Bolt Bending Behaviour in a Bolted Flanged Pipe Joint: A Comparative Study

The joint strength of a bolted flanged pipe joint depends upon its proper assembly using a suitable level pre-loading leading to a static behavioral mode whilst in operation. This is opposed to a dynamic behavioral mode observed in the gasketed joint, where there is relative movement between components, resulting in subsequent joint relaxation, fatigue mechanism and potentially ultimately joint failure. The static behavioral mode present in non-gasketed joints however shows no joint relaxation, and hence effective sealing. This paper presents results of detailed comparative experimental studies of both gasketed and non-gasketed joint behavior during assembly, and highlights bolt bending and relaxation as the main factors effecting joint performance. In addition the importance of proper bolt tightening sequences, bolt tightening methodology and the influence of the number of passes to make a joint is also presented. For the case of the gasketed joint only, the influence of different types of gaskets in the joint and their effect is discussed since such factors can lead to joint relaxation.