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4.16 COLD WEATHER PREPARATIONS

Many tanker destination ports are subject to occasional onsets of extremely cold weather and even more extreme wind-chill factors. A ship arriving at such ports must take all necessary freezing weather precautions before arrival to ensure equipment operability and prevent damage. Failure to take necessary precautions may result in cold temperature damage or impairment to fire and foam systems, steam systems, IGS water seals and P/V breaker, hydraulic systems and domestic water supplies, to the degree that the vessel may be prevented from discharging its cargo.
Cargo heating is discussed in sections 4.2 and 5.5 of this manual.
If the vessel is loading for a cold weather port where ice may be encountered, photograph the condition of hull paint before loading at the loading berth and again after discharging at the discharge berth, to substantiate owner's claim for repainting costs.

4.16.1 Inert gas system (IGS)


Case history
A vessel arrived to discharge a cargo of crude oil in temperatures of -30 C. During the cargo survey it was noted that the deck water seal heating was operational. However, shortly thereafter the water level sight glass shattered. The steam was shut off while repairs were made. After repairs were completed the steam heating lines were found to have frozen. They were eventually thawed out and heating was re-applied to the seal. It was then discovered that the IG pressure sensor line was frozen, preventing the automatic pressure regulating valve from operating. Cargo discharge commenced after a total delay of 17.5 hours.

Case analysis
Crews who do not regularly call at ports with extreme winter conditions rarely understand the details required to maintain proper operation of the IG system under such conditions. A detailed procedure for preparing and operating the vessel in extreme winter conditions should be part of the vessel's operating procedures. Steam lines should never be shut off under freezing conditions without immediate and thorough draining and blowing down. Measures to prevent other IG freezing problems are as follows:
All deck water seals, (wet, semi-dry, or dry), utilise sea water as the reverse pressure seal and must be fitted with some form of water heating system. Any heating should be activated before freezing temperatures are encountered. If the heating system has not been used for some time, it should be tested at the beginning of the loaded passage, so any defects discovered can be repaired before reaching winter conditions.
The liquid filled PV breakers must be checked to verify that they contain a correct anti-freeze/water mixture good to at least -30 C. If there is any doubt about the quality of the anti-freeze, particularly if the vessel has spent long periods trading in hot climates, then replace it.
The IG pressure sensor pipe is a cause of much lost time at the start of discharge operations in cold climates. The IG pressure regulator and transmitter line freeze up between the measuring point forward of the deck isolating valve and the bulkhead penetration into the accommodation superstructure. Freezing lines may also cause false high or low pressure readings and the automatic systems will cause the inert gas to be recirculated or vented to atmosphere instead of being delivered to the cargo tanks where it is needed. The pressure sensor lines should be at least lagged and if possible heat traced and lagged by the ship's crew, since few ship builders bother to do this. The lines should be sloped so that any moisture drains back to the IG line, preventing water accumulations which can freeze.
The IGS scrubber pump should be fed from a sea suction which is sufficiently deep to avoid clogging with ice while at the dock.


4.16.2 Ballast and cargo considerations
Change fresh water ballast or brackish water ballast for sea water prior to arrival in the cold weather zone. Vessels proceeding to Canada or the US east coast in winter should change ballast before crossing the western wall of the Gulf stream.
If the sea water temperature falls below 0 C, all water tanks adjacent to the vessel's shell plating should be reduced to 90% capacity to allow for expansion if freezing takes place.
Restrict the trim to the ship to between one and three meters to avoid the chance of ice sliding along the bottom of the ship and blocking the engine room intakes.
At the cargo berth, take on ballast as early as possible (berth depth permitting) to keep the engine room intakes immersed as deeply as possible. Keep in mind that this will keep the wing tanks immersed longer, with increased cargo cooling than if the ship were at lighter draft.

4.16.3 Hull and manoeuvring
If heavy ice is present at the berth, the ship must be moored so that the bow stems the normal flow of the ice, or the strongest flow if it reverses with the tide.
The anchor should not be used in heavy ice conditions, expect in an emergency.
When manoeuvring in ice, limit the power and speed used to that needed to maintain safe steerage and headway. This will minimise any hull damage.
Minimise the use of astern propulsion.
Examine all impact and dock landing areas of the hull closely. The hull's impact resistance is significantly reduced by extremely cold weather and may sustain damage out of proportion to the impact energy.
After proceeding through heavy ice, closely inspect all safely accessible cargo compartments, void spaces, forepeak, forward deep tanks, cofferdams and pumprooms to discover any damage.
If space, trim and stress permit, shift cargo from the forward wing tanks to the centre tanks, at the same time bringing the liquid level in the No.l wing cargo tanks down to near the water line. This will prevent or minimise pollution damage if the hull is breached at those cargo tanks.

4.16.4 Engine room operations
Avoid carrying bunkers in the deep tanks forward.
Special precautions are required to prevent the blocking of sea inlets by ice. These precautions will vary depending on the type of vessel. The required action should be planned will in advance of arrival at the cold weather port and in close consultation with owner's technical department.
In steam driven vessels, the main and auxiliary circulating pumps should be operated with the crossover open. When operating on the main circulator pump and the vacuum begins to fall off, stop the main circulator momentarily and allow the auxiliary pump to flush back the ice and clear the main injection system.
Reduce the flow of outside air into the engineering spaces by closing down one or more vent fans and throttling the dampers. In a turbine vessel with skylights, opening a skylight or hatch close to the forced draft fan inlet will partially short-circuit normal air circulation and provide warmer air to machinery spaces.
With a diesel driven engine room, caution must be exercised to avoid build-up of higher than normal vacuum inside the engine spaces if vent fans are stopped or dampers closed. Prologued recirculation of air within the engine room, without addition of outside air, will cause a build up of aromatics, hydrocarbons and noxious gasses.
Circulate or recirculate fresh water systems continuously to eliminate the possibility of freezing.

4.16.5 Emergency generator fuel tank
If the emergency fuel tank is not provided with heaters and the pour or cloud point of the fuel are not known, then:
Maintain the tank at a 90% full level to minimise condensation,
Add flow improver to the tank, particularly if it is located above the main deck in a well ventilated space,
If the temperature is expected to fall below -20 C, add one or two barrels of kerosene to the fuel tank,
Verify that the generator cooling system contains sufficient antifreeze to provide protection down to -40 C.

4.16.6 Piping systems
Drain and blow through all utility pipelines not in use, including (but not limited to):
Cargo tank steam smothering system.
Foam fire-fighting system pipelines and branch lines.
Potable water filling lines and systems.
Main fire lines and branch lines.
Cargo tank vent system.
Steam and exhaust lines in the pumproom.
Tank washing lines and branch lines.
Window washing lines.
Deck mains.
Crude oil wash lines after pressure testing (blow through with IG).
If the pumproom steam pipe work cannot be properly drained, then the steam supply must be recirculated to maintain the system warm. Cooling water lines which cannot be drained must be kept circulating while temperatures are below freezing.

4.16.7 Steam deck machinery and steam piping
Turn on deck steam when the outside temperature drops and approaches the freezing point, or during the last hours of daylight in advance of freezing weather. Set all deck machinery in motion, taking care to ensure proper rotation. When the working temperature has been reached, run each winch or windlass at 75% of rated speed, opening up the drain cocks on all cylinders and steam lines. Then shut down the steam supply at the engine room, making sure that all cylinders and pipes are well drained. If possible, the steam lines should be blown through with air.
If the steam lines cannot be drained with confidence, then the machinery must be kept in motion throughout the period of freezing conditions. In this case the machinery should be run at very slow speed, ensuring proper rotation. Painted stripes on the winch drums help to maintain a watch on the deck machinery from the bridge. Open the by-passes between the steam supply and return lines at each winch to ensure an adequate flow of heat to the return lines.

4.16.8 Cargo heating systems
If cargo is not heated, drain and blow through all cargo heating inlet lines, coils and return lines with air to remove all water.
If cargo heating is required during the voyage, carry out the following:
Turn on the cargo heating steam before encountering freezing temperatures.
Keep the heating on until reaching warmer weather; blow the coils and lines through with air immediately after turning off the steam.
Install a small diameter line (flexible jumper line), between the supply and return manifolds on the forward tanks to provide sufficient hot steam to the full length of the deck return lines.
Test all steam and exhaust valves for tightness to prevent leakage into 'dry lines'.

4.16.9 Sanitary system and accommodations
Maintain a continuous, small flow of water through the sanitary system and soil drains. Add a small amount of antifreeze or salt to unused deck drains, drain traps and toilets. Put heating on the sanitary holding tank(s) and overboard line. When possible, or if time permits, steam purge all wash water outlets that do not drain to an outlet or a level well below the water line.
Keep doors closed as much as possible. Keep accommodation and store rooms warm. Be alert to the possibility of flooding from frozen and burst water pipes.
Burst pipes normally become evident when the vessel returns to warmer waters or experiences a substantial rise in the ambient temperature. As a general precaution, all piping that has been blocked by a frozen liquid should be treated as suspect. The pipe section should be isolated and thoroughly examined and tested before being returned to normal water or other liquid service.
If pipe work is fastened to the steel structure of the accommodation, the panel over the pipes should be removed when testing for leakage.
Keep the deck and alleyways as ice free as possible to reduce the danger of slipping. Apply a generous amount of salt, sand or mixture of both to the deck where ice has formed.

4.16.10 Crew
Check that all crew members are wearing clothing and shoes that are sufficient for the weather. Be aware of the possibility of frostbite and reduce the time of exposure of lookouts, mooring crew, or cargo watch to minimise the potential for frostbite.
Vessels which transit cold weather zones must have an adequate supply of cold weather clothing on board, particularly if crew members are from tropical countries. It is the master's responsibility to ensure that all crew members are adequately protected against the weather, including cold temperatures. If adequate clothing and footgear is not on board, order the necessary coveralls and insulated boots for delivery on arrival at the offloading berth or anchorage.
Apply sand to all exterior walkways to ensure safe footing.

4.16.11 Other
Other precautions include:
Raise the pitot tube of the speed log.
Keep radar scanners turning continuously.
Protect lifeboat water supplies as far as possible.
Ensure that lifeboat engine block heaters are operating.

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