Page 138 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

Where over-pressurisation of a tank or tanks is suspected, the situation
requires appropriate corrective action. Loading of liquid should cease
---ใช้เพื่อการศึกษาเท่านั้น---
immediately.

7.2.2.4 Tank Under-Pressurisation – Causes
7.2.2.5 Tank Under-Pressurisation – Precautions andณิชย์นาวี
The causes of under-pressurisation are similar to those of
over-pressurisation, namely:

Incorrect setting of the tank’s isolating valve to the vapour line or inert
gas line.

Failure of an isolating valve on the vapour line or inert gas line.
The inert gas fan not being run due to breakdown or failure to
operate it.

Failure in one of the inert gas supply valves.
A choked flame screen on the vapour inlet line.
งานห้องสมุด ศูนย์ฝกพา
Ice forming on the vents of ballast tanks during cold weather
conditions.

Corrective Actions
ึ
The precautions to guard against under-pressurisation are the same as
those relating to over-pressurisation (see Section 7.2.2.3).

Where under-pressurisation of a tank or tanks is suspected, the situation
requires corrective action. Discharge of liquid should cease immediately.

The methods of reducing a partial vacuum in a tank are either to raise the
liquid level in the tank by running or pumping cargo or ballast into the
affected tank from another tank, or to admit inert gas or air into the tank
ullage space.

Cautions

On a ship with an inert gas system, there is a possibility that the
quality of the inert gas may be compromised by air leaking past
the seals in the tank access locations.
Admitting inert gas at a high velocity to return the tank to a positive
pressure could cause an electrostatic hazard.

The precautions identified in Section 11.8.3 should be observed
when measuring and sampling.

On ships without an inert gas system where it is not possible to
reduce the partial vacuum by raising the liquid level, care should
be exercised to ensure that the rush of air does not draw into the
tank foreign objects with a possible ignition capability, e.g. rust.

7.3 Cargo and Ballast Systems

This Section describes the pipelines and pumps used for the loading and discharging of
cargo and ballast. For the purposes of this Guide, the cargo heating system and crude
oil washing (COW) system, where fitted, are considered to be part of the cargo system.

104 © ICS/OCIMF/IAPH 2006