Application of Plastic Region Bolt Tightening Method to Larger Flange Connections

Abstract

The plastic region bolt tightening method has been applied to the smaller pipe flange connections and its advantages had been demonstrated. The scatter in axial bolt forces for the smaller pipe flange connections which applied the plastic region bolt tightening method was minimal and it was effective for the leak prevention. In addition it is possible that the bolt diameter is downsized due to an obtainment of the higher axial bolt forces. However, the behavior of the larger flange connections has not been investigated. The flange rotation of larger flanges increases when the internal pressure is applied. In addition, the gasket stress is not uniform and it may cause the leak accident. It is necessary to investigate the behavior of the larger flange connections. The present paper describes the behavior of the larger flange connections under the plastic region bolt tightening. Firstly, JPI 20-inch flange connections tightened to the plastic region by downsized bolt and superiority in the uniformity in the axial bolt forces is demonstrated. And then, the internal pressure is applied to the flange connections and the behavior of the additional axial bolt force is demonstrated. The axial bolt force decreases with an increase in the internal pressure, and the load factor is negative due to increase of the flange rotation. However, the load factor of flange connections tightened to the plastic region by using downsized bolt approached zero. Downsizing of the bolt acts on advantageously for the larger flange connections whose load factor is negative and it is effective to the leakage prevention. Moreover, the leak rate from the flange connections is measured and sufficient sealing performance is obtained.