Thermal finite element analysis of a trenched umbilical

Umbilicals are commonly laid adjacent to the flowline for the field which they are controlling. Although this can prove to be cost-effective during installation, it can also present potential issues if the flowline is transporting hot fluid which could potentially raise the temperature in the adjacent umbilical.

If the flowline and umbilical are subsequently buried following installation, this can further increase the likelihood of overheating.  Without free-flowing seawater around the flowline, the convection of heat away from the umbilical is removed.  These situations can be looked at on a case-by-case basis, depending on the maximum allowable temperature of the components within the umbilical, the temperature of the adjacent flowline and the relevant thermal conductivities of the surrounding materials.

The client for this project approached Jee during the design phase to run a thermal finite element analysis for their particular scenario, to determine whether the umbilical would remain within allowable temperature limits during operation.  For this project, there was an additional factor to include, a gas lift line which was piggybacked to the flowline.  If the umbilical components were found to exceed allowable limits, it could then be determined how far the umbilical should be displaced from the adjacent flowline, and for what proportion of the length of the line this would be required. 

Benefits to the client from the study include:

• Quick and flexible response to adaptation of input data
• Assurance of a workable solution for installing the two lines
• Wide knowledge base from Jee’s past experience in similar projects
• Determination that the temperature of the umbilical components were within acceptable limits allowing the umbilical to be laid with the flowlines
• Provide a cheaper installation cost to the client