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What is the purpose of bolt tightening sequence in flanged joints?

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Bolted flange joint is widely used in watermains. In essence, a bolt axial tension is applied by the torque control method. The preload values are recommended by gasket suppliers to control gasket crushing and to achieve proper gasket seating stress. A proper bolt tightening sequence in flanged joints is essential to control stress variation in flange joint components. Otherwise, leakage occurs at flanged pipe joints during operating conditions.

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Most joint surface of joints is not completely flat. The sequence of bolt tightening exerts a huge effect on the resulting preloads. Since joints containing gaskets have a comparatively low compressive stiffness, bolt preloads in such joints are particularly sensitive to the tightening sequence. Owing to the compression of joint surfaces, tightening one bolt close to another pre-loaded bolt will affect the preload generated by the firstly-tightened bolt. A proper bolt tightening sequence ensures that an even preload distribution is achieved in the flanged joint.

bolt tighting system in flange

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

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