Patent ID: 7744312

Claim:
A catenary riser system which includes a pipe string formed by multiple steel pipe sections connected in series by threaded pipe joints, and forming a passage ( 169 ) that fluid flows through, wherein threads of each of said pipe joints has a thread axis lying in the corresponding passage, with the pipe string extending from a floating structure that floats in a sea of a sea depth of a plurality of hundreds of meters to at least a predetermined location on the sea bed, wherein the pipe string has a catenary portion lying in the water and extending in a generally catenary curve from the floating structure to the sea floor and the pipe string has a sea floor quiescent zone (Az) resting on the sea floor, the catenary portion including a touchdown active zone (Bz) extending from the sea floor to a height of a plurality of meters above the sea floor and an upper active zone (Dz) extending a plurality of meters below the floating structure, with the pipe string being subjected to repeated bending in the touchdown zone (Bz) and in the upper zone (Dz) as the floating structure moves, the catenary portion also including an in between quiescent zone (Cz) lying between the upper active zone and the touchdown active zone, wherein: along at least one of said quiescent zones the pipe joints connecting each of a plurality of pairs of series-connected pipe sections is a lower fatigue resistance pipe joint; along at least one of said active zones the pipe joints connecting each of a plurality of pairs of series-connected pipe sections is a higher fatigue resistance pipe joint that has a higher fatigue resistance than said lower fatigue resistance pipe joints.