FEM Stress Analysis and an Evaluation of the Sealing Performance in Non-circular Box-shape Bolted Flange Connections with Gaskets Subjected to Internal Pressure

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.

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FEM Stress Analysis and the Sealing Performance Evaluation in Stainless Steel Elbow and Tee Fittings Under Internal Pressure: Case Where Internal Fluid is Liquid

Storage Tank Integrity and Materials Evaluation ◽

10.1115/pvp2004-3071 ◽

2004 ◽

Author(s):

Toshiyuki Sawa ◽

Hideaki Shimazu

Keyword(s):

Stainless Steel ◽

Internal Pressure ◽

Stress Analysis ◽

Chemical Plants ◽

Three Dimension ◽

Sealing Performance ◽

Internal Fluid ◽

Calculated Stress ◽

Stress States ◽

Screw Threads

Stainless steel fittings such as elbows, tees, nipples and so on have been widely used in mechanical structures and chemical plants, it is well known that the leakage in the fittings used sealing tapes is less than that without the sealing tapes. In a practical design, it is necessary to examine the stress states and the leakage in the fittings under internal pressure and external loads such as tensile loads, bending moments and so on. This paper deals with the FEM stress analysis of the fittings subjected to internal pressure. In the FEM calculations, the engaged screw threads are taken into consideration as helical threads in the three-dimension. The leakage tests for the fittings under internal pressure were also conducted by using liquid (oil). Using the results of the leakage tests and the calculated stress states in the fittings, the sealing performance of the fittings under internal pressure was evaluated and the effect of the tightening torque was clarified on the sealing performance. In addition, the numerical results were compared with the experimental results. As the result, the effects of the sealing tapes on the contact stress distributions were also clarified.

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