From Cargo Work: For Maritime Operations, Seventh Edition
There are three basic types of pipeline systems:
Ring main system
Free flow system.
Each system has their uses and is designed to fulfil a need in a particular type of vessel.
The direct system
This is the simplest type of pipeline system which uses fewer valves than the others. It takes oil directly from the tank to the pump and so reduces friction. This has an affect of increasing the rate of discharge, at the same time improving the tank suction. It is cheaper to install and maintain than the ring main system because there is less pipeline length and with fewer valves less likelihood of malfunction. However, the layout is not as versatile as a ring main system and problems in the event of faulty valves or leaking pipelines could prove more difficult to circumvent. Also, the washing is more difficult since there is no circular system and the washings must be flushed into the tanks Figure 5.6.
Figure 5.6: Direct line system. Used mainly on crude and black oil tankers where separation of oil grades is not so important.
The advantages are that:
it is easy to operate and less training of personnel is required
as there are fewer valves it takes less time to set up the valve system before commencing a cargo operation
contamination is unlikely, as it is easy to isolate each section.
The disadvantages are that:
it is a very inflexible system which makes it difficult to plan for...
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