A bundle, in general, comprises flowlines enclosed with carrier pipe and bulkheads at each end. Under operational load conditions, bundle expands in each end and releases forces from inner pipe and induces forces in outer pipe. The bulkheads that try to restrict the bundle expansion are subjected to interface forces on both sides and shall be designed and manufactured against the codes in compliance with DNV-OS-F101. A conventional bulkhead, referred as forged Bulkhead, is typically manufactured by a hot forging process as per the specified standard. For the forged bulkhead, the main body, surface and nibs shall be of specified material grade and the material shall be quenched and tempered after forging. Previous experience from different projects shows that it is sometimes hard for the forged bulkhead to achieve the results from mechanical testing to meet standard requirements and it is even expensive.
A bulkhead manufactured by assembled method can be considered as an alternative. The assembled bulkhead, in the present work, comprises of a plate with boreholes. The small pipe inserts of the respective borehole sizes are fitted through boreholes and circumferentially welded to the bulkhead plate. The ends of each pipe inserts are further welded with the ends of respective size of flowlines of the bundle in one side and the spools on the other side.
The work in this paper presents general design and methodology for the forged bulkhead of 4-line bundle. Further, the work also presents an alternative design for a conventional forged bulkhead. The design is based on FE analyses performed using finite element (FE) tool ANSYS and 3D FE models established by using advanced solid elements from ANSYS. For the same load conditions, the results from analyses show that the assemble bulkhead meets the acceptance criteria from the design methodology and can be considered as an alternative provided that appropriate welding techniques and NDE procedure are ensured in the weld root area of the welds between the pipe inserts and bulkhead plate.