Page 132 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

Ship’s personnel should be provided with clear, unambiguous operating
procedures for the proper management and control of the venting system and
---ใช้เพื่อการศึกษาเท่านั้น---
should have a full understanding of its capabilities.

7.1.8.1 Pressure/Vacuum Breakers
be taken into consideration when checking the liquid condition and level.ย์นาวี
Every inert gas system is required to be fitted with one or more
pressure/vacuum breakers or other approved devices. These are
designed to protect the cargo tanks against excessive pressure or
vacuum and must therefore be kept in good working order by regular
maintenance in accordance with the manufacturer’s instructions.

When these breakers are liquid filled, it is important to ensure that the
งานห้องสมุด ศูนย์ฝกพาณิช
correct fluid is used and the correct level is maintained. The level can
normally only be checked when there is no pressure in the inert gas main
line. Evaporation, condensation and possible ingress of sea water should

In heavy weather, the pressure surge caused by the motion of liquid in
the cargo tanks may cause the liquid in the pressure/vacuum breaker to
be blown out. This may be more liable to happen on combination carriers
than on tankers.

7.1.8.2 Pressure/Vacuum Valves

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These are designed to provide for the flow of the small volumes of tank
atmosphere, caused by thermal variations, in a cargo tank and should
operate in advance of the pressure/vacuum breakers. To avoid
unnecessary operation of the pressure/vacuum breaker, the
pressure/vacuum valves should be kept in good working order by regular
inspection and cleaning.

7.1.8.3 Full Flow Pressure/Vacuum Venting Arrangements
In inert gas systems fitted with tank isolating valves, secondary protection
from over and under-pressurisation of the cargo tanks may be provided
by using high velocity vent and vacuum valves as the full flow protection
device. Where this is the case, particular attention should be paid to
ensuring that the valves operate at the required pressure and vacuum
settings. Planned maintenance procedures should be established to
maintain and test these safety devices. See Section 7.2.1 for details.

7.1.8.4 Individual Tank Pressure Monitoring and Alarm
Systems
In inert gas systems fitted with tank isolating valves, indication of the
possible over and under-pressurisation of the cargo tank is provided by
using individual tank pressure sensors connected to an alarm system.
Where such systems are used, planned maintenance procedures should
be established to maintain and test these sensors and to confirm that
they are providing accurate readings.

7.1.9 Emergency Inert Gas Supply

SOLAS requires that suitable arrangements are provided to enable the inert
gas system to be connected to an external supply of inert gas.

These arrangements should consist of a 250 mm nominal pipe size bolted
flange, isolated from the inert gas main by a valve and located forward of the

98 © ICS/OCIMF/IAPH 2006