Appropriate flange tightening methods for flat face flanges with full face gaskets are discussed to improve the sealing performance of the bolted flange joints and the workability of flange tightening work.

In general, relatively larger tightening torque is required for a flat face flange with a full face gasket compared to the flange with a ring gasket when we calculate the required tightening torque based on the latest Non-mandatory Japanese Industrial Standard (JIS) evaluation method, “JIS B 2205-1991, Basis for calculation of pipe flanges”[1].

Especially, for the flat face flanges with large diameter and with fewer tightening bolts, this tendency becomes stronger.

This problem sometimes causes a conflict when the flange torque calculation of the minimum required torque value to resist hydrostatic end force at the maximum design pressure of the flange is larger than the maximum allowable torque derived from flange or bolt strength.

So, in this paper, surface stress of several diameter flange faces were measured to clarify whether or not the required stress is applied on the surface of the flat face flanges with full face gaskets.

In addition, pressure tests were carried out to clarify the sealing performance under the condition of circumferentially non-uniform tightening load in each diameter flat face flange with full face gasket.

Based on these test results, minimum flange-tightening bolt axial loads have been summarized to ensure the sealing performance of the flat face bolted flanges with full face gaskets.

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