Experimental Study on Mechanical Properties of Preloaded Diskspring Steel in Medium Temperature Range
Flange connections in petrochemical equipments easily leak high temperature gas or fluid. Configuration of flange with preloaded diskspring technique are introduced to solve this problem. However, the preloaded diskspring as an important role in flange is easily corroded at high temperature. Temperature fluctuation and strong corrosive circumstances would lower strength of diskspring and causes stress relaxation. Therefore, it is important to search suitable material for diskspring without reduction of strength and stress relaxation used in medium temperature range and strong corrosive circumstances. In this paper, precipitation hardening stainless steel 0Cr17Ni7Al (17-7PH) was studied systematically. Medium temperature mechanical properties are tested experimentally by electric stretch mechanical experiment setup with heater. The medium temperature elastic modulus variations are measured. The variation of elastic hysteresis curve loop area with reciprocating load-unload is measured at different temperature. Experimental results show that the elastic modulus of this material decreases only 0.1% from room temperature to 350°C. The elastic modulus remain almost unchanged at temperature below 300°C which ensure that the loading stability of diskspring does not change when temperature is changed under 300°C. It was found that the elastic hysteretic loop area can be minimized by five times loading-unloading at 300°C which ensure to decrease diskspring’s stress relaxation during long time use within medium temperature range, and it is a key basis for this type of diskspring making. Conclusion: 17-7PH is an ideal elastic material for diskspring used in medium temperature range and highly corrosion environment, and diskspring should be prestressing treated five times at 300°Cduring manufacture to decrease stress relaxation.
Xie Yi and Li Mi
X. Y. Zhou et al., "Experimental Study on Mechanical Properties of Preloaded Diskspring Steel in Medium Temperature Range", Advanced Materials Research, Vols. 129-131, pp. 547-551, 2010