Page 79 - International safety guide for oil tankers and terminals

HAZARDS OF PETROLEUM

natural gasolines than with crude oils. Natural gasolines suffer hardly any
decrease of TVP due to gas depletion when they begin to boil, and
---ใช้เพื่อการศึกษาเท่านั้น---
boiling is much more likely to continue in their case than in the case of
crude oils.

Curves of the kind given in Figure 2.6 suggest that the TVP at the loading์นาวี
2.5.6.2 Special Precautions with Very High Vapour Pressure
Cargoes
When unusually deep gas layers are encountered, very high
concentrations of gas, approaching 100% by volume, may be vented for
prolonged periods during loading. Excessive amounts of gas may then be
งานห้องสมุด ศูนย์ฝกพาณิชย
present on or around the tanker, which may call for special precautions to
be taken.

temperature of the cargo should be used as the criterion for determining
when special precautions are necessary. The Reid Vapour Pressure of a
cargo gives very little guidance unless the temperature of the cargo when
loaded is also specified. However, it has proved to be difficult to select
TVP criteria because they depend ultimately on subjective judgements of
acceptable gas conditions on ships. As a general guide, the information
available suggests that consideration should be given to the need for
special precautions when the TVP is expected to exceed the following
values:
For crude oils, with or without added gas, 1.0 bar. ึ
For natural gasoline type cargoes, for example pentanes plus (C5+),
0.75 bar.

For some intermediate cargoes, for example flash stabilised
condensates, some distillation overhead products and crude oils with
abnormally low methane and ethane contents, TVP limits between the
above two values might be appropriate.

When cargo temperature, crude oil stabilisation conditions and Reid
Vapour Pressures are known, True Vapour Pressures can be calculated
for checking with the above criteria.

Precautions that might then be applied are given in Section 11.1.8.

2.6 Pyrophoric Iron Sulphide

2.6.1 Pyrophoric Oxidation
In an oxygen free atmosphere where hydrogen sulphide gas is present or,
specifically, where the concentration of hydrogen sulphide exceeds that of the
oxygen, iron oxide is converted to iron sulphide. When the iron sulphide is
subsequently exposed to air, it is oxidised back to iron oxide and either free
sulphur or sulphur dioxide gas is formed. This oxidation can be accompanied
by the generation of considerable heat such that individual particles may
become incandescent. Rapid exothermic oxidation with incandescence is
termed Pyrophoric Oxidation.

Pyrophoric iron sulphide, i.e. iron sulphide capable of pyrophoric
oxidation in air, can ignite flammable hydrocarbon gas/air mixtures.

© ICS/OCIMF/IAPH 2006 45