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

Abstract

Abstract 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.