Flapper valve, Reciprocating compressors, Precision strip, martensitic stainless steel
The flapper valve is one of the most critical components of the reciprocating compressor. During the compressor’s service lifetime, the flapper valve has to open and close billions of times without failure or maintenance. Smooth and efficient operation of the compressors not only requires an optimized design of the valve but it also places high demands on its material. Material damping of the flapper valves in the reciprocating compressors positively influences the flapper valve operation by directly reducing the amplitude of the induced stress waves in the valve reeds. It has also been reported in several studies that material damping reduces the amplitude of fatigue stresses in components or specimens subjected to fatigue load conditions. The current study presents an investigation of the material damping properties of a range of hardened and tempered martensitic steels including the newly developed flapper valve steel grade, Flap-X, by voestalpine Precision Strip AB. The tested materials included three flapper valve steel grades Flap-X, AISI 420 (SS716) and AISI 1095 (20C) along with two other thin strip materials (the tool steel (S-Coat L+) and the martensitic stainless steel grade 13Cr0.7C (AEB-L). Material damping was measured using impulse excitation apparatus that measured the resonant frequencies and the loss rate of vibrations in the flexural mode in order to evaluate the material damping parameter (Q-1) at room temperature. Different frequencies were investigated in this study ranging from 50 Hz to approximately 10 kHz for all the tested materials. The measured material damping data for the tested materials showed that the damping decreased with increasing frequency above 50 Hz up to around 2000 Hz and then stabilized until approximately 10 kHz. Material damping for the Flap-X grade was found to be higher than the SS 716 grade at all the measured frequencies and higher than any other valve steel that has been measured, at higher frequencies. In addition, an effort has been made to fit the Rayleigh damping model to the obtained damping data. These results have significant implications for the impact fatigue stresses in the valves, their impact fatigue life and the noise levels they contribute to in the reciprocating compressors.