A METHOD TO REDUCE THE NUMBER OF ASSEMBLY TIGHTENING PASSES IN BOLTED FLANGE JOINTS

Bolted flange joints are extensively used in the pressure vessels and piping equipment and rotating machinery. Achieving a uniform bolt preload during the assembly process is particularly important to satisfy in bolted flange connection of oil and gas and fossil and nuclear applications. However, it is a very difficult task when tightening all bolts one by one due to elastic interaction. The risk of leakage failure under service loading is consequently increased because of the scatter of the bolt preload. This paper takes the advantage of a developed analytical model based on the theory of circular beams on linear elastic foundation that simulate the elastic interaction of bolted flange joints to reduce the number of passes while achieving bolt load uniformity. As such, a novel methodology for the optimization of the tightening sequence strategies is suggested to obtain uniform bolt tension while avoiding yield under minimum tightening passes. In this regards, based on the target preload, the load applied to each bolt in each pass is suggested. The developed approach is validated both numerically using FEM (finite element method) and experimentally on a NPS 4 class 900 welding neck flange joint using the criss-cross tightening and sequential patterns.

Investigation of large-diameter flange joint with soft-gasket

This study focuses on behaviour of the flanged joint with a soft rubber gasket, which is a common type of gasket for evaporator structures. The assembled structure is tested according to EN 13445-3, and strain values are measured using strain gauges. The numerical analysis in ABAQUS comprises several models with different levels of detail. These models are calibrated according to test data. Recommendations regarding the model complexity that is required to obtain satisfactory prediction of non-linear behaviour of flange joints are presented and documented.

Influence of Tightening Torque of Emergency Cooling Heat Exchanger Flange Studs on Strength

Previous efforts on assessing static strength of the flange joint components of the emergency cooling heat exchanger 08.8111.335 SB (ECHE) performed using the finite element method (FEM) revealed that there is an excess of permissible stress values for flange joint components of heat exchanger Dn2130 and Dn2080. These static strength calculations considered the design values for tightening of flange studs. Failure to meet the strength conditions flange joint components is due to the fact that the effect of «protrusion» under pressure of the bottom and shell attached to the flanges, as well as depending on the tightening force of the studs, the system of equilibrium applied force changes. This, in turn, leads to deformation of flange joint components. The paper presents an approach to reducing stress in flange joint components of ECHE first used at ZNPP-4. As a result of additional iterative calculations, the boundary conditions under which the strength conditions in all flange joint components of the heat exchanger are met are determined. In addition, the compliance with tightness condition for flange connections is considered. Thus, the analysis of the calculations established that when the tightening value of flange connection Dn2080 studs equal to 6800 kgf (corresponding to the torque on the key of 65 kg ∙m), the strength conditions for all groups of reduced stresses in all elements of the flange unite. In addition, at this value of stud tightening, the tightness of the flange connection Dn2080 is maintained. Analysis of similar iterative calculations of flange connection Dn2130 shows that for this flange connection it is recommended to reduce the tightening of the flange connection studs to the value of 14600 kgf, which is equal to the torque on the key of 145 kg ∙ m.