More
reliable and cost-effective FPSOs
Posted: 03 May 2004
Improved design procedures to avoid fatigue cracks and fractures
in FPSO vessels have recently been completed by DNV and a consortium
of industry participants.
The design recommendations are incorporated in the DNV guidelines
and tools and will be available to designers and construction yards.
This will lead to more reliable and cost effective FPSOs.
FPSOs (Floating Production Storage and Offloading vessels) are
used globally in remote locations. Both newbuildings and conversions
have to avoid costly production stops by enforcing stricter requirements
as to a reliable fatigue design than those which have previously
been normal for trading ships.
It is vital to design and fabricate according to procedures that
are thoroughly calibrated against reliable data, as fatigue capacity
is highly sensitive to the parameters involved. A slight mismatch
between the calculated stress when designed, and actual stress at
the location when operating, can reduce lifetime dramatically. Results
from tests in this project show that a 10% mismatch of stress can
reduce the actual fatigue lifetime by 1/3.
The improved design procedures are a result of a 5-year dedicated
effort coordinated by DNV and performed in cooperation with oil
companies, designers, operators, shipyards, universities and classification
societies. Altogether 25 industry participants have supported the
project since its initiation in 1998.
The history of structures damaged by fatigue is long and includes
numerous tragedies. There are examples of fatigue cracks in all
types of structures - in towers, bridges, ships and offshore installations.
The Alexander Kielland accident in the North Sea in 1980, where
123 people were killed, is one of the worst known to be caused by
fatigue.
The fatigue testing has been conducted at the large shipyards in
Korea and in the test laboratories at DNV’s head office in
Oslo, Norway. Numerical analyses have been performed to calibrate
the design procedures with the test data.
In total, approximately 30 papers from the project have been published
at conferences and in journals. 14 papers summarizing the project’s
main findings will be shared with the industry at the OMAE special
FPSO conference in Houston from August 31st to September 2nd 2004.
DNV was established in 1864. DNV is an independent foundation with
the objective of 'safeguarding life, property and the environment'.
DNV has a total of 5,700 employees and a network of 300 offices
in more than 100 countries. DNV's head office is in Oslo, Norway.
For more information see http://www.dnv.com/
Posted by Richard Price,
Editor Pipeline Magazine
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