Shinobu Kaneda

Application of Plastic Region Bolt Tightening to Flange Joint Assembly: Behavior of Compact Flanged Joint Subjected to Thermal Load

In the past study the plastic region tightening has been applied to the compact flange joint and its advantages have been demonstrated. However, behavior of the compact flange joint subjected to the thermal load is not investigated. There are reduction of the gasket stiffness, the flange rotation, and difference in the thermal expansion among the members making up the flange joint. It is well known that these problems cause the change in axial bolt force. The present paper describes the behavior of the compact flange joint subjected to the thermal load under the plastic region tightening. Since there is a difference in temperature between the compact flange joint and the bolts, the axial bolt force increases as the temperature of the internal fluid increases. The additional axial bolt force is positive when the thermal loads are applied to the compact flange joint. However, the additional axial bolt force was approximately 3% of the bolt yield force at maximum and the bolt had a sufficient margin for the allowable limit. Additionally, the load factor depends on the change in the elastic modulus due to change in temperature of the internal fluid.Copyright

Three Dimensional Elastic-Plastic Finite Element Simulation on Bolt Tightening Beyond Yield

This paper presents 3-dimensional elastic-plastic finite element stress analysis simulating the behaviors of bolt and nut during the tightening process beyond the bolt yield so called plastic region tightening. The finite element model has the shape of helical threads as it is shown in the actual M16 stud bolt and heavy hex nut. The stress analysis is solved as contact problem among the engaged threads and the nut bearing surface to the clamped body. Tightening torque, thread torque, bearing surface torque and bolt axial force are calculated. They are compared with the experimental test results and show a fairly good agreement. Stress distribution as well as the development of plastic zone in the bolt and nut during the tightening are also demonstrated by this simulation. In addition, the load distribution in the engaged threads are computed and clarified the difference from those based on elastic analysis.Copyright

Application of Plastic Region Bolt Tightening to Flange Joint Assembly: Behavior of Large Diameter Flange

In the past study the plastic region tightening has been applied to the bolted flange joint with smaller nominal diameter and its advantages have been demonstrated, however, behavior of the bolted flange joint with larger diameter is not investigated. Flange rotation of the bolted flange joint with large diameter increases when the internal pressure is applied. Gasket stress is not uniform and it may cause leak accident. So, it is necessary to investigate the behavior of the larger diameter flange. The present paper describes the behavior of bolted flange joint with large diameter under plastic region tightening. Firstly, API 20-inch flange joint tightened to the plastic region by bolt with a smaller diameter and superiority in the uniformity of the axial bolt force is demonstrated. And then the internal pressure is applied to the bolted flange joint and the behavior of the additional axial bolt force is demonstrated. The axial bolt force decreases with increasing the internal pressure, and the load factor is negative due to increasing of the flange rotation. However, the load factor of the bolted flange joint tightened to the plastic region by using the bolt with the smaller diameter approached zero. Using the bolts with smaller diameter is advantageous to the flange joint with the larger diamter, whose load factor is negative, to prevent the leakage. Additionally, the leak rate from the bolted flange joint is measured and the sufficient sealing performance is obtained.Copyright

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

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.Copyright

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

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.Copyright

Application of Plastic Region Tightening Bolt to Flange Joint Assembly

Elastic region tightening based on torque control method is conventional method of tightening a bolt. Axial force of the bolt is controlled by a torque wrench, however, it is not easy to achieve uniform bolt tightening force. When torque method is applied to flange joint assembly, the scatter of the bolt tightening foeces are large. They might cause the leakage of the internal fluid from a flange joint. Recently, plastic region tightening is remarked for critical applications, which provides good uniformity in bolt preloads and high preloads compared with the elastic region tightening. In this research, the plastic region tightening is applied to flange joint assembly and its superiority in uniformity of the bolt tightening force is demonstrated. For the tightening tests, JPI-4inch flange, spiral wound gaskets and M16 bolts were used. Axial force and elongation of all bolts in the flange were measured. Bolts were tightened by modified HPIS flange tightening procedure which incorporates the angle control method into the clockwise tightening sequence. Experimental results show that variations of the axial force in the plastic region was smaller than those in the clastic region. The influence of the elastic interaction on the axial force in the plastic region is also small. It is concluded that the application of plastic region tightening to flange joint assembly is effective for the leak-free joint and that the nominal diameter of the bolt can be reduced.Copyright