Judy Maksoud
International Editor

LISBON, Portugal -- Jumpers are often designed as static structures, but they are subjected to vortex induced vibration (VIV). Mark Cerkovnic, manager, integrity management, at 2H Offshore told attendees at the 17th annual International Offshore and Polar Engineering Conference on July 3 that both inline and cross flow VIV forces need to be taken into account when designing jumpers.

Jumpers connect flowlines to risers, trees to manifolds, pipelines to pipelines, and flowlines to manifolds, Cerkovnic said. When jumpers are placed subsea, they encounter forces internally from the flow of the stream moving through them and externally from currents and waves.

Because jumper welds are not qualified for fatigue, jumpers are likely to suffer fatigue damage at the connections. In addition to the issue of welds, Cerkovnic said, the thicknesses are mismatched at the bend sections.

Natural flow spots trap water, which leads to corrosion, and shutdown/startup cycles add stress to the jumpers. For these reasons, Cerkovnic said, jumpers should be considered dynamic, not static, and should be designed as such at the outset.

Cerkovnik presented a case study carried out by 2H in which a jumper was evaluated for heave motion, heave acceleration, pitch motion, pitch acceleration, surge motion, and surge acceleration under a number of cycles and varying environmental conditions. "It was definitely beneficial to conduct the analyses in a number of cycles," Cerkovnik said.

The results of the analyses indicated that VIV is an important consideration for subsea jumpers. Cerkovnik suggested that using strakes on both the horizontal and vertical sections of the jumper is advisable because jumpers without strakes have a shorter fatigue life.

Although 2H has conducted significant analysis, Cerkovnik said, "There are a number of reasons to do some more research." However, he is not convinced that the industry is interested in paying for more studies. "I don't think funding for that kind of research is forthcoming," he cautioned.

7/2/2007