J.G.A. van den Akker
Report 88.3.OS.2500, Transport Engineering and Logistics.
Subsea connectors can be used for various connections between pipe-lines
and flow-lines. Before use however, they must have a certification and
classification of an authority like Lloyd's Register of Shipping or Det
Norske Veritas etc.. Apart from these rules they must also comply to the
functional requirements given by the situation. These requirements are a
consequence of the environmental loads, product loads, installation loads
and required service life.
These rules and requirements, apart from the economical and technical
necessity, form the base for the design of connectors. It is obvious that
with many different situations where connectors have to be installed, there
are also many different types of connectors. Basic types are:
These types can either be hydraulically or mechanically activated, or
sometimes a combination, to make the connection.
- clamp type,
- sleeve type,
- ball-joint type,
- threaded type.
The hydraulically activated connectors have several advantages for use in
deep water because they can be installed diverless. Mechanically activated
connectors are apart from the threaded types mainly used for pipeline
repairs or for connecting flanges and fittings to pipe-ends. Threaded
types are actual outsiders, they are mainly used for riser connections,
however in some special occasions they are used for connections between a
production riser and a wellhead.
Before a connection can be made however, the pipe-ends must be brought into
contact. This aspect is responsible for over 60% of the total costs. Bringing
the pipe-ends into contact is done by one of the following tie-in methods;
Which method has to be used depends on the situation or, apart from the vertical
method from the allowed displacement of the pipe-ends. The displacement is
determined by whether it is a first-end or a second-end tie-in, with the last
situation having the minimum of allowed displacement of the pipe-ends.
- spool-piece method,
- pull-in method,
- lay-away method,
- vertical method.
One of the problems with subsea production systems which incorporate several
wells, is that for each well flowline connections are needed. Economically
looking at this problem shows that it is cheaper to make a bundle of all these
flowlines. This bundle generally also contains control lines and electrical
power lines. For this situation special multi-bore connectors are developed.
These connectors have special difficulties concerning thermal loads and
alignment. They are installed by using hydraulic activation methods.
Apart from connectors there are also other means for connecting pipe-ends. Two
other methods are welded and flanged connections. These methods are generally
used in shallow water with relative good weather conditions during installation.
A disadvantage is their use of equipment, personnel and time. An advantage is
their proven reliability for a long service life with less required maintenance.
As opposed to connectors about which is not much known yet concerning long
service life and required maintenance.
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