Air Filling and Sounding the Tanks of a Ship

In nautical terms, the word Sound is used to describe the process of determining the depth of water in a tank or under a ship. Tanks are sounded to determine if they are full or empty. Soundings may also be taken of the water around a ship if it is in shallow water to aid in navigation.

Tanks may be sounded manually or with electronic or mechanical automated equipment. Manual sounding is undertaken with a sounding line- a rope with a weight on the end. The steel vessels with integral tanks are required to have sounding tubes and reinforcing plates under the tubes which the weight strikes when it reaches the bottom of the tank. Sounding tubes are steel pipes which lead upwards from the ships' tanks to a place on deck.

Electronic and mechanical automated sounding may be undertaken with a variety of equipment including float level sensors, capacitance sensors, sonar, etc.

Principle of Sounding:

The process of quantifying the quantity of liquid present inside a tank is called "sounding". We all are aware of storing water in head/gravity tank in our house. Frequently we ensure the level of water is maintained by checking the level in the tank. We fill up the water to the required level and stop filling. We can also say that we “sound” the tank level. In the same way, a ship’s fuel oil (bunker) tank or cargo oil tank has to be checked for its increase/decrease of its level during the operation of the ship/operations carried out on the ship. We will learn how does sounding work in context of ship tanks and the use of marine sounding equipment.

With reference to the above pictorial illustration, "Sounding" is the measure of distance from the bottom of tank upto cargo level in the tank. "ullage" is the distance from the top of the level of cargo to the maximum level or top of the cargo tank. As sounding increases, the ullage decreases, and as ullage increases, the sounding decreaes. It is usual practice on ships to take ullage when cargo/fuel oil is highly viscous. If the cargo/ bunkered oil is viscous, and if "sounding" is taken, then the bob may get sticky and may contribute false readings.

To be clearer let us take the case of “bunker” tanks. As we are aware, bunker tanks are used to carry the entire volume of fuel required for the safe sea passage. When a ship sails from a

port to other, the fuel is getting consumed everyday and subsequent transfer which has to be done from various fuel oil bunker tanks to ships settling & service tanks for the use of propulsion. So, it is always necessary to take “sounding” of the bunker tanks to know the exact quantity of the fuel available on board. Also during bunkering operation, the quantity of fuel oil pumped on board is to be monitored continuously so that the bunker tank does not overflow. If it overflows, it may cause a “marine pollution”, and as per “marpol”, spillage of oil into the sea is prohibited.

Ships such as oil tankers, product carriers and OBO (Oil/Bulk/Ore carrier) ships as they carry oil/liquid as cargo in their cargo tanks, “sounding” of those tanks should be continuously monitored during loading/discharging operations. As tankers are loaded at a very high rate, the level in the tanks raise faster and has to monitored so that the safe quantity of liquid cargo is accommodated inside the cargo tank and changing over of next cargo tank can be done with-out cargo oil overflow as it may cause marine pollution.

A ships tank must have a pipe extending upto the bottom of the tank to a level which is safe to “sound” the contents of the tank. A sounding pipe is a simple steel pipe, which is open at the bottom so that the liquid in the tank gets filled up to the same level as in the tank. As the level in the tank rises, the liquid level in the sounding pipe also increases, thus upon taking sounding, the quantity of liquid can be known.

Within the sounding pipe, a steel flexible measuring tape, with a bob attached at the end is lowered till it strikes the bottom of the tank. When it strikes the bottom of the tank, the level of liquid in the tank, makes an impression on the “sounding tape” so that if we coil up the tape, the impression of content of the tank is seen and the readings are noted. The noted reading indicates the height of the liquid in the tank. “Sounding table” is available onboard which is calibrated in

consideration with the shape of the tank, and trim of the ship. The volume of liquid in the tank is calculated from the sounding table.

Cargo sounding table

Sounding devices are to be fitted to tanks intended to contain liquids as well as to all compartments which are not readily accessible at all times.For compartments normally intended to contain liquids, the following systems may be accepted in lieu of sounding pipes:

a level gauge of an approved type efficiently protected against shocks, or a remote level gauging system of an approved type, provided an emergency means of

sounding is available in the event of failure affecting such system.

Air and Sounding Pipes:

Air pipes are provided for all tanks to prevent air being trapped under pressure in the tank when it is filled, or a vacuum being created when it is emptied. The air pipes may be fitted at the opposite end of the tank to the filling pipe and/or at the highest point of the tank. Each air pipe from

a double bottom tank, deep tanks which extend to the ships side, or any tank which may be run up from the sea, is led up above the bulkhead deck. From oil fuel and cargo oil tanks, cofferdams, and all tanks which can be pumped up, the air pipes are led to an open deck, in a position where no danger will result from leaking oil or vapours. The heights above decks and closing arrangements are covered by the Load Line Conditions of Assignment.

Sounding pipes are provided to all tanks, and compartments not readily accessible, and are located so that soundings are taken in the vicinity of the suctions, ie. at the lowest point of the tank. Each Sounding pipe is made as straight as possible and is led above the bulkhead deck, except in some machinery spaces where this might not be practicable. A minimum bore of 32 mm is in general required for sounding pipes; but where they pass through refrigeration spaces, to allow for icing, a minimum bore of 65 mm is required where the temperature is at 0 degree or less. Underneath the sounding pipe, a striking plate is provided where the sounding rod drops in the bilge well, etc. Sometimes a slotted sounding pipe is fitted to indicate the depth of liquid present, and closed end must be substantial to allow for the sounding rod striking regularly.

Sounding of ships ballast tanks:

Ships ballast tanks contains sea water. It is difficult to trace the impression of water on the steel tape when sounding the ballast water tanks. A “water finding paste” can be used to identify the impression of the level of water present in the tank.

Method to take sounding of the ballast water tank:

1. Apply the water finding paste onto the sounding tape in the area of estimated depth. 2. Drop the sounding tape inside the sounding pipe. 3. Ensure the bob strikes the striker plate at the bottom of the tank. 4. Coil up the tape looking up for the impression. 5. The level is seen as change in color of the paste. Presence of water will turn the paste color to pink from light orange.

Other gauging methods:

Automatic/Remote sounding/gauging equipments:

Certain cargos carried onboard are toxic and hazardous. So, in that case, Sounding of tanks is dangerous. Automation & Instrumentation are used to measure the level of liquid in the tanks. Various patent tank sounding devices are available and can be fitted in lieu of sounding pipes, as long as they satisfy the requirements of classification society.

Those may be

1. mechanically operated float gauges 2. electrically powered servo-operated gauges 3. electrical capacitance gauges 4. bubbler gauges 5. differential pressure gauges 6. pneumatic/hydraulic gauges

7. sonic gauges 8. radio-active methods

Now let us go through the Rules pertaining to Filling, Sounding and Overflow pipes.

1. Air pipes

1.1 General

All internal tanks will have air pipes to prevent overpressure or vacuum in case of filling or discharging. Air pipes may end in the engine room for smaller tanks, but are normally extended to higher external decks or led directly overboard above the waterline. Where extended to higher decks or led overboard, the air pipes may be crossing other compartments and will, in service or accommodation decks, often be hidden behind panels. Some of the air pipes will be subject to a corrosive environment adversely affecting the pipe itself and also the vent heads.

Air pipes are to be fitted to all tanks, double bottoms, cofferdams, tunnels and other compartments which are not fitted with alternative ventilation arrangements, in order to allow the passage of air or liquid so as to prevent excessive pressure or vacuum in the tanks or compartments, in particular in those which are fitted with piping installations. Their open ends are to be so arranged as to prevent the free entry of sea water in the compartments.

1.2 Number and position of air pipes

a. Air pipes are to be so arranged and the upper part of compartments so designed that air or gas likely to accumulate at any point in the compartments can freely evacuate. b. Air pipes are to be fitted opposite the filling pipes and/or at the highest parts of the compartments, the ship being assumed to be on an even keel. c. In general, two air pipes are to be fitted for each compartment, except in small compartments, where only one air pipe may be accepted. When the top of the compartment is of irregular form, the position of air pipes will be given special consideration by the Society. (Two air vents are normally required for long tanks e.g. a ballast tank in a double hull ship. In machinery spaces, two air vents are not normally required). d. Where only one air pipe is provided, it is not to be used as a filling pipe.

1.3 Location of open ends of air pipes

a. Air pipes of double bottom compartments, tunnels, deep tanks and other compartments which can come into contact with the sea or be flooded in the event of hull damage are to be led to above the bulkhead deck or the freeboard deck. (In ships not provided with a double bottom, air pipes of small cofferdams or tanks not containing fuel oil or lubricating oil may discharge within the space concerned). b. Air pipes of tanks intended to be pumped up are to be led to the open above the bulkhead deck or the freeboard deck. c. Air pipes other than those of fuel oil tanks may be led to enclosed cargo spaces situated above the freeboard deck, provided that such spaces are fitted with scuppers discharging overboard, which are capable of draining all the water which may enter through the air pipes without giving rise to any water accumulation. d. Unless otherwise specified, in passenger ships the open end of air pipes terminating within a superstructure shall be at least 1 m above the waterline when the ship heels to an angle of 15°, or the maximum angle of heel during intermediate stages of flooding, as determined by direct calculation, whichever is the greater. Alternatively, air pipes from tanks other than oil tanks may discharge through the side of the superstructure. e. The air pipe of the scupper tank is to be led to above freeboard deck. f. The location of air pipes for flammable oil tanks is also to comply with relevant Rules.

1.4 Height of air pipes

a. The height of air pipes extending above the freeboard deck or superstructure deck from the deck to the point where water may have access below is to be at least:

o 760 mm on the freeboard deck, and o 450 mm on the superstructure deck.

This height is to be measured from the upper face of the deck, including sheathing or any other covering, up to the point where water may penetrate inboard.

b. Where these heights may interfere with the working of the ship, a lower height may be approved, provided the Society is satisfied that this is justified by the closing arrangements and other circumstances. Satisfactory means which are permanently attached are to be provided for closing the openings of the air pipes. c. The height of air pipes may be required to be increased on ships subject to damage stability requirements since the air pipe outlets should be above final water line at any damaged condition assumed by the Damage stability examination as defined in relevant Rules. d. The height of air pipes discharging through the side of the superstructure is to be at least 2,3 m above the summer load waterline.

Note: For ships assigned restricted navigation notation, the height of air pipes may be reduced to:

450 mm on the freeboard deck, 300 mm on the superstructure deck.

1.5 Fitting of closing appliances

a. Satisfactory appliances which are permanently attached are to be provided for closing the openings of air pipes in order to prevent the free entry of water into the spaces concerned, except for pipes of tanks fitted with cross-flooding connections. b. Automatic closing appliances are to be fitted in the following cases:

o where air pipes to ballast and other tanks extend above the freeboard or superstructure decks o where, with the ship at its summer load waterline, the openings are immersed at an angle of heel of 40° or, at the angle of down-flooding if the latter is less than 40° o where, as per 1.3 item c), air pipes terminate in enclosed spaces o where, as per 1.4 item b), air pipes have a height lower than that required in 1.4 item a) o and for ships assigned timber freeboard.

c. Automatic closing appliances are to be of a type approved by the Society. For ships subject to specific buoyancy or stability requirements, the fitting of closing appliances to air pipes will be given special consideration. d. Pressure/vacuum valves installed on cargo tanks, can be accepted as closing appliances.

1.6 Design of closing appliances

a. When closing appliances are requested to be of an automatic type, they are to comply with the following:

o They are to prevent free entry of water into the tanks. o They are to allow the passage of air or liquid to prevent excessive pressure or vacuum coming on the tank. o They are to be so designed that they withstand both ambient and working conditions up to an inclination of -40° to +40° without failure or damage.

o They are to be so designed as to allow inspection of the closure and the inside of the casing as well as changing of the seals. o Where they are of the float type, suitable guides are to be provided to ensure unobstructed operation under all working conditions of heel and trim. o Efficient seating arrangements are to be provided for the closures. o They are to be self-draining. o The clear area through an air pipe closing appliance is to be at least equal to the area of the inlet. o The maximum allowable tolerance for wall thickness of floats is not to exceed ±10% of the nominal thickness. o Their casings are to be of approved metallic materials adequately protected against corrosion. o Closures and seats made of non-metallic materials are to be compatible with the media to be carried in the tank and with sea water at ambient temperatures between -25°C and +85°C.

b. Where closing appliances are not of an automatic type, provision is to be made for relieving vacuum when the tanks are being pumped out. For this purpose, a hole of approximately 10 mm in diameter may be provided in the bend of the air pipe or at any other suitable position in the closing appliance. c. Wooden plugs and trailing canvas are not permitted.

1.7 Special arrangements for air pipes of flammable oil tanks

a. Air pipes from fuel oil and thermal oil tanks are to discharge to a safe position on the open deck where no danger will be incurred from issuing oil or gases.Where fitted, wire gauze diaphragms are to be of corrosion resistant material and readily removable for cleaning and replacement. The clear area of such diaphragms is not to be less than the cross-sectional area of the pipe. b. Air pipes of lubricating or hydraulic oil storage tanks not subject to flooding in the event of hull damage may be led to machinery spaces, provided that in the case of overflowing the oil cannot come into contact with electrical equipment, hot surfaces or other sources of ignition. c. The location and arrangement of vent pipes for fuel oil service, settling and lubrication oil tanks are to be such that in the event of a broken vent pipe there is no risk of ingress of seawater or rainwater. d. Air pipes of fuel oil service, settling and lubrication oil tanks likely to be damaged by impact forces are to be adequately reinforced. e. Where seawater or rainwater may enter fuel oil service, settling and lubrication oil tanks through broken air pipes, arrangements such as water traps with:

automatic draining, or alarm for water accumulation are to be provided.

1.8 Construction of air pipes

a. Where air pipes to ballast and other tanks extend above the freeboard deck or superstructure deck, the exposed parts of the pipes are to be of substantial construction, with a minimum wall thickness of at least:

o 6,0 mm for pipes of 80 mm or smaller external diameter o 8,5 mm for pipes of 165 mm or greater external diameter,

Intermediate minimum thicknesses may be determined by linear interpolation.

b. Air pipes with height exceeding 900 mm are to be additionally supported. c. In each compartment likely to be pumped up, and where no overflow pipe is provided, the total cross-sectional area of air pipes is not to be less than 1,25 times the cross-sectional area of the corresponding filling pipes. d. The internal diameter of air pipes is not to be less than 50 mm, except for tanks of less than 2 m3.

e. Air pipes from several tanks or spaces may be led into a common main line, provided that: o the tanks or spaces are not intended for liquids which are not compatible and that the arrangement could not effect unacceptable condition for the ship o the cross-sectional area of the air pipes main is generally not less than the aggregate cross-sectional area of the two largest pipes discharging into the main. However, a reduced value may be considered for acceptance in each particular case on the basis of back pressure calculation submitted for all normal working conditions o as far as practical, each separate air pipe is fitted to the common air pipe from the top side o where no overflow pipes are provided, the cross-sectional area of a common air pipe from several tanks is not less than 1,25 times the area of the common filling pipeline for these tanks

f. where the tanks or spaces are situated at the shell side, the connections to the air pipes main are to be above the freeboard deck. Where it is not practical, different position proposed as far as possible above the deepest load waterline may be considered for acceptance. For vessels subject to damage stability requirements these connections should be above final water line at any damaged condition assumed by the Damage stability examination as defined in relevant rules.g. Vents acting also as overflows may be accepted provided all the requirements applicable to both vents and overflows are complied with. h. Where tanks are fitted with cross flooding connections, the air pipes are to be of adequate area for these connections.

1.9 Strength requirements to resist green sea forces for the air pipes, ventilator pipes and their closing devices located within the forward quarter length

a. In addition to all other requirements specified before, the following shall apply on the exposed deck over the forward 0,25 L, applicable to:

o All ship types of sea going service of length 80 m or more, where the height of the exposed deck in way of the item is less than 0,1 L or 22 m above the summer load waterline, whichever is the lesser. The rule length "L" is the distance, in m, taken as defined in relevant rules. The requirements do not apply to the cargo tank venting systems and the inert gas systems of tankers.

b. Generally, the bending moments and stresses in air and ventilator pipes are to be calculated at following critical positions:

o at penetration pieces o at weld or flange connections o at toes of supporting brackets.

Bending stresses in the net section are not to exceed 0,8 of the specified minimum yield stress or 0,2% proof stress of the steel at room temperature. Irrespective of corrosion protection, a corrosion addition to the net section of 2,0 mm is then to be applied. Relevant drawing and calculation shall be submitted.

c. For standard air pipes of 760 mm height closed by heads of not more than the tabulated projected area, pipe thickness and bracket heights are specified in table 1 (given below). Where brackets are required, three or more radial brackets are to be fitted. Brackets are to be of gross thickness 8 mm or more, of minimum length 100 mm, and height according to table 2 (given below), but need not extend over the joint flange for the head. Bracket toes at the deck are to be suitably supported. d. For other configurations, means of support determined shall be determined in order to comply with the requirements of item b). Brackets, where fitted, are to be of suitable thickness and length according to their height. Pipe thickness is not to be taken less than as indicated in 1.8. e. For standard ventilators of 900 mm height closed by heads of not more than the tabulated projected area, pipe thickness and bracket heights are specified in table 2. Brackets, where required are to be as specified in item c).

Table 1: 760 mm air pipe thickness and bracket standards

Table 2. 900 mm ventilator pipe thickness and bracket standards

f. For ventilators of height greater than 900 mm, brackets or alternative means of support shall be fitted

according to the arrangement acceptable to the Society. Pipe thickness is not to be taken less than as indicated in 1.8. g. All component parts and connections of the air pipe or ventilator are to be capable of withstanding the loads. h. Rotating type mushroom ventilator heads are not suitable for application in the areas where these requirements are applied. i. Applied loading may be calculated:

The pressures p, in kN/m2, acting on air pipes, ventilator pipes and their closing devices may be calculated from:

p = 0,5 ρ V2 Cd Cs Cp

where: ρ : Density of sea water, equal to 1,025 t/m3

V : Velocity of water over the fore deck, equal to 13,5 m/sec

Nominal pipe diameter (mm)

Minimum fittedgross thickness (mm)

Maximum projected areaof head (cm2)

Height of brackets

(mm)40A 6.0 - 52050A 6.0 - 52065A 6.0 - 48080A 6.3 - 460100A 7.0 - 380125A 7.8 - 300150A 8.5 300175A 8.5 300200A 8.5 1900 300250A 8.5 2500 300300A 8.5 3200 300350A 8.5 3800 300400A 8.5 4500 300

Nominal pipe diameter (mm)

Minimum fittedgross thickness (mm)

Maximum projected areaof head (cm2)

Height of brackets

(mm)80A 6.3 - 460100A 7.0 - 380150A 8.5 - 300200A 8.5 550 -250A 8.5 880 -300A 8.5 1200 -350A 8.5 2000 -400A 8.5 2700 -450A 8.5 3300 -500A 8.5 4000 -

Cd : Shape coefficient, equal to:

0,5 for pipes, 1,3 for air pipe or ventilator heads in general, 0,8 for an air pipe or ventilator head of cylindrical form with its axis in the

vertical direction

Cs : Slamming coefficient, equal to 3,2

Cp : Protection coefficient, equal to:

0,7 for pipes and ventilator heads located immediately behind a breakwater or a forecastle and

1,0 elsewhere and immediately behind a bulwark.

Forces acting in the horizontal direction on the pipe and its closing device may be calculated from formula above, using the largest projected area of each component.

2. Sounding pipes

2.1 Principle

a. Sounding devices are to be fitted to tanks intended to contain liquids as well as to all compartments which are not readily accessible at all times. b. For compartments normally intended to contain liquids, the following systems may be accepted in lieu of sounding pipes:

o a level gauge of an approved type efficiently protected against shocks, or o a remote level gauging system of an approved type, provided an emergency means of sounding is available in the event of failure affecting such system.

2.2 Position of sounding pipes

Sounding pipes are to be located as close as possible to suction pipes.

9.2.3 Termination of sounding pipes

a. As a general rule, sounding pipes are to end above the bulkhead deck or the freeboard deck in easily accessible places and are to be fitted with efficient, permanently attached, metallic closing appliances. b. In machinery spaces and tunnels, where the provisions of item a) cannot be satisfied, short sounding pipes led to readily accessible positions above the floor and fitted with efficient closing appliances may be accepted.In ships required to be fitted with a double bottom, such closing appliances are to be of the self-closing type.

2.4 Special arrangements for sounding pipes of flammable oil tanks

a. Where sounding pipes are used in flammable (except lubricating) oil systems, they are to terminate in the open air, where no risk of ignition of spillage from the sounding pipe might arise. In particular, they are not to terminate in passenger or crew spaces. As a general rule, they are not to terminate in machinery spaces. However, where the Society considers that this requirement is impracticable, it may permit termination in machinery spaces on condition that the following provisions are satisfied:

1. in addition, an oil-level gauge is provided,

2. the sounding pipes terminate in locations remote from ignition hazards unless precautions are taken, such as the fitting of effective screens, to prevent the fuel oil in the case of spillage through the terminations of the sounding pipes from coming into contact with a source of ignition 3. the terminations of sounding pipes are fitted with self-closing blanking devices and with a small diameter self-closing control cock located below the blanking device for the purpose of ascertaining before the blanking device is opened that fuel oil is not present. Provision is to be made so as to ensure that any spillage of fuel oil through the control cock involves no ignition hazard.

b. For lubricating oil and fuel oil leakage tanks less than 2 m3, the oil-level gauge mentioned in a) 1) and the control cock mentioned in a) 3) need not be provided on condition that the sounding pipes are fitted with appropriate means of closure. c. Short sounding pipes may be used for tanks other than double bottom tanks without the additional closed level gauge provided an overflow system is fitted.

2.5 Closing appliances

a. Self-closing appliances are to be fitted with cylindrical plugs having counterweights such as to ensure automatic closing. b. Closing appliances not required to be of the self-closing type may consist of a metallic screw cap secured to the pipe by means of a chain or a shut-off valve.

2.6 Construction of sounding pipes

a. Sounding pipes are normally to be straight. If it is necessary to provide bends in such pipes, the curvature is to be as small as possible to permit the ready passage of the sounding apparatus. b. In cargo ships, the sounding arrangement of compartments by means of bent pipes passing through other compartments will be given special consideration by the Society. Such an arrangement is normally accepted only if the compartments passed through are cofferdams or are intended to contain the same liquid as the compartments served by the sounding pipes. c. Bent portions of sounding pipes are to have reinforced thickness and be suitably supported. d. The internal diameter of sounding pipes is not to be less than 32 mm. Where sounding pipes pass through refrigerated spaces, or through the insulation of refrigerated spaces in which the temperature may be below 0°C, their internal diameter is to be at least 60 mm. e. Doubling plates are to be placed under the lower ends of sounding pipes in order to prevent damage to the hull. When sounding pipes with closed lower ends are used, the closing plate is to have reinforced scantlings.

3. Overflow pipes

3.1 Principle

Overflow pipes are to be fitted to tanks:

which can be filled by pumping and are designed for a hydrostatic pressure lower than that corresponding to the height of the air pipe, or where the cross-sectional area of air pipes is less than that prescribed in 1.8, item d).

3.2 Design of overflow systems

a. Overflow pipes are to be led: o either outside, or o in the case of fuel oil or lubricating oil, to an overflow tank of adequate capacity or to a storage tank having a space reserved for overflow purposes.

b. Where tanks containing the same or different liquids are connected to a common overflow system, the arrangement is to be such as to prevent any risk of:

o intercommunication between the various tanks due to movements of liquid when emptying or filling, or due to the inclination of the ship o overfilling of any tank from another assumed flooded due to hull damage.

For this purpose, overflow pipes are to be led to a high enough point above the deepest load waterline or, alternatively, non-return valves are to be fitted where necessary.

c. Arrangements are to be made so that a compartment cannot be flooded from the sea through the overflow in the event of another compartment connected to the same overflow main being bilged. To this end, the openings of overflow pipes discharging overboard are as a rule to be placed above the deepest load waterline and are to be fitted where necessary with non-return valves on the plating, or, alternatively, overflow pipes from tanks are to be led to a point above the deepest load waterline. d. Where deep tanks which can be used to contain liquid or dry cargo or fuel oil are connected to a common overflow system, arrangements are to be made so that liquid or vapours from other compartments cannot enter such tanks when carrying dry cargo. e. Where tanks alternately containing fuel oil and ballast water are connected to a common overflow system, arrangements are to be made to prevent the ballast water overflowing into the tanks containing fuel oil and vice-versa.

3.3 Overflow tanks

a. Overflow tanks are to have a capacity sufficient to receive the delivery of the pumps for at least 10 minutes. b. Overflow tanks are to be fitted with an air pipe complying with rules mentioned in (1), which may serve as an overflow pipe for the same tank. When the vent pipe reaches a height exceeding the design head of the overflow tank, suitable means are to be provided to limit the actual hydrostatic head on the tank. Such means are to discharge to a position which is safe in the opinion of the Society. c. An alarm device is to be provided to give warning when the oil reaches a predetermined level in the tank, or alternatively, a sight-flow glass is to be provided in the overflow pipe to indicate when any tank is overflowing. Such sight-flow glasses are only to be placed on vertical pipes and in readily visible positions.

3.4 Specific arrangements for construction of overflow pipes

a. The internal diameter of overflow pipes is not to be less than 50 mm. b. In each compartment which can be pumped up, the total cross-sectional area of overflow pipes is not to be less than 1,25 times the cross-sectional area of the corresponding filling pipes. c. The cross-sectional area of the overflow main is not to be less than the aggregate cross-sectional area of the two largest pipes discharging into the main. d. Where overflow sight glasses are provided, they are to be in a vertically dropping line and in readily visible position, fitted with adequate protection from mechanical damage. The overflow sight glasses are not to be used in flammable oil systems except for lubricating oil.

4. Constructional requirements applying to sounding, air and overflow pipes

4.1 Materials

a. Sounding, air and overflow pipes are to be made of steel or any other material approved for the application considered. b. Exposed parts of sounding, air and overflow pipes are to be made of approved metallic materials.

4.2 Minimum thickness of steel pipes

The minimum thickness of sounding, air and overflow steel pipes is given in table under 1.9.

4.3 Passage of pipes through certain spaces

a. Air pipes and sounding pipes led through refrigerated cargo holds or spaces are to be suitably insulated. b. When sounding, air and overflow pipes made of steel are permitted to pass through ballast tanks or fuel oil tanks, they are to be of reinforced thickness. c. Sounding, air and overflow pipes passing through cargo holds are to be adequately protected.

4.4 Self-draining of pipes

Air pipes and overflow pipes are to be so arranged as to be self-draining when the ship is on an even keel.

4.5 Name plates

Nameplates are to be fixed at the upper part of air pipes and sounding pipes.

Fill and sounding pipes for fuel tanks:

  (a) Fill pipes for fuel tanks must be not less than 40 millimeters (1.5 inches) nominal pipe size.

  (b) There must be a means of accurately determining the amount of fuel in each fuel tank either by sounding, through a separate sounding pipe or a fill pipe, or by an installed marine type fuel gauge.

  (c) Where sounding pipes are used, each opening must be at least as high as the opening of the fill pipe and they must be kept closed at all times except during sounding.

  (d) Fill pipes and sounding pipes must be so arranged that overflow of liquid or vapor cannot escape to the inside of the vessel.

  (e) Fill pipes and sounding pipes must run as directly as possible, preferably in a straight line, from the deck connection to the top of the tank. Such pipes must terminate on the weather deck and must be fitted with shutoff valves, watertight deck plates, or screw caps, suitably marked for identification. Diesel fill pipes and sounding pipes may terminate at the top of the tank.

  (f) Where a flexible fill pipe section is necessary, suitable flexible tubing or hose having high resistance to salt water, petroleum oils, heat and vibration, may be used. Such hose must overlap metallic pipe ends at least 1.5 times the pipe diameter and must be secured at each end by clamps. The flexible section must be accessible and as near the upper end of the fill pipe as practicable. When the flexible section is a nonconductor of electricity, the metallic sections of the fill pipe separated thereby must be joined by a conductor for protection against generation of a static charge when filling with fuel.

One sounding pipe per tank is permitted and up to nine vertices per sounding pipe, allowing inclined, bent or curved sounding pipes.

A default sounding pipe is placed at the longitudinal and transverse position of the lowest point of the tank. If the lowest point of the tank is shared between several locations (e.g. the bottom

of the tank is flat either longitudinally or transversely) the default sounding pipe location is placed at the aft-most low point and as close to the centreline as possible. The top of the sounding pipe is taken to be level with the highest point of the tank and the default sounding pipe is assumed to be straight and vertical.

Position of sounding pipes:

Sounding pipes are to be located as close as possible to suction pipes.

Termination of sounding pipes:

a. As a general rule, sounding pipes are to end above the bulkhead deck or the freeboard deck in easily accessible places and are to be fitted with efficient, permanently attached, metallic closing appliances. b. In machinery spaces and tunnels, where the provisions of item a) cannot be satisfied, short sounding pipes led to readily accessible positions above the floor and fitted with efficient closing appliances may be accepted. In ships required to be fitted with a double bottom, such closing appliances are to be of the self-closing type.

Special arrangements for sounding pipes of flammable oil tanks:

a. Where sounding pipes are used in flammable (except lubricating) oil systems, they are to terminate in the open air, where no risk of ignition of spillage from the sounding pipe might arise. In particular, they are not to terminate in passenger or crew spaces. As a general rule, they are not to terminate in machinery spaces. However, where the Society considers that this requirement is impracticable, it may permit termination in machinery spaces on condition that the following provisions are satisfied:

1. in addition, an oil-level gauge is provided. 2. the sounding pipes terminate in locations remote from ignition hazards unless precautions

are taken, such as the fitting of effective screens, to prevent the fuel oil in the case of spillage through the terminations of the sounding pipes from coming into contact with a source of ignition

3. the terminations of sounding pipes are fitted with self-closing blanking devices and with a small diameter self-closing control cock located below the blanking device for the purpose of ascertaining before the blanking device is opened that fuel oil is not present. Provision is to be made so as to ensure that any spillage of fuel oil through the control cock involves no ignition hazard.

b. For lubricating oil and fuel oil leakage tanks less than 2 m3, the oil-level gauge and control cock mentioned in need not be provided on condition that the sounding pipes are fitted with appropriate means of closure. c. Short sounding pipes may be used for tanks other than double bottom tanks without the additional closed level gauge provided an overflow system is fitted.

Closing appliances:

a. Self-closing appliances are to be fitted with cylindrical plugs having counterweights such as to ensure automatic closing.

b. Closing appliances not required to be of the self-closing type may consist of a metallic screw cap secured to the pipe by means of a chain or a shut-off valve.

Construction of sounding pipes:

a. Sounding pipes are normally to be straight. If it is necessary to provide bends in such pipes, the curvature is to be as small as possible to permit the ready passage of the sounding apparatus. b. In cargo ships, the sounding arrangement of compartments by means of bent pipes passing through other compartments will be given special consideration by the Society. Such an arrangement is normally accepted only if the compartments passed through are cofferdams or are intended to contain the same liquid as the compartments served by the sounding pipes. c. Bent portions of sounding pipes are to have reinforced thickness and be suitably supported. d. The internal diameter of sounding pipes is not to be less than 32 mm. Where sounding pipes pass through refrigerated spaces, or through the insulation of refrigerated spaces in which the temperature may be below 0°C, their internal diameter is to be at least 60 mm. e. Doubling plates are to be placed under the lower ends of sounding pipes in order to prevent damage to the hull. When sounding pipes with closed lower ends are used, the closing plate is to have reinforced scantlings.

Ships operation , maintenance and onboard procedure

Carrying out soundings

The Chief Officer and the Chief Engineer (for Engine room) shall designate crew to carry out sounding of bilge and tanks complying with the following standards:

Bilge

(Hold, Engine Room, Cofferdam, Void space, Chain Locker, Emergency Fire Pump Room, Bow Thruster Room, etc.)

No matter whether the vessel is in port or at sea, all spaces which have a bilge sounding pipe (as per ships drawings) shall be sounded at least once a day, except during heavy weather where master finds it is unsafe to access certain locations.

When the Bilge High Level Alarm activated (where equipped), take soundings of the space immediately and keep monitoring.

Any abnormal soundings are to be investigated and reported to the concerned person.

Fresh Water Tanks

No matter whether the vessel is in port or at sea, all fresh water tanks are to be measured and monitored for consumptions at least once a day. Any abnormal findings are to be investigated and reported to the concerned person.

Ballast Water Tanks

No matter whether the vessel is in port or at sea, sound at least a day from the sounding pipe or measure by the remote level gauge.

If remote level gauges are used for the daily soundings, these shall be periodically verified for accuracy by comparing manual soundings with gauge soundings. Sounding pipes on exposed decks may not be sounded when unsafe to do so as in heavy weather. Any abnormal soundings are to be investigated and reported to the concerned person.

Record of soundings

Sounding Note of Bilge and Tanks: The Chief Officer shall prepare the Record Book for Sounding of Bilge and Tanks and shall have crew enter the result of soundings, check it every day and affix his signature. If sounding is not taken for any reason such as heavy weather, proper log entry must be made stating the reason in the Record Book.

Record of Engine Room Bilge: The Chief Engineer shall have crew enter the result of soundings of engine room bilge into the M-zero Check List (or Sounding Note of Engine Room Bilge) check it every day, and affix his signature.

Inspection of bilge high level alarm

The Chief Officer shall test the operation of Bilge High Level Alarm Systems in Cargo Holds every 3 months, and records the results.

The Chief Engineer shall test the operation of Engine Room Bilge High Level Alarm System every month, and record the results.

Note: For the Bilge management, including testing of Bilge High Alarm Systems in Pump Room onboard Tankers are to be followed.

Action in abnormal conditions

When the Chief Officer and Chief Engineer find the following abnormal conditions, he shall notify the Master, examine the cause and take measures immediately:

Abnormal increase of bilge (Confirm whether Sea water or Fresh water)

Abnormal change of tank levelExistence of Oil in the Bilge water or Ballast water

Malfunction of Bilge High Level Alarm System

Sounding of ullage and oil-water interface levels:

In some investigations there is a need to calculate the oil volume in a tank where water has penetrated. This can be done by gauging or sounding the tank’s ullage and oil-water interface level. Ullage and interface gauging is done in cargo and bunker tanks while, on the other hand, determining the sounded level is the most common method for ballast and fresh water tanks, cofferdams, etc. Sounding of interface level and ullage is normally done by means of a steel measuring tape equipped

with a ground wire. The steel measuring tape must be grounded by way of connecting the wire to the ship’s hull. Before a sounding pipe or a manhole is opened it is important to check that the cable clamp is safely contacted to the hull, if necessary, by scraping off paint, rust, etc. There is no risk of static electricity if the steel tape is electrically connected to the ship’s hull. So-called water finding paste may well be used on a normal steel measuring tape to sound the oil-water interface level. The tape is coated with this paste which turns red upon contact with water. Thus, the interface level can be read on the tape.

Alternatively the steel tape can be chalked with ordinary blackboard chalk. On some occasions the contrast between oil and water on the steel tape will be better with chalk than water finding paste. The oil-water interface level can also be sounded by a special oil-water interface meter which may consist of a steel measuring tape with a probe in one end and a handle, with an indicator, in the other end. The indicator gives a response for the conductivity of the medium into which the probe is immersed. When the probe is submerged in the oil the conductivity is rather low but when the probe reaches the water interface the conductivity increases considerably. At this point, the probe’s (and the interface’s) distance to the handle can be read on the steel tape.

Some of the points taken from DNV Rules are given below for clear understanding of provision of Air, Overflow and Sounding Pipes.

Air, Overflow and Sounding Pipes

Air pipes Air pipes shall be fitted to all tanks, cofferdams, shaft tunnels and pipe tunnels. For small dry

compartments without piping installations the requirement for fitting air pipes may be waived.

Air pipes shall not be fitted with valves that may impair the venting function. Tank air pipes shall be placed at the highest part of the tank and as far away as possible from

the filling pipes. Where the tank top is unusual or of irregular profile or of great length, the number and

positions of the air pipes will be decided in each case. For tanks with width exceeding half of the vessel's beam, air pipes on each side will be required.

Pipe tunnels of great length shall be fitted with air pipes in the fore and after ends. The shaft tunnel shall be provided with an air pipe at the after end.

Tanks with anodes for cathodic protection shall have air pipes fitted forward and aft, alternatively a single air pipe provided with a flame screen may be accepted.

Air pipes from tanks which can be filled from the sea and from sea chests shall be carried up to above the bulkhead deck.

Air pipes to fuel oil tanks, double bottom tanks, cofferdams and all other tanks which can be pumped up and to shaft tunnels and pipe tunnels, shall be carried above the bulkhead deck up to the open air.

Air pipes from lubricating oil storage tanks may terminate in the machinery space, provided that the open ends are so located that issuing oil cannot come into contact with electrical equipment or heated surfaces.

Air pipes from fuel oil daily service tanks and settling tanks shall be so arranged that possible ingress of seawater or rainwater through a broken pipe does not reach the fuel oil service tanks. If lubrication oil service tanks have air pipes extending to the open deck, the same requirements as for fuel oil apply.

Air pipes from fuel oil draining tanks with a volume less than 2 m3 and which cannot be pumped up, may terminate in the engine room.

The ends of the air pipes shall be so designed or so located that ingress of water is prevented. Where automatic vent heads with ball floats or similar devices are fitted, they shall be of an approved design.

Air pipes for tanks containing heated fuel shall comply with Rules. Where only one air pipe is fitted, it shall not be used as a filling pipe. All air pipes shall be clearly marked at the upper end. Air pipes shall be self draining under normal conditions of trim. Air pipes for tanks shall not be used as primary means for sounding.

Sectional area of air pipes For tanks which can be pumped up and for which overflow pipes are not arranged, the

sectional area of air pipes shall be dimensioned such that the structure is able to withstand the pressure when the tank is overpumped with the largest available pump.

Documentation of calculated pressure drops in air pipes for water overflow shall be submitted. The calculations shall verify that the dynamic pressure increase during water overflow does not exceed Δpdyn.

Alternatively, arrangements for prevention of overpumping of tanks may be accepted. The sectional area of the air pipes is in no case to be taken less than 125% of the sectional

area of the filling pipe. Automatic stop of ballast pumps or automatic closing of valve in the ballast filling line may

be accepted as arrangement for prevention of overpumping of tanks. Such means should be activated by a remote level gauging system or equivalent. In addition an independent visual and audible high level or high-pressure alarm will be required. The alarm should be activated prior to stop of pumps or closing of valve. Arrangements for functional testing of the automatic stop or closing and alarm systems should be provided.

For short air pipes of the gooseneck type a maximum water velocity of 4 m/s is normally acceptable. If an automatic type airvent head is fitted, the flow resistance is increased and the water velocity must be lower.

For tanks that are filled from installations outside the vessel (e.g. bunker fuel tanks) and not fitted with overflow pipes, the sectional area of air pipes shall not be less than 125% of the sectional area of the filling pipe.

Air pipes shall have an internal diameter not less than 50 mm. However, for tanks of volume less than 0.5 m3 smaller diameters may be considered for air pipes of short length.

Shaft tunnels and pipe tunnels shall be fitted with an air pipe with an internal diameter not less than 75 mm.

Overflow pipes Fuel oil and lubricating oil tanks which can be pumped up and which have openings, for

example, for a float sounding system, shall be fitted with overflow pipes discharging to an overflow tank or bunker oil tank with surplus capacity. The tank openings shall be situated above the highest point of the overflow piping.

The overflow tanks shall have a capacity large enough to take an overflow of ten minutes at the normal rate of filling.

Where a storage tank is used for overflow purposes a signboard shall be fitted to signify that sufficient volume for overflow is ensured.

The overflow system shall be fitted with an alarm device or a sight glass, easily visible from the place where the transfer pump can be stopped.

Where tanks for the carriage of oil or water ballast are connected to an overflow system, the pipe arrangement shall be such that water ballast cannot overflow into tanks containing oil.

The overflow system shall be so arranged that water from the sea cannot enter through the overflow main line into other tanks in case of any tanks being damaged.

This requirement applies if any fuel tank or overflow tank connected to a common overflow line or air vent tank is bounded by bottom shell plating or ship's side plating below the waterline. In such cases the common overflow line or air vent tank must be located higher than the deepest waterline, alternatively individual tank overflow lines must be arranged with loops extending above the waterline.

The overflow pipes shall be self draining under normal conditions of trim and ambient temperature.

Sounding pipes All tanks, cofferdams and pipe tunnels shall be provided with sounding pipes or other

approved means for ascertaining the level of liquid in the tanks. Spaces which are not always accessible, shall be provided with sounding pipes. In cargo holds, sounding pipes shall be fitted to the bilges on each side and as near the suction pipe rose boxes as practicable.

The sounding pipes shall be readily accessible at any time and clearly marked. Sounding pipes are normally to be led to the bulkhead deck. Sounding pipes from tanks that can be pumped up and contains flammable liquids shall be

carried to the open air. Sounding pipes to tanks containing liquids which have a flash point below 60°C (closed

cup), are always to be carried up to the open air. The sounding rod of these tanks shall be of spark proof material and no gauge glasses shall be fitted to these tanks if located in machinery spaces.

The sounding pipes shall be fitted with efficient closing appliances. Short sounding pipes may be fitted to double bottom oil tanks, in shaft tunnels and

machinery spaces and to tanks for lubricating oil and hydraulic oil which can be pumped up, provided the pipes are readily accessible, and the following conditions met:a) A closed type level gauging system is fitted for all passenger ships and cargo ships of 500 gross tonnage and above.b) The sounding pipes terminate in safe distance from ignition hazards. If not, other arrangements shall be made to prevent oil from coming into contact with a source of ignition.c) The terminations of sounding pipes shall be fitted with self-closing cocks having cylindrical plugs with weightloaded levers permanently attached.d) Small test cocks are fitted below the self-closing cocks.

For fuel oil tanks above double bottom short sounding pipes may be permitted on the same conditions provided that in addition the tanks are fitted with an approved oil level gauge.

Short sounding pipes to tanks not intended for oil may be fitted with a screw cap attached by chain to the pipe or with shut-off cocks.

Such arrangement may also be accepted for lubrication oil tanks and hydraulic oil tanks which cannot be pumped up and for fuel oil drain tanks less than 2 m3 which cannot be pumped up.

Oil level gauges of approved type may be installed in lieu of sounding pipes, provided adequate means to prevent release of oil in case of failure or overfilling:— in passenger ships; no penetration below the top of the tank is permitted — in cargo ships; penetrations below the top of the tank shall be fitted with self-closing valves.

Open sounding system will not be allowed for oil fuel tanks which can be heated up to above 50°C.

Remote sounding system of approved type may replace ordinary sounding pipes or gauges as follows:a) For tanks easily accessible for checking of level through for example manholes, one remote sounding system may be accepted.b) For tanks not always accessible for checking of level, two independent remote sounding systems are required. In the case of remote sounding based on the air-bubble principle, two air bubble lines per tank may be accepted provided sufficient redundancy in the central unit is provided.

Sectional area of sounding pipesThe internal diameter of sounding pipes shall not be less than 32 mm. For heavy fuel oil

tanks the internal diameter shall not be less than 50 mm.

The End