Application of Plastic Region Tightening Bolt to Flange Joint Assembly: Downsizing of Flange Joint and Behavior of Bolt Force Under Internal Pressure

Abstract

The present paper describes the behavior of plastic region tightening of a bolt in a downsized flange joint subjected to internal pressure. An API 4-inch flange joint is downsized for plastic region tightening. The bolt is reduced from M16 to M8, and the bolt pitch circle diameter and the outer diameter of the flange are decreased by 11%. The flange rigidity and the stresses of the compact flange joint are calculated and are superior to the original API flange joint. The bolt spacing is also examined, and the correction factor for bolt spacing is acceptable. Internal pressure is applied to a compact flange joint, and the behavior of additional bolt force is demonstrated. Load factor depends on the type of gasket, such that the load factor is positive for a flexible graphite sheet gasket. The load factor is in agreement with the value calculated by the Load Factor Method (LFM). When the external force is applied to the bolted joint under plastic region tightening, the allowable limit of the additional bolt force is approximately 10% of the bolt yield force. In the present experiment, the additional bolt force is as small as 1% of the bolt yield force. Therefore, the additional bolt force has sufficient margin for the allowable limit.