The trend of new projects for polyethylene plants indicates a significant increase of production capacity per year. There is a continuous enlargement of pressurised cross sections in the product line of heat exchanger, reactor and remote controlled valves. Consequently an essentially higher load has to be considered on the installed high pressure equipment. Basic knowledge about process and load conditions including pressure pulsation are the fundamental information provided by the process licensor for product optimisation. The level and amplitude of pulsation have a very significant impact on lifetime of the equipment. Cyclic load conditions and measures for improvement of fatigue strength are indicated on diagrams and described. In order to follow the process licensor and safety requirements detailed investigations on proper material selection and improvement of mechanical properties have been performed. Fatigue analysis and fatigue testing are included in the material evaluation. Modern steel technology like vacuum technology, electroslag remelting, heat treatment of special steels, several further hot and cold forming processes and autofrettage are mandatory to achieve an optimised product with satisfactory lifetime, which also fulfils the safety requirements. References to material characteristics including fatigue testing are available from literature, Universities, research laboratories and manufacturers. Parameters like geometry, surface finishing and autofrettage have also an essential impact on fatigue strength. Further activities including fatigue testing with different parameters and load conditions are needed in the future in order to extend the available information about material characteristics and design criteria for high pressure applications.

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