Page 279 - Ship Construction.DJ Eyres 6Ed

Ch23-H8070.fm Page 268 Wednesday, October 18, 2006 7:38 AM
268 Ship Construction
‘Type A’, which are designed primarily using standard traditional meth-
ods of ship-structural analysis. LPG at or near atmospheric pressure or
LNG may be carried in such tanks (see Figure 23.2).
‘Type B’, which are designed using more sophisticated analytical tools
and methods to determine stress levels, fatigue life and crack propoga-
tion characteristics. The overall design concept of these tanks is based on
the so-called ‘crack detection before failure principle’ which permits their
--- ใช้เพื่อการศึกษาเท่านั้น---
use with a reduced secondary barrier (see Figure 23.3). LNG is normally
carried in such tanks.
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
‘Type C’, which are designed as pressure vessels, the dominant design
criteria being the vapour pressure. Normally used for LPG and occasionally
ethylene.

INTERNAL INSULATION TANKS Which are non-self-supporting and
consist of thermal insulation materials, the inner surface of which is exposed
to the cargo supported by the adjacent inner hull or an independent tank.
There are two types:

‘Type 1’, where the insulation or combination of insulation and one or
ึ
more liners act only as the primary barrier. The inner hull or indepen-
dent tank forms the secondary barrier.
‘Type 2’, where the insulation or combination of insulation and one or
more liners act as both the primary and secondary barrier and are clearly
distinguishable as such.

The liners on their own do not act as liquid barriers and therefore differ
from membranes. These tanks are a later addition to the Code and Type 1
is known to have been used for the carriage of LPG.

SECONDARY BARRIER PROTECTION The requirements for secondary
barrier protection are given in Table 23.1.

Liquefied Petroleum Gas Ships
Ships carrying LPG are categorized by their cargo containment system.

FULLY PRESSURIZED TANKS The capacity of fully pressurized ships
3
is usually less than 2000 m of propane, butane or anhydrous ammonia
carried in two to six uninsulated horizontal cylindrical pressure vessels
arranged below or partly below deck. These independent tanks of Type C