A comparison of pressurised cylinders in HIP systems using CFD and FEM

Sammanfattning: A hot isostatic press (HIP) is a system which utilises high temperatures and pressure in order to densifyand enhance the material properties of components in the aerospace, automotive and additive manufacturingindustries, to mention a few. Quintus is a world leading manufacturer of HIP systems, and this master’s thesiswork has been written in collaboration with them. A HIP consists of a cylinder which gets filled with an inert gas, a gas which is then pressurised using compressors.Inside of the cylinder are heaters which ensure that the gas and load reach the desired temperature. Quintus’HIP construction has a wire wound cylinder. This means that a pre-stressed wire is wound around the cylinderfor a number of laps, resulting in the cylinder always being in a compressive stress state, thus ensuring a safeconstruction if a crack were to propagate in the material. This construction also allows for a more slim design ofthe cylinder which is beneficial when the gas is to be cooled, as the heat gets transported through the cylinder.An alternative design to this wire wound cylinder is a so called monoblock cylinder. This is a solid, thicker,cylinder, not wound by any wire. Quintus does not manufacture the monoblock HIP system, but these HIPs areon the market and therefore Quintus is keen to learn more about them. In this work, differences in the cooling capabilities with respect to the cylinders’ strength has been investigated,regarding the wire wound and monoblock cylinders. This has been done by the means of CFD and FEM(ANSYS CFX and ANSYS Mechanical), where a simplified 2D axisymmetric model of each HIP version wasused. In CFX, both a steady state and transient simulation was run for each model in order to capture the coolingof the gas. The resulting temperature load on the cylinder was then exported to the Mechanical setup to solvefor the arising stresses of the cylinders. The results of the work showed that the wire wound HIP does indeed exceed the monoblock cylinder when itcomes to the cooling rate, especially after some time when the gas has cooled off. Neither one of the cylinderswere at risk of yielding, and the monoblock cylinder was calculated to withstand >20 000 cycles, which is alsothe fatigue life of the wire in Quintus’ HIPs. The models and boundary conditions used in this work weresubjected to approximations, but the results obtained have still brought a lot of new insights to the monoblockconstruction, and have provided a good foundation for further analyses.