Conference Year

2018

Keywords

Flapper valve, Reciprocating compressors, Precision strip, martensitic stainless steel, tool steel, impact fatigue

Abstract

During the operation of the reciprocating compressors, the flapper valve closes by striking against the valve impact plate. This valve reed and impact plate interaction is repeated billions of times and is thought to play a significant role in controlling the impact fatigue life of the valve reed and, hence, the performance of the compressor. The effect on impact fatigue properties of the interaction between the valve reed and the impact plate has been recognized as one of the potentially important aspects of compressor design. The goal of this study was to understand how the performance and impact fatigue life of the flapper valves was affected by the impact plates made from different steel grades. For this purpose, the impact fatigue testing was performed for Flap-X as the valve reed material against five different steels as the impact plates. Three sets of impact plates were manufactured from the same tool steel grade (Cr-Ni-Mo alloyed steel) but heat treated in three different conditions, one was a steel grade that is frequently used for impact plates in compressors and the fifth was an austenitic stainless steel grade. Ten samples of the Flap-X valve reeds were tested against each impact plate material with 50,000,000 cycles set as the runout limit. Impact fatigue tests were conducted on a custom-built impact fatigue test rig that used air pulses to produce movement of the valve reeds at frequency of 305 Hz and pulse width of 2.2 milliseconds. The test equipment was connected to a dedicated compressor. The operating conditions of test such as the operating frequency (valve reed’s natural frequency), pulse width were carefully selected in order to ensure high values of impact velocity and amplitude of the valve reeds. The estimated average impact fatigue life of the valve reeds tested against the tool steel impact plates, in all test conditions, was found to be higher than for those tested against the currently used impact plate material in compressors and the austenitic stainless steel impact plates. The average values of the impact fatigue test parameters were analyzed in relation to the interaction of valve reeds with the impact plates from different steels. Impact plates and valve reeds were analyzed using stereo microscope and SEM to investigate and compare the damage and fracture after impact fatigue testing. Fracture surface analysis of the failed valve reeds showed possible impact fatigue crack initiation sites and their propagation behaviour.

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