TPi January 2010

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60 Tube Products International January 2010
Risers to withstand
extreme dynamic
stresses
S teel catenary risers are welded pipelines that connect
floating deep-sea production platforms to nearby
structures anchored to the seabed. Considerable bending
and continuous motion mean that they are subject to extreme
dynamic stresses. Help is provided by thickened and precisely
machined pipe ends – premium upset riser ends.
Joe Hill of Vallourec & Mannesmann Tubes states, “ Gas
and oil are as indispensable as ever for our civilisation. Most
easily accessible onshore and shallow-water reserves have
already been developed.” New reserves are now found above
all in deep water. Their development requires specialised
technologies and makes more exacting demands on materials.
The challenges facing pipe manufacturers in this sector are
illustrated by the example of the development of premium
upset riser ends (PURE) by V&M Tubes.
“Floating production installations such as Shell’s URSA
platform in the Gulf of Mexico are extremely costly. For this
The tension leg platform (TLP) in the URSA
field has a water displacement of about
97,000 tonnes (photo credit: Shell)
The URSA field was discovered in the Gulf of Mexico in 1991.
It is located in the Mississippi Canyon about 130km southeast
of New Orleans at an average depth of 4,000ft. The production
unit is a tension-leg platform (TLP) with a water displacement of
around 97,000 tonnes, and the total height from the seabed to
the top of the drilling rig is 4,285ft.
The structure was designed to withstand hurricane-strength
winds and waves, and is anchored by 16 steel tendons (four at
each corner), each of which is 3,800ft long. The tendons consist
of pipes with an inside diameter of 32" and a wall thickness of
1.5". At the seabed each tendon is connected to an anchor pile
with a diameter of 96ft and a length of 440ft, weighing about 380
tonnes. Production started on 8 March 1999 with a designed
capacity of 150,000 barrels daily from 14 boreholes.
Two steel catenary risers transfer oil and gas from the URSA
platform to pipelines on the seabed, which carry them 47 miles
to West Delta platform 143. They were installed with the help
of Derrick Barge 50. Under the leadership of Shell Deepwater
Production, the partners in the project are Shell (45%), BP (23%),
Conoco and Exxon (each 16%).