Incremental Progress Made in Riser Design

摘要

Plagued by traditional concerns, mechanical toughness, dimensional control, chemical composition and manufacturing quality, riser design, testing and installation soldiers on. As discoveries continue to be made in increasingly deeper water, riser manufacturers and designers are keeping their fingers crossed. Each depth increment increases the challenge to design a system that will perform reliably for nominally 20 years. Always an issue, strength-to-weight ratio is of primary concern as water depths increase, and current thinking favors using alloys that improve those qualities. Fatigue resistance, which manifests itself in several ways, must be a major part of any design. Naturally, the riser terminals are subjected to this stress largely because of vessel motion, but the variable velocity, meandering subsea currents impart vortex-induced vibration (VIV) that can affect the riser almost anyplace along its length. Like the Tacoma Narrows bridge disaster every engineering student has seen played back for 50 years, VIV can be an insidious and destructive force. Mechanical stress is bad enough, but designers must also cope with corrosive fluids and gases that attack the metal from the inside.