The selection of an appropriate assembly bolt load has an upper bound limited by an actual, or perceived, maximum allowable bolt load for the joint. Often, this limit may be selected based on examination of stress levels in the flanges. Present guidelines for selection of the appropriate bolt assembly stress (ASME PCC-1, [1]) use higher bolt loads than the allowable stress levels specified in the design code (ASME VIII, Div. 1, [2]), without justification of why this is an acceptable practice. The basis is, appropriately, the lack of mechanical failure of flanges within industry when bolt loads of that magnitude are employed. Since the basis is industry practice, it is difficult for the end-user to know when it is possible to extend the limits. This is particularly important in cases of joints that are problematic to seal, which may require assembly bolt loads in excess of those found in ASME PCC-1. This paper develops a complete technical basis for why it is acceptable to load flanges beyond the limits of ASME PCC-1 without risk of mechanical failure of the joint. The limits of applicability of such a bolt load selection philosophy are also defined. The paper discusses the practical application of high bolt loads in achieving leak-free joint operation.

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