Autofrettaging Procedures on LDPE Hyper-Compressor Components

Hyper-compressors operating in plants with both vessel and tubular reactors are subject to very high pressures. Many cylinder components are exposed to pressures fluctuating between suction and discharge and therefore to high fatigue loads. To reach high endurance capabilities, the cylinder components have to be pre-compressed in order to keep them operating under compressive stress whenever possible. Special materials and shrink fitting procedures are usually required. In other cases or for complex shapes, other technological processes, like autofrettage, are also applied to further improve the pre-stress level. The application of autofrettage requires special rigs to withstand the severe processing conditions and an intensifier to reach final pressures up to 1.4 GPa. Suitable sealing elements, identified through extensive experience, allow to reach very high pressures required to adequately strain the material. The pressure transmitting fluid must also have specific characteristics to avoid solidification. The autofrettage process requires special conditions to increase, maintain and remove the pressure on the system in order to achieve the desired deformation when the plastic strain region is reached. This produces an optimum autofrettage result for enhanced reliability and safe operation of the components.