Non-gasketed Joint Research Articles

AN EXPERIMENTAL STUDY ON THE RELAXATION OF BOLTS

Loss of pre-load with time, commonly known as ‘Relaxation’ is an established phenomena. Behaviour of a bolted joint depends upon the pre-load in the bolts in use, not the pre-load introduced by the mechanic. Loss of pre-load is expected due to the many factors such as embedment relaxation, gasket creep, elastic interactions, and vibration loosening or stress relaxation. In a gasketed joint, due to the gasket flexibility, relaxation is always substantial during preliminary passes, as 80 to 100% loss is not uncommon in almost all the bolts, resulting in a dynamic behaviour. Pre-load in a gasketed joint is stabilized and retained to certain extent in the final passes only. In a non-gasketed joint, due to no gasket and no rotation its static behaviour is concluded. This paper highlights the factors affecting the amount of relaxation with time and presents important considerations that can reduce this. Both the short and long term relaxations are recorded and a ‘best fit’ model for relaxation behaviour is derived.

Determination of optimized non-gasketed flange geometry for safe stress and no leak condition: Finite-element analysis approach

Performance of a flange joint is characterized mainly due to its ‘strength’ and ‘sealing capability’. Available design rules for flange joints are mainly concerned with the strength of the flanges and do not sufficiently consider for their sealing. Being continuous problems faced by the gasketed flange joints for strength and sealing based on concluded ‘dynamic mode of load’, non-gasketed joints are recommended as an alternative. The current paper presents three-dimensional non-linear finite-element analysis of non-gasketed flange joint with different flange surface profiles (positive taper, negative taper, and zero taper angles) to find out the most optimal flange geometry for safe stress and no-leak conditions under bolt up and internal pressure loading. Based on the results, optimum flange geometry is selected and further analysed under proof test pressure. A ‘static mode of load’ in positive taper angle flange is concluded, ensuring proper joint sealing, and strength.