TPi January 2010

Risers to withstand extreme dynamic stresses

The tension leg platform (TLP) in the URSA field has a water displacement of about 97,000 tonnes (photo credit: Shell)

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.

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%).

“ Floating production installations such as Shell’s URSA platform in the Gulf of Mexico are extremely costly. For this

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Tube Products International January 2010

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