In the depreciation evaluations for pressure equipment, it is important for engineers to evaluate the reduction in the sealing performance in bolted flange joints under external loading. In this study the effects of nut thinning due to corrosion on the bolt load reduction in 3 inch and 20 inch bolted flange joints under internal pressure and bending moments are investigated. The stress distributions in the bolted joints, in particular, in using bolts are examined with both FEM calculations and measurements. The obtained stress distributions in the bolts are discussed from the strength standpoint. The sealing performance of the joints with thinned nuts are measured and it is discussed concerning the effect of the thinned nuts on the sealing performance. The following results are obtained:

1) when the height of the nut was kept constant at the 2/3 height of the original dimensions according to the JPI standard, the sealing performance of the joints with the thinned nuts is the same as that with the original height nuts under internal pressure and bending moments.

2) when the height of the nut was reduced to 1/3 height of the original dimensions according to the JPI standard, the sealing performance of the joints could no longer be assured. Thus, it can be concluded that the reduction of the nuts should be checked.

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