The Branched Riser Systems: Concept Development

Abstract

A new riser system concept is being investigated for deep-water application. This is the Branched Riser Systems with its three types: the Branched Steel Catenary Riser (BSCR) System, the Branched Steel Lazy Wave Riser (BSLWR) System and the Branched Lazy Wave Hybrid Riser (BLWHR) Systems. The branched riser system consists of a large bore pipe, which is terminated at an optimized water depth considering the minimum wall thickness requirement from burst and collapse criteria. The larger bore riser pipe is extended from this cut off water depth to the seabed by two smaller riser pipes via a connecting component (connector). The concept draws benefits from the performance of smaller riser bore pipe in strength and fatigue performance besides the opportunities provided by larger bore pipe for maximum flow throughput and vessel top decongestion. Preliminary results from ongoing investigation of type 1 (BSCR) of the branched riser systems, using a 12-inch pipe in combination with two 8-inch riser pipes in a water depth of 3,000m for a cut off water depth of 1500m, indicates a reduction in overall riser weight, stress utilization and fatigue damage at the riser hang off (HO) and touch down zone (TDZ). Results obtained indicate that possible benefits can be achieved through a combination of advantages of smaller and larger bore riser pipe and justifies further research interest on the novel riser concept.

Vessel relocation solution for steel catenary riser touch down fatigue management

“…at each station will follow the pattern depicted by the damage fraction (𝑓 𝑚 ) presented in Figure 16. It should be recalled that the exposure time is 𝑇 𝐷 factored by 𝑓 𝑚 , where the 𝑓 𝑚 at each of the stations (𝑚 = 1 𝑡𝑜 𝑝) are calculated from equation (10). The exposure times at each of the 19 stations are presented in Table 7.…”

“…Substituting equation ( 9) into equation ( 4), the resulting coefficient of 𝑇 𝐷 is expressed in equation (10). This is referred to as the fatigue damage fraction, 𝑓 𝑚 .…”