Methods for Life Assessment of Hypercompressor Poppet Valves

Valves are extremely important for the availability of hypercompressors in LDPE plants. A methodology for the life assessment of these valves was developed based on numerical calculations and experimental results. A test rig was used to measure the behavior of different poppet valves in terms of differential pressure and valve lift as a function of the process flow. Water is used as the working fluid instead of ethylene, since the flow is almost incompressible. The Measured data were reduced to non-dimensional flow and drag coefficients as a non-linear function of the poppet position. The valve characteristics and real gas data were used in a one-dimensional dynamic simulator to evaluate the poppet position during a single crank cycle together with pressure losses. The calculated dynamic behavior of the poppet was correlated to the failure modes experienced in the field. A dynamic finite element analysis was used to calculate the mechanical stresses on both the poppet and valve body from impact velocities. The stresses from each impact (both during the opening and closing phases) and the axial poppet displacement were accounted for to estimate the total cumulative damage and assess the life of each valve design.