On the Strength and Tightness of ASME B16.5 and B16.47 Series A Standard Flanges

Abstract

ASME flanges are extensively used in the pressure vessels and piping industry. The origin of their class and size is not based on the amount of initial bolt load they can carry nor the level of tightness they can achieve. Their PV rating does not give an indication on the level of stress they are subject to and little is known on their ability to withstand the maximum bolt stress level they can be subjected to during initial bolt-up or under operation. The integrity and leak tightness of ASME B16.5 and B16.47 series A flanges made of SA105 material need to be analyzed individually in order to identify the flange classes and sizes that are more vulnerable to the bolt stress level. This paper proposes the use of an accurate analytical model to appropriately address the integrity and leakage tightness of the complex statically indeterminate weld neck standard flange connections based on the flexibility and the elastic interaction between the different joint elements. As such, the most critical standard flanges in terms of class and size will be identified in order to avoid failure. The model is first tested and validated using finite element method simulations on different sizes of class 900 flanges. The study investigates the effect of the initial bolt preload on parameters such as flange rotation and stresses in the flange, gaskets, and bolts. The most critical size and class flanges and their highly stressed locations will be revealed.