FEM Stress Analysis and Sealing Performance Evaluation of Large Nominal Diameter (20B) Bolted Flanged Connections with Ring Joint Gaskets under Internal Pressure

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  • 内圧を受ける大口径 (20B) リングジョイントガスケット付き管フランジ締結体の有限要素法応力解析と密封性能評価
  • ナイアツ オ ウケル ダイコウケイ(20B)リングジョイントガスケット ツキ クダフランジ テイケツタイ ノ ユウゲン ヨウソホウ オウリョク カイセキ ト ミップウ セイノウ ヒョウカ

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Abstract

The contact gasket stress in larger nominal diameter bolted flange connection (20B) with a ring joint gasket (RTJ) was analyzed using FEM and the sealing performance of flange connections with RTJ gasket was examined. The nominal size of flange used is 20B (20inch) with 24 bolts and nuts. The ring gasket type and its material are chosen as octagonal type and Cr-Mo steel. In the sealing performance measurements, the bolts were tightened in accordance with JIS B2251 and ASME PCC-1, respectively while the axial bolt forces were monitored using load cells inserted between the nuts and the flange. It was observed that the difference in scatter of bolt preloads and in the leak rate for the 20B bolted flange connection with RTJ gasket was too small between JIS B2251 and ASME PCC-1. It was also found that the leak rate for the connection decreased as the bolt preloads increased. Furthermore, the stress distributions at the contact surfaces between gasket and the flange groove were calculated using FEM. It was found that the maximum contact stress occurred at the inside of the gasket when the bolt preload was small, however, it occurred at the outside contact surface when the bolt preload was bigger. In addition, the highest contact stress moved to outermost of octagonal gasket under internal pressure. The reason why the sealing performance is better for the connection with RTJ gasket is elucidated due to the double sealing mechanism from a change of the higher contact stress the plastic deformation regions at the octagonal gasket. The tightening coefficient was obtained as 1. 90 in both the tightening methods mentioned above.

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