Bolt preload scatter and relaxation behaviour during tightening a 4 in-900# flange joint with spiral wound gasket

Abstract

Gasketed bolted flange pipe joints are found prone to leakage during operating conditions. Therefore, performance of a gasketed flange joint is highly dependent on the proper joint assembly with proper gasket, proper gasket seating stress, and proper preloading in the bolts of a joint. For a gasketed flange joint, the two main concerns are the joint strength and the sealing capability. To investigate these, a detailed three-dimensional non-linear finite-element analysis (FEA) of a gasketed joint is carried out using a spiral wound gasket. FEA results are compared with the experimental results and are found to be in good agreement, hence validating the FE model developed. Bolt scatter, bolt bending, and bolt relaxation are considered to be the main factors affecting the joint performance. In addition, the importance of proper bolt tightening sequence and number of passes and the influence of elastic and elasto-plastic material modelling on joint performance are also presented. Stress variation in the flange due to flange rotation highlighted joint strength, and gasket contact/seating stress variation highlighted the sealing performance during bolt up. Modelling the non-linearity of the spiral wound gasket using non-linear elements highlights reduced joint strength and sealing performance. Summarizing, a dynamic mode in a gasketed joint is concluded, which is the main reason for its failure.