condition.
In particular, regarding lights where incorrect closing after changing a light bulb could compromise the integrity of light.
Lights and P/R fans’ electric SMOrs locate don weather deck areas and in cargo pumprooms must be periodically inspection as per the PMS.
During inspections of electrical equipment or installations, particular attention should be paid to the following:
- Cracks in metal, cracked or broken glasses or failure of cement around cemented glasses in flameproof or explosion-proof enclosures;
- Covers of flameproof enclosures to ensure that they are tight, that no bolts are missing and that no gaskets are present between mating metal surfaces;
- Each connection to ensure that it is properly connected;
- Possible slackness of joints in conduit runs and fittings;
- Clamping of armouring of cable;
- Stresses on cables which might cause fracture;
- Condition of earth wire;
- Insulation test of ventilation SMOrs as per periodic test planning;
- Vibration analysis of the electric SMOrs in order to assess the bearing condition and prevent a sudden failure of the SMOr with associated risk of fire.
Maintenance of oil tanker piping system
Oil tanker pipes pose a hidden danger, a danger that is often forgotten about.
Pipes are silent workers, conveying fluid or allowing air to enter
or to leave a space, and are the means by which many control
systems operate. They are unnoticed until pipe failure occurs and
a machine stops operating, a space floods or oil is spilled.
Pipes
penetrate almost every enclosed space, as well as the shell both
above and below the waterline, and the weather deck. There is no
system on a ship that has such enormous potential to cause fire,
pollution, flooding or even total loss.
The majority of ships’ pipes are constructed of ferrous material,
a material that is attacked by all forms of corrosion. As a ship
ages, so does the piping system. Maintenance is not always easy,
because pipes, unlike the hull, are difficult to examine because
of their numbers and inaccessibility. It is practically impossible
to maintain them internally, where most corrosion takes place,
and at times just as difficult to maintain a pipe’s external surface.
As a result, pipes can receive minimum maintenance, and pipe
failure is often the result. As an operator once remarked when
asked, “When is it necessary to replace a pipe?”, “When it bursts.”
Failed pipes cause, or contribute to, many serious claims. Pipe
failure will only be prevented by a proactive approach to
inspection, maintenance and repair. A product tanker was gravity ballasting into a segregated tank.
The ballast line passed through a cargo tank. When ballast
stopped flowing, a corrosion hole in the line allowed oil to
escape into the sea through an open valve. Cost – $975,000.
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