Page 137 - International safety guide for oil tankers and terminals

SHIPBOARD SYSTEMS

7.2.2.2 Tank Over-Pressurisation – Causes
---ใช้เพื่อการศึกษาเท่านั้น---
Over-pressurisation usually occurs during ballasting, loading or internal
transfer of cargo or ballast. It can be caused by one of the following:
Overfilling the tank with liquid.
velocity valves or ice on the surface of the ballast. (See Sectionย์นาวี
Incorrect setting of the tank’s vapour or inert gas isolating valve to the
vapour line or inert gas line.
Failure of an isolating valve to the vapour line or inert gas line.

Failure or seizure of the venting valve or high velocity valve.
A choked flame arrester or screen.
Loading or ballasting the tank at a rate which exceeds the maximum
สมุด ศูนย์ฝกพาณิช
venting capacity. (See Section 7.3.3.1.)
Ice forming on the vents, or freezing of the pressure/vacuum or high

7.1.11.3.)
Restriction in the vapour lines caused by wax, residues or scale.

7.2.2.3 Tank Over-Pressurisation – Precautions and Corrective
Actions

ึ
The major safeguard against tank over-pressurisation is adherence to
good operating procedures. These should include:
On ships without an inert gas system, a procedure to control the
setting of the isolating valves on the vapour lines. The procedure
should include a method of recording the current position of the
isolating valves and a method for preventing them from being
incorrectly or casually operated.

On ships with inert gas systems where isolating valves are fitted to the
branch line to each tank, SOLAS requires these valves be “provided
with locking arrangements which shall be under the control of the
responsible ship’s officer”. This statement should be taken to mean
that the valves must be locked to prevent the possibility of any change
in the valve setting without application to the Responsible Officer to
obtain the means of releasing the locking system on the valve.
งานห้อง A process of regular maintenance, pre-operational testing and operator
A method of recording the status of all valves in the cargo system and

preventing them from being incorrectly or casually operated.
A system for setting the valves in the correct position for the operation,
and monitoring that they remain correctly set.

Restricting the operation of the valves to authorised personnel only.

awareness of isolating valves, pressure/vacuum valves or high velocity
vents can guard against failure during operation.
To protect against over-pressurisation through filling tanks too quickly, all
ships should have maximum filling rates for each individual tank and
these should be available for reference by ship’s personnel (see also
Section 7.3.3). Tank vents should be checked to ensure that they are
clear when the operation commences and, during freezing weather
conditions, they should be inspected at regular intervals throughout the
operation.

© ICS/OCIMF/IAPH 2006 103