Laying pipe up to a depth of 3,000m requires large capacity vertical flex-lay systems. A vertical, tiltable lay system, with a 550t top tension capacity, was required for the deployment of flexible products varying from 100 to 630mm in diameter. The 550t pipelaying vessels have been equipped with a tower featuring two 300t tensioners.
Several components have been integrated into the tower. Two A&R traction winches have been installed for handling pipes and pipeline equipment: one system operates with a 138mm wire and 610t line pull capacity, and the other with a 76mm wire and 200t capacity. They are accompanied by A&R sheaves in the tower’s top.
In addition, an under-bender chute and top-mounted aligner chute gradually bend and supply pipes to the tower’s two 300t tensioners, which transport the pipe either through the moon pool, or to the work platform and/or the PLET handling system. A crane on top of the tower can assist operations. The worktable is equipped with a 45t pipeline end terminal (PLET) skidding system to transfer PLETs and other pipeline-related equipment into the ring line.
During laying operations, pipe is fed to the under-bender chute from one of the two underdeck carousels (with product capacities of 2,500t and 1,500t) through an arrangement of winches and a pretensioner on deck. If a pipe is entirely spooled off, it can be kept in the friction hang-off clamp (610t) in the moon pool, ready to connect to a new pipe and continue the laying process. During the recovery of a pipe, the pipe is picked up from the sea bottom with the aid of the A&R winch, usually followed by a sequence of actions and handlings, reverse to that described above. The active heave compensated main crane has a capacity of 250t, and the auxiliary crane at the stern has a capacity of 20t.