Relaxation of the Bolted Flange Connection

Abstract This study researches the total relaxation of a bolted flange connection, taking into account, the relaxation of various bolt grades in conjunction with different semi-metallic gaskets. The test temperatures are: 300 °F (149 °C), 500 °F (260 °C), 650 °F (343 °C) and 800 °F (427 °C), where each temperature setting will cycle three times to obtain the relaxation value for each cycle. The three types of bolt materials for evaluation include ASTM A193 B7, ASTM A193 B16 and ASTM B8M CL2 along with gaskets styles of spiral wound gasket with inner ring, spiral wound gasket with NO inner ring and the kammprofile gasket (grooved metal gasket with covering layers), all in accordance to ASME B16.20 – 2017. The above variations and conditions will be tested at two different initial bolt stresses of 35,000 psi (241 MPa) and 65,000 psi (448 MPa) with a constant internal pressure of 150 psi (10.3 Bar). The results will show relaxation values for the different bolt and gasket types versus the various temperature cycling conditions indicated above. Focusing on: does a certain gasket style offer lower relaxation properties through less creep and/or higher recovery? Does a certain bolt grade offer better stress retention? Is there variation in initial bolt stress for the different style of gasket? How does the initial bolt stress affect the relaxation properties of the bolted connection?