The effect of external bending moments on flanged joints in pipe lines@ vessel nozzle flanges and vessel body flanges has often proven to be a difficult problem to assess. The basic design procedure presently being used in Section III@ Division 1 of the ASME Boiler and Pressure Code involves the calculation of an internal pressure that replaces the bending moment. This is referred to as the equivalent internal pressure which is added to the design pressure. The equivalent pressure approach simplifies the calculation procedure thus making them amenable to hand calculations. In recent years this procedure has been questioned. Many feel this approach is overly conservative. It is also important to realize that the equivalent pressure procedure does not take into account the flange geometry@ gasket characteristics@ joint leakage@ etc. With the increased emphasis on air pollution@ especially the EPA strict regulation of fugitive emissions@ it has become important to assess the effect of external bending moments on flange leakage. As a result@ ASME Piping Committee B-31 requested that the applicable PVRC Committee investigate this problem area to determine the adequacy of the present equivalent pressure procedure and if necessary@ develop a new or alternate procedure for adequately accounting for the effects of external bending moments on the design of bolted flanged joints. This WRC Bulletin is the first in a series covering the tests in this program. The bulletin documents PVRC Projects 94-26 and 96-01 which covers the bending moment testing on a NPS 4 class 150 weld neck and lap joint flanges with standard sheet gaskets. In these tests as well as subsequent tests@ some or all of the following parameters are to be monitored as a function of the applied bending moment: bolt load@ gasket stress distribution@ leak rate (tightness)@ flange and pipe stress levels@ and flange rotation. Tests involving spiral wound gasket without inner gage rings will monitor the phenomena of inward radial buckling to determine the influence of non-symmetric loads on this problem. The results of this test program will also assist PVRC and/or ASME in developing a strategy/procedure for re-rating standard flanges (ASME B16.5) based on the type of gasket and the associated joint tightness as well as the parameters used in developing the present rating tables. As this experimental program was being implemented@ the ASME Special Working Group on Bolted Flanged Joints (SWG-BFJ) adopted a more comprehensive method for considering External Moments and Axial Loads for its new bolted flanged joint design rules. This method@ based on the theoretical work of W. J. Koves@ does consider joint leakage via the same new rules that incorporate the PVRC gasket constants and the concept of tightness. The Koves method also considers gasket and joint stiffness although this aspect is currently not a part of the proposed new ASME Bolted Joint Design Rules. The work presented in this WRC Bulletin as well as those to follow should prove helpful in evaluating/validating Koves method
BULLETIN 450-2000 history
2000BULLETIN 450-2000 NPS 4 CLASS 150 BOLTED FLANGED JOINTS SUBJECTED TO PRESSURE AND EXTERNAL BENDING LOADS