An appropriate flange tightening methods for small bore and low rating piping flange joints are clarified to improve the sealing performance of the bolted flange joints and the workability of flange tightening work. It is said that lubricant on the screw of the bolts and the nut-seating surface can minimize the variability of axial force acting on flange bolts, while this process might make it harder to tight the bolts uniformly especially for small bore low rating flanges. So, in this paper the appropriate condition to apply lubricant is clarified by a series of bolt tightening tests and sealing tests results. On the other hand, for the bolted flanges applying spiral wound gaskets, measuring the gasket compress dimensions help us to prevent uneven tightening balance and to perform the appropriate tightening work. Appropriate gasket compress dimensions are also clarified to ensure the sealing performance for the flanges based on the sealing tests results. Based on these test results, recommended flange-tightening methods have been summarized as an instruction and tightening work procedure to improve the sealing performance of the bolted flanges and the workability of flange tightening work.

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