http://www.revistadechimie.ro REV.CHIM.(Bucharest)♦69♦No. 8 ♦2018 1954 Evaluation and Completion the Design Methods of Pressure Vessels Flange Joints VALERIU V. JINESCU*, GEORGETA URSE*, ANGELA CHELU Politehnica University of Bucharest, Industrial Process Equipment Department, 313 Splaiul Independentei, 060042, Bucharest, Romania We have provided a comparative analysis of the current international computing standards (European Standard EN 13445-3; ASME-Code, Section VIII, Division 2; British Standard (PD 5500: 2009)) that take into consideration only the static loading of flanges and bolts, if the temperatures of the flanges, bolts and sealing gasket are equal to each other and lower than creep temperature. The paper has put forth relations for completion the calculation method for flange joints in situations not taken into consideration by standards, namely: -static loading if flange temperature and bolt temperature are different; -thermal transient loading; -creep stress; -fatigue loading in the general case of a sequence of blocks of normal stresses. Furthermore, relationships have been proposed for the calculation of the maximum allowable difference between a flange and a bolt so as to ensure both the tightness and the mechanical strength of the flange joint. Keywords: flanges, joints, bolts, thermal transient, fatigue, tightness Flange joints for pressure vessels must withstand mechanical and thermal stresses, must be rigid enough lest their deformation should affect tightness and ensure sealing without loss of fluid throughout their service life. The present paper deals with the calculation of flange joints whose sealing gasket is located inside the bolts holes circle (fig. 1). -calculation of flanged joints with ribs. The works cited as dealing with the calculation of flange joints strength do not deal with the: -non-linear behavior of the design materials used in the make of the joint components, both under static and fatigue loading; -influence of damage on the strength of the flange joint components; -influence of residual stresses on the strength and rigidity of flange joint components. Problems not considered so far in the calculation of flange joints are dealt with in the papers [20 - 28] and may be adapted to their calculation. Some recent research refers to the: -influence of flange geometry (connection radius, flange neck length) on flange strength [29]; -influence of the variation of elastic washer deformation on the clamping force of bolts under creep conditions [30]; -tightness of flange joints under internal pressure and heat load [31-34], or in transient thermal mode [35]. In addition to these researches, for example, some works feature experiments with flanges without sealing gaskets [36]. A literature survey points to the fact that, in addition to official normative provisions, there are now: - results that could complement norms and allow for a closer to reality calculation of flange joints; the effect will be to reduce flange weight; - general results adaptable to the calculation of flange joints (non-linear behavior, damage, residual stress, etc.). The paper compares the methods of calculating the flange joints used in official calculation methods and makes recommendations on complementing them with the results published in literature. Comparative analysis of official methods of calculating ring flange joints under static loading For low and medium pressure, insufficient flange rigidity has the following effects: - insufficient circumferential stiffness may cause deformation between two bolts with deflection w (fig. 2, a). In this case, the solution to the problem may come from thickening the flanges; * email: vvjinescu@yahoo.com, Phone: (+40)722436555; ursegianina@yahoo.com., Phone: (+40)749092895 Fig. 1 Flange with gasket inside bolts holes circle: 1, 2 -flanges; 3 – bolt; 4 - washer; 5 -nut; 6 -sealing gasket Currently accepted computing methods for the calculation of flange joints in pressure vessels [1 - 3] involve the calculation of strength, which includes the choice of the sealing gasket; the calculations envisage neither the required rigidity of the flange joint nor its sealing. Calculations are made: - for monotonic/steady state loading under operating conditions featuring calculation parameters and under pressure test conditions. In all calculations it is considered that the flange and bolt temperatures are equal, but below creep temperature; - for fatigue loading, considering the linear - elastic behavior of the material used in the making of flanges and bolts. Works [4 - 19] go beyond official standards by taking into consideration the: -temperature difference between a flange and a bolt under operating parameters, as well as in the transient conditions and the influence of this difference upon tightness; -influence of flange rigidity on tightness; -correlation between flange joint strength, rigidity and tightness; -calculation of flange joints under load at temperatures higher than creep temperature; -calculation of the components of shock loaded flange joints;