We were hired to design a new piping system that routes piping from four relief valves on top of the FCC Fractionator to a blowdown drum. Previously, these vented to atmosphere.
For the pipe stress analysis, the main challenges were the necessity of supporting the piping independent of the Fractionator; the installation of the new piping would be phased and completed while the system was in operation, so the new piping would need to be routed to avoid the existing piping. An adjacent structure was used to support the piping, but the loading onto the relief valves became problematic due to the differential growth between the vessel and structure. The location of the supports on the structure were important to minimize any moments generated when the grows while operating. To accommodate construction and maintenance, the client later agreed to the addition of a cantilevered structure above the vessel. We were able to utilize this additional structure to optimize the design. This evaluation included numerous load cases, including various relieving cases with reaction forces, temperatures/pressures, wind and seismic, and other code and client requirements.