Failure Analysis of LDPE Compressor Bolts Available to Purchase

In Low Density Polyethylene (LDPE) plant, the ethylene gas is compressed up to a pressure of 3000 bar. This is achieved by compressing the ethylene gas using two stages as primary [18 °C (64.4 °F), 1700 bar] and secondary [90 °C (194 °F), 3000 bar] stage compressors. The studs under investigation were used to clamp the flange of the suction and discharge valves to the cylinder head (Studs from the Flanges of 1st Stage - Secondary Hyper Compressor). Six cylinders are present in each stage and 6 studs are used to fix each flange on the suction or discharge valve to the cylinder head. The material used to fabricate these studs was B7 and the threads were produced by rolling. In the 1st stage cylinders frequent failures of studs started within two months of operation. Since the start up about 11 studs from different location have been failed. A metallographic examination using optical and scanning electron microscopy as well as energy dispersive spectrometry (EDS) revealed that the failure was due to fatigue.