Page 294 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

straight pipe that will expand considerably under thermal loads. The
restraints must both allow for this thermal expansion and absorb the
---ใช้เพื่อการศึกษาเท่านั้น---
surge forces without overstressing the pipe.

Where motorised valves are installed, several steps can be taken toชย์นาวี
16.10 Reduction of Pressure Surge Hazard

16.10.1 General Precautions

If, as a result of the calculations summarised in Section 16.9, it is found
that the potential total pressure exceeds or is close to the strength of any
part of the pipeline system, it is advisable to obtain expert advice. Where
manually operated valves are used, good operating procedures should
avoid pressure surge problems. It is important that a valve at the end of a
long pipeline should not be closed suddenly against the flow and all
งานห้องสมุด ศูนย์ฝกพาณิ
changes in valve settings should be made slowly.

alleviate the problem:
Reduce the linear flow rate, i.e. the rate of transfer of cargo, to a value
that makes the likely surge pressure tolerable.
Increase the effective valve closure time. In very general terms, total
closure times should be of the order of 30 seconds, and preferably
ึ
more. Valve closure rates should be steady and reproducible, although
this may be difficult to achieve if spring return valves or actuators are
needed to ensure that valves fail safe to the closed position. A more
uniform reduction of flow may be achieved by careful attention to valve
port design, or by the use of a valve actuator that gives a very slow
rate of closure over, say, the final 15% of the port closure.
Use a pressure relief system, surge tanks or similar devices to absorb
the effects of the surge sufficiently quickly.

16.10.2 Limitation of Flow Rate to Avoid the Risk of a
Damaging Pressure Surge
In the operational context, pipeline length and, very often, valve closure
times are fixed and the only practical precaution against the
consequences of an inadvertent rapid closure is correct operation of the
valves and/or to limit the linear flow rate of the oil to a maximum value
related to the maximum tolerable surge pressure.

16.11 Pipeline Flow Control as a Static Precaution

16.11.1 General

Safety procedures for the transfer of static accumulator cargoes require
the linear flow rates of the cargo within the loading lines, both ashore and
on board, to be managed to avoid the generation of static charges during
the cargo transfer (see Chapter 3).

260 © ICS/OCIMF/IAPH 2006