Application of Plastic Region Tightening Bolt to Flange Joint Assembly: Behavior of Bolt Preload in Flange Joint Subjected to Internal Pressure

Abstract

Elastic region tightening by means of the torque control method is a conventional method to tighten bolts. The bolt axial force is controlled by a torque wrench; however, it is not easy to achieve constant bolt axial force. When the torque control method is applied to the flange joint assembly, the scatter of the bolt axial force is significant with respect to the joint reliability, such that it may cause leakage of the internal fluid from the flange joint. Recently, plastic region tightening has received considerable attention, which provides good uniformity in the bolt axial force. In a previous study, plastic region tightening was applied to a flange joint assembly, and the superior uniformity of the bolt axial force was demonstrated. The present paper describes the behavior of the plastic region tightening bolt in a flange joint subjected to internal pressure. First, the flange joint is tightened to the plastic region using a downsized bolt. The internal pressure is then applied to the flange joint, and the behavior of the additional bolt axial force is investigated. Application of plastic region tightening to the flange joint assembly is found to be effective for obtaining leak-free joints and for downsizing of the nominal diameter of the bolt. The behavior of the bolt axial force in a flange joint subjected to internal pressure was clarified. The additional bolt axial force has a sufficient margin for the allowable limit.