Section
12 Air, overflow and sounding pipes
12.1 Definitions
12.1.1 Reference
to cargo oil in this Section is to be taken to mean cargo oil which
has a flash point 60°C or above (closed cup test).
12.2 Materials
12.2.2 The
portions of air, overflow and sounding pipes fitted above the weather
deck are to be of steel or equivalent material.
12.3 Nameplates
12.3.1 Nameplates
are to be affixed to the upper ends of all air and sounding pipes.
12.4 Air pipes
12.4.1 Air
pipes are to be fitted to all tanks, cofferdams, tunnels and other
compartments which are not fitted with alternative ventilation arrangements.
12.4.2 The
air pipes are to be fitted at the opposite end of the tank to that
which the filling pipes are placed and/or at the highest part of the
tank. Where the tank top is of unusual or irregular profile, special
consideration will be given to the number and position of the air
pipes.
12.4.3 For
a normally inaccessible small void compartment such as an echo sounding
compartment, which is accessed from within a normally inaccessible
space such as a forepeak tank, alternative air pipe arrangements to
those required by Pt 5, Ch 13, 12.4 Air pipes 12.4.1 may
be considered. For such arrangements, a warning notice is to be located
in a prominent position specifying the precautions to be taken prior
opening the manhole and entering the small void compartment. Ventilation
arrangements are to be submitted to LR for approval.
12.4.4 For
unmanned pontoons not fitted with auxiliary power and where portable
pumps are provided in accordance with Pt 5, Ch 13, 10.1 Pumps 10.1.3, void spaces need not be provided with air pipes or
any other means of ventilation. In this case, a warning notice is
to be placed in a prominent position specifying the precautions to
be taken prior to opening a manhole of a void space.
12.5 Termination of air pipes
12.5.1 Air
pipes to double bottom tanks, deep tanks extending to the shelll plating,
or tanks which can be run up from the sea are to be led to above the
bulkhead deck. Air pipes to fuel oil and cargo oil tanks, cofferdams
and all tanks which can be pumped up are to be led to the open. For
height of air pipes above deck, see
Pt 3, Ch 12, 3 Air and sounding pipes.
12.5.2 Air
pipes from storage tanks containing lubricating or hydraulic oil may
terminate in the machinery space, provided that the open ends are
so situated that issuing oil cannot come into contact with electrical
equipment or heated surfaces. Air pipes from heated lubricating oil
tanks are to be led to the open.
12.5.3 The
open ends of air pipes to fuel oil and cargo oil tanks are to be situated
where no danger will be incurred from issuing oil vapour when the
tank is being filled.
12.5.4 The
location and arrangement of air pipes for fuel oil service, settling
and lubricating oil tanks are to be such that in the event of a broken
vent pipe, this does not directly lead to the risk of ingress of sea-water
or rainwater.
12.6 Gauze diaphragms
12.6.1 The
open ends of air pipes to fuel oil and cargo oil tanks are to be furnished
with a wire gauze diaphragm of incorrodible material which can be
readily removed for cleaning or renewal.
12.6.2 Where
wire gauze diaphragms are fitted at air pipe openings, the area of
the opening through the gauze is to be not less than the cross-sectional
area required for the pipe, see
Pt 5, Ch 13, 12.8 Size of air pipes.
12.7 Air pipe closing appliances
12.7.1 The
closing appliances fitted to tank air pipes in accordance with Pt 3, Ch 12, 3 Air and sounding pipes are to be of an automatic
opening type which will allow the free passage of air or liquid to
prevent the tanks being subjected to a pressure or vacuum greater
than that for which they are designed, and prevent the free entry
of water into the tanks.
12.7.3 Wood
plugs and other devices which can be secured closed are not to be
fitted at the outlets.
12.7.5 Air
pipe automatic closing devices shall be constructed to allow inspection
of the closure and the inside of the casing as well as changing the
seals.
12.7.6 Efficient
ball or float seating arrangements are to be provided for the closures.
Bars, cages or other devices are to be provided to prevent the ball
or float from contacting the inner chamber in its normal state, and
made in such a way that the ball or float is not damaged when subjected
to liquid impact due to a tank being overfilled.
12.7.7 Air
pipe automatic closing devices are to be self-draining.
12.7.8 The
clear area through an air pipe closing device in the open position
shall be at least equal to the area of the inlet.
12.7.10 The
maximum allowable tolerances for wall thickness of floats shall not
exceed ±10 per cent of thickness.
12.7.11 The inner and the outer chambers of an automatic air pipe head are to be of
a minimum thickness of 6 mm. Where side covers are provided, and their function is
integral to providing functions of the closing device as outlined in Pt 5, Ch 13, 12.7 Air pipe closing appliances 12.7.1, they shall
have a minimum wall thickness of 6 mm. If the air pipe head can meet the tightness test
in LR’s Type Approval Test Specification Number 2 without the side covers attached, then
the side covers are not considered to be integral to the closing device, in which case a
wall thickness less than 6 mm will be accepted.
12.7.12 Casings
of air pipe closing devices are to be of approved metallic materials,
adequately protected against corrosion.
12.7.13 For
galvanised steel air pipe heads, the zinc coating is to be applied
by the hot method and the thickness is to be 70 to 100 microns.
12.7.14 For
areas of the head susceptible to erosion (e.g. those parts directly
subjected to ballast water impact when the tank is being pressed up,
such as the inner chamber area above the air pipe plus an overlap
of 10° or more either side) an additional harder coating should
be applied. This is to be an aluminium-bearing epoxy, or other equivalent
coating, applied over the zinc.
12.7.15 Closures
and seats made of non-metallic materials are to be compatible with
the media intended to be carried in the tank and to sea-water, and
suitable for operating at ambient temperatures between –25°C
and 85°C.
12.8 Size of air pipes
12.8.1 For
every tank which can be filled by the ship's pumps, the total cross-sectional
area of the air pipes and the design of the air pipe closing devices
is to be such that when the tank is overflowing at the maximum pumping
capacity available for the tank, it will not be subjected to a pressure
greater than that for which it is designed.
12.8.2 In
all cases, whether a tank is filled by ship's pumps or other means,
the total cross-sectional area of the air pipes is to be not less
than 25 per cent greater than the effective area of the respective
filling pipe.
12.8.3 Where
tanks are fitted with cross-flooding connections, the air pipes are
to be of adequate area for these connections.
12.8.4 Air
pipes are to be not less than 50 mm bore.
12.9 Overflow pipes
12.9.1 For
all tanks which can be filled by the ship's pumps or by shore pumps,
overflow pipes are to be fitted where:
-
The total cross-sectional
area of the air pipe is less than that required by Pt 5, Ch 13, 12.8 Size of air pipes.
-
The pressure
head corresponding to the height of the air pipe is greater than that
for which the tank is designed.
12.9.2 In
the case of fuel oil and lubricating oil tanks, the overflow pipe
is to be led to an overflow tank of adequate capacity or to a storage
tank having a space reserved for overflow purposes. Suitable means
are to be provided to indicate when overflow is occurring, or when
the contents reach a predetermined level in the tanks.
12.9.3 Overflow
pipes are to be self-draining under normal conditions of trim.
12.9.4 Where
overflow sight glasses are provided, they are to be in a vertically
dropping line and designed such that the oil does not impinge on the
glass. The glass is to be of heat resisting quality, adequately protected
from mechanical damage and well lit.
12.10 Air and overflow systems
12.10.1 Where
a combined air or overflow system is fitted, the arrangement is to
be such that in the event of any one of the tanks being bilged, tanks
situated in other watertight compartments of the ship cannot be flooded
from the sea through combined air pipes or the overflow main. For
this purpose, it will normally be necessary to lead the overflow pipe
to a point close to the bulkhead deck.
12.10.2 Where tanks vent via a common tank, such as an overflow tank, extending to the shell
plating, flooding of this tank as a result of damage to the shell plating is not to
render the entire venting system inoperable.
12.10.3 In
the case of trawlers and fishing vessels, the arrangement is to be
such that in the event of any one of the tanks being bilged, the other
tanks cannot be flooded from the sea through the combined air pipes
or the overflow main.
12.10.5 Where
a common overflow main is provided, the main is to be sized to allow
any two tanks connected to that main to overflow simultaneously.
12.11 Sounding arrangements
12.11.1 Provision
is to be made for sounding all tanks and the bilges of those compartments
which are not at all times readily accessible. The soundings are to
be taken as near the suction pipes as practicable.
12.11.2 Bilges
of compartments which are not at all times readily accessible are
to be provided with sounding pipes.
12.11.3 Where
fitted, sounding pipes are to be as straight as practicable, and if
curved to suit the structure of the ship, the curvature must be sufficiently
easy to permit the ready passage of the sounding rod or chain.
12.11.4 Sounding
devices of approved type may be used in lieu of sounding pipes for
sounding tanks. These devices are to be tested, after fitting on board,
to the satisfaction of the Surveyors.
12.11.5 Where
gauge glasses are used for indicating the level of liquid in tanks
containing lubricating oil, fuel oil or other flammable liquid, the
glasses are to be of the flat type of heat-resisting quality, adequately
protected from mechanical damage, and fitted with self-closing valves
at the lower ends and at the top ends if these are connected to the
tanks below the maximum liquid level.
12.11.6 If
means of sounding, other than a sounding pipe, is fitted in any ship
for indicating the level of liquid in tanks containing fuel oil, lubricating
oil or other flammable liquid, failure of such means or over filling
of the tank should not result in the release of tank contents.
12.11.7 In
passenger ships, sounding devices for fuel oil tanks, lubricating
oil tanks and other tanks which may contain flammable liquids are
to be of a type which does not require penetration below the top of
the tank.
12.11.8 For
a normally inaccessible small void compartment such as an echo sounding
compartment, which is accessed from within a normally inaccessible
space such as a forepeak tank, alternative sounding arrangements to
those required by Pt 5, Ch 13, 12.11 Sounding arrangements 12.11.1 may
be considered. For such arrangements, a warning notice is to be located
in a prominent position specifying precautions to be taken prior opening
the manhole of the small void compartment. Means are to be provided
to indicate flooding of the compartment without opening, such as fitting
indicator plugs to the manhole. Sounding arrangements are to be submitted
to LR for approval.
12.12 Termination of sounding pipes
12.12.1 Sounding
pipes are to be led to positions above the bulkhead deck which are
at all times accessible and, in the case of fuel oil tanks, cargo
oil tanks, lubricating oil tanks and tanks containing other flammable
oils, the sounding pipes are to be led to safe positions on the open
deck.
12.13 Short sounding pipes
12.13.1 In
machinery spaces and tunnels, in circumstances where it is not practicable
to extend the sounding pipes as mentioned in Pt 5, Ch 13, 12.12 Termination of sounding pipes, short sounding pipes extending
to well lighted, readily accessible positions above the platform may
be fitted to double bottom tanks. Where such pipes serve tanks containing
fuel oil or other flammable liquid, an additional sounding device
of approved type is to be fitted. An additional sounding device is
not required for lubricating oil tanks. Any proposal to terminate
in the machinery space, sounding pipes to tanks, other than double
bottom tanks, will be the subject of special consideration.
12.13.2 Short
sounding pipes to fuel oil, cargo oil (flash point not less than 60°C),
lubricating oil tanks and other flammable oil tanks (flash point not
less than 60°C) are to be fitted with cocks having parallel plugs
with permanently attached handles, so loaded that, on being released,
they automatically close the cocks. In addition, a small diameter
self-closing test cock is to be fitted below the cock mentioned above
in order to ensure that the sounding pipe is not under a pressure
of oil before opening-up the sounding cock. Provision is to be made
to ensure that discharge of oil through this test cock does not present
an ignition hazard. An additional small diameter self-closing test
cock is not required for lubricating oil tanks.
12.13.3 As
a further precaution against fire, such sounding pipes are to be located
in positions as far removed as possible from any heated surface or
electrical equipment and, where necessary, effective shielding is
to be provided in way of such surfaces and/or equipment.
12.13.4 In
ships that are required to be provided with a double bottom, short
sounding pipes, where fitted to double bottom tanks, are in all cases
to be provided with self-closing cocks as described in Pt 5, Ch 13, 12.13 Short sounding pipes 12.13.2.
12.13.5 Where
a double bottom is not required to be fitted, short sounding pipes
to tanks other than oil tanks are to be fitted with shut-off cocks
or with screw caps attached to the pipes by chains.
12.13.6 In
passenger ships, short sounding pipes are permissible only for sounding
cofferdams and double bottom tanks situated in a machinery space,
and are in all cases to be fitted with self-closing cocks as described
in Pt 5, Ch 13, 12.13 Short sounding pipes 12.13.2.
12.14 Elbow sounding pipes
12.14.1 Elbow
sounding pipes are not to be used for deep tanks unless the elbows
and pipes are situated within closed cofferdams or within tanks containing
similar liquids. They may, however, be fitted to other tanks and may
be used for sounding bilges, provided that it is not practicable to
lead them direct to the tanks or compartments, and subject to any
subdivision and damage stability requirements that may apply, see
Pt 5, Ch 13, 1.2 Prevention of progressive flooding in damage condition 1.2.1.
12.14.2 The
elbows are to be of heavy construction and adequately supported.
12.14.3 In
passenger ships, elbow sounding pipes are not permissible.
12.15 Striking plates
12.15.1 Striking
plates of adequate thickness and size are to be fitted under open-ended
sounding pipes.
12.15.2 Where
slotted sounding pipes having closed ends are employed, the closing
plugs are to be of substantial construction.
12.16 Sizes of sounding pipes
12.16.1 Sounding
pipes are to be not less than 32 mm bore.
12.16.2 All
sounding pipes, whether for compartments or tanks, which pass through
refrigerated spaces or the insulation thereof, in which the temperatures
contemplated are 0°C or below, are to be not less than 65 mm bore, see also
Pt 5, Ch 13, 2.8 Piping in way of refrigerated chambers 2.8.1 for
insulation.
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