Combined loading performance analysis of gasketed bolted flange joints with emphasis on bolt scattering

Gasketed bolted flange joints (GBFJ) are commonly used in various industries however, their failure could result in significant losses not only in terms of financial but human life as well. Most of the work present on the performance of the GBFJ involves simplified assumptions by neglecting the effect of bolt scatter. Also, there is a paucity of studies investigating the sealing performance of GBFJ under combined thermal transient and structural loading. In the present study, two different flange sizes of ANSI B16.5 pressure class 900 (4in. and 6in.) are evaluated, using a detailed three-dimensional finite element analysis (FEA). ASME bolt tightening scheme was applied for the preloading of the bolts. Higher bolts and gasket stresses were observed in the case of 6in. flange joint. Also, greater variation in bolt stresses (up to 18 % of the target value) was observed for the 6 in. model which may be due to higher number of bolts resulting in greater scattering phenomena. Both models were found to be safe under the structural loading. However, large relaxation in stresses was observed at high bulk temperature. The gasket stress in 4in. flange model was observed to be less than the minimum seating stress (69 MPa) at temperatures greater than 300 °C implying possible leakage. However, stresses in the 6in. model stayed within the safe limit throughout the thermal and structural loading due to higher bolt target stresses, resulting in its proper seating even at higher temperatures.