(Paragraph 5.6.5 applies to ships constructed on or
after 1 July 2002)
5.6.1 Every cargo piping system
and cargo tank should be provided with the following valves, as applicable:
-
.1 For cargo tanks with a MARVS not exceeding 0.7 bar
gauge, all liquid and vapour connections, except safety relief valves and liquid
level gauging devices, should have shutoff valves located as close to the tank as
practicable. These valves may be remotely controlled but should be capable of
local manual operation and provide full closure. One or more remotely controlled
emergency shutdown valves should be provided on the ship for shutting down liquid
and vapour cargo transfer between ship and shore. Such valves may be arranged to
suit the ship's design and may be the same valve as required in 5.6.3 and should comply with the requirements of 5.6.4.
-
.2 For cargo tanks with a MARVS exceeding 0.7 bar
gauge, all liquid and vapour connections, except safety relief valves and liquid
level gauging devices, should be equipped with a manually operated stop valve and
a remotely controlled emergency shutdown valve. These valves should be located as
close to the tank as practicable. Where the pipe size does not exceed 50 mm in
diameter, excess flow valves may be used in lieu of the emergency shutdown valve.
A single valve may be substituted for the two separate valves provided the valve
complies with the requirements of 5.6.4, is capable of local manual operation and provides
full closure of the line.
-
.3 Cargo pumps and compressors should be arranged to
shutdown automatically if the emergency shutdown valves required by 5.6.1.1 and .2 are closed by the emergency shutdown system required by
5.6.4.
5.6.2 Cargo tank connections
for gauging or measuring devices need not be equipped with excess
flow or emergency shutdown valves provided that the devices are so
constructed that the outward flow of tank contents cannot exceed that
passed by a 1.5 mm diameter circular hole.
5.6.3 One remotely operated
emergency shutdown valve should be provided at each cargo hose connection
in use. Connections not used in transfer operations may be blinded
with blank flanges in lieu of valves.
5.6.4 The control system for
all required emergency shutdown valves should be so arranged that
all such valves may be operated by single controls situated in at
least two remote locations on the ship. One of these locations should
be the control position required by 13.1.3 or
cargo control room. The control system should also be provided with
fusible elements designed to melt at temperatures between 98°C
and 104°C which will cause the emergency shutdown valves to close
in the event of fire. Locations for such fusible elements should include
the tank domes and loading stations. Emergency shutdown valves should
be of the fail-closed (closed on loss of power) type and be capable
of local manual closing operation. Emergency shutdown valves in liquid
piping should fully close under all service conditions within 30 s
of actuation. Information about the closing time of the valves and
their operating characteristics should be available on board and the
closing time should be verifiable and reproducible. Such valves should
close smoothly.
5.6.5 The closure time of 30
s for the emergency shutdown valve referred to in 5.6.4 should be measured from the time
of manual or automatic initiation to final closure. This is called
the total shutdown time and is made up of a signal response time and
a valve closure time. The valve closure time should be such as to
avoid surge pressure in pipelines. Such valves should close in such
a manner as to cut off the flows smoothly.
5.6.6 Excess flow valves should
close automatically at the rated closing flow of vapour or liquid
as specified by the manufacturer. The piping including fittings, valves,
and appurtenances protected by an excess flow valve, should have a
greater capacity than the rated closing flow of the excess flow valve.
Excess flow valves may be designed with a bypass not exceeding an
area of 1.0 mm diameter circular opening to allow equalization of
pressure, after an operating shutdown.