Flange joint to provide a seal is constructed by inserting a gasket between the two flanges and fastening them with bolts. The gaskets can be divided into four different categories, such as sheet gaskets, corrugated metal gaskets, ring gaskets and spiral wound gaskets. Among them, the ring gaskets, known as the Ring Type Joint(RTJ), are mostly used in offshore oil and gas pipelines and are designed to work under extremely high pressure. They are solid rings of metal in different cross sections like oval, round, octagonal etc.
Since the performance of flange joint is determined by the strength and sealing capability, it is necessary to conduct the research for the behavior characteristics and the contact pressure between the flange and the gasket, in order to investigate whether the joint is able to play a role under the given conditions.
In the flange connection, it is important to maintain the appropriate contact pressure, since while the insufficient bolt tightening force reduces the sealing capability, the excessive clamping force makes shorten the service life of the connection.
In this study, finite element analysis on the contact characteristics of flange joints for CLASS 600 and CLASS 900 specified in ASME 16.5, which are widely used in the industry, was carried out in order to obtain the basic information for product development and management for the unexpected failure. First, the contact force and stress levels after the gasket was bolted up in the flange were examined for five models in each CLASS, and then the changes in the behavior characteristics and the contact force due to internal pressure were investigated to compare with previous results.
As a result, the maximum contact pressure of the oval type ring gasket is higher than that of the octagonal type ring gasket, because of the difference of the contact surface area. However, the octagonal type gasket, which has a relatively large contact area, is supposed to be more reliable from the contact stability point of view. Also, the results reveal that the maximum stress levels are slightly decreased after the fluid pressure acts upon the inner surfaces of the flange joint.