This paper describes the analytical evaluation of the thermo - mechanical stresses developed in the circular flange assemblies, of optional type, welded to the cylindrical shell of a pressure vessel. In this case, the structure is formed by welding the cylindrical shell on the inner circumference of the flange ring. Based on the theory of deformation compatibility (radial displacements and rotations), the expressions for the evaluation of radial unitary bending moments and the unitary shear forces are deduced. Subsequently, stress values can be calculated and their concentration can be evaluated along the cylindrical shell, below the separation plane of the flange ring.

This paper highlighted the shortcomings of the current international normative on the calculation of flanges joints with gasket situated inside the circle of bolts holes. The current codes do not take into account, when calculating the flanged joints of the vessels, the bending stress that occurs as a result of the movement of the plates of the joint subjected to internal pressure. The bending of the bolts influences the deformation of the sealing gasket and – namely – the sealing of the flange joint. The knowledge of the bolts bending stresses allows to increase the time between two revisions/repairs and – namely – the useful life of the sealing gasket. The experimental data, obtained with the help of a strain gage bridge and by the Digital Image Correlation method on the designed experimental installation, highlighted the bending of the flange bolts, both for pressurization and depressurization. The experiments were performed at an internal pressure of 0.5; 1.0; 1.5 and 2.0 MPa.

An analysis has been made of the behavior of flange joint components under initial stress loading (pre-clamping) and in service. There have been highlighted the drawbacks in calculating flange joints to be found in currently acknowledged methods that do not take into account: - the influence of the bending moment produced by the total hydrostatic end force on bolt strength and flange rotation; - the presence of cracks in the welding or in its thermal influence zone; - the residual stresses; � the relaxation of the sealing gasket over time. The calculation method proposed in the paper takes into account all these particularities of loading. Furthermore, alongside the strength calculation of bolts and flanges, a proposal has been put forth for the calculation of the flange joint leak-tightness.

This paper presents the comparative analysis of the existing international normative calculation (EN 13445-3 European, ASME-Code, Section VIII, British Standard (PD 5500: 2009)) on the flange gasket joint situated inside the circle location of the bolt holes. The comparative analysis was performed for the same type of flange. The paper presents a comparative study of American and European standard, in terms of cost of production for the pressure equipment to assess the strengths and weaknesses of these regulations.

This paper addresses the evaluation of thermal and mechanical stresses that occur in assemblies with flat ring flanges, of optional type. The flange rings are fixed by welding to the wall of the cylindrical body of the vessel, with a constant thickness along its length. Regarding of the above, the compatibility of the deformations of the component elements (radial displacements and rotations) is approached. A linear algebraic system is formed in which both external loads (pressure, temperature) and connecting loads (bending unit moments and unit forces) are present. The present analysis discusses the quantitative, cumulative effect of the deformed gasket and the stiffness of the curved/bent screws on the tightness of the system. The methodology is flexible by introducing selection factors so that the mentioned influences can be easily separated.